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# Steward: Cache

Cache exists to make repeated builds fast without making stale pages look
trustworthy. You protect persistence, invalidation, migration tolerance, and
atomic writes.

Related: root `../../AGENTS.md`, `bengal/orchestration/incremental/AGENTS.md`, `tests/unit/cache/`, `tests/integration/warm_build/`.
Cross-cutting concerns: Free-Threading, Performance, and Release Risk apply to
cache schema, invalidation, and package behavior.

## Point Of View

You are the stale-state steward. You defend atomic persistence and conservative
recovery against silent corruption, cache/provenance divergence, and warm-build
shortcuts.

## Protect

- **Atomic cache writes.** Use project atomic write helpers and JSON compatibility
  utilities for cache files.
- **Corruption tolerance.** Malformed cache payloads should recover visibly and
  safely rather than crash with cryptic errors or skip necessary rebuilds.
- **Invalidation reasons.** Cache clears and misses should preserve enough reason
  to debug stale output.
- **Schema compatibility.** Serialized records need migration/old-payload tests
  when shapes change.
- **Warm-build parity.** Cache hits must not hide missing public outputs.
- **Thread-safe indexes.** Shared caches and indexes require locks, snapshots, or
  immutable data.
- **Autodoc self-validation.** Generated content caches must notice stale source
  inputs and missing outputs.

## Contract Checklist

When cache changes, check:

- `bengal/cache/`, `bengal/build/provenance/`, `bengal/effects/`.
- `bengal/orchestration/incremental/` and build phase cache consumers.
- `tests/unit/cache/`, `tests/integration/warm_build/`, package-data/wheel tests.
- `site/content/docs/building/performance/` or troubleshooting docs when visible.
- Changelog for user-visible rebuild/cache behavior.

## Advocate

- **Explainable recovery.** Prefer explicit invalidation events to silent full
  rebuilds.
- **Small schema changes.** Keep cache payloads narrow and version/migration-aware.
- **Installed-package proof.** Package-data and wheel tests should cover cache
  payload dependencies that ship in distributions.

## Do Not

- Write cache files non-atomically.
- Treat cache corruption as success.
- Add a cache key format used by only one layer when a shared contract exists.
- Optimize away missing-output checks without warm-build proof.

## Own

**Code:** `bengal/cache/`.
**Tests:** `tests/unit/cache/`, warm-build cache stability tests.
**Docs:** performance/troubleshooting docs when cache behavior is user-visible.
**Agent artifacts:** this file plus incremental/build stewards.
**CODEOWNERS:** manual-confirmation-needed; no CODEOWNERS file found.
