feat(browser): CDP supervisor — dialog detection + response + cross-origin iframe eval (#14540)

* docs: browser CDP supervisor design (for upcoming PR)

Design doc ahead of implementation — dialog + iframe detection/interaction
via a persistent CDP supervisor. Covers backend capability matrix (verified
live 2026-04-23), architecture, lifecycle, policy, agent surface, PR split,
non-goals, and test plan.

Supersedes #12550.

No code changes in this commit.

* feat(browser): add persistent CDP supervisor for dialog + frame detection

Single persistent CDP WebSocket per Hermes task_id that subscribes to
Page/Runtime/Target events and maintains thread-safe state for pending
dialogs, frame tree, and console errors.

Supervisor lives in its own daemon thread running an asyncio loop;
external callers use sync API (snapshot(), respond_to_dialog()) that
bridges onto the loop.

Auto-attaches to OOPIF child targets via Target.setAutoAttach{flatten:true}
and enables Page+Runtime on each so iframe-origin dialogs surface through
the same supervisor.

Dialog policies: must_respond (default, 300s safety timeout),
auto_dismiss, auto_accept.

Frame tree capped at 30 entries + OOPIF depth 2 to keep snapshot
payloads bounded on ad-heavy pages.

E2E verified against real Chrome via smoke test — detects + responds
to main-frame alerts, iframe-contentWindow alerts, preserves frame
tree, graceful no-dialog error path, clean shutdown.

No agent-facing tool wiring in this commit (comes next).

* feat(browser): add browser_dialog tool wired to CDP supervisor

Agent-facing response-only tool. Schema:
  action: 'accept' | 'dismiss' (required)
  prompt_text: response for prompt() dialogs (optional)
  dialog_id: disambiguate when multiple dialogs queued (optional)

Handler:
  SUPERVISOR_REGISTRY.get(task_id).respond_to_dialog(...)

check_fn shares _browser_cdp_check with browser_cdp so both surface and
hide together. When no supervisor is attached (Camofox, default
Playwright, or no browser session started yet), tool is hidden; if
somehow invoked it returns a clear error pointing the agent to
browser_navigate / /browser connect.

Registered in _HERMES_CORE_TOOLS and the browser / hermes-acp /
hermes-api-server toolsets alongside browser_cdp.

* feat(browser): wire CDP supervisor into session lifecycle + browser_snapshot

Supervisor lifecycle:
  * _get_session_info lazy-starts the supervisor after a session row is
    materialized — covers every backend code path (Browserbase, cdp_url
    override, /browser connect, future providers) with one hook.
  * cleanup_browser(task_id) stops the supervisor for that task first
    (before the backend tears down CDP).
  * cleanup_all_browsers() calls SUPERVISOR_REGISTRY.stop_all().
  * /browser connect eagerly starts the supervisor for task 'default'
    so the first snapshot already shows pending_dialogs.
  * /browser disconnect stops the supervisor.

CDP URL resolution for the supervisor:
  1. BROWSER_CDP_URL / browser.cdp_url override.
  2. Fallback: session_info['cdp_url'] from cloud providers (Browserbase).

browser_snapshot merges supervisor state (pending_dialogs + frame_tree)
into its JSON output when a supervisor is active — the agent reads
pending_dialogs from the snapshot it already requests, then calls
browser_dialog to respond. No extra tool surface.

Config defaults:
  * browser.dialog_policy: 'must_respond' (new)
  * browser.dialog_timeout_s: 300 (new)
No version bump — new keys deep-merge into existing browser section.

Deadlock fix in supervisor event dispatch:
  * _on_dialog_opening and _on_target_attached used to await CDP calls
    while the reader was still processing an event — but only the reader
    can set the response Future, so the call timed out.
  * Both now fire asyncio.create_task(...) so the reader stays pumping.
  * auto_dismiss/auto_accept now actually close the dialog immediately.

Tests (tests/tools/test_browser_supervisor.py, 11 tests, real Chrome):
  * supervisor start/snapshot
  * main-frame alert detection + dismiss
  * iframe.contentWindow alert
  * prompt() with prompt_text reply
  * respond with no pending dialog -> clean error
  * auto_dismiss clears on event
  * registry idempotency
  * registry stop -> snapshot reports inactive
  * browser_dialog tool no-supervisor error
  * browser_dialog invalid action
  * browser_dialog end-to-end via tool handler

xdist-safe: chrome_cdp fixture uses a per-worker port.
Skipped when google-chrome/chromium isn't installed.

* docs(browser): document browser_dialog tool + CDP supervisor

- user-guide/features/browser.md: new browser_dialog section with
  workflow, availability gate, and dialog_policy table
- reference/tools-reference.md: row for browser_dialog, tool count
  bumped 53 -> 54, browser tools count 11 -> 12
- reference/toolsets-reference.md: browser_dialog added to browser
  toolset row with note on pending_dialogs / frame_tree snapshot fields

Full design doc lives at
developer-guide/browser-supervisor.md (committed earlier).

