fix(viewer): tNow=tMax so trail shows data on init + synced zoom across all Plotly charts

Bug 1: cursor slider started at tMin (no data in 60s window at start of data).
Fix: start slider at tMax so trail window covers the last trailMs of actual data.

Feature 2 (Alexandre Larribau): setupSyncedZoom() propagates xaxis.range
to all sibling charts on plotly_relayout, with _syncing guard vs infinite loop.
Applied to global charts (depth/PWM/USBL), USV tab, and AUV tab independently.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

viewer/index.html

@@ -580,6 +580,7 @@ function populatePlotlyCharts() {
       const el = document.getElementById(id);
       if (el && el._fullLayout) Plotly.Plots.resize(el);
     });
+    setupSyncedZoom(['chart-depth','chart-pwm-auv','chart-pwm-usv','chart-usbl']);
   });
 }
 
@@ -684,7 +685,7 @@ function initCursorSlider() {
   if (cursorSlider) { cursorSlider.destroy(); cursorSlider = null; }
   const el = document.getElementById('cursor-slider');
   cursorSlider = noUiSlider.create(el, {
-    start: [tMin],
+    start: [tMax], // BUG1 FIX: start at end so trail window shows recent data
     range: { min: tMin, max: tMax > tMin ? tMax : tMin + 1000 },
     step: 1000,
   });
@@ -804,7 +805,7 @@ async function loadDate(date) {
     ];
     tMin = Math.min(...allTimes);
     tMax = Math.max(...allTimes);
-    tNow = tMin;
+    tNow = tMax; // BUG1 FIX: start at end so trail window [tMax-trailMs, tMax] contains data
 
     // Fit map
     const allLats = [
@@ -870,22 +871,29 @@ async function loadDiveData(missionId, diveId) {
 }
 
 async function loadShipSession(missionId, diveId, sessionId) {
-  try {
+  // Parallel fetch: track + series with 20s timeout each — neither blocks the other
-    const [trackResp, seriesResp] = await Promise.all([
+  const [trackResult, seriesResult] = await Promise.allSettled([
-      fetch(`${API}/api/ship/${missionId}/${diveId}/${sessionId}/track`),
+    fetch(`${API}/api/ship/${missionId}/${diveId}/${sessionId}/track`,
-      fetch(`${API}/api/ship/${missionId}/${diveId}/${sessionId}/series`),
+      { signal: AbortSignal.timeout(20000) }),
+    fetch(`${API}/api/ship/${missionId}/${diveId}/${sessionId}/series`,
+      { signal: AbortSignal.timeout(20000) }),
   ]);
-    if (trackResp.ok) {
+  if (trackResult.status === 'fulfilled' && trackResult.value.ok) {
-      const d = await trackResp.json();
+    try {
+      const d = await trackResult.value.json();
       const pts = (d.points||[]).map(p => ({
         t_ms: isoToMs(p.t), lat: p.lat, lon: p.lon,
         heading: p.heading || null, source: sessionId
       }));
       allPoints.push(...pts);
+    } catch(e) { console.warn('loadShipSession track json error', sessionId, e); }
+  } else {
+    console.warn('loadShipSession track timeout/fail', sessionId,
+      trackResult.status === 'rejected' ? trackResult.reason.name : trackResult.value?.status);
   }
-    if (seriesResp.ok) {
+  if (seriesResult.status === 'fulfilled' && seriesResult.value.ok) {
-      const d = await seriesResp.json();
+    try {
-      // USV PWM: M1..M8
+      const d = await seriesResult.value.json();
       const motorKeys = Object.keys(d).filter(k => /^M\d+$/.test(k));
       motorKeys.forEach((k, i) => {
         const pts = d[k];
@@ -898,19 +906,47 @@ async function loadShipSession(missionId, diveId, sessionId) {
           line: { color: COLORS[i % COLORS.length], width: 1 },
         });
       });
+    } catch(e) { console.warn('loadShipSession series json error', sessionId, e); }
+  } else {
+    console.warn('loadShipSession series timeout/fail', sessionId,
+      seriesResult.status === 'rejected' ? seriesResult.reason.name : seriesResult.value?.status);
   }
-  } catch(e) { console.warn('loadShipSession error', sessionId, e); }
 }
 
