diff --git a/src/shared/text/reasoning-tags.test.ts b/src/shared/text/reasoning-tags.test.ts
new file mode 100644
index 000000000..394a914fa
--- /dev/null
+++ b/src/shared/text/reasoning-tags.test.ts
@@ -0,0 +1,122 @@
+import { describe, expect, it } from "vitest";
+import { stripReasoningTagsFromText } from "./reasoning-tags.js";
+
+describe("stripReasoningTagsFromText", () => {
+  describe("basic functionality", () => {
+    it("returns text unchanged when no reasoning tags present", () => {
+      const input = "Hello, this is a normal message.";
+      expect(stripReasoningTagsFromText(input)).toBe(input);
+    });
+
+    it("strips proper think tags", () => {
+      const input = "Hello <think>internal reasoning</think> world!";
+      expect(stripReasoningTagsFromText(input)).toBe("Hello  world!");
+    });
+
+    it("strips thinking tags", () => {
+      const input = "Before <thinking>some thought</thinking> after";
+      expect(stripReasoningTagsFromText(input)).toBe("Before  after");
+    });
+
+    it("strips thought tags", () => {
+      const input = "A <thought>hmm</thought> B";
+      expect(stripReasoningTagsFromText(input)).toBe("A  B");
+    });
+
+    it("strips antthinking tags", () => {
+      const input = "X <antthinking>internal</antthinking> Y";
+      expect(stripReasoningTagsFromText(input)).toBe("X  Y");
+    });
+
+    it("strips multiple reasoning blocks", () => {
+      const input = "<think>first</think>A<think>second</think>B";
+      expect(stripReasoningTagsFromText(input)).toBe("AB");
+    });
+  });
+
+  describe("code block preservation (issue #3952)", () => {
+    it("preserves think tags inside fenced code blocks", () => {
+      const input = "Use the tag like this:\n```\n<think>reasoning</think>\n```\nThat's it!";
+      expect(stripReasoningTagsFromText(input)).toBe(input);
+    });
+
+    it("preserves think tags inside inline code", () => {
+      const input =
+        "The `<think>` tag is used for reasoning. Don't forget the closing `</think>` tag.";
+      expect(stripReasoningTagsFromText(input)).toBe(input);
+    });
+
+    it("preserves tags in fenced code blocks with language specifier", () => {
+      const input = "Example:\n```xml\n<think>\n  <thought>nested</thought>\n</think>\n```\nDone!";
+      expect(stripReasoningTagsFromText(input)).toBe(input);
+    });
+
+    it("handles mixed real tags and code tags", () => {
+      const input = "<think>hidden</think>Visible text with `<think>` example.";
+      expect(stripReasoningTagsFromText(input)).toBe("Visible text with `<think>` example.");
+    });
+
+    it("preserves both opening and closing tags in backticks", () => {
+      const input = "Use `<think>` to open and `</think>` to close.";
+      expect(stripReasoningTagsFromText(input)).toBe(input);
+    });
+  });
+
+  describe("edge cases", () => {
+    it("preserves unclosed <think without angle bracket", () => {
+      const input = "Here is how to use <think tags in your code";
+      expect(stripReasoningTagsFromText(input)).toBe(input);
+    });
+
+    it("strips lone closing tag outside code", () => {
+      const input = "You can start with <think and then close with </think>";
+      expect(stripReasoningTagsFromText(input)).toBe(
+        "You can start with <think and then close with",
+      );
+    });
+
+    it("handles tags with whitespace", () => {
+      const input = "A < think >content< /think > B";
+      expect(stripReasoningTagsFromText(input)).toBe("A  B");
+    });
+
+    it("handles empty input", () => {
+      expect(stripReasoningTagsFromText("")).toBe("");
+    });
+
+    it("handles null-ish input", () => {
+      expect(stripReasoningTagsFromText(null as unknown as string)).toBe(null);
+    });
+  });
+
+  describe("strict vs preserve mode", () => {
+    it("strict mode truncates on unclosed tag", () => {
+      const input = "Before <think>unclosed content after";
+      expect(stripReasoningTagsFromText(input, { mode: "strict" })).toBe("Before");
+    });
+
+    it("preserve mode keeps content after unclosed tag", () => {
+      const input = "Before <think>unclosed content after";
+      expect(stripReasoningTagsFromText(input, { mode: "preserve" })).toBe(
+        "Before unclosed content after",
+      );
+    });
+  });
+
+  describe("trim options", () => {
+    it("trims both sides by default", () => {
+      const input = "  <think>x</think>  result  <think>y</think>  ";
+      expect(stripReasoningTagsFromText(input)).toBe("result");
+    });
+
+    it("trim=none preserves whitespace", () => {
+      const input = "  <think>x</think>  result  ";
+      expect(stripReasoningTagsFromText(input, { trim: "none" })).toBe("    result  ");
+    });
+
+    it("trim=start only trims start", () => {
+      const input = "  <think>x</think>  result  ";
+      expect(stripReasoningTagsFromText(input, { trim: "start" })).toBe("result  ");
+    });
+  });
+});
diff --git a/src/shared/text/reasoning-tags.ts b/src/shared/text/reasoning-tags.ts
index 822138e55..6bba914b9 100644
--- a/src/shared/text/reasoning-tags.ts
+++ b/src/shared/text/reasoning-tags.ts
@@ -2,8 +2,40 @@ export type ReasoningTagMode = "strict" | "preserve";
 export type ReasoningTagTrim = "none" | "start" | "both";
 
