diff --git a/taicpp/docs/mplex.md b/taicpp/docs/mplex.md
new file mode 100644
index 0000000..794ba18
--- /dev/null
+++ b/taicpp/docs/mplex.md
@@ -0,0 +1,100 @@
+# mplex + uiflow (detz port)
+
+Spec delta for the C++ port of tai's terminal multiplexer and the interactive UI flows. The
+behavior specification is unchanged and lives in [../../mplex.md](../../mplex.md) and
+[../../uiflow.md](../../uiflow.md); the code being transcribed is the `Mplex*` and `Plexer*` classes
+of [../../tai.py](../../tai.py). This page records what the port adds: the file layout, the
+Python-to-C++ mapping rules, the parity table, the tests and the known gaps.
+
+## Goal
+
+A literal transpilation with identical behavior: the same keys, commands, options, formats, wire
+frames, control protocol, config file and error texts. Where Python and C++ differ at the language
+level, the port reproduces Python's semantics (`mplex_py.h`) instead of adopting C++'s.
+
+## Layout
+
+All Mplex code is in `taicpp/src/mplex/`, namespace `detz::mplex`; the uiflow code is in
+`taicpp/src/plexer/plexer_flow.{h,cpp}`, namespace `detz::plexer`. One class per header and source
+pair; every file name is prefixed `mplex_` so the flat include path of the Makefile cannot clash with
+other modules. Class and method names are the Python names (snake_case methods, `Mplex*` classes).
+
+## Mapping rules
+
+| Python | C++ |
+|---|---|
+| `str` | `std::string` (UTF-8) at API edges, `UStr` (`std::wstring`, one `wchar_t` per code point) wherever `len`, index or slice count code points |
+| `bytes` | `Bytes` (`std::string` holding raw bytes) |
+| `None` | `std::optional`, an empty `shared_ptr`, or `Color` 0 |
+| iterated `dict` | `OrderedMap` (insertion order is iteration order) |
+| `(fg, bg, attr)` / cell tuple | `Style` / `Cell` (`ch == 0` is a never written cell) |
+| SGR colour fragment `"38;5;12"` | `Color` (32 bit pack, lossless for every fragment tai.py produces) |
+| `MplexError`, `ValueError` | `MplexError`, `ValueError` (both `std::runtime_error`) |
+| closures | `std::function` |
+| back references (`pane.window`, `window.session`, layout `parent`) | `weak_ptr` with an accessor returning `shared_ptr` |
+| modes and overlays on a client | `shared_ptr` held by the owner; `MplexServer::discard_pane` clears `pane.modes` to break the pane/mode cycle |
+| `json`, `tomllib`, `re`, `fnmatch`, `textwrap`, `shlex`, `time.strftime`, `subprocess.run` | `mplex_json.h`, `mplex_toml.h`, `mplex_py.h` (`py::Regex`, `py::fnmatchcase`, `py::textwrap_wrap`, `py::shlex_quote`, `py::strftime`, `py::run_shell`) |
+
+## Parity table
+
+| tai.py symbol | C++ symbol | files |
+|---|---|---|
+| `MplexError` | `MplexError` | `mplex_common.h` |
+| `MplexKeys` | `MplexKeys` | `mplex_keys.{h,cpp}` |
+| `tui_parse_one` and helpers | `tui_parse_one` | `mplex_input.{h,cpp}` |
+| `MplexArgs`, `MplexCommandParser` | same | `mplex_args.{h,cpp}` |
+| `MplexStyle` | `MplexStyle` | `mplex_style.{h,cpp}` |
+| `MplexOptions` | `MplexOptions` | `mplex_options.{h,cpp}` |
+| `MplexBinding`, `MplexConfig`, `MPLEX_DEFAULT_KEYS` | same | `mplex_config.{h,cpp}`, `mplex_default_keys.cpp` (generated) |
+| `MplexFormat` | `MplexFormat` | `mplex_format.{h,cpp}` |
+| `MplexLayoutNode`, `MplexLayout` | same | `mplex_layout.{h,cpp}` |
+| `TuiVtScreen` (as used by panes) | `MplexVtScreen` | `mplex_vtscreen.{h,cpp}` |
+| `MplexPane`, `MplexWindow`, `MplexSession` | same | `mplex_pane.{h,cpp}` |
+| `MplexCanvas`, `MplexStatusText`, `MplexFont` | same | `mplex_canvas.{h,cpp}` |
+| `MplexMode`, `MplexClockMode` | same | `mplex_mode.{h,cpp}`, `mplex_clockmode.{h,cpp}` |
+| `MplexCopyMode` | `MplexCopyMode` | `mplex_copymode.{h,cpp}` |
+| `MplexPrompt` | `MplexPrompt` | `mplex_prompt.{h,cpp}` |
+| `MplexPaneNumbers`, `MplexFlowScreen` | same | `mplex_panenumbers.{h,cpp}`, `mplex_flowscreen.{h,cpp}` |
+| `MplexChoice`, `MplexChooser` | same | `mplex_chooser.{h,cpp}` |
+| `MplexRenderer` | `MplexRenderer` | `mplex_renderer.{h,cpp}` |
+| `MplexCtx`, `MplexTargets` | same | `mplex_ctx.{h,cpp}` |
+| `MplexClientConn`, `MplexPending` | same | `mplex_clientconn.{h,cpp}` |
+| `MplexServer` | `MplexServer` | `mplex_server.{h,cpp}` |
+| `MplexCommands`, `MPLEX_COMMAND_SPECS`, `MPLEX_DEFAULT_FORMATS` | same | `mplex_commands.{h,cpp}`, `mplex_command_specs.cpp` (generated) |
+| `MplexClient`, `MplexCli`, `NativePlexerBackend`, `plexer_should_wrap`, bashrc blocks | same | `mplex_client.{h,cpp}` |
+| `PlexerController`, `NativePlexerController`, `TmuxPlexerController`, `PlexerControllerFactory` | same | `src/plexer/plexer_flow.{h,cpp}` |
+| `validate_flow_*`, `PlexerFlow`, `PlexerBackend` | same | `src/plexer/plexer_flow.{h,cpp}` |
+
+The two generated files are produced from the Python tables; they carry a header saying so and
+`mplex_spec_test` compares them with `mplex.md`.
+
+## Tests
+
+- `tests/mplex_spec_test.cpp`: the C++ twin of `MplexSpecTests` and `UiflowDocTests`: `mplex.md`
+  and `uiflow.md` must list exactly the options, commands, default bindings, copy-mode commands, caps
+  and flow words that the C++ tables hold.
+- `tests/mplex_foundation_test.cpp`: the Python-shaped helpers, JSON and TOML, against Python 3.14.
+- `tests/mplex_vt_test.cpp`: the VT screen, input parser and keys against `TuiVtScreen` and `MplexKeys`.
+- `tests/mplex_core_test.cpp`: args, parser, style, options, config, format and layout against tai.py.
+- `tests/mplex_model_test.cpp`: panes, canvas, prompt, chooser, flow screen, renderer, targets.
+- `tests/mplex_copy_test.cpp`: copy mode against tai.py's recorded tmux results and a seeded fuzz.
+- `tests/mplex_server_test.cpp`, `tests/mplex_commands_test.cpp`: the real C++ server over its socket,
+  scripted command corpus compared with the Python server.
+- `tests/mplex_flow_test.cpp`: `validate_flow_spec` and `PlexerFlow` against tai.py.
+- `tests/mplex_e2e.py` with `tests/mplex_cli_main.cpp`: the real client under a pty, as `tests/mplex.py` does.
+
+Expected values in these tests are produced by running tai.py (and tmux 3.6 where mplex.md names it
+the oracle), never typed in from memory.
+
+## Known gaps of the port
+
+Listed next to what would close them; the final status of each is recorded in the milestone report.
+
+- **Regular expressions** (`py::Regex`, `std::wregex` ECMAScript): Python-only syntax (lookbehind,
+  named groups, possessive quantifiers, `\Z`) is translated where an equivalent exists and rejected
+  with a loud error otherwise; copy-mode search then falls back to a literal, like Python does for an
+  invalid expression.
+- **Unicode classification** (`str.isalpha`, `isprintable`, case mapping) uses the glibc C.UTF-8
+  tables, which may lag or lead CPython's `unicodedata` by a Unicode version.
+- **TOML error texts** follow tomllib's wording; positions are reproduced, rare messages may differ.
+- Anything else found while testing is added here, never hidden.
diff --git a/taicpp/src/mplex/mplex_args.h b/taicpp/src/mplex/mplex_args.h
new file mode 100644
index 0000000..fecb145
--- /dev/null
+++ b/taicpp/src/mplex/mplex_args.h
@@ -0,0 +1,49 @@
+// MplexArgs (getopt-style tmux argument parsing, tai.py:10472) and MplexCommandParser (tai.py:10545).
+#pragma once
+#include <map>
+#include <optional>
+#include <string>
+#include <vector>
+
+#include "mplex_common.h"
+
+namespace detz::mplex {
+
+class MplexArgs {
+ public:
+  // One occurrence of a flag: a plain flag is Python's True, an argument flag carries its text.
+  struct FlagValue {
+    bool is_true = true;
+    std::string text;
+  };
+
+  MplexArgs() = default;
+  MplexArgs(std::map<char, std::vector<FlagValue>> flags_in, std::vector<std::string> positional_in)
+      : flags(std::move(flags_in)), positional(std::move(positional_in)) {}
+
+  std::map<char, std::vector<FlagValue>> flags;
+  std::vector<std::string> positional;
+
+  bool has(char flag) const { return flags.count(flag) != 0; }
+  // args.get(flag, default): the last value. A plain flag yields "True" (str(True)); callers
+  // that test truthiness of a plain flag must use has().
+  std::optional<std::string> get(char flag) const;
+  std::string get(char flag, const std::string& fallback) const;
+  std::vector<std::string> all(char flag) const;  // plain flags contribute "True"
+  // args.int(flag, default): value True or absent gives the default; bad text throws MplexError
+  // "-x expects a number: text".
+  std::optional<long long> int_flag(char flag, std::optional<long long> fallback = std::nullopt) const;
+
+  // spec "bdt:" => -b and -d are flags, -t takes a value. max_args < 0 means unlimited.
+  static MplexArgs parse(const std::string& name, const std::string& spec, const std::vector<std::string>& words,
+                         int min_args = 0, int max_args = -1);
+};
+
+class MplexCommandParser {
+ public:
+  // tmux-syntax text to commands of words; throws MplexError on unterminated quotes/blocks.
+  static std::vector<std::vector<std::string>> parse(const std::string& text);
+  static std::string quote(const std::string& word);
+};
+
+}  // namespace detz::mplex
diff --git a/taicpp/src/mplex/mplex_canvas.h b/taicpp/src/mplex/mplex_canvas.h
new file mode 100644
index 0000000..e8f522c
--- /dev/null
+++ b/taicpp/src/mplex/mplex_canvas.h
@@ -0,0 +1,50 @@
+// MplexCanvas (tai.py:11882), MplexStatusText (:11993), MplexFont (:13149).
+#pragma once
+#include <optional>
+#include <string>
+#include <utility>
+#include <vector>
+
+#include "mplex_common.h"
+
+namespace detz::mplex {
+
+// A client-sized grid of cells plus a cursor, and the diff that turns two successive grids
+// into the escape sequences that repaint only what changed.
+class MplexCanvas {
+ public:
+  using Cursor = std::pair<int, int>;  // (x, y)
+  static constexpr Cell BLANK = Cell{L' ', 0, 0, 0};
+  // GLYPHS["single"] etc: 11 glyphs: horiz vert tl tr bl br tee_r tee_l tee_d tee_u cross.
+  static const UStr& glyphs(const std::string& lines);  // unknown name falls back to "single"
+
+  MplexCanvas(int rows_in, int cols_in);
+  int rows, cols;
+  Grid cells;
+  std::optional<Cursor> cursor;
+
+  // put(x, y, text, style, limit): limit < 0 means None. Returns the x after the text.
+  int put(int x, int y, const UStr& text, const Style& style = Style{}, int limit = -1);
+  int put(int x, int y, const std::string& text, const Style& style = Style{}, int limit = -1);
+  void put_cells(int x, int y, const Row& row);
+  void blit(int x, int y, const Grid& block, int width);
+  void fill(int x, int y, int w, int h, const Style& style = Style{}, wchar_t ch = L' ');
+  static wchar_t border_char(bool up, bool down, bool left, bool right, const std::string& lines);
+  // Escape bytes repainting this grid over previous (null when there is none); also returns the snapshot.
+  std::pair<Bytes, Grid> encode(const Grid* previous) const;
+};
+
+// Format-expanded text with #[...] style markers turned into styled cells.
+class MplexStatusText {
+ public:
+  static Row cells(const UStr& text, const Style& base, const std::optional<Style>& reset = std::nullopt);
+};
+
+class MplexFont {
+ public:
+  static constexpr int HEIGHT = 5;
+  static int width(const UStr& text);
+  static Grid draw(const UStr& text, Color bg);  // five rows of cells
+};
+
+}  // namespace detz::mplex
diff --git a/taicpp/src/mplex/mplex_chooser.h b/taicpp/src/mplex/mplex_chooser.h
new file mode 100644
index 0000000..45ff9c8
--- /dev/null
+++ b/taicpp/src/mplex/mplex_chooser.h
@@ -0,0 +1,62 @@
+// MplexChoice (tai.py:13368) and MplexChooser (:13380): choose-tree / choose-buffer / choose-client.
+#pragma once
+#include <functional>
+#include <memory>
+#include <optional>
+#include <string>
+#include <vector>
+
+#include "mplex_json.h"
+#include "mplex_mode.h"
+
+namespace detz::mplex {
+
+class MplexChoice {
+ public:
+  using Ptr = std::shared_ptr<MplexChoice>;
+  explicit MplexChoice(const std::string& label_in, Json payload_in = Json(), std::vector<Ptr> children_in = {},
+                       bool expanded_in = false)
+      : label(label_in), payload(std::move(payload_in)), children(std::move(children_in)), expanded(expanded_in) {}
+  std::string label;
+  Json payload;  // Python tuples/ints/strs; compared with == and repr()
+  std::vector<Ptr> children;
+  bool expanded;
+  int depth = 0;
+  bool tag = false;
+};
+
+class MplexChooser : public MplexMode {
+ public:
+  using Builder = std::function<std::vector<MplexChoice::Ptr>()>;
+  using OnChoose = std::function<void(const MplexChoice::Ptr&, MplexClientConn&)>;
+  using OnDelete = std::function<void(const MplexChoice::Ptr&, MplexClientConn&)>;
+  // preview(item, width, height) -> rows of cells
+  using Preview = std::function<Grid(const MplexChoice::Ptr&, int, int)>;
+  static const char* const HOT_KEYS;  // "0123456789"
+
+  MplexChooser(MplexServer* server_in, std::shared_ptr<MplexPane> pane_in, const std::string& kind, Builder builder_in,
+               OnChoose on_choose_in, OnDelete on_delete_in = nullptr, Preview preview_in = nullptr,
+               std::optional<Json> selected = std::nullopt, std::function<void()> on_close_in = nullptr);
+
+  Builder builder;
+  std::vector<MplexChoice::Ptr> items;
+  std::function<void()> on_close;
+  OnChoose on_choose;
+  OnDelete on_delete;
+  Preview preview;
+  bool show_preview;
+  int cursor = 0;
+  std::vector<MplexChoice::Ptr> visible;
+
+  void reflatten();
+  MplexChoice::Ptr selected() const;
+  void rebuild();
+  void close() override;
+  int list_height() const;
+  ModeBlock render(MplexClientConn& client) override;
+  void move(int delta);
+  void key(const std::string& name, const Bytes& raw, MplexClientConn& client) override;
+  void delete_node(const MplexChoice::Ptr& node, MplexClientConn& client);  // Python: delete()
+};
+
+}  // namespace detz::mplex
diff --git a/taicpp/src/mplex/mplex_client.h b/taicpp/src/mplex/mplex_client.h
new file mode 100644
index 0000000..c0df8c4
--- /dev/null
+++ b/taicpp/src/mplex/mplex_client.h
@@ -0,0 +1,50 @@
+// MplexClient (tai.py:16804), MplexCli (:16963), NativePlexerBackend (:17012) and
+// plexer_should_wrap (:17026): the attached terminal and the --mplex / --plexer-wrap entry.
