Red commit: c84a8f575a (CI run: pending
push)
Fixes#1203 — path-inspector 503 storm.
Three sub-fixes, each shipped as red→green per AGENTS TDD:
**A. Singleflight on rebuild** (`ensureNeighborGraph`)
Hand-rolled `sync.Mutex + chan` singleflight — no new deps (x/sync was
not in cmd/server's go.mod). Concurrent callers attach to one in-flight
rebuild instead of N parallel `BuildFromStore` goroutines.
- Red: `7340f23b` — test asserts ≤1 build under 10 concurrent callers
(saw 10 on master)
- Green: `abac6b3c`
**B. Stale-while-revalidate** (`handlePathInspect`)
Stale non-nil graph is served immediately with `"stale": true` while a
background rebuild runs (deduped by A). The 2s synchronous gate is gone.
Stale responses are not cached, so the next request after rebuild lands
fresh.
- Red: `c84a8f57` — test asserts 200+`stale:true`+rebuild-kickoff
(master returned 503)
- Green: `5eb86975`
**C. Cold-start 503 still kicks rebuild**
True cold start (`graph == nil`) is the only path that still returns 503
`{"retry": true}`, but it now spawns an async `ensureNeighborGraph` so
the very next request warms up.
- Green test: `f5ac7059` (passed on top of A+B)
Singleflight verified: `TestEnsureNeighborGraph_Singleflight`
Stale-while-revalidate verified:
`TestHandlePathInspect_StaleWhileRevalidate`
Cold-start verified: `TestHandlePathInspect_ColdStartKicksRebuild`
**Acceptance criteria (issue #1203):**
- [x] Concurrent requests share ONE rebuild
- [x] Stale non-nil graph served with `stale:true` async
- [x] 503 only on true cold-start
- [x] Cold-start 503 kicks rebuild → follow-up warm
- [ ] p99 < 500ms under load (not unit-testable; design satisfies it)
- [x] No regression in existing tests
**Out of scope (per issue):** 5-min TTL constant, `BuildFromStore` perf,
`/api/analytics/topology`, persist-lock contention.
No new deps.
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Co-authored-by: corescope-bot <bot@corescope.local>
Co-authored-by: corescope-bot <bot@corescope.dev>
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