diff --git a/docs/MIGRATION.md b/docs/MIGRATION.md
index 5b73432..c2e10b9 100644
--- a/docs/MIGRATION.md
+++ b/docs/MIGRATION.md
@@ -30,6 +30,17 @@ assumptions. Check each:
 | **LUKS** (optional, themed prompt) | `lsblk -f` shows `crypto_LUKS` | none — LUKS is optional |
 | Already a **flake** config | `test -f /etc/nixos/flake.nix` | fine either way; you'll write a fresh flake regardless |
 
+**Installer vs migration snapshot layout.** A fresh Nomarchy install
+(disko) creates a top-level `@snapshots` subvolume mounted at
+`/.snapshots`, then a first-boot oneshot makes a *nested*
+`/home/.snapshots` under `@home` for snapper's home timeline — it does
+**not** create a separate top-level `@home-snapshots`. Migration machines
+(e.g. TuringMachine) may already use top-level `@snapshots` **and**
+`@home-snapshots`; that is fine. Snapper only needs a `.snapshots` path
+under each tracked subvolume (`/` and `/home`), so either layout works —
+reuse what you have, or create the missing pieces if you want snapper
+without reformatting.
+
 TuringMachine matches all of these, including the `@snapshots` /
 `@home-snapshots` subvolumes — so snapper works with zero disk work.