bt functions push: support raw JSON manifest for facet and inline-quickjs preprocessor types

[imen-kedir]

I want my coding agents to iterate on preprocessors and facet prompts for the Topics pipeline and push them to Braintrust through bt. Right now bt functions push can't ship either:

• Facets require function_data: {type: "facet", prompt, no_match_pattern, preprocessor: {id}}. The runner only collects what the SDK registers, and the SDK has no facet builder.
• Preprocessors that Topics will actually run must be data.type: "inline" + runtime: "quickjs". SDK push bundles via esbuild instead, and the server rejects invocation with 400: Brainstore preprocessor aggregate only supports built-in 'thread' and inline quickjs preprocessors.

The backend handles both shapes — bt topics config enable already POSTs to /insert-functions (src/topics/api.rs:1015-1060). Today the workaround is curling that endpoint directly, which bypasses bt's auth/profile resolution.

What would solve this

A manifest path on bt functions push:

bt functions push --manifest path/to/function.json -p <project>

JSON matches what /insert-functions accepts. Facet:

{
  "name": "my-lens-issues",
  "slug": "my-lens-issues-v1",
  "function_type": "facet",
  "function_data": {
    "type": "facet",
    "prompt": "...",
    "no_match_pattern": "^NONE",
    "preprocessor": { "id": "<preprocessor-function-id>", "type": "function" }
  }
}

Inline-quickjs preprocessor:

{
  "name": "my-lens-preprocessor",
  "slug": "my-lens-preprocessor-v1",
  "function_type": "preprocessor",
  "function_data": {
    "type": "code",
    "data": {
      "type": "inline",
      "code": "function handler({ span_attributes, input }) { /* ... */ }",
      "runtime_context": { "runtime": "quickjs", "version": "ES2023" }
    }
  }
}

Skip the runner for this path; reuse existing auth/project/if_exists plumbing.

Happy to send a PR — already have a draft.