feat(openai): 完善 Chat 与 Responses 参数转发

原生 Chat/Responses 改为透明转发，保留标准工具结构并保护调用方显式参数。补齐 Responses 到 Chat 的兼容转换、协议路由边界、完整响应和流式事件，并同步更新 Swagger、回归测试与真实验收脚本。

验证：
- cd apps/api && env -u AI_GATEWAY_TEST_DATABASE_URL go test ./... -count=1
- pnpm openapi
- pnpm lint
- pnpm test
- pnpm build
- gofmt -l 无输出
- git diff --check 通过

风险：
- Chat 回退无法等价表达的 Responses 原生能力现在会返回 unsupported_response_parameter
- 真实供应商 E2E 因本地没有已启用的平台模型候选而未完成

apps/api/internal/runner/responses.go

@@ -83,7 +83,8 @@ func (s *Service) prepareResponseExecution(ctx context.Context, task store.Gatew
 	return result, nil
 }
 
-func prepareResponseCandidates(candidates []store.RuntimeModelCandidate, execution responseExecutionContext) ([]store.RuntimeModelCandidate, error) {
+func prepareResponseCandidates(candidates []store.RuntimeModelCandidate, execution responseExecutionContext, body map[string]any) ([]store.RuntimeModelCandidate, error) {
+	chatCompatibilityErr := clients.ValidateResponsesChatFallback(body)
 	if execution.PreviousChain != nil {
 		for _, candidate := range candidates {
 			if candidate.PlatformModelID != execution.PreviousChain.PlatformModelID {
@@ -92,6 +93,9 @@ func prepareResponseCandidates(candidates []store.RuntimeModelCandidate, executi
 			if !candidateSupportsProtocol(candidate, execution.PreviousChain.UpstreamProtocol) {
 				break
 			}
+			if execution.PreviousChain.UpstreamProtocol == clients.ProtocolOpenAIChatCompletions && chatCompatibilityErr != nil {
+				return nil, chatCompatibilityErr
+			}
 			candidate.ResponseProtocol = execution.PreviousChain.UpstreamProtocol
 			return []store.RuntimeModelCandidate{candidate}, nil
 		}
@@ -106,6 +110,7 @@ func prepareResponseCandidates(candidates []store.RuntimeModelCandidate, executi
 	items := make([]indexedCandidate, 0, len(candidates))
 	hasAnthropicOnly := false
 	hasDeclaredUnsupported := false
+	hasChatCandidate := false
 	for index, candidate := range candidates {
 		protocols := candidateSupportedProtocols(candidate)
 		group := 1
@@ -119,11 +124,19 @@ func prepareResponseCandidates(candidates []store.RuntimeModelCandidate, executi
 				hasAnthropicOnly = true
 			}
 			continue
+		} else {
+			hasChatCandidate = true
+			if chatCompatibilityErr != nil {
+				continue
+			}
 		}
 		candidate.ResponseProtocol = protocol
 		items = append(items, indexedCandidate{candidate: candidate, index: index, group: group})
 	}
 	if len(items) == 0 {
+		if hasChatCandidate && chatCompatibilityErr != nil {
+			return nil, chatCompatibilityErr
+		}
 		if hasAnthropicOnly {
 			return nil, &clients.ClientError{Code: "unsupported_model_protocol", Message: "the selected model only supports Anthropic Messages; the public Anthropic adapter is not available", StatusCode: http.StatusBadRequest}
 		}

apps/api/internal/runner/responses_test.go

@@ -24,7 +24,7 @@ func TestPrepareResponseCandidatesPrioritizesNativeAndKeepsGroupOrder(t *testing
 		{PlatformModelID: "native-2", Capabilities: responseProtocolCapability(clients.ProtocolOpenAIResponses)},
 		{PlatformModelID: "chat-2", Capabilities: responseProtocolCapability(clients.ProtocolOpenAIChatCompletions)},
 	}
-	prepared, err := prepareResponseCandidates(candidates, responseExecutionContext{})
+	prepared, err := prepareResponseCandidates(candidates, responseExecutionContext{}, map[string]any{"input": "hello"})
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -46,7 +46,7 @@ func TestPrepareResponseCandidatesPinsPreviousPlatformModelAndProtocol(t *testin
 		{PlatformModelID: "other", Capabilities: responseProtocolCapability(clients.ProtocolOpenAIChatCompletions)},
 		{PlatformModelID: "pinned", Capabilities: responseProtocolCapability(clients.ProtocolOpenAIChatCompletions, clients.ProtocolOpenAIResponses)},
 	}
-	prepared, err := prepareResponseCandidates(candidates, responseExecutionContext{PreviousChain: &chain})
+	prepared, err := prepareResponseCandidates(candidates, responseExecutionContext{PreviousChain: &chain}, map[string]any{"input": "hello"})
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -54,14 +54,53 @@ func TestPrepareResponseCandidatesPinsPreviousPlatformModelAndProtocol(t *testin
 		t.Fatalf("previous chain was not pinned: %+v", prepared)
 	}
 
-	_, err = prepareResponseCandidates(candidates[:1], responseExecutionContext{PreviousChain: &chain})
+	_, err = prepareResponseCandidates(candidates[:1], responseExecutionContext{PreviousChain: &chain}, map[string]any{"input": "hello"})
 	if clients.ErrorCode(err) != "response_chain_unavailable" {
 		t.Fatalf("expected response_chain_unavailable, got %v", err)
 	}
 }
 
