feat: auto-dismiss native dialogs in action helpers

[edenowong]

Summary

Native dialogs (alert / confirm / prompt / beforeunload) freeze the JS thread, causing action helpers to silently hang behind a modal the agent never expected. The daemon already tracks pending dialogs via Page.javascriptDialogOpening, but helpers don't consult it. This PR makes action helpers auto-detect and dismiss after each action so a stray dialog doesn't deadlock the run.

Changes

• New private helper _check_and_dismiss_dialog(accept=True, prompt_text="") in helpers.py. Reuses the existing _send({"meta": "pending_dialog"}) daemon channel that page_info() already uses.
• Wraps four action helpers to auto-check after their CDP work:
  • goto_url (catches beforeunload)
  • click_at_xy
  • press_key
  • dispatch_key
• Logs [auto-dismissed <type>] <message> per dismissal so runs are debuggable.
• Opt out per process with BH_NO_AUTO_DISMISS=1 for callers that need to inspect dialogs manually (the existing API in interaction-skills/dialogs.md still works).
• accept=True matches the JS-stub pattern in interaction-skills/dialogs.md (confirm returns true, beforeunload leaves).

Why

Currently agents get stuck on sites that throw an unexpected confirm() mid-flow (e.g. "Are you sure you want to leave?", form-validation alerts, beforeunload on navigation). The screenshot looks normal, the click coordinates are right, but every subsequent action silently no-ops because the JS thread is frozen. The fix is one CDP call (Page.handleJavaScriptDialog) — making it implicit in the action helpers eliminates an entire class of silent-hang failure mode.

Test plan

• 9 new unit tests in test_dialog_auto_dismiss.py covering:
  • No-dialog path (no extra CDP call, no daemon round-trip when env-disabled)
  • Dialog present → Page.handleJavaScriptDialog called with correct args
  • accept=False and prompt_text= overrides
  • BH_NO_AUTO_DISMISS=1 opt-out
  • Integration through click_at_xy, press_key, goto_url
• Full existing suite still passes (10 → 19 tests, all green)

Notes

• The daemon already clears self.dialog on Page.javascriptDialogClosed (daemon.py:168), so there's no infinite-loop risk after dismissal.
• Doesn't wrap type_text / scroll / upload_file — these don't typically trigger dialogs synchronously and the next action will catch any that slip through.
• Manual API in interaction-skills/dialogs.md is unchanged; this only affects the default behavior of the wrapped helpers.

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Summary by cubic

Auto-dismiss native alert/confirm/prompt/beforeunload dialogs after each action helper to prevent runs hanging behind unexpected modals. This makes interactions more reliable by unfreezing the JS thread automatically.

• New Features
  • Added private _check_and_dismiss_dialog(accept=True, prompt_text="") that checks daemon pending_dialog and calls Page.handleJavaScriptDialog.
  • Auto-check added to goto_url, click_at_xy, press_key, and dispatch_key.
  • Logs [auto-dismissed <type>] <message> for debugging.
  • Opt out with BH_NO_AUTO_DISMISS=1 for manual dialog handling.

^{Written for commit af66c7c. Summary will update on new commits.}

[cubic-dev-ai]

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