fix(telegram): route forwarded channel media through effective_message (#76615)

[Enough1122]

Summary

_handle_media_message guarded on update.message and returned silently when it was None. Media forwarded from channels arrives with the real payload on update.effective_message (update.message is None), so forwarded photos/documents were never delivered to the agent — no log, no error.

Fix: resolve msg = self._effective_update_message(update) at the top (mirroring the text handler at ~line 8695) and use it for the auth / should-process / observe checks. The rest of the function already worked off a msg variable.

Also fixed the test helper to set effective_message explicitly (MagicMock would otherwise return an auto-mock, silently breaking effective-message routing).

Single-file change (plus tests). No public API change.

NOT doing X: not touching _handle_text_message (already correct), not changing download/cache flow.

Test plan

python -m pytest tests/gateway/test_telegram_documents.py -q
# 19 passed (17 existing + 2 new: forwarded channel photo + document
# arrive with update.message=None / effective_message=<msg> and are
# delivered as PHOTO/DOCUMENT events)

[alt-glitch]

This was generated by AI during triage.

Duplicate of #51747: both current-path patches route Telegram media through _effective_update_message() in the same adapter handler. #51747 has broader channel-post and authorization regression coverage.

[teknium1]

Thanks for addressing a real Telegram media-routing regression.

Problems

• This duplicates open PR fix(telegram): cache channel-post media via effective_message (#51543) #51747: both replace the current-main early update.message gate at plugins/platforms/telegram/adapter.py:9027 with effective-message normalization. PR fix(telegram): cache channel-post media via effective_message (#51543) #51747 commit c4fd41007a1698a00b49978584861297143ee1d5 additionally covers unauthorized channel posts and sender_chat authorization.

Suggested changes

• Consolidate onto PR fix(telegram): cache channel-post media via effective_message (#51543) #51747 rather than carrying two equivalent production patches; retain this PR's document channel-post regression test if it adds coverage not present there.

Automated hermes-sweeper review.

[Enough1122]

Duplicate of #51747 (opened 6/24, covers the same effective_message normalization for channel-post media). Closing in favor of #51747 for #76615/#51543.