feat: resource collection with E-key interaction (Phase 4.3)

Mineral veins yield metals (Fe, Cu, Zn, Au, Sn), geysers yield S/H.
Resources spawn as ECS entities with gold/orange dot sprites on tiles.
E-key collects nearest resource in range into inventory. Resources
deplete after collection. Visual feedback text. 12 new tests (174 total).

Co-authored-by: Cursor <cursoragent@cursor.com>

tests/interaction.test.ts

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+/**
+ * Resource Interaction Tests — Phase 4.3
+ *
+ * Tests: resource element picking, proximity detection,
+ * collection into inventory, resource depletion.
+ */
+
+import { describe, it, expect } from 'vitest';
+import { createWorld, addEntity, addComponent, query } from 'bitecs';
+import { Position, Resource, PlayerTag } from '../src/ecs/components';
+import { Inventory } from '../src/player/inventory';
+import {
+  pickResourceElement,
+  interactionSystem,
+  type ResourceInfo,
+  type InteractionResult,
+  MINERAL_ELEMENTS,
+  GEYSER_ELEMENTS,
+} from '../src/player/interaction';
+
+// === Helpers ===
+
+function createTestWorld() {
+  const world = createWorld();
+  const resourceData = new Map<number, ResourceInfo>();
+  const inventory = new Inventory();
+  return { world, resourceData, inventory };
+}
+
+function addPlayer(world: ReturnType<typeof createWorld>, x: number, y: number): number {
+  const eid = addEntity(world);
+  addComponent(world, eid, Position);
+  addComponent(world, eid, PlayerTag);
+  Position.x[eid] = x;
+  Position.y[eid] = y;
+  return eid;
+}
+
+function addResource(
+  world: ReturnType<typeof createWorld>,
+  resourceData: Map<number, ResourceInfo>,
+  x: number,
+  y: number,
+  itemId: string,
+  quantity: number,
+  range = 40,
+): number {
+  const eid = addEntity(world);
+  addComponent(world, eid, Position);
+  addComponent(world, eid, Resource);
+  Position.x[eid] = x;
+  Position.y[eid] = y;
+  Resource.quantity[eid] = quantity;
+  Resource.interactRange[eid] = range;
+  resourceData.set(eid, { itemId, tileX: Math.floor(x / 32), tileY: Math.floor(y / 32) });
+  return eid;
+}
+
+// === pickResourceElement ===
+
+describe('pickResourceElement', () => {
+  it('always returns element from provided list', () => {
+    for (let x = 0; x < 20; x++) {
+      for (let y = 0; y < 20; y++) {
+        const el = pickResourceElement(x, y, 12345, MINERAL_ELEMENTS);
+        expect(MINERAL_ELEMENTS).toContain(el);
+      }
+    }
+  });
+
+  it('is deterministic (same inputs → same output)', () => {
+    const a = pickResourceElement(5, 10, 42, MINERAL_ELEMENTS);
+    const b = pickResourceElement(5, 10, 42, MINERAL_ELEMENTS);
+    expect(a).toBe(b);
+  });
+
+  it('varies with different positions', () => {
+    const results = new Set<string>();
+    for (let i = 0; i < 100; i++) {
+      results.add(pickResourceElement(i, i * 7, 42, MINERAL_ELEMENTS));
+    }
+    // Should use more than one element (statistical certainty)
+    expect(results.size).toBeGreaterThan(1);
+  });
+
+  it('works with geyser elements', () => {
+    const el = pickResourceElement(3, 7, 42, GEYSER_ELEMENTS);
+    expect(GEYSER_ELEMENTS).toContain(el);
+  });
+});
+
+// === Interaction System ===
+
+describe('interactionSystem — collection', () => {
+  it('collects element when in range and pressing E', () => {
+    const { world, resourceData, inventory } = createTestWorld();
+    addPlayer(world, 100, 100);
+    addResource(world, resourceData, 120, 100, 'Fe', 5);
+
+    const result = interactionSystem(world, true, inventory, resourceData);
+
+    expect(result).not.toBeNull();
+    expect(result!.type).toBe('collected');
+    expect(result!.itemId).toBe('Fe');
+    expect(inventory.getCount('Fe')).toBe(1);
+  });
+
+  it('does nothing when E is not pressed', () => {
+    const { world, resourceData, inventory } = createTestWorld();
+    addPlayer(world, 100, 100);
+    addResource(world, resourceData, 120, 100, 'Fe', 5);
+
+    const result = interactionSystem(world, false, inventory, resourceData);
+
+    expect(result).toBeNull();
+    expect(inventory.getCount('Fe')).toBe(0);
+  });
+
+  it('does nothing when no resources in range', () => {
+    const { world, resourceData, inventory } = createTestWorld();
+    addPlayer(world, 100, 100);
+    addResource(world, resourceData, 500, 500, 'Fe', 5); // far away
+
+    const result = interactionSystem(world, true, inventory, resourceData);
+
+    expect(result).not.toBeNull();
+    expect(result!.type).toBe('nothing_nearby');
+  });
+
+  it('picks closest resource when multiple in range', () => {
+    const { world, resourceData, inventory } = createTestWorld();
+    addPlayer(world, 100, 100);
+    addResource(world, resourceData, 130, 100, 'Cu', 3); // 30px away
+    addResource(world, resourceData, 115, 100, 'Fe', 5); // 15px away (closer)
+
+    const result = interactionSystem(world, true, inventory, resourceData);
+
+    expect(result!.itemId).toBe('Fe'); // picked closer one
+  });
+
+  it('decrements resource quantity on collection', () => {
+    const { world, resourceData, inventory } = createTestWorld();
+    addPlayer(world, 100, 100);
+    const resEid = addResource(world, resourceData, 120, 100, 'Fe', 3);
+
+    interactionSystem(world, true, inventory, resourceData);
+
+    expect(Resource.quantity[resEid]).toBe(2);
+  });
+});
+
+describe('interactionSystem — depletion', () => {
+  it('depletes resource when quantity reaches 0', () => {
+    const { world, resourceData, inventory } = createTestWorld();
+    addPlayer(world, 100, 100);
+    addResource(world, resourceData, 120, 100, 'Fe', 1);
+
+    const result = interactionSystem(world, true, inventory, resourceData);
+
+    expect(result!.type).toBe('depleted');
+    expect(result!.itemId).toBe('Fe');
+    expect(resourceData.size).toBe(0);
+  });
+
+  it('removes entity from world on depletion', () => {
+    const { world, resourceData, inventory } = createTestWorld();
+    addPlayer(world, 100, 100);
+    addResource(world, resourceData, 120, 100, 'Fe', 1);
+
+    interactionSystem(world, true, inventory, resourceData);
+
+    const remaining = query(world, [Resource]);
+    expect(remaining.length).toBe(0);
+  });
+});
+
+describe('interactionSystem — inventory full', () => {
+  it('reports inventory_full when cannot add', () => {
+    const { world, resourceData } = createTestWorld();
+    const inventory = new Inventory(1, 1); // very small
+    inventory.addItem('H', 1); // fills it up
+
+    addPlayer(world, 100, 100);
+    addResource(world, resourceData, 120, 100, 'Fe', 5);
+
+    const result = interactionSystem(world, true, inventory, resourceData);
+
+    expect(result!.type).toBe('inventory_full');
+    expect(Resource.quantity[query(world, [Resource])[0]]).toBe(5); // not consumed
+  });
+});