fix: ack for an already cancelled ticket future crashes append session

[quettabit]

No description provided.

[greptile-apps]

Greptile Summary

This one-line fix adds a done() guard in _resolve_next before calling set_result on a future, mirroring the same pattern already used in _fail_all. Without it, if a caller's task is cancelled while awaiting a BatchSubmitTicket, the underlying future transitions to the cancelled state; when the ack arrives from the server, set_result raises InvalidStateError, which propagates through _run and crashes the entire append session.

Confidence Score: 5/5

Safe to merge — the fix is minimal, correct, and consistent with the existing pattern in _fail_all.

The single-line guard follows the identical pattern already present in _fail_all. No new logic is introduced; the only change is preventing set_result from being called on a future that was cancelled by an awaiting task. All remaining findings are at most P2.

No files require special attention.

Important Files Changed

Filename	Overview
src/s2_sdk/_append_session.py	Adds a done() guard in _resolve_next to skip set_result on futures already cancelled by a caller, preventing InvalidStateError from crashing the session. Fix is consistent with the existing guard in _fail_all.

Sequence Diagram

sequenceDiagram
    participant Caller as Caller Task
    participant Session as AppendSession
    participant Queue as _queue / _unacked
    participant Server as Server

    Caller->>Session: submit(inp)
    Session->>Queue: append _UnackedBatch(ack_fut, bytes)
    Session-->>Caller: BatchSubmitTicket(ack_fut)

    Caller->>Caller: await ticket (awaits ack_fut)

    Note over Caller: Task cancelled externally
    Caller->>+Caller: asyncio cancels ack_fut
    Note over Caller: ack_fut.done() → True (cancelled)

    Server-->>Session: AppendAck arrives
    Session->>Session: _resolve_next(ack)
    Session->>Queue: popleft() → _UnackedBatch
    Session->>Session: _permits.release(bytes)
    alt ack_fut already done (cancelled)
        Session->>Session: skip set_result ✓
    else ack_fut still pending
        Session->>Session: set_result(ack)
    end

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