diff --git a/backend/internal/service/gateway_request.go b/backend/internal/service/gateway_request.go
index 59442fcbca..e8154f302c 100644
--- a/backend/internal/service/gateway_request.go
+++ b/backend/internal/service/gateway_request.go
@@ -516,13 +516,22 @@ func StripEmptyTextBlocks(body []byte) []byte {
 
 // FilterThinkingBlocks removes thinking blocks from request body
 // Returns filtered body or original body if filtering fails (fail-safe)
-// This prevents 400 errors from invalid thinking block signatures
+// This prevents 400 errors from invalid thinking block signatures.
 //
-// 策略：
+// mappedModel 是「实际发给上游的模型 ID」(after account model mapping)，用于按
+// 协议族分流。仅 anthropic-strict 走原过滤逻辑；passback-required 与 unknown
+// 一律保留全部 thinking block，避免误伤第三方兼容上游
+// (DeepSeek `/anthropic`、Kimi `/coding`、GLM、Moonshot 等)，详见
+// .pensieve/short-term/knowledge/thinking-block-filter-third-party-upstream-inversion/。
+//
+// 策略 (anthropic-strict only)：
 //   - 当 thinking.type 不是 "enabled"/"adaptive"：移除所有 thinking 相关块
 //   - 当 thinking.type 是 "enabled"/"adaptive"：仅移除缺失/无效 signature 的 thinking 块（避免 400）
 //     (blocks with missing/empty/dummy signatures that would cause 400 errors)
-func FilterThinkingBlocks(body []byte) []byte {
+func FilterThinkingBlocks(body []byte, mappedModel string) []byte {
+	if !ShouldPreFilterThinkingBlocks(mappedModel) {
+		return body
+	}
 	return filterThinkingBlocksInternal(body, false)
 }
 
@@ -540,7 +549,17 @@ func FilterThinkingBlocks(body []byte) []byte {
 //   - Convert `thinking` blocks to `text` blocks (preserve the thinking content).
 //   - Remove `redacted_thinking` blocks (cannot be converted to text).
 //   - Ensure no message ends up with empty content.
-func FilterThinkingBlocksForRetry(body []byte) []byte {
+//
+// mappedModel 用于按协议族分流：仅 anthropic-strict 执行上述变形；
+// passback-required (DeepSeek/Kimi/GLM 等) 与 unknown 一律返回原 body，
+// 因为这类上游的契约就是「thinking block 原样回传」（或我们不了解），
+// retry 任何变形都不会修好 400，反而破坏契约。详见 thinking_protocol.go。
+func FilterThinkingBlocksForRetry(body []byte, mappedModel string) []byte {
+	// 仅 anthropic-strict 走整流；passback-required 与 unknown 都返回原 body。
+	if !ShouldApplyRetryFilters(mappedModel) {
+		return body
+	}
+
 	hasThinkingContent := bytes.Contains(body, patternTypeThinking) ||
 		bytes.Contains(body, patternTypeThinkingSpaced) ||
 		bytes.Contains(body, patternTypeRedactedThinking) ||
@@ -883,7 +902,14 @@ func anthropicBetaTokensContains(header, token string) bool {
 //
 // Use this only when needed: converting tool blocks to text changes model behaviour and can increase the
 // risk of prompt injection (tool output becomes plain conversation text).
-func FilterSignatureSensitiveBlocksForRetry(body []byte) []byte {
+//
+// mappedModel 同 FilterThinkingBlocksForRetry：仅 anthropic-strict 执行变形；
+// passback-required 与 unknown 都返回原 body，避免在不熟悉的上游上盲目变形。
+func FilterSignatureSensitiveBlocksForRetry(body []byte, mappedModel string) []byte {
+	if !ShouldApplyRetryFilters(mappedModel) {
+		return body
+	}
+
 	// Fast path: only run when we see likely relevant constructs.
 	if !bytes.Contains(body, []byte(`"type":"thinking"`)) &&
 		!bytes.Contains(body, []byte(`"type": "thinking"`)) &&
diff --git a/backend/internal/service/gateway_request_test.go b/backend/internal/service/gateway_request_test.go
index 7a1b6ef948..68ab6ceb60 100644
--- a/backend/internal/service/gateway_request_test.go
+++ b/backend/internal/service/gateway_request_test.go
@@ -277,7 +277,7 @@ func TestFilterThinkingBlocks(t *testing.T) {
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			result := FilterThinkingBlocks([]byte(tt.input))
+			result := FilterThinkingBlocks([]byte(tt.input), "claude-sonnet-4-5")
 
 			if tt.expectError {
 				// For invalid JSON, should return original
@@ -313,7 +313,7 @@ func TestFilterThinkingBlocksForRetry_DisablesThinkingAndPreservesAsText(t *test
 		]
 	}`)
 
