Add architect startup cheat-sheet

Capture tool locations, the --mutate-all differential gotcha, the
gherkin-mutator invocation, and the refactorer-forward no-op pattern to
speed up the next session's startup.

By architect.

docs/architect-startup.md

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+# Architect Startup Cheat-Sheet
+
+Fast-start notes for the architect role in this monorepo. Captured from the
+`topic-feed` session (2026-08-28) to make the next session's startup faster.
+
+## Tool locations (already installed — do not reinstall or re-verify)
+- Language mutation/CRAP/DRY (JavaScript): `psf-memo-client/node_modules/.bin/`
+  - `mutate4javascript`, `crap4javascript`, `dry4javascript`
+- APS Babashka tools: `tmp/aps-spec/` (run via `bb <task>` from that dir)
+  - `gherkin-parser`, `gherkin-mutator`, `gherkin-ir-dry-checker`
+- Runner adapters (for `gherkin-mutator`):
+  - DB: `psf-memo-db/acceptance/lib/runner-worker.js`
+  - Client: `psf-memo-client/acceptance/lib/runner-worker.js`
+
+## Language mutation — the `--mutate-all` gotcha (IMPORTANT)
+`mutate4javascript` runs in **differential mode** when a manifest is embedded in
+the source file: it only re-runs mutations in functions whose hash changed since
+the last run. If you add tests to kill survivors but the SOURCE is unchanged, a
+plain re-run reports `Killed: 0, Survived: 0, Uncovered: 0` and silently skips
+the survivors.
+
+**Always pass `--mutate-all` when re-running mutation on a file that already has
+a manifest** (especially right after adding hardening tests). New files (no
+manifest) run fully on the first pass.
+
+Canonical invocation (run from the component dir so `npm test` works):
+```bash
+node ../psf-memo-client/node_modules/mutate4javascript/bin/mutate4javascript.js \
+  src/<file>.js --max-workers 8 --mutate-all
+```
+
+## Gherkin soft mutation — canonical invocation
+Run from `tmp/aps-spec/`. Use `--json` and redirect stderr to `/dev/null` for a
+clean parseable report (worker logs go to stderr; the report goes to stdout).
+```bash
+bb gherkin-mutator \
+  --runner-worker "node <component>/acceptance/lib/runner-worker.js" \
+  --feature <component>/specs/<feature>.feature \
+  --work-dir <component>/tmp/acc-mut-<name> \
+  --level soft --workers 8 --status-interval 30s --json \
+  2>/dev/null > /tmp/report.json
+```
+Parse survivors with a small python one-liner over `d['results']` (filter
+`Status == 'survived'`).
+
+## Long runs
+- Mutation and gherkin-mutator runs take 60-180s each. Use `--max-workers 8` /
+  `--workers 8` and `--status-interval` so progress is visible.
+- Run verification sequentially (never concurrent with acceptance generation).
+
+## Refactorer forwards your own review commit back
+After you send a `priority: 00` review commit to coder+refactorer, the refactorer
+merges and forwards that SAME commit back to you. It is a no-op ("Already up to
+date"). Recognize it immediately and just run `done_with_current.sh` — do not
+re-process or re-verify.
+
+## Startup smoke test (fast, ~seconds)
+```bash
+psf-memo-client/node_modules/.bin/mutate4javascript 2>&1 | head -1   # usage
+psf-memo-client/node_modules/.bin/dry4javascript 2>&1 | head -1      # runs
+cd tmp/aps-spec && bb gherkin-parser --help                          # usage
+```