diff --git a/changelog.d/fixes/13652-kiro-tooldocs-repeat-every-turn.md b/changelog.d/fixes/13652-kiro-tooldocs-repeat-every-turn.md
new file mode 100644
index 00000000000..9e2ad49c793
--- /dev/null
+++ b/changelog.d/fixes/13652-kiro-tooldocs-repeat-every-turn.md
@@ -0,0 +1 @@
+- **fix(sse):** Kiro translator no longer re-prepends the full relocated tool-documentation block onto every subsequent turn of a multi-turn conversation; it now stays anchored to the turn that originally carried it. (#13652) — thanks @KelvinKSPS
diff --git a/open-sse/translator/request/openai-to-kiro.ts b/open-sse/translator/request/openai-to-kiro.ts
index 03bae61bb13..1c6238d5d2e 100644
--- a/open-sse/translator/request/openai-to-kiro.ts
+++ b/open-sse/translator/request/openai-to-kiro.ts
@@ -183,6 +183,13 @@ function convertMessages(messages, tools, model) {
   let currentRole = null;
   let toolsAttached = false;
   let toolDocs = "";
+  // The actual turn object that ends up carrying `toolDocs` (issue #13652).
+  // `buildKiroPayload()` only prepends the doc block onto `currentMessage`, so
+  // once this turn is demoted into `history` (any turn after the first, on a
+  // resent multi-turn request) we need to know it was NOT promoted, and embed
+  // the doc text directly onto it instead of letting it get re-glued onto
+  // whatever the newest turn happens to be.
+  let toolDocsCarrier = null;
 
   // Only Claude models support images in Kiro. Kiro also routes non-Claude
   // models (deepseek, minimax, glm, qwen3-coder-next) that do not accept image
@@ -242,7 +249,10 @@ function convertMessages(messages, tools, model) {
         }
         const built = buildKiroToolSpecs(tools);
         userMsg.userInputMessage.userInputMessageContext.tools = built.specs;
-        if (built.docs) toolDocs = built.docs;
+        if (built.docs) {
+          toolDocs = built.docs;
+          toolDocsCarrier = userMsg;
+        }
         toolsAttached = true;
       }
 
@@ -530,10 +540,30 @@ function convertMessages(messages, tools, model) {
     }
     const built = buildKiroToolSpecs(tools);
     currentMessage.userInputMessage.userInputMessageContext.tools = built.specs;
-    if (built.docs) toolDocs = built.docs;
+    if (built.docs) {
+      toolDocs = built.docs;
+      toolDocsCarrier = currentMessage;
+    }
     toolsAttached = true;
   }
 
+  // The relocated doc text is only safe to leave in `toolDocs` (which
+  // `buildKiroPayload()` unconditionally prepends onto `currentMessage`) when
+  // the turn that originally carried it IS `currentMessage` — true for a
+  // single-turn conversation and the "no user turn" fallback above. On any
+  // later turn of a resent multi-turn request, the tool-bearing turn has been
+  // demoted into `history` instead, so re-prepending `toolDocs` here would
+  // glue the *already delivered* doc block onto the newest turn every time
+  // (issue #13652). Embed it directly onto the carrier turn's own content —
+  // still in `history` at this point — and clear `toolDocs` so
+  // `buildKiroPayload()` does not also inject it.
+  if (toolDocs && toolDocsCarrier && toolDocsCarrier !== currentMessage) {
+    const carrierMessage = toolDocsCarrier.userInputMessage;
+    const existingContent = carrierMessage.content || "";
+    carrierMessage.content = `# Tool Documentation\n\n${toolDocs}\n\n---\n\n${existingContent}`;
+    toolDocs = "";
+  }
+
   // Clean up history for Kiro API compatibility
   history.forEach((item) => {
     if (item.userInputMessage?.userInputMessageContext?.tools) {
diff --git a/tests/unit/issue-13652-kiro-tooldocs-repeat.test.ts b/tests/unit/issue-13652-kiro-tooldocs-repeat.test.ts
new file mode 100644
index 00000000000..f4d165cc8f6
--- /dev/null
+++ b/tests/unit/issue-13652-kiro-tooldocs-repeat.test.ts
@@ -0,0 +1,83 @@
+import test from "node:test";
+import assert from "node:assert/strict";
+
+import { buildKiroPayload } from "../../open-sse/translator/request/openai-to-kiro.ts";
+
+// Issue #13652: `convertMessages()` in `openai-to-kiro.ts` is stateless per HTTP
+// request. OpenAI-compatible clients resend the full growing message array on
+// every turn, so the same tool-bearing first user message is re-scanned on
+// every subsequent request and its relocated documentation (`toolDocs`)
+// rebuilt from scratch. `buildKiroPayload()` then unconditionally prepends it
+// onto whatever the *current* turn is, so the ~10KB+ doc block keeps landing
+// on the newest user message instead of staying where it was first delivered.
+
+const DOCS_HEADING = "# Tool Documentation";
+
+function bigTool(length: number) {
+  return [
+    {
+      type: "function",
+      function: {
+        name: "big_tool",
+        description: "D".repeat(length),
+        parameters: { type: "object", properties: {} },
+      },
+    },
+  ];
+}
+
+test("issue #13652: relocated tool doc is not re-prepended to a later turn once already delivered", () => {
+  const tools = bigTool(12000);
+
+  // Turn 1: client sends only the first user message.
+  const turn1Messages = [{ role: "user", content: "hello, please help" }];
+  const payload1 = buildKiroPayload(
+    "claude-sonnet-4.5",
+    { messages: turn1Messages, tools },
+    true,
+    {}
+  );
+  const turn1Content = payload1.conversationState.currentMessage.userInputMessage.content;
+
+  assert.ok(
+    turn1Content.includes(DOCS_HEADING),
+    "turn 1: the relocated tool documentation must reach the model at least once"
+  );
+
+  // Turn 2: the OpenAI-compatible client resends the FULL prior history plus
+  // the assistant reply and a new user message. The client's own copy of turn
+  // 1's user message does NOT contain the "# Tool Documentation" block, since
+  // that was only ever prepended server-side to the outgoing Kiro payload.
+  const turn2Messages = [
+    { role: "user", content: "hello, please help" },
+    { role: "assistant", content: "Sure, how can I help?" },
+    { role: "user", content: "what is 2+2?" },
+  ];
+  const payload2 = buildKiroPayload(
+    "claude-sonnet-4.5",
+    { messages: turn2Messages, tools },
+    true,
+    {}
+  );
+  const turn2CurrentContent = payload2.conversationState.currentMessage.userInputMessage.content;
+
+  assert.ok(
+    !turn2CurrentContent.includes(DOCS_HEADING),
+    "turn 2: the tool documentation must NOT be re-prepended to the newest turn's " +
+      "content once it has already been delivered earlier in the conversation"
+  );
+
+  // The docs must not simply vanish — they must still reach the model exactly
+  // once, anchored on the turn that originally carried the tools (now in history).
+  const historyContents = payload2.conversationState.history
+    .map((h: { userInputMessage?: { content?: string } }) => h.userInputMessage?.content || "")
+    .join("\n");
+  const occurrences = (historyContents.match(new RegExp(DOCS_HEADING, "g")) || []).length;
+
+  assert.equal(
+    occurrences,
+    1,
+    "turn 2: the tool documentation must still reach the model exactly once, anchored to " +
+      "the turn that originally carried the tools"
+  );
+});
diff --git a/tests/unit/kiro-long-tool-description-docs.test.ts b/tests/unit/kiro-long-tool-description-docs.test.ts
index c7f5dcd28a1..330a2be465d 100644
--- a/tests/unit/kiro-long-tool-description-docs.test.ts
+++ b/tests/unit/kiro-long-tool-description-docs.test.ts
@@ -53,7 +53,15 @@ const TURN_SHAPES = {
   "no user messages": [{ role: "assistant", content: "only" }],
 };
 
