Move attachment list from message body to header with bottom sheet

[ryanleesipes]

Put this one together with some help from coding agents. Let me know if there is anything I totally missed or that isn't done the way we do it.

What is this patch?

Attachments were previously buried at the bottom of the message content, requiring the user to scroll past the entire message body to discover or interact with them. Placing the summary in the header makes attachments immediately visible and accessible.

Attachments are now surfaced in the message header as a compact summary line (icon + count/name + total size) with a "View all" / "View" action, rather than as cards at the bottom of the message body.

Tapping the action opens a Material bottom sheet listing each attachment with its name, size, file icon (or image thumbnail), and individual save button.

For single attachments, the summary shows the filename (ellipsized in the middle to keep the extension visible) and the action reads "View" instead of "View all".

To Test

Open a message with no attachments — verify no attachment summary row appears in the header.

Open a message with one attachment — verify the header shows the filename and size (e.g. report.pdf (1.2 MB)) with a "View" link.

Open a message with multiple attachments — verify the header shows count and total size (e.g. 3 Attachments (1.5 MB)) with a "View all" link.

Tap "View" / "View all" — verify the bottom sheet opens with a drag handle, "Attachments" title, "Save all" button, and the correct list of attachments.

Tap an attachment row in the bottom sheet — verify it opens/previews the attachment.

Tap the download button on an individual attachment — verify the save flow launches.

Verify attachments no longer appear as cards at the bottom of the message body.

Open a message with inline images — verify inline images still render correctly in the message body (the cid: URI resolution is unaffected).

Appreciate any feedback on how this patch could be improved.

[wmontwe]

Welcome as a contributor to the project!

Your changes already look and work great.

To avoid future refactoring as we migrate the surrounding codebase, we’re aiming to write all new UI in Compose. The AttachmentListBottomSheet (along with bottom_sheet_attachment_list.xml) and attachment_list_item.xml would be a perfect candidate for this.

The AI tends to add comments to the code that are not necessary to later understand what the code is doing, they usually could be removed.

To help align AI agents better with our codebase, I’ve created AGENTS.md which provides more detailed project information - you can find the current state in #10533.

[ryanleesipes]

@wmontwe took a stab at this. Threaded conversations seem to be crashing but that doesn't seem as though it is related to my changes.