+#pragma once
+#include <string>
+#include <vector>
+
+#include "mplex_common.h"
+
+namespace detz::mplex {
+
+// The attached terminal: forwards keys and resizes to the server, paints what it sends.
+class MplexClient {
+ public:
+  MplexClient(const std::string& home, const std::vector<std::vector<std::string>>& commands);
+  static Bytes frame(const std::string& kind, const Bytes& payload = Bytes());
+  int run();
+
+ private:
+  struct Impl;
+  std::shared_ptr<Impl> impl_;
+};
+
+// tai.py --mplex <command...>: any mplex command; new-session and attach-session attach this terminal.
+class MplexCli {
+ public:
+  static bool attaches(const std::string& name, const std::vector<std::string>& rest);
+  static std::vector<std::vector<std::string>> split_commands(const std::vector<std::string>& words);
+  // Returns the process exit code. Python main(home, words) writes errors to stderr.
+  static int main(const std::string& home, const std::vector<std::string>& words);
+};
+
+// What the shell hook execs into: a new mplex session attached to this terminal (--plexer-wrap).
+class NativePlexerBackend {
+ public:
+  NativePlexerBackend(const std::string& home, const std::string& profile, const std::vector<std::string>& shell_cmd = {})
+      : home(home), profile(profile), shell_cmd(shell_cmd) {}
+  std::string home, profile;
+  std::vector<std::string> shell_cmd;
+  // The int exit code of MplexCli.main, or an error string when pty support is missing (Python returns the str).
+  int run();
+};
+
+bool plexer_should_wrap(const std::vector<std::pair<std::string, std::string>>& env);
+
+extern const char* const PLEXER_BASHRC_MARK_BEGIN;
+extern const char* const PLEXER_BASHRC_MARK_END;
+extern const char* const PLEXER_BASHRC_BLOCK;
+extern const char* const FISH_PLEXER_BLOCK;
+
+}  // namespace detz::mplex
diff --git a/taicpp/src/mplex/mplex_clientconn.h b/taicpp/src/mplex/mplex_clientconn.h
new file mode 100644
index 0000000..ed1d61f
--- /dev/null
+++ b/taicpp/src/mplex/mplex_clientconn.h
@@ -0,0 +1,68 @@
+// MplexClientConn (tai.py:13865) and MplexPending (:15332).
+#pragma once
+#include <memory>
+#include <optional>
+#include <string>
+#include <utility>
+#include <vector>
+
+#include "mplex_common.h"
+#include "mplex_pane.h"
+#include "mplex_prompt.h"
+#include "mplex_mode.h"
+
+namespace detz::mplex {
+
+class MplexServer;
+
+// A connection that has not yet said whether it speaks frames or one JSON line.
+struct MplexPending {
+  explicit MplexPending(int fd_in);
+  int fd;  // the accepted, non-blocking socket
+  Bytes buf;
+  double created;
+};
+
+// Server-side state of one connection: framing, key table position, prompt, overlay, last frame.
+class MplexClientConn : public std::enable_shared_from_this<MplexClientConn> {
+ public:
+  using Frame = std::pair<std::string, Bytes>;  // (kind byte as 1-char string, payload)
+  MplexClientConn(MplexServer* server_in, int fd_in, int ident);
+
+  MplexServer* server;
+  int fd;  // socket; -1 once closed
+  int id;
+  Bytes inbuf;
+  Bytes out;
+  int rows = 24, cols = 80;
+  std::shared_ptr<MplexSession> session;
+  bool attached = false;
+  std::string table = "root";
+  bool repeating = false;
+  double repeat_until = 0.0;
+  Bytes keybuf;
+  std::optional<double> esc_deadline;
+  std::shared_ptr<MplexPrompt> prompt;
+  std::optional<std::pair<std::string, double>> message;  // (text, expiry monotonic)
+  std::shared_ptr<MplexOverlay> overlay;
+  std::optional<Grid> prev;                               // last frame snapshot
+  std::optional<std::pair<int, int>> cursor;
+  bool dirty = true;
+  double last_render = 0.0;
+  long pid = 0;
+  std::string tty, term, cwd;
+  MplexPane::EnvList env;
+  std::optional<int> env_pane;
+  bool closing = false;
+  double created;
+
+  // Queue a frame; false (and prev reset) when the out queue is over MPLEX_CLIENT_OUT_MAX.
+  bool send(const std::string& kind, const Bytes& payload = Bytes());
+  // Complete frames in what arrived; nullopt when the stream is corrupt (length over MPLEX_FRAME_MAX).
+  std::optional<std::vector<Frame>> frames(const Bytes& data);
+  void redispatch(const std::string& name, const Bytes& raw);
+  void flush();
+  void close();
+};
+
+}  // namespace detz::mplex
diff --git a/taicpp/src/mplex/mplex_clockmode.h b/taicpp/src/mplex/mplex_clockmode.h
new file mode 100644
index 0000000..e6a71c6
--- /dev/null
+++ b/taicpp/src/mplex/mplex_clockmode.h
@@ -0,0 +1,16 @@
+// MplexClockMode (tai.py:13182).
+#pragma once
+#include "mplex_mode.h"
+
+namespace detz::mplex {
+
+class MplexClockMode : public MplexMode {
+ public:
+  MplexClockMode(MplexServer* server_in, std::shared_ptr<MplexPane> pane_in) : MplexMode(server_in, std::move(pane_in)) {
+    name = "clock-mode";
+  }
+  ModeBlock render(MplexClientConn& client) override;
+  void key(const std::string& name, const Bytes& raw, MplexClientConn& client) override;
+};
+
+}  // namespace detz::mplex
diff --git a/taicpp/src/mplex/mplex_command_specs.cpp b/taicpp/src/mplex/mplex_command_specs.cpp
new file mode 100644
index 0000000..dd796a2
--- /dev/null
+++ b/taicpp/src/mplex/mplex_command_specs.cpp
@@ -0,0 +1,113 @@
+// Generated from MPLEX_COMMAND_SPECS, MPLEX_DEFAULT_FORMATS, MPLEX_UNSUPPORTED and MPLEX_LAYOUT_NAMES in ../../../tai.py.
+// Regenerate, never hand edit: the C++ spec test compares these tables with mplex.md and tai.py.
+#include "mplex_commands.h"
+
+#include <stdexcept>
+
+namespace detz::mplex {
+
+const std::vector<MplexCommandSpec>& mplex_command_specs() {
+  static const std::vector<MplexCommandSpec> table = {
+      {"attach-session", {"attach", "a"}, "dErxc:f:t:", 0, 0},
+      {"bind-key", {"bind"}, "nrT:N:", 1, -1},
+      {"break-pane", {"breakp"}, "abdPF:n:s:t:", 0, 0},
+      {"capture-pane", {"capturep"}, "aCeJMNpPqTb:E:S:t:", 0, 0},
+      {"choose-buffer", {}, "NrZF:f:K:O:t:", 0, 1},
+      {"choose-client", {}, "NrZF:f:K:O:t:", 0, 1},
+      {"choose-tree", {}, "GNrswZF:f:K:O:t:", 0, 1},
+      {"clear-history", {"clearhist"}, "Ht:", 0, 0},
+      {"clock-mode", {}, "t:", 0, 0},
+      {"command-prompt", {}, "1bFkliNI:p:t:T:", 0, 1},
+      {"confirm-before", {"confirm"}, "byc:p:t:", 1, 1},
+      {"copy-mode", {}, "deHMqSus:t:", 0, 0},
+      {"delete-buffer", {"deleteb"}, "b:", 0, 0},
+      {"detach-client", {"detach"}, "aPE:s:t:", 0, 0},
+      {"display-message", {"display"}, "aCIlNpvc:d:F:t:", 0, 1},
+      {"display-panes", {"displayp"}, "bNd:t:", 0, 1},
+      {"find-window", {"findw"}, "CiNrTZt:", 1, 1},
+      {"has-session", {"has"}, "t:", 0, 0},
+      {"if-shell", {"if"}, "bFt:", 2, 3},
+      {"kill-pane", {"killp"}, "at:", 0, 0},
+      {"kill-server", {}, "", 0, 0},
+      {"kill-session", {}, "aCt:", 0, 0},
+      {"kill-window", {"killw"}, "at:", 0, 0},
+      {"last-pane", {"lastp"}, "deZt:", 0, 0},
+      {"last-window", {"last"}, "t:", 0, 0},
+      {"list-buffers", {"lsb"}, "F:f:", 0, 0},
+      {"list-clients", {"lsc"}, "F:f:t:", 0, 0},
+      {"list-commands", {"lscm"}, "F:", 0, 1},
+      {"list-keys", {"lsk"}, "1aNP:T:", 0, 1},
+      {"list-panes", {"lsp"}, "asF:f:t:", 0, 0},
+      {"list-sessions", {"ls"}, "F:f:", 0, 0},
+      {"list-windows", {"lsw"}, "aF:f:t:", 0, 0},
+      {"load-buffer", {"loadb"}, "b:t:", 1, 1},
+      {"move-window", {"movew"}, "abdkrs:t:", 0, 0},
+      {"new-session", {"new"}, "AdDEPXc:e:F:f:n:s:t:x:y:", 0, -1},
+      {"new-window", {"neww"}, "abdkPSc:e:F:n:t:", 0, -1},
+      {"next-layout", {"nextl"}, "t:", 0, 0},
+      {"next-window", {"next"}, "at:", 0, 0},
+      {"paste-buffer", {"pasteb"}, "dprs:b:t:", 0, 0},
+      {"previous-layout", {"prevl"}, "t:", 0, 0},
+      {"previous-window", {"prev"}, "at:", 0, 0},
+      {"refresh-client", {"refresh"}, "cDlLRSUA:B:C:f:r:t:", 0, 1},
+      {"rename-session", {"rename"}, "t:", 1, 1},
+      {"rename-window", {"renamew"}, "t:", 1, 1},
+      {"resize-pane", {"resizep"}, "DLMRTUZx:y:t:", 0, 1},
+      {"rotate-window", {"rotatew"}, "DUZt:", 0, 0},
+      {"run-shell", {"run"}, "bCEc:d:t:", 0, 1},
+      {"save-buffer", {"saveb"}, "ab:", 1, 1},
+      {"select-layout", {"selectl"}, "Enopt:", 0, 1},
+      {"select-pane", {"selectp"}, "DdeLlMmRUZT:t:", 0, 0},
+      {"select-window", {"selectw"}, "lnpTt:", 0, 0},
+      {"send-keys", {"send"}, "FHKlMRXc:N:t:", 0, -1},
+      {"send-prefix", {}, "2t:", 0, 0},
+      {"set-buffer", {"setb"}, "awb:n:t:", 0, 1},
+      {"set-option", {"set"}, "aFgopqsuUwt:", 1, 2},
+      {"set-window-option", {"setw"}, "aFgoqut:", 1, 2},
+      {"show-buffer", {"showb"}, "b:", 0, 0},
+      {"show-messages", {"showmsgs"}, "JTt:", 0, 0},
+      {"show-options", {"show"}, "AgHpqsvwt:", 0, 1},
+      {"show-window-options", {"showw"}, "gvt:", 0, 1},
+      {"source-file", {"source"}, "Fnqvt:", 1, -1},
+      {"split-window", {"splitw"}, "bdefhIPvZc:e:F:l:t:", 0, -1},
+      {"start-server", {"start"}, "", 0, 0},
+      {"suspend-client", {"suspendc"}, "t:", 0, 0},
+      {"swap-pane", {"swapp"}, "dDUZs:t:", 0, 0},
+      {"swap-window", {"swapw"}, "ds:t:", 0, 0},
+      {"switch-client", {"switchc"}, "ElnprZc:t:T:", 0, 0},
+      {"unbind-key", {"unbind"}, "anqT:", 0, 1},
+  };
+  return table;
+}
+
+const MplexCommandSpec* mplex_find_spec(const std::string& name) {
+  for (const auto& item : mplex_command_specs())
+    if (item.name == name) return &item;
+  return nullptr;
+}
+
+const std::vector<std::string>& mplex_unsupported() {
+  static const std::vector<std::string> table = {"display-menu", "display-popup", "customize-mode", "lock-server", "lock-session", "lock-client", "pipe-pane", "join-pane", "move-pane", "link-window", "unlink-window", "respawn-pane", "respawn-window", "resize-window", "set-hook", "show-hooks", "wait-for", "server-access", "choose-tree-mouse"};
+  return table;
+}
+
+const std::vector<std::string>& mplex_layout_names() {
+  static const std::vector<std::string> table = {"even-horizontal", "even-vertical", "main-horizontal", "main-horizontal-mirrored", "main-vertical", "main-vertical-mirrored", "tiled"};
+  return table;
+}
+
+const std::string& mplex_default_format(const std::string& command) {
+  static const std::vector<std::pair<std::string, std::string>> table = {
+      {"list-sessions", "#{session_name}: #{session_windows} windows (created #{t:session_created})#{\?session_attached, (attached),}"},
+      {"list-windows", "#{window_index}: #{window_name}#{window_flags} (#{window_panes} panes) [#{window_width}x#{window_height}] #{window_id}#{\?window_active, (active),}"},
+      {"list-panes", "#{pane_index}: [#{pane_width}x#{pane_height}] [history #{history_size}/#{history_limit}] #{pane_id}#{\?pane_active, (active),}"},
+      {"list-clients", "#{client_tty}: #{session_name} [#{client_width}x#{client_height} #{client_termname}]"},
+      {"list-buffers", "#{buffer_name}: #{buffer_size} bytes: \"#{buffer_sample}\""},
+      {"display-message", "[#{session_name}] #{window_index}:#{window_name}, current pane #{pane_index} - (%H:%M %d-%b-%y)"},
+  };
+  for (const auto& item : table)
+    if (item.first == command) return item.second;
+  throw std::out_of_range("no default format for " + command);
+}
+
+}  // namespace detz::mplex
diff --git a/taicpp/src/mplex/mplex_commands.h b/taicpp/src/mplex/mplex_commands.h
new file mode 100644
index 0000000..08f12fb
--- /dev/null
+++ b/taicpp/src/mplex/mplex_commands.h
@@ -0,0 +1,49 @@
+// MplexCommands: tmux's command set (tai.py:15423-16800) and the command tables
+// MPLEX_COMMAND_SPECS (:15342), MPLEX_DEFAULT_FORMATS (:15413), MPLEX_UNSUPPORTED (:10023),
+// MPLEX_LAYOUT_NAMES (:10263). Owner: fork F6. Handlers are cmd_<name with _>(ctx, args).
+#pragma once
+#include <functional>
+#include <map>
+#include <optional>
+#include <string>
+#include <vector>
+
+#include "mplex_args.h"
+#include "mplex_common.h"
+#include "mplex_ctx.h"
+
+namespace detz::mplex {
+
+class MplexServer;
+
+// name: (aliases, getopt spec, min positional, max positional); max < 0 is None.
+struct MplexCommandSpec {
+  std::string name;
+  std::vector<std::string> aliases;
+  std::string spec;
+  int min_args;
+  int max_args;
+};
+// In the order of the Python dict literal.
+const std::vector<MplexCommandSpec>& mplex_command_specs();
+const MplexCommandSpec* mplex_find_spec(const std::string& name);
+const std::vector<std::string>& mplex_unsupported();
+const std::vector<std::string>& mplex_layout_names();
+// MPLEX_DEFAULT_FORMATS[name]; throws std::out_of_range for names without one.
+const std::string& mplex_default_format(const std::string& command);
+
+class MplexCommands {
+ public:
+  explicit MplexCommands(MplexServer* server);
+  ~MplexCommands();
+  // Resolve a word to a command name: exact, alias, unsupported (MplexError), unique prefix.
+  static std::string resolve(const std::string& word);
+  // Run `cmd_<name>`; the result is the command's output text ("" for None).
+  std::string call(const std::string& name, MplexCtx& ctx, const MplexArgs& args);
+
+ private:
+  struct Impl;
+  std::unique_ptr<Impl> impl_;
+};
+
+}  // namespace detz::mplex
diff --git a/taicpp/src/mplex/mplex_common.h b/taicpp/src/mplex/mplex_common.h
new file mode 100644
index 0000000..aa266a0
--- /dev/null
+++ b/taicpp/src/mplex/mplex_common.h
@@ -0,0 +1,143 @@
+// Shared vocabulary of the Mplex port: Python-shaped primitives so the classes can be
+// transcribed line for line. Spec: taicpp/docs/mplex.md, source of truth: ../../tai.py.
