Implement live accessibility announcements

The board speaks when files change under the user, per DESIGN/10 § Live
board announcements. BoardDiff is the pure snapshot summarizer (identity
sets for cards/lanes added/edited/moved/deleted — ids, not tallies, so
pro-m1's semantic commit engine can build on it; edited = rendered
content only, moved beats edited, implied events don't steal the
subject). BoardAnnouncer is the decision seam: focusOutcome computes the
vanishing-focus sentence and the walk-up-then-sideways recovery (next
lane by order, else previous, board container only when none remain,
never the trash); speech(for:) is the one-sentence precedence ladder —
raised condition > bracket completion > cleared condition > vanished
focus > digest — foreign-only for the last two rungs, so app-mediated
echoes stay silent.

BoardStore.land assembles ReloadFacts and posts exactly one sentence per
reload through the injectable announce outlet (AccessibilityAnnouncer,
medium priority, never interrupting). Selection recovery layers on top
of ItemReferenceSet re-resolution — survivors veto, the emptied
selection lands on the vanished item's lane and re-arms ⌘N's active-lane
memory. performWholesale(announcing:) arms a completion phrase consumed
by the closing reload — nil on every base bracket today; pro-m1 fills
git phrasings. Locks raised outside the reload path (vanished root,
unwritable location) announce through the same ladder, and the banner
strip is a labeled "Board status" container whose row labels are the
announced sentences (AccessibilityPhrases.bannerLabel — one string for
eye and ear).

Announcements classify at reload granularity (WatchOrigin) as a
deliberate interim: DESIGN/02's EchoLedger (per-file classification, the
announcer's specified input, git-free) was scheduled with the
auto-committer that the edition split moved to pro-m1 — filed on the
Redesign board for a ruling. 1533 unit tests green, both schemes build.

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

KanbanTests/WriterTestSupport.swift

@@ -118,6 +118,55 @@ struct WriterFixture {
     }
 }
 
+// MARK: - Snapshots
+
+/// The half of the fixture the **snapshot-comparison** suites need (`BoardDiffTests`,
+/// `BoardAnnouncerTests`): boards written as files and read back through the real loader.
+///
+/// They compare `BoardModel` values, and a hand-assembled model would be assembling something
+/// `BoardLoader` can never produce — a lane with a malformed `order`, a card whose `document` does
+/// not match its fields. Writing bytes and loading them is the only way the two snapshots in a diff
+/// are the two snapshots a reload would actually have compared.
+extension WriterFixture {
+
+    /// `<root>/index.md`, the one file every board must have.
+    @discardableResult
+    func board(title: String = "Board", body: String = "Board description.") throws -> URL {
+        try item("", "---\nschema: 1\ntitle: \(title)\n---\n\(body)\n")
+    }
+
+    @discardableResult
+    func lane(_ id: String, order: String, title: String, width: Int? = nil, body: String = "") throws -> URL {
+        let widthLine = width.map { "width: \($0)\n" } ?? ""
+        return try item(id, "---\nschema: 1\ntitle: \(title)\norder: \(order)\n\(widthLine)---\n\(body)\n")
+    }
+
+    @discardableResult
+    func card(
+        _ id: String,
+        in laneID: String,
+        order: String,
+        title: String,
+        body: String = "",
+        modified: String? = nil
+    ) throws -> URL {
+        let modifiedLine = modified.map { "modified: \($0)\n" } ?? ""
+        return try item("\(laneID)/\(id)", "---\nschema: 1\ntitle: \(title)\norder: \(order)\n\(modifiedLine)---\n\(body)\n")
+    }
+
+    /// A card written straight into `<root>/.trash/` — the materialized trash's shape, for the
+    /// diff rule that says churn in there is not a change to the board.
+    @discardableResult
+    func trashCard(_ id: String, order: String, title: String) throws -> URL {
+        try item(".trash/\(id)", "---\nschema: 1\ntitle: \(title)\norder: \(order)\n---\n\n")
+    }
+
+    /// The board as the loader reads it right now — the value a reload would have landed.
+    func snapshot() throws -> BoardModel {
+        try BoardLoader.load(boardRoot: root).model
+    }
+}
+
 // MARK: - Move/copy identities
 
 /// Literal UUID-shaped names for the move/copy suites, which need more of them than