test(routes): regression coverage for stripInkRedrawBloat

The clustering rewrite of stripInkRedrawBloat() shipped silently inside
the v0.6.7 "chore: version packages" commit (dcc814f). The previous
implementation discarded everything after the first VPA escape — silently
dropping 100KB+ of legitimate streamed response text on every long
Claude turn. The fix landed without any test coverage, so a regression
back to the old shape would be invisible until users noticed missing
conversation history.

Export the function (it's a pure (string)=>string helper) and add 12
tests covering:
  - The early-out paths (empty buffer, no VPAs, fewer than 10 VPAs)
  - Small clusters preserved (< MIN_BLOAT_SIZE = 32KB span)
  - Big clusters collapsed to a single trailing VPA
  - The silent-data-loss bug: response text BETWEEN two big clusters
    is preserved (input >280KB so any "keep just the tail" approach
    would push the response text out of its window — verified locally
    that a simulated old impl fails the assertion)
  - FRAME_GAP boundary on both sides (>8KB splits clusters; <=8KB merges)
  - Mixed small + big in the same buffer
  - Big cluster at end-of-buffer keeps the last frame
  - Idempotency: a second pass is a no-op
  - Realistic 200KB+ input shrinks by an order of magnitude

Total runtime ~12ms.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/web/routes/session-routes.ts

@@ -78,7 +78,7 @@ const LEADING_WHITESPACE_PATTERN = /^[\s\r\n]+/;
  * Without clustering, a single first-VPA-finds-all approach would discard the entire
  * conversation after Claude's first render — losing 100KB+ of legitimate scrollback.
  */
-function stripInkRedrawBloat(buffer: string): string {
+export function stripInkRedrawBloat(buffer: string): string {
   // eslint-disable-next-line no-control-regex
   const vpaRe = /\x1b\[\d+d/g;
   const positions: number[] = [];

