_model: devlog-entry
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schema_version: 1
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title: Step 6 Multi-Surface Architecture Completion and Closure
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date: 2026-09-15
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author: cgcha
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summary: Formally closed Step 6 under tag step-6-complete following Step 6.10 completion gate adjudication, with 12 architectural invariants verified and non-blocking follow-up documented.
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tags: step6, completion, architecture, closure
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source_commit: 9dcd3993dbedfea358813e0312e0d5e5098376a7
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body: |
  This devlog entry marks the formal closure of Step 6 for XZBT-NGN under annotated tag step-6-complete.

  The Step 6.10 completion gate concluded with the formal disposition: **STEP 6 COMPLETE WITH DOCUMENTED NON-BLOCKING FOLLOW-UP**.

  Milestone outcomes and adjudications:
  - **Step 6.5 Synchronization Proof:** Formally adjudicated as satisfied by existing implementation and later evidence. Multi-surface state synchronization is guaranteed by a single authoritative Exhibit State Core, snapshot and stateRevision transmission on attachment, monotonic event propagation, and routing secondary interactions through owner authority.
  - **Step 6.8 Multi-Surface Behavior:** Complete and accepted. A single session renegotiation observed once during testing could not be reproduced, had no architectural defect identified, preserved state, recovered cleanly, and remains tracked as an ongoing non-blocking observation.
  - **Architectural Invariants:** All 12 core architectural invariants were verified, confirming single-owner mutation authority, exhibit-generic host design, non-authoritative surfaces, same-origin security boundaries, and full Contract 5.3 protocol conformance.
  - **Zero Blocking Items:** No blocking defects or outstanding implementation tasks remain for Step 6. Five non-blocking follow-up items are retained for operational observation.

  The complete closure documentation is published in docs/reference/XZBT-NGN-Step6.10-Closure-Report.md.