Build the attachments sidebar section

The card's complete file inventory: compact QuickLook-thumbnail rows
over Card.attachments — no reference tracking, subfolders tolerated
and unsurfaced — with a quiet header add affordance and the drop hint
empty state. The whole window is the file-drop surface, Edit mode
included (the editor's drag types were already filtered; now tested),
sharing the board's folder-refusal semantics literally: FinderDrop
moved verbatim into its own file so both windows run the same
partition and loss row. Dragged text still lands at the caret and is
inert elsewhere — the window delegate accepts file payloads only.
Rows open on double-click or Return, drag out their file URL, and
Remove is a bracketed write through FileManager.trashItem — the system
Trash, never a hard delete, returning the in-Trash URL so the promise
is testable; the attachment listing is the guard, so traversal and
subfolder names refuse in one line. Keyboard-native per 05: the
section is one Tab stop, arrows walk rows by name, Space toggles the
shared QuickLook panel, Backspace removes. File > Add Attachment
(shift-cmd-A) comes alive through the same import path.

Claude-Session: https://claude.ai/code/session_01SR4XGjmBE16ZUYWpfFHXwY

README.md

@@ -32,7 +32,9 @@ Lanework is in early development. This list tracks what has actually shipped and
 
 - **New Board and Duplicate** — File ▸ New Board… (⌥⌘N) opens a Pages-style template chooser with a mini per-lane preview per template, then a save panel for the location; the new board's frontmatter title is the document name you chose, so the window title and the Finder name start out matching. File ▸ Duplicate (⇧⌘S) forks the frontmost board to a Finder-style "Board copy" sibling (then "copy 2", "copy 3"), preceded by the pending-work flush so the copy misses nothing and with the original left open beside it. The copy is literal: every GUID kept — a whole-board copy is a new identity namespace — tombstoned items carried, strays and timestamps untouched.
 
-- **The card window** — ⌘↩ or a double-click opens a card in its own window: two full-height, independently scrolling columns — a wide body column and a narrow attributes sidebar whose fixed width is derived from font metrics, so the window's resize flex all goes to the body. The title bar carries the card's title live and subtitles it "⟨board⟩ › ⟨lane⟩", following the card as it moves between lanes and re-reading the board's name as it's renamed. The body column shows the title, a quiet created/modified/by line built from whichever frontmatter keys exist, and the body itself; the sidebar's sections are stacked headers awaiting their content. Reopening a live card focuses the window it already has, and the window closes itself the moment its card stops being live — deleted, tombstoned, buried under a tombstoned lane, or moved to another board.
+- **The card window** — ⌘↩ or a double-click opens a card in its own window: two full-height, independently scrolling columns — a wide body column and a narrow attributes sidebar whose fixed width is derived from font metrics, so the window's resize flex all goes to the body. The title bar carries the card's title live and subtitles it "⟨board⟩ › ⟨lane⟩", following the card as it moves between lanes and re-reading the board's name as it's renamed. The body column shows the title, a quiet created/modified/by line built from whichever frontmatter keys exist, and the body itself; the sidebar leads with the Attachments section (below) and its remaining sections are stacked headers awaiting their content. Reopening a live card focuses the window it already has, and the window closes itself the moment its card stops being live — deleted, tombstoned, buried under a tombstoned lane, or moved to another board.
+
+- **Attachments** — the sidebar's first section is the card's complete file inventory: every top-level file of its `attachments/` in Finder order, body-embedded ones included, as compact rows carrying a small QuickLook thumbnail (the file's Finder icon until one is generated, and for anything QuickLook won't preview) beside a middle-truncated filename. The whole window is the drop surface — drag files anywhere in it, Edit mode and raw source included, and they import as attachments with Finder-style renames on collision, because the text editor deliberately declines file drags while dragged *text* still lands at the caret exactly as it always did. Folders refuse at the cursor and a mixed drag imports its files and says how many folders it skipped. File ▸ Add Attachment… (⇧⌘A) and a quiet plus in the section header are the same act from the menu bar and the pointer, both opening a multi-select panel into the same import path the board's own file drops use. The section is keyboard-native: it takes focus, arrows walk the rows, Space QuickLooks the selected one in the system's own panel, Return opens it in its default app, and ⌫ moves it to the **system** Trash — never a hard delete, and deliberately distinct from the board's own trash, which is why a failure there says "Couldn't move 'shot.png' to the Trash". Rows drag out their file URL, so a file goes to Finder or another app with no export path of its own; a right-click offers Open, Reveal in Finder and Remove; and File ▸ Reveal in Finder points at the selected attachment while the section holds focus, the card's folder otherwise. Every write is an ordinary bracketed one — one reload, one commit, one banner on failure — and the read-only lock disables adding and removing in place.
 
 - **The card body — Preview and Edit** — the body is read as a fully rendered Markdown preview and written as raw Markdown, never a WYSIWYG halfway house. Preview lays out headings, emphasis, code, quotes, lists, GFM tables, thematic breaks and images resolved against the card's own folder; HTML shows verbatim as code, remote images never load (Preview does no networking), links open in the browser or the file's default app, and task-list checkboxes are live — clicking one flips exactly that character in the file and touches no other byte. ⌘E toggles View ▸ Edit Body, Return in Preview enters it, Escape leaves it, and a card whose body is empty opens straight into the editor with the cursor ready. Edit is a monospaced editor with lightweight syntax highlighting — headings emphasized, bold and italic styled, code tinted, link targets and structural markers dimmed — that is presentation only: the text stays the raw Markdown character for character, smart quotes and dashes off. It saves ~700 ms after you stop typing, and flushes the moment you leave Edit or close the window, so neither the preview nor the disk ever lags what you typed. ⌘Z is the editor's own undo, scoped to the session; ⌘F is find-in-text over whichever surface is showing. Three write rules keep the file honest: a body nobody touched is never re-serialized (byte-identical on disk, modification date included), an edit typed and then undone is not written, and the app's own save echoing back through the watcher is not written again. If the file changes underneath you while the buffer has unsaved keystrokes, the buffer wins — the board, the preview and every other window take the new version while your text stays exactly where it is, and your save then lands over theirs. A close that cannot save stops and asks: try again, save a copy elsewhere, or discard.