Steps 6.4-6.7B — Local surfaces, reference-exhibit validation, SciFi Observation surface

One commit for the work accumulated in the working tree since Step 6.3,
which had never been split into per-step commits:

- src/local-surfaces.js + src/surface-url.js (new); src/ui.js,
  src/validation.js, src/connection.js and public/index.html updated for
  local-surface hosting and generic surface rendering
- tests: local-surfaces (20), scifi-surfaces (24) and postmessage-interop (7)
  new; connection/museum-gallery/surface-validation suites updated
- reference exhibits: shared/contract-core.js defaults to Contract 5.3
  (major 5, minor 3, xzbt 5.3); museum-gallery advertises its surface
  catalog; aquarium/haunted-house/planetarium adapters updated
- SciFi-XZBT (Step 6.7A/6.7B): surface-mode.js + surface-bus.js,
  Observation-surface boot branch, local-change hooks, view.pillars /
  view.warp-flight targets; fixture byte-identical to G:/.vibe/SciFi-XZBT
- SciFi-XZBT contract adapter handshake fix: the inbound bridge filter no
  longer gates on an exact advisory xzbt value (Contract 5.3 §6.5), only on
  its presence/type, matching the host's own envelope validation; the
  adapter now advertises contract minor 3 / version 5.3.0, which it already
  implemented via the 5.3 surfaces field. Root cause of the five failing
  postmessage-interop tests (host hello was silently dropped).
- docs: architecture 6.4 and 6.7A, reference 6.6 and 6.7; evidence logs;
  test-fixtures/PROVENANCE.md resync record

Test results: NGN 154/154 (was 149/154); postmessage-interop 7/7 (was 2/7);
SciFi contract harness 21/21, real-adapter suite 32/32. git diff --check
clean for changed files; two pre-existing trailing-whitespace lines remain
in test-fixtures/reference-exhibits/scifi/index.html, copied verbatim from
the authoritative SciFi source.

Step 6.7 live verification (browser Observation, packaged standalone) is
still pending and is not claimed here.

