Add plan and goal command actions

[nikita-ashihmin]

Summary

• expose collaboration_mode as an ACP session config option and restore it when sessions are resumed or loaded
• advertise /plan through neutral _meta.commandAction metadata as a stateful setConfigOption action
• handle /plan locally as a toggle without starting a model turn and publish config_option_update
• apply Codex collaboration mode through thread/settings/update
• advertise /goal as a stateful prefixPrompt action so clients collect an objective and send /goal <objective>
• publish authoritative goal snapshots in session metadata, including stable identity, status, elapsed time, and an advertised out-of-band control method
• restore or clear the current goal when an existing session is resumed or loaded, while preventing stale reads from replacing newer live updates
• support typed out-of-band Pause and Clear controls while the goal turn is active

Why

ACP available commands describe command names and arguments, but that is not enough for clients to distinguish a raw slash command from a client-side interaction. Plan changes persistent session configuration; Goal changes how the next prompt is composed, starts a goal turn, and then becomes durable session state.

The optional _meta.commandAction hint lets capable clients provide those interactions without hard-coding Codex command names. Goal state is published through session metadata so clients can render and restore a persistent goal panel. The advertised control method avoids trying to start a second ACP prompt while the goal turn is active. Start and Resume continue through the Goal prompt path because they create a model turn; Pause and Clear use the control extension because they do not.

Clients that do not understand these optional metadata fields continue to treat both entries as ordinary slash commands.

Tests

• npm test (310 passed, 28 skipped)
• npm run typecheck
• npm run build

[Ololoshechkin]

@nikita-ashihmin please check the session/goal_control method -- if it's an extension, please use https://agentclientprotocol.com/protocol/v1/extensibility guidelines

[Ololoshechkin]

@nikita-ashihmin it's non-standard method in ACP, isn't it?

[Ololoshechkin]

Couldn't find it in ACP spec, so it looks like an extension to me. The protocol reserves any method name starting with an underscore (_) for custom extensions. See https://agentclientprotocol.com/protocol/v1/extensibility

[nikita-ashihmin]

Fixed in 41ceacf: the custom request is now namespaced as _codex/session/goal_control, so it starts with the underscore reserved for ACP extension methods. The advertised controlMethod metadata and snapshots were updated as well.

[Ololoshechkin]

Is there a test for this thread matching by goalRevision?

[nikita-ashihmin]

Yes — the test "ignores an older goal refresh that completes after a newer refresh" exercises this exact goalRevision race by resolving the newer refresh first and the stale one afterward, then asserting that only the current goal is published. I reran it as part of the full suite (310 tests passed).