fix(gemini): isolate textual reasoning wrappers (#3605)

Split-out PR C from #3584. Isolates textual reasoning wrappers (<think>/<thinking>/<thought>/<internal_thought>, including malformed/open tags) into reasoning_content across both the non-streaming sanitizer and the Gemini streaming translator, with split-chunk buffering. Additive to the existing textual tool-call pipeline; does not touch the #3569 native functionResponse path. Integrated into release/v3.8.21. Thanks @dhaern!

open-sse/handlers/responseSanitizer.ts

@@ -200,8 +200,20 @@ function hasVisibleMessageContent(content: unknown): boolean {
   });
 }
 
-// Matches <think>...</think> blocks and <thinking>...</thinking> (greedy, dotAll)
-const THINK_TAG_REGEX = /<(?:think|thinking)>([\s\S]*?)<\/(?:think|thinking)>/gi;
+const REASONING_TAG_NAMES = ["think", "thinking", "thought", "internal_thought"];
+const REASONING_TAG_PATTERN = REASONING_TAG_NAMES.join("|");
+// Matches complete <think>/<thinking>/<thought>/<internal_thought> blocks.
+const THINK_TAG_REGEX = new RegExp(
+  `<(${REASONING_TAG_PATTERN})\\b[^>]*>([\\s\\S]*?)<\\/\\1>`,
+  "gi"
+);
+// Matches an unclosed reasoning tag at the end of a message. Some providers can
+// emit malformed/open reasoning wrappers (for example "<thought\n...") before a
+// tool call. Treat that tail as reasoning instead of visible assistant text.
+const UNCLOSED_REASONING_TAG_REGEX = new RegExp(
+  `<(${REASONING_TAG_PATTERN})(?:\\s[^>]*)?(?:>|\\r?\\n)([\\s\\S]*)$`,
+  "i"
+);
 
 // #638, #727: Collapse runs of 2+ consecutive newlines into \n\n
 // Tool call responses from thinking models often accumulate excessive newlines
@@ -225,7 +237,7 @@ export function extractThinkingFromContent(text: string): {
   const thinkingParts: string[] = [];
   let hasThinkTags = false;
 
-  const cleaned = text.replace(THINK_TAG_REGEX, (_, thinkContent) => {
+  let cleaned = text.replace(THINK_TAG_REGEX, (_match, _tagName, thinkContent) => {
     hasThinkTags = true;
     const trimmed = thinkContent.trim();
     if (trimmed) {
@@ -234,6 +246,15 @@ export function extractThinkingFromContent(text: string): {
     return "";
   });
 
+  const unclosedMatch = cleaned.match(UNCLOSED_REASONING_TAG_REGEX);
+  if (unclosedMatch?.index !== undefined) {
+    hasThinkTags = true;
+    const reasoning = String(unclosedMatch[2] || "").trim();
+    if (reasoning) thinkingParts.push(reasoning);
+    const prefix = cleaned.slice(0, unclosedMatch.index);
+    cleaned = /^(?:\s|§\d+§)*$/.test(prefix) ? "" : prefix;
+  }
+
   if (!hasThinkTags) {
     return { content: text, thinking: null };
   }
@@ -987,7 +1008,9 @@ export function sanitizeStreamingChunk(parsed: unknown): unknown {
 
   // Keep only standard fields — normalize id to string to avoid AI_InvalidResponseDataError
   if (parsedRecord.id !== undefined && parsedRecord.id !== null) {
-    sanitized.id = normalizeResponseId(typeof parsedRecord.id === "string" ? parsedRecord.id : String(parsedRecord.id));
+    sanitized.id = normalizeResponseId(
+      typeof parsedRecord.id === "string" ? parsedRecord.id : String(parsedRecord.id)
+    );
   }
   sanitized.object = toString(parsedRecord.object) || "chat.completion.chunk";
   if (parsedRecord.created !== undefined) sanitized.created = parsedRecord.created;

open-sse/translator/request/openai-to-gemini.ts

@@ -77,7 +77,7 @@ type GeminiRequest = {
 
 type CloudCodeEnvelope = {
   project: string;
-  model: string;
+  model?: string;
   user_prompt_id?: string;
   userAgent?: "antigravity" | "jetski" | string;
   requestId?: string;

