Completes group/1:1 attachment parity (#88983). PR #89486 covered images;
this adds the remaining half:
- The composer picker accepts any file type; kind (image/pdf/file) decides
the staging RPC. Paste handlers accept non-image files too.
- Drag & drop anywhere on the room drops into the active composer (open
reply box, else main), with a drop overlay naming the target.
- Member turns stage PDFs via pdf.attach (rendered per-page into vision
tiles by the gateway) and other files via file.attach; each returned
@file: ref is appended to that member's turn prompt so file tools can
read the artifact. Failed attaches still degrade to text-only.
- Transcript markers distinguish [attached PDF: x] / [attached file: x] /
[attached image: x]; room log renders non-image attachments as named
chips, pending chips show type icons.
Tests: 3 new vm-harness tests (per-kind RPC routing across members,
@file: ref injection into turn prompts, transcript labels); 279 total pass.
Teknium
97b41f8cf3