requirements for blueprint drops

docs/requirements.md

@@ -123,8 +123,8 @@ Output port indicators are not building tiles themselves. A building may have mo
 - REQ-DEF-ENEMY-PLACEMENT: 2 enemy defence stations are placed at the right boundary of the scrollable area at game start, and again each time a new set is spawned after a push. Stats scale with the station level (REQ-PSH-STATION-STATS).
 - REQ-DEF-ENEMY-FIRE: Enemy defence stations automatically fire at player ships within range.
 - REQ-DEF-NO-CROSSFIRE: Enemy and player defence stations are never in each other's firing range.
-- REQ-DEF-PUSH: When both enemy defence stations in a set are destroyed, the push scaling multiplier is applied (REQ-PSH-ACCUMULATION), the scrollable area is extended (REQ-GW-PUSH-EXPAND), and a new set of enemy defence stations is placed at the new boundary. The destroyed stations drop ship blueprint loot (REQ-DEF-BLUEPRINT-DROP).
-- REQ-DEF-BLUEPRINT-DROP: One ship blueprint is chosen uniformly at random from all blueprints defined in `ships.toml`. If the player does not yet have that blueprint, it is unlocked. If the player already has it, the blueprint's `[ship.blueprint].player_production_level` is incremented by 1 — so subsequent ships of that type are produced at a higher level.
+- REQ-DEF-PUSH: When both enemy defence stations in a set are destroyed, the push scaling multiplier is applied (REQ-PSH-ACCUMULATION), the scrollable area is extended (REQ-GW-PUSH-EXPAND), a new set of enemy defence stations is placed at the new boundary, and exactly one blueprint drop is awarded for the destroyed set (REQ-DEF-BLUEPRINT-DROP).
+- REQ-DEF-BLUEPRINT-DROP: Each destroyed set of enemy defence stations awards exactly one blueprint drop (not one per station). The drop is automatic — no physical item to collect. A blueprint is chosen uniformly at random from all blueprints defined in `ships.toml`. If the player does not yet have that blueprint, it is unlocked. If the player already has it, the blueprint's `[ship.blueprint].player_production_level` is incremented by 1 — so subsequent ships of that type are produced at a higher level. The player is notified via a toast (REQ-UI-BLUEPRINT-TOAST).
 
 ## Threat Level & Enemy Waves
 
@@ -176,6 +176,11 @@ The screen is divided into three vertical sections:
 
 - REQ-UI-SCROLL: The player scrolls the view horizontally across the scrollable area by pressing A (scroll left) and D (scroll right).
 - REQ-UI-NO-ZOOM: The view has a fixed zoom level; the player cannot zoom in or out.
+- REQ-UI-BLUEPRINT-TOAST: When a blueprint is unlocked or leveled up (REQ-DEF-BLUEPRINT-DROP), a transient notification toast appears in the top-right corner of the game world view for 4 seconds and then fades out. Toast text:
+  - **New unlock**: `Blueprint unlocked: <Ship Name>`
+  - **Level-up (duplicate drop)**: `<Ship Name> production level → N` (where N is the new level).
+
+  If multiple toasts arrive in close succession, they stack vertically in a queue (most recent at the top) and each fades out independently after its own 4-second lifetime.
 - REQ-UI-HOTKEYS: Global keyboard shortcuts:
   - **Space** — toggles pause. Pressing Space pauses (sets speed to 0×) and stores the previously selected non-zero speed; pressing Space again restores that speed.
   - **W** — increases game speed by one step in the sequence 0×, 0.5×, 1×, 2×, 4× (no wrap-around past 4×).