diff --git a/agent/chat_completion_helpers.py b/agent/chat_completion_helpers.py
index 85fdf40bcb..4f91ec1c36 100644
--- a/agent/chat_completion_helpers.py
+++ b/agent/chat_completion_helpers.py
@@ -1978,14 +1978,20 @@ def _reasoning_config_for_wire(agent):
     applies its own default.
     """
     cfg = agent.reasoning_config
-    if _consume_ephemeral_reasoning_off(agent):
+    ephemeral_off = _consume_ephemeral_reasoning_off(agent)
+    if getattr(agent, "_reasoning_disable_rejected", False):
+        # The route rejects disables. Resend exactly what the session has
+        # been sending — the user's own config — so the retry lands on the
+        # same provider cache key as every prior request. Only a config that
+        # is itself a disable is dropped (omitted → route default), and that
+        # session has never sent anything else, so nothing warm is lost.
+        if isinstance(cfg, dict) and (
+            cfg.get("enabled") is False or cfg.get("effort") == "none"
+        ):
+            return None
+        return cfg
+    if ephemeral_off:
         cfg = {**(cfg or {}), "enabled": False, "effort": "none"}
-    if (
-        getattr(agent, "_reasoning_disable_rejected", False)
-        and isinstance(cfg, dict)
-        and (cfg.get("enabled") is False or cfg.get("effort") == "none")
-    ):
-        return None
     return cfg
 
 
diff --git a/tests/run_agent/test_length_continuation_thinking_exhaustion.py b/tests/run_agent/test_length_continuation_thinking_exhaustion.py
index ddf4580a68..983d726e88 100644
--- a/tests/run_agent/test_length_continuation_thinking_exhaustion.py
+++ b/tests/run_agent/test_length_continuation_thinking_exhaustion.py
@@ -68,21 +68,21 @@ class TestReasoningOffOneShotOverride:
         cfg = _reasoning_config_for_wire(agent)
         assert cfg == {"enabled": False, "effort": "none"}
 
-    def test_rejected_disable_drops_every_disable_but_keeps_enabled(self):
-        """After a 'reasoning is mandatory' 400, no disable reaches the wire —
-        neither the configured one nor the one-shot continuation override —
-        while an enabled config still passes through."""
+    def test_rejected_disable_resends_users_config_verbatim(self):
+        """After a 'reasoning is mandatory' 400 the retry must land on the
+        SAME provider cache key as every prior request: the ephemeral
+        continuation override is discarded and the user's own config goes
+        out unchanged. A config that is itself a disable is omitted."""
         from agent.chat_completion_helpers import _reasoning_config_for_wire
 
-        agent = _AgentStandIn({"enabled": False})
+        agent = _AgentStandIn({"enabled": True, "effort": "high"})
         agent._reasoning_disable_rejected = True
-        assert _reasoning_config_for_wire(agent) is None
         agent._ephemeral_reasoning_off = True
-        assert _reasoning_config_for_wire(agent) is None
+        assert _reasoning_config_for_wire(agent) == {"enabled": True, "effort": "high"}
         assert agent._ephemeral_reasoning_off is False
 
-        agent.reasoning_config = {"enabled": True, "effort": "high"}
-        assert _reasoning_config_for_wire(agent) == {"enabled": True, "effort": "high"}
+        agent.reasoning_config = {"enabled": False}
+        assert _reasoning_config_for_wire(agent) is None
 
 
 @pytest.fixture()