+func TestPrepareResponseCandidatesExcludesChatForNativeOnlyParameters(t *testing.T) {
+	candidates := []store.RuntimeModelCandidate{
+		{PlatformModelID: "chat", Capabilities: responseProtocolCapability(clients.ProtocolOpenAIChatCompletions)},
+		{PlatformModelID: "native", Capabilities: responseProtocolCapability(clients.ProtocolOpenAIResponses)},
+	}
+	prepared, err := prepareResponseCandidates(candidates, responseExecutionContext{}, map[string]any{"input": "hello", "background": true})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(prepared) != 1 || prepared[0].PlatformModelID != "native" || prepared[0].ResponseProtocol != clients.ProtocolOpenAIResponses {
+		t.Fatalf("native-only request reached Chat candidates: %+v", prepared)
+	}
+
+	_, err = prepareResponseCandidates(candidates[:1], responseExecutionContext{}, map[string]any{"input": "hello", "prompt": map[string]any{"id": "pmpt_1"}})
+	if clients.ErrorCode(err) != "unsupported_response_parameter" || clients.ErrorParam(err) != "prompt" {
+		t.Fatalf("Chat-only routing must return precise incompatibility, got %v param=%q", err, clients.ErrorParam(err))
+	}
+
+	_, err = prepareResponseCandidates(candidates[:1], responseExecutionContext{}, map[string]any{
+		"input": []any{map[string]any{"type": "mcp_call", "name": "remote"}},
+	})
+	if clients.ErrorCode(err) != "unsupported_response_parameter" || clients.ErrorParam(err) != "input[0].type" {
+		t.Fatalf("native-only input item must exclude Chat with a precise path, got %v param=%q", err, clients.ErrorParam(err))
+	}
+}
+
+func TestPrepareResponseCandidatesRejectsNativeOnlyParameterOnPinnedChatChain(t *testing.T) {
+	chain := store.ResponseChain{PlatformModelID: "pinned", UpstreamProtocol: clients.ProtocolOpenAIChatCompletions}
+	candidates := []store.RuntimeModelCandidate{{
+		PlatformModelID: "pinned", Capabilities: responseProtocolCapability(clients.ProtocolOpenAIChatCompletions, clients.ProtocolOpenAIResponses),
+	}}
+	_, err := prepareResponseCandidates(candidates, responseExecutionContext{PreviousChain: &chain}, map[string]any{
+		"input": "hello", "reasoning": map[string]any{"summary": "auto"},
+	})
+	if clients.ErrorCode(err) != "unsupported_response_parameter" || clients.ErrorParam(err) != "reasoning.summary" {
+		t.Fatalf("pinned Chat chain must return precise incompatibility, got %v param=%q", err, clients.ErrorParam(err))
+	}
+}
+
 func TestPrepareResponseCandidatesRejectsAnthropicOnly(t *testing.T) {
-	_, err := prepareResponseCandidates([]store.RuntimeModelCandidate{{Capabilities: responseProtocolCapability(clients.ProtocolAnthropicMessages)}}, responseExecutionContext{})
+	_, err := prepareResponseCandidates([]store.RuntimeModelCandidate{{Capabilities: responseProtocolCapability(clients.ProtocolAnthropicMessages)}}, responseExecutionContext{}, map[string]any{"input": "hello"})
 	if clients.ErrorCode(err) != "unsupported_model_protocol" {
 		t.Fatalf("expected unsupported_model_protocol, got %v", err)
 	}
@@ -107,7 +146,7 @@ func TestCandidateProtocolOverrideAndExplicitEmpty(t *testing.T) {
 	if protocols := candidateSupportedProtocols(empty); len(protocols) != 0 {
 		t.Fatalf("an explicitly empty protocol list must not become legacy Chat: %v", protocols)
 	}
-	if _, err := prepareResponseCandidates([]store.RuntimeModelCandidate{empty}, responseExecutionContext{}); clients.ErrorCode(err) != "unsupported_model_protocol" {
+	if _, err := prepareResponseCandidates([]store.RuntimeModelCandidate{empty}, responseExecutionContext{}, map[string]any{"input": "hello"}); clients.ErrorCode(err) != "unsupported_model_protocol" {
 		t.Fatalf("expected unsupported_model_protocol, got %v", err)
 	}
 }

apps/api/internal/runner/service.go

@@ -481,7 +481,7 @@ func (s *Service) executeWithToken(ctx context.Context, task store.GatewayTask,
 		return Result{Task: failed, Output: failed.Result}, err
 	}
 	if task.Kind == "responses" {
-		candidates, err = prepareResponseCandidates(candidates, responseExecution)
+		candidates, err = prepareResponseCandidates(candidates, responseExecution, body)
 		if err != nil {
 			code, message := responseExecutionFailure(err)
 			s.recordFailedAttempt(ctx, failedAttemptRecord{Task: task, Body: body, AttemptNo: task.AttemptCount + 1, Code: code, Cause: err, Simulated: task.RunMode == "simulation", Scope: "response_protocol", Reason: code, ModelType: modelType})