open-sse/translator/response/gemini-to-openai.ts

@@ -11,6 +11,9 @@ import {
 
 type GeminiToOpenAIState = {
   functionIndex: number;
+  finishReason?: string;
+  groundingProcessed?: boolean;
+  hasEmittedContent?: boolean;
   messageId: string;
   model: string;
   pendingThoughtSignature?: string | null;
@@ -18,7 +21,20 @@ type GeminiToOpenAIState = {
   toolCalls: Map<number, unknown>;
   toolNameMap?: Map<string, string>;
   textualToolCallBuffer?: string;
-  hasEmittedContent?: boolean;
+  textualReasoningTagBuffer?: string;
+  activeTextualReasoningTag?: string;
+  textualReasoningContentBuffer?: string;
+  usage?: {
+    prompt_tokens: number;
+    completion_tokens: number;
+    total_tokens: number;
+    prompt_tokens_details?: {
+      cached_tokens: number;
+    };
+    completion_tokens_details?: {
+      reasoning_tokens: number;
+    };
+  };
 };
 
 type GeminiFunctionCallPart = {
@@ -29,6 +45,162 @@ type GeminiFunctionCallPart = {
   };
 };
 
+const REASONING_TAG_OPEN_REGEX =
+  /<(think|thinking|thought|internal_thought)(?=\s|>|\r?\n)(?:\s[^>]*)?(?:>|\r?\n)/i;
+const REASONING_TAG_OPEN_PREFIXES = ["<think", "<thinking", "<thought", "<internal_thought"];
+
+function isIgnorableReasoningTagPrefix(value: string): boolean {
+  return /^(?:\s|§\d+§)*$/.test(value);
+}
+
+function getTrailingReasoningTagPrefixStart(text: string): number {
+  const lastOpen = text.lastIndexOf("<");
+  if (lastOpen < 0) return -1;
+  const suffix = text.slice(lastOpen).toLowerCase();
+  if (!suffix || suffix.includes(">") || suffix.includes("\n") || suffix.includes("\r")) return -1;
+  return REASONING_TAG_OPEN_PREFIXES.some((prefix) => prefix.startsWith(suffix)) ? lastOpen : -1;
+}
+
+function getTrailingReasoningCloseTagPrefixStart(text: string, tagName: string): number {
+  const lastClose = text.lastIndexOf("</");
+  if (lastClose < 0) return -1;
+  const suffix = text.slice(lastClose).toLowerCase();
+  if (!suffix || suffix.includes(">") || suffix.includes("\n") || suffix.includes("\r")) return -1;
+  return `</${tagName.toLowerCase()}>`.startsWith(suffix) ? lastClose : -1;
+}
+
+function consumeTextualReasoningTags(
+  text: string,
+  state: GeminiToOpenAIState,
+  results: Array<Record<string, unknown>>
+): string {
+  const pendingTagBuffer = state.textualReasoningTagBuffer || "";
+
+  if (state.activeTextualReasoningTag && pendingTagBuffer.startsWith("</")) {
+    const combinedClose = `${pendingTagBuffer}${text}`;
+    const closeTag = `</${state.activeTextualReasoningTag}>`;
+    const lowerCombinedClose = combinedClose.toLowerCase();
+    const lowerCloseTag = closeTag.toLowerCase();
+
+    if (lowerCombinedClose.startsWith(lowerCloseTag)) {
+      emitTextDelta(state.textualReasoningContentBuffer || "", state, results, "reasoning_content");
+      state.activeTextualReasoningTag = undefined;
+      state.textualReasoningContentBuffer = undefined;
+      state.textualReasoningTagBuffer = undefined;
+      return combinedClose.slice(closeTag.length);
+    }
+
+    if (lowerCloseTag.startsWith(lowerCombinedClose)) {
+      state.textualReasoningTagBuffer = combinedClose;
+      return "";
+    }
+  }
+
+  let remaining = `${state.textualReasoningTagBuffer || ""}${text}`;
+  state.textualReasoningTagBuffer = undefined;
+
+  while (remaining) {
+    if (state.activeTextualReasoningTag) {
+      const bufferedReasoning = `${state.textualReasoningContentBuffer || ""}${remaining}`;
+      const closeRegex = new RegExp(`</${state.activeTextualReasoningTag}>`, "i");
+      const closeMatch = closeRegex.exec(bufferedReasoning);
+      if (!closeMatch || closeMatch.index < 0) {
+        const partialCloseStart = getTrailingReasoningCloseTagPrefixStart(
+          bufferedReasoning,
+          state.activeTextualReasoningTag
+        );
+        if (partialCloseStart >= 0) {
+          state.textualReasoningContentBuffer = bufferedReasoning.slice(0, partialCloseStart);
+          state.textualReasoningTagBuffer = bufferedReasoning.slice(partialCloseStart);
+          return "";