-test("relocated tool documentation reaches the current turn for every turn shape", () => {
+// Issue #13652: the doc block is anchored to the turn that originally carried
+// the tools, not unconditionally glued onto `currentMessage`. For a shape with
+// more than one user turn, the tool-bearing turn ends up demoted into
+// `history` (currentMessage becomes the newest turn instead), so the doc now
+// lives on `history[0]`'s content. Only when the tool-bearing turn IS
+// `currentMessage` (a single user turn, or the "no user turn" fallback) does
+// it stay there. Whichever turn carries it, it must reach the model exactly
+// once — resending it on both would reintroduce #13652's duplication bug.
+test("relocated tool documentation reaches exactly one turn for every turn shape", () => {
   for (const [label, messages] of Object.entries(TURN_SHAPES)) {
     const payload = buildKiroPayload(
       "claude-sonnet-4.5",
@@ -62,13 +70,21 @@ test("relocated tool documentation reaches the current turn for every turn shape
       {}
     );
     const current = payload.conversationState.currentMessage.userInputMessage;
+    const history = payload.conversationState.history as Array<{
+      userInputMessage?: { content?: string };
+    }>;
+    const allContents = [...history.map((h) => h.userInputMessage?.content || ""), current.content];
+    const combined = allContents.join("\n");
+    const occurrences = (combined.match(new RegExp(DOCS_HEADING, "g")) || []).length;
 
-    assert.ok(
-      current.content.includes(DOCS_HEADING),
-      `${label}: full tool documentation must be prepended to the current turn`
+    assert.equal(
+      occurrences,
+      1,
+      `${label}: the tool documentation must reach the model exactly once, not zero ` +
+        `(silently dropped) and not more than once (re-injected, issue #13652)`
     );
     assert.ok(
-      current.content.includes("D".repeat(12000)),
+      combined.includes("D".repeat(12000)),
       `${label}: the relocated description text itself must survive`
     );
     assert.equal(
@@ -187,12 +203,20 @@ test("only oversized descriptions are relocated in a mixed tool inventory", () =
   );
   const current = payload.conversationState.currentMessage.userInputMessage;
   const specs = current.userInputMessageContext?.tools;
+  const history = payload.conversationState.history as Array<{
+    userInputMessage?: { content?: string };
+  }>;
+  // "multi-turn conversation" demotes the tool-bearing turn into history[0]
+  // (issue #13652) — the doc block lives there, not on currentMessage.
+  const combined = [...history.map((h) => h.userInputMessage?.content || ""), current.content].join(
+    "\n"
+  );
 
   assert.equal(specs[0].toolSpecification.description, "compact");
   assert.equal(specs[1].toolSpecification.description, POINTER);
-  assert.ok(current.content.includes("## Tool: big_tool"));
+  assert.ok(combined.includes("## Tool: big_tool"));
   assert.ok(
-    !current.content.includes("## Tool: small_tool"),
+    !combined.includes("## Tool: small_tool"),
     "a tool that was never relocated must not get a documentation section"
   );
 });