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/reference-exhibits/scifi/js/surface-mode.js

@@ -0,0 +1,108 @@
+/**
+ * XZBT Surface Mode — SciFi-XZBT (Step 6.7B)
+ *
+ * Pure, testable seam for resolving which boot mode this document load is in
+ * (Contract 5.3 §31.4 query-string surface form) and for describing the
+ * exhibit's two-entry surface catalog. No DOM access, no imports, no
+ * side effects — safe to load and exercise under Node's `vm` module.
+ *
+ * Two surfaces only:
+ *   - surface.console      the full operator console (index.html, primary)
+ *   - surface.observation  the same document, rendering only the
+ *                          Observation viewscreen, addressed by
+ *                          ?surface=observation&xi=<instanceId>
+ */
+(function (root) {
+  'use strict';
+
+  var CHANNEL_PREFIX = 'xzbt-scifi-surface-v1:';
+
+  /**
+   * Resolve the boot mode + instance id for a location-like object.
+   * @param {object} locationLike anything with a `.search` (or `.href`)
+   *   string, e.g. `window.location`.
+   * @returns {{mode: 'console'|'observation', instanceId: string|null}}
+   */
+  function resolve(locationLike) {
+    var search = '';
+    if (locationLike && typeof locationLike.search === 'string') {
+      search = locationLike.search;
+    } else if (locationLike && typeof locationLike.href === 'string') {
+      var qIdx = locationLike.href.indexOf('?');
+      search = qIdx >= 0 ? locationLike.href.slice(qIdx) : '';
+    }
+
+    var params;
+    try {
+      params = new URLSearchParams(search);
+    } catch (err) {
+      params = null;
+    }
+
+    var surfaceParam = params ? params.get('surface') : null;
+    var instanceId = params ? params.get('xi') : null;
+
+    if (surfaceParam === 'observation') {
+      return { mode: 'observation', instanceId: instanceId || null };
+    }
+
+    // Unknown/absent `?surface=` values resolve to console. `xi` is
+    // meaningless in console mode.
+    return { mode: 'console', instanceId: null };
+  }
+
+  /** Mint a fresh per-document-load instance id. */
+  function newInstanceId() {
+    return 'xi-' + Math.random().toString(16).slice(2) + Date.now().toString(16);
+  }
+
+  /**
+   * The exhibit's two-entry surface catalog (Contract 5.3 §31.2/§31.3).
+   * @param {string} instanceId the live console instance id.
+   */
+  function SURFACES(instanceId) {
+    return [
+      {
+        id: 'surface.console',
+        label: 'Main Console',
+        kind: 'surface',
+        primary: true,
+        url: 'index.html',
+        role: 'control',
+        category: 'console',
+        description: 'The full SciFi-XZBT operator console.'
+      },
+      {
+        id: 'surface.observation',
+        label: 'Observation',
+        kind: 'surface',
+        primary: false,
+        url: '?surface=observation&xi=' + encodeURIComponent(instanceId),
+        role: 'ambient',
+        category: 'observation',
+        aspectRatio: '16:9',
+        requires: ['observation'],
+        description: 'Full-screen procedural viewscreen mirroring the console.'
+      }
+    ];
+  }
+
+  /** The instance-scoped BroadcastChannel name for a console instance id. */
+  function channelName(instanceId) {
+    return CHANNEL_PREFIX + instanceId;
+  }
+
+  var XZBTSurfaceMode = {
+    resolve: resolve,
+    newInstanceId: newInstanceId,
+    SURFACES: SURFACES,
+    channelName: channelName
+  };
+
+  if (typeof module !== 'undefined' && module.exports) {
+    module.exports = XZBTSurfaceMode;
+  }
+  if (root) {
+    root.XZBTSurfaceMode = XZBTSurfaceMode;
+  }
+})(typeof window !== 'undefined' ? window : (typeof globalThis !== 'undefined' ? globalThis : this));