revert(cockpit): no water read timeout, and loaded reads not raise-only

Both reviews of the timeout found that Cesium cannot cancel a full-detail
read: each one given up kept its nine picks traversing every frame, so
stalled tiles piled up a new set every 30 s, while slow but valid answers
were dropped. Raise-only loaded reads then locked in a wrong-high height.
Back to one full-detail read at a time whose answer always applies, and
loaded reads that may adjust a river height but never take it to the sea;
a coarse probe can again lower it partway until the full read lands.

Keeps the test for another ship selected inside the double-click memory,
and corrects CURRENT-STATE: a failed read keeps the height it had.

docs/CURRENT-STATE.md

@@ -1574,10 +1574,9 @@ the full-detail read replaces it; it repeats every 5 s. Only one full-detail
 read runs at a time: while one is still running, a refresh reads the loaded
 tiles instead, and the slow read applies whenever it lands. Once a
 full-detail read has answered, loaded-tile reads no longer change the height;
-before then they may only raise it. A read that sampled nothing keeps the
-height it had, and a full-detail read still running after 30 s
-(`VESSEL_WATERLINE_READ_TIMEOUT_MS`) is given up for a fresh one. A failed read keeps
-the sea surface.
+before then they may find raised water but never take it back to the sea.
+A read that sampled nothing, or failed, keeps the height it had and is
+tried again on the next refresh.
 
 The HUD keeps its frame, vision styles, briefing, weather and Display/Radio
 utilities. It names the ship, reads `{type} · LIVE AIS · EYE {height}`, shows

src/cockpitSubjects.js

@@ -38,13 +38,6 @@ export const VESSEL_WATERLINE_PROBE_COUNT = 8;
 /** How often the bridge reads the water under its ship again, ms. */
 export const VESSEL_WATERLINE_REFRESH_MS = 5000;
 
-/**
- * A full-detail water read still running after this long is given up and
- * a fresh one started, ms: tile requests can stall, and one read that never
- * lands would otherwise hold the height for the rest of the bridge.
- */
-export const VESSEL_WATERLINE_READ_TIMEOUT_MS = 30000;
-
 /** A surface less than this above sea level is the sea itself, metres. */
 export const VESSEL_WATERLINE_MIN_RISE_M = 2;
 

src/ui/cockpitBridge.test.mjs

@@ -1376,59 +1376,6 @@ test('before any full read lands, a coarse loaded read keeps the river it found'
   ship.viewer.scene.sampleHeight = () => 0.5;
   frames(ship.cockpit, clock, ship.shots, 240);
   near(eyeHeightM(ship.shots.at(-1)) - seaEyeM, 27, 'still on the river', 0.5);
-  // Nor partway down: a probe on a 15 m bank is not the river either.
-  ship.viewer.scene.sampleHeight = () => 15;
-  frames(ship.cockpit, clock, ship.shots, 240);
-  near(eyeHeightM(ship.shots.at(-1)) - seaEyeM, 27, 'not lowered partway', 0.5);
-});
-
-test('a full water read that never lands is given up for a fresh one', async (t) => {
-  const clock = manualClock(t, START_MS);
-  const sea = await bridgeAt(t, clock);
-  frames(sea.cockpit, clock, sea.shots, 60);
-  const seaEyeM = eyeHeightM(sea.shots.at(-1));
-  sea.cockpit.exit();
-
-  clock.set(START_MS);
-  const record = { ...RECORD, lastPositionEpoch: START_MS / 1000 };
-  const ship = fixture(t, { record });
-  const reads = [];
-  ship.viewer.scene.sampleHeightMostDetailed = (positions) =>
-    new Promise((resolve) => reads.push({ positions, resolve }));
-  // Coarse tiles first put the ship 27 m up; it is really at sea.
-  ship.viewer.scene.sampleHeight = () => 27;
-  ship.cockpit.enter();
-  await settle();
-  ship.cockpit.update();
-  await settle();
-  assert.equal(reads.length, 1);
-  // The first read stalls. Twenty seconds on, still no second read.
-  frames(ship.cockpit, clock, ship.shots, 400);
-  await settle();
-  assert.equal(reads.length, 1, 'not stacked while it may still land');
-  // Past the timeout, a fresh read starts, and its answer applies.
-  frames(ship.cockpit, clock, ship.shots, 300);
-  await settle();
-  assert.equal(reads.length, 2, 'a fresh read after the stalled one');
-  const answer = (read, height) =>
-    read.resolve(
-      read.positions.map((position) => Object.assign(position, { height })),
-    );
-  answer(reads[1], 0.5);
-  await settle();
-  // The eye eases down; give it time to settle.
-  frames(ship.cockpit, clock, ship.shots, 400);
-  near(eyeHeightM(ship.shots.at(-1)), seaEyeM, 'back on the sea', 0.5);
-  // The stalled read landing now changes nothing.
-  answer(reads[0], 27);
-  await settle();
-  frames(ship.cockpit, clock, ship.shots, 60);
-  near(
-    eyeHeightM(ship.shots.at(-1)),
-    seaEyeM,
-    'the given-up read is dropped',
-    0.5,
-  );
 });
 
