Fallback to available shell when run_terminal_command shell is missing

core/tools/implementations/runTerminalCommand.ts

@@ -1,5 +1,6 @@
 import iconv from "iconv-lite";
 import childProcess from "node:child_process";
+import fs from "node:fs";
 import os from "node:os";
 import { ContinueError, ContinueErrorReason } from "../../util/errors";
 // Automatically decode the buffer according to the platform to avoid garbled Chinese
@@ -26,9 +27,25 @@ function getShellCommand(command: string): { shell: string; args: string[] } {
       args: ["-NoLogo", "-ExecutionPolicy", "Bypass", "-Command", command],
     };
   } else {
-    // Unix/macOS: Use login shell to source .bashrc/.zshrc etc.
-    const userShell = process.env.SHELL || "/bin/bash";
-    return { shell: userShell, args: ["-l", "-c", command] };
+    // Unix/macOS: prefer configured shell, but gracefully fall back when unavailable
+    // (e.g. minimal dev containers without /bin/bash).
+    const configuredShell = process.env.SHELL;
+    const unixFallbacks = ["/bin/bash", "/bin/sh", "/bin/ash"];
+    const shellCandidates = configuredShell
+      ? [configuredShell, ...unixFallbacks]
+      : unixFallbacks;
+
+    const shell =
+      shellCandidates.find((candidate) => {
+        if (!candidate) return false;
+        if (!candidate.startsWith("/")) {
+          // Non-absolute shells are resolved by PATH at spawn time.
+          return true;
+        }
+        return fs.existsSync(candidate);
+      }) ?? "/bin/sh";
+
+    return { shell, args: ["-l", "-c", command] };
   }
 }
 

core/tools/implementations/runTerminalCommand.vitest.ts

@@ -142,6 +142,31 @@ describe("runTerminalCommandImpl", () => {
     expect(result[0].status).toBe("Command completed");
   });
 
+  it("should fall back to an available shell when SHELL is invalid", async () => {
+    if (process.platform === "win32") {
+      return;
+    }
+
+    const originalShell = process.env.SHELL;
+    process.env.SHELL = "/definitely-not-a-real-shell";
+
+    try {
+      const result = await runTerminalCommandImpl(
+        { command: `node -e "console.log('fallback shell works')"` },
+        createMockExtras(),
+      );
+
+      expect(result[0].status).toBe("Command completed");
+      expect(result[0].content).toContain("fallback shell works");
+    } finally {
+      if (originalShell === undefined) {
+        delete process.env.SHELL;
+      } else {
+        process.env.SHELL = originalShell;
+      }
+    }
+  });
+
   it("should stream output when onPartialOutput is provided", async () => {
     // This test uses Node to create a command that outputs data incrementally
     const command = `node -e "