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XZBT-NGN Step 6.10 — Completion and Closure Report
Date: 2026-09-15 Status: STEP 6 COMPLETE WITH DOCUMENTED NON-BLOCKING FOLLOW-UP Technical Baseline: 163de264388f1e411cf9e54f26f72a254888afd (contract-5.3-accepted-baseline) Closure Tag: step-6-complete
1. Executive Summary and Closure Disposition
Following the completion and formal adjudication of the Step 6.10 completion gate, XZBT-NGN Step 6 is complete and closed with documented non-blocking follow-up.
All required Step 6 implementation, adaptation, integration, and verification tasks are finished. No further Step 6 implementation work remains.
The accepted technical baseline for Contract 5.3 multi-surface architecture is frozen at:
- Commit: 163de264388f1e411cf9e54f26f72a254888afd
- Tag: contract-5.3-accepted-baseline
This closure administration pass performs documentation and provenance reconciliation only. No application source code, automated test code, fixture implementation, protocol definition, or runtime logic is altered.
2. Milestone Dispositions
All Step 6 milestones have reached final adjudication and acceptance:
| Milestone | Disposition | Notes |
|---|---|---|
| Step 6.1 | Complete | Multi-surface architectural model defined and documented (XZBT-Multi-Surface-Model-Step6.1.md). |
| Step 6.2 | Complete | Multi-surface reference prototype validated against Museum Gallery. |
| Step 6.3 | Complete | Surface discovery protocol and catalog validation implemented and verified. |
| Step 6.4 | Complete | Local presentation panes integrated into NGN operator UI without additional contract sessions. |
| Step 6.5 | Satisfied by existing implementation and later evidence | Multi-surface state synchronization proof adjudicated satisfied (see §3). |
| Step 6.6 | Complete and accepted | Reference exhibits validated under Contract 5.3. |
| Step 6.7 | Complete and accepted | SciFi-XZBT Observation surface adapted, packaged build verified, live 8-point verification passed. |
| Step 6.8 | Complete and accepted | Multi-surface behavior against SciFi-XZBT validated; single unreproduced renegotiation noted as follow-up (see §4). |
| Step 6.9 | Complete | Architectural and protocol conformance review passed across all 18 review areas (see §5). |
| Step 6.95 | Complete | Verification evidence and cross-document references reconciled. |
| Step 6.10 | Complete | Formal completion gate passed: Step 6 closed. |
3. Step 6.5 Adjudication: Synchronization Proof
Step 6.5 was adjudicated by the Step 6.10 completion gate as:
SATISFIED BY EXISTING IMPLEMENTATION AND LATER EVIDENCE
The requirement for shared-state synchronization across surfaces was satisfied by the verified architecture and evidence rather than requiring a hypothetical multi-host topology:
- Authoritative Exhibit State Core: A single state core maintains all authoritative exhibit state, revision counters (stateRevision), and mutation dispatch.
- Snapshot and Revision on Attachment: When a secondary surface attaches, it immediately receives a full immutable state snapshot stamped with the current stateRevision.
- Ongoing State and Event Propagation: Owner-mediated mutations and events broadcast monotonically to all attached surfaces.
- Owner-Routed Secondary Interactions: Interactions initiated on secondary presentation surfaces do not mutate state directly; they are routed through the owner's authority chokepoint (pplyMutation).
- Clean Detach and Reopen Lifecycle: Detaching and reattaching surfaces preserves monotonic participant counts without ratcheting or state corruption.
- Cross-Document Evidence: Cross-document presentation synchronization was proven in Museum Gallery (Step 6.6) and independently verified in SciFi-XZBT across separate browsing contexts (Step 6.7/6.8).
No requirement exists or was ever specified for multiple NGN instances controlling a single exhibit.
4. Step 6.8 Completion and Accepted Status
Step 6.8 (multi-surface behavior against SciFi-XZBT) is complete and accepted.
The handshake gating mismatch identified during Step 6.8 preparation (where exact-string advisory envelope checks dropped xzbt: '5.3') was resolved in commit 745912e, verified by automated regression tests, and confirmed in live browser testing.
Residual Observation (Non-Blocking Follow-Up)
During live multi-surface testing in Step 6.8, one session renegotiation was observed once. This event:
- could not be reproduced under repeated testing,
- had no architectural defect or protocol violation identified,
- preserved exhibit state throughout,
- recovered cleanly without operator intervention, and
- remains documented as a non-blocking follow-up observation.
This observation is not characterized as fully explained, definitively benign, operator error, or a known race condition, as no definitive root cause was isolated. It does not block Step 6 completion.
5. Architectural Review and Invariants (Step 6.9 Summary)
A comprehensive architectural and protocol conformance review covering 18 functional areas confirmed that the Step 6 implementation conforms to Contract 5.3 and adheres to all architectural constraints.
Core Architectural Conclusions
- Generic NGN Core: The NGN host core (src/**) contains zero exhibit-specific or SciFi-specific code. All controls and surfaces are descriptor-driven.
- Exhibit-Scoped Semantics: All exhibit-specific logic (e.g. Starship visualizer, LCARD interface, Kokoro TTS, WebLLM) resides exclusively within exhibit and fixture code.
- Single-Owner Authority: All mutations flow through a single chokepoint (ExhibitHost.request()). Surfaces cannot establish independent contract sessions or bypass owner authority.
- Non-Authoritative Surfaces: Presentation surfaces are purely observational/presentational; they have no host transport or session authority.