-	out := FilterThinkingBlocksForRetry(input)
+	out := FilterThinkingBlocksForRetry(input, "claude-sonnet-4-5")
 
 	var req map[string]any
 	require.NoError(t, json.Unmarshal(out, &req))
@@ -346,7 +346,7 @@ func TestFilterThinkingBlocksForRetry_DisablesThinkingEvenWithoutThinkingBlocks(
 		]
 	}`)
 
-	out := FilterThinkingBlocksForRetry(input)
+	out := FilterThinkingBlocksForRetry(input, "claude-sonnet-4-5")
 
 	var req map[string]any
 	require.NoError(t, json.Unmarshal(out, &req))
@@ -365,7 +365,7 @@ func TestFilterThinkingBlocksForRetry_RemovesRedactedThinkingAndKeepsValidConten
 		]
 	}`)
 
-	out := FilterThinkingBlocksForRetry(input)
+	out := FilterThinkingBlocksForRetry(input, "claude-sonnet-4-5")
 
 	var req map[string]any
 	require.NoError(t, json.Unmarshal(out, &req))
@@ -424,7 +424,7 @@ func TestFilterThinkingBlocksForRetry_EmptyContentGetsPlaceholder(t *testing.T)
 		]
 	}`)
 
-	out := FilterThinkingBlocksForRetry(input)
+	out := FilterThinkingBlocksForRetry(input, "claude-sonnet-4-5")
 
 	var req map[string]any
 	require.NoError(t, json.Unmarshal(out, &req))
@@ -450,7 +450,7 @@ func TestFilterThinkingBlocksForRetry_StripsEmptyTextBlocks(t *testing.T) {
 		]
 	}`)
 
-	out := FilterThinkingBlocksForRetry(input)
+	out := FilterThinkingBlocksForRetry(input, "claude-sonnet-4-5")
 
 	var req map[string]any
 	require.NoError(t, json.Unmarshal(out, &req))
@@ -485,7 +485,7 @@ func TestFilterThinkingBlocksForRetry_StripsNestedEmptyTextInToolResult(t *testi
 		]
 	}`)
 
-	out := FilterThinkingBlocksForRetry(input)
+	out := FilterThinkingBlocksForRetry(input, "claude-sonnet-4-5")
 
 	var req map[string]any
 	require.NoError(t, json.Unmarshal(out, &req))
@@ -513,7 +513,7 @@ func TestFilterThinkingBlocksForRetry_NestedAllEmptyGetsEmptySlice(t *testing.T)
 		]
 	}`)
 
-	out := FilterThinkingBlocksForRetry(input)
+	out := FilterThinkingBlocksForRetry(input, "claude-sonnet-4-5")
 
 	var req map[string]any
 	require.NoError(t, json.Unmarshal(out, &req))
@@ -596,7 +596,7 @@ func TestFilterThinkingBlocksForRetry_PreservesNonEmptyTextBlocks(t *testing.T)
 		]
 	}`)
 
-	out := FilterThinkingBlocksForRetry(input)
+	out := FilterThinkingBlocksForRetry(input, "claude-sonnet-4-5")
 
 	// Fast path: no thinking content, no empty content, no empty text blocks → unchanged
 	require.Equal(t, input, out)
@@ -613,7 +613,7 @@ func TestFilterSignatureSensitiveBlocksForRetry_DowngradesTools(t *testing.T) {
 		]
 	}`)
 
-	out := FilterSignatureSensitiveBlocksForRetry(input)
+	out := FilterSignatureSensitiveBlocksForRetry(input, "claude-sonnet-4-5")
 
 	var req map[string]any
 	require.NoError(t, json.Unmarshal(out, &req))
@@ -700,7 +700,7 @@ func TestFilterThinkingBlocksForRetry_RemovesClearThinkingStrategy_FastPath(t *t
 		]
 	}`)
 
-	out := FilterThinkingBlocksForRetry(input)
+	out := FilterThinkingBlocksForRetry(input, "claude-sonnet-4-5")
 
 	var req map[string]any
 	require.NoError(t, json.Unmarshal(out, &req))
@@ -726,7 +726,7 @@ func TestFilterThinkingBlocksForRetry_RemovesClearThinkingStrategy_WithThinkingB
 		]
 	}`)
 
