fix(reasoning): accumulate and strip reasoning tags from autoparser results

core/http/endpoints/openai/chat.go

@@ -86,7 +86,11 @@ func ChatEndpoint(cl *config.ModelConfigLoader, ml *model.ModelLoader, evaluator
 
 			// Prefer pre-parsed chat deltas from C++ autoparser when available
 			if tokenUsage.HasChatDeltaContent() {
-				reasoningDelta, contentDelta = tokenUsage.ChatDeltaReasoningAndContent()
+				rawReasoning, cd := tokenUsage.ChatDeltaReasoningAndContent()
+				contentDelta = cd
+				// Strip reasoning tags (e.g. <|channel>thought / <channel|>) that
+				// the C++ autoparser includes as part of reasoning content.
+				reasoningDelta = extractor.ProcessChatDeltaReasoning(rawReasoning)
 				// Keep extractor state consistent for fallback
 				extractor.ProcessToken(s)
 			} else {
@@ -149,7 +153,11 @@ func ChatEndpoint(cl *config.ModelConfigLoader, ml *model.ModelLoader, evaluator
 
 			// Prefer pre-parsed chat deltas from C++ autoparser when available
 			if usage.HasChatDeltaContent() {
-				reasoningDelta, contentDelta = usage.ChatDeltaReasoningAndContent()
+				rawReasoning, cd := usage.ChatDeltaReasoningAndContent()
+				contentDelta = cd
+				// Strip reasoning tags (e.g. <|channel>thought / <channel|>) that
+				// the C++ autoparser includes as part of reasoning content.
+				reasoningDelta = extractor.ProcessChatDeltaReasoning(rawReasoning)
 				// Keep extractor state consistent for fallback
 				extractor.ProcessToken(s)
 			} else {

core/http/endpoints/openresponses/responses.go

@@ -1823,7 +1823,9 @@ func handleOpenResponsesStream(c echo.Context, responseID string, createdAt int6
 					var reasoningDelta, contentDelta string
 					// Prefer pre-parsed chat deltas from C++ autoparser when available
 					if tokenUsage.HasChatDeltaContent() {
-						reasoningDelta, contentDelta = tokenUsage.ChatDeltaReasoningAndContent()
+						rawReasoning, cd := tokenUsage.ChatDeltaReasoningAndContent()
+						contentDelta = cd
+						reasoningDelta = extractor.ProcessChatDeltaReasoning(rawReasoning)
 						extractor.ProcessToken(token) // keep state consistent
 					} else {
 						reasoningDelta, contentDelta = extractor.ProcessToken(token)
@@ -2350,7 +2352,9 @@ func handleOpenResponsesStream(c echo.Context, responseID string, createdAt int6
 		var reasoningDelta, contentDelta string
 		// Prefer pre-parsed chat deltas from C++ autoparser when available
 		if tokenUsage.HasChatDeltaContent() {
-			reasoningDelta, contentDelta = tokenUsage.ChatDeltaReasoningAndContent()
+			rawReasoning, cd := tokenUsage.ChatDeltaReasoningAndContent()
+			contentDelta = cd
+			reasoningDelta = extractor.ProcessChatDeltaReasoning(rawReasoning)
 			extractor.ProcessToken(token) // keep state consistent
 		} else {
 			reasoningDelta, contentDelta = extractor.ProcessToken(token)

pkg/reasoning/extractor.go

@@ -21,6 +21,12 @@ type ReasoningExtractor struct {
 	lastReasoning      string
 	lastCleaned        string
 	suppressReasoning  bool
+
+	// ChatDelta reasoning accumulator — used by ProcessChatDeltaReasoning
+	// to strip reasoning tags (e.g. <|channel>thought, <channel|>) that
+	// the C++ autoparser includes in reasoning_content deltas.
+	cdReasoningAccum        string
+	cdLastStrippedReasoning string
 }
 
