fix(delegation): handle undefined totalCost in timeout error formatting

Add defensive checks in result-formatter, headless-executor, and session-manager
to prevent TypeError when delegated sessions timeout without emitting a result.
Includes 4 comprehensive unit tests for undefined/null totalCost scenarios.

Fixes formatting error that prevented timeout messages from displaying.

bin/delegation/headless-executor.js

@@ -88,7 +88,8 @@ class HeadlessExecutor {
       if (lastSession) {
         args.push('--resume', lastSession.sessionId);
         if (process.env.CCS_DEBUG) {
-          console.error(`[i] Resuming session: ${lastSession.sessionId} (${lastSession.turns} turns, $${lastSession.totalCost.toFixed(4)})`);
+          const cost = lastSession.totalCost !== undefined && lastSession.totalCost !== null ? lastSession.totalCost.toFixed(4) : '0.0000';
+          console.error(`[i] Resuming session: ${lastSession.sessionId} (${lastSession.turns} turns, $${cost})`);
         }
       } else if (sessionId) {
         args.push('--resume', sessionId);

bin/delegation/result-formatter.js

@@ -437,7 +437,9 @@ class ResultFormatter {
     // Abbreviate session ID (Git-style first 8 chars)
     const shortId = sessionId && sessionId.length > 8 ? sessionId.substring(0, 8) : sessionId;
     output += `[i] Session persisted with ID: ${shortId}\n`;
-    output += `[i] Cost: $${totalCost.toFixed(4)}\n`;
+    if (totalCost !== undefined && totalCost !== null) {
+      output += `[i] Cost: $${totalCost.toFixed(4)}\n`;
+    }
 
     return output;
   }

bin/delegation/session-manager.js

@@ -60,7 +60,8 @@ class SessionManager {
       this._saveSessions(sessions);
 
       if (process.env.CCS_DEBUG) {
-        console.error(`[i] Updated session: ${sessionId}, total: $${sessions[key].totalCost.toFixed(4)}, turns: ${sessions[key].turns}`);
+        const cost = sessions[key].totalCost !== undefined && sessions[key].totalCost !== null ? sessions[key].totalCost.toFixed(4) : '0.0000';
+        console.error(`[i] Updated session: ${sessionId}, total: $${cost}, turns: ${sessions[key].turns}`);
       }
     }
   }

tests/unit/delegation/result-formatter.test.js

@@ -284,5 +284,85 @@ runner.test('Should show file counts in info box', () => {
   assertIncludes(formatted, 'Files Modified: 1', 'Should show modified count');
 });
 
+// Test 15: Handle undefined totalCost in timeout error
+runner.test('Should handle undefined totalCost in timeout error', () => {
+  const result = {
+    profile: 'glm',
+    cwd: '/test',
+    duration: 120000,
+    sessionId: 'test-session-123',
+    totalCost: undefined,
+    numTurns: 5,
+    timedOut: true
+  };
+
+  // Should not throw TypeError
+  const formatted = ResultFormatter.format(result);
+
+  assertIncludes(formatted, 'Execution timed out', 'Should show timeout message');
+  assertIncludes(formatted, 'test-ses', 'Should show abbreviated session ID');
+  // Cost line should be omitted when undefined
+  assert(!formatted.includes('Cost: $'), 'Should not show cost when undefined');
+});
+
+// Test 16: Handle null totalCost in timeout error
+runner.test('Should handle null totalCost in timeout error', () => {
+  const result = {
+    profile: 'kimi',
+    cwd: '/test',
+    duration: 60000,
+    sessionId: 'test-session-456',
+    totalCost: null,
+    numTurns: 3,
+    timedOut: true
+  };
+
+  // Should not throw TypeError
+  const formatted = ResultFormatter.format(result);
+
+  assertIncludes(formatted, 'Execution timed out', 'Should show timeout message');
+  assert(!formatted.includes('Cost: $'), 'Should not show cost when null');
+});
+
+// Test 17: Show totalCost when defined in timeout error
+runner.test('Should show totalCost when defined in timeout error', () => {
+  const result = {
+    profile: 'glm',
+    cwd: '/test',
+    duration: 90000,
+    sessionId: 'test-session-789',
+    totalCost: 0.1234,
+    numTurns: 4,
+    timedOut: true
+  };
+
+  const formatted = ResultFormatter.format(result);
+
+  assertIncludes(formatted, 'Cost: $0.1234', 'Should show formatted cost');
+});
+
+// Test 18: Handle undefined totalCost in normal result
+runner.test('Should handle undefined totalCost in normal result', () => {
+  const result = {
+    profile: 'kimi',
+    cwd: '/test',
+    exitCode: 0,
+    stdout: 'Task completed',
+    stderr: '',
+    duration: 5000,
+    success: true,
+    sessionId: 'session-abc',
+    totalCost: undefined,
+    numTurns: 2
+  };
+
+  // Should not throw TypeError
+  const formatted = ResultFormatter.format(result);
+
+  assertIncludes(formatted, '[OK]', 'Should show success');
+  // Cost line should be omitted in info box when undefined
+  assert(!formatted.includes('Cost: $'), 'Should not show cost when undefined');
+});
+
 // Run all tests
 runner.run();