Mercury CLI
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Extend

MCPs and skills

What a session loads, its MCP servers, its skills and its extensions, is a per-repository choice with one editing surface: the MCPs & Skills row of the Boot face. The choice is recorded as deviations from everything on, resolved into a kit when a session is born, and worn by that session for its whole life.

  • MCP: Configured servers, extension servers and eligible account connectors, by their resolved names, each on or off. A server an extension ships is named ext:<extension>:<server>. Session-only servers, including Mercury's built-in mercury server and the reserved ide bridge, are not listed. The ide bridge is managed through /ide.
  • Skills: Added directory skills from the user, project and managed settings, and extension skills, each on, invocable or off. Bundled skills load in sessions but are not listed. Skills an MCP server supplies are available once a session connects that server, and the menu does not list them.
  • Extension master row: Sits above the extension's items in each section it contributes to. Items under an off master read off (extension) and keep their own state underneath.
  • NEXT SESSION: Counts what the next session gets among the listed entries, not built-in capabilities.

The empty states read no added MCPs and no added skills. They refer to the menu's inventory, not to everything a session can use. Absence from the record means on, and every toggle is saved to the record at once. The rows are enumerated through the same doors the runner reads, so the menu cannot advertise a member the session would not see.

Skill states

  • on: Ambient. The agent can reach for the skill when needed.
  • invocable: Listed, but loaded only when you enter /<name>.
  • off: Absent from the next session.

Change the next session's kit

To change the next session's kit, follow these steps:

  1. Select the MCPs & Skills row on the Boot face.
  2. Press Enter.
  3. Move to the server, skill or extension row with ↑ or ↓.
  4. Press Enter to change its state.
  5. Press Esc to return to the Boot face.
  6. Start a new session.

The session is born wearing a kit resolved from the record against the live roster, validated on the wire and stamped on the session's durable record.

Backspace restores a row's default. An extension is live for a session only when both its installed switch and its master row in that repository agree. A kit narrows only the session it was stamped on: teammates, the daemon and every non-session process are untouched. The warm runner behind New Session already wears the next birth's kit, so a menu edit costs one cold spawn before the pool is warm again.

Save a preset

To save a preset, follow these steps:

  1. Open the MCPs & Skills menu with the wanted states set.
  2. Press p.
  3. Name the preset.

Mercury saves the current deviations as a named preset, stored globally, so it travels across repositories.

Up to 200 presets are stored. A preset's deviations resolve against whatever repository wears it. A skill or extension the preset turns off stays off by name, so it also applies to a member that arrives later. An MCP server the preset excludes is absent from the membership. Deviations naming members the repository lacks are counted in the wear receipt rather than dropped.

Use a preset for the next session

To use a preset for the next session, follow these steps:

  1. Press w in the MCPs & Skills menu.
  2. Move to the preset with ↑ or ↓.
  3. Press Enter.
  4. Start a new session.

The Boot face's kit row reads next: preset '<name>', the next session born consumes the preset, and the menu's own choices resume afterwards.

Enter on the armed row disarms it. Backspace in the preset roster deletes a preset. Resuming a dead transcript while a preset is armed wears it, and hopping into a live session never spends it. A coordinator can launch a session wearing a preset by name, and an unknown name is a typed refusal naming the saved roster. Launch receipts name the road the kit came by: kit carried, kit derived or kit preset.

Session controls

  • /mcp: This session's servers, on or off. Mercury's built-in servers answer a typed exemption.
  • /skills: This session's skills, cycling on, invocable and off.

These dials are session-scoped and write no configuration file. A dial turned mid-turn is queued whole and applies when the turn ends, so the record never says off over a process still holding the member. Each applied dial lands a kit-dial receipt on the session. The per-repository record has exactly one writer, the menu.

A resumed or reactivated session is re-stamped from the record with a kit-restamp receipt naming what was displaced. A transcript resumed with no record says so on the same receipt.

MCP command-line verbs

mercury mcp manages MCP servers with the verbs add, add-json, list, get, remove and serve.

Extensions, Hooks, Sessions, Saturn scheduling