fix(vessels): pin the idle-render contract and move the entry to a fragment

- The trailing visibility frame uses the layer's injectable runtime timer and
  is cancelled by resetState as well as disable and destroy.
- An empty-feed regular pass records the camera pose, so later in-cadence
  frames do not keep scheduling trailing frames.
- New renderGovernor.test.mjs: a parked camera schedules nothing, a stopped
  camera gets exactly one trailing frame and no self-wake, a forced pass
  requests its frame, destroy cancels the timer.
- The CHANGELOG entry moves to changelog.d/871-vessels-idle-render.md; docs
  say the hold also covers vessels dimmed under a live target.

src/layers/vessels/lifecycle.js

@@ -125,7 +125,7 @@ export function createLifecycle({
     state.interactionHandlerFactory = null;
     state.interactionKeyTarget = null;
     state.preRenderRemover = null;
-    state.trailingVisibilityTimer = null;
+    components.rendering.cancelTrailingVisibilityPass();
     state.lastVisibilityUpdate = 0;
     state.lastFocusUpdate = 0;
     state.activeFocusCount = 0;

src/layers/vessels/renderGovernor.test.mjs

@@ -0,0 +1,138 @@
+import test from 'node:test';
+import assert from 'node:assert/strict';
+import { createVesselLayer } from './index.js';
+import { VISIBILITY_UPDATE_MS } from './policy.js';
+
+// Vessels move only when a poll lands, so the layer must let the scene idle:
+// it asks for frames for forced passes and one trailing frame after the camera
+// stops, and never schedules a frame from a pass the camera did not cause.
+
+const noop = () => {};
+
+function setup() {
+  let clock = 10_000;
+  const requests = [];
+  const holds = new Set();
+  const timers = new Map();
+  let nextTimer = 1;
+  const layer = createVesselLayer({
+    source: { getSnapshot: async () => ({ records: [] }) },
+    services: {
+      context: {
+        clearSelectedEntityContextForLayer: noop,
+        registerEntityContext: () => null,
+      },
+      trails: {
+        createTrail: () => ({ setPositions: noop, clear: noop, destroy: noop }),
+      },
+      labels: {},
+      picking: { unregisterPickOwner: noop },
+      overlay: {
+        setOverlayEntries: noop,
+        setOverlaySourceVisible: noop,
+        clearOverlaySource: noop,
+      },
+      geoid: {},
+      sprites: {},
+      focus: {
+        focusNowMs: () => clock,
+        getFocusTarget: () => null,
+        focusPassIsNeeded: () => false,
+        forgetSpriteFocus: noop,
+      },
+      worldFocus: {},
+      render: {
+        holdContinuousRender: (id) => holds.add(id),
+        releaseContinuousRender: (id) => holds.delete(id),
+        governorRequestRender: (reason) => requests.push(reason),
+      },
+    },
+  });
+  const camera = {
+    positionWC: { x: 0, y: 0, z: 7_000_000 },
+    heading: 0,
+    pitch: -1.2,
+    roll: 0,
+  };
+  layer.testing._setVesselStateForTest({ viewer: { camera, scene: {} } });
+  layer.testing._setAisRuntimeForTest({
+    now: () => clock,
+    setTimeout(fn, ms) {
+      const id = nextTimer++;
+      timers.set(id, { fn, at: clock + ms });
+      return id;
+    },
+    clearTimeout: (id) => timers.delete(id),
+  });
+  const advance = (ms) => {
+    clock += ms;
+    for (const [id, timer] of [...timers]) {
+      if (timer.at > clock) continue;
+      timers.delete(id);
+      timer.fn();
+    }
+  };
+  const frame = () => layer.testing._runVisibilityPassForTest();
+  return { layer, camera, requests, holds, timers, advance, frame };
+}
+
+test('a parked camera schedules no frames after the cadence pass', () => {
+  const { requests, holds, timers, advance, frame } = setup();
+  frame();
+  for (let i = 0; i < 20; i += 1) {
+    advance(100);
+    frame();
+  }
+  assert.deepEqual(requests, []);
+  assert.equal(timers.size, 0);
+  assert.equal(holds.has('ais-vessels'), false);
+});
+
+test('a camera that stops inside the cadence gets exactly one trailing frame', () => {
+  const { layer, camera, requests, timers, advance, frame } = setup();
+  frame();
+  advance(100);
+  camera.heading = 0.5;
+  frame();
+  advance(100);
+  frame();
+  assert.equal(timers.size, 1, 'one trailing frame, not one per skipped pass');
+  assert.equal(layer.testing._hasTrailingVisibilityPassForTest(), true);
+
+  advance(VISIBILITY_UPDATE_MS);
+  assert.deepEqual(requests, ['ais-vessels-visibility']);
+  // The trailing frame runs the regular pass on the pose the camera stopped
+  // on. Its own frames must not schedule another one.
+  frame();
+  for (let i = 0; i < 20; i += 1) {
+    advance(100);
+    frame();
+  }
+  assert.deepEqual(requests, ['ais-vessels-visibility']);
+  assert.equal(timers.size, 0);
+});
+
+test('a forced pass requests its own frame', () => {
+  const { layer, requests } = setup();
+  layer.testing._runVisibilityPassForTest(true);
+  assert.deepEqual(requests, ['ais-vessels-update']);
+});
+
+test('destroy cancels a pending trailing frame', (t) => {
+  const originalDocument = globalThis.document;
+  globalThis.document = { getElementById: () => null };
+  t.after(() => {
+    if (originalDocument === undefined) delete globalThis.document;
+    else globalThis.document = originalDocument;
+  });
+  const { layer, camera, requests, timers, advance, frame } = setup();
+  frame();
+  advance(100);
+  camera.heading = 0.5;
+  frame();
+  assert.equal(timers.size, 1);
+  layer.destroy();
+  assert.equal(timers.size, 0);
+  advance(VISIBILITY_UPDATE_MS);
+  assert.deepEqual(requests, []);
+});

