feat: add persistent stale-while-revalidate API cache

Introduce an actor-backed persistent cache layer at the SRHTClient boundary
for read-only SourceHut data. Cache entries now store stable metadata
including key, resource type, fetched/expires/access timestamps, payload
hash, schema version, and payload size, with bounded memory and disk usage.

Add centralized cache key builders and TTL defaults for repository, file,
ticket, build, log, profile, status, and list-style resources. Support
networkOnly, cacheOnly, cacheFirstThenRefresh, and refreshIgnoringCache
policies, plus request coalescing for duplicate in-flight cache keys.

Integrate first-pass caching into high-value low-risk read paths:
- build detail and completed/active build logs
- ticket detail
- README lookup
- repository tree, blob, and linked file reads

Keep mutation paths network-only and add simple prefix invalidation after
ticket and build mutations. Add compact cached/stale UI status rows and a
Settings action to clear the persistent cache.

Add focused cache tests covering round trips, expiration, stale fallback,
policy behavior, request coalescing, prefix invalidation, size limits, LRU
pruning, expired pruning, and mutation bypass behavior. Document storage,
key, TTL, invalidation, limitations, and next recommended targets.

1 files changed, 11 insertions, 0 deletions

diff --git a/Docs/API_CACHE.md b/Docs/API_CACHE.md
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+# SourceHut API Cache
+
+Hutch caches read-only SourceHut API responses at the `SRHTClient` boundary. The cache stores raw response bytes plus metadata on disk, with a small bounded memory layer for hot entries. Disk files are account-scoped under the app caches directory, and `PersistentAPICache` is an actor so disk I/O, pruning, and metadata updates stay off the main actor.
+
+Cache keys are built in `APICacheKeys`. Keys are explicit and include the service plus request-shaping inputs such as repository IDs, refs, tree/blob IDs, paths, owners, ticket IDs, job IDs, log URLs, cursors, and filters. Views and view models should not invent ad hoc cache strings.
+
+TTLs live in `APICacheTTLs`. Active build data uses a very short TTL, mutable ticket and list data use medium-short TTLs, repository metadata and profile data live longer, completed build logs are long-lived, and content-addressed git objects are treated as mostly immutable. Moving refs such as `HEAD` use shorter file/content TTLs.
+
+Invalidation is intentionally prefix-based. Successful ticket mutations remove ticket, ticket-list, tracker, and Home prefixes. Build retry/cancel/resubmit actions remove build detail, build-list, build-log, and Home prefixes. This avoids a dependency graph while keeping stale post-mutation data out of the high-risk paths.
+
+Known limitations: the first pass is integrated into build detail/logs, ticket detail, README lookup, and repository tree/blob/file reads. Some older list-level paths still use the legacy in-memory cache facade and should move to `APICacheKeys` plus `executeCached` next. Recommended next targets are repository lists, build lists, ticket lists, profile repositories/trackers, and Home/Work Queue sections.