docs(standards): fix the class, not the instance — canon rule + PR-template check (backend#1680)

[LukasWodka]

What

Encodes the defect pattern from today's handoff, in two places: the canon (org-standards.md, syncs fleet-wide) and the PR template (produces an artifact).

The pattern

Four instances on 2026-08-11, in two shapes — and a rule aimed only at "neighbouring bugs" catches half:

instance	shape
discover() left bare beside a wrapped load()	other call site
epoch helper used at 2 sites, a 3rd did it inline	other call site
hooksPath guard canonicalised dirname not the path → .. escaped it	other input to the same guard
hook probed make but not the venv toolchain it calls	other input to the same guard

Why the checklist line, not just the canon line

A prose rule produces nothing a reviewer can look for. The template line produces an artifact whose absence is visible:

Sibling check — what class is this bug in, and how did you cover it? (paste the grep, or "N/A — one-off")

And the argument for making it mechanical is empirical: the stuck-run detector built from today's lessons reproduced the very same mistake — it encoded the symptom (runner=NONE) rather than the condition (nothing progressing), and would have cancelled a healthy production deploy. The pattern survives being named.

Cost, stated up front

Editing the canon drifts all 19 repos and needs a sync fan-out. This is the third canon edit this week, and it is exactly the treadmill worth a decision (auto-merge on green, or batching) rather than paying again — tracked on backend#1680.

Test plan

• standards-sync selftest: 27 checks, 0 failed
• report run: the block still splices cleanly against all 19 targets (19 drifted is the expected fan-out, not a defect)

Parent epic: backend#1680.

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Note

Low Risk
Documentation and PR-template only; no product code, auth, or data paths. Canon edits trigger expected fleet CLAUDE.md drift until standards-sync PRs land.

Overview
Documents the “fix the class, not the instance” defect pattern in the fleet canon (org-standards.md Quality bar): before shipping a bug fix, name the class and sweep other call sites (grep the symbol) and other inputs to the same guard (what else hits that branch); if the class can’t be enumerated cheaply, say so in the PR.

Adds a matching Sibling check line at the top of the PR template checklist so reviewers get a concrete artifact (grep output or “N/A — one-off”) instead of relying on prose alone.

No runtime or application code changes; merging the canon edit will fan out via standards-sync to consuming repos’ CLAUDE.md blocks as usual.

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