diff --git a/extensions/matrix/src/matrix/monitor/index.test.ts b/extensions/matrix/src/matrix/monitor/index.test.ts
index 093a5102441..46e7afc80be 100644
--- a/extensions/matrix/src/matrix/monitor/index.test.ts
+++ b/extensions/matrix/src/matrix/monitor/index.test.ts
@@ -122,6 +122,7 @@ const hoisted = vi.hoisted(() => {
     resolveSharedMatrixClient,
     resolveTextChunkLimit,
     runMatrixStartupMaintenance,
+    registeredHealthySyncGetter: undefined as undefined | (() => number | undefined),
     setActiveMatrixClient,
     setMatrixRuntime,
     setStatus,
@@ -339,10 +340,12 @@ vi.mock("./direct.js", () => ({
 vi.mock("./events.js", () => ({
   registerMatrixMonitorEvents: vi.fn(
     (params: {
+      getHealthySyncSinceMs?: () => number | undefined;
       onRoomMessage: (roomId: string, event: unknown) => Promise<void>;
       runDetachedTask?: (label: string, task: () => Promise<void>) => Promise<void>;
     }) => {
       hoisted.callOrder.push("register-events");
+      hoisted.registeredHealthySyncGetter = params.getHealthySyncSinceMs;
       hoisted.registeredOnRoomMessage = (roomId: string, event: unknown) =>
         params.runDetachedTask
           ? params.runDetachedTask("test room message", async () => {
@@ -429,6 +432,7 @@ describe("monitorMatrixProvider", () => {
     });
     hoisted.getMemberDisplayName.mockReset().mockResolvedValue("Bot");
     hoisted.registeredOnRoomMessage = null;
+    hoisted.registeredHealthySyncGetter = undefined;
     hoisted.setActiveMatrixClient.mockReset();
     hoisted.stopThreadBindingManager.mockReset();
     hoisted.client.removeAllListeners();
@@ -497,6 +501,49 @@ describe("monitorMatrixProvider", () => {
     await expect(monitorPromise).resolves.toBeUndefined();
   });
 
+  it("re-arms the healthy-sync milestone across reconnect transitions", async () => {
+    vi.useFakeTimers();
+    vi.setSystemTime(new Date("2026-04-10T16:21:00.000Z"));
+    const abortController = new AbortController();
+    try {
+      const monitorPromise = monitorMatrixProvider({
+        abortSignal: abortController.signal,
+        setStatus: hoisted.setStatus,
+      });
+
+      await vi.waitFor(() => {
+        expect(hoisted.callOrder).toContain("start-client");
+      });
+
+      const getHealthySyncSinceMs = hoisted.registeredHealthySyncGetter;
+      if (!getHealthySyncSinceMs) {
+        throw new Error("expected healthy sync getter to be registered");
+      }
+
+      expect(getHealthySyncSinceMs()).toBeUndefined();
+
+      hoisted.client.emit("sync.state", "SYNCING", "RECONNECTING", undefined);
+      expect(getHealthySyncSinceMs()).toBe(Date.now());
+
+      await vi.advanceTimersByTimeAsync(5_000);
+      hoisted.client.emit("sync.state", "RECONNECTING", "SYNCING", new Error("network flap"));
+      expect(getHealthySyncSinceMs()).toBeUndefined();
+
+      await vi.advanceTimersByTimeAsync(7_000);
+      hoisted.client.emit("sync.state", "SYNCING", "RECONNECTING", undefined);
+      const rearmedHealthySyncSinceMs = Date.now();
+      expect(getHealthySyncSinceMs()).toBe(rearmedHealthySyncSinceMs);
+
+      abortController.abort();
+      await expect(monitorPromise).resolves.toBeUndefined();
+
+      hoisted.client.emit("sync.state", "RECONNECTING", "SYNCING", new Error("late noise"));
+      expect(getHealthySyncSinceMs()).toBe(rearmedHealthySyncSinceMs);
+    } finally {
+      vi.useRealTimers();
+    }
+  });
+
   it("contains room-message handler rejections inside monitor task tracking", async () => {
     const abortController = new AbortController();
     const unhandled: unknown[] = [];
diff --git a/extensions/matrix/src/matrix/monitor/index.ts b/extensions/matrix/src/matrix/monitor/index.ts
index 0c775b310f9..3f0f014d9af 100644
--- a/extensions/matrix/src/matrix/monitor/index.ts
+++ b/extensions/matrix/src/matrix/monitor/index.ts
@@ -27,6 +27,11 @@ import {
 import { releaseSharedClientInstance } from "../client/shared.js";
 import type { MatrixClient } from "../sdk.js";
 import { isMatrixStartupAbortError } from "../startup-abort.js";
+import {
+  isMatrixDisconnectedSyncState,
+  isMatrixReadySyncState,
+  type MatrixSyncState,
+} from "../sync-state.js";
 import { createMatrixThreadBindingManager } from "../thread-bindings.js";
 import { registerMatrixAutoJoin } from "./auto-join.js";
 import { resolveMatrixMonitorConfig } from "./config.js";
@@ -184,6 +189,7 @@ export async function monitorMatrixProvider(opts: MonitorMatrixOpts = {}): Promi
         await releaseSharedClientInstance(client, mode);
       }
     } finally {
+      client?.off("sync.state", onSyncState);
       syncLifecycle?.dispose();
       statusController.markStopped();
       setActiveMatrixClient(null, auth.accountId);
@@ -242,6 +248,18 @@ export async function monitorMatrixProvider(opts: MonitorMatrixOpts = {}): Promi
   const warnedEncryptedRooms = new Set<string>();
   const warnedCryptoMissingRooms = new Set<string>();
   let healthySyncSinceMs: number | undefined;
+  const noteSyncHealthState = (state: MatrixSyncState, at = Date.now()) => {
+    if (isMatrixReadySyncState(state)) {
+      healthySyncSinceMs = at;
+      return;
+    }
+    if (isMatrixDisconnectedSyncState(state)) {
+      healthySyncSinceMs = undefined;
+    }
+  };
+  const onSyncState = (state: MatrixSyncState) => {
+    noteSyncHealthState(state);
+  };
 
   try {
     client = await resolveSharedMatrixClient({
@@ -260,6 +278,7 @@ export async function monitorMatrixProvider(opts: MonitorMatrixOpts = {}): Promi
       statusController,
       isStopping: () => cleanedUp || opts.abortSignal?.aborted === true,
     });
+    client.on("sync.state", onSyncState);
     // Cold starts should ignore old room history, but once we have a persisted
     // /sync cursor we want restart backlogs to replay just like other channels.
     const dropPreStartupMessages = !client.hasPersistedSyncState();
@@ -375,7 +394,6 @@ export async function monitorMatrixProvider(opts: MonitorMatrixOpts = {}): Promi
       accountId: auth.accountId,
       abortSignal: opts.abortSignal,
     });
-    healthySyncSinceMs ??= Date.now();
     logVerboseMessage("matrix: client started");
 
     // Shared client is already started via resolveSharedMatrixClient.