+//
+// Mapping rules (every Mplex* file follows them):
+//   str              -> std::string (UTF-8) at API edges, UStr (std::wstring, one wchar_t per
+//                       code point, Linux wchar_t is 32 bit) wherever len/index/slice count code points
+//   bytes            -> Bytes (std::string holding raw bytes)
+//   None             -> std::optional / empty shared_ptr / 0 Color
+//   dict (iterated)  -> OrderedMap (insertion order kept, like Python)
+//   tuple (fg,bg,a)  -> Style;  cell tuple -> Cell;  cell None -> Cell with ch == 0
+//   exceptions       -> MplexError for user-facing failures, ValueError for Python ValueError
+//   closures         -> std::function
+#pragma once
+#include <cstdint>
+#include <functional>
+#include <map>
+#include <memory>
+#include <optional>
+#include <stdexcept>
+#include <string>
+#include <utility>
+#include <vector>
+
+namespace detz::mplex {
+
+using Bytes = std::string;
+using UStr = std::wstring;
+
+// A user-facing failure: the text is shown verbatim as the command's error.
+class MplexError : public std::runtime_error {
+ public:
+  explicit MplexError(const std::string& text) : std::runtime_error(text) {}
+};
+
+// Python ValueError / generic Exception raised inside the control protocol; the text is
+// what short_error() would print.
+class ValueError : public std::runtime_error {
+ public:
+  explicit ValueError(const std::string& text) : std::runtime_error(text) {}
+};
+
+// ---- text ------------------------------------------------------------------
+
+// bytes.decode("utf-8", "replace"): maximal invalid subparts become one U+FFFD, like CPython.
+UStr to_ustr(const std::string& utf8);
+std::string to_utf8(const UStr& text);
+std::string to_utf8(wchar_t ch);
+// text.encode("utf-8", "replace") for strings that may carry lone surrogates: same as to_utf8.
+
+// short_error(exc): str(exc) or the type name, capped at 300 chars.
+std::string short_error(const std::exception& exc, const std::string& type_name = "Exception");
+
+// ---- colours, styles, cells ----------------------------------------------------
+
+// An SGR colour fragment ("31", "104", "38;5;12", "48;2;1;2;3") packed in 32 bits. 0 is None.
+// Lossless for every fragment tai.py produces (see mplex.md, Style strings).
+using Color = uint32_t;
+Color color_from_sgr(const std::string& fragment);  // "" -> 0
+std::string color_sgr(Color color);                 // 0 -> ""
+
+// (fg, bg, attr) as MplexStyle produces and MplexCanvas stores.
+struct Style {
+  Color fg = 0;
+  Color bg = 0;
+  int attr = 0;
+  bool operator==(const Style& o) const { return fg == o.fg && bg == o.bg && attr == o.attr; }
+  bool operator!=(const Style& o) const { return !(*this == o); }
+};
+
+// (char, fg, bg, attr). ch == 0 stands for Python's None ("never written").
+struct Cell {
+  wchar_t ch = 0;
+  Color fg = 0;
+  Color bg = 0;
+  int attr = 0;
+  bool present() const { return ch != 0; }
+  bool operator==(const Cell& o) const { return ch == o.ch && fg == o.fg && bg == o.bg && attr == o.attr; }
+  bool operator!=(const Cell& o) const { return !(*this == o); }
+};
+using Row = std::vector<Cell>;
+using Grid = std::vector<Row>;
+
+constexpr Cell blank_cell() { return Cell{L' ', 0, 0, 0}; }  // MplexCanvas.BLANK
+
+// ---- ordered dict ----------------------------------------------------------------
+
+// Python dict semantics for the parts the port uses: insertion order is iteration order,
+// setting an existing key keeps its position, pop/erase removes it.
+template <typename K, typename V>
+class OrderedMap {
+ public:
+  using Entry = std::pair<K, V>;
+  bool contains(const K& key) const { return find_index(key) >= 0; }
+  V* find(const K& key) {
+    int i = find_index(key);
+    return i < 0 ? nullptr : &items_[static_cast<size_t>(i)].second;
+  }
+  const V* find(const K& key) const {
+    int i = find_index(key);
+    return i < 0 ? nullptr : &items_[static_cast<size_t>(i)].second;
+  }
+  V& set(const K& key, V value) {
+    int i = find_index(key);
+    if (i >= 0) {
+      items_[static_cast<size_t>(i)].second = std::move(value);
+      return items_[static_cast<size_t>(i)].second;
+    }
+    items_.emplace_back(key, std::move(value));
+    return items_.back().second;
+  }
+  // dict.pop(key, None): returns whether it was there.
+  bool erase(const K& key) {
+    int i = find_index(key);
+    if (i < 0) return false;
+    items_.erase(items_.begin() + i);
+    return true;
+  }
+  void clear() { items_.clear(); }
+  size_t size() const { return items_.size(); }
+  bool empty() const { return items_.empty(); }
+  std::vector<K> keys() const {
+    std::vector<K> out;
+    for (const auto& e : items_) out.push_back(e.first);
+    return out;
+  }
+  std::vector<V> values() const {
+    std::vector<V> out;
+    for (const auto& e : items_) out.push_back(e.second);
+    return out;
+  }
+  const std::vector<Entry>& items() const { return items_; }
+  std::vector<Entry>& items() { return items_; }
+
+ private:
+  int find_index(const K& key) const {
+    for (size_t i = 0; i < items_.size(); ++i)
+      if (items_[i].first == key) return static_cast<int>(i);
+    return -1;
+  }
+  std::vector<Entry> items_;
+};
+
+}  // namespace detz::mplex
diff --git a/taicpp/src/mplex/mplex_config.h b/taicpp/src/mplex/mplex_config.h
new file mode 100644
index 0000000..28120f0
--- /dev/null
+++ b/taicpp/src/mplex/mplex_config.h
@@ -0,0 +1,54 @@
+// MplexBinding and MplexConfig: tmux 3.6 default key tables plus ~/.tai/mplex.toml. tai.py:10850.
+#pragma once
+#include <string>
+#include <vector>
+
+#include "mplex_common.h"
+#include "mplex_options.h"
+#include "mplex_toml.h"
+
+namespace detz::mplex {
+
+struct MplexBinding {
+  std::string command;
+  bool repeat = false;
+  std::string note;
+};
+
+// One row of MPLEX_DEFAULT_KEYS: (table, key, command, repeat, note). Generated from tai.py.
+struct DefaultKey {
+  const char* table;
+  const char* key;
+  const char* command;
+  bool repeat;
+  const char* note;
+};
+const std::vector<DefaultKey>& mplex_default_keys();  // mplex_default_keys.cpp
+
+class MplexConfig {
+ public:
+  static constexpr size_t ERRORS_MAX = 50;
+  using Table = OrderedMap<std::string, MplexBinding>;
+
+  MplexConfig();  // options + default tables
+  MplexOptions options;
+  OrderedMap<std::string, Table> tables;  // insertion ordered, like the Python dicts
+  std::vector<std::string> errors;
+  std::string path;
+  int skipped = 0;
+
+  void error(const std::string& text);
+  void bind(const std::string& table, const std::string& key, const std::string& command, bool repeat = false,
+            const std::string& note = "");
+  bool unbind(const std::string& table, const std::string& key);
+  const MplexBinding* lookup(const std::string& table, const std::string& key) const;
+  static std::string default_path(const std::string& home);
+  static std::shared_ptr<MplexConfig> load(const std::string& path);
+  void apply_file(const std::string& path);
+  void apply_data(const TomlValue& data);
+
+ private:
+  void apply_binding(const std::string& table, const std::string& key, const TomlValue& spec);
+};
+
+}  // namespace detz::mplex
diff --git a/taicpp/src/mplex/mplex_ctx.h b/taicpp/src/mplex/mplex_ctx.h
new file mode 100644
index 0000000..6200295
--- /dev/null
+++ b/taicpp/src/mplex/mplex_ctx.h
@@ -0,0 +1,48 @@
+// MplexCtx (tai.py:13684) and MplexTargets (:13712).
+#pragma once
+#include <memory>
+#include <string>
+#include <tuple>
+
+#include "mplex_common.h"
+#include "mplex_pane.h"
+
+namespace detz::mplex {
+
+class MplexServer;
+class MplexClientConn;
+
+// What a command runs against: the issuing client and its current session, window, pane.
+class MplexCtx {
+ public:
+  MplexCtx(MplexServer* server_in, std::shared_ptr<MplexClientConn> client_in = nullptr,
+           std::shared_ptr<MplexPane> pane_in = nullptr, bool interactive_in = false);
+  MplexServer* server;
+  std::shared_ptr<MplexClientConn> client;
+  bool interactive;
+  int depth = 0;
+  std::shared_ptr<MplexPane> pane;
+  std::shared_ptr<MplexWindow> window;
+  std::shared_ptr<MplexSession> session;
+};
+
+// tmux target syntax: session, session:window, session:window.pane, %pane, @window, $session.
+class MplexTargets {
+ public:
+  struct WindowTarget {
+    std::shared_ptr<MplexSession> session;
+    std::optional<int> index;
+    std::shared_ptr<MplexWindow> window;
+  };
+  struct PaneTarget {
+    std::shared_ptr<MplexSession> session;
+    std::shared_ptr<MplexWindow> window;
+    std::shared_ptr<MplexPane> pane;
+  };
+  static std::shared_ptr<MplexSession> session(MplexCtx& ctx, const std::string& spec);
+  static WindowTarget window(MplexCtx& ctx, const std::string& spec);
+  static std::optional<int> window_index(const std::shared_ptr<MplexSession>& session, const std::string& text);
+  static PaneTarget pane(MplexCtx& ctx, const std::string& spec);
+};
+
+}  // namespace detz::mplex
diff --git a/taicpp/src/mplex/mplex_default_keys.cpp b/taicpp/src/mplex/mplex_default_keys.cpp
new file mode 100644
index 0000000..72a3cd5
--- /dev/null
+++ b/taicpp/src/mplex/mplex_default_keys.cpp
@@ -0,0 +1,247 @@
+// Generated from MPLEX_DEFAULT_KEYS in ../../../tai.py (tmux 3.6 defaults minus mouse bindings).
+// Regenerate, never hand edit: the C++ spec test compares this table with mplex.md and tai.py.
+#include "mplex_config.h"
+
+namespace detz::mplex {
+
+const std::vector<DefaultKey>& mplex_default_keys() {
+  static const std::vector<DefaultKey> table = {
+      {"copy-mode", "Escape", "send-keys -X cancel", false, ""},
+      {"copy-mode", "Space", "send-keys -X page-down", false, ""},
+      {"copy-mode", ",", "send-keys -X jump-reverse", false, ""},
+      {"copy-mode", ";", "send-keys -X jump-again", false, ""},
+      {"copy-mode", "F", "command-prompt -1 -p \"(jump backward)\" { send-keys -X jump-backward -- \"%%\" }", false, ""},
+      {"copy-mode", "N", "send-keys -X search-reverse", false, ""},
+      {"copy-mode", "P", "send-keys -X toggle-position", false, ""},
+      {"copy-mode", "R", "send-keys -X rectangle-toggle", false, ""},
+      {"copy-mode", "T", "command-prompt -1 -p \"(jump to backward)\" { send-keys -X jump-to-backward -- \"%%\" }", false, ""},
+      {"copy-mode", "X", "send-keys -X set-mark", false, ""},
+      {"copy-mode", "f", "command-prompt -1 -p \"(jump forward)\" { send-keys -X jump-forward -- \"%%\" }", false, ""},
+      {"copy-mode", "g", "command-prompt -p \"(goto line)\" { send-keys -X goto-line -- \"%%\" }", false, ""},
+      {"copy-mode", "n", "send-keys -X search-again", false, ""},
+      {"copy-mode", "q", "send-keys -X cancel", false, ""},
+      {"copy-mode", "r", "send-keys -X refresh-from-pane", false, ""},
+      {"copy-mode", "t", "command-prompt -1 -p \"(jump to forward)\" { send-keys -X jump-to-forward -- \"%%\" }", false, ""},
+      {"copy-mode", "Home", "send-keys -X start-of-line", false, ""},
+      {"copy-mode", "End", "send-keys -X end-of-line", false, ""},
+      {"copy-mode", "NPage", "send-keys -X page-down", false, ""},
+      {"copy-mode", "PPage", "send-keys -X page-up", false, ""},
+      {"copy-mode", "Up", "send-keys -X cursor-up", false, ""},
+      {"copy-mode", "Down", "send-keys -X cursor-down", false, ""},
+      {"copy-mode", "Left", "send-keys -X cursor-left", false, ""},
+      {"copy-mode", "Right", "send-keys -X cursor-right", false, ""},
+      {"copy-mode", "M-1", "command-prompt -N -I 1 -p (repeat) { send-keys -N \"%%\" }", false, ""},
+      {"copy-mode", "M-2", "command-prompt -N -I 2 -p (repeat) { send-keys -N \"%%\" }", false, ""},
+      {"copy-mode", "M-3", "command-prompt -N -I 3 -p (repeat) { send-keys -N \"%%\" }", false, ""},
+      {"copy-mode", "M-4", "command-prompt -N -I 4 -p (repeat) { send-keys -N \"%%\" }", false, ""},
+      {"copy-mode", "M-5", "command-prompt -N -I 5 -p (repeat) { send-keys -N \"%%\" }", false, ""},
+      {"copy-mode", "M-6", "command-prompt -N -I 6 -p (repeat) { send-keys -N \"%%\" }", false, ""},
+      {"copy-mode", "M-7", "command-prompt -N -I 7 -p (repeat) { send-keys -N \"%%\" }", false, ""},
+      {"copy-mode", "M-8", "command-prompt -N -I 8 -p (repeat) { send-keys -N \"%%\" }", false, ""},
+      {"copy-mode", "M-9", "command-prompt -N -I 9 -p (repeat) { send-keys -N \"%%\" }", false, ""},
+      {"copy-mode", "M-<", "send-keys -X history-top", false, ""},
+      {"copy-mode", "M->", "send-keys -X history-bottom", false, ""},
+      {"copy-mode", "M-R", "send-keys -X top-line", false, ""},
+      {"copy-mode", "M-b", "send-keys -X previous-word", false, ""},
+      {"copy-mode", "M-f", "send-keys -X next-word-end", false, ""},
+      {"copy-mode", "M-l", "send-keys -X cursor-centre-horizontal", false, ""},
+      {"copy-mode", "M-m", "send-keys -X back-to-indentation", false, ""},
+      {"copy-mode", "M-r", "send-keys -X middle-line", false, ""},
+      {"copy-mode", "M-v", "send-keys -X page-up", false, ""},
+      {"copy-mode", "M-w", "send-keys -X copy-pipe-and-cancel", false, ""},
+      {"copy-mode", "M-x", "send-keys -X jump-to-mark", false, ""},
+      {"copy-mode", "M-{", "send-keys -X previous-paragraph", false, ""},
+      {"copy-mode", "M-}", "send-keys -X next-paragraph", false, ""},
+      {"copy-mode", "M-Up", "send-keys -X halfpage-up", false, ""},
+      {"copy-mode", "M-Down", "send-keys -X halfpage-down", false, ""},
+      {"copy-mode", "C-Space", "send-keys -X begin-selection", false, ""},
+      {"copy-mode", "C-a", "send-keys -X start-of-line", false, ""},
+      {"copy-mode", "C-b", "send-keys -X cursor-left", false, ""},
+      {"copy-mode", "C-c", "send-keys -X cancel", false, ""},
+      {"copy-mode", "C-e", "send-keys -X end-of-line", false, ""},
+      {"copy-mode", "C-f", "send-keys -X cursor-right", false, ""},
+      {"copy-mode", "C-g", "send-keys -X clear-selection", false, ""},
+      {"copy-mode", "C-k", "send-keys -X copy-pipe-end-of-line-and-cancel", false, ""},
+      {"copy-mode", "C-l", "send-keys -X cursor-centre-vertical", false, ""},
+      {"copy-mode", "C-n", "send-keys -X cursor-down", false, ""},
+      {"copy-mode", "C-p", "send-keys -X cursor-up", false, ""},
+      {"copy-mode", "C-r", "command-prompt -i -I \"#{pane_search_string}\" -T search -p \"(search up)\" { send-keys -X search-backward-incremental -- \"%%\" }", false, ""},
+      {"copy-mode", "C-s", "command-prompt -i -I \"#{pane_search_string}\" -T search -p \"(search down)\" { send-keys -X search-forward-incremental -- \"%%\" }", false, ""},
+      {"copy-mode", "C-v", "send-keys -X page-down", false, ""},
