make ships claim targets

docs/requirements.md

@@ -4,7 +4,7 @@
 
 Config files use the TOML format. The following config files drive game parameters:
 
-- **world.toml** — world dimensions, region widths, expansion amounts, building refund percentage, wave timing, boss wave timing, enemy ship level formula, belt speed, starting building blocks, departure interval, ship orbit factor, rally orbit radius.
+- **world.toml** — world dimensions, region widths, expansion amounts, building refund percentage, wave timing, boss wave timing, enemy ship level formula, belt speed, starting building blocks, departure interval, ship orbit factor, rally orbit radius, and combat target-selection parameters (target score formula, overclaim penalty formula, target hysteresis).
 - **buildings.toml** — building block cost and construction time per building type.
 - **recipes.toml** — crafting recipes: inputs, outputs, quantities, durations, and reprocessing plant probabilities. Assembler recipe entries may optionally define `unlock_at_station_level` (integer): -1 means the recipe is explicitly unlocked at game start; a value ≥ 0 means the recipe starts locked and a schematic for it can be awarded via defence station destruction (see REQ-LOCK-EXPLICIT, REQ-DEF-SCHEMATIC-DROP).
 - **ships.toml** — per schematic: a human-readable display name (used in the UI), hull stats (HP, max linear speed, sensor range, main acceleration, maneuvering acceleration, angular acceleration, max rotation speed) as formulas of ship level, required build materials, player production level, the station level at which the schematic becomes available for unlock (`unlock_at_station_level`; -1 means the player starts with the schematic already unlocked), a layout grid defining the ship's module slots, a `scrap_drop` loot value, and a `default_modules` list used for enemy wave ships (see REQ-WAV-DEFAULT-MODULES).
@@ -179,6 +179,9 @@ Modules in `modules.toml` define a `surface_mask` — a list of strings that des
   Each repair module instance operates independently: it has its own repair rate (`repair_rate`) and repair range (`repair_range`). On each tick, a module first attempts to heal the ship's current behavior-level navigation target if that target is within the module's `repair_range` and is damaged (HP above zero and below maximum HP). If those conditions are not met — because the target is out of the module's `repair_range`, already at full health, or destroyed — the module independently searches for the nearest damaged friendly (player ship or player defence station) within its own `repair_range` and heals that instead. If no valid target is found within range, the module idles. A ship with multiple repair modules can therefore heal different targets simultaneously. Navigation is driven solely by the behavior-level target; individual module fallback targets do not affect which direction the ship moves. Repair healing is a world-state change applied every tick regardless of which behavior the ship is currently executing.
 - REQ-SHP-RETREAT: **Player ships retreat to the rally point (REQ-SHP-RALLY) when threatened.** A ship retreats while either condition holds: (a) its HP is below a low-HP threshold (currently 30% of its maximum HP); or (b) it has no weapon modules and an enemy ship is within its sensor range. Retreating takes priority over the ship's other behaviors and moves it toward the rally point; the ship resumes its normal behavior once neither condition holds. Enemy ships never retreat (REQ-SHP-ENEMY-AI).
 - REQ-SHP-ENEMY-AI: **Enemy ships** — engage the closest valid target (player defence station, HQ, or player ship) within their sensor range, orbiting the engaged target at the combat orbit radius (REQ-SHP-ORBIT). If no target is in sensor range, they move toward the asteroid (leftward in world coordinates).
+- REQ-SHP-TARGET-SELECT: **Combat target selection.** Both player combat ships (REQ-SHP-COMBAT) and enemy ships (REQ-SHP-ENEMY-AI) pick which hostile to engage by scoring every valid target (an opposing-faction ship, defence station, or HQ) within sensor range and engaging the highest-scoring one. A target's score is the product of a **base desirability** and an **overclaim penalty** (REQ-SHP-TARGET-CLAIM). The base desirability is `world.toml [targeting].target_score_formula` evaluated with `x` set to the target's distance from the ship divided by the ship's maximum weapon `attack_range` (falling back to sensor range for a ship with no weapon), clamped to a minimum of 0. The default formula `1 / (1 + x)` decreases with distance, so — absent any claims — the nearest target is chosen, realizing the closest-target priority referenced by REQ-SHP-COMBAT and REQ-SHP-ENEMY-AI. A ship engages at most one target at a time; all of its weapons fire on that target subject to their own range and rate checks (REQ-SHP-FIRING).
+- REQ-SHP-TARGET-CLAIM: **Overclaim penalty.** To stop every ship from dogpiling the same hostile, each target a ship is currently engaging counts as a **claim** on that target. When scoring a candidate, its base desirability (REQ-SHP-TARGET-SELECT) is multiplied by `world.toml [targeting].overclaim_penalty_formula` evaluated with `x` set to the number of ships currently claiming that candidate — a ship never counts its own claim against the target it already holds — clamped to the range [0, 1]. The penalty is 1 (no reduction) at zero claims and decreases as claims accumulate, so heavily-claimed targets become less attractive and ships spread across the available hostiles. The default formula `max(0.5, 1 - 0.1*x)` reduces desirability by 0.1 per claim down to a floor of 0.5. Because claims reflect the previous tick's engagements, target distribution converges over successive ticks rather than instantaneously.
+- REQ-SHP-TARGET-HYSTERESIS: **Target stickiness.** A ship keeps engaging its current target as long as that target remains valid and within sensor range, switching to a different target only when the best alternative's score exceeds the current target's score by more than the fractional margin `world.toml [targeting].target_hysteresis` (default 0.10). This prevents ships from rapidly oscillating between targets of near-equal score and preserves focus fire.
 - REQ-SHP-SCHEMATICS: The player selects a schematic per shipyard by clicking it. New schematics are unlocked by destroying enemy defence station sets (REQ-DEF-SCHEMATIC-DROP) — there is no physical loot to collect.
 
 ## Ship Modules