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/agent/test_gemini_native_adapter.py

@@ -326,3 +326,27 @@ def test_stream_event_translation_keeps_identical_calls_in_distinct_parts():
     assert tool_chunks[0].choices[0].delta.tool_calls[0].index == 0
     assert tool_chunks[1].choices[0].delta.tool_calls[0].index == 1
     assert tool_chunks[0].choices[0].delta.tool_calls[0].id != tool_chunks[1].choices[0].delta.tool_calls[0].id
+
+
+def test_max_tokens_none_defaults_to_gemini_output_ceiling():
+    """max_tokens=None must send the model's full output ceiling, not omit it.
+
+    Gemini's native generateContent applies a low internal default when
+    maxOutputTokens is absent, truncating tool calls mid-stream. Hermes passes
+    None to mean "unlimited", so the adapter must translate that to the
+    published 65,535 ceiling rather than leaving the field unset.
+    """
+    from agent.gemini_native_adapter import (
+        build_gemini_request,
+        GEMINI_DEFAULT_MAX_OUTPUT_TOKENS,
+    )
+
+    req = build_gemini_request(messages=[{"role": "user", "content": "hi"}], max_tokens=None)
+    assert req["generationConfig"]["maxOutputTokens"] == GEMINI_DEFAULT_MAX_OUTPUT_TOKENS == 65535
+
+
+def test_explicit_max_tokens_is_respected():
+    from agent.gemini_native_adapter import build_gemini_request
+
+    req = build_gemini_request(messages=[{"role": "user", "content": "hi"}], max_tokens=4096)
+    assert req["generationConfig"]["maxOutputTokens"] == 4096

tests/agent/transports/test_chat_completions.py

@@ -859,3 +859,53 @@ class TestChatCompletionsCacheStats:
         r = SimpleNamespace(usage=SimpleNamespace(prompt_tokens_details=details))
         result = transport.extract_cache_stats(r)
         assert result == {"cached_tokens": 500, "creation_tokens": 100}
+
+
+class TestChatCompletionsGeminiNativeExtraBodyStrip:
+    """Profile extra_body (e.g. Nous portal tags) must not reach a native
+    Gemini endpoint — Google's REST API rejects unknown fields with HTTP 400.
+    """
+
+    def _nous_profile(self):
+        from providers import get_provider_profile
+        return get_provider_profile("nous")
+
+    def test_tags_stripped_when_endpoint_is_native_gemini(self, transport):
+        kw = transport.build_kwargs(
+            "anthropic/claude-sonnet-4.6",
+            [{"role": "user", "content": "hi"}],
+            None,
+            provider_profile=self._nous_profile(),
+            base_url="https://generativelanguage.googleapis.com/v1beta",
+            session_id="s1",
+            max_tokens=None,
+        )
+        eb = kw.get("extra_body")
+        assert not eb or "tags" not in eb
+
+    def test_tags_preserved_on_nous_endpoint(self, transport):
+        kw = transport.build_kwargs(
+            "hermes-3-405b",
+            [{"role": "user", "content": "hi"}],
+            None,
+            provider_profile=self._nous_profile(),
+            base_url="https://inference.nousresearch.com/v1",
+            session_id="s1",
+            max_tokens=None,
+        )
+        eb = kw.get("extra_body")
+        assert eb and "tags" in eb
+
+    def test_tags_pass_through_on_gemini_openai_compat(self, transport):
+        # /openai compat endpoint is not "native" — unchanged behavior.
+        kw = transport.build_kwargs(
+            "anthropic/claude-sonnet-4.6",
+            [{"role": "user", "content": "hi"}],
+            None,
+            provider_profile=self._nous_profile(),
+            base_url="https://generativelanguage.googleapis.com/v1beta/openai",
+            session_id="s1",
+            max_tokens=None,
+        )
+        eb = kw.get("extra_body")
+        assert eb and "tags" in eb