feat: add external terminal support with cross-platform detection

Add support for opening worktree directories in external terminals
(iTerm2, Warp, Ghostty, System Terminal, etc.) while retaining the
integrated terminal as the default option.

Changes:
- Add terminal detection for macOS, Windows, and Linux
- Add "Open in Terminal" split-button in worktree dropdown
- Add external terminal selection in Settings > Terminal
- Add default open mode setting (new tab vs split)
- Display branch name in terminal panel header
- Support 20+ terminals across platforms

Part of #558, Closes #550

apps/server/src/routes/worktree/index.ts

@@ -30,6 +30,12 @@ import {
   createRefreshEditorsHandler,
 } from './routes/open-in-editor.js';
 import { createOpenInTerminalHandler } from './routes/open-in-terminal.js';
+import {
+  createGetAvailableTerminalsHandler,
+  createGetDefaultTerminalHandler,
+  createRefreshTerminalsHandler,
+  createOpenInExternalTerminalHandler,
+} from './routes/open-in-terminal.js';
 import { createInitGitHandler } from './routes/init-git.js';
 import { createMigrateHandler } from './routes/migrate.js';
 import { createStartDevHandler } from './routes/start-dev.js';
@@ -106,6 +112,13 @@ export function createWorktreeRoutes(
   router.get('/default-editor', createGetDefaultEditorHandler());
   router.get('/available-editors', createGetAvailableEditorsHandler());
   router.post('/refresh-editors', createRefreshEditorsHandler());
+
+  // External terminal routes
+  router.get('/available-terminals', createGetAvailableTerminalsHandler());
+  router.get('/default-terminal', createGetDefaultTerminalHandler());
+  router.post('/refresh-terminals', createRefreshTerminalsHandler());
+  router.post('/open-in-external-terminal', createOpenInExternalTerminalHandler());
+
   router.post('/init-git', validatePathParams('projectPath'), createInitGitHandler());
   router.post('/migrate', createMigrateHandler());
   router.post(

apps/server/src/routes/worktree/routes/open-in-terminal.ts

@@ -1,14 +1,30 @@
 /**
- * POST /open-in-terminal endpoint - Open a terminal in a worktree directory
+ * Terminal endpoints for opening worktree directories in terminals
  *
- * This module uses @automaker/platform for cross-platform terminal launching.
+ * POST /open-in-terminal - Open in system default terminal (integrated)
+ * GET /available-terminals - List all available external terminals
+ * GET /default-terminal - Get the default external terminal
+ * POST /refresh-terminals - Clear terminal cache and re-detect
+ * POST /open-in-external-terminal - Open a directory in an external terminal
  */
 
 import type { Request, Response } from 'express';
 import { isAbsolute } from 'path';
-import { openInTerminal } from '@automaker/platform';
+import {
+  openInTerminal,
+  clearTerminalCache,
+  detectAllTerminals,
+  detectDefaultTerminal,
+  openInExternalTerminal,
+} from '@automaker/platform';
+import { createLogger } from '@automaker/utils';
 import { getErrorMessage, logError } from '../common.js';
 
+const logger = createLogger('open-in-terminal');
+
+/**
+ * Handler to open in system default terminal (integrated terminal behavior)
+ */
 export function createOpenInTerminalHandler() {
   return async (req: Request, res: Response): Promise<void> => {
     try {
@@ -48,3 +64,125 @@ export function createOpenInTerminalHandler() {
     }
   };
 }
+
+/**
+ * Handler to get all available external terminals
+ */
+export function createGetAvailableTerminalsHandler() {
+  return async (_req: Request, res: Response): Promise<void> => {
+    try {
+      const terminals = await detectAllTerminals();
+      res.json({
+        success: true,
+        result: {
+          terminals,
+        },
+      });
+    } catch (error) {
+      logError(error, 'Get available terminals failed');
+      res.status(500).json({ success: false, error: getErrorMessage(error) });
+    }
+  };
+}
+
+/**
+ * Handler to get the default external terminal
+ */
+export function createGetDefaultTerminalHandler() {
+  return async (_req: Request, res: Response): Promise<void> => {
+    try {
+      const terminal = await detectDefaultTerminal();
+      res.json({
+        success: true,
+        result: terminal
+          ? {
+              terminalId: terminal.id,
+              terminalName: terminal.name,
+              terminalCommand: terminal.command,
+            }
+          : null,
+      });
+    } catch (error) {
+      logError(error, 'Get default terminal failed');
+      res.status(500).json({ success: false, error: getErrorMessage(error) });
+    }
+  };
+}
+
+/**
+ * Handler to refresh the terminal cache and re-detect available terminals
+ * Useful when the user has installed/uninstalled terminals
+ */
+export function createRefreshTerminalsHandler() {
+  return async (_req: Request, res: Response): Promise<void> => {
+    try {
+      // Clear the cache
+      clearTerminalCache();
+
+      // Re-detect terminals (this will repopulate the cache)
+      const terminals = await detectAllTerminals();
+
+      logger.info(`Terminal cache refreshed, found ${terminals.length} terminals`);
+
+      res.json({
+        success: true,
+        result: {
+          terminals,
+          message: `Found ${terminals.length} available external terminals`,
+        },
+      });
+    } catch (error) {
+      logError(error, 'Refresh terminals failed');
+      res.status(500).json({ success: false, error: getErrorMessage(error) });
+    }
+  };
+}
+
+/**
+ * Handler to open a directory in an external terminal
+ */
+export function createOpenInExternalTerminalHandler() {
+  return async (req: Request, res: Response): Promise<void> => {
+    try {
+      const { worktreePath, terminalId } = req.body as {
+        worktreePath: string;
+        terminalId?: string;
+      };
+
+      if (!worktreePath) {
+        res.status(400).json({
+          success: false,
+          error: 'worktreePath required',
+        });
+        return;
+      }
+
+      // Security: Validate that worktreePath is an absolute path
+      if (!isAbsolute(worktreePath)) {
+        res.status(400).json({
+          success: false,
+          error: 'worktreePath must be an absolute path',
+        });
+        return;
+      }
+
+      try {
+        const result = await openInExternalTerminal(worktreePath, terminalId);
+        res.json({
+          success: true,
+          result: {
+            message: `Opened ${worktreePath} in ${result.terminalName}`,
+            terminalName: result.terminalName,
+          },
+        });
+      } catch (terminalError) {
+        // Terminal failed to open
+        logger.warn(`Failed to open in terminal: ${getErrorMessage(terminalError)}`);
+        throw terminalError;
+      }
+    } catch (error) {
+      logError(error, 'Open in external terminal failed');
+      res.status(500).json({ success: false, error: getErrorMessage(error) });
+    }
+  };
+}