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@@ -13454,3 +13454,35 @@ lines.
 
 Full analysis, with the headless test's structural immunity explained:
 [`2026-08-05-local-player-child-propagation.md`](research/2026-08-05-local-player-child-propagation.md)
+
+## #321 — `DatSoundCacheTests` concurrent-decode-dedup fails under full-suite load
+
+**Status:** OPEN
+**Severity:** LOW (test-only so far; no production symptom observed)
+**Filed:** 2026-08-05
+**Component:** content / audio cache
+
+Surfaced during C5a's commit-1 standalone verification: a concurrent
+decode-dedup fact in `DatSoundCacheTests` failed once under full-suite load in
+`AcDream.Core.Tests` and passed cleanly when re-run standalone.
+
+**Filed separately ON PURPOSE.** It is NOT #302 (`PortalProjectionTests`
+GC-allocation assertion, App.Tests) and NOT #308 (`NakEmissionTests.LossSoak_…`
+wall-clock deadline, Core.Net.Tests). The standing handoff rule is that those
+two must never be conflated; a THIRD load-sensitive failure absorbed into "the
+flake class" is exactly how a real intermittent defect gets dismissed as noise.
+
+**What is actually unknown:** whether this is a test-harness race (two threads
+racing the dedup latch in the fixture) or a genuine thread-safety defect in the
+decode cache itself. The distinction matters — `DatCollection` is already
+recorded in project memory as NOT thread-safe, and an audio decode cache racing
+under load would be the same family rather than a coincidence.
+
+**First step, before treating it as noise:** run `AcDream.Core.Tests` alone
+under repeat/stress to see whether it reproduces without full-suite load. If it
+only fails under load it is scheduling pressure; if it reproduces in isolation
+under repetition, it is a real race and should be escalated out of LOW.
+
+Do not add a retry, a `Skip`, or a delay to make it green — this campaign's
+standing rule is no workarounds without explicit approval, and a masked race is
+strictly worse than a red test.