Implement Enhancements, Mainline modifiers and Maneuvers; fix unplayable track

test/apply.test.ts

@@ -57,6 +57,7 @@ const straight = (standing: TrackCard['standing'] = []): TrackCard => ({
   standing,
   facility: null,
   modifiers: [],
+  enhancements: [],
 });
 
 // ---------------------------------------------------------------------------
@@ -325,6 +326,7 @@ describe('Freight Agent operations (§6.3)', () => {
         usedThisStage: { laborers: 0, porters: 0 },
       },
       modifiers: [],
+  enhancements: [],
     });
     return coord;
   }
@@ -421,6 +423,7 @@ describe('Load/Unload: the four-action freight pipeline (§9.3)', () => {
         usedThisStage: { laborers: 0, porters: 0 },
       },
       modifiers: [],
+  enhancements: [],
     });
     s.clock.phase = 'loadUnload';
     return coord;
@@ -561,6 +564,7 @@ describe('legalActions shares its rules with apply (component 6)', () => {
         usedThisStage: { laborers: 0, porters: 0 },
       },
       modifiers: [],
+  enhancements: [],
     });
     assert.deepEqual(chooseOptions(s), ['draw', 'freightAgent', 'switch']);
   });