[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_outputs_unit.py

@@ -4,12 +4,12 @@ These exercise pure logic and pydantic models without booting FastAPI.
 The integration surface (routes) lives in `test_api_outputs.py`.
 
 Covers:
-  - outputs.py helpers: _resolve_model, _validate_against_schema,
+  - outputs.py helpers: _validate_against_schema,
     _build_data_injection, _inject_data_into_html,
     _inject_token_into_relative_urls (every branch in
     _ABSOLUTE_URL_PREFIXES + token-already-present + fragment),
     _decode_data_param, _walk_directory.
-  - On-disk store helpers: _save / _load / load_output / _load_all.
+  - On-disk store helpers: _save / _load / _load_all.
   - Models: legacy `frontend_code` / `backend_code` / `schema_json`
     migration into `files`, plus the property accessors.
   - executor.execute_backend_code: happy path, stdout capture,
@@ -35,12 +35,9 @@ from backend.apps.outputs.outputs import (
     _inject_token_into_relative_urls,
     _load,
     _load_all,
-    _resolve_model,
     _save,
     _validate_against_schema,
     _walk_directory,
-    load_output,
-    MODEL_MAP,
 )
 from backend.apps.outputs.models import (
     AutoRunConfig,
@@ -55,22 +52,6 @@ from backend.apps.outputs.executor import (
 )
 
 
-# ---------------------------------------------------------------------------
-# _resolve_model
-# ---------------------------------------------------------------------------
-
-
-def test_resolve_model_known_short_name():
-    assert _resolve_model("sonnet") == MODEL_MAP["sonnet"]
-    assert _resolve_model("opus") == MODEL_MAP["opus"]
-    assert _resolve_model("haiku") == MODEL_MAP["haiku"]
-
-
-def test_resolve_model_unknown_passthrough():
-    assert _resolve_model("claude-3-5-haiku") == "claude-3-5-haiku"
-    assert _resolve_model("") == ""
-
-
 # ---------------------------------------------------------------------------
 # _validate_against_schema
 # ---------------------------------------------------------------------------
@@ -272,7 +253,7 @@ def test_walk_directory_skips_unreadable(tmp_path):
 
 
 # ---------------------------------------------------------------------------
-# _load_all / _save / _load / load_output
+# _load_all / _save / _load
 # ---------------------------------------------------------------------------
 
 
@@ -291,18 +272,6 @@ def test_load_missing_raises_404(tmp_data_dirs):
     assert exc.value.status_code == 404
 
 
-def test_load_output_returns_none_for_missing(tmp_data_dirs):
-    assert load_output("does-not-exist") is None
-
-
-def test_load_output_returns_resolved(tmp_data_dirs):
-    out = Output(name="x")
-    _save(out)
-    fetched = load_output(out.id)
-    assert fetched is not None
-    assert fetched.name == "x"
-
-
 def test_load_all_picks_up_saved(tmp_data_dirs):
     a = Output(name="a")
     b = Output(name="b")