diff --git a/tests/test_judge.py b/tests/test_judge.py
index 904eb6ec..4c2a8738 100644
--- a/tests/test_judge.py
+++ b/tests/test_judge.py
@@ -949,6 +949,29 @@ class TestModelAliasResolution:
         # alias's configured value, inherited through the lane.
         assert alias_provider.create_completion.call_args.kwargs["temperature"] == 0.3
 
+    def test_constructor_resolves_from_one_config_fetch(self):
+        """The constructor consumes the ModelConfig that registry.resolve()
+        already returned (the ``cfg=`` pass-through) — ZERO independent
+        get_config fetches, so a registry hot-reload between two lookups
+        cannot bind the resolved client/window to a different capability
+        generation."""
+        alias_provider = _make_mock_provider(response_content=_good_verdict_json())
+        registry = self._make_alias_registry(
+            "judge-mini",
+            alias_provider,
+            MagicMock(base_url="https://a/v1", api_key="k"),
+            "local-9b",
+        )
+        IntentJudge(
+            config=JudgeConfig(enabled=True, model="judge-mini"),
+            session_provider=_make_mock_provider(),
+            session_client=MagicMock(base_url="https://s/v1", api_key="s"),
+            session_model="session-model",
+            session_capabilities=MagicMock(context_window=100_000),
+            model_registry=registry,
+        )
+        assert registry.get_config.call_count == 0
+
     def test_fallback_threads_session_capabilities_to_wire(self):
         """No judge alias → the judge inherits the session model AND the
         session's resolved capabilities, threaded to ``create_completion``."""
diff --git a/tests/test_model_turn.py b/tests/test_model_turn.py
index d7486e12..0cdd9da7 100644
--- a/tests/test_model_turn.py
+++ b/tests/test_model_turn.py
@@ -368,12 +368,50 @@ def test_temperature_caller_value_wins_over_lane() -> None:
     assert provider.calls[0]["temperature"] == 0.9
 
 
-def test_temperature_omitted_when_unresolved() -> None:
-    # No caller value, no lane value → the kwarg is omitted entirely and
-    # the provider default applies (house rule: code never pins one).
+def test_temperature_unresolved_passes_none_and_wire_omits_it() -> None:
+    # No caller value, no lane value → model_turn passes temperature=None,
+    # and the PROVIDER layer omits the field from the wire so the server
+    # default applies (house rule: code never pins one).  Both halves are
+    # pinned: a Python-signature default of 0.5 anywhere on this path is a
+    # hidden universal pin — the exact bug the second xhigh review caught.
     provider = _FakeProvider([CompletionResult(content="")])
     model_turn(_lane(provider), [Turn.user("x")])
-    assert "temperature" not in provider.calls[0]
+    assert provider.calls[0]["temperature"] is None
+
+    from turnstone.core.providers._openai_common import apply_temperature
+
+    kwargs: dict[str, Any] = {}
+    apply_temperature(kwargs, ModelCapabilities(), None, "medium")
+    assert "temperature" not in kwargs  # None never reaches the wire
+    apply_temperature(kwargs, ModelCapabilities(), 1.0, "medium")
+    assert kwargs["temperature"] == 1.0  # a real value still does
+
+
+def test_resolve_lane_global_config_store_rung() -> None:
+    # ModelConfig.temperature=None means "use the global default from
+    # ConfigStore" (the documented ladder) — resolve_lane climbs it.
+    provider = _FakeProvider([])
+    registry = _fake_registry(temperature=None)
+    store = SimpleNamespace(get=lambda key: 1.0 if key == "model.temperature" else None)
+    lane = resolve_lane(provider, object(), "m", alias="ali", registry=registry, config_store=store)
+    assert lane.temperature == 1.0
+    # The per-model value wins over the global rung.
+    registry2 = _fake_registry(temperature=0.3)
+    lane2 = resolve_lane(
+        provider, object(), "m", alias="ali", registry=registry2, config_store=store
+    )
+    assert lane2.temperature == 0.3
+
+
+def test_model_turn_fetches_config_once_per_call() -> None:
+    # ONE get_config per plant call feeds both live flags (replay + vLLM
+    # attach) — a hot-reload between them cannot mix config generations
+    # within a single request.
+    registry = _fake_registry(replay=True)
+    provider = _FakeProvider([CompletionResult(content="")])
+    lane = _lane(provider, alias="ali", registry=registry)
+    model_turn(lane, [Turn.user("x")])
+    assert registry.get_config.call_count == 1
 
 
 def test_resolve_lane_inherits_config_temperature() -> None:
diff --git a/tests/test_session.py b/tests/test_session.py
index b8e7fe77..41da4122 100644
--- a/tests/test_session.py
+++ b/tests/test_session.py
@@ -7715,6 +7715,21 @@ def test_web_fetch_extraction_caps_max_tokens_to_window_reserve():
     assert kw["max_tokens"] == 2048  # context_window // 4, not the 16384 session value
 