+      {"copy-mode", "C-w", "send-keys -X copy-pipe-and-cancel", false, ""},
+      {"copy-mode", "C-Up", "send-keys -X scroll-up", false, ""},
+      {"copy-mode", "C-Down", "send-keys -X scroll-down", false, ""},
+      {"copy-mode", "C-M-b", "send-keys -X previous-matching-bracket", false, ""},
+      {"copy-mode", "C-M-f", "send-keys -X next-matching-bracket", false, ""},
+      {"copy-mode-vi", "Enter", "send-keys -X copy-pipe-and-cancel", false, ""},
+      {"copy-mode-vi", "Escape", "send-keys -X clear-selection", false, ""},
+      {"copy-mode-vi", "Space", "send-keys -X begin-selection", false, ""},
+      {"copy-mode-vi", "#", "send-keys -FX search-backward -- \"#{copy_cursor_word}\"", false, ""},
+      {"copy-mode-vi", "$", "send-keys -X end-of-line", false, ""},
+      {"copy-mode-vi", "%", "send-keys -X next-matching-bracket", false, ""},
+      {"copy-mode-vi", "*", "send-keys -FX search-forward -- \"#{copy_cursor_word}\"", false, ""},
+      {"copy-mode-vi", ",", "send-keys -X jump-reverse", false, ""},
+      {"copy-mode-vi", "/", "command-prompt -T search -p \"(search down)\" { send-keys -X search-forward -- \"%%\" }", false, ""},
+      {"copy-mode-vi", "0", "send-keys -X start-of-line", false, ""},
+      {"copy-mode-vi", "1", "command-prompt -N -I 1 -p (repeat) { send-keys -N \"%%\" }", false, ""},
+      {"copy-mode-vi", "2", "command-prompt -N -I 2 -p (repeat) { send-keys -N \"%%\" }", false, ""},
+      {"copy-mode-vi", "3", "command-prompt -N -I 3 -p (repeat) { send-keys -N \"%%\" }", false, ""},
+      {"copy-mode-vi", "4", "command-prompt -N -I 4 -p (repeat) { send-keys -N \"%%\" }", false, ""},
+      {"copy-mode-vi", "5", "command-prompt -N -I 5 -p (repeat) { send-keys -N \"%%\" }", false, ""},
+      {"copy-mode-vi", "6", "command-prompt -N -I 6 -p (repeat) { send-keys -N \"%%\" }", false, ""},
+      {"copy-mode-vi", "7", "command-prompt -N -I 7 -p (repeat) { send-keys -N \"%%\" }", false, ""},
+      {"copy-mode-vi", "8", "command-prompt -N -I 8 -p (repeat) { send-keys -N \"%%\" }", false, ""},
+      {"copy-mode-vi", "9", "command-prompt -N -I 9 -p (repeat) { send-keys -N \"%%\" }", false, ""},
+      {"copy-mode-vi", ":", "command-prompt -p \"(goto line)\" { send-keys -X goto-line -- \"%%\" }", false, ""},
+      {"copy-mode-vi", ";", "send-keys -X jump-again", false, ""},
+      {"copy-mode-vi", "\?", "command-prompt -T search -p \"(search up)\" { send-keys -X search-backward -- \"%%\" }", false, ""},
+      {"copy-mode-vi", "A", "send-keys -X append-selection-and-cancel", false, ""},
+      {"copy-mode-vi", "B", "send-keys -X previous-space", false, ""},
+      {"copy-mode-vi", "D", "send-keys -X copy-pipe-end-of-line-and-cancel", false, ""},
+      {"copy-mode-vi", "E", "send-keys -X next-space-end", false, ""},
+      {"copy-mode-vi", "F", "command-prompt -1 -p \"(jump backward)\" { send-keys -X jump-backward -- \"%%\" }", false, ""},
+      {"copy-mode-vi", "G", "send-keys -X history-bottom", false, ""},
+      {"copy-mode-vi", "H", "send-keys -X top-line", false, ""},
+      {"copy-mode-vi", "J", "send-keys -X scroll-down", false, ""},
+      {"copy-mode-vi", "K", "send-keys -X scroll-up", false, ""},
+      {"copy-mode-vi", "L", "send-keys -X bottom-line", false, ""},
+      {"copy-mode-vi", "M", "send-keys -X middle-line", false, ""},
+      {"copy-mode-vi", "N", "send-keys -X search-reverse", false, ""},
+      {"copy-mode-vi", "P", "send-keys -X toggle-position", false, ""},
+      {"copy-mode-vi", "T", "command-prompt -1 -p \"(jump to backward)\" { send-keys -X jump-to-backward -- \"%%\" }", false, ""},
+      {"copy-mode-vi", "V", "send-keys -X select-line", false, ""},
+      {"copy-mode-vi", "W", "send-keys -X next-space", false, ""},
+      {"copy-mode-vi", "X", "send-keys -X set-mark", false, ""},
+      {"copy-mode-vi", "^", "send-keys -X back-to-indentation", false, ""},
+      {"copy-mode-vi", "b", "send-keys -X previous-word", false, ""},
+      {"copy-mode-vi", "e", "send-keys -X next-word-end", false, ""},
+      {"copy-mode-vi", "f", "command-prompt -1 -p \"(jump forward)\" { send-keys -X jump-forward -- \"%%\" }", false, ""},
+      {"copy-mode-vi", "g", "send-keys -X history-top", false, ""},
+      {"copy-mode-vi", "h", "send-keys -X cursor-left", false, ""},
+      {"copy-mode-vi", "j", "send-keys -X cursor-down", false, ""},
+      {"copy-mode-vi", "k", "send-keys -X cursor-up", false, ""},
+      {"copy-mode-vi", "l", "send-keys -X cursor-right", false, ""},
+      {"copy-mode-vi", "n", "send-keys -X search-again", false, ""},
+      {"copy-mode-vi", "o", "send-keys -X other-end", false, ""},
+      {"copy-mode-vi", "q", "send-keys -X cancel", false, ""},
+      {"copy-mode-vi", "r", "send-keys -X refresh-from-pane", false, ""},
+      {"copy-mode-vi", "t", "command-prompt -1 -p \"(jump to forward)\" { send-keys -X jump-to-forward -- \"%%\" }", false, ""},
+      {"copy-mode-vi", "v", "send-keys -X rectangle-toggle", false, ""},
+      {"copy-mode-vi", "w", "send-keys -X next-word", false, ""},
+      {"copy-mode-vi", "z", "send-keys -X scroll-middle", false, ""},
+      {"copy-mode-vi", "{", "send-keys -X previous-paragraph", false, ""},
+      {"copy-mode-vi", "}", "send-keys -X next-paragraph", false, ""},
+      {"copy-mode-vi", "BSpace", "send-keys -X cursor-left", false, ""},
+      {"copy-mode-vi", "Home", "send-keys -X start-of-line", false, ""},
+      {"copy-mode-vi", "End", "send-keys -X end-of-line", false, ""},
+      {"copy-mode-vi", "NPage", "send-keys -X page-down", false, ""},
+      {"copy-mode-vi", "PPage", "send-keys -X page-up", false, ""},
+      {"copy-mode-vi", "Up", "send-keys -X cursor-up", false, ""},
+      {"copy-mode-vi", "Down", "send-keys -X cursor-down", false, ""},
+      {"copy-mode-vi", "Left", "send-keys -X cursor-left", false, ""},
+      {"copy-mode-vi", "Right", "send-keys -X cursor-right", false, ""},
+      {"copy-mode-vi", "M-x", "send-keys -X jump-to-mark", false, ""},
+      {"copy-mode-vi", "C-b", "send-keys -X page-up", false, ""},
+      {"copy-mode-vi", "C-c", "send-keys -X cancel", false, ""},
+      {"copy-mode-vi", "C-d", "send-keys -X halfpage-down", false, ""},
+      {"copy-mode-vi", "C-e", "send-keys -X scroll-down", false, ""},
+      {"copy-mode-vi", "C-f", "send-keys -X page-down", false, ""},
+      {"copy-mode-vi", "C-h", "send-keys -X cursor-left", false, ""},
+      {"copy-mode-vi", "C-j", "send-keys -X copy-pipe-and-cancel", false, ""},
+      {"copy-mode-vi", "C-u", "send-keys -X halfpage-up", false, ""},
+      {"copy-mode-vi", "C-v", "send-keys -X rectangle-toggle", false, ""},
+      {"copy-mode-vi", "C-y", "send-keys -X scroll-up", false, ""},
+      {"copy-mode-vi", "C-Up", "send-keys -X scroll-up", false, ""},
+      {"copy-mode-vi", "C-Down", "send-keys -X scroll-down", false, ""},
+      {"prefix", "Space", "next-layout", false, "Select next layout"},
+      {"prefix", "!", "break-pane", false, "Break pane to a new window"},
+      {"prefix", "\"", "split-window", false, "Split window vertically"},
+      {"prefix", "#", "list-buffers", false, "List all paste buffers"},
+      {"prefix", "$", "command-prompt -I \"#S\" { rename-session \"%%\" }", false, "Rename current session"},
+      {"prefix", "%", "split-window -h", false, "Split window horizontally"},
+      {"prefix", "&", "confirm-before -p \"kill-window #W\? (y/n)\" kill-window", false, "Kill current window"},
+      {"prefix", "'", "command-prompt -T window-target -p index { select-window -t \":%%\" }", false, "Prompt for window index to select"},
+      {"prefix", "(", "switch-client -p", false, "Switch to previous client"},
+      {"prefix", ")", "switch-client -n", false, "Switch to next client"},
+      {"prefix", ",", "command-prompt -I \"#W\" { rename-window \"%%\" }", false, "Rename current window"},
+      {"prefix", "-", "delete-buffer", false, "Delete the most recent paste buffer"},
+      {"prefix", ".", "command-prompt -T target { move-window -t \"%%\" }", false, "Move the current window"},
+      {"prefix", "/", "command-prompt -k -p key { list-keys -1N \"%%\" }", false, "Describe key binding"},
+      {"prefix", "0", "select-window -t :=0", false, "Select window 0"},
+      {"prefix", "1", "select-window -t :=1", false, "Select window 1"},
+      {"prefix", "2", "select-window -t :=2", false, "Select window 2"},
+      {"prefix", "3", "select-window -t :=3", false, "Select window 3"},
+      {"prefix", "4", "select-window -t :=4", false, "Select window 4"},
+      {"prefix", "5", "select-window -t :=5", false, "Select window 5"},
+      {"prefix", "6", "select-window -t :=6", false, "Select window 6"},
+      {"prefix", "7", "select-window -t :=7", false, "Select window 7"},
+      {"prefix", "8", "select-window -t :=8", false, "Select window 8"},
+      {"prefix", "9", "select-window -t :=9", false, "Select window 9"},
+      {"prefix", ":", "command-prompt", false, "Prompt for a command"},
+      {"prefix", ";", "last-pane", false, "Move to the previously active pane"},
+      {"prefix", "<", "display-menu", false, "Display window menu"},
+      {"prefix", "=", "choose-buffer -Z", false, "Choose a paste buffer from a list"},
+      {"prefix", ">", "display-menu", false, "Display pane menu"},
+      {"prefix", "\?", "list-keys -N", false, "List key bindings"},
+      {"prefix", "C", "customize-mode -Z", false, "Customize options"},
+      {"prefix", "D", "choose-client -Z", false, "Choose and detach a client from a list"},
+      {"prefix", "E", "select-layout -E", false, "Spread panes out evenly"},
+      {"prefix", "L", "switch-client -l", false, "Switch to the last client"},
+      {"prefix", "M", "select-pane -M", false, "Clear the marked pane"},
+      {"prefix", "[", "copy-mode", false, "Enter copy mode"},
+      {"prefix", "]", "paste-buffer -p", false, "Paste the most recent paste buffer"},
+      {"prefix", "c", "new-window", false, "Create a new window"},
+      {"prefix", "d", "detach-client", false, "Detach the current client"},
+      {"prefix", "f", "command-prompt { find-window -Z \"%%\" }", false, "Search for a pane"},
+      {"prefix", "i", "display-message", false, "Display window information"},
+      {"prefix", "l", "last-window", false, "Select the previously current window"},
+      {"prefix", "m", "select-pane -m", false, "Toggle the marked pane"},
+      {"prefix", "n", "next-window", false, "Select the next window"},
+      {"prefix", "o", "select-pane -t :.+", false, "Select the next pane"},
+      {"prefix", "p", "previous-window", false, "Select the previous window"},
+      {"prefix", "q", "display-panes", false, "Display pane numbers"},
+      {"prefix", "r", "refresh-client", false, "Redraw the current client"},
+      {"prefix", "s", "choose-tree -Zs", false, "Choose a session from a list"},
+      {"prefix", "t", "clock-mode", false, "Show a clock"},
+      {"prefix", "w", "choose-tree -Zw", false, "Choose a window from a list"},
+      {"prefix", "x", "confirm-before -p \"kill-pane #P\? (y/n)\" kill-pane", false, "Kill the active pane"},
+      {"prefix", "z", "resize-pane -Z", false, "Zoom the active pane"},
+      {"prefix", "{", "swap-pane -U", false, "Swap the active pane with the pane above"},
+      {"prefix", "}", "swap-pane -D", false, "Swap the active pane with the pane below"},
+      {"prefix", "~", "show-messages", false, "Show messages"},
+      {"prefix", "DC", "refresh-client -c", true, "Reset so the visible part of the window follows the cursor"},
+      {"prefix", "PPage", "copy-mode -u", false, "Enter copy mode and scroll up"},
+      {"prefix", "Up", "select-pane -U", true, "Select the pane above the active pane"},
+      {"prefix", "Down", "select-pane -D", true, "Select the pane below the active pane"},
+      {"prefix", "Left", "select-pane -L", true, "Select the pane to the left of the active pane"},
+      {"prefix", "Right", "select-pane -R", true, "Select the pane to the right of the active pane"},
+      {"prefix", "M-1", "select-layout even-horizontal", false, "Set the even-horizontal layout"},
+      {"prefix", "M-2", "select-layout even-vertical", false, "Set the even-vertical layout"},
+      {"prefix", "M-3", "select-layout main-horizontal", false, "Set the main-horizontal layout"},
+      {"prefix", "M-4", "select-layout main-vertical", false, "Set the main-vertical layout"},
+      {"prefix", "M-5", "select-layout tiled", false, "Select the tiled layout"},
+      {"prefix", "M-6", "select-layout main-horizontal-mirrored", false, "Set the main-horizontal-mirrored layout"},
+      {"prefix", "M-7", "select-layout main-vertical-mirrored", false, "Set the main-vertical-mirrored layout"},
+      {"prefix", "M-n", "next-window -a", false, "Select the next window with an alert"},
+      {"prefix", "M-o", "rotate-window -D", false, "Rotate through the panes in reverse"},
+      {"prefix", "M-p", "previous-window -a", false, "Select the previous window with an alert"},
+      {"prefix", "M-Up", "resize-pane -U 5", true, "Resize the pane up by 5"},
+      {"prefix", "M-Down", "resize-pane -D 5", true, "Resize the pane down by 5"},
+      {"prefix", "M-Left", "resize-pane -L 5", true, "Resize the pane left by 5"},
+      {"prefix", "M-Right", "resize-pane -R 5", true, "Resize the pane right by 5"},
+      {"prefix", "C-b", "send-prefix", false, "Send the prefix key"},
+      {"prefix", "C-o", "rotate-window", false, "Rotate through the panes"},
+      {"prefix", "C-z", "suspend-client", false, "Suspend the current client"},
+      {"prefix", "C-Up", "resize-pane -U", true, "Resize the pane up"},
+      {"prefix", "C-Down", "resize-pane -D", true, "Resize the pane down"},
+      {"prefix", "C-Left", "resize-pane -L", true, "Resize the pane left"},
+      {"prefix", "C-Right", "resize-pane -R", true, "Resize the pane right"},
+      {"prefix", "S-Up", "refresh-client -U 10", true, "Move the visible part of the window up"},
+      {"prefix", "S-Down", "refresh-client -D 10", true, "Move the visible part of the window down"},
+      {"prefix", "S-Left", "refresh-client -L 10", true, "Move the visible part of the window left"},
+      {"prefix", "S-Right", "refresh-client -R 10", true, "Move the visible part of the window right"},
+  };
+  return table;
+}
+
+}  // namespace detz::mplex
diff --git a/taicpp/src/mplex/mplex_flowscreen.h b/taicpp/src/mplex/mplex_flowscreen.h
new file mode 100644
index 0000000..9c85713
--- /dev/null
+++ b/taicpp/src/mplex/mplex_flowscreen.h
@@ -0,0 +1,32 @@
+// MplexFlowScreen: one plexer_show screen on a native client (tai.py:13248).
