Agent guide v6 - warn against lane-glob moves

A real agent incident (2026-07-29): moving cards with mv <lane>/* swept
the lane's own index.md along with the card folders, overwriting the
destination lane's identity file and leaving the source lane index-less
(the Implementation board briefly lost its lane titles; restored from
its auto-commit history). Both guide generations taught the correct
named-folder form but never said why it is load-bearing.

v6 adds the one-folder-at-a-time bullet to Moving and reordering:
a lane folder holds its own index.md beside its cards, so a glob
sweeps the identity file with them. Boards heal to v6 on their next
open per the first-line marker rule. The guide tests now derive
their expected marker and current/newer versions from
AgentGuide.version instead of a hardcoded literal, so the next bump
cannot silently break them.

1669 green on both schemes.

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

Kanban/Storage/AgentGuide.swift

@@ -44,8 +44,11 @@ enum AgentGuide {
 
     /// The guide the app ships. **v4 was the pathfinder's**, and real boards carry it; v5 is the
     /// rewrite's guide (lanes, `.trash/`, `attachments/`, `modified-by`, the `CLAUDE.user.md`
-    /// pointer) and supersedes it on the next open.
-    static let version = 5
+    /// pointer) and supersedes it on the next open. v6 adds the one-folder-at-a-time move warning:
+    /// a real agent incident (2026-07-29) showed `mv <lane>/*` sweeping the lane's own `index.md`
+    /// along with the cards and destroying the destination lane's identity — the guide now says
+    /// *why* the named-folder form is load-bearing, not just what to type.
+    static let version = 6
 
     // MARK: - The version marker
 
@@ -327,6 +330,10 @@ enum AgentGuide {
     - Move to another lane: `mv <laneA>/<card-uuid> <laneB>/` — the folder move
       IS the move. Then set the card's `order` to place it among the
       destination's cards, update `modified`, and re-stamp `modified-by`.
+    - Move folders **one at a time, by name** — never `mv <laneA>/* <laneB>/`.
+      A lane folder holds its own `index.md` beside its cards, so a glob
+      sweeps the lane's identity file along with them and overwrites the
+      destination lane's.
     - Reorder within a lane: rewrite only that card's `order`.
 
     ## Editing and deleting