From 757bfebc316c5cbeaa9769a39379e548b950103b Mon Sep 17 00:00:00 2001
From: Gustavo Madeira Santana <gumadeiras@gmail.com>
Date: Mon, 9 Mar 2026 04:42:41 -0400
Subject: [PATCH] Matrix: align reaction routing with thread bindings

---
 .../matrix/src/matrix/monitor/handler.test.ts | 62 +++++++++++++++++++
 .../src/matrix/monitor/reaction-events.ts     | 28 ++++++---
 2 files changed, 83 insertions(+), 7 deletions(-)

diff --git a/extensions/matrix/src/matrix/monitor/handler.test.ts b/extensions/matrix/src/matrix/monitor/handler.test.ts
index c49ac0a0cdd..c826dc6e576 100644
--- a/extensions/matrix/src/matrix/monitor/handler.test.ts
+++ b/extensions/matrix/src/matrix/monitor/handler.test.ts
@@ -314,6 +314,68 @@ describe("matrix monitor handler pairing account scope", () => {
     );
   });
 
+  it("routes reaction notifications for bound thread messages to the bound session", async () => {
+    registerSessionBindingAdapter({
+      channel: "matrix",
+      accountId: "ops",
+      listBySession: () => [],
+      resolveByConversation: (ref) =>
+        ref.conversationId === "$root"
+          ? {
+              bindingId: "ops:!room:example.org:$root",
+              targetSessionKey: "agent:bound:session-1",
+              targetKind: "session",
+              conversation: {
+                channel: "matrix",
+                accountId: "ops",
+                conversationId: "$root",
+                parentConversationId: "!room:example.org",
+              },
+              status: "active",
+              boundAt: Date.now(),
+              metadata: {
+                boundBy: "user-1",
+              },
+            }
+          : null,
+      touch: vi.fn(),
+    });
+
+    const { handler, enqueueSystemEvent } = createMatrixHandlerTestHarness({
+      client: {
+        getEvent: async () =>
+          createMatrixTextMessageEvent({
+            eventId: "$reply1",
+            sender: "@bot:example.org",
+            body: "follow up",
+            relatesTo: {
+              rel_type: "m.thread",
+              event_id: "$root",
+              "m.in_reply_to": { event_id: "$root" },
+            },
+          }),
+      },
+      isDirectMessage: false,
+    });
+
+    await handler(
+      "!room:example.org",
+      createMatrixReactionEvent({
+        eventId: "$reaction-thread",
+        targetEventId: "$reply1",
+        key: "🎯",
+      }),
+    );
+
+    expect(enqueueSystemEvent).toHaveBeenCalledWith(
+      "Matrix reaction added: 🎯 by sender on msg $reply1",
+      {
+        sessionKey: "agent:bound:session-1",
+        contextKey: "matrix:reaction:add:!room:example.org:$reply1:@user:example.org:🎯",
+      },
+    );
+  });
+
   it("ignores reactions that do not target bot-authored messages", async () => {
     const { handler, enqueueSystemEvent, resolveAgentRoute } = createReactionHarness({
       targetSender: "@other:example.org",
diff --git a/extensions/matrix/src/matrix/monitor/reaction-events.ts b/extensions/matrix/src/matrix/monitor/reaction-events.ts
index 5631ec3a781..2eef8f06f39 100644
--- a/extensions/matrix/src/matrix/monitor/reaction-events.ts
+++ b/extensions/matrix/src/matrix/monitor/reaction-events.ts
@@ -3,7 +3,9 @@ import type { CoreConfig } from "../../types.js";
 import { resolveMatrixAccountConfig } from "../accounts.js";
 import { extractMatrixReactionAnnotation } from "../reaction-common.js";
 import type { MatrixClient } from "../sdk.js";
-import type { MatrixRawEvent } from "./types.js";
+import { resolveMatrixInboundRoute } from "./route.js";
+import { resolveMatrixThreadRootId } from "./threads.js";
+import type { MatrixRawEvent, RoomMessageEventContent } from "./types.js";
 
 export type MatrixReactionNotificationMode = "off" | "own";
 
@@ -60,14 +62,26 @@ export async function handleInboundMatrixReaction(params: {
     return;
   }
 
-  const route = params.core.channel.routing.resolveAgentRoute({
+  const targetContent =
+    targetEvent && targetEvent.content && typeof targetEvent.content === "object"
+      ? (targetEvent.content as RoomMessageEventContent)
+      : undefined;
+  const threadRootId = targetContent
+    ? resolveMatrixThreadRootId({
+        event: targetEvent as MatrixRawEvent,
+        content: targetContent,
+      })
+    : undefined;
+  const { route } = resolveMatrixInboundRoute({
     cfg: params.cfg,
-    channel: "matrix",
     accountId: params.accountId,
-    peer: {
-      kind: params.isDirectMessage ? "direct" : "channel",
-      id: params.isDirectMessage ? params.senderId : params.roomId,
-    },
+    roomId: params.roomId,
+    senderId: params.senderId,
+    isDirectMessage: params.isDirectMessage,
+    messageId: reaction.eventId,
+    threadRootId,
+    eventTs: params.event.origin_server_ts,
+    resolveAgentRoute: params.core.channel.routing.resolveAgentRoute,
   });
   const text = `Matrix reaction added: ${reaction.key} by ${params.senderLabel} on msg ${reaction.eventId}`;
   params.core.system.enqueueSystemEvent(text, {