Fix chart tail viewport after 5m/15m timeframe switches.

Snap to latest candles on period change and only preserve scroll position when viewing history.

Co-authored-by: Cursor <cursoragent@cursor.com>

manual_trading_hub/static/chart.js

@@ -178,6 +178,7 @@
   let exhaustedLeft = false;
   let loadingLeft = false;
   let chartDataLoading = false;
+  let chartViewEpoch = 0;
   let priceTagTimer = null;
   let tfDigitBuf = "";
   let tfDigitTimer = null;
@@ -2025,6 +2026,22 @@
     return true;
   }
 
+  function isViewingChartTail(range, candleCount) {
+    if (!range || candleCount <= 0) return true;
+    const maxTo = candleCount - 1 + RIGHT_OFFSET_BARS;
+    return range.to >= maxTo - 24;
+  }
+
+  function tailVisibleLogicalRange(candleCount) {
+    const n = Math.max(0, Number(candleCount) || 0);
+    if (n <= 0) return null;
+    const visible = Math.min(DEFAULT_VISIBLE_BARS, n);
+    return {
+      from: Math.max(0, n - visible),
+      to: n - 1 + RIGHT_OFFSET_BARS,
+    };
+  }
+
   function clearChartSeriesData() {
     lastCandles = [];
     candleByTime = {};
@@ -2149,9 +2166,12 @@
     if (!exKey || !sym || !lastCandles.length || chartDataLoading) return;
     if (!lastViewKey || vKey !== lastViewKey) return;
     const myToken = loadToken;
+    const epochAtStart = chartViewEpoch;
     const candleCountBefore = lastCandles.length;
     let savedRange = null;
     if (chart) savedRange = chart.timeScale().getVisibleLogicalRange();
+    const wasViewingTail =
+      !savedRange || isViewingChartTail(savedRange, candleCountBefore);
     try {
       const data = await fetchChartChunk({
         exchange_key: exKey,
@@ -2161,6 +2181,7 @@
       });
       if (myToken !== loadToken) return;
       if (vKey !== lastViewKey) return;
+      if (epochAtStart !== chartViewEpoch) return;
       if (!data.ok || !data.candles || !data.candles.length) return;
       if (data.price_tick != null) {
         priceTick = data.price_tick;
@@ -2172,13 +2193,23 @@
         }
       }
       applyCandlesToChart(mergeCandles(lastCandles, alignCandlesToTick(data.candles), { prepend: false }), 0);
-      if (
+      if (epochAtStart !== chartViewEpoch) return;
+      const n = lastCandles.length;
+      const curRange = chart && chart.timeScale().getVisibleLogicalRange();
+      if (wasViewingTail) {
+        const tailRange = tailVisibleLogicalRange(n);
+        if (tailRange) chart.timeScale().setVisibleLogicalRange(tailRange);
+      } else if (
         savedRange &&
-        isVisibleRangeValidForCandles(savedRange, lastCandles.length) &&
+        isVisibleRangeValidForCandles(savedRange, n) &&
-        Math.abs(lastCandles.length - candleCountBefore) < chartChunkLimit(tf)
+        Math.abs(n - candleCountBefore) < chartChunkLimit(tf)
       ) {
         chart.timeScale().setVisibleLogicalRange(savedRange);
+      } else if (!isVisibleRangeValidForCandles(curRange, n)) {
+        const tailRange = tailVisibleLogicalRange(n);
+        if (tailRange) chart.timeScale().setVisibleLogicalRange(tailRange);
       }
+      updateVisibleRangeMarkers();
       if (posContext) {
         updateLivePosPnl();
         refreshPosPnlFromBoard();
@@ -2200,18 +2231,17 @@
 
   function applyDefaultVisibleRange() {
     if (!chart || !lastCandles.length) return;
-    const n = lastCandles.length;
+    function applyOnce() {
-    const visible = Math.min(DEFAULT_VISIBLE_BARS, n);
+      if (!chart || !lastCandles.length) return;
-    const from = Math.max(0, n - visible);
+      const r = tailVisibleLogicalRange(lastCandles.length);
-    const to = n - 1 + RIGHT_OFFSET_BARS;
+      if (!r) return;
-    applyChartRightGap();
+      applyChartRightGap();
-    requestAnimationFrame(function () {
+      chart.timeScale().setVisibleLogicalRange(r);
-      requestAnimationFrame(function () {
+      updateVisibleRangeMarkers();
-        if (!chart || !lastCandles.length) return;
+    }
-        chart.timeScale().setVisibleLogicalRange({ from: from, to: to });
+    applyOnce();
-        updateVisibleRangeMarkers();
+    requestAnimationFrame(applyOnce);
-      });
+    setTimeout(applyOnce, 0);
-    });
   }
 
   function updateVisibleRangeMarkers() {
@@ -2429,6 +2459,7 @@
     const resetView = !!force || vKey !== lastViewKey;
     chartDataLoading = true;
     if (resetView) {
+      chartViewEpoch += 1;
       resetChartHistoryState();
       lastViewKey = "";
       clearChartSeriesData();
@@ -2592,6 +2623,7 @@
     if (elFsTf) {
       elFsTf.addEventListener("change", function () {
         currentTf = elFsTf.value || "1d";
+        lastViewKey = "";
         syncMainFromFsToolbar();
         tickLiveClock();
         loadChart(false);