# mcpctl × prime-agent

## What `mcpctl config prime-agent --project X` wires up

| Piece | Where | Purpose |
|-------|-------|---------|
| Proxy MCP | `~/.prime/agent/settings.json` | `{ type: "http", url: "<gateway>/projects/X/mcp" }` |
| Bearer credential | `~/.prime/agent/auth.json` | `mcp:X` → a minted mcpctl PAT |
| Skills | `~/.prime/agent/skills/` | the project's `SKILL.md` bundles |
| `/mcpctl` switcher | `~/.prime/agent/extensions/mcpctl-switch.ts` | switch projects, and the active-project indicator |

Unlike Claude Code (a stdio bridge, no token) and pi (native tools over
JSON-RPC), prime-agent talks to the **HTTP gateway**, so the switch is really
three things: a credential, a settings entry, and a reload.

## Credentials are the fragile part

`config prime-agent` mints an `mcptoken` per project, stores it under
`mcp:<project>`, and retires the one it replaced. Three rules make that safe:

- **A key being present proves nothing.** A revoked token would short-circuit
  provisioning and leave prime-agent unable to reach the gateway while the
  command reported success. mcptokens are shown once, so the stored token's
  16-char `tokenPrefix` is compared against the project's *active* tokens rather
  than sending the secret.
- **No credential means the switch fails.** Non-zero exit, `settings.json`
  untouched, so the previously active project keeps working instead of being
  replaced by a mount that 401s — and the `/mcpctl` switcher, which reads that
  exit code, reports failure rather than success over a project with no tools.
- **Only the token we replaced is revoked.** Sweeping every `prime-agent` token
  for a project would kill the one another machine is using. Anything else that
  looks orphaned is reported, not deleted.

This plumbing is shared with `config opencode`, parameterised by agent rather
than copied.

## The `/mcpctl` switcher

`pi.registerCommand('mcpctl', …)` opens a picker, shells out to
`mcpctl config prime-agent --project X --skip-extension --skip-marker`, then
calls `ctx.reload()` — which re-reads `settings.json` and `auth.json` and
rebuilds the MCP map, so the switch lands without restarting the app.

`--skip-extension` stops it rewriting the very file it is running from;
`--skip-marker` stops it re-scoping whatever repository prime-agent was started
in, which Claude Code's own skills sync would then pick up.

Above 20 projects it asks for a filter first: prime-agent's selector is an
arrow-key list with no search, and real installs run to hundreds of projects.
(opencode's dialog filters as you type, so its switcher needs no such prompt.)

## The active-project indicator

Published with `ctx.ui.setStatus('mcpctl', …)`, which prime-agent renders in its
tray line next to the model name.

Two quirks worth knowing:

- prime-agent emits `session_start` **only from `reload()`**, never at startup —
  so the indicator is also published on `turn_start`, the earliest moment with a
  real UI context bound.
- `resetExtensionUI()` clears extension statuses *after* `session_start`, so the
  indicator set there is wiped before anyone sees it. It is re-published on a
  short retry schedule to land after that reset.

> The rendering itself only exists in prime-agent from
> `prime-agent-extension-status.patch` (upstream PR pending). On an unpatched
> build `setStatus` silently does nothing and no indicator appears.

## The extension is real source now

It used to exist **only** as a string literal inside
`src/cli/src/config/prime-agent-extension.ts` — so nothing typechecked or linted
it, which is precisely the gap that let a wrong `ctx.ui.select()` option shape
ship in the pi extension.

It now lives at `src/prime-agent-ext/mcpctl-switch.ts`, checked against the real
`@earendil-works/pi-coding-agent` types:

```bash
pnpm typecheck:prime-agent-ext
npx tsx scripts/generate-prime-agent-extension.ts   # after editing it
```

A test fails if the embed goes stale. Extracting it found six lint problems in
code that had never been linted — all null-guard and return-type issues rather
than live bugs, but exactly the class of thing that ships silently when nothing
is looking.

## What it deliberately does *not* do

The MCP entry is still **named after the project**, not the constant `mcpctl`
that `config claude` and `config opencode` now use. prime-agent's switcher
already unmounts the previous project, so it never accumulates entries the way
`config claude` did — the bug the constant name fixes does not exist here.

The remaining difference is tool-prefix stability: switching changes tool names,
so the model can hold stale ones. Moving prime-agent to a constant name would
also re-key `auth.json` from `mcp:<project>` to `mcp:mcpctl`, giving up
per-project token caching and needing a migration. Worth doing, but as its own
change rather than folded into a parity pass.