Problem

When a channel plugin lacks a custom buildToolContext in its threading adapter (e.g. Telegram), the fallback path in buildThreadingToolContext() did not include currentThreadTs from the inbound MessageThreadId.

This caused resolveTelegramAutoThreadId() to return undefined (because it requires both currentThreadTs AND currentChannelId), so any message(action=send) without an explicit threadId would route to the main chat instead of the originating DM topic.

Reproduction

1. Open a DM topic with the bot (e.g. topic 1045687)
2. Send a message in another topic or main chat (updates lastThreadId in session entry)
3. Return to original topic - agent sends message(action=send) with buttons/media without explicit threadId
4. Result: Message arrives in main chat instead of topic

Fix

Add currentThreadTs derived from sessionCtx.MessageThreadId to the fallback return in buildThreadingToolContext() when threading?.buildToolContext is absent.

This ensures resolveTelegramAutoThreadId() can auto-inject the correct message_thread_id for Telegram DM topics, matching the behavior that channels with custom buildToolContext already have.

Changes

• src/auto-reply/reply/agent-runner-utils.ts: Add currentThreadTs to fallback path (3 lines)

Testing

• Existing threading tests pass (message-action-runner.threading.test.ts, channel.test.ts)
• Manually verified: message(action=send) without threadId now correctly routes to topic after the user interacts with main chat

Fixes #52217