fix(auto-reply): tighten custom token prefix matching to avoid false suppression

Simon-XYDT · claude · Simon-XYDT · commit 5f9ccbe1a804 · 2026-07-04T23:43:27.000+08:00
For custom tokens with non-letter characters (e.g., HELP-QUIET), require the
streamed prefix to include at least one of those non-letter characters before
marking it as silent. Pure-letter prefixes like "HE" for "HELP-QUIET" can no
longer suppress natural language text that happens to share the prefix.

Co-Authored-By: Claude Opus 4.6 &lt;noreply@anthropic.com&gt;
diff --git a/src/auto-reply/tokens.test.ts b/src/auto-reply/tokens.test.ts
@@ -284,18 +284,27 @@ describe("isSilentReplyPrefixText", () => {
 
   it("matches custom tokens with digits", () => {
     expect(isSilentReplyPrefixText("NOREPLY2", "NOREPLY2")).toBe(true);
-    expect(isSilentReplyPrefixText("NORE", "NOREPLY2")).toBe(true);
-    expect(isSilentReplyPrefixText("NOR", "NOREPLY2")).toBe(true);
+    expect(isSilentReplyPrefixText("NOREPLY", "NOREPLY2")).toBe(false);
+    expect(isSilentReplyPrefixText("NORE", "NOREPLY2")).toBe(false);
+    expect(isSilentReplyPrefixText("NOR", "NOREPLY2")).toBe(false);
   });
 
   it("matches custom tokens with hyphens", () => {
     expect(isSilentReplyPrefixText("NO-ANSWER", "NO-ANSWER")).toBe(true);
     expect(isSilentReplyPrefixText("NO-AN", "NO-ANSWER")).toBe(true);
+    expect(isSilentReplyPrefixText("NO-", "NO-ANSWER")).toBe(true);
   });
 
   it("rejects non-matching prefixes for custom tokens", () => {
     expect(isSilentReplyPrefixText("HE", "NOREPLY2")).toBe(false);
     expect(isSilentReplyPrefixText("HELLO", "NO-ANSWER")).toBe(false);
     expect(isSilentReplyPrefixText("NO-", "NOREPLY2")).toBe(false);
   });
+
+  it("rejects pure-letter prefixes for punctuated tokens to avoid false suppression", () => {
+    expect(isSilentReplyPrefixText("HE", "HELP-QUIET")).toBe(false);
+    expect(isSilentReplyPrefixText("HELP", "HELP-QUIET")).toBe(false);
+    expect(isSilentReplyPrefixText("HELP-", "HELP-QUIET")).toBe(true);
+    expect(isSilentReplyPrefixText("HELP-QUIET", "HELP-QUIET")).toBe(true);
+  });
 });
diff --git a/src/auto-reply/tokens.ts b/src/auto-reply/tokens.ts
@@ -308,13 +308,16 @@ export function isSilentReplyPrefixText(
   if (normalized.includes("_")) {
     return true;
   }
-  // For tokens without underscore, only allow bare "NO" as a partial prefix
-  // for NO_REPLY (NO_REPLY streaming can transiently emit that fragment).
-  // Custom tokens containing non-letter characters (digits, hyphens) are safe
-  // for partial prefix matching because their prefixes won't match natural
-  // language words. Full-token match is also safe for any token.
-  if (normalized === tokenUpper || /[^A-Z_]/.test(tokenUpper)) {
+  // Full-token match is safe for any token.
+  if (normalized === tokenUpper) {
     return true;
   }
+  // For custom tokens containing non-letter characters (digits, hyphens),
+  // only match if the prefix includes at least one non-letter character
+  // from the token. Otherwise, a pure-letter prefix like "HE" for "HELP-QUIET"
+  // would suppress natural language that happens to share that prefix (#100007).
+  if (/[^A-Z_]/.test(tokenUpper)) {
+    return [...tokenUpper].some((ch) => /[^A-Z_]/.test(ch) && normalized.includes(ch));
+  }
   return tokenUpper === SILENT_REPLY_TOKEN && normalized === "NO";
 }
