rigging: the fabric bet is reachable — F cycles cloth/membrane in prep

FABRIC and setFabric() shipped in SPRINT6 and the sim honoured porosity
all along, but no key, click or HUD line ever reached them — every rig
ever played was DEFAULT_FABRIC. F toggles the two entries, the panel
shows the fabric, the splash teaches it, the blurb announces the switch.
Session-level assert pins the cycle, the $0 price, and the refusal of
unknown ids.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

web/world/js/hud.js

@@ -516,6 +516,7 @@ export function createHud(d) {
             ['click', 'pick an anchor · again to unpick'],
             ['[ ]', 'tension the rig — tighter holds shape, and breaks harder'],
             ['S', 'buy a spare shackle'],
+            ['F', 'choose the fabric — cloth breathes, membrane stops the rain'],
             ['E', 'repair a blown corner (ladder if it is up high)'],
             ['C', 'brace against the wind'],
             ['Enter', 'commit the rig and start the night'],

web/world/js/rigging.js

@@ -514,6 +514,15 @@ export async function createRiggingUI({
     if (ev.key === '[') session.setTension(session.tension - 0.05);
     else if (ev.key === ']') session.setTension(session.tension + 0.05);
     else if (ev.key.toLowerCase() === 's') say(session.setSpares(session.spares ? 0 : 1));
+    else if (ev.key.toLowerCase() === 'f') {
+      // The forecast bet, finally reachable. FABRIC and setFabric() shipped in
+      // SPRINT6 and the sim honoured porosity all along — but no key, click or
+      // HUD line ever reached them, so every rig ever played was DEFAULT_FABRIC.
+      // Two entries, so F is a toggle; announce the blurb because the panel
+      // line alone doesn't say what the bet IS.
+      const next = FABRIC[(FABRIC.indexOf(session.fabric) + 1) % FABRIC.length];
+      if (say(session.setFabric(next.id)).ok) onMessage(`${next.name} — ${next.blurb}`);
+    }
     else return;
     ev.preventDefault();
     refresh();
@@ -585,14 +594,14 @@ export async function createRiggingUI({
       : null;
     el.textContent = [
       `PREP — rig four corners        $${s.budget} left`,
-      `tension ${s.tension.toFixed(2)}   spare x${s.spares}${area ? `   sail ${area.toFixed(0)} m2` : ''}`,
+      `tension ${s.tension.toFixed(2)}   spare x${s.spares}   ${s.fabric.name}${area ? `   sail ${area.toFixed(0)} m2` : ''}`,
       '',
       ...rows,
       ...(standingLine ? ['', standingLine] : []),
       '',
       s.canStart ? 'ENTER to start the storm' : `pick ${MAX_CORNERS - session.picks.length} more corner(s)`,
       'click anchor: rig / cycle hw   shift-click: remove',
-      '[ ] tension    S spare    RMB orbit',
+      '[ ] tension    S spare    F fabric    RMB orbit',
     ].join('\n');
   }
 

web/world/js/rigging.selftest.js

@@ -6,7 +6,7 @@
  * js/tests/b.test.js) and node.
  */
 
-import { RiggingSession } from './rigging.js';
+import { RiggingSession, FABRIC } from './rigging.js';
 import { SailRig, TENSION_MIN, TENSION_MAX } from './sail.js';
 import { HARDWARE, START_BUDGET, SPARE_COST } from './contracts.js';
 
@@ -344,6 +344,21 @@ test('reset() returns a used session to a fresh prep phase', () => {
   return 'budget, picks, tension, spares all fresh; rig-able again';
 });
 
+test('fabric is a bet the F key can actually place (SPRINT15 — the dead mechanic)', () => {
+  const s = session();
+  assert(s.fabric.id === 'cloth', `default fabric should be cloth, got ${s.fabric.id}`);
+  // the exact call the F key makes: cycle to the other entry by id
+  const next = FABRIC[(FABRIC.indexOf(s.fabric) + 1) % FABRIC.length];
+  assert(s.setFabric(next.id).ok, 'cycling to membrane refused');
+  assert(s.fabric.id === 'membrane' && s.fabric.porosity === 0, 'membrane not applied');
+  assert(s.budget === START_BUDGET, 'fabric is a bet, not a purchase — budget must not move');
+  assert(s.summary.fabric.id === 'membrane', 'the panel reads fabric off summary and must see the change');
+  // wrap-around brings it home, and garbage is refused loudly
+  assert(s.setFabric(FABRIC[(FABRIC.indexOf(s.fabric) + 1) % FABRIC.length].id).ok && s.fabric.id === 'cloth', 'cycle should wrap back to cloth');
+  assert(s.setFabric('hessian').ok === false, 'unknown fabric must refuse, not default');
+  return 'cloth -> membrane -> cloth, $0 both ways, hessian refused';
+});
+
 export const RIGGING_TESTS = TESTS;
 
 export function runRiggingSelftest() {