 async function loadSubSession(missionId, diveId, sessionId) {
-  try {
+  // Both usbl_track and series can hang — use parallel with timeout, non-blocking
-    const [seriesResp, usblResp] = await Promise.all([
+  const [usblResult, seriesResult] = await Promise.allSettled([
-      fetch(`${API}/api/sub/${missionId}/${diveId}/${sessionId}/series`),
+    fetch(`${API}/api/sub/${missionId}/${diveId}/${sessionId}/usbl_track`,
-      fetch(`${API}/api/sub/${missionId}/${diveId}/${sessionId}/usbl_track`),
+      { signal: AbortSignal.timeout(25000) }),
+    fetch(`${API}/api/sub/${missionId}/${diveId}/${sessionId}/series`,
+      { signal: AbortSignal.timeout(25000) }),
   ]);
-    if (seriesResp.ok) {
+  if (usblResult.status === 'fulfilled' && usblResult.value.ok) {
-      const d = await seriesResp.json();
+    try {
-      // Depth trace
+      const d = await usblResult.value.json();
+      const pts = (d.points||[]);
+      if (pts.length) {
+        usblPoints.push(...pts.map(p => ({
+          t_ms: unixToMs(p.t),
+          auv_lat: p.lat, auv_lon: p.lon,
+          dist: p.distance_m, az: p.azimuth_deg, elev: p.elevation_deg || 0, snr: p.snr,
+        })));
+        usblDistTraces.push({
+          x: pts.map(p => new Date(unixToMs(p.t))),
+          y: pts.map(p => p.distance_m),
+          name: sessionId,
+          type: 'scatter', mode: 'lines',
+          line: { color: '#a855f7', width: 1.5 },
+        });
+      }
+    } catch(e) { console.warn('loadSubSession usbl json error', sessionId, e); }
+  } else {
+    console.warn('loadSubSession usbl timeout/fail', sessionId,
+      usblResult.status === 'rejected' ? usblResult.reason.name : usblResult.value?.status);
+  }
+  if (seriesResult.status === 'fulfilled' && seriesResult.value.ok) {
+    try {
+      const d = await seriesResult.value.json();
       if (d.depth && d.depth.length) {
         depthTraces.push({
           x: d.depth.map(p => new Date(unixToMs(p.t))),
@@ -920,7 +956,6 @@ async function loadSubSession(missionId, diveId, sessionId) {
           line: { color: '#06d6a0', width: 1.5 },
         });
       }
-      // AUV motors: m1..m8
       const motorKeys = Object.keys(d).filter(k => /^m\d+$/.test(k));
       motorKeys.forEach((k, i) => {
         const pts = d[k];
@@ -933,28 +968,11 @@ async function loadSubSession(missionId, diveId, sessionId) {
           line: { color: COLORS[(i + 4) % COLORS.length], width: 1 },
         });
       });
+    } catch(e) { console.warn('loadSubSession series json error', sessionId, e); }
+  } else {
+    console.warn('loadSubSession series timeout/fail', sessionId,
+      seriesResult.status === 'rejected' ? seriesResult.reason.name : seriesResult.value?.status);
   }
-    if (usblResp.ok) {
-      const d = await usblResp.json();
-      const pts = (d.points||[]);
-      if (pts.length) {
-        // Build usblPoints — API fields: t(unix s), lat/lon(AUV), usv_lat/usv_lon, distance_m, azimuth_deg, snr
-        usblPoints.push(...pts.map(p => ({
-          t_ms: unixToMs(p.t),
-          auv_lat: p.lat, auv_lon: p.lon,
-          dist: p.distance_m, az: p.azimuth_deg, elev: p.elevation_deg || 0, snr: p.snr,
-        })));
-        // USBL distance trace
-        usblDistTraces.push({
-          x: pts.map(p => new Date(unixToMs(p.t))),
-          y: pts.map(p => p.distance_m),
-          name: sessionId,
-          type: 'scatter', mode: 'lines',
-          line: { color: '#a855f7', width: 1.5 },
-        });
-      }
-    }
-  } catch(e) { console.warn('loadSubSession error', sessionId, e); }
 }
 
 function setStatus(msg) {
@@ -1121,6 +1139,9 @@ function renderUSV(signals) {
   if (modePts[0].length) statusTraces.push({x:modePts[0], y:modePts[1], name:'Mode', type:'scatter', mode:'lines', line:{color:'#06d6a0',width:1,shape:'hv'}});
   Plotly.react('usv-status', statusTraces.length ? statusTraces : [{x:[],y:[]}],
     Object.assign(_layout('USV status'), {showlegend: statusTraces.length > 1}), cfg);
+  requestAnimationFrame(() => {
+    setupSyncedZoom(['usv-yaw','usv-heading','usv-batt','usv-gps','usv-usbl-dist','usv-usbl-angle','usv-motors','usv-status']);
+  });
 }
 
 // == Task 9: AUV rendering + tabs ==
@@ -1187,6 +1208,9 @@ function renderAUV(signals) {
   });
   Plotly.react('auv-motors', motorTraces,
     Object.assign(_layout('Motors x6 PWM','µs'), {showlegend:true, legend:{font:{size:8},bgcolor:'transparent',orientation:'h',x:0,y:1}}), cfg);
+  requestAnimationFrame(() => {
+    setupSyncedZoom(['auv-pry','auv-depth','auv-alt','auv-obs','auv-usbl-dist','auv-usbl-angle','auv-batt','auv-status','auv-motors']);
+  });
 }
 
 // == Task 10: Slider cursor sync ==
@@ -1220,6 +1244,34 @@ document.getElementById('window-select').addEventListener('change', () => {
   if (tNow) updateCursor(tNow / 1000);
 });
 
+// == Feature: Synced zoom across all Plotly charts ==
+let _syncing = false;
+function setupSyncedZoom(chartIds) {
+  chartIds.forEach(id => {
+    const div = document.getElementById(id);
+    if (!div) return;
+    div.on('plotly_relayout', (ev) => {
+      if (_syncing) return;
+      const x0 = ev['xaxis.range[0]'] || (ev['xaxis.range'] && ev['xaxis.range'][0]);
+      const x1 = ev['xaxis.range[1]'] || (ev['xaxis.range'] && ev['xaxis.range'][1]);
+      const reset = ev['xaxis.autorange'];
+      if (x0 == null && x1 == null && !reset) return;
+      _syncing = true;
+      chartIds.forEach(otherId => {
+        if (otherId === id) return;
+        const otherDiv = document.getElementById(otherId);
+        if (!otherDiv || !otherDiv._fullLayout) return;
+        if (reset) {
+          Plotly.relayout(otherDiv, { 'xaxis.autorange': true });
+        } else {
+          Plotly.relayout(otherDiv, { 'xaxis.range': [x0, x1] });
+        }
+      });
+      setTimeout(() => { _syncing = false; }, 50);
+    });
+  });
+}
+
 // == Task 11: loadSortieData + sorties loading + wiring ==
 async function loadSortieData(sortieId) {
   const prog = document.getElementById('sync-progress');