src/layers/vessels/rendering.js

@@ -223,7 +223,7 @@ export function createRendering({
       0,
       VISIBILITY_UPDATE_MS - (now - state.lastVisibilityUpdate),
     );
-    state.trailingVisibilityTimer = setTimeout(() => {
+    state.trailingVisibilityTimer = vesselState._aisRuntime.setTimeout(() => {
       state.trailingVisibilityTimer = null;
       if (state.feed.enabled) governorRequestRender('ais-vessels-visibility');
     }, waitMs);
@@ -231,7 +231,7 @@ export function createRendering({
 
   function cancelTrailingVisibilityPass() {
     if (!state.trailingVisibilityTimer) return;
-    clearTimeout(state.trailingVisibilityTimer);
+    vesselState._aisRuntime.clearTimeout(state.trailingVisibilityTimer);
     state.trailingVisibilityTimer = null;
   }
 
@@ -256,7 +256,15 @@ export function createRendering({
     if (focusPass) state.lastFocusUpdate = now;
     if (!state.records.all.length) {
       // No records — flush any lingering card entries (vanished-feed case).
-      if (regularPass) updateClusteredLabels([]);
+      // Still record the pose this pass evaluated, or every later frame that
+      // falls inside the cadence would schedule another trailing frame.
+      if (regularPass) {
+        if (state.viewer?.camera)
+          vesselState._lastCamPoseSig = cameraPoseSignature(
+            state.viewer.camera,
+          );
+        updateClusteredLabels([]);
+      }
       if (focusPass) {
         state.activeFocusCount = 0;
         releaseContinuousRender('ais-vessels');

src/layers/vessels/testing.js

@@ -151,6 +151,18 @@ export function createTesting({
     };
   }
 
+  /** Run one preRender visibility/focus pass. Test-only seam. */
+
+  function _runVisibilityPassForTest(force = false) {
+    components.rendering.updateVisibility(force);
+  }
+
+  /** True while a trailing visibility frame is scheduled. Test-only seam. */
+
+  function _hasTrailingVisibilityPassForTest() {
+    return state.trailingVisibilityTimer !== null;
+  }
+
   /**
    * Read lifecycle ownership state without exposing the mutable state object.
    * Test-only seam.
@@ -176,5 +188,7 @@ export function createTesting({
     _setAisRuntimeForTest,
     _getVesselFeedStateForTest,
     _getVesselStateForTest,
+    _runVisibilityPassForTest,
+    _hasTrailingVisibilityPassForTest,
   };
 }