 // NewReasoningExtractor creates a new extractor for the given thinking token and config.
@@ -64,6 +70,61 @@ func (e *ReasoningExtractor) ProcessToken(token string) (reasoningDelta, content
 	return reasoningDelta, contentDelta
 }
 
+// ProcessChatDeltaReasoning accumulates raw reasoning text from C++ autoparser
+// ChatDeltas, strips any embedded reasoning tags (e.g. <|channel>thought …
+// <channel|> for Gemma 4), and returns only the new stripped delta.
+// This prevents tag tokens from leaking into the reasoning field of SSE chunks.
+//
+// When the C++ autoparser already strips tags (e.g. <think> models), the text
+// passes through unchanged — ExtractReasoning finds no tags so we use the raw text.
+func (e *ReasoningExtractor) ProcessChatDeltaReasoning(rawDelta string) string {
+	if rawDelta == "" {
+		return ""
+	}
+	e.cdReasoningAccum += rawDelta
+
+	// Try to strip reasoning tags from accumulated ChatDelta reasoning.
+	stripped, cleaned := ExtractReasoning(e.cdReasoningAccum, &e.config)
+
+	if stripped == "" {
+		// ExtractReasoning found no reasoning content. This happens when:
+		// a) A complete start tag was found but has no content after it yet
+		//    (cleaned == "" because everything is inside the unclosed tag)
+		//    → keep buffering
+		// b) We're accumulating a partial multi-token start tag
+		//    (e.g. "<|channel>" before "thought" arrives)
+		//    → keep buffering
+		// c) No tags at all — C++ already stripped them
+		//    → pass through the raw text as-is
+		if cleaned == "" && strings.TrimSpace(e.cdReasoningAccum) != "" {
+			// Case (a): tag found, unclosed, no content yet
+			stripped = ""
+		} else if e.thinkingStartToken != "" &&
+			len(strings.TrimSpace(e.cdReasoningAccum)) < len(e.thinkingStartToken) &&
+			strings.HasPrefix(e.thinkingStartToken, strings.TrimSpace(e.cdReasoningAccum)) {
+			// Case (b): partial start tag prefix
+			stripped = ""
+		} else {
+			// Case (c): no tags found — text is already clean from C++
+			stripped = e.cdReasoningAccum
+		}
+	}
+
+	// Compute delta from stripped reasoning
+	var delta string
+	if len(stripped) > len(e.cdLastStrippedReasoning) && strings.HasPrefix(stripped, e.cdLastStrippedReasoning) {
+		delta = stripped[len(e.cdLastStrippedReasoning):]
+	} else if stripped != e.cdLastStrippedReasoning && stripped != "" {
+		delta = stripped
+	}
+	e.cdLastStrippedReasoning = stripped
+
+	if e.suppressReasoning {
+		return ""
+	}
+	return delta
+}
+
 // Reasoning returns the total accumulated reasoning after streaming.
 func (e *ReasoningExtractor) Reasoning() string {
 	return e.lastReasoning
@@ -84,6 +145,8 @@ func (e *ReasoningExtractor) Reset() {
 	e.accumulated = ""
 	e.lastReasoning = ""
 	e.lastCleaned = ""
+	e.cdReasoningAccum = ""
+	e.cdLastStrippedReasoning = ""
 }
 
 // ResetAndSuppressReasoning clears state and suppresses future reasoning deltas.
@@ -95,6 +158,8 @@ func (e *ReasoningExtractor) ResetAndSuppressReasoning() {
 	e.accumulated = ""
 	e.lastReasoning = ""
 	e.lastCleaned = ""
+	e.cdReasoningAccum = ""
+	e.cdLastStrippedReasoning = ""
 	e.suppressReasoning = true
 }
 

