docs(perception): record cross-host canary failure and joint startup gate

docs/adr/0049-stream-first-perception-profiles.md

@@ -848,3 +848,24 @@ Of72 measured observations,60 meet conditional≤5ms; min/median/max uncertainty
 does not claim full-graph cross-host freshness and does not cherry-pick a passing sample.
 The next full-graph run must consume continuous mapping state and carry uncertainty to
 the receiving freshness decision. [Detailed report](../../experiments/perception/PERCEPTION_STREAM_STAGE2_CONTROL_CLOCK_2026-09-02.md).
+
+## Stage 2 increment 15: acknowledged clocks in the full cross-host graph (2026-09-02)
+
+The Worker validates a one-use echoed Poll challenge before accepting responder-side
+clock evidence and the immutable source anchor. Clock validity is checked continuously,
+including idle periods, input admission and GPU/CPU/publication boundaries. Unknown or
+excess uncertainty enters WAIT without releasing resident models/local ownership.
+Upper age bounds govern source cutoff; scene and cell freshness include uncertainty.
+Each assessment uses one immutable clock snapshot, and EOF acknowledgement precedes
+data-channel retirement. Early transport loss after grant admission but before OPEN
+must also enter WAIT; malformed unbound data cannot stop the owner.
+
+The final full-graph Mac source/receiver canary is **not qualified**:13 source WAIT skips,
+17 synchronization skips,2/32 receipts (frames30–31), both after source-window EOF.
+Latency143.881/155.743ms; no hidden losses, no model reload, sampled VRAM2365MiB,
+not a24GiB limit.297 local and173 Worker tests PASS;
+early disconnect additionally12/12 across six repeats. Source-first clock readiness
+and a fixed2s lead do not establish Worker readiness. Next gate separates two-sided
+clock warmup from source-anchor activation before1x starts; after start the source
+timeline remains immutable through outages. No gate widening, backlog replay,
+standalone or Stage3 promotion. [Evidence and rejected attempts](../../experiments/perception/PERCEPTION_STREAM_STAGE2_CROSSHOST_GRAPH_2026-09-02.md).