From 0809c8d29a674d18198795dc16447c9c72934172 Mon Sep 17 00:00:00 2001
From: Gustavo Madeira Santana <gumadeiras@gmail.com>
Date: Thu, 2 Apr 2026 02:32:35 -0400
Subject: [PATCH] fix(matrix): preserve legacy mention edits

---
 .../src/matrix/actions/messages.test.ts       | 38 +++++++++++++++++
 extensions/matrix/src/matrix/send.test.ts     | 42 +++++++++++++++++++
 extensions/matrix/src/matrix/send.ts          | 27 +++++++++++-
 3 files changed, 106 insertions(+), 1 deletion(-)

diff --git a/extensions/matrix/src/matrix/actions/messages.test.ts b/extensions/matrix/src/matrix/actions/messages.test.ts
index a173ba95aa8..bdf111c2f1e 100644
--- a/extensions/matrix/src/matrix/actions/messages.test.ts
+++ b/extensions/matrix/src/matrix/actions/messages.test.ts
@@ -148,6 +148,44 @@ describe("matrix message actions", () => {
     );
   });
 
+  it("does not re-notify legacy mentions when action edits target pre-m.mentions messages", async () => {
+    installMatrixActionTestRuntime();
+    const sendMessage = vi.fn().mockResolvedValue("evt-edit");
+    const client = {
+      getEvent: vi.fn().mockResolvedValue({
+        content: {
+          body: "hello @alice:example.org",
+        },
+      }),
+      getJoinedRoomMembers: vi.fn().mockResolvedValue([]),
+      getUserId: vi.fn().mockResolvedValue("@bot:example.org"),
+      sendMessage,
+      prepareForOneOff: vi.fn(async () => undefined),
+      start: vi.fn(async () => undefined),
+      stop: vi.fn(() => undefined),
+      stopAndPersist: vi.fn(async () => undefined),
+    } as unknown as MatrixClient;
+
+    const result = await editMatrixMessage(
+      "!room:example.org",
+      "$original",
+      "hello again @alice:example.org",
+      { client },
+    );
+
+    expect(result).toEqual({ eventId: "evt-edit" });
+    expect(sendMessage).toHaveBeenCalledWith(
+      "!room:example.org",
+      expect.objectContaining({
+        "m.mentions": {},
+        "m.new_content": expect.objectContaining({
+          body: "hello again @alice:example.org",
+          "m.mentions": { user_ids: ["@alice:example.org"] },
+        }),
+      }),
+    );
+  });
+
   it("includes poll snapshots when reading message history", async () => {
     const { client, doRequest, getEvent, getRelations } = createMessagesClient({
       chunk: [
diff --git a/extensions/matrix/src/matrix/send.test.ts b/extensions/matrix/src/matrix/send.test.ts
index 1c7397c2ebc..414d8c976a5 100644
--- a/extensions/matrix/src/matrix/send.test.ts
+++ b/extensions/matrix/src/matrix/send.test.ts
@@ -611,6 +611,48 @@ describe("editMessageMatrix mentions", () => {
       },
     });
   });
+
+  it("does not re-notify legacy mentions when the prior event body already mentioned the user", async () => {
+    const { client, sendMessage, getEvent } = makeClient();
+    getEvent.mockResolvedValue({
+      content: {
+        body: "hello @alice:example.org",
+      },
+    });
+
+    await editMessageMatrix("room:!room:example", "$original", "hello again @alice:example.org", {
+      client,
+    });
+
+    expect(sendMessage.mock.calls[0]?.[1]).toMatchObject({
+      "m.mentions": {},
+      "m.new_content": {
+        body: "hello again @alice:example.org",
+        "m.mentions": { user_ids: ["@alice:example.org"] },
+      },
+    });
+  });
+
+  it("keeps explicit empty prior m.mentions authoritative", async () => {
+    const { client, sendMessage, getEvent } = makeClient();
+    getEvent.mockResolvedValue({
+      content: {
+        body: "`@alice:example.org`",
+        "m.mentions": {},
+      },
+    });
+
+    await editMessageMatrix("room:!room:example", "$original", "@alice:example.org", {
+      client,
+    });
+
+    expect(sendMessage.mock.calls[0]?.[1]).toMatchObject({
+      "m.mentions": { user_ids: ["@alice:example.org"] },
+      "m.new_content": {
+        "m.mentions": { user_ids: ["@alice:example.org"] },
+      },
+    });
+  });
 });
 
 describe("sendPollMatrix mentions", () => {
diff --git a/extensions/matrix/src/matrix/send.ts b/extensions/matrix/src/matrix/send.ts
index 6fcc42cbea3..50c3b73a763 100644
--- a/extensions/matrix/src/matrix/send.ts
+++ b/extensions/matrix/src/matrix/send.ts
@@ -98,6 +98,27 @@ function resolvePreviousEditContent(previousEvent: unknown): Record<string, unkn
     : content;
 }
 
+function hasMatrixMentionsMetadata(content: Record<string, unknown> | undefined): boolean {
+  return Boolean(content && Object.hasOwn(content, "m.mentions"));
+}
+
+async function resolvePreviousEditMentions(params: {
+  client: MatrixClient;
+  content: Record<string, unknown> | undefined;
+}) {
+  if (hasMatrixMentionsMetadata(params.content)) {
+    return extractMatrixMentions(params.content);
+  }
+  const body = typeof params.content?.body === "string" ? params.content.body : "";
+  if (!body) {
+    return {};
+  }
+  return await resolveMatrixMentionsForBody({
+    client: params.client,
+    body,
+  });
+}
+
 export function prepareMatrixSingleText(
   text: string,
   opts: {
@@ -459,9 +480,13 @@ export async function editMessageMatrix(
       });
       const previousEvent = await getPreviousMatrixEvent(client, resolvedRoom, originalEventId);
       const previousContent = resolvePreviousEditContent(previousEvent);
+      const previousMentions = await resolvePreviousEditMentions({
+        client,
+        content: previousContent,
+      });
       const replaceMentions = diffMatrixMentions(
         extractMatrixMentions(newContent),
-        extractMatrixMentions(previousContent),
+        previousMentions,
       );
 
       const replaceRelation: Record<string, unknown> = {