feat: add command_session tool for interactive long-running commands

[OSN64]

Summary

This PR implements a new `command_session` tool that allows the agent to run long-running interactive commands in the background, poll for output, send input, and terminate them.

Features

• Start: Launch a command in a PTY-backed session
• Poll: Get incremental output from a running session
• Write: Send input to a running session
• Interrupt: Send SIGINT to a session
• Terminate: Kill a session
• List: List all active sessions

Implementation

• `packages/core/src/command-session.ts`: CommandSession service with PTY support
• `packages/schema/src/command-event.ts`: Event schema for command lifecycle
• `packages/opencode/src/tool/command-session.ts`: Tool definition with JSON Schema parameters
• `packages/core/test/command-session/`: Integration tests

Configuration

• Added localized `.opencode/opencode.jsonc` with provider config
• Uses existing PTY infrastructure for terminal features (colors, cursor movement)

Notes

• Timeout: 2 minutes default max runtime, 5 minutes inactivity timeout
• Process group kill (kills entire process tree on terminate)
• Requires `OPENCODE_EXPERIMENTAL_BACKGROUND_SUBAGENTS=true` env var

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[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Found a related PR! Here's what I discovered:

Related PR Found:

• PR feat(tool): add interactive terminal tool with persistent PTY sessions #23794: feat(tool): add interactive terminal tool with persistent PTY sessions
  • This PR also implements PTY-based terminal sessions for interactive command execution, which appears to be very similar functionality to the command_session tool being added in PR feat: add command_session tool for interactive long-running commands #35293.

This earlier PR (#23794) should be reviewed to understand if there's existing implementation that could be reused, refactored, or if these serve different purposes despite similar PTY-based session management approaches.