fix: include signal info in exec error when process is killed

The close handler only read the exit code, producing a misleading
"exit code null" message when a child process was killed by a signal.
Now handles (code, signal) and reports the signal name in the error.

Author: fernandomg

AGENTS.md

@@ -63,7 +63,7 @@ Key directories:
 - **Run tests:** `pnpm test` / `pnpm test:coverage`
 - **Structure:** `source/__tests__/` mirrors `source/` layout. Operations tests live in `source/__tests__/operations/`
 - **What to test:** Non-interactive agentic flow (validation, JSON output), operations (correct shell commands), config, utils
-- **What not to test:** React/Ink components, `exec.ts` internals (mocked in all consumers)
+- **What not to test:** React/Ink components
 - **Mocking pattern:** Operations tests mock `exec`/`execFile` from `source/operations/exec.js`. Non-interactive tests mock the entire operations layer
 - **Coverage:** Focus on the agentic interface. Test files and `source/components/` are excluded from coverage
 

architecture.md

@@ -94,7 +94,7 @@ Two helpers with different security profiles:
 - **`execFile(file, args, options)`** — wraps `child_process.spawn` without a shell. Arguments are passed as an array, so user input cannot be interpreted as shell metacharacters. Use this whenever user-provided values (e.g., `projectName`) appear in the command.
 - **`exec(command, options)`** — wraps `child_process.spawn` to run `/bin/sh -c <command>` (spawns a shell). Only for commands that require shell features like `$(...)` substitution. Never interpolate user input into the command string.
 
-Both helpers use `spawn` with stdout ignored and stderr piped. They do not capture or return stdout — output is not buffered for the caller. They throw on non-zero exit codes with the stderr message.
+Both helpers use `spawn` with stdout ignored and stderr piped. They do not capture or return stdout — output is not buffered for the caller. They throw on non-zero exit codes with the stderr message, or report the signal name when the process is killed by a signal.
 
 ## Data Flow
 

source/__tests__/operations/exec.test.ts

@@ -0,0 +1,133 @@
+import { type ChildProcess, spawn } from 'node:child_process'
+import { EventEmitter } from 'node:events'
+import { beforeEach, describe, expect, it, vi } from 'vitest'
+
+vi.mock('node:child_process', () => ({
+  spawn: vi.fn(),
+}))
+
+const { exec, execFile } = await import('../../operations/exec.js')
+
+type StderrEmitter = EventEmitter & { on: (event: string, cb: (data: Buffer) => void) => void }
+
+function createMockChild(): ChildProcess {
+  const child = new EventEmitter() as ChildProcess
+  child.stderr = new EventEmitter() as StderrEmitter
+  return child
+}
+
+function mockSpawnWith(child: ChildProcess): void {
+  vi.mocked(spawn).mockReturnValue(child)
+}
+
+describe('exec', () => {
+  beforeEach(() => {
+    vi.clearAllMocks()
+  })
+
+  it('resolves when process exits with code 0', async () => {
+    const child = createMockChild()
+    mockSpawnWith(child)
+
+    const promise = exec('echo hello')
+    child.emit('close', 0, null)
+
+    await expect(promise).resolves.toBeUndefined()
+  })
+
+  it('rejects with stderr when process exits with non-zero code', async () => {
+    const child = createMockChild()
+    mockSpawnWith(child)
+
+    const promise = exec('false')
+    child.stderr?.emit('data', Buffer.from('something went wrong'))
+    child.emit('close', 1, null)
+
+    await expect(promise).rejects.toThrow('something went wrong')
+  })
+
+  it('rejects with exit code message when stderr is empty', async () => {
+    const child = createMockChild()
+    mockSpawnWith(child)
+
+    const promise = exec('false')
+    child.emit('close', 1, null)
+
+    await expect(promise).rejects.toThrow('Command failed with exit code 1')
+  })
+
+  it('rejects with signal name when process is killed by a signal', async () => {
+    const child = createMockChild()
+    mockSpawnWith(child)
+
+    const promise = exec('sleep 999')
+    child.emit('close', null, 'SIGTERM')
+
+    await expect(promise).rejects.toThrow('Process killed by signal SIGTERM')
+  })
+
+  it('rejects with stderr over signal message when both are available', async () => {
+    const child = createMockChild()
+    mockSpawnWith(child)
+
+    const promise = exec('sleep 999')
+    child.stderr?.emit('data', Buffer.from('Terminated'))
+    child.emit('close', null, 'SIGTERM')
+
+    await expect(promise).rejects.toThrow('Terminated')
+  })
+
+  it('rejects when spawn emits an error', async () => {
+    const child = createMockChild()
+    mockSpawnWith(child)
+
+    const promise = exec('nonexistent')
+    child.emit('error', new Error('spawn ENOENT'))
+
+    await expect(promise).rejects.toThrow('spawn ENOENT')
+  })
+
+  it('spawns /bin/sh -c with the command string', async () => {
+    const child = createMockChild()
+    mockSpawnWith(child)
+
+    const promise = exec('echo hello', { cwd: '/tmp' })
+    child.emit('close', 0, null)
+    await promise
+
+    expect(spawn).toHaveBeenCalledWith('/bin/sh', ['-c', 'echo hello'], {
+      cwd: '/tmp',
+      stdio: ['ignore', 'ignore', 'pipe'],
+    })
+  })
+})
+
+describe('execFile', () => {
+  beforeEach(() => {
+    vi.clearAllMocks()
+  })
+
+  it('spawns the file directly with args array', async () => {
+    const child = createMockChild()
+    mockSpawnWith(child)
+
+    const promise = execFile('rm', ['-rf', 'dist'], { cwd: '/project' })
+    child.emit('close', 0, null)
+    await promise
+
+    expect(spawn).toHaveBeenCalledWith('rm', ['-rf', 'dist'], {
+      cwd: '/project',
+      stdio: ['ignore', 'ignore', 'pipe'],
+    })
+  })
+
+  it('rejects with signal name when killed', async () => {
+    const child = createMockChild()
+    mockSpawnWith(child)
+
+    const promise = execFile('sleep', ['999'])
+    child.emit('close', null, 'SIGKILL')
+
+    await expect(promise).rejects.toThrow('Process killed by signal SIGKILL')
+  })
+})

source/operations/exec.ts

@@ -12,11 +12,15 @@ function run(command: string, args: string[], options: SpawnOptions): Promise<vo
       stderr += data.toString()
     })
 
-    child.on('close', (code) => {
+    child.on('close', (code, signal) => {
       if (code === 0) {
         resolve()
       } else {
-        const message = stderr.trim() || `Command failed with exit code ${code}`
+        const fallback =
+          signal !== null
+            ? `Process killed by signal ${signal}`
+            : `Command failed with exit code ${code}`
+        const message = stderr.trim() || fallback
         reject(new Error(message))
       }
     })