test/strip-ink-redraw-bloat.test.ts

@@ -0,0 +1,225 @@
+/**
+ * Regression tests for stripInkRedrawBloat() in session-routes.ts.
+ *
+ * Background: this helper trims the dense VPA (CSI n d) escape clusters that
+ * Ink emits while animating the spinner / status bar so terminal-tail responses
+ * stay manageable. The previous implementation collapsed *everything* after
+ * the first VPA, which silently discarded 100KB+ of legitimate streamed
+ * response text. The clustering rewrite shipped silently inside the v0.6.7
+ * "chore: version packages" commit (dcc814f) — these tests lock the algorithm
+ * down so neither the silent data-loss bug nor the threshold constants
+ * (FRAME_GAP=8KB, MIN_BLOAT_SIZE=32KB) regress.
+ *
+ * Pure (string)=>string helper, no I/O — synchronous tests, no port needed.
+ */
+
+import { describe, it, expect } from 'vitest';
+import { stripInkRedrawBloat } from '../src/web/routes/session-routes.js';
+
+const VPA = '\x1b[10d'; // VPA escape: move cursor to row 10. 5 bytes.
+const VPA_LEN = VPA.length;
+// Single counting regex shared across tests so the no-control-regex
+// disable lives in one place.
+// eslint-disable-next-line no-control-regex
+const VPA_RE = /\x1b\[\d+d/g;
+function countVpa(s: string): number {
+  return (s.match(VPA_RE) || []).length;
+}
+
+/** Build a buffer of `count` VPAs with `gap` bytes of filler between them. */
+function vpaCluster(count: number, gap: number, fillerChar = ' '): string {
+  const filler = fillerChar.repeat(gap);
+  const parts: string[] = [];
+  for (let i = 0; i < count; i++) {
+    if (i > 0) parts.push(filler);
+    parts.push(VPA);
+  }
+  return parts.join('');
+}
+
+/** Span (bytes from first VPA's start to last VPA's start) of a cluster
+ * built by vpaCluster(count, gap). */
+function clusterSpan(count: number, gap: number): number {
+  return (count - 1) * (gap + VPA_LEN);
+}
+
+describe('stripInkRedrawBloat', () => {
+  // ─── Early-out paths ─────────────────────────────────────────────────────
+
+  it('returns empty buffer unchanged', () => {
+    expect(stripInkRedrawBloat('')).toBe('');
+  });
+
+  it('returns buffer with no VPA escapes unchanged', () => {
+    const buf = 'Hello, this is a normal Claude response.\n'.repeat(100);
+    expect(stripInkRedrawBloat(buf)).toBe(buf);
+  });
+
+  it('returns buffer with fewer than 10 VPAs unchanged (even if total is large)', () => {
+    // 9 VPAs is below the early-out threshold; helper returns input verbatim
+    // regardless of how much filler sits between them.
+    const buf = vpaCluster(9, 50_000); // ~450KB of filler
+    expect(stripInkRedrawBloat(buf)).toBe(buf);
+  });
+
+  // ─── Small cluster preserved ─────────────────────────────────────────────
+
+  it('preserves a cluster smaller than MIN_BLOAT_SIZE (32KB span)', () => {
+    // 50 VPAs, 100B apart -> span ~5.2KB, well under 32KB
+    const cluster = vpaCluster(50, 100);
+    expect(clusterSpan(50, 100)).toBeLessThan(32 * 1024);
+    const buf = 'PREFIX\n' + cluster + '\nSUFFIX';
+    expect(stripInkRedrawBloat(buf)).toBe(buf);
+  });
+
+  // ─── Big cluster collapsed ───────────────────────────────────────────────
+
+  it('collapses a single big cluster but preserves bytes before and after', () => {
+    // 50 VPAs, 700B apart -> span 49*(700+5) = 34_545B, comfortably over 32KB
+    const cluster = vpaCluster(50, 700);
+    expect(clusterSpan(50, 700)).toBeGreaterThanOrEqual(32 * 1024);
+    const prefix = 'BEFORE_THE_BLOAT\n';
+    const suffix = '\nAFTER_THE_BLOAT_THIS_IS_THE_RESPONSE_TEXT_THAT_USED_TO_BE_LOST';
+    const buf = prefix + cluster + suffix;
+
+    const out = stripInkRedrawBloat(buf);
+
+    // Both ends survive — that was the silent bug
+    expect(out.startsWith(prefix)).toBe(true);
+    expect(out.endsWith(suffix)).toBe(true);
+    // Output is much shorter than the input
+    expect(out.length).toBeLessThan(buf.length);
+    // Exactly one VPA remains (the last frame's), not all 50
+    expect(countVpa(out)).toBe(1);
+  });
+
+  // ─── THE REGRESSION: response text BETWEEN big clusters survives ─────────
+
+  it('preserves response text between two big clusters (the silent-data-loss bug)', () => {
+    // Make each cluster large enough that an old "keep just the tail" approach
+    // (the audit described it as "keep only the last 64KB after the first VPA")
+    // would push any in-between response text out of the kept window.
+    // 200 VPAs at 700B gap -> ~140KB span per cluster, total buffer >300KB.
+    const clusterA = vpaCluster(200, 700);
+    const clusterB = vpaCluster(200, 700);
+    expect(clusterSpan(200, 700)).toBeGreaterThan(64 * 1024);
+
+    const responseText =
+      '\n\n## Here is my detailed answer\n\n' +
+      'This is the kind of streamed response text that the old first-VPA\n' +
+      'algorithm silently dropped. Multiple paragraphs of it. Indented blocks,\n' +
+      'code samples, the entire conversation. Losing this was a silent bug\n' +