 
+def test_resolve_capabilities_raises_loudly_on_registry_failure():
+    """The session lane must NOT silently cache degraded static-table caps:
+    a get_config failure on the session's own alias PROPAGATES (pre-#827
+    semantics) — the never-crash defensive fetch is a judge-constructor
+    property, and applying it here would let one transient registry hiccup
+    pin wrong capabilities (window, thinking mode, token param) onto the
+    session cache for its whole lifetime."""
+    session = _make_session()
+    session._registry = MagicMock()
+    session._registry.get_config.side_effect = ValueError("Unknown model alias")
+    session._model_alias = "primary"
+    with pytest.raises(ValueError):
+        session._get_capabilities()
+
+
 def test_record_aux_usage_skips_when_usage_missing():
     """A provider that reports no usage object must not emit a phantom
     zero-token row."""
diff --git a/tests/test_session_chat_reasoning_replay.py b/tests/test_session_chat_reasoning_replay.py
index b3cd5106..40d6267e 100644
--- a/tests/test_session_chat_reasoning_replay.py
+++ b/tests/test_session_chat_reasoning_replay.py
@@ -27,6 +27,7 @@ import httpx
 import pytest
 
 from tests._session_helpers import make_session as _make_session
+from tests._session_helpers import mock_completion_result
 from turnstone.core.providers._anthropic import AnthropicProvider
 from turnstone.core.providers._openai_chat import OpenAIChatCompletionsProvider
 from turnstone.core.providers._openai_responses import OpenAIResponsesProvider
@@ -403,14 +404,7 @@ class TestCallSitesInvokeMaybeAttach:
 
         def capture_completion(**kwargs: Any) -> Any:
             captured.update(kwargs)
-            return SimpleNamespace(
-                content="",
-                tool_calls=None,
-                finish_reason="stop",
-                usage=None,
-                provider_blocks=[],
-                reasoning="",
-            )
+            return mock_completion_result("")
 
         provider = OpenAIChatCompletionsProvider()
         provider.create_completion = capture_completion  # type: ignore[method-assign]
diff --git a/tests/test_session_replay_reasoning.py b/tests/test_session_replay_reasoning.py
index 91e5fcde..39a96a69 100644
--- a/tests/test_session_replay_reasoning.py
+++ b/tests/test_session_replay_reasoning.py
@@ -27,6 +27,7 @@ from typing import Any
 from unittest.mock import MagicMock, patch
 
 from tests._session_helpers import make_session as _make_session
+from tests._session_helpers import mock_completion_result
 from turnstone.core.trajectory import Turn
 
 
@@ -627,14 +628,7 @@ class TestUtilityCompletionPassesFlag:
 
         def capture_completion(**kwargs: Any) -> Any:
             captured.update(kwargs)
-            return SimpleNamespace(
-                content="title",
-                tool_calls=None,
-                finish_reason="stop",
-                usage=None,
-                provider_blocks=[],
-                reasoning="",
-            )
+            return mock_completion_result("title")
 
         mock_provider = MagicMock()
         mock_provider.create_completion = capture_completion
diff --git a/tests/test_session_synth_reasoning_block.py b/tests/test_session_synth_reasoning_block.py
index a6ca7784..7f0cd656 100644
--- a/tests/test_session_synth_reasoning_block.py
+++ b/tests/test_session_synth_reasoning_block.py
@@ -1,14 +1,16 @@
-"""Tests for ChatSession synthetic ``reasoning_text`` block stamping (Phase 3 path 3).
+"""Tests for the synthetic ``reasoning_text`` block stamping (Phase 3 path 3).
 
 Path 3 covers OpenAI Chat Completions endpoints — vLLM with
 ``--reasoning-parser``, llama.cpp with ``reasoning_format``, Gemini's
 ``/v1beta/openai/`` endpoint, and any other server that surfaces
 ``delta.reasoning_content`` Pydantic extras.  These have no native
-provider_blocks shape on the wire, so ``ChatSession._stream_response``
-captures the streamed reasoning text into ``reasoning_parts`` and
-``_maybe_synth_reasoning_block`` stamps it onto ``_provider_content``
-as a synthetic ``{type: "reasoning_text"}`` block at the end of the
-turn.
+provider_blocks shape on the wire, so the captured reasoning text is
+stamped onto ``_provider_content`` as a synthetic
+``{type: "reasoning_text"}`` block at the end of the turn by
+``model_turn.synth_reasoning_block`` — the one synthesizer every lane
+runs (the main loop reaches it through ``ChatSession._stream_response``
+→ ``_finalize_provider_blocks``; agents and judges through
+``model_turn``).
 
 These tests pin:
 1. The synthesizer fires only when no native blocks were emitted AND
diff --git a/turnstone/core/judge.py b/turnstone/core/judge.py
index 3540b082..c0bc1ec2 100644
--- a/turnstone/core/judge.py
+++ b/turnstone/core/judge.py
@@ -977,12 +977,15 @@ class IntentJudge:
         rule_registry: Any | None = None,
         model_registry: Any | None = None,
         session_model_alias: str = "",
+        config_store: Any | None = None,
     ) -> None:
         self._config = config
         self._rule_registry = rule_registry
-        # Carried into the per-evaluation ModelLane so extra_params and the
-        # live operator flags resolve from the registry like every other lane.
+        # Carried into the per-evaluation ModelLane so extra_params, the
+        # live operator flags, and the temperature ladder (per-model value →
+        # global ``model.temperature``) resolve like every other lane.
         self._model_registry = model_registry
+        self._config_store = config_store
         # The caller (ChatSession) resolves the session model's real caps from
         # _get_capabilities (config/registry-aware) and passes them in; they are
         # this judge's wire capabilities and window when it inherits the session
@@ -1022,8 +1025,12 @@ class IntentJudge:
                     # sized into the judge's window budget right below (the
                     # static caps table reports 200000 for local models, which
                     # would silently over-budget them).
+                    # ``cfg=model_cfg`` reuses the config resolve() already
+                    # fetched — one lookup, one generation; a hot-reload
+                    # between two fetches cannot mix client/window with
+                    # foreign capability overrides.
                     self._capabilities = resolve_capabilities(
-                        self._provider, self._model, config.model, model_registry
+                        self._provider, self._model, config.model, model_registry, cfg=model_cfg
                     )
                     # Use the registry's per-model context window, NOT
                     # ``provider.get_capabilities().context_window``: the static
@@ -1329,8 +1336,14 @@ class IntentJudge:
             tools = list(_JUDGE_TOOL_SCHEMAS)
 