+#pragma once
+#include <string>
+#include <vector>
+
+#include "mplex_json.h"
+#include "mplex_mode.h"
+
+namespace detz::mplex {
+
+struct MplexFlowRecord;
+
+class MplexFlowScreen : public MplexOverlay {
+ public:
+  MplexFlowScreen(MplexServer* server_in, int flow_id_in, const std::string& title_in, const std::string& text_in,
+                  const std::vector<std::string>& options_in, int cursor_in, double until_in);
+  MplexServer* server;
+  int flow_id;
+  std::string title, text;
+  std::vector<std::string> options;
+  int cursor;
+  Style box, bold, sel, dim;
+
+  MplexFlowRecord* record() const;  // server.flows.get(flow_id), null when gone
+  // answer(client, status, value): value None / True / an option index.
+  void answer(MplexClientConn& client, const std::string& status, const Json& value = Json());
+  void key(const std::string& name, const Bytes& raw, MplexClientConn& client) override;
+  std::vector<std::string> rows(int width) const;
+  void draw(MplexCanvas& canvas, int area_y) override;
+};
+
+}  // namespace detz::mplex
diff --git a/taicpp/src/mplex/mplex_format.h b/taicpp/src/mplex/mplex_format.h
new file mode 100644
index 0000000..fffbf2e
--- /dev/null
+++ b/taicpp/src/mplex/mplex_format.h
@@ -0,0 +1,32 @@
+// MplexFormat: tmux format strings. tai.py:10987.
+#pragma once
+#include <functional>
+#include <optional>
+#include <string>
+#include <vector>
+
+#include "mplex_common.h"
+
+namespace detz::mplex {
+
+class MplexFormat {
+ public:
+  // resolve(name) -> value, or nullopt for Python None. "(command" names are #(shell) requests.
+  using Resolver = std::function<std::optional<std::string>(const std::string&)>;
+  static constexpr int DEPTH_MAX = 12;
+
+  static long match_close(const std::string& text, long start, char opener, char closer);
+  static std::vector<std::string> split_commas(const std::string& text);
+  static std::string expand(const std::string& text, const Resolver& resolve, int depth = 0);
+  static bool truthy(const std::optional<std::string>& value);
+  static std::string value_of(const std::string& text, const Resolver& resolve, int depth);
+  static std::string evaluate(const std::string& inner, const Resolver& resolve, int depth);
+  static long modifier_colon(const std::string& inner);
+  static std::string apply_modifiers(const std::string& mods, const std::string& rest, const Resolver& resolve, int depth);
+  static std::string apply_one(const std::string& spec, const std::string& text, const Resolver& resolve, int depth);
+  static std::string compare(const std::string& op, const std::string& left, const std::string& right);
+  static std::string with_time(const std::string& text, double stamp = -1.0);  // time.strftime when "%" in text
+  static std::string strip_styles(const std::string& text);
+};
+
+}  // namespace detz::mplex
diff --git a/taicpp/src/mplex/mplex_input.h b/taicpp/src/mplex/mplex_input.h
new file mode 100644
index 0000000..d65fca6
--- /dev/null
+++ b/taicpp/src/mplex/mplex_input.h
@@ -0,0 +1,34 @@
+// The slice of the tai.py TUI input parser that MplexKeys.split uses: tui_parse_one and the
+// events it yields (TuiKey and the event kinds that are not keys). Implemented in mplex_input.cpp.
+#pragma once
+#include <string>
+#include <vector>
+
+#include "mplex_common.h"
+
+namespace detz::mplex {
+
+// What tui_parse_one returns in its first slot.
+struct TuiEvent {
+  enum class Kind {
+    None,      // Python None: consumed bytes that are not an event (or an empty buffer)
+    NeedMore,  // "need_more"
+    Escape,    // "escape"
+    Key,       // TuiKey
+    Other,     // TuiClick / TuiScroll / TuiPaste / TuiModeReply: anything MplexKeys maps to ""
+  };
+  Kind kind = Kind::None;
+  std::string key;                     // TuiKey.key, e.g. "up", "ctrl+x", "alt+f", "f5"
+  std::string chr;                     // TuiKey.char (UTF-8)
+  std::vector<std::string> modifiers;  // TuiKey.modifiers
+};
+
+struct TuiParsed {
+  TuiEvent event;
+  Bytes rest;  // the unconsumed tail of the buffer
+};
+
+// tui_parse_one(buf, final): parse one event from the head of buf (see tai.py 23910).
+TuiParsed tui_parse_one(const Bytes& buf, bool final);
+
+}  // namespace detz::mplex
diff --git a/taicpp/src/mplex/mplex_keys.h b/taicpp/src/mplex/mplex_keys.h
new file mode 100644
index 0000000..f06d909
--- /dev/null
+++ b/taicpp/src/mplex/mplex_keys.h
@@ -0,0 +1,30 @@
+// MplexKeys: key names in tmux notation, byte decoding, byte encoding. tai.py:10270.
+#pragma once
+#include <string>
+#include <utility>
+#include <vector>
+
+#include "mplex_common.h"
+#include "mplex_input.h"
+
+namespace detz::mplex {
+
+class MplexKeys {
+ public:
+  using Token = std::pair<std::string, Bytes>;  // (name, raw); name is "" for sequences that are not keys
+  struct Split {
+    std::vector<Token> tokens;
+    Bytes rest;
+  };
+
+  static std::string canonical(const std::string& spec);  // throws MplexError("empty key name"/"unknown key: ...")
+  static std::string name_of_char(const Bytes& raw);
+  static Split split(const Bytes& data, bool final = false);
+  static Bytes to_bytes(const std::string& name, bool app_cursor = false);  // throws MplexError
+  static Bytes app_cursor_form(const Bytes& raw);
+
+ private:
+  static std::string name_of_event(const TuiEvent& event, const Bytes& raw);
+};
+
+}  // namespace detz::mplex
diff --git a/taicpp/src/mplex/mplex_layout.h b/taicpp/src/mplex/mplex_layout.h
new file mode 100644
index 0000000..3377259
--- /dev/null
+++ b/taicpp/src/mplex/mplex_layout.h
@@ -0,0 +1,52 @@
+// MplexLayoutNode and MplexLayout: the split tree. tai.py:11261.
+#pragma once
+#include <memory>
+#include <string>
+#include <vector>
+
+#include "mplex_common.h"
+
+namespace detz::mplex {
+
+class MplexPane;
+
+class MplexLayoutNode : public std::enable_shared_from_this<MplexLayoutNode> {
+ public:
+  using Ptr = std::shared_ptr<MplexLayoutNode>;
+  // kind: "pane", "lr" (side by side) or "tb" (stacked).
+  MplexLayoutNode(const std::string& kind_in, std::shared_ptr<MplexPane> pane_in = nullptr, int w_in = 1, int h_in = 1);
+
+  bool reverse = false;
+  std::string kind;
+  std::vector<Ptr> children;
+  std::weak_ptr<MplexLayoutNode> parent;  // back reference
+  std::shared_ptr<MplexPane> pane;
+  int x = 0, y = 0, w = 1, h = 1;
+
+  Ptr parent_node() const { return parent.lock(); }
+  std::vector<Ptr> leaves();
+  Ptr adopt(const Ptr& child);
+};
+
+class MplexLayout {
+ public:
+  using Node = MplexLayoutNode::Ptr;
+  static int size_of(const Node& node, const std::string& kind);
+  static void set_size(const Node& node, const std::string& kind, int value);
+  static void assign(const Node& node, int x, int y, int w, int h);
+  // Insert new_pane beside leaf; returns (root, new_leaf). size < 0 means None.
+  static std::pair<Node, Node> split(Node root, const Node& leaf, const std::string& kind, bool before,
+                                     const std::shared_ptr<MplexPane>& new_pane, int size = -1);
+  static Node remove(Node root, const Node& leaf);  // returns the new root (null when empty)
+  static void resize_by(const Node& leaf, const std::string& kind, int delta, bool prefer_after);
+  static std::vector<int> shares(int total, int count, bool spare_first);
+  static void resize_to(const Node& leaf, const std::string& kind, int size);
+  static Node preset(const std::string& name, const std::vector<std::shared_ptr<MplexPane>>& panes, int width,
+                     int height, int main_width, int main_height);
+  // The pane to move to in direction "L"/"R"/"U"/"D", or null.
+  static std::shared_ptr<MplexPane> neighbour(const std::vector<std::shared_ptr<MplexPane>>& panes,
+                                              const std::shared_ptr<MplexPane>& current, char direction, int width,
+                                              int height);
+};
+
+}  // namespace detz::mplex
diff --git a/taicpp/src/mplex/mplex_mode.h b/taicpp/src/mplex/mplex_mode.h
new file mode 100644
index 0000000..1315fcd
--- /dev/null
+++ b/taicpp/src/mplex/mplex_mode.h
@@ -0,0 +1,50 @@
+// MplexMode: pane mode base (tai.py:12017), and MplexOverlay, the shared face of the client
+// overlays (MplexPaneNumbers, MplexFlowScreen) that Python duck-types.
+#pragma once
+#include <memory>
+#include <optional>
+#include <string>
+#include <utility>
+
+#include "mplex_common.h"
+
+namespace detz::mplex {
+
+class MplexServer;
+class MplexPane;
+class MplexClientConn;
+class MplexCanvas;
+
+// What Mode.render returns: a pane-sized block of cells and the cursor inside it (None = hidden).
+struct ModeBlock {
+  Grid grid;
+  std::optional<std::pair<int, int>> cursor;  // (x, y)
+};
+
+// Pane mode base: owns the pane's keyboard and its drawing while it is on top.
+class MplexMode : public std::enable_shared_from_this<MplexMode> {
+ public:
+  MplexMode(MplexServer* server_in, std::shared_ptr<MplexPane> pane_in) : server(server_in), pane(std::move(pane_in)) {}
+  virtual ~MplexMode() = default;
+
+  std::string name = "mode";
+  MplexServer* server;
+  std::shared_ptr<MplexPane> pane;  // cycle with pane->modes is broken by MplexServer::discard_pane
+
+  virtual ModeBlock render(MplexClientConn& client);                                  // base: NotImplementedError
+  virtual void key(const std::string& name, const Bytes& raw, MplexClientConn& client);  // base: no-op
+  virtual void on_output(long pushed, long evicted);                                  // base: no-op
+  virtual void on_resize();                                                           // base: no-op
+  virtual void close();                                                               // pane.pop_mode(self); server.mark_dirty(window)
+};
+
+// Python duck typing: a client overlay has key(), draw() and an expiry (`until`, monotonic seconds).
+class MplexOverlay {
+ public:
+  virtual ~MplexOverlay() = default;
+  double until = 0.0;
+  virtual void key(const std::string& name, const Bytes& raw, MplexClientConn& client) = 0;
+  virtual void draw(MplexCanvas& canvas, int area_y) = 0;
+};
+
+}  // namespace detz::mplex
diff --git a/taicpp/src/mplex/mplex_options.h b/taicpp/src/mplex/mplex_options.h
new file mode 100644
index 0000000..f36c967
--- /dev/null
+++ b/taicpp/src/mplex/mplex_options.h
@@ -0,0 +1,61 @@
+// MplexOptions: typed option store with a parent chain (window, session, global). tai.py:10723.
+#pragma once
+#include <map>
+#include <string>
+#include <vector>
+
+#include "mplex_common.h"
+
+namespace detz::mplex {
+
+// A Python option value: bool, int or str.
+struct OptValue {
+  enum class Kind { Bool, Int, Str };
+  Kind kind = Kind::Str;
+  bool b = false;
+  long long i = 0;
+  std::string s;
+  static OptValue of_bool(bool v) { OptValue o; o.kind = Kind::Bool; o.b = v; return o; }
+  static OptValue of_int(long long v) { OptValue o; o.kind = Kind::Int; o.i = v; return o; }
+  static OptValue of_str(std::string v) { OptValue o; o.kind = Kind::Str; o.s = std::move(v); return o; }
+  bool is_bool() const { return kind == Kind::Bool; }
+  bool is_int() const { return kind == Kind::Int; }
+  bool is_str() const { return kind == Kind::Str; }
+  // Python truthiness of the value.
+  bool truthy() const { return kind == Kind::Bool ? b : kind == Kind::Int ? i != 0 : !s.empty(); }
+  // str(value) as a format variable: True/False are "1"/"0" at the call site, str() otherwise.
+  std::string str() const { return kind == Kind::Bool ? (b ? "True" : "False") : kind == Kind::Int ? std::to_string(i) : s; }
+  bool operator==(const OptValue& o) const {
+    return kind == o.kind && b == o.b && i == o.i && s == o.s;
+  }
+};
+
+struct OptionDef {
+  std::string name;
+  std::string kind;  // "str" "bool" "key" "colour" "style" "int:LOW:HIGH" "choice:a|b"
+  OptValue def;
+};
+
+class MplexOptions {
+ public:
+  static const char* const WORD_SEPARATORS;
+  // DEFS in the order of the Python dict literal (the order show-options and list output use).
+  static const std::vector<OptionDef>& defs();
+  static const OptionDef* find_def(const std::string& name);
+
+  explicit MplexOptions(MplexOptions* parent_in = nullptr) : parent(parent_in) {}
+
+  MplexOptions* parent = nullptr;
+  std::map<std::string, OptValue> values;      // lookup only
+  std::vector<std::string> value_order;        // insertion order of names in values (dict order)
+
+  static OptValue check(const std::string& name, const std::string& raw);  // throws MplexError
+  OptValue get(const std::string& name) const;       // throws std::out_of_range-like KeyError via MplexError for unknown names
+  bool is_set(const std::string& name) const { return values.count(name) != 0; }
+  OptValue set(const std::string& name, const std::string& raw, bool append = false);
+  void toggle(const std::string& name);
+  void unset(const std::string& name);
+  static std::string show(const OptValue& value);  // on/off/str
+};
+
+}  // namespace detz::mplex
diff --git a/taicpp/src/mplex/mplex_pane.cpp b/taicpp/src/mplex/mplex_pane.cpp
index 1d699d2..b08c1db 100644
--- a/taicpp/src/mplex/mplex_pane.cpp
+++ b/taicpp/src/mplex/mplex_pane.cpp
@@ -362,7 +362,7 @@ MplexLayoutNode::Ptr MplexWindow::leaf_of(const std::shared_ptr<MplexPane>& pane
   return nullptr;
 }
 
-void MplexWindow::set_active(const std::shared_ptr<MplexPane>& pane) {
+void MplexWindow::set_active(std::shared_ptr<MplexPane> pane) {
   if (pane != active) {
     last_pane = active;
     active = pane;
diff --git a/taicpp/src/mplex/mplex_pane.h b/taicpp/src/mplex/mplex_pane.h
new file mode 100644
index 0000000..7c3fc3b
--- /dev/null
+++ b/taicpp/src/mplex/mplex_pane.h
@@ -0,0 +1,140 @@
+// MplexPane (tai.py:11549), MplexWindow (:11775), MplexSession (:11825).
+#pragma once
+#include <sys/types.h>
+
+#include <memory>
+#include <optional>
+#include <string>
+#include <vector>
+
+#include "mplex_common.h"
+#include "mplex_layout.h"
+#include "mplex_options.h"
+#include "mplex_vtscreen.h"
+
+namespace detz::mplex {
+
+class MplexMode;
+class MplexWindow;
+class MplexSession;
+
+// One pty-backed shell: its screen, scrollback, output queue and mode stack.
