Develop Dynamic Cordis Plugins

First determine whether a capability belongs on Host or Client, then query the real interface before writing code. Never infer a complete API from a Service name, Event payload, Slot props, theme token, or example.

Standard workflow

1. Call cordis_inspect_list to obtain the Providers, methods, and schemas currently registered on Host and Client.
2. Select the smallest set of cordis_inspect_query calls needed to read the exact Services, Events, Builtins, Slots, Theme tokens, or Tools that the implementation will use.
3. For a new Plugin, design its first Package. To modify an existing Plugin, first use cordis_inspect_self(pluginId, packageId) to read the base source and diagnostics.
4. Write plain JavaScript in code.host, code.client, or both, then call cordis_define.
5. Call cordis_run with the final pluginId and packageId returned by define.
6. Handle approval, waiting, Client loading, and render failures from the Run card, steering messages, or cordis_inspect_self.
7. Use cordis_stop to disable the Plugin temporarily. Use cordis_undefine only when it is no longer needed.

Do not wait in the same turn for user approval or asynchronous browser results. After cordis_run returns awaiting-approval or starting, end the current Tool flow and wait for the system to report the final outcome through state updates and steering.

Tool usage guidance

Choose a platform

Prefer the capability closest to the data owner. If Slot props already provide the Conversation Snapshot, do not fetch it again through Host. If only the Package's own styles need to change, do not override the global theme. If only a small entry point is needed, do not replace an entire product UI region.

Provider navigation

Select methods from the actual cordis_inspect_list result. Common initial methods include:

• Service.listService: without service, returns every callable Service with its purpose and exact method signatures. Query the selected service again for access rules, structured method descriptions/parameters/returns, and only its referenced types.
• Event.listEvents: without event, returns every Event with its purpose, dispatch mode, and exact listener signature. Query the selected event again for its structured listener contract and only its referenced types; a Waterfall listener must call next().
• Builtin.listBuiltins: returns evaluator-provided symbols and signatures that cannot be obtained through ctx.get().
• Slots.listSubTree: without root, returns compact live trees with each Slot's purpose, kind, scope, registration keys, replacement risk, and children. With an exact root, it also returns that selected Slot's full contract, props, and current occupants while keeping descendants compact.
• Theme.listTokens: returns theme tokens that may currently be queried and overridden; it does not modify the theme.
• Tool.listTools: returns Tool schemas actually visible to the current Agent, including dynamically registered Tools.

Provider names, methods, and inputs must come from the current list result. The Service/Event Catalog describes which interfaces this version permits; it does not guarantee that a Service is currently mounted. At runtime, use real Services and Events rather than caching or displaying Catalog query results.

Execution environment

Both code.host and code.client are plain JavaScript function bodies that return a Cordis Plugin. They are not compiled by TypeScript, JSX, or a bundler.

Do not use:

• import, require, TypeScript types, as, decorators, or JSX;
• globals not confirmed by Builtin.listBuiltins;
• guessed access to window, document, process, Buffer, fetch, or native timers.

Client React code must use React.createElement(...).

Correct:

return {
  apply(ctx) {
    const slots = ctx.get('slots')
    if (slots === undefined) return
    slots.inject('tool.view.cordis', () => slots.register(
      { name: 'tool.view.cordis', key: 'self' },
      () => React.createElement('div', null, 'Hello'),
    ))
  },
}

Incorrect:

return {
  apply(ctx) {
    return <div>Hello</div>
  },
}

JSX is not the only problem in this example. apply() registers lifecycle contributions and cannot return a React Element as the Plugin result. UI must be registered in a queried Slot.

Access Services

Read optional capabilities with ctx.get(name) by default and handle their absence:

return {
  apply(ctx) {
    const service = ctx.get('serviceName')
    if (service === undefined) return
    service.someMethod()
  },
}

Declare inject only when a Service is a hard dependency and the Plugin must enter waiting until Cordis reactivates it after the Service appears:

return {
  inject: ['requiredService'],
  apply(ctx) {
    ctx.requiredService.someMethod()
  },
}

Do not overuse inject merely to avoid an undefined check. Do not access ctx.requiredService without declaring the injection; the Guard rejects undeclared dependencies.

Manage side effects

Every contribution must be removed after the Plugin is stopped, updated, or removed. Prefer Cordis lifecycle APIs:

• Use ctx.on() to register Event listeners.
• Use ctx.effect() to own an external subscription that returns a disposer.
• Retain disposers returned by Cordis Service, Tool, Slot, timer, and theme APIs.
• Do not create process-wide or page-wide side effects at module scope or outside apply().

