Add CLAUDE.md as a short card for agent sessions

CLAUDE.md

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+# cosyte/config
+
+The pnpm workspace that publishes the toolchain every `@cosyte/*` repo builds, lints and tests
+with: eight packages under `packages/`, the PHI-scan engine in `script-utils` among them. It
+also holds the estate baseline, `drift-manifest.json`, which `scripts/drift-check.js` checks.
+
+## Gate
+
+Required checks: `verify (22)` and `verify (24)` (one job, Node 22 and 24) and `actionlint`. Run
+from the repo root after `git add`, since the em-dash gate reads only `git ls-files` (#56):
+
+```sh
+node scripts/changeset-guard.mjs
+node scripts/release-notes.mjs prepare --repo . --out "$RUNNER_TEMP/release-notes"
+node scripts/credential-surface.mjs
+node scripts/install-hardening.mjs
+node scripts/readme-check.mjs
+node scripts/drift-check.js
+pnpm install --frozen-lockfile
+pnpm check:no-emdash
+pnpm format:check
+pnpm typecheck
+pnpm lint
+pnpm test
+pnpm build
+pnpm attw
+actionlint
+```
+
+- Outside CI: set `RUNNER_TEMP` to a scratch directory; make every `pnpm` on `PATH` 10.34.5, since
+  scripts and tests call a bare `pnpm` and a newer one fails them; and run `drift-check.js` from a
+  copy at `<dir>/config/`, since under any other directory name it exits 2, "nothing was graded".
+- Not required, but red if they fail: CI's `release-dry-run` job (publish and pack dry runs), and
+  `no-emdash.yml`, which also reads the PR title, the PR body and every commit message.
+
+## Hazard: a change here reaches every repo
+
+The PHI-scan engine in `packages/script-utils/phi-scan.js` runs in the parsers' commit gates, and
+every new parser starts as `scripts/parser-template/`. A change that narrows a pattern, skips a
+path or reports clean after reading nothing turns PHI detection off wherever they run, silently.
+
+- Prove an engine or template change red before green against a leak it must still catch (#114:
+  `OK: no hits` over an emptied `src`). A change that makes the engine refuse less names what still
+  refuses in `documentation/decisions/0003-the-phi-scan-engine-gap-settlements.md`.
+- A hit names the place and the rule, never the matched value: reports used to copy it into the CI
+  log (`packages/script-utils/CHANGELOG.md`, "a finding names a position").
+
+## Rules
+
+- A change to what a package ships needs a changeset that bumps it; anything else gets none. A
+  changeset that bumped nothing withheld a whole release on a green run (#41).
+- Nothing that packs, publishes or installs goes in a `prepublishOnly`: it broke every version bump
+  (#40). A gate or test spawning npm or pnpm checks which `npm_config_*` the child inherits (#47).
+- A gate that could not read its input exits 2 (0 is clean, 1 a finding), and its tests assert the
+  CLI's exit code, each new case seen red first: gates exited 0 on a defect (#42) and unrun (#48).
+- The template's own `test/` never runs here: cover a template change in the root suites that run
+  the real scaffolder (`test/*scaffold*.test.ts`); new parsers were born red (#43, #57).
+- Keep `fetch-depth: 0` in `verify` and the release jobs, and `persist-credentials: false` on the
+  version job: without them the notes gate passes blind and a Version PR gets no checks (#45).