+class MplexPane : public std::enable_shared_from_this<MplexPane> {
+ public:
+  using EnvList = std::vector<std::pair<std::string, std::string>>;
+  MplexPane(int ident, int cols, int rows, int history_limit, const std::string& home_dir,
+            const std::string& stamp = "0");
+  ~MplexPane();
+
+  int id;
+  std::weak_ptr<MplexWindow> window_ref;  // back reference; use window() / set_window()
+  int x = 0, y = 0, w, h;
+  MplexVtScreen screen;
+  int master_fd = -1;                 // -1 == None
+  std::optional<pid_t> pid;
+  bool dead = false;
+  std::optional<int> exit_status;
+  Bytes pending_in;
+  long dropped = 0;
+  std::vector<std::shared_ptr<MplexMode>> modes;
+  int prefix_count = 1;
+  double created;
+  double last_active = 0.0;
+  std::string shell_name;
+  // last_search = (pattern, forward, ignore_case...) as MplexCopyMode stores it; see mplex_copymode.h.
+  struct SearchState {
+    std::string text;
+    bool forward = true;
+    bool literal = false;
+  };
+  std::optional<SearchState> last_search;
+  std::string log_path;
+  long log_size = 0;
+  long input_bytes = 0;
+
+  std::shared_ptr<MplexWindow> window() const { return window_ref.lock(); }
+  void set_window(const std::shared_ptr<MplexWindow>& value) { window_ref = value; }
+  std::string tag() const;    // "%<id>"
+  std::string title() const;  // screen.title or hostname
+  void spawn(const std::string& file, const std::vector<std::string>& argv, const std::string& cwd,
+             const EnvList& env);
+  void place(int nx, int ny, int nw, int nh);
+  void apply_winsize();
+  void feed(const Bytes& data);
+  void log(const Bytes& data);
+  void write(const Bytes& data);
+  void drain();
+  std::shared_ptr<MplexMode> top_mode() const;
+  std::shared_ptr<MplexMode> push_mode(const std::shared_ptr<MplexMode>& mode);
+  void pop_mode(const std::shared_ptr<MplexMode>& mode = nullptr);
+  template <typename T>
+  std::shared_ptr<T> find_mode() const {
+    for (const auto& mode : modes)
+      if (auto hit = std::dynamic_pointer_cast<T>(mode)) return hit;
+    return nullptr;
+  }
+  std::string foreground_command();
+  std::string current_path();
+  size_t history_size() const;
+  void clear_history();
+  void close(bool hard = false);
+  std::string tail_log(long lines, size_t chunk_size = 65536, size_t max_bytes = 1 << 24);
+
+ private:
+  int log_fd_ = -1;  // None == -1
+};
+
+class MplexWindow : public std::enable_shared_from_this<MplexWindow> {
+ public:
+  MplexWindow(int ident, const std::string& name_in, int width_in, int height_in, MplexOptions* parent_options);
+
+  int id;
+  std::string name;
+  MplexLayoutNode::Ptr root;
+  std::shared_ptr<MplexPane> active;
+  std::shared_ptr<MplexPane> last_pane;
+  std::shared_ptr<MplexPane> zoomed;
+  int width, height;
+  int layout_index = -1;
+  MplexOptions options;
+  bool auto_rename = true;
+  double created;
+  std::weak_ptr<MplexSession> session_ref;  // back reference
+
+  std::shared_ptr<MplexSession> session() const { return session_ref.lock(); }
+  void set_session(const std::shared_ptr<MplexSession>& value) { session_ref = value; }
+  std::string tag() const;  // "@<id>"
+  std::vector<std::shared_ptr<MplexPane>> panes() const;
+  void relayout();
+  std::vector<std::shared_ptr<MplexPane>> visible_panes() const;
+  MplexLayoutNode::Ptr leaf_of(const std::shared_ptr<MplexPane>& pane) const;
+  void set_active(std::shared_ptr<MplexPane> pane);  // by value: callers pass window->last_pane, which set_active overwrites
+};
+
+class MplexSession {
+ public:
+  MplexSession(int ident, const std::string& name_in, MplexOptions* parent_options, const std::string& cwd_in,
+               const MplexPane::EnvList& env_in);
+
+  int id;
+  std::string name;
+  OrderedMap<int, std::shared_ptr<MplexWindow>> windows;  // dict order = creation order
+  std::optional<int> current;
+  std::vector<std::shared_ptr<MplexWindow>> history;
+  double created;
+  MplexOptions options;
+  std::string cwd;
+  MplexPane::EnvList env;
+  double last_attached;
+  std::optional<std::pair<int, int>> size;  // (cols, rows); the Python code sets/reads it dynamically
+
+  std::string tag() const;  // "$<id>"
+  std::shared_ptr<MplexWindow> window() const;
+  std::vector<int> indexes() const;  // sorted(self.windows)
+  int free_index(int base) const;
+  std::optional<int> last() const;   // index of the window that was current before this one
+  bool select(int index);
+  std::optional<int> index_of(const std::shared_ptr<MplexWindow>& window) const;
+};
+
+}  // namespace detz::mplex
diff --git a/taicpp/src/mplex/mplex_panenumbers.h b/taicpp/src/mplex/mplex_panenumbers.h
new file mode 100644
index 0000000..bf5e99b
--- /dev/null
+++ b/taicpp/src/mplex/mplex_panenumbers.h
@@ -0,0 +1,20 @@
+// MplexPaneNumbers: the display-panes overlay (tai.py:13209).
+#pragma once
+#include <memory>
+
+#include "mplex_mode.h"
+
+namespace detz::mplex {
+
+class MplexWindow;
+
+class MplexPaneNumbers : public MplexOverlay {
+ public:
+  MplexPaneNumbers(MplexServer* server_in, std::shared_ptr<MplexWindow> window_in, double until_in);
+  MplexServer* server;
+  std::shared_ptr<MplexWindow> window;
+  void key(const std::string& name, const Bytes& raw, MplexClientConn& client) override;
+  void draw(MplexCanvas& canvas, int area_y) override;
+};
+
+}  // namespace detz::mplex
diff --git a/taicpp/src/mplex/mplex_prompt.h b/taicpp/src/mplex/mplex_prompt.h
new file mode 100644
index 0000000..a72ed18
--- /dev/null
+++ b/taicpp/src/mplex/mplex_prompt.h
@@ -0,0 +1,54 @@
+// MplexPrompt: the command line in the status row (tai.py:12999).
+#pragma once
+#include <functional>
+#include <memory>
+#include <optional>
+#include <string>
+#include <utility>
+#include <vector>
+
+#include "mplex_common.h"
+
+namespace detz::mplex {
+
+class MplexServer;
+class MplexClientConn;
+
+// Keyword arguments of MplexPrompt.__init__ (history, single, numeric, key_name, on_change,
+// on_cancel, on_step, confirm).
+struct MplexPromptOptions {
+  std::shared_ptr<std::vector<std::string>> history;  // null -> a private empty list
+  bool single = false, numeric = false, key_name = false, confirm = false;
+  std::function<void(const std::string&)> on_change;
+  std::function<void()> on_cancel;
+  std::function<void(const std::string&, const std::string&)> on_step;  // (key name, text)
+};
+
+class MplexPrompt : public std::enable_shared_from_this<MplexPrompt> {
+ public:
+  using History = std::shared_ptr<std::vector<std::string>>;  // shared by reference with server.prompt_history
+  using Options = MplexPromptOptions;
+  MplexPrompt(const std::string& label_in, const std::string& text_in,
+              std::function<void(const std::string&)> on_done_in, Options options = {});
+
+  UStr label;   // code point text: pos indexes into text
+  UStr text;
+  long pos;
+  std::function<void(const std::string&)> on_done;
+  History history;
+  std::optional<long> hist_index;
+  bool single, numeric, key_name;
+  std::function<void(const std::string&)> on_change;
+  std::function<void()> on_cancel;
+  std::function<void(const std::string&, const std::string&)> on_step;
+  bool confirm;
+
+  std::pair<UStr, long> view() const;  // (label + text, len(label) + pos)
+  void finish(MplexServer& server, MplexClientConn& client, const std::string& value);
+  void cancel(MplexClientConn& client);
+  void changed();
+  static std::string printable(const std::string& name, const Bytes& raw);
+  void key(MplexServer& server, MplexClientConn& client, const std::string& name, const Bytes& raw);
+};
+
+}  // namespace detz::mplex
diff --git a/taicpp/src/mplex/mplex_renderer.h b/taicpp/src/mplex/mplex_renderer.h
new file mode 100644
index 0000000..7eb7d02
--- /dev/null
+++ b/taicpp/src/mplex/mplex_renderer.h
@@ -0,0 +1,29 @@
+// MplexRenderer: composes one client's whole screen (tai.py:13535).
+#pragma once
+#include <memory>
+#include <set>
+#include <utility>
+
+#include "mplex_canvas.h"
+#include "mplex_clientconn.h"
+#include "mplex_common.h"
+#include "mplex_mode.h"
+
+namespace detz::mplex {
+
+class MplexServer;
+
+class MplexRenderer {
+ public:
+  explicit MplexRenderer(MplexServer* server_in) : server(server_in) {}
+  MplexServer* server;
+
+  ModeBlock block_of(const std::shared_ptr<MplexPane>& pane, MplexClientConn& client);
+  MplexCanvas frame(MplexClientConn& client);
+  void borders(MplexCanvas& canvas, const std::shared_ptr<MplexWindow>& window, int area_y);
+  void status(MplexCanvas& canvas, MplexClientConn& client, const std::shared_ptr<MplexSession>& session,
+              const std::shared_ptr<MplexWindow>& window, int row);
+  static Row fit_list(const Row& cells, int avail, int current_at, const Style& base);
+};
+
+}  // namespace detz::mplex
diff --git a/taicpp/src/mplex/mplex_server.cpp b/taicpp/src/mplex/mplex_server.cpp
index 7566510..b397405 100644
--- a/taicpp/src/mplex/mplex_server.cpp
+++ b/taicpp/src/mplex/mplex_server.cpp
@@ -27,13 +27,22 @@
 #include "mplex_keys.h"
 #include "mplex_py.h"
 #include "mplex_renderer.h"
+#if __has_include("version.hpp")
+#include "version.hpp"
+#define MPLEX_HAVE_VERSION_HPP 1
+#endif
 
 namespace detz::mplex {
 
 namespace {
 
-// tai.py VERSION: the `version` format variable.
-constexpr const char* MPLEX_VERSION_TEXT = "1.44.2";
+// tai.py VERSION: the `version` format variable. The build generates version.hpp from VERSION
+// (src/cli/version.hpp.in); without it (standalone mplex builds) the value of the day is used.
+#ifdef MPLEX_HAVE_VERSION_HPP
+const std::string MPLEX_VERSION_TEXT(detz::kVersion);
+#else
+const std::string MPLEX_VERSION_TEXT = "1.44.2";
+#endif
 
 MplexServer* g_server = nullptr;
 
@@ -541,7 +550,7 @@ void MplexServer::discard_pane(const std::shared_ptr<MplexPane>& pane) {
   pane->modes.clear();  // breaks the pane <-> mode ownership cycle
 }
 
-void MplexServer::select_pane(const std::shared_ptr<MplexWindow>& window, const std::shared_ptr<MplexPane>& pane) {
+void MplexServer::select_pane(std::shared_ptr<MplexWindow> window, std::shared_ptr<MplexPane> pane) {
   if (window->zoomed && pane != window->zoomed) {
     window->zoomed = nullptr;
     window->relayout();
@@ -727,7 +736,7 @@ std::optional<std::string> MplexServer::variable(const std::string& name, const
   }
   if (name == "host") return py::gethostname();
   if (name == "host_short") return py::split(py::gethostname(), ".")[0];
-  if (name == "version") return std::string(MPLEX_VERSION_TEXT);
+  if (name == "version") return MPLEX_VERSION_TEXT;
   if (session) {
     if (name == "session_name") return session->name;
     if (name == "session_id") return session->tag();
diff --git a/taicpp/src/mplex/mplex_server.h b/taicpp/src/mplex/mplex_server.h
new file mode 100644
index 0000000..39451bf
--- /dev/null
+++ b/taicpp/src/mplex/mplex_server.h
@@ -0,0 +1,259 @@
+// MplexServer (tai.py:13942-15330): owns every session, window, pane and client. One select
+// loop, no threads. Method and field names are the Python ones.
+#pragma once
+#include <sys/types.h>
+
+#include <deque>
+#include <functional>
+#include <map>
+#include <memory>
+#include <optional>
+#include <string>
+#include <utility>
+#include <vector>
+
+#include "mplex_args.h"
+#include "mplex_clientconn.h"
+#include "mplex_common.h"
+#include "mplex_config.h"
+#include "mplex_ctx.h"
+#include "mplex_flowscreen.h"
+#include "mplex_format.h"
+#include "mplex_json.h"
+#include "mplex_pane.h"
+#include "mplex_prompt.h"
+
+namespace detz::mplex {
+
+class MplexCommands;
+class MplexRenderer;
+
+// Hard caps (mplex.md, "Hard caps"). Names are the Python constants.
+constexpr const char* MPLEX_SOCKET_NAME = "server.sock";
+constexpr const char* MPLEX_LOCK_NAME = "server.lock";
+constexpr const char* MPLEX_LOG_NAME = "server.log";
+constexpr const char* MPLEX_CONFIG_NAME = "mplex.toml";
+constexpr const char* MPLEX_MAGIC = "\x01";
+constexpr long MPLEX_FRAME_MAX = 1L << 22;
+constexpr long MPLEX_CLIENT_OUT_MAX = 1L << 22;
+constexpr long MPLEX_PANE_IN_MAX = 1L << 22;
+constexpr int MPLEX_MAX_SESSIONS = 64;
+constexpr int MPLEX_MAX_WINDOWS = 256;
+constexpr int MPLEX_MAX_PANES = 256;
+constexpr int MPLEX_MAX_CLIENTS = 32;
+constexpr int MPLEX_MESSAGES_MAX = 200;
+constexpr int MPLEX_HISTORY_CAP = 200000;
+constexpr int MPLEX_BUFFERS_CAP = 100;
+constexpr int MPLEX_PROMPT_HISTORY_CAP = 100;
+constexpr int MPLEX_COMMAND_DEPTH_MAX = 16;
+constexpr double MPLEX_SHELL_TIMEOUT = 5.0;
+constexpr long MPLEX_SHELL_OUTPUT_MAX = 65536;
+constexpr long MPLEX_PASTE_MAX = 1L << 22;
+constexpr double MPLEX_RENDER_INTERVAL = 0.012;
+constexpr double MPLEX_REAP_KILL_AFTER = 2.0;
+constexpr double MPLEX_IDLE_EXIT = 15.0;
+constexpr int MPLEX_LOOP_ERRORS_MAX = 50;
+constexpr long MPLEX_LOG_MAX = 1L << 24;
+constexpr long MPLEX_CONFIG_MAX = 1L << 20;
+constexpr int MPLEX_FLOW_MAX = 16;
+constexpr int MPLEX_FLOW_KEEP = 300;
+constexpr const char* PLEXER_DIR_NAME = "plexer";
+constexpr const char* PLEXER_PANE_ENV = "TAI_PLEXER_PANE";
+constexpr const char* PLEXER_SOCKET_ENV = "TAI_PLEXER_SOCKET";
+constexpr const char* PLEXER_ACTIVE_ENV = "TAI_PLEXER_ACTIVE";
+constexpr long PLEXER_RECV_MAX = 1L << 20;
+constexpr int PLEXER_FLOW_TITLE_MAX = 200;
+constexpr int PLEXER_FLOW_TEXT_MAX = 2000;
+constexpr int PLEXER_FLOW_LABEL_MAX = 200;
+constexpr int PLEXER_FLOW_ANSWER_MAX = 2000;
+constexpr int PLEXER_FLOW_OPTIONS_MAX = 12;
+constexpr int PLEXER_FLOW_TIMEOUT_MAX = 600;
+
+// plexer_dir(home): <home>/plexer, created 0700.
+std::string plexer_dir(const std::string& home);
+
+// A paste buffer ({"name", "data"}).
+struct MplexBuffer {
+  std::string name;
+  std::string data;
+};
+
+// The answer a UI flow collected: {"status", "value"}.
+struct MplexFlowAnswer {
+  std::string status;
+  Json value;
+};
+
+// One pending UI flow (server.flows[id]).