+        }
+        state.textualReasoningContentBuffer = bufferedReasoning;
+        return "";
+      }
+
+      emitTextDelta(
+        bufferedReasoning.slice(0, closeMatch.index),
+        state,
+        results,
+        "reasoning_content"
+      );
+      state.activeTextualReasoningTag = undefined;
+      state.textualReasoningContentBuffer = undefined;
+      const closeEnd = bufferedReasoning.indexOf(">", closeMatch.index);
+      remaining = bufferedReasoning.slice(
+        closeEnd >= 0 ? closeEnd + 1 : closeMatch.index + closeMatch[0].length
+      );
+      continue;
+    }
+
+    const openMatch = REASONING_TAG_OPEN_REGEX.exec(remaining);
+    if (!openMatch || openMatch.index < 0) {
+      const partialStart = getTrailingReasoningTagPrefixStart(remaining);
+      if (partialStart >= 0) {
+        state.textualReasoningTagBuffer = remaining.slice(partialStart);
+        const prefix = remaining.slice(0, partialStart);
+        return isIgnorableReasoningTagPrefix(prefix) ? "" : prefix;
+      }
+      return remaining;
+    }
+
+    const before = remaining.slice(0, openMatch.index);
+    if (before && !isIgnorableReasoningTagPrefix(before)) {
+      emitTextDelta(before, state, results, "content");
+    }
+
+    const tagName = openMatch[1];
+    const bodyStart = openMatch.index + openMatch[0].length;
+    const afterOpen = remaining.slice(bodyStart);
+    const closeRegex = new RegExp(`</${tagName}>`, "i");
+    const closeMatch = closeRegex.exec(afterOpen);
+    if (!closeMatch || closeMatch.index < 0) {
+      state.activeTextualReasoningTag = tagName;
+      state.textualReasoningContentBuffer = afterOpen;
+      return "";
+    }
+
+    emitTextDelta(afterOpen.slice(0, closeMatch.index), state, results, "reasoning_content");
+    remaining = afterOpen.slice(closeMatch.index + closeMatch[0].length);
+  }
+
+  return "";
+}
+
+function flushOpenTextualReasoning(
+  state: GeminiToOpenAIState,
+  results: Array<Record<string, unknown>>
+): void {
+  if (!state.activeTextualReasoningTag && !state.textualReasoningContentBuffer) return;
+  emitTextDelta(state.textualReasoningContentBuffer || "", state, results, "reasoning_content");
+  state.activeTextualReasoningTag = undefined;
+  state.textualReasoningContentBuffer = undefined;
+  state.textualReasoningTagBuffer = undefined;
+}
+
+function emitTextDelta(
+  content: string,
+  state: GeminiToOpenAIState,
+  results: Array<Record<string, unknown>>,
+  field: "content" | "reasoning_content" = "content"
+) {
+  if (!content) return;
+  if (field === "content") state.hasEmittedContent = true;
+  results.push({
+    id: `chatcmpl-${state.messageId}`,
+    object: "chat.completion.chunk",
+    created: Math.floor(Date.now() / 1000),
+    model: state.model,
+    choices: [
+      {
+        index: 0,
+        delta: { [field]: content },
+        finish_reason: null,
+      },
+    ],
+  });
+}
+
 function normalizeToolCallArgs(args: unknown): unknown {
   if (typeof args !== "string") return args;
   const trimmed = args.trim();
@@ -215,6 +387,9 @@ export function geminiToOpenAIResponse(chunk, state) {
         }
 
         if (hasFunctionCall) {
+          state.activeTextualReasoningTag = undefined;
+          state.textualReasoningTagBuffer = undefined;
+          state.textualReasoningContentBuffer = undefined;
           emitFunctionCallPart(part, state, results);
         }
         continue;
@@ -226,7 +401,10 @@ export function geminiToOpenAIResponse(chunk, state) {
       // back to a structured OpenAI tool call so clients/tools do not see it as
       // assistant prose.
       if (part.text !== undefined && part.text !== "") {
-        let accumulated = (state.textualToolCallBuffer || "") + part.text;
+        const afterReasoning = consumeTextualReasoningTags(part.text, state, results);
+        if (!afterReasoning) continue;
+
+        let accumulated = (state.textualToolCallBuffer || "") + afterReasoning;
 
         let candidate = parseTextualToolCallCandidate(accumulated);
 
