fix(telegram): complete 3-layer defense against invalid thread_id in non-forum DMs

[MacroAnarchy]

What does this PR do?

Comprehensive fix for Telegram DM sends failing with Message thread not found when replying to messages in non-forum chats. Addresses the root cause at three layers for defense-in-depth.

Related Issue

Fixes #3206

Type of Change

🐛 Bug fix (non-breaking change that fixes an issue)

Root Cause

Telegram sets message_thread_id on incoming reply-chain messages in non-forum DMs. This value is not valid for outgoing send_message() calls — Telegram rejects it with BadRequest: Message thread not found. The error cascades through streaming, progress messages, and all send types, causing 1000+ errors per session.

Changes Made — 3 Layers

Layer 1 — Source (telegram.py: _build_message_event)

Drop spurious message_thread_id when no forum topic was resolved. Prevents invalid thread IDs from entering the system.

Layer 2 — Send fallback (telegram.py: send)

When send_message() gets "Message thread not found", clear effective_thread_id and retry immediately — instead of retrying 3x with the same broken value. Catches both Exception and NetworkError paths.

Layer 3 — Progress messages (run.py: _progress_thread_id)

The event_message_id fallback in _progress_thread_id was designed for Slack (where message IDs are valid thread identifiers). On Telegram, this re-introduces invalid thread IDs even when Layers 1-2 correctly handle the send path. Now platform-aware:

• Slack/Discord: source.thread_id or event_message_id (correct for their threading model)
• Telegram & others: source.thread_id only (no message ID fallback)

Without Layer 3, the bug persists — progress/status messages bypass the telegram.py fixes entirely via run.py.

Why this supersedes #3207 and #3218

• fix(telegram): ignore invalid message_thread_id in non-forum DMs #3207 implements Layer 1 only (source-level drop)
• fix(telegram): graceful fallback when send fails with 'Message thread not found' #3218 implements Layer 2 only (send-level fallback)
• Neither addresses Layer 3 — the run.py progress message path that re-introduces invalid thread IDs from a Slack-specific fallback

This PR combines all three layers into a single coherent fix.

How to Test

1. Open a Telegram DM (non-forum chat) with the bot
2. Reply to an existing message (creates a reply chain with message_thread_id)
3. Trigger the bot to respond (streaming or normal)
4. Verify: no "Message thread not found" errors in logs, messages send successfully

Checklist

• I've read the Contributing Guide
• My commit messages follow Conventional Commits
• I searched for existing PRs before opening this one
• Only 2 files changed, minimal diff, no unrelated changes

[teknium1]

The core issue (invalid thread_id causing 'Message thread not found' failures) is already fixed on main via PR #3390 (commit 41d9d08). That fix handles BadRequest at the send layer, clears thread_id, and retries. Thanks for the thorough defense-in-depth approach though!