Comments, phase 3 — search, the thread find, announcements, and a11y

Board search reaches comment bodies through a search-owned transient
index: the first live-query keystroke sweeps comments/*/index.md
off-actor (.draft and comments/.trash excluded), keystrokes re-filter
in memory, the index discards on clear — the snapshot stays O(cards).
⌘F routes by focus: the comments pane gets an app-owned find bar
spanning the whole rendered thread (next/prev cross rows with
wraparound); body and composer keep NSTextFinder; Find Next/Previous
graduate from FutureCommands. Foreign comment changes speak
path-shaped beside the announcer's ladder ("New comment on 'X'",
plural folds), narrowed by EchoLedger receipts consumed through
CommentPath.classify — and that read fixed a latent footprint bug
where a comment receipt resolved against the card's attachment
listing, read .absent, and classified the user's own write as
foreign. The pane completes its a11y story: flattened comment
elements with Edit/Delete/Reveal custom actions (un-flattening
during inline edit), phrase-table vocabulary, labeled composer and
sort control, and an audit over the open pane on a comment-seeded
fixture (runnable only where automation permission exists).

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

Kanban/LiveStore/BoardStoreComments.swift

@@ -83,6 +83,21 @@ extension BoardStore {
         return CommentThread.loadDraft(inCard: card.folder)
     }
 
+    /// **Which of this card's comments the app itself just wrote** — the ledger's receipts, classified
+    /// by path shape and retired (`EchoLedger.vouchedComments(inCard:cardPath:)`).
+    ///
+    /// The card window asks this on every landed reload, before deciding whether its thread's changes
+    /// are worth announcing: "app-mediated echoes never announce" (10-accessibility.md ▸ Live board
+    /// announcements) needs a per-comment answer, and the board reload cannot give one because comments
+    /// are not in the snapshot it compares.
+    ///
+    /// `[]` for a card that is gone — the same vanished-target answer every other card-scoped call
+    /// gives, and the conservative direction: nothing vouched for means everything speaks.
+    public func vouchedComments(inCard id: ItemID) -> Set<ItemID> {
+        guard let card = commentSubject(id) else { return [] }
+        return echoes.vouchedComments(inCard: card.folder, cardPath: card.path)
+    }
+
     // MARK: The draft
 
     /// Saves the composer's draft — one bracket, no step.