Implement versiond M1: inotify monitor, versioning, diff, restore, systemd install

FastAPI service on 127.0.0.1:9922 that monitors user-chosen directories
with pruned inotify watches, stores versions in a local content-addressed
spool indexed in SQLite, coalesces bursts (first + last), and offers
history, diff and dry-run-first bulk restore. Includes a CLI with a
systemd user unit installer.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/versiond/diff.py

@@ -0,0 +1,72 @@
+"""Text diffs between stored versions or a version and the working copy."""
+
+from __future__ import annotations
+
+import difflib
+import re
+from typing import Any
+
+_WS = re.compile(r"\s+")
+
+
+def _lines(content: bytes) -> list[str]:
+    return content.decode("utf-8", errors="replace").splitlines(keepends=True)
+
+
+def _normalize(line: str, ignore_whitespace: bool, ignore_eol: bool) -> str:
+    if ignore_whitespace:
+        return _WS.sub(" ", line).strip()
+    if ignore_eol:
+        return line.rstrip("\r\n")
+    return line
+
+
+def hunks(
+    a: bytes,
+    b: bytes,
+    context: int = 3,
+    ignore_whitespace: bool = False,
+    ignore_eol: bool = False,
+) -> list[dict[str, Any]]:
+    a_lines, b_lines = _lines(a), _lines(b)
+    a_norm = [_normalize(x, ignore_whitespace, ignore_eol) for x in a_lines]
+    b_norm = [_normalize(x, ignore_whitespace, ignore_eol) for x in b_lines]
+    matcher = difflib.SequenceMatcher(None, a_norm, b_norm, autojunk=False)
+    result = []
+    for group in matcher.get_grouped_opcodes(context):
+        first, last = group[0], group[-1]
+        lines = []
+        for tag, i1, i2, j1, j2 in group:
+            if tag == "equal":
+                lines += [{"op": " ", "text": x} for x in a_lines[i1:i2]]
+                continue
+            if tag in ("replace", "delete"):
+                lines += [{"op": "-", "text": x} for x in a_lines[i1:i2]]
+            if tag in ("replace", "insert"):
+                lines += [{"op": "+", "text": x} for x in b_lines[j1:j2]]
+        result.append({
+            "old_start": first[1] + 1,
+            "old_lines": last[2] - first[1],
+            "new_start": first[3] + 1,
+            "new_lines": last[4] - first[3],
+            "lines": lines,
+        })
+    return result
+
+
+def unified(hunk_list: list[dict[str, Any]], from_label: str, to_label: str) -> str:
+    if not hunk_list:
+        return ""
+    out = [f"--- {from_label}\n", f"+++ {to_label}\n"]
+    for h in hunk_list:
+        out.append(f"@@ -{h['old_start']},{h['old_lines']} +{h['new_start']},{h['new_lines']} @@\n")
+        for line in h["lines"]:
+            text = line["text"]
+            out.append(line["op"] + text + ("" if text.endswith("\n") else "\n\\ No newline at end of file\n"))
+    return "".join(out)
+
+
+def side_by_side_html(a: bytes, b: bytes, from_label: str, to_label: str, context: int = 3) -> str:
+    return difflib.HtmlDiff(wrapcolumn=100).make_file(
+        _lines(a), _lines(b), from_label, to_label, context=True, numlines=context
+    )