fix(gemini): default native maxOutputTokens + strip OpenAI extra_body on Gemini endpoints (#39730)

* fix: respect disabled auto-compaction on context overflow

Port from anomalyco/opencode#30749.

When compression.enabled is false, NO automatic compaction trigger may
fire. The proactive token-threshold paths (preflight + post-response
should_compress gate) already honoured the setting, but the three
provider-overflow recovery paths in the agent loop — long-context-tier
429, 413 payload-too-large, and context-overflow — called
_compress_context() unconditionally, silently compressing and rotating
the session against the user's explicit choice.

Add a single guard at the top of the overflow-recovery dispatch: when
compression is disabled and the error is one of those three overflow
classes, surface a terminal error (compaction_disabled: True) telling the
user to /compress manually, /new, switch to a larger-context model, or
reduce attachments. Manual /compress (force=True) is unaffected — it never
enters this loop.

Tests: new TestOverflowWithCompactionDisabled (413 + 400 overflow don't
compress when disabled; control case still compresses when enabled).
Existing overflow-recovery tests updated to enable compaction explicitly
(they verify the recovery fires); fixture defaults flipped to True to
match production (compression.enabled defaults to True).

* fix(gemini): default native maxOutputTokens + strip OpenAI extra_body on Gemini endpoints

Two distinct failures hit users on the gemini provider with only Google
AI Studio keys set.

1. Truncation loop: build_gemini_request() only set maxOutputTokens when
   max_tokens was non-None. Hermes passes None to mean "unlimited", but
   Gemini's native generateContent does NOT treat an absent maxOutputTokens
   as full budget — it applies a low internal default and stops early with
   finishReason=MAX_TOKENS, truncating tool calls. The agent then retries
   3x and refuses the incomplete call. Now default to the published 65,535
   ceiling (shared by all current Gemini text models) when max_tokens=None.

2. HTTP 400 on Gemini endpoint: the chat_completions transport assembles
   profile extra_body (Nous portal 'tags', reasoning, provider prefs) and
   sends it via the OpenAI client to whatever base_url is resolved. When a
   profile that emits extra_body (e.g. Nous) is active but the endpoint is a
   native Gemini base_url — typical when only Google creds exist and a
   fallback/aux call lands on Gemini — Google rejects the unknown 'tags'
   field with a non-retryable 400. Strip all non-thinking_config extra_body
   keys when the resolved endpoint is native Gemini.

Verified E2E against real transport code: tags stripped on native Gemini,
preserved on Nous and the /openai compat endpoint; maxOutputTokens=65535
on None, explicit values respected.

tests/run_agent/test_413_compression.py

@@ -94,7 +94,11 @@ def agent():
         a._cached_system_prompt = "You are helpful."
         a._use_prompt_caching = False
         a.tool_delay = 0
-        a.compression_enabled = False
+        # Default matches production (`compression.enabled` defaults to True).
+        # Overflow-recovery tests below verify that 413 / context-overflow
+        # errors DO trigger compression; the disabled-path behavior is
+        # covered explicitly by TestOverflowWithCompactionDisabled.
+        a.compression_enabled = True
         a.save_trajectories = False
         return a
 
@@ -415,6 +419,13 @@ class TestPreflightCompression:
 
     def test_compress_context_emits_lifecycle_status_before_work(self, agent):
         """Direct context compression should tell gateway users why the turn paused."""
+        # This test calls _compress_context directly and asserts the FIRST
+        # status event is the lifecycle "Compacting context" message. With
+        # compaction enabled the lazy feasibility probe would emit an
+        # aux-provider warning first (no aux key in the hermetic test env),
+        # displacing events[0]. The flag value is irrelevant to what this
+        # test asserts, so disable it to suppress the probe.
+        agent.compression_enabled = False
         events = []
         agent.status_callback = lambda ev, msg: events.append((ev, msg))
 