Recommended:

return {
  apply(ctx) {
    const service = ctx.get('serviceName')
    if (service === undefined) return
    ctx.effect(() => service.subscribe((value) => {
      console.log(value)
    }))
  },
}

If subscribe() does not return a disposer, first query whether the Service provides a supported cleanup mechanism. Do not assume unload automatically removes arbitrary third-party callbacks.

Host and Client timers

On both platforms, the timer is a Service named timer with the same interface; it is not a Builtin. Query { "service": "timer" } through the corresponding platform's Service.listService before using it. Declare inject: ['timer'] before using the timer mixin.

One-shot delay:

return {
  inject: ['timer'],
  apply(ctx) {
    const onClick = () => {
      ctx.timeout(() => console.log('done'), 300)
    }
    // Pass onClick to a queried Slot UI.
  },
}

Periodic work in a React component:

return {
  inject: ['timer'],
  apply(ctx) {
    function Clock() {
      React.useEffect(() => ctx.interval(() => console.log('tick'), 1000), [])
      return React.createElement('div', null, 'Running')
    }
    // Register Clock in a queried Slot.
  },
}

Incorrect:

return {
  apply(ctx) {
    ctx.timeout(() => console.log('invalid'), 300)
  },
}

setTimeout(() => console.log('invalid'), 300)

The first example does not declare the timer hard dependency. The second uses a global timer that does not exist.

Listen to Events

Query the Event Provider first to confirm the platform, parameter order, return value, and mode.

Ordinary emit Event:

return {
  apply(ctx) {
    ctx.on('some/event', (payload) => {
      console.log(payload)
    })
  },
}

The last parameter of a Waterfall Event is next. Unless the listener intentionally stops downstream processing, it must call and return it:

return {
  apply(ctx) {
    ctx.on('some/waterfall', (payload, next) => {
      console.log(payload)
      return next()
    })
  },
}

Register Client UI

Query Slots.listSubTree without root to choose a target from the compact purpose and topology tree, then query the exact Slot with root before writing its registration. The exact result determines:

• the Slot's purpose in the layout;
• whether its registration protocol is single, list, keyed, or chain;
• registration options;
• scope standard props and business owner props;
• current occupants, replacement risks, and descendant Slots.

Use ctx.get('slots') and handle its absence. Then use slots.inject to wait for the Slot declaration and call slots.register inside the callback:

return {
  apply(ctx) {
    const slots = ctx.get('slots')
    if (slots === undefined) return
    slots.inject('target.slot', () => slots.register(
      { name: 'target.slot', id: 'my-view' },
      (props) => React.createElement('div', null, String(props.someValue)),
    ))
  },
}

ctx.get('slots') does not require an injection. Do not rewrite it as ctx.slots unless inject: ['slots'] is declared:

return {
  apply(ctx) {
    ctx.slots.register({ name: 'target.slot' }, () => null)
  },
}

Do not guess an id, key, selector, or props before querying the Slot protocol. Do not default to root-level root, sidebar, conversation, or details Slots; replacing an entire occupant also removes the descendant Slots it declares.

Settings pages

A full settings UI should usually register its own section through settings.section to obtain a complete content area. settings.general.item is only appropriate for one compact, general-purpose preference. Query the actual subtree, options, and props for both, then select the narrowest entry point that is still sufficient.

Dynamic Plugins are temporary and process-local, so their settings UI does not need persistent storage. Do not add durable settings or another persistence mechanism for it. Register the UI in the appropriate settings Slot and keep any transient interaction state in memory for the lifetime of the Plugin.

Session and page data

A session-scoped Slot may provide useSession, useSessions, useWorkspaces, useProjection, input state, or actions through standard props. Follow the query result and prefer owner or standard props directly; do not add a Host RPC for data already present there.

Select only the fields that the UI actually needs. Do not copy or render an entire Conversation Snapshot, Session, Tool call, or Slot props object.

Cordis Run-specific panel

To place interactive UI in the latest cordis_run card, register tool.view.cordis with key: 'self':

When the feature needs user interaction tied to this Package's result, this region is often a good fit because it keeps the controls in the conversation flow beside the Run card. It is not the default target for every Client UI: settings, sidebars, message actions, and overlays should use their own queried Slots when those locations better match the feature.

return {
  apply(ctx) {
    const slots = ctx.get('slots')
    if (slots === undefined) return
    slots.inject('tool.view.cordis', () => slots.register(
      { name: 'tool.view.cordis', key: 'self' },
      (props) => React.createElement('div', null, `Package ${props.packageId}`),
    ))
  },
}

At runtime, self binds to pluginId + packageId. Do not include pluginRunId in the key. When the same Package runs multiple times, the latest Run card hosts the UI and older cards automatically degrade.

