fix(telegram): address PR review comments

- Export pickFirstExistingAgentId and use it to validate topic agentId
- Properly update mainSessionKey when overriding route agent
- Fix docs example showing incorrect session key for topic 3

Fixes issue where non-existent agentId would create orphaned sessions.
Fixes issue where DM topic replies would route to wrong agent.

docs/channels/telegram.md

@@ -466,7 +466,7 @@ curl "https://api.telegram.org/bot<bot_token>/getUpdates"
     }
     ```
 
-    Each topic then has its own session key: `agent:main:telegram:group:-1001234567890:topic:3`
+    Each topic then has its own session key: `agent:zu:telegram:group:-1001234567890:topic:3`
 
     Template context includes:
 

src/routing/resolve-route.ts

@@ -143,7 +143,7 @@ function resolveAgentLookupCache(cfg: OpenClawConfig): AgentLookupCache {
   return next;
 }
 
-function pickFirstExistingAgentId(cfg: OpenClawConfig, agentId: string): string {
+export function pickFirstExistingAgentId(cfg: OpenClawConfig, agentId: string): string {
   const lookup = resolveAgentLookupCache(cfg);
   const trimmed = (agentId ?? "").trim();
   if (!trimmed) {

src/telegram/bot-message-context.ts

@@ -40,10 +40,15 @@ import { logVerbose, shouldLogVerbose } from "../globals.js";
 import { recordChannelActivity } from "../infra/channel-activity.js";
 import {
   buildAgentSessionKey,
+  pickFirstExistingAgentId,
   resolveAgentRoute,
   type ResolvedAgentRoute,
 } from "../routing/resolve-route.js";
-import { DEFAULT_ACCOUNT_ID, resolveThreadSessionKeys } from "../routing/session-key.js";
+import {
+  DEFAULT_ACCOUNT_ID,
+  buildAgentMainSessionKey,
+  resolveThreadSessionKeys,
+} from "../routing/session-key.js";
 import { resolvePinnedMainDmOwnerFromAllowlist } from "../security/dm-policy-shared.js";
 import { withTelegramApiErrorLogging } from "./api-logging.js";
 import {
@@ -215,8 +220,10 @@ export const buildTelegramMessageContext = async ({
     parentPeer,
   });
   // Per-topic agentId override: re-derive session key under the topic's agent.
-  const topicAgentId = topicConfig?.agentId?.trim();
-  if (topicAgentId) {
+  const rawTopicAgentId = topicConfig?.agentId?.trim();
+  if (rawTopicAgentId) {
+    // Validate agentId against configured agents; falls back to default if not found.
+    const topicAgentId = pickFirstExistingAgentId(freshCfg, rawTopicAgentId);
     const overrideSessionKey = buildAgentSessionKey({
       agentId: topicAgentId,
       channel: "telegram",
@@ -225,10 +232,14 @@ export const buildTelegramMessageContext = async ({
       dmScope: freshCfg.session?.dmScope,
       identityLinks: freshCfg.session?.identityLinks,
     }).toLowerCase();
+    const overrideMainSessionKey = buildAgentMainSessionKey({
+      agentId: topicAgentId,
+    }).toLowerCase();
     route = {
       ...route,
       agentId: topicAgentId,
       sessionKey: overrideSessionKey,
+      mainSessionKey: overrideMainSessionKey,
     };
     logVerbose(
       `telegram: per-topic agent override: topic=${resolvedThreadId ?? dmThreadId} agent=${topicAgentId} sessionKey=${overrideSessionKey}`,