-	out := FilterThinkingBlocksForRetry(input)
+	out := FilterThinkingBlocksForRetry(input, "claude-sonnet-4-5")
 
 	var req map[string]any
 	require.NoError(t, json.Unmarshal(out, &req))
@@ -750,7 +750,7 @@ func TestFilterThinkingBlocksForRetry_NoContextManagement_Unaffected(t *testing.
 		"messages":[{"role":"user","content":[{"type":"text","text":"Hi"}]}]
 	}`)
 
-	out := FilterThinkingBlocksForRetry(input)
+	out := FilterThinkingBlocksForRetry(input, "claude-sonnet-4-5")
 
 	var req map[string]any
 	require.NoError(t, json.Unmarshal(out, &req))
@@ -773,7 +773,7 @@ func TestFilterSignatureSensitiveBlocksForRetry_RemovesClearThinkingStrategy(t *
 		]
 	}`)
 
-	out := FilterSignatureSensitiveBlocksForRetry(input)
+	out := FilterSignatureSensitiveBlocksForRetry(input, "claude-sonnet-4-5")
 
 	var req map[string]any
 	require.NoError(t, json.Unmarshal(out, &req))
@@ -804,7 +804,7 @@ func TestFilterSignatureSensitiveBlocksForRetry_PreservesNonThinkingStrategies(t
 		]
 	}`)
 
-	out := FilterSignatureSensitiveBlocksForRetry(input)
+	out := FilterSignatureSensitiveBlocksForRetry(input, "claude-sonnet-4-5")
 
 	var req map[string]any
 	require.NoError(t, json.Unmarshal(out, &req))
@@ -830,7 +830,7 @@ func TestFilterSignatureSensitiveBlocksForRetry_NoThinkingField_ContextManagemen
 		]
 	}`)
 
-	out := FilterSignatureSensitiveBlocksForRetry(input)
+	out := FilterSignatureSensitiveBlocksForRetry(input, "claude-sonnet-4-5")
 
 	var req map[string]any
 	require.NoError(t, json.Unmarshal(out, &req))
diff --git a/backend/internal/service/gateway_service.go b/backend/internal/service/gateway_service.go
index 5e333ae7e4..5a4af000da 100644
--- a/backend/internal/service/gateway_service.go
+++ b/backend/internal/service/gateway_service.go
@@ -4957,6 +4957,19 @@ func (s *GatewayService) Forward(ctx context.Context, c *gin.Context, account *A
 	if err := replaceBody(StripEmptyTextBlocks(body)); err != nil {
 		return nil, err
 	}
+	// Pre-filter: remove thinking blocks with missing/invalid signatures before forwarding.
+	// Clients (e.g. Claude Code) sometimes send multi-turn conversations where a historical
+	// assistant message contains a thinking block that is missing the required "signature" field,
+	// causing upstream to reject the request with 400 "thinking.signature: Field required".
+	// FilterThinkingBlocks removes only the invalid blocks; thinking blocks with valid signatures
+	// are preserved. This avoids relying solely on the post-error retry path, which can time out
+	// (maxRetryElapsed = 10s) for long conversations before the retry budget is exhausted.
+	//
+	// 仅 anthropic-strict 模型族执行此过滤；passback-required 上游 (DeepSeek/Kimi/GLM 等)
+	// 要求历史 thinking block 原样回传，过滤反而制造 400。reqModel 此时已是映射后的模型 ID。
+	if err := replaceBody(FilterThinkingBlocks(body, reqModel)); err != nil {
+		return nil, err
+	}
 
 	// 重试循环
 	var resp *http.Response
@@ -5007,7 +5020,7 @@ func (s *GatewayService) Forward(ctx context.Context, c *gin.Context, account *A
 			if readErr == nil {
 				_ = resp.Body.Close()
 
-				if s.shouldRectifySignatureError(ctx, account, respBody) {
+				if s.shouldRectifySignatureError(ctx, account, respBody, reqModel) {
 					appendOpsUpstreamError(c, OpsUpstreamErrorEvent{
 						Platform:           account.Platform,
 						AccountID:          account.ID,
@@ -5047,7 +5060,7 @@ func (s *GatewayService) Forward(ctx context.Context, c *gin.Context, account *A
 					// 2) Only if upstream still errors AND error message points to tool/function signature issues:
 					//    also downgrade tool_use/tool_result blocks to text.
 