Ordinary Tool cards

To customize the call card for an ordinary model Tool, query tool.call.toolview. Its key is the Tool name; registering an existing key may replace the product's default card. When customizing only a newly added Tool, first verify its schema with Tool.listTools, then query the complete ToolCallOwnerProps.

Overlays and local entry points

• For toasts, status notices, and frame-wide overlays, query shell.overlay first; observe its pointer-events and ordering rules.
• When the selected target is a global overlay Slot, decide whether the UI should be draggable, how the user shows and hides it, and which existing layers it must cover or remain below.
• For small sidebar actions, prefer additive inner Slots such as sidebar.footer.action; do not replace the entire sidebar.
• For supplementary content after a conversation turn, query conversation.chat.turnTail and register according to its returned chain selector and fallback rules.

Themes and styles

Determine the scope of the change first:

1. Global theme: first query Theme.listTokens, then query { "service": "theme" } through Client Service.listService. Supply light and dark values for each override as required by the query, and retain the returned disposer.
2. The Package's own components: use styles.insert(css) and prefer theme CSS variables for colors.
3. New visible content: choose a Slot first, then decide between local CSS and global tokens.

Do not manipulate document.body, window, or hard-coded product DOM selectors. The theme Service changes tokens but does not create UI. Slots create UI but do not replace the theme system.

Call Host from Client

Host registers a Package-private method with harness.handle(method, handler), and Client invokes it with host.call(method, args). This is Client→Host JSON RPC.

Host:

return {
  apply(ctx) {
    harness.handle('read-state', async (args) => {
      return { value: args.key }
    })
  },
}

Client:

return {
  async apply(ctx) {
    const result = await host.call('read-state', { key: 'demo' })
    console.log(result.value)
  },
}

Arguments and return values must be lossless JSON. Do not pass functions, React elements, class instances, Contexts, Services, or other runtime objects; return null when there is no response data. Do not register a public Remote Service or use ctx.remote for Package-private communication.

Register a dynamic model Tool

Host can use harness to register a Tool callable in the next model step. First query the current harness signature with Host Builtin.listBuiltins, then inspect existing Tool names and schemas with Tool.listTools to avoid conflicts.

Tool arguments and return values must be JSON-compatible. execute owns the business result; render and presentation own only what the model and native UI see. Tool registration must belong to the current Plugin Fiber so it is automatically removed after stop or update.

Handle internal live data

Service instances, Event payloads, Slot props, Session and Conversation Snapshots, Tool state, and other DSH/Cordis objects are internal live data.

Do not:

• call JSON.stringify or structuredClone on these objects or their descendants;
• recursively enumerate, fully copy, or display them as a whole;
• place Host objects in the Package's long-lived state or RPC return values.

Read only the leaf fields required by the current feature. Extract the minimum strings, numbers, booleans, and other scalar values before constructing owned JSON.

Versions, approval, and repair

• A Plugin is the stable instance identified by pluginId.
• A Package is an immutable code version identified by packageId.
• Every activation attempt has its own pluginRunId.
• currentPackageId is the latest successful version; it does not imply that the Plugin is currently running.
• nextPackageId is the target awaiting approval, activating, awaiting Client activation, or most recently failed.

Choose the cordis_run mode as follows:

An unauthorized Client Package returns awaiting-approval. A single check mark authorizes only the current Package; double check marks authorize future versions of the same Plugin. A grant remains after a technical runtime failure. An authorized Package returns starting and completes asynchronously in the browser.

After a technical failure:

1. Use cordis_inspect_self(pluginId, packageId) to read the failed version's source and exact diagnostics.
2. If the error involves an unknown capability, list and query the corresponding Provider again.
3. Define a new Package under the same Plugin; do not overwrite the failed Package.
4. Run again with the new packageId and the correct mode.

Do not retry automatically after the user rejects approval. A failed update does not automatically restore the old physical Run; explicitly run current when recovery is required.

Modify @pluginId

When the user identifies a target with @pluginId, do not create another Plugin. The injected context contains only identity, version pointers, and the default base Package, not source code.

Modify it as follows:

1. Read the base Package with cordis_inspect_self(pluginId, packageId).
2. Preserve the Host or Client half that does not need to change and modify only the target code.
3. Call cordis_define with plugin.kind: 'existing' and the original pluginId.
4. Use the returned packageId; when current exists, activate the new version with update in the usual case.

If the reference is unavailable, explain that the Plugin was removed, belongs to another Session, or was lost on process restart. Do not create a same-named replacement.

Common failure checks