diff --git a/CHANGELOG.md b/CHANGELOG.md
index 05cef55abea..29c8dfad271 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -120,6 +120,7 @@ Docs: https://docs.openclaw.ai
 - LINE/context and routing synthesis: fix group/room peer routing and command-authorization context propagation, and keep processing later events in mixed-success webhook batches. (from #21955, #24475, #27035, #28286) Thanks @lailoo, @mcaxtr, @jervyclaw, @Glucksberg, and @Takhoffman.
 - LINE/status/config/webhook synthesis: fix status false positives from snapshot/config state and accept LINE webhook HEAD probes for compatibility. (from #10487, #25726, #27537, #27908, #31387) Thanks @BlueBirdBack, @stakeswky, @loiie45e, @puritysb, and @mcaxtr.
 - LINE cleanup/test follow-ups: fold cleanup/test learnings into the synthesis review path while keeping runtime changes focused on regression fixes. (from #17630, #17289) Thanks @Clawborn and @davidahmann.
+- Mattermost/interactive buttons hardening: scope interaction HMAC secrets per account, route DM button-click sessions by sender identity, and restore Mattermost send test mocks for channel-name resolution coverage. (#19957) thanks @tonydehnke.
 
 ## 2026.3.2
 
diff --git a/extensions/mattermost/src/channel.ts b/extensions/mattermost/src/channel.ts
index 401ddabf38b..5897c11277a 100644
--- a/extensions/mattermost/src/channel.ts
+++ b/extensions/mattermost/src/channel.ts
@@ -164,7 +164,7 @@ const mattermostMessageActions: ChannelMessageActionAdapter = {
     let props: Record<string, unknown> | undefined;
     if (params.buttons && Array.isArray(params.buttons)) {
       const account = resolveMattermostAccount({ cfg, accountId: resolvedAccountId });
-      if (account.botToken) setInteractionSecret(account.botToken);
+      if (account.botToken) setInteractionSecret(account.accountId, account.botToken);
       const callbackUrl = resolveInteractionCallbackUrl(account.accountId, cfg);
 
       // Flatten 2D array (rows of buttons) to 1D — core schema sends Array<Array<Button>>
@@ -191,6 +191,7 @@ const mattermostMessageActions: ChannelMessageActionAdapter = {
       props = {
         attachments: buildButtonAttachments({
           callbackUrl,
+          accountId: account.accountId,
           buttons,
           text: attachmentText,
         }),
diff --git a/extensions/mattermost/src/mattermost/interactions.test.ts b/extensions/mattermost/src/mattermost/interactions.test.ts
index c3aefca32ae..0e24ae4a4ee 100644
--- a/extensions/mattermost/src/mattermost/interactions.test.ts
+++ b/extensions/mattermost/src/mattermost/interactions.test.ts
@@ -103,6 +103,16 @@ describe("generateInteractionToken / verifyInteractionToken", () => {
     const reorderedContext = { action: "do", action_id: "bm_do", tweet_id: "999" };
     expect(verifyInteractionToken(reorderedContext, token)).toBe(true);
   });
+
+  it("scopes tokens per account when account secrets differ", () => {
+    setInteractionSecret("acct-a", "bot-token-a");
+    setInteractionSecret("acct-b", "bot-token-b");
+    const context = { action_id: "do_now", item_id: "123" };
+    const tokenA = generateInteractionToken(context, "acct-a");
+
+    expect(verifyInteractionToken(context, tokenA, "acct-a")).toBe(true);
+    expect(verifyInteractionToken(context, tokenA, "acct-b")).toBe(false);
+  });
 });
 
 // ── Callback URL registry ────────────────────────────────────────────
diff --git a/extensions/mattermost/src/mattermost/interactions.ts b/extensions/mattermost/src/mattermost/interactions.ts
index 5a52e630a59..be305db4ba3 100644
--- a/extensions/mattermost/src/mattermost/interactions.ts
+++ b/extensions/mattermost/src/mattermost/interactions.ts
@@ -63,32 +63,58 @@ export function resolveInteractionCallbackUrl(
 // ── HMAC token management ──────────────────────────────────────────────
 // Secret is derived from the bot token so it's stable across CLI and gateway processes.
 