@@ -802,3 +813,95 @@ class TestToolResultPreflightCompression:
 
         mock_compress.assert_called_once()
         assert result["completed"] is True
+
+
+# ---------------------------------------------------------------------------
+# Disabled auto-compaction on overflow (port of anomalyco/opencode#30749)
+# ---------------------------------------------------------------------------
+
+class TestOverflowWithCompactionDisabled:
+    """When ``compression.enabled`` is False, NO automatic compaction may
+    fire — including the provider/request-size overflow recovery paths.
+
+    Ported from anomalyco/opencode#30749: the proactive token-threshold
+    path already honoured the setting, but provider overflow errors
+    (413 payload-too-large, context-overflow, long-context-tier 429) still
+    silently compressed + rotated the session. The fix surfaces a terminal
+    error so the user can compact manually, start fresh, or switch models.
+    """
+
+    @staticmethod
+    def _prefill():
+        return [
+            {"role": "user", "content": "previous question"},
+            {"role": "assistant", "content": "previous answer"},
+        ]
+
+    def test_413_does_not_compress_when_disabled(self, agent):
+        """413 must NOT call _compress_context when compaction is disabled."""
+        agent.compression_enabled = False
+        err_413 = _make_413_error()
+        # If the guard fails, a second (success) response would be consumed.
+        agent.client.chat.completions.create.side_effect = [err_413, _mock_response()]
+
+        with (
+            patch.object(agent, "_compress_context") as mock_compress,
+            patch.object(agent, "_persist_session") as mock_persist,
+            patch.object(agent, "_save_trajectory"),
+            patch.object(agent, "_cleanup_task_resources"),
+        ):
+            result = agent.run_conversation("hello", conversation_history=self._prefill())
+
+        mock_compress.assert_not_called()
+        mock_persist.assert_called()
+        assert result.get("failed") is True
+        assert result.get("compaction_disabled") is True
+        assert "auto-compaction is disabled" in result["error"]
+
+    def test_context_overflow_does_not_compress_when_disabled(self, agent):
+        """400 'prompt is too long' must NOT compress when compaction disabled."""
+        agent.compression_enabled = False
+        err_400 = Exception(
+            "Error code: 400 - {'type': 'error', 'error': {'type': "
+            "'invalid_request_error', 'message': 'prompt is too long: "
+            "233153 tokens > 200000 maximum'}}"
+        )
+        err_400.status_code = 400
+        agent.client.chat.completions.create.side_effect = [err_400, _mock_response()]
+
+        with (
+            patch.object(agent, "_compress_context") as mock_compress,
+            patch.object(agent, "_persist_session"),
+            patch.object(agent, "_save_trajectory"),
+            patch.object(agent, "_cleanup_task_resources"),
+        ):
+            result = agent.run_conversation("hello", conversation_history=self._prefill())
+
+        mock_compress.assert_not_called()
+        assert result.get("compaction_disabled") is True
+
+    def test_413_still_compresses_when_enabled(self, agent):
+        """Control: with compaction enabled, 413 still triggers compression.
+
+        Guards against the disabled-path guard accidentally swallowing the
+        enabled path.
+        """
+        agent.compression_enabled = True
+        err_413 = _make_413_error()
+        ok_resp = _mock_response(content="Recovered", finish_reason="stop")
+        agent.client.chat.completions.create.side_effect = [err_413, ok_resp]
+
+        with (
+            patch.object(agent, "_compress_context") as mock_compress,
+            patch.object(agent, "_persist_session"),
+            patch.object(agent, "_save_trajectory"),
+            patch.object(agent, "_cleanup_task_resources"),
+        ):
+            mock_compress.return_value = (
+                [{"role": "user", "content": "hello"}], "compressed",
+            )
+            result = agent.run_conversation("hello", conversation_history=self._prefill())
+
+        mock_compress.assert_called_once()
+        assert result["completed"] is True
+        assert result.get("compaction_disabled") is not True