The acknowledgment explains one PR's unattributable emitted-artifact delta.
The moment that PR merges the delta is in the base, so the acknowledgment can
never clear anything again — its useful life is exactly the PR's open window.
It is stored in permanent, shared, merge-path state. That single lifetime
mismatch is the origin of six consecutive rounds of defect-and-fix (#2789,
#2914, #3078, #3823, #3842, #3875), each fix generating the next defect, ending
in a scheduled sweeper whose own PR (#3927) could not merge itself.
ADR-3942 supersedes ADR-2719 section 3 only, and its #2789 Amendment. Sections
1, 2 and 4-7 are retained and depended upon: the conservation law itself is not
in question, only where its escape hatch is stored.
Also lands the root-cause research note behind the decision, and regenerates
the ADR index.
Two corrections to earlier framing, recorded here rather than dropped:
- Per-commit trailers do NOT reliably survive squash-merge; the repo's own
ship.md:306 reconstructs a gate trail precisely because squash discards it.
The ADR therefore claims no durable audit record on next. Non-survival is the
property being bought, not a cost.
- The test job checks out at depth 1 (test.yml:107-110, no fetch-depth key). A
depth-1 checkout cannot see the PR's commit range and fails VACUOUSLY rather
than erroring, so fetch-depth: 0 is a named decision in the ADR and the
acceptance criterion requires a test that fails under depth 1.
Docs-only; no code, no changeset.
Refs #3942
Co-authored-by: sim <sim@local>
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