Codex/sandbox command streaming

[Dingway98]

Summary

Changes

Validation

• ruff check
• pytest

---

Note

Medium Risk
Changes core sandbox exec/start wire protocol and timeout/error behavior; requires a streaming-capable receiver and can surface new failure modes if receiver and SDK versions are mismatched.

Overview
Sandbox command execution now streams output over SSE instead of blocking on /sandbox/exec or a non-streaming process start. exec() and processes.start() open a streaming POST /sandbox/processes, buffer stdout/stderr in the SDK (default 64 MiB via max_output_bytes), and support live stream(), disconnect(), and reattach semantics documented in the README.

Shared ProcessOutput validates sequenced events, enforces output limits (output_limit_exceeded / incomplete_output), and assembles final SandboxProcessResult including new output_truncated / last_seq fields. Sync and async transports gain POST SSE, a 60s read-idle timeout after headers (heartbeats reset it), streaming_not_supported when the receiver is too old (no automatic retry), and sync socket shutdown for clean disconnect.

Local wait(timeout_...) on an active collector raises TimeoutError / asyncio.TimeoutError while collection continues; reattached processes with truncated retained output fail on wait().

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