-					filteredBody := FilterThinkingBlocksForRetry(body)
+					filteredBody := FilterThinkingBlocksForRetry(body, reqModel)
 					retryCtx, releaseRetryCtx := detachStreamUpstreamContext(ctx, reqStream)
 					retryReq, retryWireBody, buildErr := s.buildUpstreamRequest(retryCtx, c, account, filteredBody, token, tokenType, reqModel, reqStream, shouldMimicClaudeCode)
 					releaseRetryCtx()
@@ -5088,7 +5101,7 @@ func (s *GatewayService) Forward(ctx context.Context, c *gin.Context, account *A
 								msg2 := extractUpstreamErrorMessage(retryRespBody)
 								if looksLikeToolSignatureError(msg2) && time.Since(retryStart) < maxRetryElapsed {
 									logger.LegacyPrintf("service.gateway", "Account %d: signature retry still failing and looks tool-related, retrying with tool blocks downgraded", account.ID)
-									filteredBody2 := FilterSignatureSensitiveBlocksForRetry(body)
+									filteredBody2 := FilterSignatureSensitiveBlocksForRetry(body, reqModel)
 									retryCtx2, releaseRetryCtx2 := detachStreamUpstreamContext(ctx, reqStream)
 									retryReq2, retryWireBody2, buildErr2 := s.buildUpstreamRequest(retryCtx2, c, account, filteredBody2, token, tokenType, reqModel, reqStream, shouldMimicClaudeCode)
 									releaseRetryCtx2()
@@ -7379,7 +7392,14 @@ func truncateForLog(b []byte, maxBytes int) string {
 
 // shouldRectifySignatureError 统一判断是否应触发签名整流（strip thinking blocks 并重试）。
 // 根据账号类型检查对应的开关和匹配模式。
-func (s *GatewayService) shouldRectifySignatureError(ctx context.Context, account *Account, respBody []byte) bool {
+//
+// mappedModel 用于按 thinking 协议族分流：passback-required (DeepSeek/Kimi/GLM 等) 上游
+// 的 400 不是签名缺失问题，retry 任何 thinking 变形都会破坏「原样回传」契约——直接透传
+// 错误给客户端。详见 thinking_protocol.go。
+func (s *GatewayService) shouldRectifySignatureError(ctx context.Context, account *Account, respBody []byte, mappedModel string) bool {
+	if !ShouldRectifyThinkingSignatureError(mappedModel) {
+		return false
+	}
 	if account.Type == AccountTypeAPIKey {
 		// API Key 账号：独立开关，一次读取配置
 		settings, err := s.settingService.GetRectifierSettings(ctx)
@@ -9814,10 +9834,10 @@ func (s *GatewayService) ForwardCountTokens(ctx context.Context, c *gin.Context,
 	}
 
 	// 检测 thinking block 签名错误（400）并重试一次（过滤 thinking blocks）
-	if resp.StatusCode == 400 && s.shouldRectifySignatureError(ctx, account, respBody) {
+	if resp.StatusCode == 400 && s.shouldRectifySignatureError(ctx, account, respBody, reqModel) {
 		logger.LegacyPrintf("service.gateway", "Account %d: detected thinking block signature error on count_tokens, retrying with filtered thinking blocks", account.ID)
 
