feat: add atomic machine attach v2

[schickling-assistant]

Summary

• add one strictly framed machine-attach-v2 boundary with atomic same-socket admission
• publish exact revisioned terminal output and child input-mode state
• bound framing and per-client output so slow consumers cannot stall peers
• remove the unreleased v1 descriptor path and its compatibility surface
• add real adapter/daemon/process coverage for exact input bytes, typed outcomes, and stale generations

Verification

• tsc -p tsconfig.json --noEmit
• tsc -p tsconfig.build.json
• 61 focused protocol/server/adapter/process tests
• 63 focused CLI/help/completion/adapter/process tests after v1 removal
• strict VRS validation

Draft while the Fractal consumer is exercised against the pinned build. Architecture discussion: #155.

[myobie]

Nathan reviewed this direction and accepts the product boundary. Please proceed.

The accepted boundary is:

• machine-attach-v2 has no automatic fallback.
• A new client rejects an old daemon with a clear error and does not restart or change the session.
• An explicit old client is the debugging path for an old daemon.
• Existing sessions restart only at deliberate safe points. This is not an all-at-once cutover.

Before merge, please add or link a short rollout and debugging note. It must tell an operator to record pty --version, resolve the installed package with realpath "$(command -v pty)", and preserve the exact built checkout before upgrade. The explicit debug command has this form:

PTY_ROOT=<original-pty-root> \
  ~/.local/share/pty/legacy/<old-commit>/bin/pty attach <session-id>

The package is currently private and is not published to the npm registry, so npx @compoundingtech/pty@<version> is not a recovery path.

Recommended rollout: preserve the old checkout on each host, install the new build, restart one low-value session, test local and remote attach/detach/resize/reconnect, and then restart other sessions only when safe. Keep the old client until no old daemon remains.

This comment approves the direction. It does not authorize a production rollout or automatic session restarts.

[myobie]

I’m taking the requested independent evidence/docs pass on the accepted boundary, without rewriting or policing this shared branch. I’ll work from exact head ea7bc1063bfb16309de5e2717c548c70605839e4 and preserve an exact built pre-upgrade checkout. Scope: (A) exercise the PR client+daemon through attach, explicit detach, resize, reconnect, and verify a new client rejects an old daemon without restart or session mutation; (B) prove the preserved old checkout, invoked with explicit PTY_ROOT, still attaches to that old daemon. I’ll also propose the concise rollout/debug note Nathan requested. Any contribution will be append-only with an ordinary push after rechecking the remote head; if the branch advances, I’ll merge/converge normally rather than rewrite it. No fallback, bulk restart, deployment, or production recovery.

[myobie]

Scope correction from Nathan: Johannes owns PR #156 and may proceed with the accepted machine-attach-v2 direction. I will not add work, change this branch, create a successor, deploy, or restart sessions. My preceding note is superseded; I’ll provide read-only support only if Johannes asks. The earlier accepted-boundary comment remains the rollout/debug contract.

[schickling-assistant]

We will not merge this PR.

The current PTY protocol remains the baseline. Fractal will first return to one current-protocol path. The long-term embedded terminal work moves to pty-rust.

We will preserve this PR as design and test evidence. Useful behavior cases will move to the shared corpus in compoundingtech/pty-rust#4.

Closing this PR as superseded. This does not change or restart any PTY session.