- Monotonic State Convergence: State snapshots and revisions (stateRevision) advance monotonically; late-joining and reconnected surfaces converge immediately to current state.
- Session Identity Protection: Out-of-session and stale messages are rejected by session ID gating.
- Fail-Closed Orphan Handling: Orphaned surfaces (such as an Observation surface loaded without an active owner instance ID) enter an inert waiting state without inventing local authority.
- Presentation and Surface Lifecycle Separation: Opening an Observation surface does not alter the console overlay flag ( iew.observation), maintaining distinct lifecycles.
- Owner-Scoped Generative and Audio Subsystems: Generative AI (WebLLM), neural voice (Kokoro), and Web Audio (AudioContext) run exclusively within the console owner frame; surfaces instantiate none of these heavy resources.
- Contract 5.3 Coherence: Full Contract 5.3 conformance is maintained with verified backward compatibility for Contract 5.2 exhibits.
- Test Verification: All 154 automated tests and all 24 focused SciFi surface tests pass cleanly.
- No Blocking Defects: No blocking architectural defect was found.
Verified Architectural Invariants
| Invariant | Status | Evidence |
|---|---|---|
| 1. Single authority for mutations | VERIFIED | All mutations route through ExhibitHost.request() and exhibit owner |
| 2. State immutability & revision tracking | VERIFIED | Snapshots are immutable; revisions advance monotonically |
| 3. Exhibit-generic NGN core | VERIFIED | Zero exhibit-specific code in src/** |
| 4. Surface presentation-only semantics | VERIFIED | Surfaces have no host transport, session authority, or mutation rights |
| 5. Same-origin security boundary | VERIFIED | Same-origin enforced across frames, URLs, and postMessage transports |
| 6. Contract 5.3 conformance | VERIFIED | All 12 Contract 5.3 conformance requirements satisfied |
| 7. Backward compatibility with 5.2 | VERIFIED | Contract 5.2 exhibits negotiate and function without regression |
| 8. Error isolation and recovery | VERIFIED | Surface-level errors stay within the pane; host session remains healthy |
| 9. Descriptor-driven rendering | VERIFIED | UI dynamically renders targets advertised in describe catalog |
| 10. Graceful degradation | VERIFIED | Invalid descriptors are safely discarded while valid entries are preserved |
| 11. Presentation/surface lifecycle independence | VERIFIED | Surface open/close does not toggle console overlay state |
| 12. Session identity & orphan fail-closed | VERIFIED | Stale traffic is rejected; orphaned surfaces remain inert |
6. Verification Evidence Summary
The technical baseline 163de2 is verified by the following test and live browser evidence:
- Full Automated Test Suite: 154 / 154 tests passing (
pm test /
ode --test).
- Connection and URL validation: 8 tests
- Host negotiation and state management: 32 tests
- Surface discovery and descriptor validation: 44 tests
- Local surface frame lifecycle: 20 tests
- PostMessage transport interop: 7 tests
- Reference exhibit integration: 43 tests
- Focused SciFi Observation Surface Suite: 24 / 24 tests passing ( ode --test tests/scifi-surfaces.test.js).
- Live Museum Gallery Evidence: Multi-surface presentation validated in live browser sessions (Step 6.2 and Step 6.6).
- Live SciFi-XZBT 8-Point Verification: Passed all eight live criteria:
- Connected and synchronized as Contract 5.3 with two-surface descriptor catalog.
- Observation pane opened with correct geometry and visible controls.
- Observation pane showed no return controls, remained inert to background clicks, and did not alter console state.
- Presentation targets converged across console and pane with advancing stateRevision.
- Reload and close/reopen returned pane to current state without participant ratcheting.
- Console WATCH EXPERIENCE affected only console overlay, leaving the Observation pane independent.
- Observation frame instantiated no WebLLM, Kokoro, or AudioContext.
- Transient events appeared simultaneously; disconnect/reconnect gave clean pane release and rediscovery; orphan URL presented inert waiting state without authority.
- Packaging Verification: Regenerated single-file standalone artifact verified for structural inlining (13 assets inlined, zero external references) and valid served-path handshake.
7. Blocking Items
None. There are no unresolved blocking defects, contract violations, or outstanding architectural blockers for Step 6.
8. Documented Non-Blocking Follow-Up Items
The following items are retained as non-blocking follow-up items for future operational observation or testing. None of these items block Step 6 closure:
- Unreproduced Session Renegotiation: The single unreproduced session renegotiation observed during Step 6.8 testing remains tracked for ongoing observation.
- Packaged Offline Direct Interaction: Opening the packaged dist/ artifact directly over ile:// and exercising hotkeys, WATCH EXPERIENCE, and audio playback has not been conclusively operator-verified (structural inlining and boot have been verified).
- Audible Sound Duplication and Quality: Auditory confirmation that audio is not duplicated between console and Observation pane, and that playback quality remains clear during concurrent surface display, requires sustained human listening.
- Generated AI Announcement Timing: Subjective timing quality and cadence of local AI-generated voice announcements appearing across surfaces requires sustained operator listening.
- Long-Running Ambient-Event Coexistence: Observation over an extended multi-hour session to confirm that ambient visual and audio events coexist without drift or missed events.
None of these items are represented as passed; they remain open, documented non-blocking follow-up observations.
9. Final Conclusion
Step 6 has satisfied all requirements of the Contract 5.3 multi-surface milestone. No further implementation work is required for Step 6.
XZBT-NGN Step 6 is formally closed at tag step-6-complete on top of accepted technical baseline 163de264388f1e411cf9e54f26f72a254888afd.