* fix(browser): reconnect loop + recent_dialogs for Browserbase visibility

Found via Browserbase E2E test that revealed two production-critical issues:

1. **Supervisor WebSocket drops when other clients disconnect.** Browserbase's
   CDP proxy tears down our long-lived WebSocket whenever a short-lived
   client (e.g. agent-browser CLI's per-command CDP connection) disconnects.
   Fixed with a reconnecting _run loop that re-attaches with exponential
   backoff on drops. _page_session_id and _child_sessions are reset on each
   reconnect; pending_dialogs and frames are preserved across reconnects.

2. **Browserbase auto-dismisses dialogs server-side within ~10ms.** Their
   Playwright-based CDP proxy dismisses alert/confirm/prompt before our
   Page.handleJavaScriptDialog call can respond. So pending_dialogs is
   empty by the time the agent reads a snapshot on Browserbase.

   Added a recent_dialogs ring buffer (capacity 20) that retains a
   DialogRecord for every dialog that opened, with a closed_by tag:
     * 'agent'       — agent called browser_dialog
     * 'auto_policy' — local auto_dismiss/auto_accept fired
     * 'watchdog'    — must_respond timeout auto-dismissed (300s default)
     * 'remote'      — browser/backend closed it on us (Browserbase)

   Agents on Browserbase now see the dialog history with closed_by='remote'
   so they at least know a dialog fired, even though they couldn't respond.

3. **Page.javascriptDialogClosed matching bug.** The event doesn't include a
   'message' field (CDP spec has only 'result' and 'userInput') but our
   _on_dialog_closed was matching on message. Fixed to match by session_id
   + oldest-first, with a safety assumption that only one dialog is in
   flight per session (the JS thread is blocked while a dialog is up).

Docs + tests updated:
  * browser.md: new availability matrix showing the three backends and
    which mode (pending / recent / response) each supports
  * developer-guide/browser-supervisor.md: three-field snapshot schema
    with closed_by semantics
  * test_browser_supervisor.py: +test_recent_dialogs_ring_buffer (12/12
    passing against real Chrome)

E2E verified both backends:
  * Local Chrome via /browser connect: detect + respond full workflow
    (smoke_supervisor.py all 7 scenarios pass)
  * Browserbase: detect via recent_dialogs with closed_by='remote'
    (smoke_supervisor_browserbase_v2.py passes)

Camofox remains out of scope (REST-only, no CDP) — tracked for
upstream PR 3.

* feat(browser): XHR bridge for dialog response on Browserbase (FIXED)

Browserbase's CDP proxy auto-dismisses native JS dialogs within ~10ms, so
Page.handleJavaScriptDialog calls lose the race. Solution: bypass native
dialogs entirely.

The supervisor now injects Page.addScriptToEvaluateOnNewDocument with a
JavaScript override for window.alert/confirm/prompt. Those overrides
perform a synchronous XMLHttpRequest to a magic host
('hermes-dialog-bridge.invalid'). We intercept those XHRs via Fetch.enable
with a requestStage=Request pattern.

Flow when a page calls alert('hi'):
  1. window.alert override intercepts, builds XHR GET to
     http://hermes-dialog-bridge.invalid/?kind=alert&message=hi
  2. Sync XHR blocks the page's JS thread (mirrors real dialog semantics)
  3. Fetch.requestPaused fires on our WebSocket; supervisor surfaces
     it as a pending dialog with bridge_request_id set
  4. Agent reads pending_dialogs from browser_snapshot, calls browser_dialog
  5. Supervisor calls Fetch.fulfillRequest with JSON body:
     {accept: true|false, prompt_text: '...', dialog_id: 'd-N'}
  6. The injected script parses the body, returns the appropriate value
     from the override (undefined for alert, bool for confirm, string|null
     for prompt)

This works identically on Browserbase AND local Chrome — no native dialog
ever fires, so Browserbase's auto-dismiss has nothing to race. Dialog
policies (must_respond / auto_dismiss / auto_accept) all still work.

Bridge is installed on every attached session (main page + OOPIF child
sessions) so iframe dialogs are captured too.

Native-dialog path kept as a fallback for backends that don't auto-dismiss
(so a page that somehow bypasses our override — e.g. iframes that load
after Fetch.enable but before the init-script runs — still gets observed
via Page.javascriptDialogOpening).