pkg/reasoning/extractor_test.go

@@ -195,4 +195,91 @@ var _ = Describe("ReasoningExtractor", func() {
 			Expect(ext.CleanedContent()).To(Equal("visible content"))
 		})
 	})
+
+	Context("ProcessChatDeltaReasoning with Gemma 4 tags", func() {
+		It("should strip <|channel>thought and <channel|> tags from streaming deltas", func() {
+			ext := NewReasoningExtractor("<|channel>thought", Config{})
+
+			// Simulate C++ autoparser sending tag tokens as reasoning
+			d1 := ext.ProcessChatDeltaReasoning("<|channel>")
+			Expect(d1).To(BeEmpty(), "start tag prefix should be buffered, not emitted")
+
+			d2 := ext.ProcessChatDeltaReasoning("thought")
+			Expect(d2).To(BeEmpty(), "start tag suffix should be buffered, not emitted")
+
+			d3 := ext.ProcessChatDeltaReasoning("\n")
+			Expect(d3).To(BeEmpty(), "newline after start tag should not emit yet")
+
+			d4 := ext.ProcessChatDeltaReasoning("The")
+			Expect(d4).To(Equal("The"))
+
+			d5 := ext.ProcessChatDeltaReasoning(" user")
+			Expect(d5).To(Equal(" user"))
+
+			d6 := ext.ProcessChatDeltaReasoning(" asks")
+			Expect(d6).To(Equal(" asks"))
+
+			// Trailing newline gets TrimSpaced by ExtractReasoning,
+			// so it appears delayed with the next non-whitespace token
+			d7 := ext.ProcessChatDeltaReasoning("\n")
+			Expect(d7).To(BeEmpty(), "trailing newline is buffered by TrimSpace")
+
+			d8 := ext.ProcessChatDeltaReasoning("2+2=4")
+			Expect(d8).To(Equal("\n2+2=4"), "delayed newline emitted with next content")
+
+			d9 := ext.ProcessChatDeltaReasoning("<channel|>")
+			Expect(d9).To(BeEmpty(), "close tag should be consumed, not emitted")
+		})
+
+		It("should handle empty deltas", func() {
+			ext := NewReasoningExtractor("<|channel>thought", Config{})
+			d := ext.ProcessChatDeltaReasoning("")
+			Expect(d).To(BeEmpty())
+		})
+
+		It("should pass through reasoning without tags unchanged", func() {
+			ext := NewReasoningExtractor("<think>", Config{})
+
+			// When C++ autoparser already strips tags (e.g. <think> models),
+			// reasoning arrives clean — just pass it through.
+			d1 := ext.ProcessChatDeltaReasoning("I need to")
+			Expect(d1).To(Equal("I need to"))
+
+			d2 := ext.ProcessChatDeltaReasoning(" think carefully")
+			Expect(d2).To(Equal(" think carefully"))
+		})
+
+		It("should strip <think> tags if C++ autoparser includes them", func() {
+			ext := NewReasoningExtractor("<think>", Config{})
+
+			d1 := ext.ProcessChatDeltaReasoning("<think>")
+			Expect(d1).To(BeEmpty())
+
+			d2 := ext.ProcessChatDeltaReasoning("reasoning")
+			Expect(d2).To(Equal("reasoning"))
+
+			d3 := ext.ProcessChatDeltaReasoning("</think>")
+			Expect(d3).To(BeEmpty())
+		})
+
+		It("should respect suppressReasoning", func() {
+			ext := NewReasoningExtractor("<|channel>thought", Config{})
+			ext.ResetAndSuppressReasoning()
+
+			d := ext.ProcessChatDeltaReasoning("some reasoning")
+			Expect(d).To(BeEmpty())
+		})
+
+		It("should reset ChatDelta state on Reset", func() {
+			ext := NewReasoningExtractor("<|channel>thought", Config{})
+
+			ext.ProcessChatDeltaReasoning("<|channel>thought")
+			ext.ProcessChatDeltaReasoning("\nfirst reasoning")
+			ext.Reset()
+
+			// After reset, should start fresh
+			d := ext.ProcessChatDeltaReasoning("clean reasoning")
+			Expect(d).To(Equal("clean reasoning"))
+		})
+	})
 })