fix(chat): drain queue entries enqueued during lock release

[salmundani]

Summary

Fixes #928

Test plan

Six new tests added that fail in the old code and pass with the fix.

pnpm validate also passes

Checklist

• All commits are signed and verified
• All commits are signed off for the DCO (git commit -s)
• pnpm validate passes
• Changeset added (or N/A — see CONTRIBUTING.md)
• Documentation updated (or N/A)

[salmundani]

By the way, exposing the class's internal synchronization primitives isn't usually the best idea (check "Java Concurrency in Practice" for practical examples). The bug I fixed is probably still latent in the failure paths of the code.

Redesigning the StateAdapter so it has the following methods would be much cleaner in the long term.

export interface StateAdapter {
  // Everything above stays. The drop strategy and the fallback still use it.

  /**
   * Atomically: take the lock if it is free, otherwise add the entry to the
   * queue. When `enqueueOnClaim` is true, the entry is also queued on claim,
   * which debounce and burst need.
   */
  claimOrEnqueue?(
    threadId: string,
    entry: QueueEntry,
    options: {
      ttlMs: number;
      maxSize: number;
      onQueueFull: "drop-oldest" | "drop-newest";
      enqueueOnClaim: boole
    }
  ): Promise<ClaimResult>;

  /**
   * Atomically and token-checked: pop all pending entries, or release the
   * lock if the queue is e token no longer holds
   * the lock, and then pop
   */
  takeOrRelease?(lock: Lock): Promise<TakeResult>;
}

export type ClaimResult =
  | { status: "claimed"; lock: Lock }
  | { status: "queued"; dep
  | { status: "dropped"; depth: number };

export type TakeResult =
  | { status: "taken"; entries: QueueEntry[] }
  | { status: "released" }
  | { status: "lost" };

Similar to the atomic putIfAbsent in Java's ConcurrentHashMap.

These new methods should be optional as to not break 3rd party adapters, or otherwise be part of a major release.