E2E VERIFIED:
  * Local Chrome: 13/13 pytest tests green (12 original + new
    test_bridge_captures_prompt_and_returns_reply_text that asserts
    window.__ret === 'AGENT-SUPPLIED-REPLY' after agent responds)
  * Browserbase: smoke_bb_bridge_v2.py runs 4/4 PASS:
    - alert('BB-ALERT-MSG') dismiss → page.alert_ret = undefined ✓
    - prompt('BB-PROMPT-MSG', 'default-xyz') accept with 'AGENT-REPLY'
      → page.prompt_ret === 'AGENT-REPLY' ✓
    - confirm('BB-CONFIRM-MSG') accept → page.confirm_ret === true ✓
    - confirm('BB-CONFIRM-MSG') dismiss → page.confirm_ret === false ✓

Docs updated in browser.md and developer-guide/browser-supervisor.md —
availability matrix now shows Browserbase at full parity with local
Chrome for both detection and response.

* feat(browser): cross-origin iframe interaction via browser_cdp(frame_id=...)

Adds iframe interaction to the CDP supervisor PR (was queued as PR 2).

Design: browser_cdp gets an optional frame_id parameter. When set, the
tool looks up the frame in the supervisor's frame_tree, grabs its child
cdp_session_id (OOPIF session), and dispatches the CDP call through the
supervisor's already-connected WebSocket via run_coroutine_threadsafe.

Why not stateless: on Browserbase, each fresh browser_cdp WebSocket
must re-negotiate against a signed connectUrl. The session info carries
a specific URL that can expire while the supervisor's long-lived
connection stays valid. Routing via the supervisor sidesteps this.

Agent workflow:
  1. browser_snapshot → frame_tree.children[] shows OOPIFs with is_oopif=true
  2. browser_cdp(method='Runtime.evaluate', frame_id=<OOPIF frame_id>,
                 params={'expression': 'document.title', 'returnByValue': True})
  3. Supervisor dispatches the call on the OOPIF's child session

Supervisor state fixes needed along the way:
  * _on_frame_detached now skips reason='swap' (frame migrating processes)
  * _on_frame_detached also skips when the frame is an OOPIF with a live
    child session — Browserbase fires spurious remove events when a
    same-origin iframe gets promoted to OOPIF
  * _on_target_detached clears cdp_session_id but KEEPS the frame record
    so the agent still sees the OOPIF in frame_tree during transient
    session flaps

E2E VERIFIED on Browserbase (smoke_bb_iframe_agent_path.py):
  browser_cdp(method='Runtime.evaluate',
              params={'expression': 'document.title', 'returnByValue': True},
              frame_id=<OOPIF>)
  → {'success': True, 'result': {'value': 'Example Domain'}}

  The iframe is <iframe src='https://example.com/'> inside a top-level
  data: URL page on a real Browserbase session. The agent Runtime.evaluates
  INSIDE the cross-origin iframe and gets example.com's title back.

Tests (tests/tools/test_browser_supervisor.py — 16 pass total):
  * test_browser_cdp_frame_id_routes_via_supervisor — injects fake OOPIF,
    verifies routing via supervisor, Runtime.evaluate returns 1+1=2
  * test_browser_cdp_frame_id_missing_supervisor — clean error when no
    supervisor attached
  * test_browser_cdp_frame_id_not_in_frame_tree — clean error on bad
    frame_id

Docs (browser.md and developer-guide/browser-supervisor.md) updated with
the iframe workflow, availability matrix now shows OOPIF eval as shipped
for local Chrome + Browserbase.

* test(browser): real-OOPIF E2E verified manually + chrome_cdp uses --site-per-process

When asked 'did you test the iframe stuff' I had only done a mocked
pytest (fake injected OOPIF) plus a Browserbase E2E. Closed the
local-Chrome real-OOPIF gap by writing /tmp/dialog-iframe-test/
smoke_local_oopif.py:

  * 2 http servers on different hostnames (localhost:18905 + 127.0.0.1:18906)
  * Chrome with --site-per-process so the cross-origin iframe becomes a
    real OOPIF in its own process
  * Navigate, find OOPIF in supervisor.frame_tree, call
    browser_cdp(method='Runtime.evaluate', frame_id=<OOPIF>) which routes
    through the supervisor's child session
  * Asserts iframe document.title === 'INNER-FRAME-XYZ' (from the
    inner page, retrieved via OOPIF eval)

PASSED on 2026-04-23.

Tried to embed this as a pytest but hit an asyncio version quirk between
venv (3.11) and the system python (3.13) — Page.navigate hangs in the
pytest harness but works in standalone. Left a self-documenting skip
test that points to the smoke script + describes the verification.

chrome_cdp fixture now passes --site-per-process so future iframe tests
can rely on OOPIF behavior.

Result: 16 pass + 1 documented-skip = 17 tests in
tests/tools/test_browser_supervisor.py.

* docs(browser): add dialog_policy + dialog_timeout_s to configuration.md, fix tool count

Pre-merge docs audit revealed two gaps:

1. user-guide/configuration.md browser config example was missing the
   two new dialog_* knobs. Added with a short table explaining
   must_respond / auto_dismiss / auto_accept semantics and a link to
   the feature page for the full workflow.