-		filteredBody := FilterThinkingBlocksForRetry(body)
+		filteredBody := FilterThinkingBlocksForRetry(body, reqModel)
 		retryReq, retryWireBody, buildErr := s.buildCountTokensRequest(ctx, c, account, filteredBody, token, tokenType, reqModel, shouldMimicClaudeCode)
 		if buildErr == nil {
 			retryResp, retryErr := s.httpUpstream.DoWithTLS(retryReq, proxyURL, account.ID, account.Concurrency, s.tlsFPProfileService.ResolveTLSProfile(account))
diff --git a/backend/internal/service/gemini_messages_compat_service.go b/backend/internal/service/gemini_messages_compat_service.go
index 375fb05326..f041292e2f 100644
--- a/backend/internal/service/gemini_messages_compat_service.go
+++ b/backend/internal/service/gemini_messages_compat_service.go
@@ -835,12 +835,12 @@ func (s *GeminiMessagesCompatService) Forward(ctx context.Context, c *gin.Contex
 				switch signatureRetryStage {
 				case 0:
 					// Stage 1: disable thinking + thinking->text
-					strippedClaudeBody = FilterThinkingBlocksForRetry(originalClaudeBody)
+					strippedClaudeBody = FilterThinkingBlocksForRetry(originalClaudeBody, originalModel)
 					stageName = "thinking-only"
 					signatureRetryStage = 1
 				default:
 					// Stage 2: additionally downgrade tool_use/tool_result blocks to text
-					strippedClaudeBody = FilterSignatureSensitiveBlocksForRetry(originalClaudeBody)
+					strippedClaudeBody = FilterSignatureSensitiveBlocksForRetry(originalClaudeBody, originalModel)
 					stageName = "thinking+tools"
 					signatureRetryStage = 2
 				}
diff --git a/backend/internal/service/thinking_protocol.go b/backend/internal/service/thinking_protocol.go
new file mode 100644
index 0000000000..b7c0f2bc01
--- /dev/null
+++ b/backend/internal/service/thinking_protocol.go
@@ -0,0 +1,106 @@
+package service
+
+import "strings"
+
+// ThinkingProtocol 描述上游对 thinking block 的处理契约。
+// 不同上游对历史 thinking block 的语义要求是相反的：
+//   - Anthropic 官方：要求 thinking block 携带有效 signature，否则 400
+//     "thinking.signature: Field required"
+//   - DeepSeek `/anthropic`、Kimi `/coding` 等第三方 Anthropic 兼容上游：
+//     要求历史 thinking block 原样回传，否则 400
+//     "The content[].thinking in the thinking mode must be passed back to the API"
+//
+// 见 .pensieve/short-term/knowledge/thinking-block-filter-third-party-upstream-inversion/
+type ThinkingProtocol int
+
+const (
+	// ThinkingProtocolUnknown 表示无法识别协议族（默认保守不剥离）。
+	ThinkingProtocolUnknown ThinkingProtocol = iota
+
+	// ThinkingProtocolAnthropicStrict 表示 Anthropic 官方语义：
+	// 历史 thinking block 必须携带有效 signature，缺失/非法签名应剥离。
+	ThinkingProtocolAnthropicStrict
+
+	// ThinkingProtocolPassbackRequired 表示第三方兼容上游语义：
+	// 所有历史 thinking block 必须原样回传，预过滤会破坏契约。
+	ThinkingProtocolPassbackRequired
+)
+
+// ResolveThinkingProtocol 根据「实际发给上游的模型 ID」推断 thinking 协议族。
+// 必须传入映射后的模型 ID（mappedModel），不要传客户端原始请求模型 ID（reqModel），
+// 否则用户配置「claude-sonnet-4-6 → deepseek-v4-pro」时会判错。
+//
+// 匹配规则按厂商前缀硬编码：
+//   - anthropic-strict: claude-* / opus-* / sonnet-* / haiku-*
+//   - passback-required: deepseek-* / kimi-* / moonshot-* / glm-* /
+//     minimax-* / minimax-m* / (qwen-|qwen2-|qwen3-|qwen4-)*-thinking
+//   - unknown: 其他模型（保守不剥离）
+//
+// 已知局限：前缀贪婪匹配（如 `claudette-`、`claude-foreign-relay-` 也会被分类为
+// strict）。当遇到伪装命名时改成显式名单匹配，但现实场景几乎不会出现。
+//
+// 不覆盖的厂商（截至 2026-04）：
+//   - Doubao / Seed (ByteDance)：走 Volcano Engine OpenAI 协议，非 Anthropic 路径
+//   - Hunyuan T1 (Tencent)：未提供 Anthropic 兼容端点
+//   - 若未来出现这些厂商的 Anthropic 兼容代理，需扩展前缀列表
+func ResolveThinkingProtocol(modelID string) ThinkingProtocol {
+	if modelID == "" {
+		return ThinkingProtocolUnknown
+	}
+	id := strings.ToLower(modelID)
+
+	// Passback-required 优先匹配（特定厂商前缀），避免误判 claude-* 时也命中。
