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fix: cap terminal writes at 48KB/frame to prevent page unresponsive freezes

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Root cause was NOT WebGL — breadcrumbs showed 141KB single-frame
terminal.write() calls freezing Chrome for 2+ minutes even with the
canvas renderer. During heavy Ink output, multiple SSE terminal events
accumulate between animation frames and flush all at once.

Fix: split flushPendingWrites at DEC 2026 sync segment boundaries with
a 48KB per-frame budget. Each segment is a complete Ink redraw, so
splitting between them preserves atomicity (no flicker). Excess
segments are deferred to the next requestAnimationFrame.

Also re-enable WebGL since it was not the cause — the flush cap
protects both renderers equally.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
This commit is contained in:
arkon
2026-03-05 18:36:27 +01:00
co-authored by Claude Opus 4.6
parent 525f02f502
commit b620511d0e
1 changed files with 41 additions and 12 deletions
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src/web/public/app.js
+41 -12
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@@ -1381,21 +1381,50 @@ class CodemanApp {
const segments = extractSyncSegments(joined);
// Write all segments in a single batch (atomic within this frame).
// xterm.js internally batches multiple write() calls within same frame.
// Never discard content from incomplete sync blocks — xterm.js doesn't support
// DEC 2026 natively anyway, so strip the marker and write content regardless.
// Discarding causes real data loss (including Ink's erase-line escapes).
for (const segment of segments) {
if (segment) {
const content = segment.startsWith(DEC_SYNC_START)
? segment.slice(DEC_SYNC_START.length)
: segment;
if (content) this.terminal.write(content);
// Write segments respecting a per-frame byte budget.
// Each DEC 2026 sync segment is a complete Ink redraw — writing whole segments
// preserves atomicity (no flicker). But when total data exceeds 48KB, defer
// remaining segments to the next frame to prevent terminal.write() from blocking
// the main thread. 141KB single-frame writes have been observed to freeze Chrome
// for 2+ minutes even with the canvas renderer.
const MAX_FRAME_BYTES = 49152; // 48KB budget per frame
let bytesThisFrame = 0;
let deferred = false;
for (let i = 0; i < segments.length; i++) {
const segment = segments[i];
if (!segment) continue;
const content = segment.startsWith(DEC_SYNC_START)
? segment.slice(DEC_SYNC_START.length)
: segment;
if (!content) continue;
// If we'd exceed the budget, defer this and all remaining segments
if (bytesThisFrame > 0 && bytesThisFrame + content.length > MAX_FRAME_BYTES) {
// Re-queue remaining segments as raw content for next flush
const remaining = segments.slice(i).map(s => {
if (!s) return '';
return s.startsWith(DEC_SYNC_START) ? s.slice(DEC_SYNC_START.length) : s;
}).filter(Boolean).join('');
if (remaining) {
this.pendingWrites.push(remaining);
if (!this.writeFrameScheduled) {
this.writeFrameScheduled = true;
requestAnimationFrame(() => {
this.flushPendingWrites();
this.writeFrameScheduled = false;
});
}
}
deferred = true;
break;
}
this.terminal.write(content);
bytesThisFrame += content.length;
}
const _dt = performance.now() - _t0;
if (_dt > 100) console.warn(`[CRASH-DIAG] flushPendingWrites took ${_dt.toFixed(0)}ms (${_joinedLen} bytes)`);
if (_dt > 100 || deferred) console.warn(`[CRASH-DIAG] flushPendingWrites: ${_dt.toFixed(0)}ms, ${(bytesThisFrame/1024).toFixed(0)}KB written${deferred ? ', rest deferred' : ''} (total ${(_joinedLen/1024).toFixed(0)}KB)`);
// Sticky scroll: if user was at bottom, keep them there after new output
if (this._wasAtBottomBeforeWrite) {