         # The judge's resolved lane for this evaluation: fresh client per run
-        # (thread isolation), constructor-resolved capabilities, extra_params
-        # and live operator flags from the registry like every other lane.
+        # (thread isolation), extra_params / live flags / temperature ladder
+        # from the registry like every other lane.  Capabilities are
+        # DELIBERATELY the constructor-frozen set (not re-resolved here):
+        # the judge's window budget was sized against them at construction,
+        # and the session swaps the whole judge on model/credential change —
+        # an in-place capabilities edit to the same alias applies on the
+        # next judge swap, keeping caps and window from ever disagreeing
+        # within one judge lifetime.
         lane = resolve_lane(
             self._provider,
             client,
@@ -1338,6 +1351,7 @@ class IntentJudge:
             alias=self._alias,
             registry=self._model_registry,
             capabilities=self._capabilities,
+            config_store=self._config_store,
         )
 
         # Multi-turn judge loop
diff --git a/turnstone/core/model_turn.py b/turnstone/core/model_turn.py
index 61162352..d56e5168 100644
--- a/turnstone/core/model_turn.py
+++ b/turnstone/core/model_turn.py
@@ -98,7 +98,7 @@ def resolve_capabilities(
     alias: str,
     registry: ModelRegistry | None,
     *,
-    cfg: Any | None = None,
+    cfg: Any | EllipsisType = ...,
 ) -> ModelCapabilities:
     """Provider static capabilities, merged with registry alias overrides.
 
@@ -109,14 +109,16 @@ def resolve_capabilities(
     judges' old mirror — capability resolution must never crash a judge
     turn).  *cfg* accepts a pre-fetched ModelConfig so a caller resolving
     several lane facets reads ONE config generation (see
-    :func:`resolve_lane`); omitted, the config is fetched defensively.
+    :func:`resolve_lane`); ``None`` means "fetched and missed" (no second
+    lookup), and the ``...`` sentinel default means "fetch defensively for
+    me".
     NOTE the window landmine documented on #826:
     ``ModelConfig.context_window`` is a separate top-level column and is
     deliberately NOT merged here; callers that need the operator window
     must read it off the config themselves.
     """
     caps = provider.get_capabilities(model)
-    if cfg is None:
+    if cfg is ...:
         cfg = _get_config_or_none(registry, alias)
     if cfg is not None:
         overrides_raw = getattr(cfg, "capabilities", None)
@@ -133,7 +135,7 @@ def provider_extra_params(
     registry: ModelRegistry | None,
     alias: str,
     *,
-    cfg: Any | None = None,
+    cfg: Any | EllipsisType = ...,
 ) -> dict[str, Any] | None:
     """Operator ``server_compat["extra_body"]`` pins for the OpenAI-shaped
     lanes (and the anthropic-compatible lane, whose SDK also takes
@@ -147,7 +149,7 @@ def provider_extra_params(
 
     if provider.provider_name not in ("openai", "openai-compatible", "anthropic-compatible"):
         return None
-    if cfg is None:
+    if cfg is ...:
         cfg = _get_config_or_none(registry, alias)
     server_compat = getattr(cfg, "server_compat", None) if cfg is not None else None
     extra = merge_server_compat(None, server_compat if isinstance(server_compat, dict) else {})
@@ -184,6 +186,7 @@ def resolve_replay_reasoning_to_model(
     alias: str,
     *,
     caps: ModelCapabilities | None = None,
+    cfg: Any | EllipsisType = ...,
 ) -> bool:
     """Operator ``ModelConfig.replay_reasoning_to_model`` for an alias.
 
@@ -197,13 +200,15 @@ def resolve_replay_reasoning_to_model(
     ``caps.supports_reasoning_replay`` (mirrors the gate in
     ``OpenAIResponsesProvider._build_kwargs``); omitted, the operator flag
     passes through unchanged for callers that haven't threaded caps.
+    *cfg* follows the shared sentinel contract (``...`` = fetch for me,
+    ``None`` = fetched-and-missed) so ``model_turn`` reads ONE config
+    generation per call across both per-call flags.
     """
-    if not registry or not alias:
-        return False
-    try:
-        operator_on = bool(registry.get_config(alias).replay_reasoning_to_model)
-    except Exception:
+    if cfg is ...:
+        cfg = _get_config_or_none(registry, alias)
+    if cfg is None:
         return False
+    operator_on = bool(getattr(cfg, "replay_reasoning_to_model", False))
     if caps is None:
         return operator_on
     return operator_on and bool(caps.supports_reasoning_replay)
@@ -214,6 +219,8 @@ def maybe_attach_vllm_chat_reasoning(
     provider: LLMProvider,
     registry: ModelRegistry | None,
     alias: str,
+    *,
+    cfg: Any | EllipsisType = ...,
 ) -> list[dict[str, Any]]:
     """Phase 5 of reasoning persistence: attach vLLM's non-standard
     ``reasoning`` field to outgoing assistant messages so a vLLM-served
@@ -235,7 +242,8 @@ def maybe_attach_vllm_chat_reasoning(
 
     if not isinstance(provider, OpenAIChatCompletionsProvider):
         return messages
-    cfg = _get_config_or_none(registry, alias)
+    if cfg is ...:
+        cfg = _get_config_or_none(registry, alias)
     if cfg is None:
         return messages
     # Both gate fields read off the single ``cfg`` fetch (no second
@@ -289,6 +297,7 @@ def resolve_lane(
     registry: ModelRegistry | None = None,
     capabilities: ModelCapabilities | None = None,
     extra_params: dict[str, Any] | None | EllipsisType = ...,
+    config_store: Any | None = None,
 ) -> ModelLane:
     """Build a :class:`ModelLane`, resolving what the caller didn't supply.
 
