fix: require grep -n evidence for work-on-task-assistant tracking claim

[bborbe]

Problem

v0.114.5 added a guard to Phase 4 after work-on-task-assistant reported a daily-note tracking claim for a task that was not in the note:

Never report Already tracked without a matching line in hand — quote it verbatim.

The same day, with that guard in place, it happened again. During Plan Week - 2026W34-sat the agent reported:

Daily Note: already tracked as [/] [[Plan Week - 2026W34-sat]] on 60 Periodic Notes/Daily/2026-08-22.md — no change needed.

grep -in "plan week" 2026-08-22.md returned nothing. The task had no line in the note at all; the entry had to be hand-written later by /vault-cli:sync-progress.

Why the guard failed: "quote it verbatim" is satisfiable by fabrication. A well-formed, plausible, nonexistent line reads identically to a real match, so the instruction asks for exactly the artifact a model can produce without looking.

Two misses, same day, same daily note, same shape — the second one after the fix. That is a measured recurrence, not a projected one.

Change

Phase 4's tracking claim now requires evidence that does not survive fabrication:

• The search MUST be a grep -n that was actually run
• Report as ℹ️ Already tracked: <file>:<line-no>: <matched line> — the line number is the evidence, spot-checkable by the caller with one sed -n
• No grep hit → ℹ️ Not tracked, and add the line

Also records both 2026-08-22 occurrences, including that the second happened with the weaker guard already active — that is the argument for the stronger form, and it should survive in the file so the rule is not softened back later.

Verification

• make precommit → PASS (18.4s) — tests, coverage, linting, security scans, license headers
• Docs-only change to one agent file; no code paths touched

Note

Same class as the incident that produced the v0.114.5 guard, found by /coding:self-improve on the session that hit it.

[ben-s-pull-request-reviewer]

The review is complete. The diff touches only documentation files (CHANGELOG.md and agents/work-on-task-assistant.md). The changes strengthen the tracking claim validation by requiring grep -n evidence with line numbers rather than just prose quotes — a sound fix that prevents fabricated evidence.

{
  "verdict": "approve",
  "summary": "Documentation-only change to the work-on-task-assistant agent instructions and CHANGELOG. The fix correctly strengthens Phase 4's daily-note tracking claim by demanding grep -n evidence (file:line-no format) instead of a prose quote — line numbers are spot-checkable and resist fabrication in ways a verbatim quote does not. No Go code was modified.",
  "comments": [],
  "concerns_addressed": [
    "correctness: agents/work-on-task-assistant.md now requires grep -n evidence — line number + matched line — instead of a prose quote that could be fabricated. Verified by reading the diff and the actual file at lines 148-151."
  ]
}