@@ -238,10 +416,7 @@ export function geminiToOpenAIResponse(chunk, state) {
           }
           if (toolCallIndex < 0) {
             const lastParen = accumulated.lastIndexOf("(");
-            if (
-              lastParen !== -1 &&
-              "(empty)[Tool call:".startsWith(accumulated.slice(lastParen))
-            ) {
+            if (lastParen !== -1 && "(empty)[Tool call:".startsWith(accumulated.slice(lastParen))) {
               toolCallIndex = lastParen;
             } else {
               const lastBracket = accumulated.lastIndexOf("[");
@@ -293,7 +468,7 @@ export function geminiToOpenAIResponse(chunk, state) {
         }
 
         if (state.textualToolCallBuffer) {
-          const flushedText = state.textualToolCallBuffer + part.text;
+          const flushedText = state.textualToolCallBuffer + afterReasoning;
           state.textualToolCallBuffer = "";
           state.hasEmittedContent = true;
           results.push({
@@ -321,7 +496,7 @@ export function geminiToOpenAIResponse(chunk, state) {
           choices: [
             {
               index: 0,
-              delta: { content: part.text },
+              delta: { content: afterReasoning },
               finish_reason: null,
             },
           ],
@@ -444,6 +619,8 @@ export function geminiToOpenAIResponse(chunk, state) {
 
   // Finish reason - include usage in final chunk
   if (candidate.finishReason) {
+    flushOpenTextualReasoning(state, results);
+
     if (state.textualToolCallBuffer) {
       const remainingText = state.textualToolCallBuffer;
       state.textualToolCallBuffer = "";

tests/unit/response-sanitizer.test.ts

@@ -63,6 +63,23 @@ test("sanitizeOpenAIResponse extracts thinking, collapses newlines, preserves re
   assert.deepEqual((sanitized as any).choices[0].message.function_call, { name: "legacy" });
 });
 
+test("sanitizeOpenAIResponse extracts unclosed reasoning wrappers into reasoning_content", () => {
+  const sanitized = sanitizeOpenAIResponse({
+    model: "gpt-4.1",
+    choices: [
+      {
+        message: {
+          role: "assistant",
+          content: "§54§ <thought\ninternal planning\n",
+        },
+      },
+    ],
+  });
+
+  assert.equal((sanitized as any).choices[0].message.content, "");
+  assert.equal((sanitized as any).choices[0].message.reasoning_content, "internal planning");
+});
+
 test("sanitizeOpenAIResponse preserves native reasoning_content when no visible content remains", () => {
   const sanitized = sanitizeOpenAIResponse({
     model: "gpt-4.1",

tests/unit/translator-resp-gemini-to-openai.test.ts

@@ -381,6 +381,118 @@ test("Gemini stream: converts textual Tool call block to structured tool_calls",
   assert.equal(result.at(-1).choices[0].finish_reason, "tool_calls");
 });
 