@@ -298,6 +307,15 @@ def resolve_lane(
     pass.  ``...`` (the sentinel default) means "resolve for me" —
     ``None`` is a valid resolved value for *extra_params*.
 
+    The lane temperature climbs the documented ladder
+    (``ModelConfig.temperature`` docstring: "None = use global default
+    from ConfigStore"): the alias's per-model value, else the operator's
+    global ``model.temperature`` when *config_store* is supplied, else
+    ``None`` — which the providers translate to omitting the field so the
+    SERVER default applies.  This mirrors the session_factory / ``/model``
+    switch resolution so a judge or single-shot lane samples exactly like
+    the main loop on the same model.
+
     All resolved facets read ONE defensively-fetched ModelConfig, so a
     registry hot-reload mid-resolution cannot mix config generations, and
     an alias that raced away degrades every facet to its miss behavior
@@ -310,6 +328,15 @@ def resolve_lane(
         if extra_params is ...
         else extra_params
     )
+    temperature = getattr(cfg, "temperature", None) if cfg is not None else None
+    if temperature is None and config_store is not None:
+        try:
+            temperature = config_store.get("model.temperature")
+        except Exception:
+            # Best-effort global rung — a broken store degrades to the
+            # server default, never crashes lane resolution.
+            log.debug("config_store model.temperature lookup failed", exc_info=True)
+            temperature = None
     return ModelLane(
         provider=provider,
         client=client,
@@ -318,7 +345,7 @@ def resolve_lane(
         capabilities=caps,
         extra_params=extra,
         registry=registry,
-        temperature=getattr(cfg, "temperature", None) if cfg is not None else None,
+        temperature=temperature,
     )
 
 
@@ -496,6 +523,21 @@ class ModelTurnResult:
         return self.turn.text
 
 
+def cap_tool_calls(result: ModelTurnResult, max_calls: int) -> tuple[list[dict[str, Any]], Turn]:
+    """Degenerate-repetition guard shared by the bounded tool loops (eval,
+    optimizer analyst): cap the mirror at *max_calls* and return the turn to
+    append.  A capped turn is rebuilt WITHOUT its native lane — a full lane
+    beside a truncated mirror would replay orphan native tool blocks the
+    mirror no longer carries (the same native↔mirror rule
+    :func:`finalize_provider_blocks` enforces).
+    """
+    capped = result.tool_calls[:max_calls]
+    turn = result.turn
+    if len(result.tool_calls) > len(capped):
+        turn = Turn.assistant(result.content, tool_calls=turn.tool_calls[: len(capped)])
+    return capped, turn
+
+
 def model_turn(
     lane: ModelLane,
     turns: Sequence[Turn],
@@ -553,29 +595,34 @@ def model_turn(
             "model_turn: mint requires wire_id_map — minted ids are "
             "unrestorable on the wire without the recovery map"
         )
+    # ONE config fetch per plant call feeds both live per-call flags — a
+    # registry hot-reload cannot hand the replay gate and the attach gate
+    # different config generations within a single request.
+    cfg = _get_config_or_none(lane.registry, lane.alias)
     wire = restore_provider_tool_ids(
         sanitize_tool_call_arguments(dicts_from_turns(list(turns))),
         wire_id_map if wire_id_map is not None else {},
     )
-    wire = maybe_attach_vllm_chat_reasoning(wire, lane.provider, lane.registry, lane.alias)
+    wire = maybe_attach_vllm_chat_reasoning(wire, lane.provider, lane.registry, lane.alias, cfg=cfg)
     call_kwargs: dict[str, Any] = {
         "client": lane.client,
         "model": lane.model,
         "messages": wire,
         "tools": tools,
         "max_tokens": max_tokens,
+        # None temperature flows through to the providers, which OMIT the
+        # field from the wire so the server default applies (house rule: a
+        # Python-level constant anywhere on this path is a hidden pin).
+        "temperature": temperature if temperature is not None else lane.temperature,
         "reasoning_effort": reasoning_effort,
         "extra_params": lane.extra_params,
         "capabilities": lane.capabilities,
         "replay_reasoning_to_model": resolve_replay_reasoning_to_model(
-            lane.registry, lane.alias, caps=lane.capabilities
+            lane.registry, lane.alias, caps=lane.capabilities, cfg=cfg
         ),
     }
     if resolve_attachments is not None:
         call_kwargs["resolve_attachments"] = resolve_attachments
-    effective_temperature = temperature if temperature is not None else lane.temperature
-    if effective_temperature is not None:
-        call_kwargs["temperature"] = effective_temperature
     result = lane.provider.create_completion(**call_kwargs)
 
