fix(discord): wire voice input callback at adapter connect time

[isheng-eqi]

Fixes #60623

_voice_input_callback was only set in _handle_voice_channel_join, not at adapter connect or reconnect. Voice transcription was logged but never forwarded as an inbound message without explicit /voice join.

Wire the callback at both connect and reconnect paths.

[teknium1]

Thanks for tracing both connection paths. The callback gap is present on current main, but the proposed wiring does not yet make an automatic/programmatic voice join usable end-to-end.

Problems

• gateway/run.py:12907-12909 returns before dispatch when the guild lacks _voice_text_channels[guild_id]. That binding is only established by the successful /voice join flow at gateway/run.py:12807-12809; DiscordAdapter.join_voice_channel() starts the listener but does not create it (plugins/platforms/discord/adapter.py:2852-2893). The new callback alone therefore still drops transcripts for the path described in the PR.
• The PR changes startup and reconnect delivery behavior but adds no regression coverage. Current reconnect tests use the generic StubAdapter in tests/gateway/test_platform_reconnect.py:14-74 and do not assert the callback contract.

Suggested changes

• Define the automatic/programmatic join's text-channel and SessionSource binding, then establish it before voice input can be dispatched.
• Add startup and reconnect tests that assert callback wiring and a bound transcript reaching the standard handler.

Automated hermes-sweeper review.

[isheng-eqi]

Thanks for the thorough review! I've addressed both concerns:

1. Text-channel binding for automatic joins: Added optional text_channel_id and source parameters to DiscordAdapter.join_voice_channel(). When provided, the adapter stores them in _voice_text_channels[guild_id] and _voice_sources[guild_id] — the same binding that /voice join establishes — so automatic/programmatic voice joins can route transcripts through _handle_voice_channel_input without requiring the slash command.

2. Callback wiring tests: Added TestVoiceInputCallbackWiring with:

   • test_startup_wires_voice_input_callback — asserts _voice_input_callback is set on the Discord adapter during cold-start connect
   • test_reconnect_wires_voice_input_callback — asserts the callback is re-wired after reconnect

Please take another look!

[teknium1]

Merged into main via consolidated salvage PR #73517 (merge b8c38a451a). Your _voice_input_callback wiring at start() + reconnect watcher and join_voice_channel(text_channel_id=…) binding were cherry-picked (3 commits) with your authorship.

Your contribution is credited to you in git history. Thank you! Closing this PR as merged-via-salvage.