fix: drop the duplicate **Timestamp** line from audit blocks (2.6.4)

[warren830]

Summary

Audit blocks carried a duplicate **Timestamp**: line. renderAuditBlock writes the timestamp itself, but did not filter the key out of caller-supplied fields, so the three emitters that passed it rendered two identically-marked lines in one block.

The consequence is not cosmetic for anything that reads audit.md as a whole file: a reader that pairs **Timestamp** occurrences with **Event** occurrences desynchronises at the first parked workflow and misattributes the time of every later event.

Fixes #715.

Changes

Fixed at both layers, which is what the issue proposes:

• Render layer — core/tools/aidlc-audit.ts: new EMITTER_OWNED_FIELD_KEYS (Timestamp, Event) is skipped in the fields loop, so no caller can produce a second line.
• Caller layer — core/tools/aidlc-state.ts: park, unpark, and the practices-promote write-failure path stop passing the redundant field. Both local timestamp values are still used for Last Updated / Parked, so nothing else moves.
• Reference — core/knowledge/aidlc-shared/audit-format.md: WORKFLOW_PARKED field order corrected to Timestamp, Stage, matching every neighbouring row (the reversed order was an artifact of the buggy emit order).

Timestamp deliberately stays out of RESERVED_FIELD_KEYS. Adding it there is the tempting wrong fix: it would break the public audit append --field Timestamp=... contract that t261-audit-authority-floor pins. The value is now dropped at render instead of refused, so that test stays green — only its stale rationale comment is updated.

User experience

The rendered timestamp value is unchanged; only the redundant second line is gone. Existing audit.md shards need no migration — the duplicate was redundant rather than wrong, and the first occurrence was always the authoritative one.

Checklist

• I have read the contributing guidelines
• I have performed a self-review of my code
• I have tested my changes
• I have documented my changes (CHANGELOG entry + audit-format reference)

Test Plan

Two new tests, both in files whose covers: headers already carry the right tokens, so no coverage-registry regeneration:

• tests/unit/t111.test.ts — render-layer contract: a caller-supplied Timestamp leaves exactly one **Timestamp** and one **Event** in the block, the surviving line is the emitter's, the caller's value is absent entirely, and sibling fields are undisturbed.
• tests/unit/t17.test.ts — the reporter's actual symptom: across park + unpark, the file-wide **Timestamp** count equals the block count.

Verified locally (bun 1.3.11; CI pins 1.3.14):

bun scripts/package.ts && bun scripts/package.ts --check   # exit 0, all 7 harness trees in sync
bun run check                                              # exit 0 (parity + typecheck + lint)
bun tests/run-tests.ts --smoke --unit --parallel 8

The suite result is identical to the pre-change baseline on this branch point: the same 2 files fail (t248-codekb-scope-diff, t255-workspace-sync) with the same 9 assertions, both unrelated to audit rendering (t255's failures are ~5s timeouts on live git remote queries and look environmental here). Total assertions went 6038 → 6040, the two added above. Targeted runs t111, t17, t261, t68 all pass.

Version bumped to 2.6.4 rather than 2.6.3, since #754 and #758 both already claim 2.6.3.

Acknowledgment

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of the project license.

[apackeer]

Warren, this PR fixes #715 by filtering emitter-owned audit fields at the shared renderer, removing the three redundant Timestamp caller fields, and regenerating every harness distribution. I reviewed the issue and the implementation against origin/v2; the duplicate structured-event fields are reproducible there, and the code change is narrowly scoped.

Part A - Direction: sound. The problem exists, core/tools/aidlc-audit.ts is the correct harness-neutral enforcement point, and the caller cleanup in core/tools/aidlc-state.ts closes the known sources without changing the public command surface. bun scripts/package.ts --check passes for all seven harnesses.

Part B - Review: request changes.

1. docs/reference/12-state-machine.md:451 is stale after this change. It still says park/unpark carry a caller-supplied Timestamp and rely on the emitter's line being first. The PR now removes those fields and drops public --field Timestamp=... values at render time. Please update this contract paragraph to match the new behavior.

The independent review's three notes do not add blocking findings: the accepted-but-dropped Timestamp value is deliberate and tested, 2.6.4 is the correct current version slot, and append-raw is a pre-existing path outside the structured renderer.

Verification: bun scripts/package.ts --check passed; focused tests passed twice at tests/logs/2026-08-14T08-06-47Z-p2 and tests/logs/2026-08-14T08-08-24Z-p7894, each with 4 files and 202 assertions; git diff --check passed. Version, changelog heading, and README badge are synchronized, and no new numbered test file was introduced.

Part C - UX impact. There are no command, flag, prompt, stage, default, or error changes. New structured audit rows stop duplicating timestamps; audit append --field Timestamp=... remains accepted but now silently ignores the supplied value. Historical audit data remains byte-unchanged and requires no engine migration.