Build the semantic commit-message engine

CommitMessageEngine replaces the interim composer as the wired
default: a pure total function from two snapshots + changed paths to
a message. Full vocabulary — Add / Delete / Move / Rename / Edit /
Restyle / Resize / Reorder over cards, lanes, board; Attach / Remove;
Repair for the duplicate remint (detected as a heal-classed
rename-paired arrival whose id the previous snapshot never held —
the loader withholds duplicates, so the shape is a bare arrival);
the trash triple by diff shape alone (into .trash = Delete, out =
Restore, leaving the tree = Permanently delete); Relabel / Assign /
Set due date plus the named generic for custom keys. Plural folding
with shared destinations, implied events as body bullets never
subjects, ~40-char subject truncation, "(untitled)". Bookkeeping
(sequence-preserving renumbers, stamps, backfilled kind) composes
nothing. Non-snapshot paths compose path-shaped events — CLAUDE.md
reads "Update agent guide (vN)" via the marker line (the m10 card's
deferred bullet lands here), everything else "Update '<path>'".

The comment verb family per 01's ruling (comments shipped, so 06
gains the verbs): Comment on / Edit comment on / Delete comment on /
Draft comment on / Permanently delete comment on '<card>', grouped
one event per comment folder, classified ahead of the model-silence
rules, card title resolved from either snapshot. GIT_DELTA_ADDED is
surfaced as GitChangedPath.isArrival — post vs edit is unanswerable
from snapshots that exclude comments by ruling. A card moving with
its thread swallows the comment events (implied-events one level
down).

The previous snapshot is HEAD's tree, materialized per flush into a
temp dir (index.md blobs in full, other blobs zero-byte — the model
reads attachment names, never bytes) and re-parsed through the one
BoardLoader; never a value carried forward. changedPaths is a hard
filter per split commit, which also earns the stage-around and kills
phantom events. Launch catch-up and foreign windows compose through
the same engine.

48 new tests (35 pure + comment family + engine-level); 2293 tests /
394 suites green; InertGitTests untouched.

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

Kanban/Git/GitCommitOperation.swift

@@ -90,10 +90,21 @@ public struct GitChangedPath: Sendable, Equatable, Hashable {
     /// deletion on disk that the window must not be demoted by.
     public let isRename: Bool
 
-    public init(path: String, isDeletion: Bool, isRename: Bool) {
+    /// Whether the path is **new in this commit** — git's own `GIT_DELTA_ADDED` (and a rename's
+    /// arriving end), surfaced rather than inferred.
+    ///
+    /// It exists for the comment verb family (01-storage-format.md § Enhanced schema): comments are
+    /// window-scoped and the board snapshot never carries them, so "Comment on 'X'" and "Edit comment
+    /// on 'X'" cannot be told apart by a diff of two snapshots — the only thing that distinguishes a
+    /// comment folder arriving from one being rewritten is whether HEAD already had it, which is
+    /// exactly the question this diff already answered.
+    public let isArrival: Bool
+
+    public init(path: String, isDeletion: Bool, isRename: Bool, isArrival: Bool = false) {
         self.path = path
         self.isDeletion = isDeletion
         self.isRename = isRename
+        self.isArrival = isArrival
     }
 }
 
@@ -331,7 +342,7 @@ enum GitCommitOperation {
 
         var found: [String: GitChangedPath] = [:]
 
-        func record(_ path: String?, isDeletion: Bool, isRename: Bool) {
+        func record(_ path: String?, isDeletion: Bool, isRename: Bool, isArrival: Bool = false) {
             guard let path, !path.isEmpty else { return }
             let existing = found[path]
             found[path] = GitChangedPath(
@@ -339,7 +350,10 @@ enum GitCommitOperation {
                 // Present wins where two deltas disagree: staging asks "is it there now", and the
                 // `modified-by` demotion must not fire for a file the window ends with.
                 isDeletion: (existing?.isDeletion ?? true) && isDeletion,
-                isRename: (existing?.isRename ?? false) || isRename
+                isRename: (existing?.isRename ?? false) || isRename,
+                // New wins, for the mirror of that reason: one delta calling a path an addition is
+                // enough to know HEAD did not have it, which is the whole content of the bit.
+                isArrival: (existing?.isArrival ?? false) || isArrival
             )
         }
 
@@ -350,9 +364,12 @@ enum GitCommitOperation {
                 record(string(delta.old_file.path), isDeletion: true, isRename: false)
             case GIT_DELTA_RENAMED:
                 // Both ends, and neither is a deletion the window may be demoted by: the departure
-                // has to leave the index and the arrival has to enter it.
+                // has to leave the index and the arrival has to enter it. The arriving end is new at
+                // its path, which is what the comment family reads a post by.
                 record(string(delta.old_file.path), isDeletion: true, isRename: true)
-                record(string(delta.new_file.path), isDeletion: false, isRename: true)
+                record(string(delta.new_file.path), isDeletion: false, isRename: true, isArrival: true)
+            case GIT_DELTA_ADDED, GIT_DELTA_COPIED, GIT_DELTA_UNTRACKED:
+                record(string(delta.new_file.path), isDeletion: false, isRename: false, isArrival: true)
             default:
                 record(string(delta.new_file.path), isDeletion: false, isRename: false)
             }