Files
tai/research/shell-multiplexer-auto-attach/gitlab-mr-3383-stdin-stdout-isatty-mismatch.md
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retoorandClaude Sonnet 5 9dbd1fe667 Add plexer subsystem, container test infra, and last-resort opencode box backend
- Plexer: always-active terminal multiplexing. NativePlexerController/
  TmuxPlexerController share one interface, chosen by which env var is
  already set (TAI_PLEXER_SOCKET vs TMUX_PANE); NativePlexerBackend is
  the pty.fork()-based wrapper (raw mode, SIGWINCH resize forwarding,
  a Unix-socket control protocol, continuous session logging, a
  Ctrl+A prefix key distinct from tmux's own Ctrl+B). Auto-wraps new
  interactive shells via a .bashrc hook mirroring the existing
  command-not-found install pattern, gated on $TMUX/$TAI_PLEXER_ACTIVE/
  a $HOME/.tai-no-plexer bypass. New plexer_send/read/type/status
  tools, env-gated on a detected controller.
- tests/container.py + docker-compose.yml + tests/docker/Dockerfile:
  a disposable podman/docker image for the tests that must never touch
  a real machine (installing the plexer hook into a real ~/.bashrc, a
  live tmux session). Required suite (test_seal.py, test_tai.py,
  tests/plexer.py, tests/bashrc.py) gates the result; tests/rag.py
  runs as best-effort since its real-LLM dependency can't be satisfied
  inside a disposable container with no nested engine.
- tests/bashrc.py: real end-to-end hook install + bash -i auto-wrap,
  anti-recursion, tmux-active skip, non-interactive skip, a live
  TmuxPlexerController test, and an install/uninstall round-trip.
- tests/plexer.py: NativePlexerBackend under a real pty, plus a
  dedicated robustness pass (file permissions, >64KB payload framing,
  a malformed control request, a genuine self-deadlock fix in the
  write-to-child path).
- tai_test.py: the shared async process-driving framework (pipe/pty
  transport, group-wide kill-and-reap, a StdinBridge for --interactive)
  both test files build on.
- ChatClient last-resort backend: when there's no local opencode CLI
  but the sandbox box is already running, install opencode into it
  (official Node tarball, not apt -- apt's nodejs/npm pull in
  webpack/babel/jest as transitive deps) and route through it instead
  of giving up. Only reachable after the first retry round already
  failed everything else; never creates the box itself. TmuxPlexerController.status()
  fixed to use `list-panes` instead of `display-message -p`, which
  silently fell back to the default pane instead of erroring against
  a dead target.
- Fix 4 pre-existing test_tai.py bugs surfaced by running it in a
  clean environment for the first time: two stale mock signatures
  (subprocess.run's stdout= kwarg, Chat.complete's deadline= kwarg),
  one $TMUX-dependent catalog assertion, one tty-dependent color
  assertion.
- research/: a sourced research archive (Source Dossier/Citation
  Card/Conclusion tiers) backing the above design decisions, with its
  own audit.py consistency checker.
- .gitignore: fix a blanket *.md rule that was about to silently drop
  the entire research/ archive from version control; add __pycache__/
  and the one-off debug transcript this session started from.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
2026-10-10 04:36:05 +02:00

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2.1 KiB
Markdown

# Check stdin rather than stdout for interactive terminals (GitLab MR #3383)
## Metadata
| Field | Value |
|---|---|
| Institute | Molodetz Institute — Research & Retrieval Division |
| Subject | shell-multiplexer-auto-attach |
| Document type | Source Dossier |
| Tier | 1 |
| Source title | Check stdin rather than stdout for interactive terminals |
| Source URL | https://gitlab.com/gitlab-org/gitlab-development-kit/-/merge_requests/3383/pipelines |
| Source publisher / author | GitLab (gitlab-development-kit project) |
| Source type | repository |
| Source date (published) | Unknown — not stated |
| Date researched | 2026-10-09 |
| Researched by | tai (agent), model: Claude Sonnet 5, on behalf of retoor |
| Research method | web search synthesis |
| Confidence | Medium |
| Status | Active |
## Summary
A real-world merge request fixing an interactivity check that tested `stdout.isatty()` when it should have tested `stdin.isatty()` — the two can legitimately disagree (e.g. output piped to a pager while input stays a real terminal, or vice versa).
## Key findings
- `stdin.isatty()` and `stdout.isatty()` are independent facts and can differ in either direction in real, common shell usage (piping, redirection).
- Which one is the "right" one to check depends on what the check is actually trying to answer (can I read user input? vs. can I write formatted/colored output?) — conflating them is a real, shipped bug class.
## Pros / strengths
- A fixed, real production bug (not a hypothetical) — concrete evidence this mismatch actually bites people, not just a theoretical edge case.
## Cons / limitations / caveats
- Specific to one project's bug fix; doesn't generalize a universal rule beyond "check the stream that matches what you actually need, and don't assume stdin/stdout agree."
## Relevance to tai
A direct implementation warning for the proposal's `.bashrc` detection logic: if it ever needs to distinguish "can prompt a human" from "output looks like a terminal," check `stdin` specifically (`[ -t 0 ]`), not `stdout`, and never assume the two will match.
## Changelog
| Date | Change |
|---|---|
| 2026-10-09 | Initial dossier created. |