feat: crafting system with chemistry engine integration (Phase 4.4)

craftFromInventory checks reagent availability, runs ReactionEngine,
consumes reagents on success, adds products. Failed attempts return
educational reasons (noble gas inertness, missing conditions, etc.).
11 new tests (185 total).

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

tests/crafting.test.ts

@@ -0,0 +1,189 @@
+/**
+ * Crafting System Tests — Phase 4.4
+ *
+ * Tests: crafting from inventory, reagent consumption,
+ * product addition, failure reasons, condition checks.
+ */
+
+import { describe, it, expect } from 'vitest';
+import { Inventory } from '../src/player/inventory';
+import { craftFromInventory, type CraftInput } from '../src/player/crafting';
+
+describe('craftFromInventory — success', () => {
+  it('crafts NaCl from Na + Cl', () => {
+    const inv = new Inventory();
+    inv.addItem('Na', 3);
+    inv.addItem('Cl', 2);
+
+    const inputs: CraftInput[] = [
+      { id: 'Na', count: 1 },
+      { id: 'Cl', count: 1 },
+    ];
+    const result = craftFromInventory(inv, inputs);
+
+    expect(result.success).toBe(true);
+    expect(result.products).toContainEqual({ id: 'NaCl', count: 1 });
+    // Reagents consumed
+    expect(inv.getCount('Na')).toBe(2);
+    expect(inv.getCount('Cl')).toBe(1);
+    // Product added
+    expect(inv.getCount('NaCl')).toBe(1);
+  });
+
+  it('returns reaction data on success', () => {
+    const inv = new Inventory();
+    inv.addItem('Na', 1);
+    inv.addItem('Cl', 1);
+
+    const result = craftFromInventory(inv, [
+      { id: 'Na', count: 1 },
+      { id: 'Cl', count: 1 },
+    ]);
+
+    expect(result.success).toBe(true);
+    expect(result.reaction).toBeDefined();
+    expect(result.reaction!.id).toBe('synth_nacl');
+  });
+
+  it('reports consumed reactants', () => {
+    const inv = new Inventory();
+    inv.addItem('Na', 5);
+    inv.addItem('Cl', 5);
+
+    const inputs: CraftInput[] = [
+      { id: 'Na', count: 1 },
+      { id: 'Cl', count: 1 },
+    ];
+    const result = craftFromInventory(inv, inputs);
+
+    expect(result.consumedReactants).toEqual(inputs);
+  });
+});
+
+describe('craftFromInventory — insufficient materials', () => {
+  it('fails when missing reagent', () => {
+    const inv = new Inventory();
+    inv.addItem('Na', 1);
+    // No Cl in inventory
+
+    const result = craftFromInventory(inv, [
+      { id: 'Na', count: 1 },
+      { id: 'Cl', count: 1 },
+    ]);
+
+    expect(result.success).toBe(false);
+    expect(result.failureReason).toContain('Cl');
+    // Na not consumed
+    expect(inv.getCount('Na')).toBe(1);
+  });
+
+  it('fails when not enough of a reagent', () => {
+    const inv = new Inventory();
+    inv.addItem('Na', 1);
+    inv.addItem('Cl', 1);
+
+    const result = craftFromInventory(inv, [
+      { id: 'Na', count: 5 }, // need 5, have 1
+      { id: 'Cl', count: 1 },
+    ]);
+
+    expect(result.success).toBe(false);
+    expect(result.failureReason).toContain('Na');
+  });
+});
+
+describe('craftFromInventory — unknown reaction', () => {
+  it('fails with educational reason for no known reaction', () => {
+    const inv = new Inventory(5000); // large capacity for heavy elements
+    inv.addItem('Fe', 5);
+    inv.addItem('Au', 5);
+
+    const result = craftFromInventory(inv, [
+      { id: 'Fe', count: 1 },
+      { id: 'Au', count: 1 },
+    ]);
+
+    expect(result.success).toBe(false);
+    expect(result.failureReason).toBeDefined();
+    expect(result.failureReason!.length).toBeGreaterThan(10); // educational reason
+    // Reagents not consumed
+    expect(inv.getCount('Fe')).toBe(5);
+    expect(inv.getCount('Au')).toBe(5);
+  });
+
+  it('explains noble gas inertness', () => {
+    const inv = new Inventory();
+    inv.addItem('He', 5);
+    inv.addItem('O', 5);
+
+    const result = craftFromInventory(inv, [
+      { id: 'He', count: 1 },
+      { id: 'O', count: 1 },
+    ]);
+
+    expect(result.success).toBe(false);
+    expect(result.failureReason).toContain('noble gas');
+  });
+});
+
+describe('craftFromInventory — conditions', () => {
+  it('fails when temperature requirement not met', () => {
+    const inv = new Inventory();
+    inv.addItem('Fe', 5);
+    inv.addItem('S', 5);
+
+    // Fe + S → FeS requires minTemp: 500
+    const result = craftFromInventory(inv, [
+      { id: 'Fe', count: 1 },
+      { id: 'S', count: 1 },
+    ]);
+
+    expect(result.success).toBe(false);
+    expect(result.failureReason).toContain('temperature');
+    // Reagents not consumed
+    expect(inv.getCount('Fe')).toBe(5);
+  });
+
+  it('succeeds when conditions are met', () => {
+    const inv = new Inventory();
+    inv.addItem('Fe', 5);
+    inv.addItem('S', 5);
+
+    const result = craftFromInventory(inv, [
+      { id: 'Fe', count: 1 },
+      { id: 'S', count: 1 },
+    ], { minTemp: 500 });
+
+    expect(result.success).toBe(true);
+    expect(result.products).toContainEqual({ id: 'FeS', count: 1 });
+    expect(inv.getCount('Fe')).toBe(4);
+    expect(inv.getCount('S')).toBe(4);
+  });
+});
+
+describe('craftFromInventory — edge cases', () => {
+  it('handles empty reactants list', () => {
+    const inv = new Inventory();
+    inv.addItem('Na', 5);
+
+    const result = craftFromInventory(inv, []);
+
+    expect(result.success).toBe(false);
+  });
+
+  it('handles inventory full for products', () => {
+    const inv = new Inventory(100, 2); // Only 2 slots
+    inv.addItem('Na', 1);
+    inv.addItem('Cl', 1);
+
+    // After crafting: Na consumed (slot freed), Cl consumed (slot freed), NaCl added
+    // This should work since slots are freed before products are added
+    const result = craftFromInventory(inv, [
+      { id: 'Na', count: 1 },
+      { id: 'Cl', count: 1 },
+    ]);
+
+    expect(result.success).toBe(true);
+    expect(inv.getCount('NaCl')).toBe(1);
+  });
+});