fix(discord): tolerate poisoned delivery-state mutex

[Yeachan-Heo]

Fixes #351.

What

src/discord.rs was the only production path in the crate locking its shared Mutex with expect(...) (5 sites: allow_request, rate_limit_delay, record_success, record_failure, DLQ bury). All five now go through one poison-tolerant state() accessor using PoisonError::into_inner.

Why

DiscordState guards the rate limiter, the per-target circuit breakers, and the DLQ buffer. One panic unwinding while that guard was held poisoned the mutex, so every later Discord delivery decision and DLQ bury panicked for the rest of the daemon's lifetime — permanently losing the whole Discord lane, including the DLQ capture that exists precisely to preserve undelivered messages.

The rest of the crate already tolerates poisoning (daemon.rs, dispatch.rs, gjc_lane.rs, source/subscription.rs, source/git.rs, source/tmux.rs, lifecycle.rs), so this aligns Discord with the existing convention rather than introducing a new policy. All three guarded structures are individually recoverable, so recovery degrades to possibly-stale counters instead of an unrecoverable panic loop.

Verification

• cargo test --bin clawhip → 1101 passed, 0 failed
• cargo fmt --check → clean
• cargo clippy --all-targets -- -D warnings → clean
• New regression test discord::tests::poisoned_delivery_state_still_serves_limiter_circuit_and_dlq poisons the state from a panicking thread, then asserts the limiter delay, the circuit-breaker open transition, and the DLQ path all still work.
• Negative control: with the accessor temporarily reverted to expect(...), that test fails with panicked at src/discord.rs:751: discord state lock: PoisonError { .. }, confirming the test actually covers the regression.

Base dev@c4774562c6b073d4d6e1481aeb10ee8aa68afbad. No config/schema/behavioral change on the healthy path.

—
[repo owner's gaebal-gajae (clawdbot) 🦞]

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