     raw_calls: list[dict[str, Any]] = list(result.tool_calls or [])
diff --git a/turnstone/core/output_guard_judge.py b/turnstone/core/output_guard_judge.py
index 40093ad8..aa212462 100644
--- a/turnstone/core/output_guard_judge.py
+++ b/turnstone/core/output_guard_judge.py
@@ -270,11 +270,14 @@ class OutputGuardJudge:
         model_registry: Any | None = None,
         session_capabilities: ModelCapabilities | None = None,
         session_model_alias: str = "",
+        config_store: Any | None = None,
     ) -> None:
         self._config = config
-        # Carried into the per-evaluation ModelLane so extra_params and the
-        # live operator flags resolve from the registry like every other lane.
+        # Carried into the per-evaluation ModelLane so extra_params, the
+        # live operator flags, and the temperature ladder resolve from the
+        # registry like every other lane.
         self._model_registry = model_registry
+        self._config_store = config_store
         # Caller's resolved session-model caps (config/registry-aware): the wire
         # capabilities + window when this judge inherits the session model, and
         # the alias path's window fallback.  The window comes ONLY from these
@@ -308,10 +311,17 @@ class OutputGuardJudge:
                     )
                     self._model = model_name
                     self._judge_model_alias = config.output_guard_model
+                    self._lane_alias = config.output_guard_model
                     # Shared lane resolver (model_turn); ModelConfig.context_window
                     # stays separate and is sized into the guard window below.
+                    # ``cfg=model_cfg`` reuses the config resolve() already
+                    # fetched — one lookup, one generation.
                     self._capabilities = resolve_capabilities(
-                        self._provider, self._model, config.output_guard_model, model_registry
+                        self._provider,
+                        self._model,
+                        config.output_guard_model,
+                        model_registry,
+                        cfg=model_cfg,
                     )
                     self._judge_context_window = _positive_window(
                         getattr(model_cfg, "context_window", None),
@@ -338,10 +348,18 @@ class OutputGuardJudge:
                 session_client, session_provider.provider_name
             )
             self._model = session_model
-            # Inherit the session's registry alias so the lane resolves
-            # extra_params / replay flag exactly like every other lane on
-            # the same model (see IntentJudge's fallback for the rationale).
-            self._judge_model_alias = session_model_alias
+            # AUDIT label keeps its pre-#827 fallback semantics: "" here so
+            # recorded verdicts show ``judge_model = self._model`` (the raw
+            # model id), not the session alias — threading the alias into
+            # this field would silently change recorded judge_model values
+            # across the upgrade on default-config installs.
+            self._judge_model_alias = ""
+            # LANE alias inherits the session's registry alias so the lane
+            # resolves extra_params / replay flag / temperature exactly like
+            # every other lane on the same model (see IntentJudge's fallback
+            # for the rationale).  Lane resolution and audit labeling are
+            # different roles — hence two fields.
+            self._lane_alias = session_model_alias
             # Wire caps: the caller's resolved session caps, or the provider's
             # static table as a last resort for degraded / legacy callers.
             self._capabilities = (
@@ -508,15 +526,18 @@ class OutputGuardJudge:
         # worker is non-daemon, and concurrent.futures joins it from an atexit
         # hook regardless of shutdown(wait=False) — so a wedged upstream call
         # would otherwise hang shutdown.)
-        # Single-shot lane: constructor-resolved capabilities, extra_params
-        # and live operator flags from the registry like every other lane.
+        # Single-shot lane: constructor-frozen capabilities (window-coupled,
+        # refreshed on judge swap — see IntentJudge's lane note), extra_params
+        # / live flags / temperature ladder from the registry like every
+        # other lane.  ``_lane_alias``, not the audit label.
         lane = resolve_lane(
             self._provider,
             client,
             self._model,
-            alias=self._judge_model_alias,
+            alias=self._lane_alias,
             registry=self._model_registry,
             capabilities=self._capabilities,
+            config_store=self._config_store,
         )
         # Temperature deliberately not pinned (house rule) — the lane
         # inherits the guard model's configured temperature.
diff --git a/turnstone/core/perception.py b/turnstone/core/perception.py
index 920a1e87..2237bd41 100644
--- a/turnstone/core/perception.py
+++ b/turnstone/core/perception.py
@@ -75,6 +75,9 @@ def describe(
     model: str,
     parts: list[dict[str, Any]],
     prompt: str = _DESCRIBE_PROMPT,
+    alias: str = "",
+    registry: Any | None = None,
+    config_store: Any | None = None,
 ) -> str:
     """Perceive ``parts`` via the perception model, returning the text.
 
@@ -82,10 +85,16 @@ def describe(
     image/PDF-page perception, ``input_audio`` for audio.  The trajectory
     carries them by reference; ``model_turn`` hands the resolver to the
     provider translator, which materializes the placeholder into these exact
-    parts (one ref may expand to many, e.g. a rasterized PDF).  Temperature
-    is not pinned (house rule) — the perception model's own configuration
-    governs sampling.  Raises :class:`PerceptionBackendError` if the backend
-    call fails.  Never caches — see :func:`describe_cached`.
+    parts (one ref may expand to many, e.g. a rasterized PDF).
+
+    *alias* / *registry* / *config_store* make the perception lane a real
+    lane: the alias's capability overrides, ``server_compat.extra_body``
+    pins, and the temperature ladder (per-model → global
+    ``model.temperature`` → server default; house rule: no code pins) all
+    reach the wire, so an operator can actually remediate a degraded,
+    memoized description from the Models tab.  Raises
+    :class:`PerceptionBackendError` if the backend call fails.  Never
+    caches — see :func:`describe_cached`.
     """
     if not parts:
         return ""
@@ -99,7 +108,9 @@ def describe(
             ),
         )
     ]
-    lane = resolve_lane(provider, client, model)
+    lane = resolve_lane(
+        provider, client, model, alias=alias, registry=registry, config_store=config_store
+    )
     try:
         result = model_turn(
             lane,
@@ -136,6 +147,8 @@ def describe_cached(
     content_hash: str,
     parts: list[dict[str, Any]],
     prompt: str = _DESCRIBE_PROMPT,
+    registry: Any | None = None,
+    config_store: Any | None = None,
 ) -> str:
     """Memoized, non-raising :func:`describe` for the wire fallback.
 
