client-reliability-8: route measured active media cancellation and spec correction

docs/agents/prompts/client-reliability.md

@@ -1,6 +1,16 @@
 # Area: Client reliability (client-reliability)
 
-## Current assignment: client-reliability-8 — active URL-media cancellation investigation
+## Current assignment: client-reliability-8 — active URL-media cancellation
+
+### Implementation routing after independent evidence
+
+Dispatch independently ran nine scratch modes: disposed/fifo new cancellation assertions fail naturally after cleanup, seven shared/cross/legacy/rejoin/timeout/error/replacement controls pass. Final-owner media retains1source/3listeners/1timer/1slot/unsettled promise; source-backed Stage3 and owner continuation require releasing obsolete active work. Minimal implementation now authorized ONLY js/ui/urlHealthController.js (retainUrlProbe final-owner cancellation hook, record cancelled state, active media settle/cleanup) plus tests/url-health-lifecycle.test.mjs and unique integrity/spec/evidence notes. Existing observer/cache/HEAD/HLS/torrent/app modules remain read-only. Supersedes investigation-only prohibition for this boundary.
+
+Use existing cancellation paths to settle null, suppress cache/mirrors/stale badge writes, release slot and advance FIFO once. Mark cancelled record unavailable synchronously for same-turn rejoin; old settlement must never remove/paint/cache over replacement. Test both immediate same-turn rejoin and rejoin after microtask, sharing before final release, cross-controller sharing, ownerless legacy consumers, queued competition/FIFO, replacement identity, late success/error/timeout callbacks and cleanup idempotence. Clean src/listeners/timer and pause/load boundary; do not force exit or wait for original timeout. Preserve live-owner healthy/offline caching and normal timeout/retry, shared work, slot cap/FIFO and previous queued/mirror guards.
+
+Explicit spec correction permitted for active-disposed success/offline-cache and disposed-timeout/rejoin expectations ONLY: the old queued-only contract intentionally allowed completed work after disposal; new owner instruction plus Stage3 requires immediate active media cancellation once final registered owner leaves. Replace these with equally strict resource cleanup/null settlement/no cache/no mirrors/no stale writes/fresh replacement assertions; keep separate live-owner success/error/timeout controls. Record Test Integrity Note (spec_correction and new_tests, exact old→new contract/spec source, any did_relax explanation honest) and unique spec change note; do not silently delete scenarios. Every new scenario needs a restored mutant that fails naturally. Mutants must reject disabled cancellation, retained source/listeners/timer, cache-on-cancel, lost shared owner, stale inflight deletion, FIFO disruption as applicable. Report surviving mutants instead of weakening assertions.
+
+Focused real lifecycle/adjacent URL/controller/observer checks and lint now. No browser/full/build yet; request slot when focused results/mutants/lint and merged-tree candidate are ready. Normal unchanged full gate and durable landing/ancestry required before closure. Send READY with files/counts/mutants/contract diff and unverified scopes. No wider Stage3 claim; actual browser/network/HEAD/HLS/torrent remain unverified. Dispatch will coordinate final validation and preview.
 
 Owner exact continuation recorded in PROGRAM supersedes the review idle hold only for this bounded slice. Read RULE-CHANGES newest first, PROGRAM, KNOWN_ISSUES, performance-efficiency-plan Stage3 and test-integrity before work. Claim item8 on integrated current unstable after this coordination commit lands; merge, never rebase. First investigate actual URL observer→controller active media last-owner disposal with controlled external IO. No product or committed-test edits yet; scratch reproduction and unique evidence only. No full/build/browser until explicit slot grant; cheap focused checks allowed.