+	switch {
+	case strings.HasPrefix(id, "deepseek-"),
+		strings.HasPrefix(id, "kimi-"),
+		strings.HasPrefix(id, "moonshot-"),
+		strings.HasPrefix(id, "glm-"):
+		return ThinkingProtocolPassbackRequired
+	}
+	// MiniMax M 系列：走 https://api.minimax.io/anthropic 端点，
+	// 官方明文要求 thinking block round-trip（interleaved thinking 协议）。
+	// 实例：MiniMax-M2、MiniMax-M2.1、MiniMax-M2.5、MiniMax-M2.7、MiniMax-M2.7-highspeed
+	// 大小写在 ToLower 后统一为 minimax-。
+	if strings.HasPrefix(id, "minimax-m") {
+		return ThinkingProtocolPassbackRequired
+	}
+	// Qwen thinking 变体：覆盖 qwen-/qwen2-/qwen3-/qwen4- 前缀 + 包含 -thinking
+	// 实例：qwen3-235b-a22b-thinking-2507、qwen3-next-80b-a3b-thinking、qwen-3-72b-thinking
+	if (strings.HasPrefix(id, "qwen-") ||
+		strings.HasPrefix(id, "qwen2-") ||
+		strings.HasPrefix(id, "qwen3-") ||
+		strings.HasPrefix(id, "qwen4-")) && strings.Contains(id, "-thinking") {
+		return ThinkingProtocolPassbackRequired
+	}
+
+	switch {
+	case strings.HasPrefix(id, "claude-"),
+		strings.HasPrefix(id, "opus-"),
+		strings.HasPrefix(id, "sonnet-"),
+		strings.HasPrefix(id, "haiku-"):
+		return ThinkingProtocolAnthropicStrict
+	}
+
+	return ThinkingProtocolUnknown
+}
+
+// ShouldPreFilterThinkingBlocks 判断是否应在转发前剥离无效 thinking block。
+// 仅 anthropic-strict 协议族需要预过滤；passback-required/unknown 都跳过，
+// 因为「保留 thinking block」对 anthropic-strict 之外的上游一律更安全。
+func ShouldPreFilterThinkingBlocks(modelID string) bool {
+	return ResolveThinkingProtocol(modelID) == ThinkingProtocolAnthropicStrict
+}
+
+// ShouldRectifyThinkingSignatureError 判断是否应在 400 后触发 thinking 签名整流 retry。
+// 仅 anthropic-strict 触发；passback-required 路径的 400 一般不是签名缺失问题，
+// retry 任何 thinking 变形都不会修好，反而会破坏契约。unknown 同理保守不 retry。
+func ShouldRectifyThinkingSignatureError(modelID string) bool {
+	return ResolveThinkingProtocol(modelID) == ThinkingProtocolAnthropicStrict
+}
+
+// ShouldApplyRetryFilters 判断是否应执行 retry 路径的 thinking/tool block 整流。
+// 与预过滤保持对称：仅 anthropic-strict 走变形；passback-required 与 unknown
+// 一律返回原 body 不变形——避免在不熟悉的上游上做出可能破坏契约的猜测。
+func ShouldApplyRetryFilters(modelID string) bool {
+	return ResolveThinkingProtocol(modelID) == ThinkingProtocolAnthropicStrict
+}
diff --git a/backend/internal/service/thinking_protocol_filter_integration_test.go b/backend/internal/service/thinking_protocol_filter_integration_test.go
new file mode 100644
index 0000000000..989a0d509d
--- /dev/null
+++ b/backend/internal/service/thinking_protocol_filter_integration_test.go
@@ -0,0 +1,80 @@
+package service
+
+import (
+	"bytes"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+// 第三方 Claude 兼容上游 (DeepSeek/Kimi/GLM 等) 要求历史 thinking block 原样回传，
+// 任何过滤都会破坏「thinking 必须 round-trip」契约。这些测试锁住「mappedModel 命中
+// passback-required 时，3 个过滤函数都返回原 body」的行为，避免回归。
+// 详见 .pensieve/short-term/knowledge/thinking-block-filter-third-party-upstream-inversion/
+
+const passbackThinkingBody = `{
+	"model":"deepseek-v4-pro",
+	"thinking":{"type":"enabled","budget_tokens":1024},
+	"messages":[
+		{"role":"user","content":[{"type":"text","text":"Hi"}]},
+		{"role":"assistant","content":[
+			{"type":"thinking","thinking":"Let me think..."},
+			{"type":"text","text":"Answer"}
+		]}
+	]
+}`
+
+func TestFilterThinkingBlocks_SkipsForPassbackRequired(t *testing.T) {
+	in := []byte(passbackThinkingBody)
+	out := FilterThinkingBlocks(in, "deepseek-v4-pro")
+	// passback-required: 原样回传 body（byte-for-byte 不变）
+	require.True(t, bytes.Equal(in, out), "passback-required 上游不应过滤 thinking block")
+}
+
+func TestFilterThinkingBlocksForRetry_SkipsForPassbackRequired(t *testing.T) {
+	in := []byte(passbackThinkingBody)
+	out := FilterThinkingBlocksForRetry(in, "kimi-coding")
