Use only explicitly enabled extensions

[tenshiak]

Short description

Dreamer loads the full suite of extensions that it doesn't need. It shouldn't

What problem does this solve?

Currently, extensions may hoist tools, add system prompts that conflict with the historian/dreamer, and add tools they were not intended to have. Magic-context does no filtering by default and loads the full pi. This, as an example, results in a full aft-pi system prompt addition to be appended, among other things.

Proposed solution

Start the background pi processes with --no-extensions and load only extensions that are explicitly enabled in the magic-context's configuration file. This still allows users to load extensions that implement custom providers that pi doesn't support out of the box. Append each extension using the command line --extension <extensionpath>, similar to pi's built-in settings.json.

Magic-context started with --no-extensions as a default, but users complained that their custom provider's extensions weren't working with it. This proposal resolves this issue.

Alternatives considered

No response

Area

Pi plugin

Additional context

No response

[ualtinok]

Implemented on the working branch, shipping in the next release. The shape follows your proposal with one adjustment: rather than flipping the default, the allowlist is opt-in via a new user-config key:

{
  "pi": {
    "subagent_extensions": [
      "npm:my-provider-extension",
      "./extensions/custom-provider.ts"
    ]
  }
}

When set, Magic Context's child processes (historian, dreamer, sidekick) spawn with --no-extensions and load only the listed entries via --extension, so provider extensions keep working while unrelated extensions can no longer add tools or system prompts to the children. Relative paths resolve from ~/.pi/agent (the same base as Pi's own settings.json package entries); npm: sources pass through unchanged. When unset, behavior is unchanged from today.

One note: the key is deliberately user-level only — project-level config cannot control which extensions your child processes load.