@@ -154,6 +167,9 @@ def describe_cached(
             model=model,
             parts=parts,
             prompt=prompt,
+            alias=alias,
+            registry=registry,
+            config_store=config_store,
         )
     except PerceptionBackendError as exc:
         log.warning("perception fallback failed (alias=%s): %s", alias, exc)
diff --git a/turnstone/core/providers/_anthropic.py b/turnstone/core/providers/_anthropic.py
index f39ca8d6..2107b320 100644
--- a/turnstone/core/providers/_anthropic.py
+++ b/turnstone/core/providers/_anthropic.py
@@ -407,7 +407,7 @@ class AnthropicProvider:
         reasoning_effort: str,
         extra_params: dict[str, Any] | None,
         max_tokens: int,
-        temperature: float,
+        temperature: float | None,
         converted_msgs: list[dict[str, Any]],
         system_prompt: str,
         model: str,
@@ -453,7 +453,10 @@ class AnthropicProvider:
             # 90% input cost reduction on cache hits; 1.25x write on first turn.
             "cache_control": {"type": "ephemeral"},
         }
-        if caps.supports_temperature:
+        # None temperature is never written — the request omits the field so
+        # the server default applies (house rule: no code pins).  The
+        # thinking branches above still force 1.0 where the API requires it.
+        if caps.supports_temperature and temperature is not None:
             kwargs["temperature"] = temperature
         if system_prompt:
             kwargs["system"] = system_prompt
@@ -1075,7 +1078,7 @@ class AnthropicProvider:
         messages: list[dict[str, Any]],
         tools: list[dict[str, Any]] | None = None,
         max_tokens: int = 4096,
-        temperature: float = 0.5,
+        temperature: float | None = None,
         reasoning_effort: str = "medium",
         extra_params: dict[str, Any] | None = None,
         deferred_names: frozenset[str] | None = None,
diff --git a/turnstone/core/providers/_openai_chat.py b/turnstone/core/providers/_openai_chat.py
index 547a4266..79724910 100644
--- a/turnstone/core/providers/_openai_chat.py
+++ b/turnstone/core/providers/_openai_chat.py
@@ -312,7 +312,7 @@ class OpenAIChatCompletionsProvider:
         messages: list[dict[str, Any]],
         tools: list[dict[str, Any]] | None = None,
         max_tokens: int = 4096,
-        temperature: float = 0.5,
+        temperature: float | None = None,
         reasoning_effort: str = "medium",
         extra_params: dict[str, Any] | None = None,
         deferred_names: frozenset[str] | None = None,
diff --git a/turnstone/core/providers/_openai_common.py b/turnstone/core/providers/_openai_common.py
index 567a599b..dd982aaa 100644
--- a/turnstone/core/providers/_openai_common.py
+++ b/turnstone/core/providers/_openai_common.py
@@ -361,16 +361,22 @@ def lookup_openai_capabilities(model: str) -> ModelCapabilities:
 def apply_temperature(
     kwargs: dict[str, Any],
     caps: ModelCapabilities,
-    temperature: float,
+    temperature: float | None,
     reasoning_effort: str,
 ) -> None:
     """Conditionally add temperature to *kwargs*.
 
+    - ``None`` temperature is never written: the request omits the field
+      so the SERVER default applies.  House rule: code never pins a
+      temperature — a Python-level constant here would silently re-pin
+      every lane that deliberately left it unresolved.
     - Models with ``supports_temperature=False`` (GPT-5 base, O-series)
       never receive temperature.
     - Models that list ``"none"`` in their effort values (GPT-5.1/5.2)
       only receive temperature when reasoning is inactive.
     """
+    if temperature is None:
+        return
     if not caps.supports_temperature:
         return
     if "none" in caps.reasoning_effort_values and reasoning_effort not in ("none", ""):
@@ -381,7 +387,7 @@ def apply_temperature(
 def apply_temperature_and_effort(
     kwargs: dict[str, Any],
     caps: ModelCapabilities,
-    temperature: float,
+    temperature: float | None,
     reasoning_effort: str,
 ) -> None:
     """Conditionally add temperature and reasoning_effort to *kwargs*.
diff --git a/turnstone/core/providers/_openai_responses.py b/turnstone/core/providers/_openai_responses.py
index 5a2421fe..58d71739 100644
--- a/turnstone/core/providers/_openai_responses.py
+++ b/turnstone/core/providers/_openai_responses.py
@@ -354,7 +354,7 @@ class OpenAIResponsesProvider:
         messages: list[dict[str, Any]],
         tools: list[dict[str, Any]] | None,
         max_tokens: int,
-        temperature: float,
+        temperature: float | None,
         reasoning_effort: str,
         deferred_names: frozenset[str] | None,
         capabilities: ModelCapabilities | None = None,
@@ -676,7 +676,7 @@ class OpenAIResponsesProvider:
         messages: list[dict[str, Any]],
         tools: list[dict[str, Any]] | None = None,
         max_tokens: int = 4096,
-        temperature: float = 0.5,
+        temperature: float | None = None,
         reasoning_effort: str = "medium",
         extra_params: dict[str, Any] | None = None,
         deferred_names: frozenset[str] | None = None,
diff --git a/turnstone/core/providers/_protocol.py b/turnstone/core/providers/_protocol.py
index 09204e33..7865220a 100644
--- a/turnstone/core/providers/_protocol.py
+++ b/turnstone/core/providers/_protocol.py
@@ -469,7 +469,7 @@ class LLMProvider(Protocol):
         messages: list[dict[str, Any]],
         tools: list[dict[str, Any]] | None = None,
         max_tokens: int = 4096,
-        temperature: float = 0.5,
+        temperature: float | None = None,
         reasoning_effort: str = "medium",
         extra_params: dict[str, Any] | None = None,
         deferred_names: frozenset[str] | None = None,
@@ -480,6 +480,12 @@ class LLMProvider(Protocol):
     ) -> CompletionResult:
         """Create a non-streaming request, returning a normalized result.
 
