[arnav] remove dead code identified by audit

Each removal verified by checking actual production callers (frontend,
electron, internal HTTP, MCP-server subprocesses) — not just test
references. Symbols whose only callers were tests are removed along
with those tests.

Production removals (~390 LOC):

- backend/main.py
  - websocket_session: drop `agent:edit_message` WS branch. Frontend
    only ever uses HTTP `POST /api/agents/sessions/{id}/edit_message`
    (frontend/src/shared/state/agentsSlice.ts); nothing on the wire
    sends a WS message of this type.

- backend/apps/agents/agent_manager.py
  - AgentManager._build_connected_tools_context (~80 LOC): zero call
    sites in production; the connected-tools system-prompt context is
    built inline in _compose_system_prompt now.
  - AgentManager._approx_tokens / _summarize_message_block: pure
    helpers whose only callers were tests. The compaction path uses
    LLM-driven _maybe_compact instead.

- backend/apps/agents/browser_agent.py
  - clear_browser_history: only used by tests. _browser_history is
    pruned via the size cap inline.
  - MODEL_MAP constant: never read.

- backend/apps/agents/mcp_preflight.py
  - DISCOVERY_SCAFFOLDING (~25-line system-prompt block): defined but
    never appended anywhere. The header comment described an intended
    use that the codebase no longer has.

- backend/apps/agents/providers/registry.py
  - thinking_params_for, _is_9router_available, OPENROUTER_BASE_URL,
    get_context_window: zero callers in production. Thinking-params
    routing is done by the provider classes directly; 9Router presence
    is detected at request time; context-window numbers are stamped
    onto sessions from BUILTIN_MODELS at launch.

- backend/apps/agents/tools/{base,web}.py
  - BaseTool.get_schema (abstract) + WebSearchTool/WebFetchTool
    overrides: production code in backend/apps/web/web.py instantiates
    these tools and only calls .execute(); the JSON-schema lives in
    the HTTP wrapper, not on the tool class.

- backend/apps/outputs/outputs.py
  - _resolve_model + MODEL_MAP: tests-only.
  - load_output: docstring claimed it was a public helper for "other
    modules" but no module imported it.

- backend/apps/service/client.py
  - set_user_id, the _user_id module global, and the dead cache short-
    circuit in _get_user_id: setter was tests-only. _get_user_id now
    reads user_email directly from settings on every call.

- backend/apps/settings/credentials.py
  - get_provider_credentials: zero callers. The sibling get_agent_sdk_env
    is kept (it has the explicit "Legacy helpers" keep-comment).

Test updates:

- test_agent_manager_unit.py: drop _approx_tokens / _summarize_message_block
  cases (5 tests), update module docstring index.
- test_browser_agent_unit.py: drop clear_browser_history cases (2 tests)
  and the unused _Boom helper class in the repr-fallback test.
- test_outputs_unit.py: drop _resolve_model / load_output cases
  (4 tests), update docstring + import list.
- test_v2_invariants.py: drop get_context_window tests + get_schema
  assertions on web tools (kept name + BaseTool inheritance checks).
- test_service.py: rewrite the 4 set_user_id-driven tests to drive
  user_id through settings.user_email instead, so _get_user_id's live
  envelope-stamping path stays covered.

Verification:
- ruff --select F401,F811,F841 backend/  →  clean.
- pytest backend/tests/ → 1167 passed, 1 deselected (pre-existing
  sandbox git test, unrelated). No tests dropped silently — every
  deletion is paired with the corresponding test removal/rewrite.
- Dead-code scan re-run: dead WS events 1→0, Tier-2 high-confidence
  14→11 (residue is SDK-callback `context` params + Pydantic `cls`
  validators — both false positives vulture can't see through),
  vulture total 165→145.

Total diff: -565 / +34 LOC across 15 files.

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/tests/test_service.py

@@ -45,7 +45,6 @@ def patch_settings(tmp_path):
 def fresh_client(tmp_path):
     import backend.apps.service.client as client
     client._install_id = None
-    client._user_id = None
     client._test_sink = None
     spool = tmp_path / "spool.db"
     with patch.object(client, "_spool_path", lambda: str(spool)):
@@ -78,35 +77,42 @@ def test_sync_carries_install_id(sink):
     assert body["client_state"]["install_id"] == "test-install-abc"
 
 
-def test_sync_carries_user_id_when_set(sink):
-    from backend.apps.service.client import sync, set_user_id
-    set_user_id("alice@example.com")
-    sync({})
+def test_sync_carries_user_id_when_set_in_settings(tmp_path, sink):
+    """User id is read from settings.user_email at envelope-build time."""
+    sf = tmp_path / "settings_with_email.json"
+    sf.write_text(json.dumps({
+        "installation_id": "test-install-abc",
+        "analytics_opt_in": True,
+        "user_email": "alice@example.com",
+    }))
+    import backend.apps.settings.settings as settings_mod
+    with patch.object(settings_mod, "SETTINGS_FILE", str(sf)):
+        from backend.apps.service.client import sync
+        sync({})
     _, body = sink[0]
     assert body["client_state"]["user_id"] == "alice@example.com"
 
 
-def test_sync_no_user_id_when_not_set(sink):
+def test_sync_no_user_id_when_email_not_set(sink):
+    """No user_email in settings → user_id absent from envelope."""
     from backend.apps.service.client import sync
     sync({})
     _, body = sink[0]
     assert "user_id" not in body["client_state"]
 
 
-def test_sync_user_id_cleared_with_none(sink):
-    from backend.apps.service.client import sync, set_user_id
-    set_user_id("alice")
-    set_user_id(None)
-    sync({})
-    _, body = sink[0]
-    assert "user_id" not in body["client_state"]
-
-
-def test_sync_user_id_cleared_with_empty(sink):
-    from backend.apps.service.client import sync, set_user_id
-    set_user_id("alice")
-    set_user_id("")
-    sync({})
+def test_sync_no_user_id_when_email_empty(tmp_path, sink):
+    """Empty-string user_email is treated like missing."""
+    sf = tmp_path / "settings_empty_email.json"
+    sf.write_text(json.dumps({
+        "installation_id": "test-install-abc",
+        "analytics_opt_in": True,
+        "user_email": "",
+    }))
+    import backend.apps.settings.settings as settings_mod
+    with patch.object(settings_mod, "SETTINGS_FILE", str(sf)):
+        from backend.apps.service.client import sync
+        sync({})
     _, body = sink[0]
     assert "user_id" not in body["client_state"]