add requirements for beam rendering if shooter or target is already destroyed

docs/requirements.md

@@ -114,8 +114,8 @@ Output port indicators are not building tiles themselves. A building may have mo
 - REQ-SHP-MOVEMENT: Ships move in straight lines toward their current destination at the speed defined by their speed formula. Ship position refers to the ship's center for all range, sensor, and attack checks.
 - REQ-SHP-NO-COLLISION: Ships do not collide with each other or with defence stations; they may visually overlap.
 - REQ-SHP-SENSOR: A ship perceives only entities within its sensor range. Behavior is driven by what is in sensor range; entities outside sensor range are ignored.
-- REQ-SHP-FIRING: All weapons — on ships and on defence stations — are hitscan lasers. When a weapon is off cooldown and its target is within attack range, it fires: damage is applied instantly to the target with no projectile entity, no travel time, and no intervening collision. The weapon's cooldown then begins, derived from its fire rate formula.
+- REQ-SHP-FIRING: All weapons — on ships and on defence stations — fire when off cooldown and the target is within attack range. Firing emits a fire event and starts a 0.15-second damage delay (half the beam duration). When that delay expires, damage is applied to the target — unless the target has already been destroyed, in which case the damage is silently dropped. If the shooter is destroyed before the delay expires, damage is still applied when the delay expires. There is no projectile entity and no intervening collision. The weapon's cooldown begins at the moment of firing, not at damage application.
-- REQ-SHP-FIRING-BEAM: Each fire event produces a visual laser beam drawn from the shooter's position to the target's position for 0.3 seconds. The beam is a pure rendering effect and has no simulation state (does not block movement, does not re-apply damage over its lifetime). Beams follow the shooter and target positions if either moves during the 0.3-second window.
+- REQ-SHP-FIRING-BEAM: Each fire event produces a visual laser beam drawn from the shooter's position to the target's position for 0.3 seconds. The beam is a pure rendering effect and has no simulation state (does not block movement, does not re-apply damage over its lifetime). Beams follow the shooter and target positions if either moves during the 0.3-second window. The beam is rendered for its full 0.3-second duration even if the shooter or target is destroyed before it expires.
 - REQ-SHP-COMBAT: **Combat ships** (player) — engage enemy ships within sensor range. The player can configure the following per shipyard (applied to all ships produced by that shipyard):
   - Stance: aggressive (advance toward enemies) / defensive (hold position near asteroid).
   - Target priority: closest / highest HP / structures first.