+        ``temperature=None`` (the default) means the field is OMITTED from
+        the wire request and the server's own default applies — it must
+        never be replaced by a Python-level constant (house rule: code
+        never pins a temperature; ``model_turn`` resolves the operator's
+        ladder and passes ``None`` when nothing is configured).
+
         ``replay_reasoning_to_model`` mirrors the per-model
         ``model_definitions`` operator flag.  Anthropic uses it to
         gate the verbatim ``_provider_content`` replay (Phase 2);
diff --git a/turnstone/core/providers/_xai.py b/turnstone/core/providers/_xai.py
index 8c7882fa..afa38ecd 100644
--- a/turnstone/core/providers/_xai.py
+++ b/turnstone/core/providers/_xai.py
@@ -164,7 +164,7 @@ class XAIProvider(OpenAIResponsesProvider):
         messages: list[dict[str, Any]],
         tools: list[dict[str, Any]] | None,
         max_tokens: int,
-        temperature: float,
+        temperature: float | None,
         reasoning_effort: str,
         deferred_names: frozenset[str] | None,
         capabilities: ModelCapabilities | None = None,
diff --git a/turnstone/core/session.py b/turnstone/core/session.py
index d5aa875d..77de21cd 100644
--- a/turnstone/core/session.py
+++ b/turnstone/core/session.py
@@ -124,7 +124,6 @@ from turnstone.core.metacognition import (
     should_nudge,
 )
 from turnstone.core.model_turn import (
-    ModelLane,
     ModelTurnResult,
     ensure_tool_call_ids,
     finalize_provider_blocks,
@@ -132,6 +131,7 @@ from turnstone.core.model_turn import (
     model_turn,
     provider_extra_params,
     resolve_capabilities,
+    resolve_lane,
     resolve_replay_reasoning_to_model,
 )
 from turnstone.core.nudge_queue import (
@@ -2043,9 +2043,14 @@ class ChatSession:
         """Get model capabilities, applying config.toml overrides if present.
 
         Delegates to :func:`turnstone.core.model_turn.resolve_capabilities` —
-        the one resolution path every lane shares (#827).
+        the one resolution path every lane shares (#827) — but fetches the
+        config ITSELF, uncaught: a registry failure on the session's own
+        alias must raise loudly (pre-#827 semantics), never silently cache
+        degraded static-table caps for the session lifetime.  The defensive
+        never-crash fetch is a judge-constructor property, not a session one.
         """
-        return resolve_capabilities(provider, model, alias or "", self._registry)
+        cfg = self._registry.get_config(alias) if (self._registry and alias) else None
+        return resolve_capabilities(provider, model, alias or "", self._registry, cfg=cfg)
 
     def _get_capabilities(self, provider: Any = None, model: str = "") -> ModelCapabilities:
         """Get capabilities for a model. Cached for the primary session model."""
@@ -4234,6 +4239,14 @@ class ChatSession:
                 alias=alias,
                 content_hash=content_hash,
                 parts=parts,
+                # Thread the registry + config store so the perception lane
+                # resolves the alias's extra_params / capability overrides /
+                # temperature ladder like every other lane — without these,
+                # operator settings on the perception alias never reach the
+                # wire and there is no remediation path for a degraded,
+                # memoized description.
+                registry=self._registry,
+                config_store=self._config_store,
             )
         if not text:
             return None
@@ -4762,14 +4775,15 @@ class ChatSession:
         """
         caps = self._get_capabilities()
         clamped = min(max_tokens, caps.max_output_tokens) if caps.max_output_tokens else max_tokens
-        lane = ModelLane(
-            provider=self._provider,
-            client=self.client,
-            model=self.model,
+        lane = resolve_lane(
+            self._provider,
+            self.client,
+            self.model,
             alias=self._model_alias or "",
+            registry=self._registry,
             capabilities=caps,
             extra_params=self._provider_extra_params(),
-            registry=self._registry,
+            config_store=self._config_store,
         )
         result = model_turn(
             lane,
@@ -7754,6 +7768,8 @@ class ChatSession:
                 # model — thread its alias too, so the lane resolves
                 # extra_params / live flags like every other session lane.
                 session_model_alias=self._model_alias or "",
+                # For the temperature ladder's global rung (model.temperature).
+                config_store=self._config_store,
             )
         except Exception:
             log.warning("judge.init_failed", exc_info=True)
@@ -7789,6 +7805,8 @@ class ChatSession:
                 # source IntentJudge gets via _ensure_judge.
                 session_capabilities=self._get_capabilities(),
                 session_model_alias=self._model_alias or "",
+                # For the temperature ladder's global rung (model.temperature).
+                config_store=self._config_store,
             )
         except Exception:
             log.warning("output_guard_judge.init_failed", exc_info=True)
@@ -15064,18 +15082,24 @@ class ChatSession:
         # operator flags (replay-reasoning, Phase 5 vLLM attach) re-resolve
         # inside ``model_turn`` through the carried registry, so mid-session
         # admin toggles keep applying exactly as they did pre-extraction.
+        # Temperature follows the AGENT model's own ladder (its ModelConfig,
+        # else the global ``model.temperature``) — relaying the session
+        # model's value here would make a task alias's configured
+        # temperature unreachable (house rule: the model's configuration is
+        # the source of truth).
         # Agent trajectories stay excluded from the persistence/replay
         # contract — history is in-memory, rebuilt per ``_run_agent``
         # invocation; the native lane carried here serves the WITHIN-RUN
         # reasoning continuity of the agent's own tool loop.
-        lane = ModelLane(
-            provider=agent_provider,
-            client=agent_client,
-            model=agent_model,
+        lane = resolve_lane(
+            agent_provider,
+            agent_client,
+            agent_model,
             alias=agent_alias or "",
+            registry=self._registry,
             capabilities=agent_caps,
             extra_params=agent_extra,
-            registry=self._registry,
+            config_store=self._config_store,
         )
 
