Re-point stale-reading fix covers three widgets; the seam and the other 13 do not

[mairas]

What

#534 was fixed in the three ng-gauges (radial, linear, compass) by comparing widgetPathSignature() across effect runs and clearing the reading when it changes. The same defect is still live in every other widget that holds stream-derived presentation state, and the scaffolding still emits the vulnerable shape.

Why it happens

WidgetStreamsDirective rebuilds a subscription on a re-point, and DataService seeds each path with a BehaviorSubject, so the new path's value replays immediately — for most widgets that replay includes a leading null, which clears the display on its own. A widget that sets suppressBootstrapNull: true filters that null, so against a path that reports nothing the callback never runs at all and the previous path's reading stays on screen, presented as a live reading of the new path.

Scope

• grep -rl streams.observe src/app/widgets matches 16 components; three carry the fix.
• widget-gauge-steel still has the pre-fix shape, including the unconditional effectiveUnit.set('') the linear gauge replaced.
• widget-simple-linear keeps dataValue / dataLabelValue / effectiveUnit across a re-point.
• widget-numeric rolls its own subscription signature (including updateInterval, and without path normalization) and its own reset — a second convention for one concept.
• tools/schematics/create-host2-widget/.../widget-__name@dasherize__.component.ts.template scaffolds if (pathCfg.path) { this.streams.observe(...) } with no clear, so a widget generated the documented way starts out with the bug.

Two other findings from the same review

• The reset sits in the wrong place. WidgetStreamsDirective already computes the signature and already knows the moment it rebuilds a subscription (it stores {sub, signature} per path). A hook there would fix every consumer at once and remove the need to export widgetPathSignature at all. The current arrangement also depends on each widget passing a new closure to observe() on every effect run: the directive compares callback identity, so a stable reference — which the directive's own docs recommend — would make it early-return and leave the gauge blank on a live path until the next delta. widget-numeric already sits on that side.
• Zone bands are not covered by the widget-side clear. WidgetMetadataDirective.observe() returns early on a falsy path without resetting _meta, and the gauges' highlights computed gates on zones/cfg/theme but never on whether a path is configured. Clearing a widget's path therefore leaves the previous path's warn/alarm bands painted around a gauge showing --. Verified against the real directive: zones().length stayed at 2 after applyMetaConfigDiff with path: null and with path: ''. widget-metadata.directive.ts has no spec file at all.

Suggested order

Move the reset into WidgetStreamsDirective, migrate the three gauges and widget-numeric onto it, fix the schematic template, then handle the metadata directive's cleared-path case.