+	require.True(t, bytes.Equal(in, out), "passback-required 上游 retry 不应剥离 thinking block")
+}
+
+func TestFilterSignatureSensitiveBlocksForRetry_SkipsForPassbackRequired(t *testing.T) {
+	in := []byte(passbackThinkingBody)
+	out := FilterSignatureSensitiveBlocksForRetry(in, "glm-5.1")
+	require.True(t, bytes.Equal(in, out), "passback-required 上游不应降级 thinking/tool block")
+}
+
+// 反向验证：anthropic-strict 路径仍然按原逻辑剥离无 signature 的 thinking block
+func TestFilterThinkingBlocks_StripsForAnthropicStrict(t *testing.T) {
+	in := []byte(passbackThinkingBody)
+	out := FilterThinkingBlocks(in, "claude-sonnet-4-5")
+	// anthropic-strict: thinking.type=enabled 且 thinking block 无 signature → 应剥离
+	require.False(t, bytes.Equal(in, out), "anthropic-strict 上游应剥离无 signature 的 thinking block")
+	require.NotContains(t, string(out), `"type":"thinking"`)
+}
+
+// Unknown 协议族保守不过滤（与 passback-required 一致）
+func TestFilterThinkingBlocks_SkipsForUnknownModel(t *testing.T) {
+	in := []byte(passbackThinkingBody)
+	out := FilterThinkingBlocks(in, "yi-large")
+	require.True(t, bytes.Equal(in, out), "unknown 协议族保守不过滤")
+}
+
+func TestFilterThinkingBlocks_SkipsForEmptyModel(t *testing.T) {
+	in := []byte(passbackThinkingBody)
+	out := FilterThinkingBlocks(in, "")
+	require.True(t, bytes.Equal(in, out), "空 model 保守不过滤")
+}
+
+// retry 路径上 unknown 与 passback-required 行为对称：都返回原 body。
+// 避免「预过滤跳过但 retry 仍剥离」的语义裂缝。
+func TestFilterThinkingBlocksForRetry_SkipsForUnknownModel(t *testing.T) {
+	in := []byte(passbackThinkingBody)
+	out := FilterThinkingBlocksForRetry(in, "yi-large")
+	require.True(t, bytes.Equal(in, out), "unknown 协议族 retry 不应剥离 thinking block")
+}
+
+func TestFilterSignatureSensitiveBlocksForRetry_SkipsForUnknownModel(t *testing.T) {
+	in := []byte(passbackThinkingBody)
+	out := FilterSignatureSensitiveBlocksForRetry(in, "gpt-5.1")
+	require.True(t, bytes.Equal(in, out), "unknown 协议族不应降级 thinking/tool block")
+}
diff --git a/backend/internal/service/thinking_protocol_test.go b/backend/internal/service/thinking_protocol_test.go
new file mode 100644
index 0000000000..3ca860bb1c
--- /dev/null
+++ b/backend/internal/service/thinking_protocol_test.go
@@ -0,0 +1,120 @@
+package service
+
+import "testing"
+
+func TestResolveThinkingProtocol(t *testing.T) {
+	tests := []struct {
+		name    string
+		modelID string
+		want    ThinkingProtocol
+	}{
+		// Anthropic 官方
+		{"claude-sonnet-4-5", "claude-sonnet-4-5", ThinkingProtocolAnthropicStrict},
+		{"claude-opus-4-5", "claude-opus-4-5-20251101", ThinkingProtocolAnthropicStrict},
+		{"claude-haiku full id", "claude-haiku-4-5-20251001", ThinkingProtocolAnthropicStrict},
+		{"opus short", "opus-4-5", ThinkingProtocolAnthropicStrict},
+		{"sonnet short", "sonnet-4-5", ThinkingProtocolAnthropicStrict},
+		{"haiku short", "haiku-4-5", ThinkingProtocolAnthropicStrict},
+		{"upper case Claude", "Claude-Sonnet-4-5", ThinkingProtocolAnthropicStrict},
+
+		// 第三方兼容上游
+		{"deepseek-v4-pro", "deepseek-v4-pro", ThinkingProtocolPassbackRequired},
+		{"deepseek-r2-thinking", "deepseek-r2-thinking", ThinkingProtocolPassbackRequired},
+		{"kimi-coding", "kimi-coding-v2", ThinkingProtocolPassbackRequired},
+		{"kimi-k2-thinking", "kimi-k2-thinking", ThinkingProtocolPassbackRequired},
+		{"moonshot-v1", "moonshot-v1-32k", ThinkingProtocolPassbackRequired},
+		{"glm-5.1", "glm-5.1", ThinkingProtocolPassbackRequired},
+		{"qwen-2 thinking variant", "qwen-2-72b-thinking", ThinkingProtocolPassbackRequired},
+		{"qwen3 thinking (real Alibaba naming)", "qwen3-235b-a22b-thinking-2507", ThinkingProtocolPassbackRequired},
+		{"qwen3-next thinking", "qwen3-next-80b-a3b-thinking", ThinkingProtocolPassbackRequired},