 const QUICK_TAG_RE = /<\s*\/?\s*(?:think(?:ing)?|thought|antthinking|final)\b/i;
-const FINAL_TAG_RE = /<\s*\/?\s*final\b[^>]*>/gi;
-const THINKING_TAG_RE = /<\s*(\/?)\s*(?:think(?:ing)?|thought|antthinking)\b[^>]*>/gi;
+const FINAL_TAG_RE = /<\s*\/?\s*final\b[^<>]*>/gi;
+const THINKING_TAG_RE = /<\s*(\/?)\s*(?:think(?:ing)?|thought|antthinking)\b[^<>]*>/gi;
+
+interface CodeRegion {
+  start: number;
+  end: number;
+}
+
+function findCodeRegions(text: string): CodeRegion[] {
+  const regions: CodeRegion[] = [];
+
+  const fencedRe = /(^|\n)(```|~~~).*?\n[\s\S]*?\n\2/g;
+  for (const match of text.matchAll(fencedRe)) {
+    const start = (match.index ?? 0) + match[1].length;
+    regions.push({ start, end: start + match[0].length - match[1].length });
+  }
+
+  const inlineRe = /`+[^`]+`+/g;
+  for (const match of text.matchAll(inlineRe)) {
+    const start = match.index ?? 0;
+    const end = start + match[0].length;
+    const insideFenced = regions.some((r) => start >= r.start && end <= r.end);
+    if (!insideFenced) {
+      regions.push({ start, end });
+    }
+  }
+
+  regions.sort((a, b) => a.start - b.start);
+  return regions;
+}
+
+function isInsideCode(pos: number, regions: CodeRegion[]): boolean {
+  return regions.some((r) => pos >= r.start && pos < r.end);
+}
 
 function applyTrim(value: string, mode: ReasoningTagTrim): string {
   if (mode === "none") return value;
@@ -24,14 +56,21 @@ export function stripReasoningTagsFromText(
   const mode = options?.mode ?? "strict";
   const trimMode = options?.trim ?? "both";
 
+  const codeRegions = findCodeRegions(text);
+
   let cleaned = text;
   if (FINAL_TAG_RE.test(cleaned)) {
     FINAL_TAG_RE.lastIndex = 0;
-    cleaned = cleaned.replace(FINAL_TAG_RE, "");
+    cleaned = cleaned.replace(FINAL_TAG_RE, (match, offset) => {
+      if (isInsideCode(offset, codeRegions)) return match;
+      return "";
+    });
   } else {
     FINAL_TAG_RE.lastIndex = 0;
   }
 
+  const updatedCodeRegions = findCodeRegions(cleaned);
+
   THINKING_TAG_RE.lastIndex = 0;
   let result = "";
   let lastIndex = 0;
@@ -41,6 +80,10 @@ export function stripReasoningTagsFromText(
     const idx = match.index ?? 0;
     const isClose = match[1] === "/";
 
+    if (isInsideCode(idx, updatedCodeRegions)) {
+      continue;
+    }
+
     if (!inThinking) {
       result += cleaned.slice(lastIndex, idx);
       if (!isClose) {