+test("Gemini stream: routes textual reasoning tags to reasoning_content before tool calls", () => {
+  const state = createStreamingState();
+  const result = geminiToOpenAIResponse(
+    {
+      responseId: "resp-textual-thought-tool",
+      modelVersion: "gemini-3.5-flash-high",
+      candidates: [
+        {
+          content: {
+            parts: [
+              {
+                text: "§54§ <thought\nNeed to inspect first.",
+              },
+              {
+                functionCall: {
+                  id: "call_grep",
+                  name: "grep",
+                  args: { pattern: "Host", path: "/tmp/file" },
+                },
+              },
+            ],
+          },
+          finishReason: "STOP",
+        },
+      ],
+    },
+    state
+  );
+
+  assert.equal(
+    result.some((event: any) => event.choices?.[0]?.delta?.content?.includes("<thought")),
+    false
+  );
+  assert.equal(
+    result.find((event: any) => event.choices?.[0]?.delta?.reasoning_content)?.choices[0].delta
+      .reasoning_content,
+    "Need to inspect first."
+  );
+  const toolCall = result.find((event: any) => event.choices?.[0]?.delta?.tool_calls)?.choices[0]
+    .delta.tool_calls[0];
+  assert.equal(toolCall.id, "call_grep");
+  assert.equal(result.at(-1).choices[0].finish_reason, "tool_calls");
+});
+
+test("Gemini stream: keeps textual reasoning hidden across split chunks", () => {
+  const state = createStreamingState();
+
+  const first = geminiToOpenAIResponse(
+    {
+      responseId: "resp-split-thought",
+      modelVersion: "gemini-3.5-flash-high",
+      candidates: [{ content: { parts: [{ text: "§54§ <tho" }] } }],
+    },
+    state
+  );
+  assert.equal(
+    first.some((event: any) => event.choices?.[0]?.delta?.content),
+    false
+  );
+
+  const second = geminiToOpenAIResponse(
+    {
+      responseId: "resp-split-thought",
+      modelVersion: "gemini-3.5-flash-high",
+      candidates: [{ content: { parts: [{ text: "ught\nNeed to inspect" }] } }],
+    },
+    state
+  );
+  assert.equal(
+    (second ?? []).some((event: any) =>
+      event.choices?.[0]?.delta?.content?.includes("Need to inspect")
+    ),
+    false
+  );
+
+  const third = geminiToOpenAIResponse(
+    {
+      responseId: "resp-split-thought",
+      modelVersion: "gemini-3.5-flash-high",
+      candidates: [{ content: { parts: [{ text: " more</tho" }] } }],
+    },
+    state
+  );
+  assert.equal(
+    (third ?? []).some((event: any) => event.choices?.[0]?.delta?.content?.includes("more")),
+    false
+  );
+
+  const fourth = geminiToOpenAIResponse(
+    {
+      responseId: "resp-split-thought",
+      modelVersion: "gemini-3.5-flash-high",
+      candidates: [{ content: { parts: [{ text: "ught>Visible answer" }] } }],
+    },
+    state
+  );
+  assert.equal(
+    fourth.some(
+      (event: any) => event.choices?.[0]?.delta?.reasoning_content === "Need to inspect more"
+    ),
+    true
+  );
+  assert.equal(
+    fourth.some((event: any) => event.choices?.[0]?.delta?.content?.includes("ught>")),
+    false
+  );
+  assert.equal(
+    fourth.find((event: any) => event.choices?.[0]?.delta?.content)?.choices[0].delta.content,
+    "Visible answer"
+  );
+});
+
 test("Gemini stream: converts prefixed textual Tool call block with zero-width chars", () => {
   const state = createStreamingState();
   const result = geminiToOpenAIResponse(
@@ -826,7 +938,7 @@ test("Gemini stream: index mismatch regression test with zero-width characters i
           content: {
             parts: [
               {
-                text: "\u200BКак исправить: [Tool call: terminal]\nArguments: {\"command\":\"whoami\"}",
+                text: '\u200BКак исправить: [Tool call: terminal]\nArguments: {"command":"whoami"}',
               },
             ],
           },
@@ -837,7 +949,9 @@ test("Gemini stream: index mismatch regression test with zero-width characters i
     state
   );
 
-  const leakedContent = result.map((event: any) => event.choices?.[0]?.delta?.content || "").join("");
+  const leakedContent = result
+    .map((event: any) => event.choices?.[0]?.delta?.content || "")
+    .join("");
   assert.equal(leakedContent, "Как исправить: ");
 
   const toolCalls = result.flatMap((event: any) => event.choices?.[0]?.delta?.tool_calls || []);
@@ -870,7 +984,7 @@ test("Gemini stream: partial tool call with (empty) prefix check at chunk end do
         content: {
           parts: [
             {
-              text: "ll: terminal]\nArguments: {\"command\":\"whoami\"}",
+              text: 'll: terminal]\nArguments: {"command":"whoami"}',
             },
           ],
         },
@@ -942,7 +1056,7 @@ test("Gemini stream: parses textual tool call that starts in a subsequent chunk
 
 test("Gemini stream: checks lastParen before lastBracket when identifying partial (empty) markers with distinct chuncks", () => {
   const state = createStreamingState() as any;
-  
+
   // Имитируем чанк, который кончается на частичный "(empty)[Tool call:" маркер, например "(em"
   const chunk1 = {
     responseId: "resp-test-empty-partial",
@@ -982,7 +1096,7 @@ test("Gemini stream: checks lastParen before lastBracket when identifying partia
         content: {
           parts: [
             {
-              text: ' call: my_tool]\nArguments: {}',
+              text: " call: my_tool]\nArguments: {}",
             },
           ],
         },
@@ -1008,6 +1122,3 @@ test("Gemini stream: checks lastParen before lastBracket when identifying partia
   assert.equal(toolCall.function.name, "my_tool");
   assert.equal(toolCall.function.arguments, "{}");
 });
-
-
-