feat(runner): write a screenshot to stdout with --out -

[Goran Gajic (gorangajic)]

Relates to WIZ-11974

Overview of Changes

qawolf runner screenshot only wrote a file. The Tester session, which wants the bytes in a process, had to reserve a temp path, hand it to the sandboxed user, run the command, read the file back and delete it on every computer-use step.

--out - now writes the decoded JPEG to stdout, the same - that already means stdin for act and exec. Stdout carries the image alone: the confirmation, and the JSON line under --json, goes to stderr so nothing follows the bytes into a reader that treats stdout as the file. A terminal on stdout is refused, since nothing there can read the bytes. The help text, the runner guide and the skill say so.

Raw bytes rather than a base64 field in the JSON answer, because the repo's rule is to decode next to the write so nobody files base64 text as a JPEG, and because a byte stream is what a reader that pipes the command into a file or a viewer expects.

Testing

bun run typecheck
bun run lint
bun run format:check
bun run knip
bun run test
bun run build

Added tests: the writer sends decoded bytes to stdout and nothing to disk, refuses a non-JPEG answer for stdout too, and reports a closed pipe without letting the stream's error event crash the process (the doubles are real Writable streams for that reason); the handler keeps every confirmation off stdout in json and agent mode, refuses a terminal on stdout, and names stdout rather than a file when the pipe fails.

Checklist

• Changes follow the code style of this project
• Self-review completed
• Tests added/updated (or not applicable)
• No breaking changes (or described below)

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