Summary

extensions/signal plugin outbound sendMedia drops mediaLocalRoots before calling sendMessageSignal.

Repro (deterministic)

1. Open extensions/signal/src/channel.ts.
2. In sendSignalOutbound, note the options passed to send(...) do not include mediaLocalRoots.
3. Open src/signal/send.ts; sendMessageSignal supports mediaLocalRoots and uses it in resolveOutboundAttachmentFromUrl(..., { localRoots: opts.mediaLocalRoots }).

Expected

mediaLocalRoots passed into outbound sendMedia should be forwarded to sendMessageSignal so local media paths allowed by agent/workspace roots can resolve.

Actual

mediaLocalRoots is dropped in the extension adapter, so local-root context is lost before media resolution.

Root cause

sendSignalOutbound and outbound.sendMedia in extensions/signal/src/channel.ts do not thread mediaLocalRoots through.