Execution Session and PTY Runtime

Execution Session and PTY Runtime

The Plugin Task API uses an independent Execution Session for a long-lived coding-agent process. A Task stores a non-owning sessionId; the Session Manager owns lifecycle and the PTY Runtime owns bounded interactive I/O. Task Graph Sessions additionally persist taskId and subtaskId, and their Session events carry both associations so parallel worktree-local journals cannot be misattributed across sibling subtasks.

Task --sessionId--> Session Manager --owns--> PTY Session Host --owns--> Implementer CLI

Sessions are scoped by canonical repository root, Agent identity, and effective executable. A healthy match is reused across Task dispatches and review rework. A Task does not restart or close its Session simply because a review round changed.

Lifecycle and tools

starting -> running <-> busy -> idle
                 \-> exited | failed

The Plugin exposes six bounded MCP tools:

Tool	Purpose
coordinate_agents_session_open	Resolve the configured executable and start or reuse a Session.
coordinate_agents_session_status	Read state, root, command, timestamps, PID, and exit facts.
coordinate_agents_session_inspect	Read-only status plus bounded redacted recent output.
coordinate_agents_session_write	Send structured input to the owned process; no shell parsing.
coordinate_agents_session_read	Read bounded buffered output using a cursor.
coordinate_agents_session_close	Gracefully interrupt, then boundedly close the owned process.

resize and interrupt are internal Runtime operations for adapters and diagnostics. They do not provide desktop UI automation.

Task and review loop

task dispatch validates the final executable, sends IMPLEMENT, and opens or reuses the Session. If the adapter did not consume the first specification as launch arguments, the Runtime writes it into the PTY. A short grace period captures immediate completion evidence; otherwise the Task remains WAITING_IMPLEMENTER while the Session stays inspectable.

After CHANGES_REQUESTED, the next explicit dispatch writes the new feedback into the same healthy Session. If the Session is exited or failed, the Runtime reports that fact; replacement requires the normal explicit dispatch path and never an infinite retry loop. recover inspect is facts-only and does not restart, replay input, resume a Task, or attach to an arbitrary PID.

For Task Graph execution, task graph-status/graph-inspect expose the same Session facts together with the parent Task, subtask, Agent, worktree, and verified completion evidence. graph-recover records an interrupted subtask when its Session host is no longer healthy and never treats a filename or prose message as proof. graph-resume reuses only a verified healthy Session rooted at the matching Runtime-owned worktree; an exited/failed Session is returned to READY for an explicit replacement dispatch. graph-stop and graph-cleanup close only Runtime-owned graph Sessions under a bounded timeout and preserve user worktrees, branches, refs, commits, and evidence when cleanup fails.

Executable and platform rules

Resolution is exact and fail-closed:

explicit project command > user command > Adapter default

Agent identity is not executable identity. antigravity configured with agy-proxy launches agy-proxy, never a guessed agy. Arguments are passed as arrays, so Windows paths with spaces, .cmd wrappers, PowerShell entry points, Unicode, and ANSI output are handled without shell-string assembly.

node-pty is preferred. A direct Plugin checkout without installed package dependencies, or a platform/Node combination where the native PTY cannot initialize, may use the same owned Session protocol over bounded stdio pipes as a degraded compatibility backend. In either mode, the Session Host can interrupt or terminate only the process it created. Metadata excludes environment variables, output is bounded/redacted, roots are validated, and the Runtime never controls the Codex App Terminal UI.