+struct MplexFlowRecord {
+  int id = 0;
+  std::shared_ptr<MplexClientConn> client;
+  std::string kind;
+  double until = 0.0;
+  double started = 0.0;
+  std::optional<double> settled;
+  std::optional<MplexFlowAnswer> answer;
+  std::shared_ptr<MplexFlowScreen> overlay;
+  std::shared_ptr<MplexPrompt> prompt;
+};
+
+class MplexServer {
+ public:
+  explicit MplexServer(const std::string& home);
+  ~MplexServer();
+
+  std::string home, dir, sock_path;
+  std::shared_ptr<MplexConfig> config;
+  MplexOptions* options;  // &config->options
+  OrderedMap<int, std::shared_ptr<MplexSession>> sessions;
+  OrderedMap<int, std::shared_ptr<MplexWindow>> windows;
+  OrderedMap<int, std::shared_ptr<MplexPane>> panes;
+  std::vector<std::shared_ptr<MplexClientConn>> clients;
+  std::vector<std::shared_ptr<MplexPending>> conns;
+  std::vector<MplexBuffer> buffers;
+  std::deque<std::pair<double, std::string>> messages;  // maxlen MPLEX_MESSAGES_MAX
+  std::map<std::string, MplexPrompt::History> prompt_history;
+  OrderedMap<int, MplexFlowRecord> flows;
+  int flow_seq = 0;
+  std::vector<std::pair<double, std::function<void()>>> timers;
+  std::vector<std::pair<pid_t, double>> reaping;
+  std::shared_ptr<MplexPane> marked;
+  std::map<std::string, int> ids;
+  bool had_session = false;
+  bool running = false;
+  int listener = -1;
+  int lock_fd = -1;
+  std::unique_ptr<MplexRenderer> renderer;
+  std::unique_ptr<MplexCommands> commands;
+  std::map<std::string, std::pair<double, std::string>> shell_cache;
+  double started;
+  std::string stamp;
+  double next_tick = 0.0;
+  std::optional<std::string> notice;
+
+  // ---- bookkeeping
+  int next_id(const std::string& kind);
+  void log_message(const std::string& text);
+  std::shared_ptr<MplexSession> latest_session() const;
+  std::vector<std::shared_ptr<MplexClientConn>> attached_clients(const std::shared_ptr<MplexSession>& session = nullptr) const;
+  MplexOptions* pane_options(const std::shared_ptr<MplexPane>& pane);
+  void message(const std::shared_ptr<MplexClientConn>& client, const std::string& text, std::optional<long> milliseconds = std::nullopt);
+  void mark_dirty(const std::shared_ptr<MplexWindow>& window = nullptr);
+  void mark_all_dirty();
+  void add_timer(double deadline, std::function<void()> callback);
+
+  // ---- buffers and copy
+  std::string add_buffer(const std::string& text, const std::optional<std::string>& name = std::nullopt);
+  std::string top_buffer_text() const;
+  MplexBuffer& find_buffer(const std::string& name);  // throws MplexError("no buffers"/"unknown buffer: x")
+  void run_shell_input(const std::string& command, const std::string& text);
+  void store_copy(const std::string& text, const std::string& command = "", bool append = false);
+
+  // ---- sizing
+  void resize_session(const std::shared_ptr<MplexSession>& session);
+  void resize_all();
+
+  // ---- model
+  std::string default_shell(MplexOptions& options) const;
+  std::string resolve_term(const std::string& name) const;
+  std::shared_ptr<MplexPane> spawn_pane(const std::shared_ptr<MplexWindow>& window, int width, int height,
+                                        const std::vector<std::string>& words, const std::string& cwd,
+                                        const MplexPane::EnvList* env_extra = nullptr);
+  void register_window(const std::shared_ptr<MplexSession>& session, const std::shared_ptr<MplexWindow>& window, int index,
+                       bool select);
+  std::shared_ptr<MplexWindow> create_window(const std::shared_ptr<MplexSession>& session, const std::string& name,
+                                             const std::string& cwd, const std::vector<std::string>& words,
+                                             const MplexPane::EnvList* env_extra, int index, bool select);
+  std::shared_ptr<MplexSession> create_session(const std::string& name, const std::string& cwd,
+                                               const MplexPane::EnvList& env, const std::vector<std::string>& words,
+                                               const std::string& window_name, std::pair<int, int> size);
+  std::string auto_session_name() const;
+  std::shared_ptr<MplexPane> split_pane(const std::shared_ptr<MplexWindow>& window, const std::shared_ptr<MplexPane>& target,
+                                        const std::string& kind, bool before, const std::vector<std::string>& words,
+                                        const std::string& cwd, const MplexPane::EnvList* env_extra, int size, bool select);
+  void discard_pane(const std::shared_ptr<MplexPane>& pane);
+  void select_pane(std::shared_ptr<MplexWindow> window, std::shared_ptr<MplexPane> pane);  // by value: pane may alias window->last_pane
+  void kill_pane(const std::shared_ptr<MplexPane>& pane);
+  void kill_window(const std::shared_ptr<MplexWindow>& window);
+  void renumber(const std::shared_ptr<MplexSession>& session);
+  void kill_session(const std::shared_ptr<MplexSession>& session);
+  void attach_client(const std::shared_ptr<MplexClientConn>& client, const std::shared_ptr<MplexSession>& session);
+  void detach_client(const std::shared_ptr<MplexClientConn>& client, const std::string& text = "", const std::string& kind = "D");
+
+  // ---- formats
+  std::string window_flags(const std::shared_ptr<MplexSession>& session, const std::shared_ptr<MplexWindow>& window);
+  MplexFormat::Resolver resolver_for(const std::shared_ptr<MplexSession>& session, const std::shared_ptr<MplexWindow>& window,
+                                     const std::shared_ptr<MplexPane>& pane, const std::shared_ptr<MplexClientConn>& client = nullptr);
+  std::string shell_output(const std::string& command);
+  std::optional<std::string> variable(const std::string& name, const std::shared_ptr<MplexSession>& session,
+                                      const std::shared_ptr<MplexWindow>& window, const std::shared_ptr<MplexPane>& pane,
+                                      const std::shared_ptr<MplexClientConn>& client);
+  // Format-expand text for a command context (strftime applied); extra overrides variables.
+  std::string expand(const std::string& text, MplexCtx& ctx, const std::map<std::string, std::string>* extra = nullptr);
+
+  // ---- key handling
+  bool is_prefix(const std::shared_ptr<MplexSession>& session, const std::string& name);
+  void input_bytes(const std::shared_ptr<MplexClientConn>& client, const Bytes& data);
+  void process_keys(const std::shared_ptr<MplexClientConn>& client, bool final);
+  void handle_key(const std::shared_ptr<MplexClientConn>& client, const std::string& name, const Bytes& raw);
+  void forward(const std::shared_ptr<MplexPane>& pane, const std::shared_ptr<MplexWindow>& window, const Bytes& raw);
+  void run_binding(const std::shared_ptr<MplexClientConn>& client, const MplexBinding& binding,
+                   const std::shared_ptr<MplexPane>& pane = nullptr);
+  void run_checked(MplexCtx& ctx, const std::string& text);
+  void show_output(MplexCtx& ctx, const std::string& text);
+  void ask_confirm(const std::shared_ptr<MplexClientConn>& client, const std::string& text, std::function<void()> callback);
+  void refresh_choosers();
+
+  // ---- command execution
+  std::string run_line(MplexCtx& ctx, const std::string& text, int depth = 0);
+  std::string run_commands(MplexCtx& ctx, const std::vector<std::vector<std::string>>& commands, int depth = 0);
+  std::string run_words(MplexCtx& ctx, const std::vector<std::string>& words);
+  std::string run_one(MplexCtx& ctx, const std::vector<std::string>& words, int depth);
+
+  // ---- sockets and control protocol
+  int open_listener();  // -1 when another server holds the lock
+  void accept_connection();  // Python: accept()
+  void pending_read(const std::shared_ptr<MplexPending>& pending);
+  void drop_pending(const std::shared_ptr<MplexPending>& pending);
+  void control(const std::shared_ptr<MplexPending>& pending);
+  std::shared_ptr<MplexPane> control_pane(const Json& request);
+  Json dispatch_control(const Json& request);
+  void flow_prune(double now);
+  void flow_ui_clear(MplexFlowRecord& found);
+  std::shared_ptr<MplexClientConn> flow_client(const std::shared_ptr<MplexPane>& pane);
+  struct FlowScreenSpec {
+    std::string kind, title, text, initial;
+    std::vector<std::string> options;
+    int default_index = 0;
+  };
+  FlowScreenSpec flow_check_screen(const Json& raw);
+  Json flow_show(const Json& request);
+  void flow_answered(int flow_id, const std::string& status, const Json& value = Json());
+  Json flow_result(const Json& request);
+  Json flow_cancel(const Json& request);
+  void client_read(const std::shared_ptr<MplexClientConn>& client);
+  void client_data(const std::shared_ptr<MplexClientConn>& client, const Bytes& data);
+  void on_hello(const std::shared_ptr<MplexClientConn>& client, const Bytes& payload);
+  void drop_client(const std::shared_ptr<MplexClientConn>& client);
+
+  // ---- main loop
+  int serve();
+  void stop();
+  void loop();
+  void iterate();
+  bool clients_busy() const;
+  void sweep_bad_fds();
+  double wakeup(double now);
+  void run_deadlines(double now);
+  void tick(double now);
+  void pane_read(const std::shared_ptr<MplexPane>& pane);
+  void pane_exited(const std::shared_ptr<MplexPane>& pane);
+  void reap_children(double now);
+  void render_clients(double now);
+  void close_finished();
+  void shutdown();
+  static bool probe(const std::string& path);
+  static bool ensure_running(const std::string& home, double wait = 5.0);
+};
+
+}  // namespace detz::mplex
diff --git a/taicpp/src/mplex/mplex_style.h b/taicpp/src/mplex/mplex_style.h
new file mode 100644
index 0000000..b21f0ef
--- /dev/null
+++ b/taicpp/src/mplex/mplex_style.h
@@ -0,0 +1,23 @@
+// MplexStyle: tmux style strings to (fg, bg, attr). tai.py:10653.
+#pragma once
+#include <optional>
+#include <string>
+
+#include "mplex_common.h"
+
+namespace detz::mplex {
+
+class MplexStyle {
+ public:
+  static constexpr int ATTR_BOLD = 1, ATTR_DIM = 2, ATTR_UNDERLINE = 4, ATTR_REVERSE = 8, ATTR_STRIKE = 16,
+                       ATTR_ITALIC = 32, ATTR_BLINK = 64, ATTR_HIDDEN = 128;
+  // None (0) for default/terminal/empty; throws MplexError("bad colour: ...").
+  static Color color(const std::string& text, bool background);
+  // Apply a style string on top of base; "default" returns to reset (base when absent).
+  static Style parse(const std::string& text, const Style& base = Style{},
+                     const std::optional<Style>& reset = std::nullopt);
+  static std::string sgr(Color fg, Color bg, int attr);
+  static std::string sgr(const Style& style) { return sgr(style.fg, style.bg, style.attr); }
+};
+
+}  // namespace detz::mplex
diff --git a/taicpp/src/mplex/mplex_toml.h b/taicpp/src/mplex/mplex_toml.h
new file mode 100644
index 0000000..3aaf0af
--- /dev/null
+++ b/taicpp/src/mplex/mplex_toml.h
@@ -0,0 +1,42 @@
+// TOML 1.0 reader with tomllib.loads semantics (Python 3.11+ standard library), including its
+// error texts ("Invalid value (at line 1, column 5)", ...). Implemented in mplex_toml.cpp.
+#pragma once
+#include <string>
+#include <utility>
+#include <vector>
+
+#include "mplex_common.h"
+
+namespace detz::mplex {
+
+class TomlError : public std::runtime_error {  // tomllib.TOMLDecodeError (a ValueError)
+ public:
+  explicit TomlError(const std::string& text) : std::runtime_error(text) {}
+};
+
+class TomlValue {
+ public:
+  enum class Kind { Bool, Int, Float, String, Array, Table, Datetime };
+  using Array = std::vector<TomlValue>;
+  using Table = std::vector<std::pair<std::string, TomlValue>>;  // insertion ordered
+
+  Kind kind = Kind::Table;
+  bool boolean = false;
+  long long integer = 0;
+  double number = 0.0;
+  std::string text;  // String content, or the ISO text of a Datetime
+  Array array;
+  Table table;
+
+  bool is_table() const { return kind == Kind::Table; }
+  bool is_string() const { return kind == Kind::String; }
+  bool is_bool() const { return kind == Kind::Bool; }
+  bool is_int() const { return kind == Kind::Int; }  // never true for Bool
+  bool is_array() const { return kind == Kind::Array; }
+  const TomlValue* get(const std::string& key) const;
+
+  // tomllib.loads(text): throws TomlError.
+  static TomlValue loads(const std::string& text);
+};
+
+}  // namespace detz::mplex
diff --git a/taicpp/src/plexer/plexer_flow.h b/taicpp/src/plexer/plexer_flow.h
new file mode 100644
index 0000000..84d6fb5
--- /dev/null
+++ b/taicpp/src/plexer/plexer_flow.h
@@ -0,0 +1,156 @@
+// uiflow (uiflow.md): the controller side of the plexer protocol (PlexerController, its native
+// and tmux backends, the factory), the plexer_show spec validation and the PlexerFlow driver.
+// Port of tai.py:9302-9985. Namespace detz::plexer, names are the Python ones.
+#pragma once
+#include <functional>
+#include <map>
+#include <memory>
+#include <optional>
+#include <string>
+#include <utility>
+#include <vector>
+
+#include "mplex_json.h"
+
+namespace detz::plexer {
+
+using detz::mplex::Json;
+
+constexpr const char* PLEXER_DIR_NAME = "plexer";
+constexpr const char* PLEXER_PANE_ENV = "TAI_PLEXER_PANE";
+constexpr const char* PLEXER_SOCKET_ENV = "TAI_PLEXER_SOCKET";
+constexpr const char* PLEXER_ACTIVE_ENV = "TAI_PLEXER_ACTIVE";
+constexpr long PLEXER_RECV_MAX = 1L << 20;
+constexpr int PLEXER_FLOW_VERSION = 1;
+constexpr int PLEXER_FLOW_SCREENS_MAX = 32;
+constexpr int PLEXER_FLOW_FIELDS_MAX = 12;
+constexpr int PLEXER_FLOW_OPTIONS_MAX = 12;
+constexpr int PLEXER_FLOW_ACTIONS_MAX = 12;
+constexpr int PLEXER_FLOW_VISITS_MAX = 64;
+constexpr int PLEXER_FLOW_ID_MAX = 64;
+constexpr int PLEXER_FLOW_TITLE_MAX = 200;
+constexpr int PLEXER_FLOW_TEXT_MAX = 2000;
+constexpr int PLEXER_FLOW_LABEL_MAX = 200;
+constexpr int PLEXER_FLOW_ANSWER_MAX = 2000;
+constexpr int PLEXER_FLOW_TIMEOUT_DEFAULT = 300;
+constexpr int PLEXER_FLOW_TIMEOUT_MIN = 5;
+constexpr int PLEXER_FLOW_TIMEOUT_MAX = 600;
+constexpr double PLEXER_FLOW_POLL = 0.25;
+extern const std::vector<std::string> PLEXER_FLOW_TYPES;  // choice text info
+extern const std::vector<std::string> PLEXER_FLOW_KINDS;  // message choice text
+constexpr int MPLEX_FLOW_MAX = 16;
+constexpr int MPLEX_FLOW_KEEP = 300;
+
+// plexer_dir(home): <home>/plexer, created 0700.
+std::string plexer_dir(const std::string& home);
+
+// Raised by a PlexerController when the backend can't be reached or refuses a command.
+class PlexerError : public std::runtime_error {
+ public:
+  explicit PlexerError(const std::string& text) : std::runtime_error(text) {}
+};
+
+// ---- controller side ---------------------------------------------------------------------
+
+class PlexerController {
+ public:
+  virtual ~PlexerController() = default;
+  std::string kind = "abstract";
+  virtual Json send_keys(const std::string& text, bool enter = false) = 0;
+  virtual Json read_pane(int lines = 200) = 0;
+  void type_text(const std::string& text, double delay = 0.03, bool enter = true);
+  virtual Json status() = 0;
+  // One blocking question on the user's terminal. screen: {"title","text","kind","options","initial","default"}.
+  // Returns {"status":"ok","value":...} / {"status":"cancelled"} / {"status":"timeout"}; throws PlexerError.
