# Concelier Advisory Chunk Cache

Status: draft · aligned with LNM v1 (frozen 2025-11-17)

## Purpose
- Reduce repeated `/advisories/{key}/chunks` rebuilds while preserving determinism and provenance integrity.
- Provide consoles and debugging tools with transparent cache provenance (key material and TTL) to keep evidence chains auditable.

## Cache key (deterministic)
- Inputs (pipe-delimited, all lower-case where applicable):
  - `tenant`
  - `advisoryKey`
  - `chunkLimit`
  - `observationLimit`
  - `minimumLength`
  - `sectionFilter` (sorted, case-insensitive)
  - `formatFilter` (sorted, case-insensitive)
  - advisory fingerprint (hash of canonical advisory)
  - ordered observations: each `observationId@contentHash@createdAtTicks@format`
- Implementation: `AdvisoryChunkCacheKey.Create` (WebService). Normalized ordering ensures replayability across nodes.
- External disclosure: headers expose a hashed cache key (see below) rather than the full raw key.

## Response transparency headers
- `X-Stella-Cache-Key`: SHA-256 hex of the cache key (default 16 chars) for tamper-evident correlation.
- `X-Stella-Cache-Hit`: `1` on hit, `0` on miss.
- `X-Stella-Cache-Ttl`: configured TTL in seconds (0 when caching disabled).
- Consumers may log these headers; do **not** treat them as stable API contract for filtering.

## Determinism & safety
- No PII in keys or headers; key inputs are tenant/advisory identifiers already present in requests.
- Timestamps use UTC ticks; content hashes retain upstream digest prefix (e.g., `sha256:`) to distinguish sources.
- Cache TTL defaults to 0 (disabled) unless configured; safe for offline/air-gapped deployments.

## Testing notes
- Unit coverage: `AdvisoryChunkCacheKeyTests` (ordering, filter casing) and `AdvisoryChunkBuilderTests` (observationPath pointers influence chunk IDs).
- Integration tests should assert headers when cache is enabled; disable cache for tests that assert body-only determinism.

## TODOs / follow-ups
- Add integration test that exercises a cache hit path and validates transparency headers.
- Document cache configuration knobs in `appsettings.*` once finalized.