From 2715a4b8b211eb960c5ef8c5dd7c44a53b2cb9d6 Mon Sep 17 00:00:00 2001
From: Vincent Koc <vincentkoc@ieee.org>
Date: Sat, 7 Mar 2026 08:20:44 -0800
Subject: [PATCH] iMessage: hash full self-chat text

---
 src/imessage/monitor/self-chat-cache.test.ts | 12 ++++++++----
 src/imessage/monitor/self-chat-cache.ts      | 11 +----------
 2 files changed, 9 insertions(+), 14 deletions(-)

diff --git a/src/imessage/monitor/self-chat-cache.test.ts b/src/imessage/monitor/self-chat-cache.test.ts
index 50a829c7d8d..cf3a245ba30 100644
--- a/src/imessage/monitor/self-chat-cache.test.ts
+++ b/src/imessage/monitor/self-chat-cache.test.ts
@@ -58,15 +58,19 @@ describe("createSelfChatCache", () => {
     expect(cache.has({ ...directLookup, text: "message-512", createdAt: 512 })).toBe(true);
   });
 
-  it("handles long texts without requiring the full body in the cache key", () => {
+  it("does not collide long texts that differ only in the middle", () => {
     vi.useFakeTimers();
     vi.setSystemTime(new Date("2026-03-07T00:00:00Z"));
 
     const cache = createSelfChatCache();
-    const longText = `${"a".repeat(800)}middle${"b".repeat(800)}`;
+    const prefix = "a".repeat(256);
+    const suffix = "b".repeat(256);
+    const longTextA = `${prefix}${"x".repeat(300)}${suffix}`;
+    const longTextB = `${prefix}${"y".repeat(300)}${suffix}`;
 
-    cache.remember({ ...directLookup, text: longText, createdAt: 123 });
+    cache.remember({ ...directLookup, text: longTextA, createdAt: 123 });
 
-    expect(cache.has({ ...directLookup, text: longText, createdAt: 123 })).toBe(true);
+    expect(cache.has({ ...directLookup, text: longTextA, createdAt: 123 })).toBe(true);
+    expect(cache.has({ ...directLookup, text: longTextB, createdAt: 123 })).toBe(false);
   });
 });
diff --git a/src/imessage/monitor/self-chat-cache.ts b/src/imessage/monitor/self-chat-cache.ts
index d9884a26a76..a2c4c31ccd9 100644
--- a/src/imessage/monitor/self-chat-cache.ts
+++ b/src/imessage/monitor/self-chat-cache.ts
@@ -21,8 +21,6 @@ export type SelfChatCache = {
 const SELF_CHAT_TTL_MS = 10_000;
 const MAX_SELF_CHAT_CACHE_ENTRIES = 512;
 const CLEANUP_MIN_INTERVAL_MS = 1_000;
-const DIGEST_TEXT_HEAD_CHARS = 256;
-const DIGEST_TEXT_TAIL_CHARS = 256;
 
 function normalizeText(text: string | undefined): string | null {
   if (!text) {
@@ -36,15 +34,8 @@ function isUsableTimestamp(createdAt: number | undefined): createdAt is number {
   return typeof createdAt === "number" && Number.isFinite(createdAt);
 }
 
-function buildDigestSource(text: string): string {
-  if (text.length <= DIGEST_TEXT_HEAD_CHARS + DIGEST_TEXT_TAIL_CHARS) {
-    return text;
-  }
-  return `${text.slice(0, DIGEST_TEXT_HEAD_CHARS)}\u0000${text.length}\u0000${text.slice(-DIGEST_TEXT_TAIL_CHARS)}`;
-}
-
 function digestText(text: string): string {
-  return createHash("sha256").update(buildDigestSource(text)).digest("hex");
+  return createHash("sha256").update(text).digest("hex");
 }
 
 function buildScope(parts: SelfChatCacheKeyParts): string {