 test('a client clock minutes fast does not age the bridge into a stale feed', async (t) => {

src/ui/cockpitCamera.js

@@ -9,7 +9,6 @@ import {
 } from '../cockpitMath.js';
 import {
   VESSEL_DEAD_RECKON_MAX_S,
-  VESSEL_WATERLINE_READ_TIMEOUT_MS,
   VESSEL_WATERLINE_REFRESH_MS,
   deadReckonVesselFix,
   vesselCameraProfile,
@@ -111,11 +110,10 @@ export function update() {
  * every frame until it settles): while one is still running, a refresh
  * reads the loaded tiles instead, and the slow read applies whenever it
  * lands. Once a full-detail read has answered, only full-detail reads
- * change the height; before then a loaded-tile read may only raise it, so
- * one coarse probe cannot drop a river bridge, and a read that sampled
- * nothing keeps the height it had. A full-detail read still running after
- * VESSEL_WATERLINE_READ_TIMEOUT_MS is given up for a fresh one, so a
- * stalled read cannot hold a wrong height for the whole bridge.
+ * change the height; before then a loaded-tile read may find raised water
+ * but never takes a raised height back to the sea. One coarse probe cannot
+ * drop a river bridge to the sea, and a read that sampled nothing keeps
+ * the height it had.
  * @param {{latitude: number, longitude: number}} [at] Where to read the
  *   water: the dead-reckoned position the camera rides.
  * @returns {number} Ellipsoidal metres.
@@ -142,49 +140,35 @@ function vesselSurfaceM(info, nowMs, at = info) {
         // Whether a full-detail read has answered for this ship.
         landed: false,
         inFlight: false,
-        // The running full-detail read: its number and start time.
-        attempt: 0,
-        startedMs: 0,
       };
       this.vesselWaterline = read;
     } else {
       read.sampledMs = nowMs;
       if (read.inFlight && !read.landed) {
         const loadedM = loadedWaterlineM(scene, probes, seaM);
-        // Lowering the water is the full-detail read's to say.
-        if (
-          Number.isFinite(loadedM) &&
-          !(Number.isFinite(read.heightM) && loadedM < read.heightM)
-        )
-          read.heightM = loadedM;
+        // Taking a river back to the sea is the full-detail read's to say.
+        const lowers =
+          Number.isFinite(read.heightM) &&
+          read.heightM > seaM &&
+          !(loadedM > seaM);
+        if (Number.isFinite(loadedM) && !lowers) read.heightM = loadedM;
       }
-      if (
-        read.inFlight &&
-        nowMs - read.startedMs >= VESSEL_WATERLINE_READ_TIMEOUT_MS
-      )
-        read.inFlight = false;
     }
-    if (!read.inFlight)
-      readWaterline.call(this, read, scene, probes, seaM, nowMs);
+    if (!read.inFlight) readWaterline.call(this, read, scene, probes, seaM);
   }
   return read && Number.isFinite(read.heightM)
     ? Math.max(seaM, read.heightM)
     : seaM;
 }
 
-/**
- * Start one full-detail water read for `read`; its answer lands on it
- * unless it was given up for a newer read.
- */
-function readWaterline(read, scene, probes, seaM, nowMs) {
-  const attempt = ++read.attempt;
+/** Start one full-detail water read for `read`; its answer lands on it. */
+function readWaterline(read, scene, probes, seaM) {
   read.inFlight = true;
-  read.startedMs = nowMs;
   Promise.resolve()
     .then(() => scene.sampleHeightMostDetailed(probes))
     .then(
       (samples) => {
-        if (this.vesselWaterline !== read || attempt !== read.attempt) return;
+        if (this.vesselWaterline !== read) return;
         read.inFlight = false;
         // However late it lands, it applies; one that sampled nothing (tiles
         // not loaded yet) is no answer and keeps the height already read.
@@ -194,8 +178,7 @@ function readWaterline(read, scene, probes, seaM, nowMs) {
         read.heightM = vesselWaterlineM(seaM, heights);
       },
       () => {
-        if (this.vesselWaterline === read && attempt === read.attempt)
-          read.inFlight = false;
+        if (this.vesselWaterline === read) read.inFlight = false;
       },
     );
 }