feat(web): upload-first attachments, files, video, and document preview

[TheDarkPhantom]

PR #253 landed the server and contracts half of upstream's file attachments. The composer still sent images as inline data URLs, documents as text only, and could not attach anything else. This is the web half, one commit per upstream item.

What landed

1. Type guards (feat(server): accept PDF, ZIP, and other file uploads up to 50MB pingdotgg/t3code#8235 web part). ChatUnknownAttachment joins the ChatAttachment union, so a type from a newer build decodes instead of failing the whole message. The chat view, timeline, and offline outbox read attachments through isImageAttachment / isDocumentAttachment / isFileAttachment. The Normalizer rejects unknown types on a turn.
2. Upload-first images (feat(web): upload image attachments before sending pingdotgg/t3code#8048, with fix(web): retry failed attachment uploads after reconnect pingdotgg/t3code#10338). When the server advertises attachmentUploads, images upload as soon as they are attached, with progress, retry, and automatic retry after a reconnect. The send references the pending id. Offline sends and servers without the capability keep the inline payload. Held and queued turns keep their pending ids. One shared helper (lib/composerTurnAttachments.ts) builds the payload for normal send, plan follow-up, and fork edit.
3. Files (feat(web): attach PDFs, ZIPs, and other files to a turn pingdotgg/t3code#8236). When fileAttachments is advertised, anything that is not an image or an extractable document attaches as a file up to the limit, by drop, paste, or a new paperclip picker. Files show as rows with size, progress, retry, and remove. Documents keep the fork's local text extraction and also upload their original as type: "file", then send { type: "document", id, extractedText }. A document whose text cannot be read falls back to a plain file attachment. Drafts persist a file's finished upload id (never its bytes) and verify it after a reload. An interrupted or expired upload becomes an "Attach again" row. In the timeline, sent files are download rows that save under their real name through a same-origin blob. Retry and fork edit re-upload them.
4. Video (feat(web): play video attachments in chat pingdotgg/t3code#8688). Videos mint inline asset URLs with their video type, and the server serves them without a download disposition. The desktop CSP gains media-src 'self' <scheme>: blob:. Timeline play tiles and composer play buttons open the expanded preview with native controls. Formats the player cannot decode offer a download instead.
5. Document preview (feat(web): preview document attachments in the file viewer pingdotgg/t3code#9292). Sent PDF and HTML attachments open as attachment tabs in the right panel, next to a download button. This reuses the file viewer's frame, moved to a shared BrowserDocumentFrame. Fork documents whose PDF original the server kept open the same way. AssetResource gains disposition. The server honors inline only for pdf/html extensions it assigned, with a sandbox CSP for HTML.

Left out (recorded in FUTURE_ENHANCEMENTS): stashing files (they stay in the draft when you stash), moving files between projects, composer video thumbnails, and previews for TXT/MD/CSV/DOCX documents.

Verification. Focused tests cover the upload queue (reconnect retry, persisted verification, needs-reattach), upload state, turn payload building, draft file persistence, type guards, attachment file classification, the timeline and dialog rendering, right-panel attachment surfaces, and the server inline video and document headers. Typecheck is clean for web, server, desktop, contracts, and client-runtime. check:avicode and the changelog parser pass. An integrated desktop pass is still needed (see the checklist in the report).

Model: Claude Opus 5.5 (1M context), harness: Claude Code

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