[Bug]: A hook with a list-valued command passes manifest validation, then crashes extension add and leaves files behind #5080

Bug Description

ExtensionManifest checks only that a hook's command is truthy (src/specify_cli/extensions/__init__.py:435), so a list such as command: [speckit.test-ext.hello] is accepted. During install, HookExecutor.register_hooks uses the command as a dictionary key (__init__.py:5872), which raises TypeError: unhashable type: 'list'.

By then the extension directory has been copied and the agent skill has been written. The except handler in install_from_directory only rolls back when the generic agent is active (__init__.py:3132). With any other agent the files stay on disk, and no registry entry is written. The TypeError is not one of the exceptions specify extension add handles, so the user sees a raw traceback.

Steps to Reproduce

Save this as repro.py and run uv run python -I repro.py from the repository root.

import os, tempfile, traceback
from pathlib import Path
from typer.testing import CliRunner
from specify_cli import app

root = Path(tempfile.mkdtemp())
ext = root / "test-ext"
(ext / "commands").mkdir(parents=True)
(ext / "commands/hello.md").write_text("---\ndescription: hi\n---\n\nHello $ARGUMENTS\n")
(ext / "extension.yml").write_text("""schema_version: "1.0"
extension: {id: test-ext, name: Test, version: 1.0.0, description: d}
requires: {speckit_version: ">=0.1.0"}
provides:
  commands:
    - {name: speckit.test-ext.hello, file: commands/hello.md, description: x}
hooks:
  after_tasks:
    command: [speckit.test-ext.hello]
""")
proj = root / "project"
(proj / ".specify").mkdir(parents=True)
(proj / ".claude/skills").mkdir(parents=True)
os.chdir(proj)

r = CliRunner().invoke(app, ["extension", "add", "--dev", str(ext)])
print("exit code:", r.exit_code)
print("".join(traceback.format_exception(r.exception)[-3:]))
print("registry:", (proj / ".specify/extensions/.registry").read_text()
      if (proj / ".specify/extensions/.registry").exists() else "<none>")
print("left on disk:", sorted(str(p.relative_to(proj)) for p in proj.rglob("*") if "test-ext" in str(p)))

Expected Behavior

The manifest is rejected with a ValidationError and nothing is installed. extensions/EXTENSION-API-REFERENCE.md:72 documents the field as command: string. The ExtensionManifest.__init__ docstring says it "Raises: ValidationError: If manifest is invalid" (__init__.py:243-244).

Actual Behavior

exit code: 1
registry: <none>
left on disk: ['.claude/skills/speckit-test-ext-hello', '.claude/skills/speckit-test-ext-hello/SKILL.md', '.specify/extensions/test-ext', '.specify/extensions/test-ext/.specify-dev', '.specify/extensions/test-ext/.specify-dev/agent-commands', '.specify/extensions/test-ext/.specify-dev/agent-commands/claude', '.specify/extensions/test-ext/.specify-dev/agent-commands/claude/speckit-test-ext-hello', '.specify/extensions/test-ext/.specify-dev/agent-commands/claude/speckit-test-ext-hello/SKILL.md', '.specify/extensions/test-ext/commands', '.specify/extensions/test-ext/commands/hello.md', '.specify/extensions/test-ext/extension.yml']

The command exits 1. The extension is not in the registry, but .claude/skills/speckit-test-ext-hello/SKILL.md and .specify/extensions/test-ext/ remain on disk.

Specify CLI Version

1.2.4.dev0 (main at 27d14e2)

AI Agent

Claude Code

Operating System

Linux 6.18 (Ubuntu container)

Python Version

Python 3.12.3

Error Logs

  File "<checkout>/src/specify_cli/extensions/__init__.py", line 3084, in install_from_directory
    hook_executor.register_hooks(manifest)
  File "<checkout>/src/specify_cli/extensions/__init__.py", line 5872, in register_hooks
    if command in new_entries:
       ^^^^^^^^^^^^^^^^^^^^^^
TypeError: unhashable type: 'list'

Additional Context

Hook command values of other non-string types (a mapping, for example) take the same path. The failure-path rollback only covers the generic agent, so any other failure after command registration (for example, an unwritable .specify/extensions.yml) is likely to leave the same leftovers. That was not tested separately. Rejecting non-string hook commands in _validate would fix the reported case.

Also reproduced on macOS (Darwin 25.6, arm64) with Python 3.14.4 and uv run python -I repro.py against 27d14e2; the output matches the above.

AI Disclosure

Found and reproduced with Claude Code (model: Claude Opus 4.8), run autonomously under human supervision. The human reporter re-ran every reproduction above before filing.