+		{"upper case Deepseek", "DeepSeek-V4-Pro", ThinkingProtocolPassbackRequired},
+
+		// MiniMax M 系列（Anthropic 兼容端点要求 thinking round-trip）
+		{"MiniMax-M2 (case-sensitive original)", "MiniMax-M2", ThinkingProtocolPassbackRequired},
+		{"MiniMax-M2.1", "MiniMax-M2.1", ThinkingProtocolPassbackRequired},
+		{"MiniMax-M2.5", "MiniMax-M2.5", ThinkingProtocolPassbackRequired},
+		{"MiniMax-M2.7", "MiniMax-M2.7", ThinkingProtocolPassbackRequired},
+		{"MiniMax-M2.7-highspeed", "MiniMax-M2.7-highspeed", ThinkingProtocolPassbackRequired},
+		{"minimax-m2 lowercase", "minimax-m2", ThinkingProtocolPassbackRequired},
+
+		// 未知 / 保守
+		{"empty", "", ThinkingProtocolUnknown},
+		{"gpt-5", "gpt-5.1", ThinkingProtocolUnknown},
+		{"gemini", "gemini-3-pro-preview", ThinkingProtocolUnknown},
+		{"qwen3 non-thinking", "qwen3-32b", ThinkingProtocolUnknown},
+		{"qwen2 non-thinking", "qwen-2-72b", ThinkingProtocolUnknown},
+		{"random vendor", "yi-large", ThinkingProtocolUnknown},
+		// MiniMax 非 M 系列（如 abab、speech 等其他产品线）—— unknown
+		{"minimax abab non-M", "abab6.5-chat", ThinkingProtocolUnknown},
+		// Doubao 走 OpenAI 协议，不属于本网关 Anthropic 路径——归 unknown
+		{"doubao goes via openai", "doubao-1-5-thinking-vision-pro-250428", ThinkingProtocolUnknown},
+		// Hunyuan T1 未暴露 Anthropic 端点——归 unknown
+		{"hunyuan t1 no anthropic endpoint", "hunyuan-t1", ThinkingProtocolUnknown},
+		{"hy-t1 short alias", "hy-t1", ThinkingProtocolUnknown},
+		// claude-something 但不是 anthropic 官方命名风格——也归 strict（前缀匹配优先）
+		{"weird claude prefix", "claude-experimental-fork", ThinkingProtocolAnthropicStrict},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := ResolveThinkingProtocol(tt.modelID)
+			if got != tt.want {
+				t.Errorf("ResolveThinkingProtocol(%q) = %v, want %v", tt.modelID, got, tt.want)
+			}
+		})
+	}
+}
+
+func TestShouldPreFilterThinkingBlocks(t *testing.T) {
+	tests := []struct {
+		modelID string
+		want    bool
+	}{
+		{"claude-sonnet-4-5", true},
+		{"deepseek-v4-pro", false},
+		{"kimi-coding", false},
+		{"glm-5.1", false},
+		{"gpt-5.1", false},
+		{"", false},
+	}
+	for _, tt := range tests {
+		t.Run(tt.modelID, func(t *testing.T) {
+			if got := ShouldPreFilterThinkingBlocks(tt.modelID); got != tt.want {
+				t.Errorf("ShouldPreFilterThinkingBlocks(%q) = %v, want %v", tt.modelID, got, tt.want)
+			}
+		})
+	}
+}
+
+func TestShouldRectifyThinkingSignatureError(t *testing.T) {
+	if !ShouldRectifyThinkingSignatureError("claude-sonnet-4-5") {
+		t.Error("anthropic-strict should rectify signature error")
+	}
+	if ShouldRectifyThinkingSignatureError("deepseek-v4-pro") {
+		t.Error("passback-required must NOT rectify (would break protocol contract)")
+	}
+	if ShouldRectifyThinkingSignatureError("gpt-5.1") {
+		t.Error("unknown should NOT rectify (conservative default)")
+	}
+	if ShouldRectifyThinkingSignatureError("") {
+		t.Error("empty model id should NOT rectify")
+	}
+}
+
+// ShouldApplyRetryFilters 与 ShouldPreFilterThinkingBlocks 必须语义一致：
+// 仅 anthropic-strict 走变形，避免预过滤跳过但 retry 路径反而剥离的语义裂缝。
+func TestShouldApplyRetryFiltersMirrorsPreFilter(t *testing.T) {
+	models := []string{
+		"claude-sonnet-4-5", "claude-opus-4-5-20251101", "haiku-4-5",
+		"deepseek-v4-pro", "kimi-coding", "glm-5.1",
+		"qwen3-235b-a22b-thinking-2507", "qwen3-32b",
+		"gpt-5.1", "gemini-3-pro-preview", "yi-large", "",
+	}
+	for _, m := range models {
+		t.Run(m, func(t *testing.T) {
+			if got := ShouldApplyRetryFilters(m); got != ShouldPreFilterThinkingBlocks(m) {
+				t.Errorf("ShouldApplyRetryFilters(%q)=%v but ShouldPreFilterThinkingBlocks=%v — must match",
+					m, got, ShouldPreFilterThinkingBlocks(m))
+			}
+		})
+	}
+}