Discord REST client, cache and #225 settings (server-26#225 S2)

New app/internal/discord_rest.py: one shared httpx client with the
DiscordBot User-Agent, per-token rate-limit buckets (X-RateLimit-Bucket +
guild), one retry on a 429 of <=3s, global-429 pause per token, and a
process-wide breaker at 4000 401/403/unshared-429 responses per 10 min so
C2 can never get the shared egress IP banned. Tokens are never logged.

inspect_token / refresh_membership / leave_guild / TokenRejected move off
discord_leases onto it. /users/@me/guilds now follows after= pages (it read
one page of 200 and silently dropped the rest); a failed page is unknown,
never a truncated list.

guild_snapshot(token_doc, guild_id): cached, single-flight read of
/guilds/{g}, the bot's own member and /channels for S3's permission check.
401 marks the token invalid; 10004/10007 drop the server from guild_ids;
50001 is confirmed with one membership read and never changes guild_ids
on its own. TTLs: ok 120s, not-member/invalid 600s, unknown 30s.

config.py gets every setting the #225 slices use (perm-check kill switch,
TTLs, breaker budget, OAuth redirect URI, discord_pool_bot_guild_cap=90).
No behaviour change beyond pagination, User-Agent and the breaker.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

drb-c2-core/app/internal/discord_streams.py

@@ -49,6 +49,7 @@ from typing import Optional
 from app.config import settings
 from app.internal import firestore as fstore
 from app.internal import discord_leases as leases
+from app.internal import discord_rest
 from app.internal.logger import logger
 
 STREAMS = leases.STREAMS
@@ -416,7 +417,7 @@ async def _start_locked(*, org_id: str, guild_id: str, channel_id: str, system_i
             tokens = await fstore.collection_list(leases.TOKENS)
             stale = [t["token_id"] for t in tokens
                      if t.get("token_id") and t.get("guild_ids") is not None and guild_id not in t["guild_ids"]]
-            if await leases.refresh_membership(stale):
+            if await discord_rest.refresh_membership(stale):
                 res = await leases.lease_for_stream(stream_id, node_id=node["node_id"], org_id=org_id,
                                                     preferred_token_id=preferred_token_id, stream_fields=fields)
         if res.ok:
@@ -604,7 +605,7 @@ async def handle_actual(node_id: str, payload: dict) -> None:
                 "actual": {"state": state, "error": error, "code": code, "since": since, "at": now},
             })
     if recheck:
-        await leases.refresh_membership(sorted(recheck))
+        await discord_rest.refresh_membership(sorted(recheck))
 
     if "sessions" in payload:
         sessions = {str(t) for t in (payload.get("sessions") or [])}