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feat(sdk): add opt-in stdin for detached commands - #365
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runCommand accepts `stdin: true` (detached only), and Command gains writeStdin() and closeStdin(). Writes are serialized per command, split into 512 KiB chunks, and never retried so bytes can't be delivered twice.
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Workflow DevKit retries failed steps by default, which could resend stdin bytes, so writeStdin and closeStdin now run with maxRetries 0. Rate limited writes are retried again since they were never applied. A write that fails after possibly delivering data now blocks later writes instead of appending to a partial message, an abort while waiting in the queue takes effect, and CommandFinished rejects stdin calls with a clear error.
Each workflow step gets a freshly deserialized Command, so the write queue and the rejection after a failed write don't carry across steps.
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Each stdin request now carries the position it starts at, so a request that fails on a dropped connection or a restarting server is resent without delivering the same bytes twice. Timeouts are only resent while the process keeps reading.
Passing a Readable such as process.stdin as `stdin` pipes it to the command and closes stdin when it ends, with or without `detached`.
kishorekrd
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October 8, 2026 21:00
- Close stdin at the position the API reports once a write has failed, instead of a stale one the API rejects. - Treat a client error that follows a resent request as possibly written, so later writes are rejected. - Use the bytes written a timeout reports instead of asking for them. - Report a stream failure to one wait() and let later calls wait for exit, keep piping when a wait is aborted, close stdin when the stream is destroyed before it ends, and read a stream the caller paused.
QuiiBz
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Oct 9, 2026
QuiiBz
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Oct 9, 2026
QuiiBz
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Oct 9, 2026
QuiiBz
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Oct 9, 2026
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Adds stdin for commands, mainly to run stdio MCP servers (like
agent-browser mcp) in a sandbox.stdin: trueneedsdetached: true. AReadableis written in order with backpressure, and stdin closes when it ends. The caller's stream is never destroyed.runCommandrejects and kills the command. When detached, the nextwait()rejects instead.closeStdinstill works.@vercel/sandbox-mocksupport is a follow-up.Needs backend support that ships separately. The integration tests fail until it's deployed.