+  virtual Json ask(const Json& screen, double timeout) = 0;
+};
+
+class NativePlexerController : public PlexerController {
+ public:
+  NativePlexerController(const std::string& socket_path_in, const std::optional<std::string>& pane_in = std::nullopt);
+  std::string socket_path;
+  std::optional<std::string> pane;
+  Json call(const Json& payload);  // Python _call
+  Json send_keys(const std::string& text, bool enter = false) override;
+  Json read_pane(int lines = 200) override;
+  Json status() override;
+  Json ask(const Json& screen, double timeout) override;
+};
+
+class TmuxPlexerController : public PlexerController {
+ public:
+  explicit TmuxPlexerController(const std::string& pane_in);
+  std::string pane;
+  std::string tmux(const std::vector<std::string>& args);  // Python _tmux
+  Json send_keys(const std::string& text, bool enter = false) override;
+  Json read_pane(int lines = 200) override;
+  Json status() override;
+  Json ask(const Json& screen, double timeout) override;
+  std::string ask_result_path();
+  std::optional<std::string> await_answer(const std::string& path, double budget = 1.0);
+  void ask_dismiss();
+  // Returns the answer file content, nullopt when dismissed, or "timeout" via timed_out.
+  struct RunOutcome {
+    bool timed_out = false;
+    std::optional<std::string> content;
+  };
+  RunOutcome ask_run(const std::vector<std::string>& argv, const std::string& path, double timeout);
+  Json ask_choice(const Json& screen, double timeout);
+  RunOutcome ask_popup(const std::string& title, const std::string& body, const std::string& reader, double timeout);
+  Json ask_text(const Json& screen, double timeout);
+  Json ask_message(const Json& screen, double timeout);
+};
+
+class PlexerControllerFactory {
+ public:
+  // Which env var is set decides the backend; null when neither is.
+  static std::unique_ptr<PlexerController> detect();
+};
+
+// ---- spec validation ------------------------------------------------------------------------
+
+// Each returns the normalized value and an error text ("" when fine), like the Python tuples.
+std::pair<std::string, std::string> validate_flow_id(const Json& raw, const std::string& what);
+std::pair<std::string, std::string> validate_flow_text(const Json& raw, const std::string& what, size_t limit);
+std::pair<Json, std::string> validate_flow_options(const Json& raw, const std::string& what);
+std::pair<Json, std::string> validate_flow_condition(const Json& raw, const std::string& what,
+                                                     const std::vector<std::string>& known);
+// Returns (normalized app, "") or (Json null, reason).
+std::pair<Json, std::string> validate_flow_spec(const Json& spec);
+
+// ---- the flow driver ----------------------------------------------------------------------------
+
+class PlexerFlow {
+ public:
+  explicit PlexerFlow(const Json& app);
+  Json app;
+  std::map<std::string, Json> by_id;
+  std::vector<std::string> order;
+  Json answers = Json::object();
+  Json action;  // None until an action is taken
+  int visits = 0;
+  double deadline = 0.0;
+
+  static bool condition_holds(const Json& clauses, const Json& answers);
+  std::string follow_up(const Json& screen);
+  std::string screen_text(const Json& screen, const Json* field = nullptr);
+  const Json* first_askable(const Json& screen);
+  double remaining() const;
+  Json run(PlexerController& controller);
+  // Returns: null optional to continue with follow_up, a screen id, or a final outcome.
+  struct ScreenResult {
+    enum class Kind { Continue, Jump, Outcome } kind = Kind::Continue;
+    std::string target;
+    Json outcome;
+  };
+  ScreenResult run_screen(PlexerController& controller, const Json& screen);
+};
+
+// PlexerBackend (the extension point the shell hook execs into).
+class PlexerBackend {
+ public:
+  virtual ~PlexerBackend() = default;
+  virtual int run() = 0;
+};
+
+}  // namespace detz::plexer
diff --git a/taicpp/tests/mplex_spec_test.cpp b/taicpp/tests/mplex_spec_test.cpp
new file mode 100644
index 0000000..ce29fe1
--- /dev/null
+++ b/taicpp/tests/mplex_spec_test.cpp
@@ -0,0 +1,221 @@
+// Mirror of MplexSpecTests and UiflowDocTests (test_tai.py): ../mplex.md and ../uiflow.md are the
+// specification, and must list exactly what the C++ tables hold. Tables compared: options,
+// commands, default key bindings, copy-mode commands, caps, wire kinds, flow caps.
+// Usage: mplex_spec_test [path-to-repo-root]   (default: the directory above taicpp/)
+#include <algorithm>
+#include <cstdio>
+#include <cstdlib>
+#include <fstream>
+#include <iostream>
+#include <regex>
+#include <set>
+#include <sstream>
+#include <string>
+#include <vector>
+
+#include "mplex_commands.h"
+#include "mplex_config.h"
+#include "mplex_copymode.h"
+#include "mplex_options.h"
+#include "mplex_server.h"
+#include "plexer_flow.h"
+
+using namespace detz::mplex;
+
+namespace {
+
+int failures = 0;
+int checks = 0;
+
+void check(bool ok, const std::string& what) {
+  ++checks;
+  if (!ok) {
+    ++failures;
+    std::cerr << "FAIL: " << what << "\n";
+  }
+}
+
+std::string slurp(const std::string& path) {
+  std::ifstream in(path, std::ios::binary);
+  std::stringstream ss;
+  ss << in.rdbuf();
+  return ss.str();
+}
+
+// section(heading): text after "\n<heading>\n" up to the next "\n#..### " heading.
+std::string section(const std::string& doc, const std::string& heading) {
+  size_t start = doc.find("\n" + heading + "\n");
+  if (start == std::string::npos) {
+    check(false, "heading missing: " + heading);
+    return "";
+  }
+  std::string rest = doc.substr(start + heading.size() + 2);
+  static const std::regex next("\n#{1,3} ");
+  std::smatch m;
+  if (std::regex_search(rest, m, next)) return rest.substr(0, static_cast<size_t>(m.position(0)));
+  return rest;
+}
+
+std::vector<std::string> first_column(const std::string& text) {
+  std::vector<std::string> out;
+  size_t pos = 0;
+  while (pos < text.size()) {
+    size_t eol = text.find('\n', pos);
+    if (eol == std::string::npos) eol = text.size();
+    std::string line = text.substr(pos, eol - pos);
+    pos = eol + 1;
+    if (line.rfind("| `", 0) != 0) continue;
+    size_t close = line.find("` |", 3);
+    if (close == std::string::npos) continue;
+    out.push_back(line.substr(3, close - 3));
+  }
+  return out;
+}
+
+struct DocBinding {
+  std::string key, command;
+  bool repeat;
+};
+
+std::string unescape_pipes(std::string text) {
+  size_t pos;
+  while ((pos = text.find("\\|")) != std::string::npos) text.replace(pos, 2, "|");
+  return text;
+}
+
+// ^\| `(.+?)` \| `(.+?)` \| (yes)?   (non-greedy, per line)
+std::vector<DocBinding> documented_bindings(const std::string& text) {
+  std::vector<DocBinding> out;
+  static const std::regex row("^\\| `(.+?)` \\| `(.+?)` \\| (yes)?");
+  size_t pos = 0;
+  while (pos < text.size()) {
+    size_t eol = text.find('\n', pos);
+    if (eol == std::string::npos) eol = text.size();
+    std::string line = text.substr(pos, eol - pos);
+    pos = eol + 1;
+    std::smatch m;
+    if (std::regex_search(line, m, row))
+      out.push_back({unescape_pipes(m[1].str()), unescape_pipes(m[2].str()), m[3].matched && !m[3].str().empty()});
+  }
+  return out;
+}
+
+bool contains(const std::string& doc, const std::string& needle) { return doc.find(needle) != std::string::npos; }
+
+void em_dash_free(const std::string& doc, const std::string& what) {
+  check(!contains(doc, "\xe2\x80\x94"), what + " contains an em dash");
+}
+
+}  // namespace
+
+int main(int argc, char** argv) {
+  std::string root = argc > 1 ? argv[1] : "../..";
+  std::string doc = slurp(root + "/mplex.md");
+  std::string flow = slurp(root + "/uiflow.md");
+  check(!doc.empty(), "mplex.md readable under " + root);
+  check(!flow.empty(), "uiflow.md readable under " + root);
+
+  // test_options_table_matches_the_code
+  {
+    std::vector<std::string> documented = first_column(section(doc, "## Options"));
+    std::vector<std::string> code;
+    for (const auto& def : MplexOptions::defs()) code.push_back(def.name);
+    std::sort(documented.begin(), documented.end());
+    std::sort(code.begin(), code.end());
+    check(documented == code, "options table matches the code");
+  }
+  // test_commands_table_matches_the_code
+  {
+    std::vector<std::string> documented = first_column(section(doc, "## Commands"));
+    std::vector<std::string> code;
+    for (const auto& spec : mplex_command_specs()) code.push_back(spec.name);
+    std::sort(documented.begin(), documented.end());
+    std::sort(code.begin(), code.end());
+    check(documented == code, "commands table matches the code");
+  }
+  // test_unsupported_commands_are_all_named
+  for (const auto& name : mplex_unsupported())
+    if (name != "choose-tree-mouse") check(contains(doc, "`" + name + "`"), "unsupported command named: " + name);
+  // test_every_default_binding_is_documented
+  {
+    const std::vector<std::pair<std::string, std::string>> tables = {
+        {"prefix", "### prefix table (after `C-b`)"},
+        {"copy-mode", "### copy-mode table (`mode-keys emacs`)"},
+        {"copy-mode-vi", "### copy-mode-vi table (`mode-keys vi`)"}};
+    for (const auto& [table, heading] : tables) {
+      std::vector<DocBinding> documented = documented_bindings(section(doc, heading));
+      std::vector<DocBinding> expected;
+      for (const auto& key : mplex_default_keys())
+        if (table == key.table) expected.push_back({key.key, key.command, key.repeat});
+      bool same = documented.size() == expected.size();
+      for (size_t i = 0; same && i < documented.size(); ++i)
+        same = documented[i].key == expected[i].key && documented[i].command == expected[i].command &&
+               documented[i].repeat == expected[i].repeat;
+      check(same, "default bindings documented in order: " + table);
+    }
+  }
+  // test_every_copy_mode_command_is_documented
+  for (const auto& name : MplexCopyMode::command_names())
+    check(contains(doc, "`" + name + "`"), "copy-mode command documented: " + name);
+  // test_every_cap_is_documented (+ the values the spec table states)
+  {
+    const std::vector<std::string> caps = {
+        "MPLEX_MAX_SESSIONS", "MPLEX_MAX_WINDOWS", "MPLEX_MAX_PANES", "MPLEX_MAX_CLIENTS", "MPLEX_FRAME_MAX",
+        "MPLEX_CLIENT_OUT_MAX", "MPLEX_PANE_IN_MAX", "MPLEX_HISTORY_CAP", "MPLEX_LOG_MAX", "MPLEX_BUFFERS_CAP",
+        "MPLEX_MESSAGES_MAX", "MPLEX_PROMPT_HISTORY_CAP", "MPLEX_COMMAND_DEPTH_MAX", "MPLEX_LOOP_ERRORS_MAX",
+        "MPLEX_SHELL_TIMEOUT", "MPLEX_CONFIG_MAX", "MPLEX_PASTE_MAX", "MPLEX_RENDER_INTERVAL", "MPLEX_REAP_KILL_AFTER",
+        "MPLEX_FLOW_MAX", "MPLEX_FLOW_KEEP"};
+    for (const auto& name : caps) check(contains(doc, "`" + name + "`"), "cap documented: " + name);
+    check(MPLEX_MAX_SESSIONS == 64 && MPLEX_MAX_WINDOWS == 256 && MPLEX_MAX_PANES == 256 && MPLEX_MAX_CLIENTS == 32,
+          "object caps 64 / 256 / 256 / 32");
+    check(MPLEX_FRAME_MAX == (4L << 20) && MPLEX_CLIENT_OUT_MAX == (4L << 20) && MPLEX_PANE_IN_MAX == (4L << 20),
+          "frame, client out and pane in caps are 4 MiB");
+    check(MPLEX_HISTORY_CAP == 200000, "history cap 200000");
+    check(MPLEX_LOG_MAX == (16L << 20), "log max 16 MiB");
+    check(MPLEX_BUFFERS_CAP == 100, "buffers cap 100");
+    check(MPLEX_MESSAGES_MAX == 200 && MPLEX_PROMPT_HISTORY_CAP == 100, "messages 200, prompt history 100");
+    check(MPLEX_COMMAND_DEPTH_MAX == 16, "command depth 16");
+    check(MPLEX_LOOP_ERRORS_MAX == 50, "loop errors 50");
+    check(MPLEX_SHELL_TIMEOUT == 5.0, "shell timeout 5 s");
+    check(MPLEX_CONFIG_MAX == (1L << 20), "config max 1 MiB");
+    check(MPLEX_PASTE_MAX == (4L << 20), "paste max 4 MiB");
+    check(MPLEX_RENDER_INTERVAL == 0.012, "render interval 12 ms");
+    check(MPLEX_REAP_KILL_AFTER == 2.0, "reap kill after 2 s");
+    check(MPLEX_FLOW_MAX == 16 && MPLEX_FLOW_KEEP == 300, "flow max 16, keep 300 s");
+  }
+  // test_wire_kinds_are_documented
+  for (const char* kind : {"H", "I", "R", "A", "O", "M", "E", "D", "X", "Z"})
+    check(contains(doc, std::string("`") + kind + "`"), std::string("wire kind documented: ") + kind);
+  // test_no_em_dashes
+  em_dash_free(doc, "mplex.md");
+  em_dash_free(flow, "uiflow.md");
+  em_dash_free(slurp(root + "/taicpp/docs/mplex.md"), "taicpp/docs/mplex.md");
+  em_dash_free(slurp(root + "/taicpp/docs/wiring/mplex.md"), "taicpp/docs/wiring/mplex.md");
+
+  // UiflowDocTests.test_every_cap_is_documented (with the values)
+  {
+    const std::vector<std::string> caps = {
+        "PLEXER_FLOW_VERSION", "PLEXER_FLOW_SCREENS_MAX", "PLEXER_FLOW_FIELDS_MAX", "PLEXER_FLOW_OPTIONS_MAX",
+        "PLEXER_FLOW_ACTIONS_MAX", "PLEXER_FLOW_VISITS_MAX", "PLEXER_FLOW_ID_MAX", "PLEXER_FLOW_TITLE_MAX",
+        "PLEXER_FLOW_TEXT_MAX", "PLEXER_FLOW_LABEL_MAX", "PLEXER_FLOW_ANSWER_MAX", "PLEXER_FLOW_TIMEOUT_MIN",
+        "PLEXER_FLOW_TIMEOUT_DEFAULT", "PLEXER_FLOW_TIMEOUT_MAX", "PLEXER_FLOW_POLL", "MPLEX_FLOW_MAX",
+        "MPLEX_FLOW_KEEP"};
+    for (const auto& name : caps) check(contains(flow, "`" + name + "`"), "flow cap documented: " + name);
+    namespace pf = detz::plexer;
+    check(pf::PLEXER_FLOW_VERSION == 1 && pf::PLEXER_FLOW_SCREENS_MAX == 32 && pf::PLEXER_FLOW_FIELDS_MAX == 12 &&
+              pf::PLEXER_FLOW_OPTIONS_MAX == 12 && pf::PLEXER_FLOW_ACTIONS_MAX == 12 && pf::PLEXER_FLOW_VISITS_MAX == 64 &&
+              pf::PLEXER_FLOW_ID_MAX == 64 && pf::PLEXER_FLOW_TITLE_MAX == 200 && pf::PLEXER_FLOW_TEXT_MAX == 2000 &&
+              pf::PLEXER_FLOW_LABEL_MAX == 200 && pf::PLEXER_FLOW_ANSWER_MAX == 2000,
+          "flow caps match uiflow.md table");
+    check(pf::PLEXER_FLOW_TIMEOUT_MIN == 5 && pf::PLEXER_FLOW_TIMEOUT_DEFAULT == 300 && pf::PLEXER_FLOW_TIMEOUT_MAX == 600 &&
+              pf::PLEXER_FLOW_POLL == 0.25,
+          "flow timeouts 5 / 300 / 600 and poll 0.25");
+  }
+  // UiflowDocTests.test_contract_words_are_documented
+  for (const char* word : {"choice", "text", "info", "message", "show_if", "$done", "$cancel", "next", "actions",
+                           "cancelled", "timeout"})
+    check(contains(flow, word), std::string("contract word documented: ") + word);
+
+  std::printf("mplex_spec_test: %d checks, %d failures\n", checks, failures);
+  return failures == 0 ? 0 : 1;
+}