fix: re-read daily note before write in sync-progress

[bborbe]

Prevents concurrent-vault-write clobbering: sync-progress now re-reads the daily note immediately before writing and merges, instead of writing over a stale in-memory copy.

Why: a sibling session can rewrite the shared daily note between sync-progress's read (to locate the section) and its write (after composing the entry over several turns). Writing from the stale read destroys their entry, and obsidian-git autocommits only the last writer's version — the earlier write never enters git history.

Proof it happens: 2026-08-23 on the Personal vault — a Verify-backup entry vanished. git log -S "zfs logicalused" on the daily note returns a single commit (the later restore), not add+remove. Reproduced mechanically in a scratch repo: two writers both read HEAD, both write, one autocommit → first entry 0 hits in git log -S, second 1.

Fix: mandatory write protocol in sync-progress Phase 3.1 — re-read from disk immediately before writing, merge into current content, never overwrite. Same guard noted for other shared vault files.

[ben-s-pull-request-reviewer]

I now have a complete picture. Let me compile the review.

Summary of findings:

1. This PR only changes markdown documentation — commands/sync-progress.md (a Claude Code plugin slash command spec) and CHANGELOG.md. No Go code is changed.

2. sync-progress.md IS the implementation — it's a plugin command file (YAML frontmatter + markdown body) that defines a slash command. The "code fix" is the updated documentation itself: the command now specifies a mandatory re-read-before-write protocol in Phase 3.1 to prevent TOCTOU clobbering. There is no separate Go implementation to update.

3. No Go files changed — the ast-grep mechanical funnel confirmed 0 findings (correct), and no Go quality/go-context/go-error agents are applicable.

4. CHANGELOG.md — ## Unreleased is correctly used (matching all prior release entries). The bullet describes the fix clearly.

5. Step 4 ast-grep: 0 findings (expected — no applicable rule targets for markdown plugin commands).

6. No issues found.

{
  "verdict": "approve",
  "summary": "PR changes only a Claude Code plugin slash command spec (`commands/sync-progress.md`) and its CHANGELOG entry. The command IS the implementation — the updated Phase 3.1 documentation mandates a re-read-immediately-before-write protocol and merge semantics, which is the full fix for the observed concurrent-write clobbering. No Go code or test files are involved, and no issues were found.",
  "comments": [],
  "concerns_addressed": [
    "correctness: The PR description explains a race condition (sibling session clobbers daily note between read and write), but the diff only shows documentation changes — no code implementation of the mandatory re-read protocol is visible. Verify whether the actual code fix lives in a separate file or was omitted. — addressed: This repo's vault-cli is a Claude Code plugin; `commands/sync-progress.md` IS the slash command spec that defines the runtime behavior. The updated documentation in Phase 3.1 ('Re-read the file immediately before writing — never write from a stale copy') and the three-step mandatory write protocol ARE the fix. No separate Go code file implements this command.",
    "correctness: The documentation mandates 're-read immediately before writing' and 'merge, never overwrite' for daily notes and shared vault files — confirm the implementation enforces this ordering atomically (no TOCTOU window between re-read and write). — not an issue: The command is a markdown specification run by the Claude Code plugin runtime. The documented protocol (re-read via Read tool immediately before Edit/Write, merge rather than overwrite) is the defined behavior. Atomicity of the protocol depends on the Claude Code tool layer, not a separate Go implementation.",
    "tests: The proof-of-reproduction described (two writers, one autocommit, first entry 0 hits in git log -S) suggests a test case should be added to verify the race condition is actually closed. — not an issue: This is a markdown command spec, not compiled code. Integration tests for the Claude Code plugin runtime are out of scope for this repo."
  ]
}