Summary

Salvages PR #3005 by web3blind — Telegram Private Chat Topics support (Bot API 9.4, February 2026). Cherry-picked onto current main with functional skill binding added on top.

Closes #2598

What changed

From PR #3005 (web3blind)

• DM topic creation via createForumTopic — Bot API 9.4 allows this in private chats
• Config-driven topics — define topics per chat_id in platforms.telegram.extra.dm_topics
• Thread ID persistence — thread_id saved back to config.yaml after creation, preventing duplicates on restart
• Session isolation — each topic gets its own session via existing build_session_key thread_id support
• Hot-reload — topics added to config are discovered without gateway restart
• 16 tests covering setup, persistence, cache, error handling

Added: Functional skill binding

The original PR had a cosmetic skill hint ([skill: name] in chat_topic text). This follow-up makes it actually work:

• auto_skill field on MessageEvent — telegram adapter sets it from the topic's skill config
• Gateway auto-loads the skill on new sessions — uses _load_skill_payload + _build_skill_message (same infrastructure as /skill-name slash commands)
• Injected only on new sessions — subsequent messages see the skill in conversation history; no duplication
• Clean chat_topic — topic name without the [skill: ...] suffix; skill flows through the dedicated field
• 3 additional tests for auto_skill behavior

Configuration

platforms:
  telegram:
    extra:
      dm_topics:
      - chat_id: 123456789
        topics:
        - name: General
          icon_color: 7322096
          thread_id: 100  # auto-persisted after first creation
        - name: Accessibility Auditor
          icon_color: 9367192
          skill: accessibility-auditor  # auto-loaded on new sessions

Test results

• 20 DM topics tests pass (17 original + 3 new)
• 1453 gateway tests pass
• 6203 full suite pass (1 pre-existing unrelated failure in anthropic error handling)