mcpctl/docs/opencode-extension.md

# mcpctl × opencode — project switching from the TUI

## Motivation

`mcpctl config claude` and `mcpctl config prime-agent` both work the same way:
write the project's MCP server into the host's config file, then restart the
host so it picks the change up. That is fine when you pick a project once, and
tiresome when you switch between `homeautomation`, `sre` and `docmost` all day.

[opencode](https://opencode.ai) can do better, because it exposes two things
the other hosts do not:

- an **HTTP API for its own MCP registry** (`POST /mcp`,
  `/mcp/{name}/disconnect`) — so a mount can be re-pointed while the app runs;
- a **TUI plugin API** (`tui.json`) with slash commands, dialogs and UI slots —
  so the switcher can be a first-class part of the interface rather than a
  shell command you run in another terminal.

So the opencode integration does not write an MCP entry into `opencode.json` at
all. It ships two plugins, and switching projects takes effect on the next turn
with no restart.

## How it works

```
~/.mcpctl/opencode-state.json   (0600)
   { project, gatewayUrl, tokens: { <project>: <mcpctl PAT> } }
        │
        │ read by both plugins
        ▼
~/.config/opencode/plugin/mcpctl.ts        server plugin  ─┐
~/.config/opencode/mcpctl/mcpctl-tui.tsx   TUI plugin     ─┤
                                                           │  client.mcp.add({
                                                           │    name: "mcpctl",
                                                           ▼    type: "remote", url, headers })
                                              opencode's MCP registry
                                                           │
                                                           ▼
                              https://<gateway>/projects/<project>/mcp
```

### The state file, not `opencode.json`

Two reasons the project does not live in opencode's own config:

1. **The token.** The gateway needs `Authorization: Bearer <mcpctl PAT>`.
   `opencode.json` is a mode-0644 file people paste into bug reports;
   `~/.mcpctl/opencode-state.json` is 0600, like every other mcpctl credential.
2. **The restart.** A config file is read at startup. Re-pointing the mount
   through the running server's MCP API is what makes `/mcpctl` instant.

Tokens are kept **per project**, so switching back to a project you have
already used needs no new mint — and a failed mint for project B cannot cost
you the credential for project A.

### The server plugin (`plugin/mcpctl.ts`)

Auto-discovered by opencode. It mounts the active project's gateway under the
fixed MCP server name `mcpctl`, on the first server event and again before
every user turn.

Two details matter:

- **The name is constant.** Tools keep a stable `mcpctl_*` prefix across
  switches, and because opencode re-resolves the tool list per request, the
  model simply sees the new project's tools on its next turn. (Contrast pi,
  where the extension has to *tell* the model its old tool names are dead.)
- **It does not re-register an unchanged mount.** `mcp.add` rebuilds the
  connection, and mcplocal binds a gated project's unlocked state to that
  connection's `mcp-session-id` — re-adding every turn would re-lock a project
  you had just opened with `begin_session`.

It also exists so that **headless** runs (`opencode run …`), which load no TUI
plugins at all, still get the project's tools.

> The mount is deliberately *not* performed during plugin setup. Setup runs
> before opencode's server accepts connections, and `client.mcp.add` calls back
> into that same server — awaiting it there hangs the app on a blank screen
> before the TUI ever draws.

### The TUI plugin (`mcpctl/mcpctl-tui.tsx`)

Registered in `~/.config/opencode/tui.json` (opencode does not auto-discover
TUI plugins). It adds:

| Command | What it does |
|---------|--------------|
| `/mcpctl` | Filterable project picker; switches live |
| `/mcpctl-status` | Active project, mount state, gateway URL |
| `/mcpctl-skills` | Re-sync this project's skills |

and a `mcpctl:<project>` indicator in the prompt footer, next to the model name
and one line above the token counter.

Switching delegates to the CLI —
`mcpctl config opencode --project X --skip-plugin --skip-marker` — so token
minting, state and skills stay in one place and the plugin stays a UI shell.
`--skip-plugin` avoids rewriting the very file opencode has already loaded;
`--skip-marker` stops a switch from silently re-scoping whichever repository
opencode happened to be started in.

The picker needs no pre-filter prompt (unlike the pi and prime-agent
switchers): opencode's select dialog filters as you type, so the plugin only
has to order the list — active project first, then alphabetical.

The indicator is published through `api.kv`, which is a reactive store: writing
it re-renders the slot with no signal plumbing, and it persists across sessions
so the label is right on the first frame.

#### Why the footer and not the status bar

opencode exposes UI slots, not arbitrary layout. In the footer region the
options are:

| Slot | Result |
|------|--------|
| `session_prompt_right` / `home_prompt_right` | **used** — renders on the prompt's bottom line, right of the model name, directly above the token counter |
| `home_footer` | sits on the counter's line, but *replaces* the cwd/version footer instead of adding to it |
| `app_bottom` | costs a whole extra terminal row |

There is no slot on the status-bar line itself. On the home screen the prompt
box is narrow, so a long project name wraps onto a second line; in a session
(where the prompt is full width) it always fits on one.

### Skills

opencode implements the Agent Skills standard and loads `SKILL.md` trees from
`~/.config/opencode/skill/` (XDG-aware). `mcpctl skills sync --agent opencode`
syncs there, with the same shared-tree semantics as `--agent pi` and
`--agent prime-agent`: a flat tree with per-project ownership, its own state
file (`~/.mcpctl/skills-state-opencode.json`), no SessionStart hooks, no
`postInstall`, and untracked skill directories are never clobbered.

## Usage

```bash
mcpctl config opencode --project monitoring
```

That mints (or reuses) the project token, writes the 0600 state file, installs
both plugins, registers the TUI plugin in `tui.json`, and runs an initial
skills sync. Start opencode and the project's tools are there.

Skip individual steps:

```bash
mcpctl config opencode --project monitoring --token mcpctl_pat_xxx  # provide token, don't mint
mcpctl config opencode --project monitoring --skip-skills           # don't sync skills
mcpctl config opencode --project monitoring --skip-plugin           # state only, leave plugins alone
mcpctl config opencode --project monitoring --skip-marker           # don't touch .mcpctl-project here
mcpctl config opencode --project monitoring --dry-run               # print the plan, write nothing
mcpctl config opencode --project monitoring --opencode-dir /path    # non-default opencode config dir
```

## Failure semantics

- **No usable credential → the switch fails.** The command exits non-zero and
  leaves the state file untouched, so the previously active project keeps
  working rather than being replaced by a mount that 401s. `/mcpctl` reads that
  exit code and reports the switch as failed instead of claiming success over a
  project with no tools.
- **Gateway unreachable → no mcpctl tools.** Never a failed startup: the server
  plugin swallows mount errors.
- **Corrupt `tui.json` → refuses to write.** One syntax error must not silently
  drop every other TUI plugin you installed.

## Files

| Path | Purpose |
|------|---------|
| `src/opencode-ext/mcpctl-opencode.ts` | Server plugin source |
| `src/opencode-ext/mcpctl-opencode-tui.tsx` | TUI plugin source |
| `src/cli/src/config/opencode-extension.ts` | Generated embed of both (do not edit) |
| `scripts/generate-opencode-extension.ts` | Regenerates that embed |
| `src/cli/src/utils/opencode-settings.ts` | Install / register / state helpers |

The plugin sources are **embedded** in the CLI so `mcpctl config opencode`
works from an installed binary with no source tree. After editing either
source, re-run:

```bash
npx tsx scripts/generate-opencode-extension.ts
```

A test fails if you forget. They are typechecked against the real
`@opencode-ai/plugin` types via `pnpm typecheck:opencode-ext`.