diff --git a/MIGRATION-ROADMAP.md b/MIGRATION-ROADMAP.md
index 656b1f93..8db38a48 100644
--- a/MIGRATION-ROADMAP.md
+++ b/MIGRATION-ROADMAP.md
@@ -160,6 +160,24 @@ Bukan hanya namespace `Illuminate\*` yang bertabrakan. **Fork dan stock keduanya
 - **Fase 5 gate:** `composer require laravel/framework:^13` **hanya** setelah blok `replace` fork
   **kosong** (0 entry tersisa) — kalau tidak, resolver deadlock antara dua `laravel/framework`.
 
+### 1b. Vendor-floor collision — prasyarat installability tiap swap (VERIFIED 2026-09-17)
+
+Selain replace-collision (§1a), swap-per-cluster punya prasyarat **kedua yang lebih dasar**: floor
+dependency fork harus ≥ floor L13. Terverifikasi empiris (`migration/4.1-scc1-core-cutover`):
+
+| dep | fork sekarang | L13.30.1 floor |
+|---|---|---|
+| `symfony/*` | `~6.4` | `^7.4.0 \|\| ^8.0.0` |
+| `nesbot/carbon` | `^2.71` | `^3.8.4` |
+| `monolog/monolog` | `^2.10` | `^3.10` |
+| baru (hard-require) | — | `brick/math`, `league/flysystem ^3.25`, `symfony/uid`, `league/uri ^7.5` |
+
+`illuminate/<pkg>:^13` menyeret floor v13 di atas → **konflik constraint langsung** dgn pin fork →
+interim-state `fork + illuminate/*:^13` **tak resolvable** sampai floor fork di-bump. Ini **bukan**
+tercakup daftar prereq 4.1 (semuanya reshape API internal) maupun Wave 0 → dicatat sebagai enabler
+**4.0** (bump Symfony 7 / carbon 3 / monolog 3 + port komponen fork yang masih pakai Symfony langsung).
+Konsekuensi: **4.0 mem-block SEMUA swap Wave 4**, bukan cuma SCC-1.
+
 ---
 
 ## 2. Dependency graph (bottom-up, per layer) — swap **bottom-up per cluster**
diff --git a/MIGRATION-TASKS.md b/MIGRATION-TASKS.md
index 0a95c77a..89dc6193 100644
--- a/MIGRATION-TASKS.md
+++ b/MIGRATION-TASKS.md
@@ -311,9 +311,27 @@ kerjakan sampai "Done when" terpenuhi, centang, lanjut. Tiap task **independen &
 > Namespace `Illuminate\*` collide + fork/stock sama-sama `laravel/framework` yang `replace`
 > illuminate/* → **tak bisa co-install**. Swap **per-cluster**: tiap langkah **hapus entry dari
 > blok `replace` fork** lalu `composer require illuminate/<pkg>:^13`. Interim = fork +
-> `illuminate/<swapped>:^13` individual. Prasyarat tiap swap: Wave 1–2 komponen terkait ✅.
-
-- [ ] **4.1 — SCC-1 core cutover (satu window)** `[fork · XL]` · blocked-by: 1.1–1.4, 2.2, 2.4, 2.5, 2.9, 2.10, 2.12, 2.13
+> `illuminate/<swapped>:^13` individual. Prasyarat tiap swap: Wave 1–2 komponen terkait ✅
+> **DAN 4.0 (vendor floor L13) sudah landas** — tanpa itu tak ada `illuminate/*:^13` yang resolvable.
+
+- [ ] **4.0 — 🔴 Enabler: bump vendor floor fork ke L13 (Symfony 7 / carbon 3 / monolog 3)** `[fork · XL]` · blocked-by: — (prasyarat SEMUA swap Wave 4)
+  - Why (VERIFIED 2026-09-17, empiris di `migration/4.1-scc1-core-cutover`): interim-state Wave 4
+    (`fork` + `illuminate/<pkg>:^13`) **tak resolvable**. Fork pin `symfony/*: ~6.4`,
+    `nesbot/carbon: ^2.71`, `monolog/monolog: ^2.10`; floor L13.30.1 = `symfony/*: ^7.4||^8`,
+    `nesbot/carbon: ^3.8.4`, `monolog/monolog: ^3.10` + hard-require baru `brick/math`,
+    `league/flysystem: ^3.25`, `symfony/uid`, `league/uri: ^7.5`. `composer require illuminate/*:^13`
+    narik floor v13 → konflik constraint langsung dgn pin fork. **Gap roadmap:** daftar prereq 4.1
+    cuma reshape API internal (Cache/Events/pluck/…), tak pernah cakup bump vendor ini — Wave 0 juga
+    tidak (monolog 3 baru setengah diakui di 2.13; Symfony 6.4→7 & carbon 2→3 tak disebut sama sekali).
+  - Steps: bump `composer.json` fork → `symfony/*: ^7.4`, `nesbot/carbon: ^3`, `monolog/monolog: ^3`
+    (+ `brick/math`, `league/flysystem: ^3.25`, `symfony/uid`, `league/uri: ^7.5`, dev `phpunit ~11/12`);
+    port komponen fork yang **masih di-provide** & pakai Symfony langsung ke API Symfony 7 (Http/Console/
+    Routing/Session/Foundation/Mail — BC HttpFoundation/HttpKernel/Console); serap carbon 3 + monolog 3
+    (LogRecord/`Level` enum, sinkron dgn 2.13). Gate empiris = `./vendor/bin/phpunit` fork hijau
+    (baseline pra-bump 2026-09-17 = 1647 test hijau, exit 0).
+  - Done when: `composer update` fork resolve dgn floor v13; suite fork hijau; swap SCC-1 (4.1) jadi installable.
+
+- [ ] **4.1 — SCC-1 core cutover (satu window)** `[fork · XL]` · blocked-by: 4.0, 1.1–1.4, 2.2, 2.4, 2.5, 2.9, 2.10, 2.12, 2.13
   - Cluster: `contracts+reflection+support+container` (jangkar) + `http, session, cache, cookie,
     encryption, events, filesystem, redis, database` + **`bus`** (transitif hard-require `events`).
     Swap ke `illuminate/*` v13 **bersamaan**.