diff --git a/agent/BACKLOG.md b/agent/BACKLOG.md
index 6e7acdb..ddd7081 100644
--- a/agent/BACKLOG.md
+++ b/agent/BACKLOG.md
@@ -78,6 +78,41 @@ cable leaves. Capture steps in HARDWARE-QUEUE.
 
 ## NEXT
 
+### 128. Auto-prune NixOS generations: >30 days, but keep ≥3 past
+
+Bernardo 2026-07-15: automatic cleanup of **NixOS** (system) generations
+so the boot menu and store do not grow without bound, with a safety floor:
+
+1. **Age:** candidates older than **30 days** may be removed.
+2. **Count floor:** always keep the **current** generation and at least
+   **3 past** generations — even if those three are older than 30 days.
+3. Combined: delete only gens that are **both** older than 30 days **and**
+   older than the third-most-recent past generation. Gens within 30 days
+   stay regardless of how many there are (until they age out).
+
+**Why this shape:** pure age GC (`--delete-older-than`) can wipe a machine
+that is rarely rebuilt down to one generation and remove useful rollback
+targets; pure count limits (`configurationLimit`) drop recent work just
+because the user iterates a lot. Age + floor keeps travel-laptop machines
+safe and busy desktops tidy.
+
+**Today:** `nix.gc` is already weekly with `--delete-older-than 14d`
+(`modules/nixos/default.nix`) — store GC, no min-generation floor, and
+14d not 30d. This item should replace/refine that policy (or add a
+dedicated generation pruner if stock GC cannot express the floor).
+
+**Scope (settle if needed):** system profile only vs also Home Manager
+user generations (desktop rollback in Recovery). Bootloader list
+(`boot.loader.systemd-boot.configurationLimit`) may need to stay in
+sync so removed profiles do not leave dead boot entries.
+
+Pass = weekly (or post-rebuild) cleanup enforces 30d + keep ≥3 past on
+system generations; a machine with only old gens never goes below
+current+3; docs/RECOVERY still matches the boot-menu story; doctor or a
+check asserts the timer/unit exists and the prune script's dry-run
+logic. V3: run on a box with many gens and confirm boot menu +
+`nix-env -p /nix/var/nix/profiles/system --list-generations`.
+
 ### 120. A netinstall ISO, next to the fat offline one
 
 Bernardo 2026-07-14, after seeing the measured size: **keep the current ISO
diff --git a/agent/JOURNAL.md b/agent/JOURNAL.md
index f8d01a9..2f121a3 100644
--- a/agent/JOURNAL.md
+++ b/agent/JOURNAL.md
@@ -19,6 +19,15 @@ Template:
 
 ---
 
+## 2026-07-15 — File #128 generation auto-prune policy (no code)
+- **Task:** Bernardo: auto-clean NixOS gens older than 30 days but always
+  keep ≥3 past generations.
+- **Did:** NEXT **#128**. Policy restated; noted existing `nix.gc` weekly
+  `--delete-older-than 14d` has no min-generation floor.
+- **Verified:** V0 (docs/agent only).
+- **Pending:** implement when picked; optional HM gens scope.
+- **Next suggestion:** implement #128, or human #115/#120.
+
 ## 2026-07-15 — #111 Recovery + #105 System IA + #110 retire Control Center
 - **Task:** Scope-first Recovery, System submenu IA, retire Control Center.
 - **Did:** System → Connectivity / Devices / Recovery / Preferences. Recovery: