About this mod

mode-registry

One /mode switch that every plugin can offer a mode to. You install the registry once; a model router, an "artifact mode", or the effort modes beside this template each add their own mode to it. You see the active mode as a dim label in the prompt footer (review mode, beside focus and the others) and switch with /mode.

This is the "mods composing" pattern: the registry doesn't know what any mode does. It keeps the list and the current choice. Each plugin reads the choice and changes its own behaviour.

What you can do

| You type | What happens | | --- | --- | | /mode | Opens a picker above the prompt: one button per mode (hotkeys 1-9, 0 for off) and Close. Click it or press ctrl+x tab to give it the keys. | | /mode review | Switches to the mode with id review. The footer reads review mode. | | /mode off | Clears the mode (none and clear work too). | | /mode list | Prints every mode on offer, the plugin that offers it, and which one is on. |

The active mode lives in $.state for the session and isn't saved between sessions (to save it, write it to $.store as well). The registry doesn't reset it on /clear. Whether the engine keeps $.state across a /clear has not been checked.

What it costs

No model calls, ever. The footer label and the picker are UI only and never enter the context. Each /mode command adds one short line to the transcript, which the model reads (about 10-20 tokens; /mode list is about 15 tokens per mode). A press in the picker adds nothing: it switches the mode silently, so the model isn't told (use /mode <id> when you want it to know). That line is appended after the cached prefix, so it never breaks the prompt cache. Whatever a mode costs is up to the plugin that offers it. For example, effort-modes' switch costs one cache rebuild (see its README).

Offering a mode from your plugin

The contract is types/index.d.ts. It has three values this plugin owns:

• mode-registry.catalog: ModeSpec[], every mode on offer
• mode-registry.active: string | null, the active mode's id
• mode-registry.isPicking: boolean, whether the picker is open

Only the registry writes them. You offer a mode by hooking the registry's write to catalog and adding yours:

on('state.set', { plugin: 'mode-registry', key: 'catalog' }, ($, e, next) =>
  next({
    ...e,
    value: [
      ...e.value.filter(m => m.id !== 'router'),
      { id: 'router', label: 'Router', description: 'Picks the model per turn', owner: 'my-router' },
    ],
  }),
)

Then read the active mode wherever your behaviour lives:

const { value: active = null } = await $.state.get({ plugin: 'mode-registry', key: 'active' })
if (active !== 'router') return next(e)

Some details that matter:

• Filter your own id before adding it. The registry rewrites the catalog at session start and on every /mode. Filtering first keeps your offer from appearing twice.
• Read active in the hook that acts. Don't copy it into a module variable you keep across turns: a hot reload wipes module variables, and a value read inside a ui.render subscribes you to redraws.
• If the registry isn't installed, nothing breaks. active reads as undefined at version 0, your state.set hook never fires, and your plugin runs its default behaviour.
• To switch modes from code (an auto-router that flips to review when it sees a diff), call $.command.run({ command: 'mode', args: 'review' }). It goes through the same path and the same vetoes as the person typing it. It queues until the session is idle.
• To refuse or redirect a switch, hook state.set on { plugin: 'mode-registry', key: 'active' } and pass next another value. /mode reports what actually landed, so the person sees the veto.

For type-checking, list the registry in your plugin.json: "dependencies": ["mode-registry"]. The engine then writes this contract into your plugin's .claude-plugin/types/mode-registry/ when it loads it from your folder, and your tsconfig.json picks it up (effort-modes does this). The catch: a plugin with that dependency doesn't load at all without the registry. If yours should also work alone, leave the dependency out and run /plugin-types in a session where mode-registry is enabled instead. Never copy the file into your plugin by hand.

Composes with

• effort-modes (beside this template): offers ui, api and review.
• Any plugin that draws in the SessionMode footer or the AbovePrompt band. The registry adds its label to e.props.modes and passes the rest on, and draws {await next(e)} under its picker.

Install / load

claude plugin validate templates/mode-registry
claude plugin test templates/mode-registry           # 4 tests, incl. a veto from a third plugin
claude --plugin-dir templates/mode-registry --plugin-dir templates/effort-modes

Function hooks are early access. If your build doesn't load hooks modules by default, set CLAUDE_CODE_ENABLE_FUNCTION_HOOKS=1. That setting loads the hooks module of every installed plugin that ships one, not only this one.