Agents can now attach any file type as a downloadable chat artifact,
where previously the stored-file allowlist rejected types like `.zip`.
The reason arbitrary types were blocked is that a single media-type list
(`codersdk.AllChatAttachmentMediaTypes`) was doing three different jobs
at once: gating what users may upload as prompt input, deciding what is
safe to render inline in the browser, and admitting what the agent's
`attach_file` could store. Because the agent storage path reused that
same list as an admission gate, any artifact outside it was rejected
even though agent artifacts are only ever downloaded by the user and are
never forwarded to the model, so the prompt-input and inline-render
constraints did not actually apply to them.
This splits those concerns. `PrepareStoredFile` now only normalizes the
name and classifies the bytes, and the prompt-input allowlist is
enforced inline at `postChatFile` instead, which is the correct layer
for user-provided input.
User uploads are unchanged and still limited to the allowed prompt-input
media types, and unsafe or unknown types remain download-only because
`IsInlineRenderableStoredMediaType` still refuses to render them inline.
Model replay is also unchanged: assistant and tool attachments are never
forwarded to the LLM.
Closes CODAGT-654
The agent chat composer only advertised image uploads to the OS file
picker and filtered drag-and-drop and paste events to `image/*`, even
though the backend accepts text, CSV, JSON, PDF, and a narrower set of
image types.
Move the allowed chat attachment media types into `codersdk` so the
frontend picker and backend enforcement share one source of truth. Use
the generated TypeScript list to drive the file input `accept` attribute
and the drag-and-drop and paste filters, while adding common text
extensions so platforms without MIME registrations still surface those
files in the picker.
Renders the durable file attachments introduced in #24280 in the chat
interface. Without this, attachments were stored and served correctly
but the UI showed raw file parts with no previews or download UX.
Every attachment gets a download affordance, split into three rendering
tiers:
- **Images** — thumbnail with a hover/focus overlay containing a
download link. `onFocusCapture`/`onBlurCapture` with
`contains(relatedTarget)` keeps the overlay open while tabbing between
the image and its download link.
- **Text-like files** (`text/*`, `application/json`) — expandable
preview button with loading + error-with-retry states and the same
download overlay. Preview fetches throw a typed
`FetchTextAttachmentError` with a `.status` field instead of a
stringly-typed error.
- **Everything else** — compact `FileCard` with extension badge,
filename, and download link.
User-side and assistant-side rendering now share `AttachmentBlocks.tsx`
(`AttachmentPreviewFrame`, `TextAttachmentButton`,
`ImageAttachmentButton`, `FileCard`, plus
`getAttachmentHref`/`getAttachmentName`) instead of two near-duplicate
implementations. The text-attachment overlay anchors to the preview
surface so the download button stays pinned even when a loading/error
status line widens the row below.
`ComputerRenderer` detects when a screenshot was stored as a durable
attachment (`attachment_file_id`) and suppresses the stale base64
rendering — the screenshot appears as a proper file part instead.
`ToolLabel` shows the attached filename for `attach_file` tool calls.
Storybook coverage in `ConversationTimeline.stories.tsx` was expanded to
cover every tier (single/multiple images, inline + file-id text, JSON,
download-only files, fetch-failure retry, mixed attachments + file
references) with play-function assertions.
<img width="811" height="150" alt="image"
src="https://github.com/user-attachments/assets/27c71081-3502-4e80-92a7-d8adf1ff9323"
/>
## Cleanup
Per Mathias' post-merge suggestion on #24280, this PR also relocates
`coderd/chatfiles` → `coderd/x/chatfiles` so the durable-attachment
helpers live beside the rest of the `chatd` experimental surface.
Closes CODAGT-91
Ethan