docs: post-mortem on the guards arc — what shipped, and what did not work

[Polichinel]

Full post-mortem in reports/post_mortems/2026-08-12_the_guards_that_did_not_guard.md, following the platform convention (views-faoapi's shape).

Covers PR #239 through the release #240, epic #241, and register C-89…C-97.

The substance

We built a cross-repository guard surface. A post-merge review found fifteen defects in the change that built the newest part of it — all reproduced. Three would have shipped in the release:

• the guard against publishing a coordinate value printed it, on the one event it fires for, into a world-readable CI log
• the drift check fired on 12 of 25 rows this partner never reads
• 15 of 29 markdown assignment forms escaped the no-copy scan

The remedy was deletion three times out of five.

The process section is the point

Lines added to code	341
Lines added to docs/register	452
Commits per story	7 · 7 · 12 · 5

Four named failures, worst first:

1. A governance rule repealed in a permanent ADR on a claim false by six hours. views-crafdapi#53 closed at 12:15; the commit said it hadn't landed at 18:18.
2. Each remediation introduced a defect of the class it was fixing — a tautology inside the fix for a tautology; a cry-wolf helper that was strictly worse than plain in.
3. Numbers quoted from memory, wrong twice in consecutive tracking comments.
4. A review reported as running when nothing had been launched.

The root cause is architectural, not personal

ADR-016 and ADR-017 contain descriptions of current implementation — "this is the shape the registry check now has". An ADR records a decision; the moment it also describes the code it becomes a second copy of the code, and it rots on every change. Most of #248's twelve commits were repairing exactly that. It is the rule #250 will land.

What worked

Independent review — five parallel reviewers found what four rounds of self-review had not, and the adversarial mutation reviewer was the single highest-value input. Deletion as default remedy. Refusing to chase five surviving mutations in writing. And the mid-sprint intervention, after which #248 took twelve commits and #243 took five.

Every figure was produced by a command and re-verified before commit — the rule this arc had to adopt halfway through.

🤖 Generated with Claude Code