fix: handle stdin unavailability and timeout to prevent hook hangs

Fixes #727 (PostToolUse hooks hanging at "1/2 done")
Addresses #646 (Bun stdin EINVAL crash)

Root causes:
1. Bun crashes with EINVAL when Claude Code doesn't provide valid stdin fd
2. stdin.on('end') never fires if Claude Code doesn't close stdin properly

Changes:
- Add isStdinAvailable() to safely check stdin before reading
- Wrap stdin access in try-catch to handle Bun's lazy fstat crash
- Add 5-second timeout to prevent indefinite hangs
- Gracefully return undefined instead of crashing on stdin errors
- Properly clean up event listeners to prevent memory leaks

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/cli/stdin-reader.ts

@@ -1,16 +1,103 @@
 // Stdin reading utility extracted from hook patterns
 // See src/hooks/save-hook.ts for the original pattern
 
+// Timeout for stdin reading - if Claude Code doesn't close stdin within this time,
+// we parse whatever data we have. This fixes issue #727 where hooks hang at "1/2 done"
+// because stdin.on('end') never fires.
+const STDIN_TIMEOUT_MS = 5000;
+
+/**
+ * Check if stdin is available and readable.
+ *
+ * Bun has a bug where accessing process.stdin can crash with EINVAL
+ * if Claude Code doesn't provide a valid stdin file descriptor (#646).
+ * This function safely checks if stdin is usable.
+ */
+function isStdinAvailable(): boolean {
+  try {
+    // Accessing stdin properties can trigger Bun's lazy fstat() call
+    // which crashes if the fd is invalid
+    const stdin = process.stdin;
+
+    // If stdin is a TTY, we're running interactively (not from Claude Code hook)
+    if (stdin.isTTY) {
+      return false;
+    }
+
+    // Check if we can access basic stdin properties without crashing
+    // This triggers Bun's lazy initialization
+    const readable = stdin.readable;
+    return readable !== false;
+  } catch (err) {
+    // Bun crashed trying to access stdin (EINVAL from fstat)
+    // This is expected when Claude Code doesn't provide valid stdin
+    return false;
+  }
+}
+
 export async function readJsonFromStdin(): Promise<unknown> {
+  // First, check if stdin is even available
+  // This catches the Bun EINVAL crash from issue #646
+  if (!isStdinAvailable()) {
+    return undefined;
+  }
+
   return new Promise((resolve, reject) => {
     let input = '';
-    process.stdin.on('data', (chunk) => input += chunk);
-    process.stdin.on('end', () => {
+    let resolved = false;
+
+    const cleanup = () => {
+      try {
+        process.stdin.removeAllListeners('data');
+        process.stdin.removeAllListeners('end');
+        process.stdin.removeAllListeners('error');
+      } catch {
+        // Ignore cleanup errors
+      }
+    };
+
+    const resolveWithData = () => {
+      if (resolved) return;
+      resolved = true;
+      cleanup();
       try {
         resolve(input.trim() ? JSON.parse(input) : undefined);
       } catch (e) {
         reject(new Error(`Failed to parse hook input: ${e}`));
       }
-    });
+    };
+
+    // Timeout handler - resolve with whatever data we have
+    // This fixes issue #727 where stdin.on('end') never fires
+    const timeoutId = setTimeout(() => {
+      if (!resolved) {
+        resolveWithData();
+      }
+    }, STDIN_TIMEOUT_MS);
+
+    try {
+      process.stdin.on('data', (chunk) => {
+        input += chunk;
+      });
+
+      process.stdin.on('end', () => {
+        clearTimeout(timeoutId);
+        resolveWithData();
+      });
+
+      process.stdin.on('error', (err) => {
+        if (resolved) return;
+        resolved = true;
+        clearTimeout(timeoutId);
+        cleanup();
+        // Don't reject on stdin errors - just return undefined
+        // This is more graceful for hook execution
+        resolve(undefined);
+      });
+    } catch (err) {
+      // If attaching listeners fails (Bun stdin issue), resolve with undefined
+      clearTimeout(timeoutId);
+      resolve(undefined);
+    }
   });
 }