refactor(discord): extract VoiceReceiver into voice_receiver (adapter.py god-file slice R1)

[andrexibiza]

Summary

discord adapter.py god-file slice R1: extract VoiceReceiver from plugins/platforms/discord/adapter.py (10,138 lines) into plugins/platforms/discord/voice_receiver.py. Part of the repo-wide large-file decomposition (tracker #78647).

What changed and why

• VoiceReceiver (window 514–897, 383 lines, 13 members) moved byte-verbatim (golden hash 8085b15e… verified) into voice_receiver.py; adapter.py re-exports all 13 names identity-preserving (re-export mandatory — test_discord_race_polish.py patches the adapter-module global)
• Zero intra-R1 coupling; 2 later call sites (4176, 4529) resolve through the re-export
• 3 existing test files already treat VR as a unit (test_voice_command.py, test_voice_channel_flow.py, test_discord_race_polish.py)
• Double-blind: 2 analysts → consensus (R1-CONSENSUS.md — pass B's pick won over pass A's Liveness on the refactor(discord): extract authorization cluster into DiscordAuthorizationMixin #75735 collision evidence) → implementer → 2 blind re-reviewers

Testing

• 98 tests passed (voice command + channel flow + race polish + 20 new seam tests), 0 failed
• Seam identity: adapter.VoiceReceiver is voice_receiver.VoiceReceiver verified live
• ruff F401 clean · git diff --check clean · LF-only · DCO signed

Coordination / interlock

• Epic: Part of [COMPLETE] Large-file decomposition: 20/20 done #78647 · Target: Part of Shard plugins/platforms/discord/adapter.py (god-file decomposition) #78634
• KILL LOCK: this shard is part of the discord adapter kill record (posted on Shard plugins/platforms/discord/adapter.py (god-file decomposition) #78634) — the 10,138-line whole, the mess it caused (Extract the authorization cluster from DiscordAdapter (god-file decomposition) #75734 buried auth, [Bug]: /handoff discord creates private thread with only the bot as member — destination user never added, thread invisible #67702, security(discord): bound image/animation/attachment HTTP response reads #60395 security, Bug: Discord reply_to_mode: false regresses to first on current runtime #29623), the shard wave, and the open fixer PRs (docs(discord): correct Echo Prevention mechanics + Server Members Intent conditional + close env-var docs class (resolves #11349) #78164 feat(line): signature enforcement, DISCORD quality, state_lock, tests, doc/ci fixes #78291 fix(discord): add home-channel owner to handoff thread (#67702) #67801 fix(gateway): normalise legacy bool reply_to_mode before Discord adapter (#29623) #58664 feat(discord): final response inline, tool progress in thread #68409 feat: make gateway document types configurable #50562 feat(webhooks): create a Discord thread for each event #70608 fix(discord): recall prior thread context after bot replies #52650 fix(discord): add config-backed auto-thread channels #54285 feat(sync): support bidirectional platform command sync (Issue #4) #61169 fix(discord): honor retry_after in auto-thread creation instead of dropping messages on 429 #76060 fix(discord): schedule approval boxes on the gateway loop #74471 fix(discord): stop the typing indicator sticking on the stale-result path #71471 fix(discord): anchor handoff threads in parent channel #63459 fix(discord): prioritize plugin commands under slash cap #76209 feat(discord): outbound @Name → <@id> via config.yaml (re-scope of #69206) + forum path #75633 feat: add Discord Kanban approval gates #68789 feat(gateway): add structured operator cards for Discord #67234 feat(discord): gate shared threads by mention #73487 fix: add usedforsecurity=False to hashlib in tools/ and plugins/ (FIPS compliance) #65570 fix(gateway): support Discord progress cleanup #42661 fix(discord): truncate auto-thread and handoff thread names by UTF-16 units #60252 feat(discord): add explicit review debate command (/review slash) #71164 fix(discord): accept relay-lane kwargs in native rename_thread (#78487) #78495 refactor(discord): extract authorization cluster into DiscordAuthorizationMixin #75735 fix(approval): explain requested action and permission #51397 fix(discord): opt threaded free-response channels in #62814 fix(security): scrub credentials from ffmpeg/ffprobe media helpers #73879 fix(discord): add space separator after bare URLs in agent output (#78359) #78417 security(discord): bound image/animation/attachment HTTP response reads #60395). Indexed by large-file decomposition meta-issue [COMPLETE] Large-file decomposition: 20/20 done #78647.
• refactor(discord): extract authorization cluster into DiscordAuthorizationMixin #75735 (DiscordAuthorizationMixin): owns the auth cluster + class-bases line — this slice avoids both; coordination posted
• Sibling PRs: the 4 other discord slices (standalone-send, gate, media, recovery-backfill) — disjoint windows
• Dedup: no existing PR extracts VoiceReceiver (60-PR open sweep)

Part of #78647
Part of #78634

Part of #79564
Part of #79772