fix: merge client anthropic-beta tags to unblock 1M context (#54)

ccproxy/plugins/claude_api/adapter.py

@@ -88,12 +88,14 @@ async def prepare_provider_request(
 
         # Minimal beta tags required for OAuth-based Claude Code auth
         filtered_headers["anthropic-version"] = "2023-06-01"
-        filtered_headers["anthropic-beta"] = "claude-code-20250219,oauth-2025-04-20"
+        filtered_headers["anthropic-beta"] = self._merge_anthropic_beta(
+            headers.get("anthropic-beta") or headers.get("Anthropic-Beta")
+        )
 
-        # Add CLI headers if available, but never allow overriding auth or beta
+        # Add CLI headers if available, but never allow overriding auth
         cli_headers = self._collect_cli_headers()
         if cli_headers:
-            blocked_overrides = {"authorization", "x-api-key", "anthropic-beta"}
+            blocked_overrides = {"authorization", "x-api-key"}
             for key, value in cli_headers.items():
                 lk = key.lower()
                 if lk in blocked_overrides:
@@ -103,6 +105,11 @@ async def prepare_provider_request(
                         reason="preserve_oauth_auth_header",
                     )
                     continue
+                if lk == "anthropic-beta":
+                    filtered_headers[lk] = self._merge_anthropic_beta(
+                        value, base=filtered_headers.get("anthropic-beta")
+                    )
+                    continue
                 filtered_headers[lk] = value
 
         return json.dumps(body_data).encode(), filtered_headers
@@ -272,6 +279,26 @@ def _resolve_system_prompt_value(self, mode: str) -> Any:
 
         return None
 
+    @staticmethod
+    def _merge_anthropic_beta(client_value: str | None, base: str | None = None) -> str:
+        """Merge required OAuth beta tags with client-provided beta tags.
+
+        Required tags are always present; additional client tags (e.g.
+        context-1m-2025-08-07 for 1M context) are preserved.
+        """
+        required = ["claude-code-20250219", "oauth-2025-04-20"]
+        tags: list[str] = []
+        seen: set[str] = set()
+        for source in (base, client_value, ",".join(required)):
+            if not source:
+                continue
+            for tag in source.split(","):
+                tag = tag.strip()
+                if tag and tag not in seen:
+                    seen.add(tag)
+                    tags.append(tag)
+        return ",".join(tags)
+
     def _collect_cli_headers(self) -> dict[str, str]:
         """Collect safe CLI headers from detection cache for request forwarding."""
 

tests/plugins/claude_api/unit/test_adapter.py

@@ -107,6 +107,103 @@ async def test_prepare_provider_request_basic(
         # Headers should be filtered and enhanced
         assert result_headers["content-type"] == "application/json"
         assert result_headers["authorization"] == "Bearer test-token"
+        # Required OAuth beta tags must always be present
+        beta_tags = set(result_headers["anthropic-beta"].split(","))
+        assert "claude-code-20250219" in beta_tags
+        assert "oauth-2025-04-20" in beta_tags
+
+    @pytest.mark.asyncio
+    async def test_prepare_provider_request_merges_client_beta(
+        self, adapter: ClaudeAPIAdapter
+    ) -> None:
+        """Client-provided anthropic-beta tags must be preserved alongside required tags."""
+        body = json.dumps(
+            {
+                "model": "claude-3-5-sonnet-20241022",
+                "messages": [{"role": "user", "content": "Hello"}],
+                "max_tokens": 100,
+            }
+        ).encode()
+        headers = {
+            "content-type": "application/json",
+            "anthropic-beta": "context-1m-2025-08-07,custom-tag",
+        }
+
+        _, result_headers = await adapter.prepare_provider_request(
+            body, headers, "/v1/messages"
+        )
+
+        beta_tags = set(result_headers["anthropic-beta"].split(","))
+        assert "claude-code-20250219" in beta_tags
+        assert "oauth-2025-04-20" in beta_tags
+        assert "context-1m-2025-08-07" in beta_tags
+        assert "custom-tag" in beta_tags
+
+    @pytest.mark.asyncio
+    async def test_prepare_provider_request_merges_cli_detected_beta(
+        self,
+        mock_detection_service: ClaudeAPIDetectionService,
+        mock_auth_manager: Mock,
+        mock_http_pool_manager: Mock,
+    ) -> None:
+        """CLI-detected beta tags from detection cache must flow through to upstream request."""
+        mock_detection_service.get_detected_headers = Mock(  # type: ignore[method-assign]
+            return_value=DetectedHeaders(
+                {
+                    "anthropic-beta": "claude-code-20250219,oauth-2025-04-20,context-1m-2025-08-07,interleaved-thinking-2025-05-14",
+                }
+            )
+        )
+        from ccproxy.plugins.claude_api.config import ClaudeAPISettings
+
+        adapter = ClaudeAPIAdapter(
+            detection_service=mock_detection_service,
+            config=ClaudeAPISettings(),
+            auth_manager=mock_auth_manager,
+            http_pool_manager=mock_http_pool_manager,
+        )
+
+        body = json.dumps(
+            {
+                "model": "claude-3-5-sonnet-20241022",
+                "messages": [{"role": "user", "content": "Hello"}],
+                "max_tokens": 100,
+            }
+        ).encode()
+        headers = {
+            "content-type": "application/json",
+            "anthropic-beta": "client-only-tag",
+        }
+
+        _, result_headers = await adapter.prepare_provider_request(
+            body, headers, "/v1/messages"
+        )
+
+        beta_tags = set(result_headers["anthropic-beta"].split(","))
+        assert "claude-code-20250219" in beta_tags
+        assert "oauth-2025-04-20" in beta_tags
+        assert "context-1m-2025-08-07" in beta_tags
+        assert "interleaved-thinking-2025-05-14" in beta_tags
+        assert "client-only-tag" in beta_tags
+
+    def test_merge_anthropic_beta_helper(self) -> None:
+        """_merge_anthropic_beta deduplicates and always includes required tags."""
+        result = ClaudeAPIAdapter._merge_anthropic_beta(None)
+        assert set(result.split(",")) == {
+            "claude-code-20250219",
+            "oauth-2025-04-20",
+        }
+
+        result = ClaudeAPIAdapter._merge_anthropic_beta(
+            "context-1m-2025-08-07, claude-code-20250219"
+        )
+        tags = result.split(",")
+        assert len(tags) == len(set(tags))
+        assert set(tags) == {
+            "claude-code-20250219",
+            "oauth-2025-04-20",
+            "context-1m-2025-08-07",
+        }
 
     @pytest.mark.asyncio
     async def test_prepare_provider_request_with_system_prompt(