phase: 178_split_thinking_levels

## Phase 178 — final verification pass: 100% green

**Verified (all 5 tasks complete in `complete/178_split_thinking_levels/`):**
- `config.py` rename (`llm_chat_thinking_level` default `low`) + new `llm_summary_thinking_level` (default `""`); two `CATALOG` rows; `.env.example` replaced; no stale old-key references (only intentional negative pins in tests)
- Wire split: `chat_stream()` → chat level, one-shot `chat()` → summary level (absent `extra_body` when empty); per-turn line reads chat level only

**Gates:**
- `uv run pytest -k "config and thinking" -v` → 7 passed (defaults + env overrides both knobs)
- `uv run pytest` (unit + integration) → 4170 tests, exit 0; `--cov=app` → **99%** (>90% ✓)
- `uv run ruff check .` clean; `uv run pyright` clean
- `uv run pytest tests/e2e/test_split_thinking_levels.py -v --no-cov` → 3 passed in isolation
- `test_admin_settings_panel.py` + `test_admin_settings_layout.py` → 17 passed in isolation

**Completion criteria:** all 6 test/doc criteria ✅ (admin GET lists both keys, old key gone — integration + E2E pins); commit + phase-dir move = harness's job.

**Documentation:** README.md — both new env vars correctly documented in the LLM (aipi) table with defaults/wire-mapping/off-rule, defaults match `config.py`, all `.env.example` vars covered: verified consistent, no changes needed. AGENTS.md — all referenced files/commands verified to exist, no phase-178 impact (no UI code change, A4): verified consistent, no changes needed.

**Decisions:** none required — no live changes made (E2E booted its own app subprocess against the existing DB).

**Next pending phase:** none — 178 is the last phase in `todo/`.

app/rag/llm.py

@@ -10,13 +10,18 @@ pipeline. Chat streaming yields typed :class:`StreamPiece` values
 its reasoning as ``delta.reasoning_content`` chunks (deepseek/litellm
 wire convention, verified live 2026-08-23) **before** the answer's
 ``delta.content`` chunks, and reasoning counts against ``max_tokens``
-(an answer can in principle be empty). The operator's thinking level
-(phase 172, ``BOR_LLM_THINKING_LEVEL``, default ``low``) rides every
-chat-completions request (one-shot ``chat`` and streaming ``chat_stream``)
-as the top-level ``reasoning_effort`` parameter (via the SDK's
-``extra_body``); an empty value is the off switch — the parameter is
-absent, the request is byte-identical to pre-phase-172, and the
-embeddings path never carries it.
+(an answer can in principle be empty). The operator's thinking levels
+(phase 178) ride chat-completions requests as the top-level
+``reasoning_effort`` parameter (via the SDK's ``extra_body``), split
+per surface (A3): the chat turn's level (``BOR_LLM_CHAT_THINKING_LEVEL``,
+default ``low``; the phase-172 knob, renamed) rides streaming
+``chat_stream``, and the one-shot level (``BOR_LLM_SUMMARY_THINKING_LEVEL``,
+default EMPTY = off) rides ``chat`` — document summaries, folder
+summaries, the KB overview, and the ``check_models`` probe (a
+reachability ping, off by default, no special-casing). An empty value is
+the off switch — the parameter is absent (never a literal ``"none"``),
+the request is byte-identical to pre-phase-172, and the embeddings path
+never carries it.
 
 Fail-loud rule (PLAN A6): the ``chunks.embedding`` column is fixed at 768
 dimensions when the table is created, so a model that returns a different
@@ -46,15 +51,17 @@ if TYPE_CHECKING:
 logger = logging.getLogger("app.llm")
 
 
-def _thinking_extra_body(settings: Settings) -> dict[str, str] | None:
-    """The phase-172 thinking level as the chat-completions extra body.
+def _thinking_extra_body(level: str) -> dict[str, str] | None:
+    """The thinking level as the chat-completions extra body (phase 178).
 
     Non-empty (trimmed) value → ``{"reasoning_effort": <value>}`` (the
-    OpenAI-standard top-level parameter, A1); empty/whitespace → ``None``
-    (the off switch — the parameter is ABSENT from the request, A2).
+    OpenAI-standard top-level parameter, phase-172 A1); empty /
+    whitespace → ``None`` (the off switch — the parameter is ABSENT
+    from the request, phase-172 A2; never a literal ``"none"`` or
+    ``"off"``).
     """
-    level = settings.llm_thinking_level.strip()
-    return {"reasoning_effort": level} if level else None
+    trimmed = level.strip()
+    return {"reasoning_effort": trimmed} if trimmed else None
 
 
 class EmbeddingError(RuntimeError):
@@ -429,7 +436,7 @@ class LLMClient:
         ``finish_reason``) for an empty reply — the one failure class
         :meth:`chat` retries — and :class:`LLMError` for everything else.
         """
-        extra = _thinking_extra_body(self.settings)
+        extra = _thinking_extra_body(self.settings.llm_summary_thinking_level)
         extra_kwargs: dict[str, Any] = (
             {"extra_body": extra} if extra is not None else {}
         )
@@ -440,8 +447,11 @@ class LLMClient:
                 temperature=0.2,
                 max_tokens=2048,
                 stream=False,
-                # Phase 172 (A1/A2): the thinking level rides as
-                # reasoning_effort; the key is absent (never None) when off.
+                # Phase 178 (A3/A2): the **summary** level rides as
+                # reasoning_effort (document summaries, folder summaries,
+                # KB overview, the ``check_models`` probe); the key is
+                # absent (never None) when off — the default (empty)
+                # keeps one-shot requests byte-identical to pre-phase-172.
                 **extra_kwargs,
             )
         except LLMError:
@@ -622,8 +632,10 @@ class LLMClient:
         }
         if tools is not None:
             kwargs["tools"] = tools
-        if (extra := _thinking_extra_body(self.settings)) is not None:
-            # Phase 172 (A1/A2): the thinking level rides as
+        if (
+            extra := _thinking_extra_body(self.settings.llm_chat_thinking_level)
+        ) is not None:
+            # Phase 178 (A3/A2): the **chat** level rides as
             # reasoning_effort; the key is absent (never None) when off.
             kwargs["extra_body"] = extra
         stream: AsyncStream[ChatCompletionChunk] | None = None