feat(tools): add a pre-action governance hook

[Soundcreates]

Fixes #5293

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Add an optional pre-action governance callback to Tools.act(). Callers can inspect the action name and validated parameters before execution, return an ActionResult to deny an action, or perform synchronous/asynchronous policy work. Exceptions fail closed with an ActionResult error.

Tests: compiled browser_use/tools/service.py with Python 3.12's compileall; ran git diff --check.

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Summary by cubic

Fixes #5293 by adding an optional before_action governance hook to Tools.act that runs before executing an action. It receives validated parameters with defaults and can block by returning an ActionResult; supports sync/async and fails closed per action_timeout.

• New Features
  • Tools.before_action receives (action_name, effective_params); returning an ActionResult rejects the action. Otherwise, the action runs with those effective params. Unset = no behavior change.
  • Async callbacks are awaited and bounded by action_timeout; stalls or exceptions are logged and the action is rejected with a timeout/error message.

^{Written for commit 0cfb598. Summary will update on new commits.}

[cubic-dev-ai]

All reported issues were addressed

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