jhonny-editor/code/uxp-spike

UXP Spike

A throwaway UXP plugin that answers two questions we cannot answer from the docs. It is not part of the MCP server and nothing depends on it.

Why

1. Is issue #9 fixable?

Documented ExtendScript has no frame-export method at all. Sequence exposes only exportAsMediaDirect, exportAsProject, and exportAsFinalCutProXML — there is no exportFramePNG. That is why capture_frame reaches into the undocumented QE DOM, and why #9 reports it returning false and writing nothing on both PPro 2025 and 2026. It isn't a bug we can fix; it's a hole in the API.

UXP has a supported Exporter.exportSequenceFrame(). Probe A finds out whether it works.

Frame capture is the only tool that gives an agent visual evidence of the timeline. Without it there is no way to verify a color grade, a transition, or a title actually landed. It's worth a spike on its own.

2. Can we drop the temp-file bridge?

Today the CEP panel polls a temp directory every 200ms for .jsx files. UXP has WebSocket and fetch, which would be a strict upgrade. But:

• Adobe's UXP docs never mention localhost or 127.0.0.1 — not once, anywhere.
• UXP WebSockets are client-only: a plugin "cannot host or accept incoming connections", so the MCP server must be the server. (Fine — that's the direction we want anyway.)
• macOS is documented to restrict http://. Whether that extends to ws:// is unstated.
• wss:// with a self-signed cert is explicitly broken on macOS per Adobe's known-issues page.

So both obvious loopback options sit in undocumented-or-blocked territory. Probes B–E find out what actually connects. This determines our entire transport, so it's worth knowing before we commit to a port rather than after.

Running it

You need Premiere Pro 25.6 or newer (that's when UXP went GA) and the UXP Developer Tool 2.2+.

1. Start the spike server. Zero dependencies, so there is nothing to install:

node uxp-spike/server.mjs        # listens on 127.0.0.1:7777

2. Enable Premiere's developer mode. Settings → Plugins → Enable developer mode, then restart Premiere.

3. Side-load the plugin. In UXP Developer Tool: Add Plugin → select uxp-spike/manifest.json → Load & Watch.

4. Open a project with a sequence, put the playhead somewhere with visible picture, and open Window → UXP Plugins → MCP UXP Spike.

5. Click "Run all probes."

Reading the result

The panel prints a JSON verdict and writes it to /tmp/mcp-uxp-spike-report.json. The server also logs every transport that reaches it.

The two lines that matter:

Issue #9 (frame capture): FIXED by UXP | still broken
Transport:                websocket | http-fetch | file-bridge

Probe A does not trust exportSequenceFrame's return value — the QE DOM lies about this in both directions, so success is decided purely by whether a file exists on disk afterwards.

A failing probe is a result, not an error. "Loopback WebSocket is blocked" is exactly the kind of thing worth learning in an afternoon rather than three weeks into a port.

Please paste the JSON verdict into the tracking issue

If you can run this against a real Premiere, that's genuinely the most useful thing anyone can do for this project right now. Neither of these questions can be settled from Adobe's documentation.