fix(levelBased): drop hold zone, route through MGC.setDemand, add holdLevel + integrator variant pick; slim npm pack

levelBased ramp + engagement:
- Ramp foot is now max(startLevel, holdLevel) — was max(startLevel,
  inflowLevel). inflowLevel is basin geometry, not a control setpoint;
  the implicit hold zone it created was causing pumps to "start at
  inflowLevel" instead of startLevel.
- New optional `holdLevel` config (defaults to startLevel = no hold band).
  When raised, pumps engage at startLevel and hold at 0 % = MGC flow.min
  across [startLevel, holdLevel], then ramp 0..100 % to maxLevel.
- Engagement decided in run() (not in `_applyMachineGroupLevelControl`):
  rising-edge hysteresis arming gates a clean turnOff early-return.
  Once armed, the helper always forwards setDemand(pct, '%') — 0 %
  legitimately means "engaged at min flow", no more soft-turnOff at
  the boundary.
- Disengagement paths (minLevel hard-stop, stopLevel falling-edge,
  pre-arming idle) now all clear the shifted-ramp hysteresis state too.
- Threshold validator drops the startLevel ≤ inflowLevel rule; adds
  startLevel ≤ holdLevel < maxLevel (only checked when holdLevel is
  explicitly set, so default-null doesn't false-flag).

MGC unit math:
- Replace direct group.handleInput(percent) with group.setDemand(pct, '%')
  in _applyMachineGroupLevelControl. The percent → m³/s resolution now
  lives in MGC.setDemand (committed separately in the MGC submodule).

FlowAggregator variant picking:
- New _pickFlowSum() helper mirrors selectBestNetFlow's variant
  precedence (measured first, then predicted) and resolves each side
  independently. Realistic mixed case — real measured upstream sensor +
  predicted pump outflow — now feeds the predicted-volume integrator.
  Was reading only `flow.predicted.*` so a real upstream sensor
  (which writes `flow.measured.*`) never moved the level.

Editor:
- New `holdLevel` and `deadZoneKeepAlivePercent` defaults + side-panel
  input rows in the levelbased mode preview.
- Add the missing `ps-mode-line-holdLevel` SVG marker (was declared in
  the side-panel coupling but the SVG element didn't exist, so the
  dashed line never rendered).
- Relax stopLevel marker gate so it renders for any non-negative typed
  value — start/stop ordering is the ribbon's job, not the marker's
  (was hiding the line whenever startLevel was momentarily smaller).
- Add holdLevel to the marker loop in mode-preview so changes track.
- Add stopLevel + holdLevel + maxLevel to all three bindRedraw lists
  (basin-diagram, mode-preview, bounds.apply) so the SVG, validation
  ribbon, and HTML5 min/max attrs update on every edit.
- Initialise stopLevel + holdLevel + deadZoneKeepAlivePercent inputs
  in oneditprepare so reopening the editor shows the saved values.
- nodeClass passes holdLevel + deadZoneKeepAlivePercent into the
  domain config.

Tests:
- New test/basic/_probe_upstream_emit.test.js: confirms the parent
  surfaces flow.measured.upstream.* on Port 0 after a measurement
  child write — pins the previously-invisible measured variant flow.
- flowAggregator.basic.test.js: two new regression cases — measured
  inflow when predicted side is empty, and the measured-in /
  predicted-out mixed case.
- control-levelBased.basic.test.js: new cases for the holdLevel hold
  band, the [stopLevel, startLevel] keep-alive, the engagement gate,
  and the "0 % at startLevel = setDemand" contract.
- specificClass.test.js: zone tests adjusted to the new ramp foot.
  Shifted-ramp tests pin holdLevel = 3 explicitly so their legacy
  arithmetic (ramp foot at inflowLevel) stays self-consistent.
- shifted-ramp-end-to-end.test.js: same holdLevel pin for the same
  reason.

Packaging:
- Add .gitignore + .npmignore so the published tarball drops the
  wiki/, simulations/, test/, tools/, .claude/ etc. The pack went
  from 1.5 MB (72 files) to ~57 KB (30 files).

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

src/editor/mode-preview.js

@@ -23,13 +23,16 @@
       const svg = document.getElementById('ps-levelbased-mode-diagram');
       if (!svg) return;
       const start = fNum('startLevel');
+      const hold  = fNum('holdLevel');
       const inlet = fNum('inflowLevel');
       const max = fNum('maxLevel');
       // Optional stopLevel — explicit pump-off threshold. Drawn as its
-      // own marker line; does NOT shift the ramp foot. Must be < startLevel
-      // for the marker to render.
+      // own marker line; does NOT shift the ramp foot. Renders as long as
+      // the typed value is a non-negative number — the start-vs-stop
+      // ordering check belongs to the validation ribbon, not the visual
+      // marker (otherwise the line vanishes while the user is mid-edit).
       const stopRaw = fNum('stopLevel');
-      const stop = Number.isFinite(stopRaw) && stopRaw >= 0 && Number.isFinite(start) && stopRaw < start ? stopRaw : null;
+      const stop = Number.isFinite(stopRaw) && stopRaw >= 0 ? stopRaw : null;
       // dryRunLevel is derived from the basin's outflowLevel + dryRun%
       // (no separate input). Below dryRunLevel the runtime hard-stops;
       // we draw it as the leftmost vertical marker so the user sees
@@ -91,18 +94,17 @@
       };
 
       // Up curve. Engagement edge is startLevel (pump-on threshold); the
-      // ramp foot is inflowLevel — matching the runtime in
-      // _controlLevelBased, which scales demand over [inflowLevel, maxLevel].
-      // The OFF baseline is drawn for level < startLevel; between startLevel
-      // and inflowLevel demand sits flat at 0 % (system armed but not yet
-      // ramping); from inflowLevel demand ramps to 100 % at maxLevel.
+      // ramp foot is holdLevel, with a Math.max(startLevel, …) safety
+      // floor — matching the runtime in levelBased.run.
+      //   - holdLevel == startLevel (default): no hold band, 0..100 % across
+      //     [startLevel, maxLevel].
+      //   - holdLevel > startLevel: pumps engaged across [startLevel,
+      //     holdLevel] at 0 % (= MGC flow.min), then 0..100 % across
+      //     [holdLevel, maxLevel].
       const up = document.getElementById('ps-mode-curve-up');
       const down = document.getElementById('ps-mode-curve-down');
       const downLabel = document.getElementById('ps-mode-curve-down-label');
-      // Runtime falls back to startLevel when inflowLevel is missing
-      // (basin?.inflowLevel ?? cfg.inflowLevel ?? startLevel); mirror that
-      // in the preview so the curve is still drawn instead of blank.
-      const upFoot = Number.isFinite(inlet) && inlet > start ? inlet : start;
+      const upFoot = Number.isFinite(hold) && hold > start ? hold : start;
       if (up) up.setAttribute('points', buildPath(start, upFoot, max));
 
       // Shifted-DOWN curve (only when shift enabled): represents the
@@ -167,6 +169,7 @@
         ['dryRunLevel', dryRun],
         ['startLevel', start],
         ['stopLevel', stop],
+        ['holdLevel', hold],
         ['inflowLevel', inlet],
         ['maxLevel', max],
         ['overflowLevel', overflow],