diff --git a/static/chart.js b/static/chart.js
index f70f012..e95802c 100644
--- a/static/chart.js
+++ b/static/chart.js
@@ -2514,10 +2514,18 @@ class ConfluenceChart {
           if (bar.t >= level.anchor_t && bar.t <= cutoff) stamps.add(bar.t);
         }
       } else {
+        const displayed = this.bars.filter(bar => bar.t >= level.anchor_t && bar.t <= cutoff);
         for (const time of ConfluenceChart.sourceTimes(source) || []) {
-          if (time >= first && time <= lastBar && time >= level.anchor_t && time <= cutoff) {
-            stamps.add(time);
+          if (time < first || time > lastBar || time < level.anchor_t || time > cutoff) continue;
+          let lo = 0;
+          let hi = displayed.length;
+          while (lo < hi) {
+            const mid = (lo + hi) >> 1;
+            if (displayed[mid].t < time) lo = mid + 1;
+            else hi = mid;
           }
+          const bar = displayed[lo] || displayed[displayed.length - 1];
+          if (bar) stamps.add(bar.t);
         }
         if (lastBar >= level.anchor_t && lastBar <= cutoff) stamps.add(lastBar);
       }
diff --git a/tests/e2e/trendline.test.mjs b/tests/e2e/trendline.test.mjs
index 7ddfa83..56da4ca 100644
--- a/tests/e2e/trendline.test.mjs
+++ b/tests/e2e/trendline.test.mjs
@@ -94,9 +94,10 @@ test('a 30m line keeps source geometry when the 1m window starts after its ancho
         'the rollback path no longer restores displayed-grid geometry');
       assert.equal(result.shifted, result.sourceSecondBar,
         'a source-timeframe nudge did not move by one 30m bar');
-      assert.deepEqual(result.sampledTimes.slice(0, result.displayedTimes.length), result.displayedTimes,
-        'manual line samples no longer match the displayed candle grid');
-      assert.ok(result.sampledTimes.slice(result.displayedTimes.length)
+      const historical = result.sampledTimes.filter(time => time <= result.displayedTimes.at(-1));
+      assert.deepEqual(historical, [result.displayedTimes[0], result.displayedTimes.at(-1)],
+        'a 30m line on 1m should sample source-bar times, not every 1m candle');
+      assert.ok(result.sampledTimes.slice(historical.length)
         .every(time => time > result.displayedTimes.at(-1)),
       'manual-line extension mixed future points into candle history');
       assert.deepEqual(result.trimmedTimes, result.expectedTrimmedTimes,
@@ -353,6 +354,62 @@ test('a short final data gap does not kink a future trendline',
     });
   });
 
+test('a 30m line stays straight on 1m when the bucket is missing its first minutes',
+  { timeout: 180000 }, async () => {
+    await withChart(async page => {
+      const result = await page.evaluate(() => {
+        const c = window.__chart;
+        const minute = 60;
+        const half = 30 * minute;
+        const open = 400000;
+        const bars = [];
+        for (let t = open - 2 * half; t < open; t += minute) {
+          bars.push({ tf: '1m', t, o: 100, h: 101, l: 99, c: 100, v: 1, closed: true });
+        }
+        for (let t = open + 9 * minute; t < open + 2 * half; t += minute) {
+          bars.push({ tf: '1m', t, o: 100, h: 101, l: 99, c: 100, v: 1, closed: true });
+        }
+        const line = {
+          id: 'late-open', kind: 'manual', tf: '30m', side: 'support', label: 'late',
+          anchor_t: open - 2 * half, anchor_p: 100, last_t: open,
+          slope: 3 / half, cutoff_t: null, hidden: false, color: '#65b7cf',
+          line_width: 2, provisional: false,
+        };
+        c.setDisplayFutureTimes(Array.from(
+          { length: ConfluenceChart.FUTURE_SLOTS }, (_, index) => bars.at(-1).t + (index + 1) * minute,
+        ));
+        c.setBars(bars);
+        c.setTrendlineGeometry({
+          mode: 'source_tf',
+          series: { '30m': { times: [open - 2 * half, open - half, open, open + half], duration: half } },
+        });
+        c.syncLevels([line]);
+        const data = c.levelSeries.get(line.id).series.data();
+        const point = time => {
+          const row = data.find(value => Number(value.time) === time);
+          return {
+            x: c.chart.timeScale().timeToCoordinate(time),
+            y: row ? c.candles.priceToCoordinate(row.value) : null,
+          };
+        };
+        const a = point(open - half);
+        const b = point(open + 9 * minute);
+        const d = point(open + half);
+        return {
+          snappedOpen: data.some(value => Number(value.time) === open + 9 * minute),
+          injectedOpen: data.some(value => Number(value.time) === open),
+          lateSlope: (b.y - a.y) / (b.x - a.x),
+          fullSlope: (d.y - b.y) / (d.x - b.x),
+        };
+      });
+      assert.equal(result.injectedOpen, false, '30m open that is not a 1m bar was placed on the scale');
+      assert.equal(result.snappedOpen, true, 'missing 30m open was not snapped to the first 1m bar');
+      assert.ok(Math.abs(result.lateSlope - result.fullSlope) < 1e-6,
+        `late-open 30m segment kinked from ${result.lateSlope} to ${result.fullSlope}`);
+      assertNoPageErrors(page, assert);
+    });
+  });
+
 test('painted canvas pixels keep the same slope through the live edge',
   { timeout: 180000 }, async () => {
     await withChart(async page => {