-let interactionSecret: string | undefined;
+const interactionSecrets = new Map<string, string>();
+let defaultInteractionSecret: string | undefined;
 
-export function setInteractionSecret(botToken: string): void {
-  interactionSecret = createHmac("sha256", "openclaw-mattermost-interactions")
-    .update(botToken)
-    .digest("hex");
+function deriveInteractionSecret(botToken: string): string {
+  return createHmac("sha256", "openclaw-mattermost-interactions").update(botToken).digest("hex");
 }
 
-export function getInteractionSecret(): string {
-  if (!interactionSecret) {
-    throw new Error(
-      "Interaction secret not initialized — call setInteractionSecret(botToken) first",
-    );
+export function setInteractionSecret(accountIdOrBotToken: string, botToken?: string): void {
+  if (typeof botToken === "string") {
+    interactionSecrets.set(accountIdOrBotToken, deriveInteractionSecret(botToken));
+    return;
   }
-  return interactionSecret;
+  // Backward-compatible fallback for call sites/tests that only pass botToken.
+  defaultInteractionSecret = deriveInteractionSecret(accountIdOrBotToken);
 }
 
-export function generateInteractionToken(context: Record<string, unknown>): string {
-  const secret = getInteractionSecret();
+export function getInteractionSecret(accountId?: string): string {
+  const scoped = accountId ? interactionSecrets.get(accountId) : undefined;
+  if (scoped) {
+    return scoped;
+  }
+  if (defaultInteractionSecret) {
+    return defaultInteractionSecret;
+  }
+  // Fallback for single-account runtimes that only registered scoped secrets.
+  if (interactionSecrets.size === 1) {
+    const first = interactionSecrets.values().next().value;
+    if (typeof first === "string") {
+      return first;
+    }
+  }
+  throw new Error(
+    "Interaction secret not initialized — call setInteractionSecret(accountId, botToken) first",
+  );
+}
+
+export function generateInteractionToken(
+  context: Record<string, unknown>,
+  accountId?: string,
+): string {
+  const secret = getInteractionSecret(accountId);
   // Sort keys for stable serialization — Mattermost may reorder context keys
   const payload = JSON.stringify(context, Object.keys(context).sort());
   return createHmac("sha256", secret).update(payload).digest("hex");
 }
 
-export function verifyInteractionToken(context: Record<string, unknown>, token: string): boolean {
-  const expected = generateInteractionToken(context);
+export function verifyInteractionToken(
+  context: Record<string, unknown>,
+  token: string,
+  accountId?: string,
+): boolean {
+  const expected = generateInteractionToken(context, accountId);
   if (expected.length !== token.length) {
     return false;
   }
@@ -133,6 +159,7 @@ function sanitizeActionId(id: string): string {
 
 export function buildButtonAttachments(params: {
   callbackUrl: string;
+  accountId?: string;
   buttons: Array<{
     id: string;
     name: string;
@@ -147,7 +174,7 @@ export function buildButtonAttachments(params: {
       action_id: safeId,
       ...btn.context,
     };
-    const token = generateInteractionToken(context);
+    const token = generateInteractionToken(context, params.accountId);
     return {
       id: safeId,
       type: "button" as const,
@@ -225,7 +252,7 @@ export function createMattermostInteractionHandler(params: {
   botUserId: string;
   accountId: string;
   callbackUrl: string;
-  resolveSessionKey?: (channelId: string) => Promise<string>;
+  resolveSessionKey?: (channelId: string, userId: string) => Promise<string>;
   dispatchButtonClick?: (opts: {
     channelId: string;
     userId: string;
@@ -236,7 +263,7 @@ export function createMattermostInteractionHandler(params: {
   }) => Promise<void>;
   log?: (message: string) => void;
 }): (req: IncomingMessage, res: ServerResponse) => Promise<void> {
-  const { client, botUserId, accountId, log } = params;
+  const { client, accountId, log } = params;
   const core = getMattermostRuntime();
 
   return async (req: IncomingMessage, res: ServerResponse) => {
@@ -292,7 +319,7 @@ export function createMattermostInteractionHandler(params: {
 
     // Strip _token before verification (it wasn't in the original context)
     const { _token, ...contextWithoutToken } = context;
-    if (!verifyInteractionToken(contextWithoutToken, token)) {
+    if (!verifyInteractionToken(contextWithoutToken, token, accountId)) {
       log?.("mattermost interaction: invalid _token");
       res.statusCode = 403;
       res.setHeader("Content-Type", "application/json");
@@ -323,7 +350,7 @@ export function createMattermostInteractionHandler(params: {
         `in channel ${payload.channel_id}`;
 
       const sessionKey = params.resolveSessionKey
-        ? await params.resolveSessionKey(payload.channel_id)
+        ? await params.resolveSessionKey(payload.channel_id, payload.user_id)
         : `agent:main:mattermost:${accountId}:${payload.channel_id}`;
 
       core.system.enqueueSystemEvent(eventLabel, {
diff --git a/extensions/mattermost/src/mattermost/monitor.ts b/extensions/mattermost/src/mattermost/monitor.ts
index 1a3a50ba035..13864a33f44 100644
--- a/extensions/mattermost/src/mattermost/monitor.ts
+++ b/extensions/mattermost/src/mattermost/monitor.ts
@@ -448,7 +448,7 @@ export async function monitorMattermostProvider(opts: MonitorMattermostOpts = {}
 
