Inbox: markdown images in messages request /api/image, which the Inbox server doesn't serve (404) #1813

Version: v0.28.8 (also master at b0f60ec), Linux.

Repro: an agent calls the MCP tool send_message with a body containing ![alt](.walkthrough/shots/after.png), relative to project_path (the file exists).

What happens: the Inbox UI renders <img src="/api/image?path=.walkthrough%2Fshots%2Fafter.png">, and the Inbox server answers {"error":"Not found","code":"not_found"} from the /api/ fallthrough in packages/server/inbox.ts (~L873).

Why: getImageSrc in packages/ui/components/ImageThumbnail.tsx defaults to /api/image?path=…. The Inbox app never calls setImageSrcResolver (packages/ui/configure.ts only applies one a host passes; packages/inbox/App.tsx passes none), and the Inbox server mounts no /api/image route (it exists only in the annotate/review/plan servers via shared-handlers.ts). Other routes don't help either:

• absolute https images are blocked by the Inbox CSP img-src 'self' data: blob: (inbox.ts ~L214);
• a .png in attachments is refused ("not a file the Inbox can open").

What works today: attaching an HTML file whose relative <img> tags load through /api/html-assets/<token>/, or an inline data: URI in the markdown.

Expected: markdown images in Inbox messages render, e.g. a project-scoped image route restricted to project_path (same rules as attachments), or a resolver that maps image refs onto the existing html-assets mechanism. At minimum, document the HTML-attachment / data: workaround. The :::question image-context example in apps/skills/core/plannotator/SKILL.md (~L236) likely hits the same 404.