diff --git a/src/features/context-injector/injector.test.ts b/src/features/context-injector/injector.test.ts
index 09de376fe..840998222 100644
--- a/src/features/context-injector/injector.test.ts
+++ b/src/features/context-injector/injector.test.ts
@@ -106,6 +106,8 @@ describe("createContextInjectorMessagesTransformHook", () => {
     expect(
       "synthetic" in secondSyntheticPart && secondSyntheticPart.synthetic === true
     ).toBe(true)
+    expect(typeof secondSyntheticPart.id).toBe("string")
+    expect(secondSyntheticPart.id.startsWith("prt_")).toBe(true)
     expect(secondSyntheticPart.id).toBe(firstSyntheticPart.id)
   })
 
diff --git a/src/features/context-injector/injector.ts b/src/features/context-injector/injector.ts
index 8a52de914..1fe8850a6 100644
--- a/src/features/context-injector/injector.ts
+++ b/src/features/context-injector/injector.ts
@@ -148,7 +148,7 @@ export function createContextInjectorMessagesTransformHook(
 
       // synthetic part pattern (minimal fields)
       const syntheticPart = {
-        id: `synthetic_hook_${sessionID}`,
+        id: `prt_synthetic_hook_${sessionID}`,
         messageID: lastUserMessage.info.id,
         sessionID: (lastUserMessage.info as { sessionID?: string }).sessionID ?? "",
         type: "text" as const,