feat(pumpingstation): warn when control engages with no machine group registered

A station engaged above startLevel computes a real demand, but if no machine
group is registered (e.g. the Port 2 parent↔group registration was dropped by a
partial redeploy) the demand is silently forwarded nowhere and the pumps never
react — invisible to the operator. levelBased now warns once when engaged with
an empty machineGroups map (throttled via host._warnedNoMachineGroup, re-arms
when a group reappears); manual.forwardDemand warns when neither a group nor a
direct machine is registered.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

test/basic/control-levelBased.basic.test.js

@@ -182,3 +182,51 @@ test('no valid level → warns and returns without mutating percControl or calli
     assert.equal(g._calls.handleInput.length, 0);
   }
 });
+
+// Regression: a station engaged above startLevel but with no machine group
+// registered (e.g. the Port 2 parent↔group registration was dropped by a
+// partial redeploy) computes a real demand that goes nowhere. The strategy
+// must surface this once, not fail silently. See the 2026-05-27 "PS not
+// reacting to level" trace.
+test('engaged with NO machine group registered → warns once (throttled via host)', async () => {
+  const ctx = makeCtx(3, { levelbased: { holdLevel: 2 } }); // level 3 > startLevel 2 → engaged
+  ctx.machineGroups = {};                                   // registration lost
+  ctx.host = {};
+  const warns = [];
+  ctx.logger.warn = (m) => warns.push(m);
+
+  const state = { percControl: 0 };
+  await levelBased.run(ctx, state);
+
+  assert.ok(state.percControl > 0, 'demand is computed even though there is no group');
+  assert.equal(warns.length, 1, 'warns exactly once');
+  assert.match(warns[0], /no machine group is registered/i);
+  assert.equal(ctx.host._warnedNoMachineGroup, true);
+
+  // Subsequent ticks while still group-less stay quiet (no log spam).
+  await levelBased.run(ctx, state);
+  assert.equal(warns.length, 1, 'throttled: no repeat warning on the next tick');
+});
+
+test('warning re-arms after a group reappears then disappears again', async () => {
+  const ctx = makeCtx(3, { levelbased: { holdLevel: 2 } });
+  ctx.host = {};
+  const warns = [];
+  ctx.logger.warn = (m) => warns.push(m);
+  const state = { percControl: 0 };
+
+  ctx.machineGroups = {};
+  await levelBased.run(ctx, state);
+  assert.equal(warns.length, 1);
+
+  // Group registers again → flag clears, no new warning.
+  ctx.machineGroups = { a: makeGroup('A') };
+  await levelBased.run(ctx, state);
+  assert.equal(warns.length, 1);
+  assert.equal(ctx.host._warnedNoMachineGroup, false);
+
+  // Group lost again → warns once more.
+  ctx.machineGroups = {};
+  await levelBased.run(ctx, state);
+  assert.equal(warns.length, 2, 're-armed after recovery');
+});