# Tasks: Add Deterministic Core

> **Execution shape:** Group 1 (build-spike) is a **sequential gate** — it MUST
> complete and be visually confirmed in a real session before any other group
> starts. Once it lands, Groups 2 (scanner) and 3 (state store) are **independent
> and run in parallel** (no shared state). Group 4 (reminder hook) is **sequential
> after Group 3** — it reads and writes `last_reminded` through the state store.
> Group 5 (cross-seam verification) runs last. Model routing: all scripts are
> deterministic (no model); per CLAUDE.md, write them with **Haiku**.

## 1. Build-Spike — SessionStart banner (SEQUENTIAL GATE, do FIRST)

- [x] 1.1 Author a trivial `hooks/hooks.json` at the plugin root wiring a
      `SessionStart` hook (`matcher: startup|resume`) that emits a fixed
      `systemMessage` banner, with `timeout` ≤ 5s and exit 0.
- [x] 1.2 **Acceptance criterion (implementation-time):** start a real Claude Code
      session with the plugin enabled and **visually confirm the banner renders**
      to the user. The rest of this change does not start until this is confirmed.
- [x] 1.3 Record the confirmed hook entry format (plugin-root `hooks/hooks.json`,
      nested hooks array, `systemMessage` field) so Group 4 reuses it. This is the
      first CC hook in the collection — capture the working shape.

## 2. Scanner (`doc-scanner`) — parallel with Group 3 after the gate

- [x] 2.1 Implement a `Scanner` class with injected filesystem/root and scope
      globs; walk scoped files under the resolved project root. No model.
- [x] 2.2 Implement the exclusion pipeline, applied **before** signal computation
      and short-circuiting: (a) dir-prune `scan.excluded_dirs` (`build`, `vendor`,
      `archive`, `graphify-out`, `.dochygiene`) at the directory level, including
      self-exclusion of `.dochygiene/`; (b) `.dochygiene-ignore` pattern match;
      (c) `hygiene: frozen` frontmatter; (d) append-only-log detection.
- [x] 2.3 Implement deterministic per-path **signal** computation (objective facts
      only: broken references, version skew, edit-recency vs git churn, location,
      append-only growth, archive-to-live ratio, frontmatter markers).
- [x] 2.4 Emit the **intermediate artifact** (`shortlist` + per-path `signals`) as
      structured JSON with a correct exit code. Do NOT emit `entries`, `category`,
      `op`, `token_estimate`, or a machine report.
- [x] 2.5 **Tests — exclusions (invariant #9):** fixtures proving a `hygiene:
      frozen` file, a `.dochygiene-ignore`-matched file, and an append-only log
      (positive + negative fixture) are each present in the tree and absent from
      the shortlist; and that `.dochygiene/` and excluded dirs are never scanned.
- [x] 2.6 **Tests — signals:** one fixture per signal type asserts the expected
      signal appears on the right path with no classification attached.

## 3. State store (`state-store`) — parallel with Group 2 after the gate

- [x] 3.1 Implement `resolve_project_root(start_dir)` — nearest ancestor `.git`,
      fallback cwd — as a pure function over injected filesystem.
- [x] 3.2 Implement a `StateStore` class confining all writes to
      `<project_root>/.dochygiene/`; create the dir as needed; maintain no global
      index; never open or edit `.gitignore`.
- [x] 3.3 Implement lifecycle timestamp read/write (`last_check`, `last_clean`,
      `last_reminded`) in `state.json`; absent timestamps read as unset.
- [x] 3.4 Implement atomic writes (write-temp → fsync → `os.replace`) for
      `state.json` and report files.
- [x] 3.5 Implement report rollover: delete any prior `.md` + `.json` report pair
      before writing the new pair; exactly one pair retained (invariant #4).
- [x] 3.6 **Tests — root resolution (invariant #3):** git-root case, cwd-fallback
      case, and that no path outside the resolved root is written; assert
      `.gitignore` is never edited.
- [x] 3.7 **Tests — atomic write & rollover (invariants #3, #4):** torn-write
      safety (reader sees old-or-new, never partial); two sequential report writes
      leave exactly one latest pair on disk.
- [x] 3.8 **Tests — timestamps:** round-trip read/write with an injected clock;
      absent timestamp reads as unset.

## 4. Reminder hook (`session-reminder`) — SEQUENTIAL after Group 3

- [x] 4.1 Replace the spike's fixed banner: implement a `Reminder` decision pure
      over `(last_check, last_reminded, now, threshold)` per design D5 — silent
      when fresh; banner when stale and not snoozed; snooze keyed on **calendar
      day** via `last_reminded`.
- [x] 4.2 Implement the reminder script: read state via the Group 3 store with an
      injected clock; on banner, emit `systemMessage` (naming the slash command)
      and write `last_reminded = now`; on silent, write nothing; always exit 0;
      treat missing/unreadable state as never-checked (stale). No scan, no model
      (invariant #1).
- [x] 4.3 Update `hooks/hooks.json` to invoke the reminder script (reusing the
      confirmed entry format from 1.3), keeping `timeout` ≤ 5s.
- [x] 4.4 **Tests — injected clock (invariants #1, #2):** fresh → silent; stale +
      never-reminded → banner; stale + reminded same calendar day → silent (covers
      repeated startup/resume within a day); stale + reminded prior day → banner; assert no
      file is mutated except `last_reminded`, and only on banner.

## 5. Cross-seam verification & wiring

- [x] 5.1 Confirm no seam imports or invokes a model and the scanner makes no
      network/API call (invariant #6 review).
- [x] 5.2 Confirm the scanner output is the intermediate artifact (no `entries`,
      no report) and references the frozen `report-schema` shapes only as consumed.
- [x] 5.3 Generate a `CONTEXT.md` for `scripts/` (progressive disclosure) indexing
      the reminder, scanner, and state-store modules.
- [x] 5.4 Run `openspec validate add-deterministic-core --strict` and confirm it
      passes.