docs: record the phase 6 scenario evidence and status

Add the Phase 6 evidence record, update the implementation status,
verification gates, gap-closure decisions, implementation plan and README
for the scenario director, and state plainly that Phase 6 is not accepted
until its two-hour real-duration soak is observed.

Co-Authored-By: Claude Opus 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01M7dgfQ12mpM4JjSMv3inLA

docs/XZBT_0-1_Gap_Closure_Decisions.md

@@ -4,6 +4,15 @@
 **Status:** Phase 0 GC1–GC5 decisions and shared contract evidence complete; GC6/GC7 implementation evidence remains scheduled\
 **Related resources:** [PRD](../XZBT_0-1_MVP_Product_Requirements_Document.md), [format specification](XZBT_0-1_Format_Specification.md), [verification gates](XZBT_0-1_Verification_Gates.md)
 
+**Phase 6 implementation checkpoint (September 6, 2026):** Format Specification section
+21 completes the previously deferred scenario trigger/timeline shapes while preserving
+GC5 hook ordering, ownership, deferred expiry and bounded cleanup. One active instance
+per definition, symmetric exclusivity, cooldown from termination, dependency-resolved
+first timestamps and one lazy record per repeated entry make admission and finite
+execution explicit. Scenario streams are isolated per definition/instance. Production
+GC5 and accelerated Exhibit E evidence is [recorded here](evidence/phase6/2026-09-06-scenario-director.md).
+The real two-hour development soak and earlier hardware/listening gates remain pending.
+
 Numbering preserves the seven gaps discussed during PRD preparation. Recording a decision closes a design question; it does not establish that a browser feature, performance target, or lifecycle guarantee has passed testing.
 
 | Gap | Primary PRD placement | Supporting verification |