fix: strip ANSI escape codes from session persistence hooks (#642) (#684)

Windows terminals emit control sequences (cursor movement, screen
clearing) that leaked into session.tmp files and were injected
verbatim into Claude's context on the next session start.

Add a comprehensive stripAnsi() to utils.js that handles CSI, OSC,
charset selection, and bare ESC sequences. Apply it in session-end.js
(when extracting user messages from the transcript) and in
session-start.js (safety net before injecting session content).

tests/lib/utils.test.js

@@ -2424,6 +2424,65 @@ function runTests() {
     }
   })) passed++; else failed++;
 
+  // ─── stripAnsi ───
+  console.log('\nstripAnsi:');
+
+  if (test('strips SGR color codes (\\x1b[...m)', () => {
+    assert.strictEqual(utils.stripAnsi('\x1b[31mRed text\x1b[0m'), 'Red text');
+    assert.strictEqual(utils.stripAnsi('\x1b[1;36mBold cyan\x1b[0m'), 'Bold cyan');
+  })) passed++; else failed++;
+
+  if (test('strips cursor movement sequences (\\x1b[H, \\x1b[2J, \\x1b[3J)', () => {
+    // These are the exact sequences reported in issue #642
+    assert.strictEqual(utils.stripAnsi('\x1b[H\x1b[2J\x1b[3JHello'), 'Hello');
+    assert.strictEqual(utils.stripAnsi('before\x1b[Hafter'), 'beforeafter');
+  })) passed++; else failed++;
+
+  if (test('strips cursor position sequences (\\x1b[row;colH)', () => {
+    assert.strictEqual(utils.stripAnsi('\x1b[5;10Hplaced'), 'placed');
+  })) passed++; else failed++;
+
+  if (test('strips erase line sequences (\\x1b[K, \\x1b[2K)', () => {
+    assert.strictEqual(utils.stripAnsi('line\x1b[Kend'), 'lineend');
+    assert.strictEqual(utils.stripAnsi('line\x1b[2Kend'), 'lineend');
+  })) passed++; else failed++;
+
+  if (test('strips OSC sequences (window title, hyperlinks)', () => {
+    // OSC terminated by BEL (\x07)
+    assert.strictEqual(utils.stripAnsi('\x1b]0;My Title\x07content'), 'content');
+    // OSC terminated by ST (\x1b\\)
+    assert.strictEqual(utils.stripAnsi('\x1b]8;;https://example.com\x1b\\link\x1b]8;;\x1b\\'), 'link');
+  })) passed++; else failed++;
+
+  if (test('strips charset selection (\\x1b(B)', () => {
+    assert.strictEqual(utils.stripAnsi('\x1b(Bnormal'), 'normal');
+  })) passed++; else failed++;
+
+  if (test('strips bare ESC + letter (\\x1bM reverse index)', () => {
+    assert.strictEqual(utils.stripAnsi('line\x1bMup'), 'lineup');
+  })) passed++; else failed++;
+
+  if (test('handles mixed ANSI sequences in one string', () => {
+    const input = '\x1b[H\x1b[2J\x1b[1;36mSession\x1b[0m summary\x1b[K';
+    assert.strictEqual(utils.stripAnsi(input), 'Session summary');
+  })) passed++; else failed++;
+
+  if (test('returns empty string for non-string input', () => {
+    assert.strictEqual(utils.stripAnsi(null), '');
+    assert.strictEqual(utils.stripAnsi(undefined), '');
+    assert.strictEqual(utils.stripAnsi(42), '');
+  })) passed++; else failed++;
+
+  if (test('preserves string with no ANSI codes', () => {
+    assert.strictEqual(utils.stripAnsi('plain text'), 'plain text');
+    assert.strictEqual(utils.stripAnsi(''), '');
+  })) passed++; else failed++;
+
+  if (test('handles CSI with question mark parameter (DEC private modes)', () => {
+    // e.g. \x1b[?25h (show cursor), \x1b[?25l (hide cursor)
+    assert.strictEqual(utils.stripAnsi('\x1b[?25hvisible\x1b[?25l'), 'visible');
+  })) passed++; else failed++;
+
   // Summary
   console.log('\n=== Test Results ===');
   console.log(`Passed: ${passed}`);