docs(agents): give findings a home, and say which one

[explosivebit]

Docs only. No code, no artifacts.

Why

A finding that lives only in a reply is gone at the end of the session. That has cost real work here twice:

• a measurement across 465 artifacts that cancelled a planned fix existed nowhere but a chat message until someone thought to file it;
• a handoff document pointed at a scratch directory that did not survive the session it described.

What it says

Three kinds of finding, three homes:

Finding	Home
a rule that changes how an agent works	AGENTS.md
work someone should do	GitHub issue, open
a measured dead end — checked, decided not to do	GitHub issue, closed on arrival, label measured-not-planned

The third row is the one people skip and the one that pays. A measurement that cancels work is worth as much as one that starts it, and it evaporates faster — nobody files "we checked and it does not matter", so the next person smells the same thing and re-derives it. #476 is the worked example: two plausible check_stub defects, both measured, both left alone, numbers on the record.

Filing rules: numbers not adjectives; every finding carries a trigger phrased as a condition, not a date; say what was rejected and why; search before creating.

Revisit is a step, not a habit — before opening a release/v* PR, list the measured-not-planned issues and re-check their triggers. That puts it next to the existing pre-release Dependabot check (RED LINE #10) rather than relying on someone remembering.

Two mechanics that silently do nothing

• Closes #N in a PR body is inert when merging into dev. GitHub honours closing keywords only on merges into the default branch, and ours is main. validate: нет ни одного правила для NFR (50 из 79 PRD без секции, никто не возразил) #449 and validate: нет правила «каждый Requirement в SPEC имеет Scenario» — инвариант держит только TDD-потребитель #450 stayed open after [PROB-105] The SPEC validator passed empty templates and blocked real specs #472 merged, with no error anywhere. Convention recorded: close by hand at dev-merge, naming the merge commit.
• An empty gh result is not proof of absence. A GraphQL EOF prints nothing and can exit through a pipe as success. Hit while verifying the new label — the listing came back empty and the label was in fact applied.

Plus the zsh PIPESTATUS trap, filed into the existing disk-full family in Parallel agents and the build directory: ${PIPESTATUS[0]} is a bashism that expands to empty in zsh, so a guard prints exit= and reads as fine. Same shape as passed=0 failed=0 on a full disk — the number is real, it is just measuring tail.

Infrastructure

Label measured-not-planned created and applied to #476, so the convention is a command (gh issue list --state closed --label measured-not-planned) rather than a good intention.