test-fixtures/evidence/step6.4-museum-local.txt

@@ -0,0 +1,172 @@
+- banner:
+  - heading "XZBT-NGN Exhibit Engine" [level=1]
+  - paragraph: Contract 5.2/5.3 · One exhibit at a time
+- main:
+  - heading "Connection" [level=2]
+  - generic: Exhibit URL (same origin)
+  - textbox "Exhibit URL (same origin)":
+    - /placeholder: /public/exhibits/example/index.html
+    - text: http://127.0.0.1:4173/test-fixtures/reference-exhibits/museum-gallery/control.html
+  - button "Load exhibit"
+  - button "Reconnect"
+  - button "Disconnect"
+  - paragraph: Enter a trusted exhibit's local served path or a URL on this origin. Load exhibit also switches exhibits. Reconnect starts a new session, or reloads the last exhibit after disconnect.
+  - status: connected · synchronized
+  - paragraph: Museum Gallery · 0.1.0 · Contract 5.3
+  - paragraph: "Exhibit location: http://127.0.0.1:4173/test-fixtures/reference-exhibits/museum-gallery/control.html"
+  - iframe:
+    - banner:
+      - heading "Museum Gallery — Control Room" [level=1]
+      - generic: Primary surface · Contract 5.3 · standalone-capable
+      - generic: host attached
+    - main:
+      - paragraph: The Orrery
+      - paragraph: "Lighting: 60%"
+      - paragraph: "Rotation: 0.4x"
+      - paragraph: "Labels: ON"
+      - paragraph: "Attached non-primary surfaces: 0"
+    - complementary:
+      - heading "Artifact" [level=2]
+      - generic: Selected artifact
+      - combobox "Selected artifact":
+        - option "The Orrery" [selected]
+        - option "Star Map"
+        - option "Meteorite Fragment"
+      - heading "Environment" [level=2]
+      - generic: Lighting level
+      - generic: 60%
+      - slider "Lighting level 60%"
+      - generic: Rotation speed
+      - generic: 0.4x
+      - slider "Rotation speed 0.4x"
+      - generic: Labels enabled
+      - button "Toggle" [pressed]
+      - heading "Actions" [level=2]
+      - button "Flash spotlight"
+    - contentinfo:
+      - generic: Control Room
+      - generic: Control Room standing by.
+  - heading "Exhibit controls (5)" [level=2]
+  - generic "Capabilities"
+  - paragraph: Reported values are authoritative. New values are drafts; select Set or Invoke to submit. Rediscovery resets drafts.
+  - heading "gallery" [level=3]
+  - article:
+    - heading "Selected Artifact" [level=3]
+    - code: artifact.selected
+    - paragraph: selection · readable · writable
+    - status: "Reported value: \"the-orrery\""
+    - generic "Target descriptor"
+    - paragraph
+    - text: New value
+    - combobox "New value":
+      - option "The Orrery" [selected]
+      - option "Star Map"
+      - option "Meteorite Fragment"
+    - button "Set"
+  - article:
+    - heading "Lighting Level" [level=3]
+    - code: lighting.level
+    - paragraph: range · readable · writable
+    - status: "Reported value: 0.6"
+    - generic "Target descriptor"
+    - paragraph
+    - text: New value
+    - spinbutton "New value": "0.6"
+    - button "Set"
+  - article:
+    - heading "Rotation Speed" [level=3]
+    - code: rotation.speed
+    - paragraph: range · readable · writable
+    - status: "Reported value: 0.4"
+    - generic "Target descriptor"
+    - paragraph
+    - text: New value
+    - spinbutton "New value": "0.4"
+    - button "Set"
+  - article:
+    - heading "Labels Enabled" [level=3]
+    - code: labels.enabled
+    - paragraph: state · readable · writable
+    - status: "Reported value: true"
+    - generic "Target descriptor"
+    - paragraph
+    - text: New value
+    - checkbox "New value" [checked]
+    - button "Set"
+  - heading "action" [level=3]
+  - article:
+    - heading "Spotlight Flash" [level=3]
+    - code: action.spotlight-flash
+    - paragraph: impulse · not readable · not writable
+    - status: No persistent value reported.
+    - generic "Target descriptor"
+    - paragraph
+    - button "Invoke"
+  - heading "Presentation surfaces (3)" [level=2]
+  - paragraph: Open Contract 5.3 presentation surfaces locally below. URLs resolve against the supplying exhibit. Disconnecting or switching exhibits closes these views. Remote/cast displays remain deferred.
+  - article:
+    - heading "Control Room" [level=3]
+    - code: surface.control
+    - generic: Primary
+    - generic: "Role: control"
+    - paragraph: "URL: control.html"
+    - status: Open in the authoritative control frame. Use Connection controls to reload or disconnect.
+    - button "Open" [disabled]
+    - button "Reload" [disabled]
+    - button "Close" [disabled]
+  - article:
+    - heading "Artifact Display" [level=3]
+    - code: surface.artifact
+    - generic: Non-primary
+    - generic: "Role: ambient"
+    - paragraph: "URL: artifact.html"
+    - status: open
+    - button "Open" [disabled]
+    - button "Reload"
+    - button "Close"
+    - iframe:
+      - banner:
+        - heading "Museum Gallery — Artifact Display" [level=1]
+        - generic: Non-primary surface · attaches to the Control Room
+        - generic: surface
+      - main:
+        - paragraph: The Orrery
+        - paragraph: "Lighting: 60%"
+        - paragraph: "Rotation: 0.4x"
+        - paragraph:
+          - button "Cycle artifact"
+        - paragraph: Attached to Control Room.
+      - contentinfo:
+        - generic: Artifact Display
+        - generic: Waiting for shared state.
+  - article:
+    - heading "Information Wall" [level=3]
+    - code: surface.info-wall
+    - generic: Non-primary
+    - generic: "Role: information"
+    - paragraph: "URL: info-wall.html"
+    - status: open
+    - button "Open" [disabled]
+    - button "Reload"
+    - button "Close"
+    - iframe:
+      - banner:
+        - heading "Museum Gallery — Information Wall" [level=1]
+        - generic: Non-primary surface · attaches to the Control Room
+        - generic: surface
+      - main:
+        - paragraph: The Orrery
+        - paragraph: "Labels: ON"
+        - paragraph:
+          - button "Toggle labels"
+        - paragraph: Attached to Control Room.
+      - contentinfo:
+        - generic: Information Wall
+        - generic: Waiting for shared state.
+  - heading "State and metadata" [level=2]
+  - button "Refresh state"
+  - generic "Session and exhibit metadata"
+  - generic "Current persistent state"
+  - heading "Protocol diagnostics" [level=2]
+  - generic "Incoming events"
+  - generic "Protocol and errors"