+      'that the changelog mentioned but no test had ever locked down.\n\n' +
+      '```ts\n' +
+      'function example() { return 42; }\n' +
+      '```\n\n' +
+      'And a closing paragraph.';
+    // Gap between clusters must exceed FRAME_GAP (8KB) so they're treated
+    // as separate clusters, not merged into one giant one.
+    const padded = responseText + '\n' + ' '.repeat(8 * 1024 + 100);
+    const buf = 'INTRO\n' + clusterA + padded + clusterB + '\nOUTRO';
+    expect(buf.length).toBeGreaterThan(280 * 1024); // sanity: well past any 64KB window
+
+    const out = stripInkRedrawBloat(buf);
+
+    // Every paragraph of response text survives intact. This is the assertion
+    // that would have caught the silent-data-loss bug — under a "keep the last
+    // 64KB after the first VPA" approach, all of responseText falls outside
+    // the kept window and is lost.
+    expect(out).toContain('Here is my detailed answer');
+    expect(out).toContain('the old first-VPA');
+    expect(out).toContain('function example() { return 42; }');
+    expect(out).toContain('And a closing paragraph.');
+    // Bookends survive too.
+    expect(out.startsWith('INTRO\n')).toBe(true);
+    expect(out.endsWith('\nOUTRO')).toBe(true);
+    // Each big cluster collapses to a single VPA (its last frame).
+    expect(countVpa(out)).toBe(2);
+  });
+
+  // ─── Mixed: small clusters preserved alongside big ones ──────────────────
+
+  it('preserves small clusters when a big cluster is also present', () => {
+    const small = vpaCluster(50, 100); // ~5.2KB span, kept as-is
+    const big = vpaCluster(50, 700); // ~34KB span, collapsed
+    // Separate them with > FRAME_GAP filler so they stay distinct clusters.
+    const gap = ' '.repeat(8 * 1024 + 100);
+    const buf = small + gap + 'MID_CONTENT' + gap + big + 'TAIL';
+
+    const out = stripInkRedrawBloat(buf);
+
+    // Small cluster survives intact: all 50 VPAs still there.
+    // Big cluster collapsed to 1 VPA. Total = 50 + 1 = 51.
+    expect(countVpa(out)).toBe(51);
+    expect(out).toContain('MID_CONTENT');
+    expect(out.endsWith('TAIL')).toBe(true);
+  });
+
+  // ─── FRAME_GAP boundary: two clusters separated by exactly > 8KB ─────────
+
+  it('treats VPAs separated by > FRAME_GAP (8KB) as different clusters', () => {
+    // Two big clusters with a 9KB gap between them must NOT be merged.
+    const clusterA = vpaCluster(50, 700);
+    const clusterB = vpaCluster(50, 700);
+    const gap = ' '.repeat(9 * 1024); // > 8KB FRAME_GAP
+
+    const buf = clusterA + gap + clusterB;
+    const out = stripInkRedrawBloat(buf);
+
+    // Two separate big clusters -> 2 VPAs survive.
+    expect(countVpa(out)).toBe(2);
+    // Gap content survives.
+    expect(out).toContain(gap);
+  });
+
+  it('treats VPAs separated by <= FRAME_GAP (8KB) as the same cluster', () => {
+    // Two would-be-separate clusters with a 1KB gap merge into one big cluster.
+    const left = vpaCluster(30, 700);
+    const right = vpaCluster(30, 700);
+    const gap = ' '.repeat(1024); // well under 8KB FRAME_GAP
+    const buf = left + gap + right;
+
+    const out = stripInkRedrawBloat(buf);
+    // Merged into one big cluster -> 1 VPA survives, gap content is gone too.
+    expect(countVpa(out)).toBe(1);
+  });
+
+  // ─── Big cluster at end of buffer ────────────────────────────────────────
+
+  it('preserves the last frame when a big cluster is at the end of the buffer', () => {
+    const cluster = vpaCluster(50, 700);
+    const buf = 'HEAD\n' + cluster;
+    const out = stripInkRedrawBloat(buf);
+
+    expect(out.startsWith('HEAD\n')).toBe(true);
+    // Exactly one VPA (the last frame's) at the tail.
+    expect(countVpa(out)).toBe(1);
+    expect(out.endsWith(VPA)).toBe(true);
+  });
+
+  // ─── Idempotency ─────────────────────────────────────────────────────────
+
+  it('is idempotent: stripping an already-stripped buffer is a no-op', () => {
+    // After one pass a big cluster shrinks to ~1 VPA, putting the buffer
+    // below the early-out threshold (positions.length < 10), so a second
+    // pass returns it untouched.
+    const buf = 'A' + vpaCluster(50, 700) + 'B';
+    const once = stripInkRedrawBloat(buf);
+    const twice = stripInkRedrawBloat(once);
+    expect(twice).toBe(once);
+  });
+
+  // ─── Realistic size guardrail ────────────────────────────────────────────
+
+  it('shrinks a 200KB Ink-bloat buffer down by an order of magnitude', () => {
+    // Roughly the shape of a real "Claude is thinking" terminal buffer.
+    const cluster = vpaCluster(300, 700); // ~210KB span
+    const buf = 'Question: Tell me about TypeScript.\n' + cluster + '\nAnswer: TypeScript is...';
+
+    const out = stripInkRedrawBloat(buf);
+    expect(buf.length).toBeGreaterThan(200 * 1024);
+    expect(out.length).toBeLessThan(buf.length / 10);
+    expect(out).toContain('Question: Tell me about TypeScript.');
+    expect(out).toContain('Answer: TypeScript is...');
+  });
+});