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).

scripts/hooks/session-start.js

@@ -15,6 +15,7 @@ const {
   findFiles,
   ensureDir,
   readFile,
+  stripAnsi,
   log,
   output
 } = require('../lib/utils');
@@ -42,7 +43,8 @@ async function main() {
     const content = readFile(latest.path);
     if (content && !content.includes('[Session context goes here]')) {
       // Only inject if the session has actual content (not the blank template)
-      output(`Previous session summary:\n${content}`);
+      // Strip ANSI escape codes that may have leaked from terminal output (#642)
+      output(`Previous session summary:\n${stripAnsi(content)}`);
     }
   }