         def _api_call(
@@ -15098,7 +15122,6 @@ class ChatSession:
                         turns,
                         tools=_tools,
                         max_tokens=self.max_tokens,
-                        temperature=self.temperature,
                         reasoning_effort=reasoning_effort or self.reasoning_effort,
                         mint=mint,
                         wire_id_map=wire_id_map,
diff --git a/turnstone/eval/core.py b/turnstone/eval/core.py
index b2a0df69..edfa5c31 100644
--- a/turnstone/eval/core.py
+++ b/turnstone/eval/core.py
@@ -30,7 +30,7 @@ from typing import Any
 
 from openai import OpenAI
 
-from turnstone.core.model_turn import ModelLane, model_turn
+from turnstone.core.model_turn import cap_tool_calls, model_turn, resolve_lane
 from turnstone.core.providers import LLMProvider, create_client, create_provider
 from turnstone.core.session import ChatSession
 from turnstone.core.storage import get_storage, init_storage, reset_storage
@@ -306,14 +306,14 @@ class HeadlessSession(ChatSession):
         # The eval lane — resolved once per run, like the sub-agent seam.
         # ``temperature`` relays the harness's operator-resolved knob per
         # call below (house rule: relay, never pin).
-        lane = ModelLane(
-            provider=self._provider,
-            client=self.client,
-            model=self.model,
+        lane = resolve_lane(
+            self._provider,
+            self.client,
+            self.model,
             alias=self._model_alias or "",
+            registry=self._registry,
             capabilities=self._get_capabilities(),
             extra_params=self._provider_extra_params(),
-            registry=self._registry,
         )
 
         for turn in range(max_turns):
@@ -345,18 +345,10 @@ class HeadlessSession(ChatSession):
                 self._total_usage["prompt"] += result.usage.prompt_tokens
                 self._total_usage["completion"] += result.usage.completion_tokens
 
-            # Cap parallel tool calls to prevent degenerate repetition.  The
-            # cap applies to the mirror AND the appended turn; a capped turn
-            # drops its native lane rather than replaying orphan native
-            # tool_use blocks the mirror no longer carries.
-            capped_calls = (result.tool_calls or [])[:10]
-            assistant_turn = result.turn
-            if len(result.tool_calls) > len(capped_calls):
-                assistant_turn = Turn(
-                    role=Role.ASSISTANT,
-                    content=assistant_turn.content,
-                    tool_calls=assistant_turn.tool_calls[: len(capped_calls)],
-                )
+            # Cap parallel tool calls to prevent degenerate repetition
+            # (shared guard — see model_turn.cap_tool_calls for the
+            # native-lane-drop rationale on capped turns).
+            capped_calls, assistant_turn = cap_tool_calls(result, 10)
 
             self.messages.append(assistant_turn)
             msg_len = len(result.content or "")
diff --git a/turnstone/optimizer.py b/turnstone/optimizer.py
index 3d1b9fb8..9c34ba4c 100644
--- a/turnstone/optimizer.py
+++ b/turnstone/optimizer.py
@@ -27,7 +27,7 @@ from typing import Any
 
 from openai import OpenAI
 
-from turnstone.core.model_turn import model_turn, resolve_lane
+from turnstone.core.model_turn import cap_tool_calls, model_turn, resolve_lane
 from turnstone.core.providers import LLMProvider, create_provider
 from turnstone.core.session import ChatSession
 from turnstone.core.trajectory import Role, Turn
@@ -776,15 +776,9 @@ def _run_analyst(
             reasoning_effort="medium",
         )
 
-        # Same degenerate-repetition cap as before; a capped turn drops its
-        # native lane rather than replay orphan native tool blocks the
-        # mirror no longer carries.
-        capped = mtr.tool_calls[:5]
-        assistant_turn = mtr.turn
-        if len(mtr.tool_calls) > len(capped):
-            assistant_turn = Turn.assistant(
-                mtr.content, tool_calls=mtr.turn.tool_calls[: len(capped)]
-            )
+        # Same degenerate-repetition cap as before (shared guard — see
+        # model_turn.cap_tool_calls for the native-lane-drop rationale).
+        capped, assistant_turn = cap_tool_calls(mtr, 5)
         turns.append(assistant_turn)
 
         if not capped: