feat(web): debug-surface parity — BifrostState + AdminEvents + Tools panes, PAD-poll fix, reasoning indicator

Bring the browser surface to TUI parity as the primary debug surface:

- Tools inventory (GET /sessions/{id}/tools) folded into the tools pane —
  what the LLM has at turn-fire, above the live tool events.
- BifrostState pane (GET /admin/sessions/{id}/bifrost) — admin-scoped
  dispatch state; the admin key stays server-side (app.state.admin_key),
  never reaches the browser (INV-003 precedent).
- AdminEvents pane (GET /admin/events SSE) — admin lifecycle, session-
  filtered SERVER-side (heartbeats + other-session events dropped); one
  fixed "admin_event" browser event so every type renders (no drops).
- PAD refresh: poll a window (1.5/3.5/6.5/10.5s) instead of a single 2s
  shot that raced the post-turn-async affect.emit (issue #18 foot-gun).
- Reasoning indicator: ephemeral "<Agent> is pondering…" in the transcript
  on `thinking` deltas, cleared when text begins — clearly non-engine.

Admin key wired through entrypoint -> create_app. 9 new respx/route tests
(admin-bearer override, filter unit, SSE stream-filter); 59 web tests pass.
Live-proven against ratatoskr:sindra (bifrost connected, both caps; 253
thinking events -> indicator fires; affect emit lands -> PAD poll catches it).

tests/test_web_server.py

@@ -1062,3 +1062,123 @@ class TestAffectStateEndpoint:
         resp = TestClient(app).get("/api/affect/ratatoskr:sindra")
         assert resp.status_code == 400
         assert resp.json()["error_code"] == "missing_end_user_id"
+
+
+class TestSessionToolsEndpoint:
+    """session_tools_endpoint — proxy owner-scoped GET /sessions/{id}/tools (#183)."""
+
+    @respx.mock
+    def test_happy_returns_inventory(self) -> None:
+        """happy [tracer]: 200 inventory → 200 verbatim."""
+        respx.get("https://w.example/sessions/s-1/tools").mock(
+            return_value=httpx.Response(200, json={
+                "agent_id": "ratatoskr:sindra",
+                "builtin_tools": ["echo"],
+                "bifrost_tools": [{"name": "memory.search"}],
+            })
+        )
+        from ratatoskr.web.server import create_app
+        resp = TestClient(create_app(_mock_client_factory())).get("/api/sessions/s-1/tools")
+        assert resp.status_code == 200
+        assert resp.json()["agent_id"] == "ratatoskr:sindra"
+
+    @respx.mock
+    def test_upstream_404_status_preserving_envelope(self) -> None:
+        """error: upstream 404 → 404 session_tools_unavailable envelope."""
+        respx.get("https://w.example/sessions/s-1/tools").mock(
+            return_value=httpx.Response(404, content=b"nope")
+        )
+        from ratatoskr.web.server import create_app
+        resp = TestClient(create_app(_mock_client_factory())).get("/api/sessions/s-1/tools")
+        assert resp.status_code == 404
+        assert resp.json()["error_code"] == "session_tools_unavailable"
+
+
+class TestSessionBifrostEndpoint:
+    """session_bifrost_endpoint — proxy admin-scoped GET /admin/sessions/{id}/bifrost (#176)."""
+
+    @respx.mock
+    def test_happy_overrides_with_admin_bearer(self) -> None:
+        """happy [tracer]: 200 state → 200; request carries the ADMIN bearer, not consumer."""
+        route = respx.get("https://w.example/admin/sessions/s-1/bifrost").mock(
+            return_value=httpx.Response(200, json={
+                "endpoint_url": "http://x:8392", "connected": True,
+                "capabilities_granted": ["memory", "affect"], "tools": [],
+            })
+        )
+        from ratatoskr.web.server import create_app
+        app = create_app(_mock_client_factory(), admin_key="adm-key")
+        resp = TestClient(app).get("/api/sessions/s-1/bifrost")
+        assert resp.status_code == 200
+        assert resp.json()["connected"] is True
+        assert route.calls.last.request.headers["Authorization"] == "Bearer adm-key"
+
+    def test_no_admin_key_fails_visible_400(self) -> None:
+        """error: no admin key configured → 400 admin_key_not_configured, no upstream call."""
+        from ratatoskr.web.server import create_app
+        app = create_app(_mock_client_factory())  # no admin_key
+        resp = TestClient(app).get("/api/sessions/s-1/bifrost")
+        assert resp.status_code == 400
+        assert resp.json()["error_code"] == "admin_key_not_configured"
+
+    @respx.mock
+    def test_upstream_404_status_preserving_envelope(self) -> None:
+        """error: upstream 404 (not bound) → 404 bifrost_state_unavailable envelope."""
+        respx.get("https://w.example/admin/sessions/s-1/bifrost").mock(
+            return_value=httpx.Response(404, content=b"nope")
+        )
+        from ratatoskr.web.server import create_app
+        app = create_app(_mock_client_factory(), admin_key="adm-key")
+        resp = TestClient(app).get("/api/sessions/s-1/bifrost")
+        assert resp.status_code == 404
+        assert resp.json()["error_code"] == "bifrost_state_unavailable"
+
+
+class TestAdminEventsEndpoint:
+    """admin_events_endpoint — SSE proxy of GET /admin/events, session-filtered (#11)."""
+
+    def test_filter_semantics(self) -> None:
+        """unit: heartbeats drop, system.* pass, else match on session_id."""
+        from ratatoskr.sse_client import AdminEvent
+        from ratatoskr.web.server import _admin_event_matches_web
+
+        def mk(t: str, sid: "str | None" = None) -> AdminEvent:
+            return AdminEvent(id=1, type=t, timestamp=None,
+                              data={"session_id": sid} if sid else {})
+
+        assert _admin_event_matches_web(mk("system.heartbeat"), "s-1") is False
+        assert _admin_event_matches_web(mk("system.degraded"), "s-1") is True
+        assert _admin_event_matches_web(mk("session.created", "s-1"), "s-1") is True
+        assert _admin_event_matches_web(mk("session.created", "other"), "s-1") is False
+        assert _admin_event_matches_web(mk("session.created", "s-1"), None) is False
+
+    def test_no_admin_key_fails_visible_400(self) -> None:
+        """error: no admin key → 400 admin_key_not_configured (no stream opened)."""
+        from ratatoskr.web.server import create_app
+        app = create_app(_mock_client_factory())
+        resp = TestClient(app).get("/api/admin/events?session_id=s-1")
+        assert resp.status_code == 400
+        assert resp.json()["error_code"] == "admin_key_not_configured"
+
+    @respx.mock
+    def test_streams_filtered_events_fixed_name(self) -> None:
+        """happy: SSE → only session-matching + system.* forwarded, as `admin_event`."""
+        stream = (
+            b'event: session.created\n'
+            b'data: {"type":"session.created","data":{"session_id":"s-1"}}\n\n'
+            b'event: system.heartbeat\n'
+            b'data: {"type":"system.heartbeat","data":{}}\n\n'
+            b'event: turn.started\n'
+            b'data: {"type":"turn.started","data":{"session_id":"other"}}\n\n'
+            b'event: system.degraded\n'
+            b'data: {"type":"system.degraded","data":{}}\n\n'
+        )
+        respx.get("https://w.example/admin/events").mock(return_value=_sse_resp(stream))
+        from ratatoskr.web.server import create_app
+        app = create_app(_mock_client_factory(), admin_key="adm-key")
+        body = TestClient(app).get("/api/admin/events?session_id=s-1").text
+        assert "event: admin_event" in body          # fixed browser-facing name
+        assert '"type": "session.created"' in body    # matches active session → forwarded
+        assert "system.degraded" in body              # system.* → forwarded
+        assert "system.heartbeat" not in body         # heartbeat → dropped
+        assert "turn.started" not in body             # other session → dropped