[docs] session retrospective: three meta-lessons captured

[trilamsr]

Summary

Three observations from the recent session that didn't fit the structured surfaces (already used for the load-bearing AGENTS.md entries in PR #81 and the agent-internal notes in PR #82). Each captured via the learn-from-mistakes flow and lands in its existing topic note.

.claude/notes/automation.md — Memory captures rationale; hooks enforce. The pre-PR checklist personal memory landed mid-session was followed by a lint failure shipped to CI within the hour. The same gap closed reliably by the PreToolUse hook installed shortly after. For any "always do X before Y" pattern, prefer the hook; the memory documents why the hook exists.

docs/notes/ci.md — Frame CI / perf projections as ranges, not single numbers. PR #72's 155s wall-time projection vs 242s actual cost an investigation round (later landed in PR #77) because the projection's setup-go-cache amortization assumption was unverified. Either verify assumptions empirically before publishing the number, or frame as a range.

.claude/notes/review-patterns.md — Self-rate work, then write criteria for the next grade up. Forces articulation of measurable improvements rather than free-form "anything else?". PR #76's B+ → A → A+ came from two iterations of this exact pattern; each iteration closed real structural gaps.

A fourth lesson — "fix existing tools before proposing new ones" — was captured to personal memory (no PR, lives in ~/.claude/projects/.../memory/), not the repo, because it's a judgment heuristic about my own decision-making rather than a repo-resident convention.

Test plan

• make doc-check clean (banned-phrase lint, link resolution, all gates).
• learn-from-mistakes format check: banned vocabulary absent, no first-person AI phrasing, no AI attribution, all three entries carry Anchor: lines pointing at concrete PRs.
• CI on this PR exercises doc-check + pr-lint.

Rollback

Each entry is a self-contained ### title + body + Anchor: block at the top of its file. No dependents elsewhere; reverting is a single Edit per file.

NONE — documentation only. Three meta-lessons from a recent session retrospective land in their existing topic notes (`automation.md`, `ci.md`, `review-patterns.md`). No runtime behavior change.