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).

agent/conversation_loop.py

@@ -2720,6 +2720,61 @@ def run_conversation(
                 # compress history and retry, not abort immediately.
                 status_code = getattr(api_error, "status_code", None)
 
+                # ── Respect disabled auto-compaction on overflow ──────
+                # Ported from anomalyco/opencode#30749.  When the user has
+                # turned auto-compaction off (``compression.enabled: false``),
+                # NO automatic compaction trigger may fire — including the
+                # provider/request-size overflow recovery paths below
+                # (long-context-tier 429, 413 payload-too-large, and
+                # context-overflow).  Without this guard the proactive
+                # threshold path correctly honours the setting (see the
+                # preflight check and the post-response ``should_compress``
+                # gate) but a provider overflow error would still silently
+                # compress + rotate the session, bypassing the user's
+                # explicit choice.  Surface a terminal error instead so the
+                # user can compact manually (``/compress``), start fresh
+                # (``/new``), switch to a larger-context model, or reduce
+                # attachments.  Forced compaction via ``/compress``
+                # (``force=True``) is unaffected — it never reaches this loop.
+                _overflow_reasons = {
+                    FailoverReason.long_context_tier,
+                    FailoverReason.payload_too_large,
+                    FailoverReason.context_overflow,
+                }
+                if (
+                    classified.reason in _overflow_reasons
+                    and not getattr(agent, "compression_enabled", True)
+                ):
+                    agent._flush_status_buffer()
+                    agent._vprint(
+                        f"{agent.log_prefix}❌ Context overflow, but auto-compaction is disabled "
+                        f"(compression.enabled: false).",
+                        force=True,
+                    )
+                    agent._vprint(
+                        f"{agent.log_prefix}   💡 Run /compress to compact manually, /new to start fresh, "
+                        f"switch to a larger-context model, or reduce attachments.",
+                        force=True,
+                    )
+                    logger.error(
+                        f"{agent.log_prefix}Context overflow ({classified.reason.value}) with "
+                        f"auto-compaction disabled — not compressing."
+                    )
+                    agent._persist_session(messages, conversation_history)
+                    return {
+                        "messages": messages,
+                        "completed": False,
+                        "api_calls": api_call_count,
+                        "error": (
+                            "Context overflow and auto-compaction is disabled "
+                            "(compression.enabled: false). Run /compress to compact manually, "
+                            "/new to start fresh, or switch to a larger-context model."
+                        ),
+                        "partial": True,
+                        "failed": True,
+                        "compaction_disabled": True,
+                    }
+
                 # ── Anthropic Sonnet long-context tier gate ───────────
                 # Anthropic returns HTTP 429 "Extra usage is required for
                 # long context requests" when a Claude Max (or similar)

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

tests/run_agent/test_run_agent.py

@@ -3903,6 +3903,7 @@ class TestRunConversation:
     def test_glm_prompt_exceeds_max_length_triggers_compression(self, agent):
         """GLM/Z.AI uses 'Prompt exceeds max length' for context overflow."""
         self._setup_agent(agent)
+        agent.compression_enabled = True  # this test verifies overflow→compression fires
         err_400 = Exception(
             "Error code: 400 - {'error': {'code': '1261', 'message': 'Prompt exceeds max length'}}"
         )
@@ -3937,6 +3938,7 @@ class TestRunConversation:
         to the generic 128K fallback tier.
         """
         self._setup_agent(agent)
+        agent.compression_enabled = True  # this test verifies overflow→compression fires
         agent.provider = "minimax"
         agent.model = "MiniMax-M2.7-highspeed"
         agent.base_url = "https://api.minimax.io/anthropic"
@@ -3982,6 +3984,7 @@ class TestRunConversation:
         rely on compression — see #33669 / PR #33826.
         """
         self._setup_agent(agent)
+        agent.compression_enabled = True  # this test verifies overflow→compression fires
         agent.provider = "openrouter"
         agent.model = "some/unknown-model"
         agent.base_url = "https://openrouter.ai/api/v1"