2. reference/tools-reference.md header said '54 built-in tools' — real
   count on main is 54, this branch adds browser_dialog so it's 55.
   Fixed the header.  (browser count was already correctly bumped
   11 -> 12 in the earlier docs commit.)

No code changes.

website/docs/user-guide/features/browser.md

@@ -355,7 +355,50 @@ browser_cdp(method="Runtime.evaluate",
 browser_cdp(method="Network.getAllCookies")
 ```
 
-Browser-level methods (`Target.*`, `Browser.*`, `Storage.*`) omit `target_id`. Page-level methods (`Page.*`, `Runtime.*`, `DOM.*`, `Emulation.*`) require a `target_id` from `Target.getTargets`. Each call is independent — sessions do not persist between calls.
+Browser-level methods (`Target.*`, `Browser.*`, `Storage.*`) omit `target_id`. Page-level methods (`Page.*`, `Runtime.*`, `DOM.*`, `Emulation.*`) require a `target_id` from `Target.getTargets`. Each stateless call is independent — sessions do not persist between calls.
+
+**Cross-origin iframes:** pass `frame_id` (from `browser_snapshot.frame_tree.children[]` where `is_oopif=true`) to route the CDP call through the supervisor's live session for that iframe. This is how `Runtime.evaluate` inside a cross-origin iframe works on Browserbase, where stateless CDP connections would hit signed-URL expiry. Example:
+
+```
+browser_cdp(
+  method="Runtime.evaluate",
+  params={"expression": "document.title", "returnByValue": True},
+  frame_id="<frame_id from browser_snapshot>",
+)
+```
+
+Same-origin iframes don't need `frame_id` — use `document.querySelector('iframe').contentDocument` from a top-level `Runtime.evaluate` instead.
+
+### `browser_dialog`
+
+Responds to a native JS dialog (`alert` / `confirm` / `prompt` / `beforeunload`). Before this tool existed, dialogs would silently block the page's JavaScript thread and subsequent `browser_*` calls would hang or throw; now the agent sees pending dialogs in `browser_snapshot` output and responds explicitly.
+
+**Workflow:**
+1. Call `browser_snapshot`. If a dialog is blocking the page, it shows up as `pending_dialogs: [{"id": "d-1", "type": "alert", "message": "..."}]`.
+2. Call `browser_dialog(action="accept")` or `browser_dialog(action="dismiss")`. For `prompt()` dialogs, pass `prompt_text="..."` to supply the response.
+3. Re-snapshot — `pending_dialogs` is empty; the page's JS thread has resumed.
+
+**Detection happens automatically** via a persistent CDP supervisor — one WebSocket per task that subscribes to Page/Runtime/Target events. The supervisor also populates a `frame_tree` field in the snapshot so the agent can see the iframe structure of the current page, including cross-origin (OOPIF) iframes.
+
+**Availability matrix:**
+
+| Backend | Detection via `pending_dialogs` | Response (`browser_dialog` tool) |
+|---|---|---|
+| Local Chrome via `/browser connect` or `browser.cdp_url` | ✓ | ✓ full workflow |
+| Browserbase | ✓ | ✓ full workflow (via injected XHR bridge) |
+| Camofox / default local agent-browser | ✗ | ✗ (no CDP endpoint) |
+
+**How it works on Browserbase.** Browserbase's CDP proxy auto-dismisses real native dialogs server-side within ~10ms, so we can't use `Page.handleJavaScriptDialog`. The supervisor injects a small script via `Page.addScriptToEvaluateOnNewDocument` that overrides `window.alert`/`confirm`/`prompt` with a synchronous XHR. We intercept those XHRs via `Fetch.enable` — the page's JS thread stays blocked on the XHR until we call `Fetch.fulfillRequest` with the agent's response. `prompt()` return values round-trip back into page JS unchanged.
+
+**Dialog policy** is configured in `config.yaml` under `browser.dialog_policy`:
+
+| Policy | Behavior |
+|--------|----------|
+| `must_respond` (default) | Capture, surface in snapshot, wait for explicit `browser_dialog()` call. Safety auto-dismiss after `browser.dialog_timeout_s` (default 300s) so a buggy agent can't stall forever. |
+| `auto_dismiss` | Capture, dismiss immediately. Agent still sees the dialog in `browser_state` history but doesn't have to act. |
+| `auto_accept` | Capture, accept immediately. Useful when navigating pages with aggressive `beforeunload` prompts. |
+
+**Frame tree** inside `browser_snapshot.frame_tree` is capped to 30 frames and OOPIF depth 2 to keep payloads bounded on ad-heavy pages. A `truncated: true` flag surfaces when limits were hit; agents needing the full tree can use `browser_cdp` with `Page.getFrameTree`.
 
 ## Practical Examples