   // ─── Interactive buttons registration ──────────────────────────────────────
   // Derive a stable HMAC secret from the bot token so CLI and gateway share it.
-  setInteractionSecret(botToken);
+  setInteractionSecret(account.accountId, botToken);
 
   // Register HTTP callback endpoint for interactive button clicks.
   // Mattermost POSTs to this URL when a user clicks a button action.
@@ -465,7 +465,7 @@ export async function monitorMattermostProvider(opts: MonitorMattermostOpts = {}
       botUserId,
       accountId: account.accountId,
       callbackUrl,
-      resolveSessionKey: async (channelId: string) => {
+      resolveSessionKey: async (channelId: string, userId: string) => {
         const channelInfo = await resolveChannelInfo(channelId);
         const kind = mapMattermostChannelTypeToChatType(channelInfo?.type);
         const teamId = channelInfo?.team_id ?? undefined;
@@ -476,7 +476,7 @@ export async function monitorMattermostProvider(opts: MonitorMattermostOpts = {}
           teamId,
           peer: {
             kind,
-            id: kind === "direct" ? botUserId : channelId,
+            id: kind === "direct" ? userId : channelId,
           },
         });
         return route.sessionKey;
@@ -495,7 +495,7 @@ export async function monitorMattermostProvider(opts: MonitorMattermostOpts = {}
           teamId,
           peer: {
             kind,
-            id: kind === "direct" ? botUserId : opts.channelId,
+            id: kind === "direct" ? opts.userId : opts.channelId,
           },
         });
         const to = kind === "direct" ? `user:${opts.userId}` : `channel:${opts.channelId}`;
diff --git a/extensions/mattermost/src/mattermost/send.test.ts b/extensions/mattermost/src/mattermost/send.test.ts
index ce2044f749d..364a4c91744 100644
--- a/extensions/mattermost/src/mattermost/send.test.ts
+++ b/extensions/mattermost/src/mattermost/send.test.ts
@@ -12,7 +12,9 @@ const mockState = vi.hoisted(() => ({
   createMattermostClient: vi.fn(),
   createMattermostDirectChannel: vi.fn(),
   createMattermostPost: vi.fn(),
+  fetchMattermostChannelByName: vi.fn(),
   fetchMattermostMe: vi.fn(),
+  fetchMattermostUserTeams: vi.fn(),
   fetchMattermostUserByUsername: vi.fn(),
   normalizeMattermostBaseUrl: vi.fn((input: string | undefined) => input?.trim() ?? ""),
   uploadMattermostFile: vi.fn(),
@@ -30,7 +32,9 @@ vi.mock("./client.js", () => ({
   createMattermostClient: mockState.createMattermostClient,
   createMattermostDirectChannel: mockState.createMattermostDirectChannel,
   createMattermostPost: mockState.createMattermostPost,
+  fetchMattermostChannelByName: mockState.fetchMattermostChannelByName,
   fetchMattermostMe: mockState.fetchMattermostMe,
+  fetchMattermostUserTeams: mockState.fetchMattermostUserTeams,
   fetchMattermostUserByUsername: mockState.fetchMattermostUserByUsername,
   normalizeMattermostBaseUrl: mockState.normalizeMattermostBaseUrl,
   uploadMattermostFile: mockState.uploadMattermostFile,
@@ -71,11 +75,16 @@ describe("sendMessageMattermost", () => {
     mockState.createMattermostClient.mockReset();
     mockState.createMattermostDirectChannel.mockReset();
     mockState.createMattermostPost.mockReset();
+    mockState.fetchMattermostChannelByName.mockReset();
     mockState.fetchMattermostMe.mockReset();
+    mockState.fetchMattermostUserTeams.mockReset();
     mockState.fetchMattermostUserByUsername.mockReset();
     mockState.uploadMattermostFile.mockReset();
     mockState.createMattermostClient.mockReturnValue({});
     mockState.createMattermostPost.mockResolvedValue({ id: "post-1" });
+    mockState.fetchMattermostMe.mockResolvedValue({ id: "bot-user" });
+    mockState.fetchMattermostUserTeams.mockResolvedValue([{ id: "team-1" }]);
+    mockState.fetchMattermostChannelByName.mockResolvedValue({ id: "town-square" });
     mockState.uploadMattermostFile.mockResolvedValue({ id: "file-1" });
   });