fix(streaming): pass agent.reasoning_effort into WebUI agents (salvages #1531)

Spliced from #1531 by @Asunfly: take Change-1 only (the actual bug fix +
cache signature inclusion) and skip Change-2 (auxiliary title-route
extra_body change) which is a separate scope concern.

## What

Two surgical fixes in api/streaming.py:

1. Line 1820 — `_cfg.cfg.get(...)` → `_cfg.get(...)`. `get_config()` returns
   a plain dict (not a wrapper exposing `.cfg`).  The buggy line raised
   AttributeError that the surrounding try/except swallowed, so
   `_reasoning_config` was always None regardless of what `/reasoning
   <level>` had been set to.  Verified locally — `api/streaming.py:1959`
   already correctly used `_cfg.get(...)` in the same function, so the
   same `_cfg` was being read two different ways in one file.

2. Line 1888 — added `_reasoning_config or {}` to `_sig_blob`.  Without
   this, switching effort mid-session would fail to take effect because
   the per-session agent cache key would still match the old entry.
   Mirrors how `resolved_provider` / `resolved_base_url` already
   participate in the signature.

## Why splice instead of merge #1531 directly

@Asunfly force-pushed a Change-2 onto #1531 after the original review
that removes `extra_body={"reasoning": {"enabled": False}}` from
`generate_title_raw_via_aux` (the auxiliary title-generation route).
That intent is reasonable (let operator-configured `extra_body.reasoning`
flow through to the title route) but it touches a different surface and
deserves its own PR.

The narrow concern is operators who selected a reasoning-capable
auxiliary title model without explicitly setting
`reasoning.enabled=False` in the task config — pre-Change-2 the WebUI
defended against accidental reasoning on the title hot path; post-Change-2
those configs would reason on every new conversation`s title, with cost
and latency implications.

## What is NOT in this PR

- The `generate_title_raw_via_aux` extra_body refactor (Change-2 from #1531).
- The `test_does_not_override_configured_reasoning_extra_body` test (guards
  Change-2). Asunfly can re-open that as its own focused PR.

## Tests

Two new R17b/R17c regression assertions in tests/test_regressions.py:

- `test_streaming_reads_reasoning_effort_from_config_dict` — static-source
  guard: `_cfg.cfg` must not return to streaming.py
- `test_streaming_agent_cache_signature_includes_reasoning_config` —
  catches removal of `_reasoning_config` from `_sig_blob`

## Closes

- Closes #1531 (the Change-1 portion ships here; Asunfly can re-open
  Change-2 as a separate PR if desired)

Co-authored-by: Asunfly <[email protected]>

api/streaming.py

@@ -1817,7 +1817,7 @@ def _run_agent_streaming(
             # the key is absent or invalid, pass None → agent uses its default.
             try:
                 from api.config import parse_reasoning_effort as _parse_reff
-                _effort_cfg = _cfg.cfg.get('agent', {}) if isinstance(_cfg.cfg, dict) else {}
+                _effort_cfg = _cfg.get('agent', {}) if isinstance(_cfg, dict) else {}
                 _effort_raw = _effort_cfg.get('reasoning_effort') if isinstance(_effort_cfg, dict) else None
                 _reasoning_config = _parse_reff(_effort_raw)
             except Exception:
@@ -1885,6 +1885,7 @@ def _run_agent_streaming(
                     _max_tokens_cfg or '',
                     _fallback_resolved or {},
                     sorted(_toolsets) if _toolsets else [],
+                    _reasoning_config or {},
                 ], sort_keys=True)
                 _agent_sig = _hashlib.sha256(_sig_blob.encode()).hexdigest()[:16]
 

tests/test_regressions.py

@@ -608,6 +608,38 @@ def test_streaming_bridge_accepts_current_tool_progress_callback_signature(clean
         "streaming.py must emit live tool completion SSE events"
 
 
+def test_streaming_reads_reasoning_effort_from_config_dict(cleanup_test_sessions):
+    """R17b: WebUI must read agent.reasoning_effort from the dict returned by get_config().
+
+    `get_config()` returns a plain dict (not a wrapper exposing `.cfg`).  The
+    pre-fix line `_cfg.cfg.get('agent', {})` raised AttributeError that the
+    surrounding try/except swallowed, so `_reasoning_config` was always None
+    regardless of what `/reasoning <level>` had been set to.  This static
+    source assertion pins the fix because the runtime symptom is silent.
+    """
+    src = (REPO_ROOT / "api/streaming.py").read_text()
+    assert "_cfg.cfg" not in src, \
+        "get_config() returns a dict; accessing _cfg.cfg drops reasoning_config to None"
+    assert "_cfg.get('agent', {})" in src or '_cfg.get("agent", {})' in src, \
+        "streaming.py must read agent.reasoning_effort via the config dict"
+
+
+def test_streaming_agent_cache_signature_includes_reasoning_config(cleanup_test_sessions):
+    """R17c: changing reasoning effort mid-session must rebuild the cached per-session agent.
+
+    Without `_reasoning_config` participating in `_sig_blob`, the cache key
+    matches the old entry and the operator's `/reasoning xhigh` change has
+    no effect on the live session.
+    """
+    src = (REPO_ROOT / "api/streaming.py").read_text()
+    start = src.find("_sig_blob = _json.dumps")
+    end = src.find("_agent_sig", start)
+    assert start >= 0 and end > start, "agent cache signature block not found"
+    sig_block = src[start:end]
+    assert "_reasoning_config" in sig_block, \
+        "agent cache signature must include reasoning_config so xhigh/medium changes take effect"
+
+
 def test_messages_js_supports_live_reasoning_and_tool_completion(cleanup_test_sessions):
     """R18: messages.js must render live reasoning and react to tool completion events.
     Without these handlers, the operator only sees generic Thinking… or nothing