test(gateway): cover UTF-16 tail cap through merge path

steipete · steipete · commit 6c55764fc32b · 2026-07-09T08:19:10.000+01:00
diff --git a/src/gateway/live-chat-projector.test.ts b/src/gateway/live-chat-projector.test.ts
diff --git a/src/gateway/live-chat-projector.ts b/src/gateway/live-chat-projector.ts
@@ -33,7 +33,7 @@ export function resolveAssistantLiveChatInput(
   };
 }
 
-export function capLiveAssistantBuffer(text: string): string {
+function capLiveAssistantBuffer(text: string): string {
   if (text.length <= MAX_LIVE_CHAT_BUFFER_CHARS) {
     return text;
   }
diff --git a/src/gateway/server-chat.stream-text-merge.test.ts b/src/gateway/server-chat.stream-text-merge.test.ts
@@ -93,4 +93,15 @@ describe("server chat stream text merge", () => {
     expect(result).toHaveLength(MAX_LIVE_CHAT_BUFFER_CHARS);
     expect(result.endsWith("bbbb")).toBe(true);
   });
+
+  it("does not start the capped tail with the low half of a surrogate pair", () => {
+    const safeTail = "y".repeat(MAX_LIVE_CHAT_BUFFER_CHARS - 1);
+    const result = resolveMergedAssistantText({
+      previousText: "",
+      nextText: `x🚀${safeTail}`,
+      nextDelta: "",
+    });
+
+    expect(result).toBe(safeTail);
+  });
 });

Original file line number	Diff line number	Diff line change
`@@ -33,7 +33,7 @@ export function resolveAssistantLiveChatInput(`
`33`	`33`	`};`
`34`	`34`	`}`
`35`	`35`
`36`		`-export function capLiveAssistantBuffer(text: string): string {`
	`36`	`+function capLiveAssistantBuffer(text: string): string {`
`37`	`37`	`if (text.length <= MAX_LIVE_CHAT_BUFFER_CHARS) {`
`38`	`38`	`return text;`
`39`	`39`	`}`