fix(acp): classify the executable before choosing the client terminal

The terminal selector matched only the argument shape and the non-interactive
env, so any other caller spawning `<binary> -c <script>` with the same env
was routed to the client terminal, which can refuse to run that binary.
Require the executable to be a shell as well.

Author: elkaix

.changeset/acp-local-execution-and-stdio-mcp.md

@@ -2,4 +2,4 @@
 "@pymodel/pythinker-code": patch
 ---
 
-Run shell commands locally when an ACP client provides no terminal, accept stdio MCP servers in ACP sessions, and let a reloaded ACP session bind its runtime again.
+Run a command locally when an ACP client provides no terminal or the command is not a shell, accept stdio MCP servers in ACP sessions, and let a reloaded ACP session bind its runtime again.

packages/acp-server/src/acp-terminal/acpTerminalRunner.ts

@@ -24,8 +24,25 @@ const OUTPUT_BYTE_LIMIT = 4 * 1024 * 1024;
 const OUTPUT_POLL_MS = 250;
 let nextGeneration = 1;
 
-function isBashToolInvocation(args: readonly string[], options?: HostProcessOptions): boolean {
+const SHELL_EXECUTABLES = new Set(['sh', 'bash', 'zsh', 'dash', 'ksh', 'fish']);
+
+/**
+ * The Bash tool always spawns the configured shell. Classifying the executable
+ * keeps another caller's `-c` invocation — `python -c ...` carrying the same
+ * non-interactive env — on the local path, where the client cannot refuse it.
+ */
+function isShellExecutable(command: string): boolean {
+  const base = (command.split(/[\\/]/).pop() ?? command).toLowerCase();
+  return SHELL_EXECUTABLES.has(base.endsWith('.exe') ? base.slice(0, -4) : base);
+}
+
+function isBashToolInvocation(
+  command: string,
+  args: readonly string[],
+  options?: HostProcessOptions,
+): boolean {
   return (
+    isShellExecutable(command) &&
     args.length === 2 &&
     args[0] === '-c' &&
     options?.env?.['NO_COLOR'] === '1' &&
@@ -55,7 +72,7 @@ class AcpProcessService implements IHostProcessService {
     args: readonly string[] = [],
     options?: HostProcessOptions,
   ): Promise<IHostProcess> {
-    if (!this.connection.terminalEnabled || !isBashToolInvocation(args, options)) {
+    if (!this.connection.terminalEnabled || !isBashToolInvocation(command, args, options)) {
       return this.local.spawn(command, args, { ...options, cwd: options?.cwd ?? this.cwd });
     }
 

packages/acp-server/test/acp-terminal.test.ts

@@ -175,6 +175,45 @@ describe('AcpProcessService local fallback', () => {
     });
   });
 
+  it('falls back to local execution for a non-shell -c command carrying the Bash env', async () => {
+    let created = 0;
+    const connection = makeConnection({
+      terminalEnabled: true,
+      createTerminal: () => {
+        created += 1;
+        return makeTerminalHandle();
+      },
+    });
+    const { local, calls } = makeLocalProcessService();
+    const runtime = await bindRuntime(makeEnvironment(), { connection, local });
+
+    await runtime.process!.spawn('python', ['-c', 'print(1)'], { env: { ...bashEnv } });
+
+    expect(created).toBe(0);
+    expect(calls).toHaveLength(1);
+    expect(calls[0]).toMatchObject({ command: 'python', args: ['-c', 'print(1)'] });
+  });
+
+  it('routes a shell spawn to the terminal regardless of the shell binary or its path', async () => {
+    for (const shell of ['/bin/zsh', '/usr/local/bin/fish', 'C:\\Program Files\\Git\\bin\\bash.exe']) {
+      let created = 0;
+      const connection = makeConnection({
+        terminalEnabled: true,
+        createTerminal: () => {
+          created += 1;
+          return makeTerminalHandle();
+        },
+      });
+      const { local, calls } = makeLocalProcessService();
+      const runtime = await bindRuntime(makeEnvironment(), { connection, local });
+
+      await runtime.process!.spawn(shell, ['-c', 'echo hi'], { env: { ...bashEnv } });
+
+      expect(created, shell).toBe(1);
+      expect(calls, shell).toHaveLength(0);
+    }
+  });
+
   it('falls back to local execution for non-Bash spawns even with the terminal capability', async () => {
     let created = 0;
     const connection = makeConnection({