strictNullChecks slice 2: instrument widgets + context-less misfiling fix (#6, #209)

[mairas]

Slice 2 of the strictNullChecks migration (#6), plus the folded-in #209 fix you OK'd.

Widget slice (268 issues, betterer baseline 842 → 574)

The mechanical instrument-widget families, migrated by three Sonnet agents on disjoint files under hard guardrails (no !, casts, any, or suppressions — honest type widening + real guards only). I reconciled, scanned every diff, and reviewed the null-semantics.

• gauges — gauge-steel, gauge-ng-linear, gauge-ng-radial, simple-linear: optional inputs typed T | undefined; theme() guarded before deref; cfg/theme effects early-return during the pre-merge startup window.
• boolean SVG — button/switch/light: data/theme inputs and colour fields widened to their real null defaults (colour fields feed [attr.*] bindings, which accept null); guards mirror the parent widget.
• numeric/slider — SK values widened to number | null and skipped (not coerced) when null, so a timeout/sensor-loss null can't corrupt tracked min/max or reach .toFixed(); canvas context threaded as a narrowed local.

Two edge-case behavior fixes (deliberate — flagging per behavior-preservation)

The honest typing surfaced two genuine bugs; both are consciously fixed, not preserved:

• gauge-steel zone bounds: a zone with an undefined bound previously produced a NaN steelseries section bound (the !== null clamp missed undefined → convertToUnit(units, undefined) → NaN). Now clamps to min/max, as the adjacent comment always intended. Real-bounded zones are unchanged.
• minichart.verticalChart: typed boolean | null (was inferred null) so widget-numeric can assign it. Null default and truthy usage unchanged — a one-line cross-file unblock.

#209 — context-less values misfiled

DataService.setPathContext filed a delta value with an empty/absent context under a literal "undefined.<path>" key, so widgets subscribed to self.<path> never saw it. Folded empty/undefined context to the self root (per the ISkPathData/IMeta "empty context assumes Self" contract). Foreign contexts still route to their own root. Two end-to-end DataService tests pin both directions.

Coverage note

The touched widgets have no unit specs (canvas rendering isn't unit-testable and none existed). Validated via AOT build (strictTemplates over every widened binding), lint, and betterer:ci. The #209 fix has real tests.

Remaining under #6

Charts — widget-data-chart (164) and widget-windtrends-chart (100) — are the least mechanical and stay for slice 3, along with widget-autopilot (65) and the remaining components.

Verification

npm run lint, npm run build:dev (AOT/strictTemplates), and betterer:ci (574) all pass; no file regressed vs the baseline; data.service specs pass locally.

Refs #6
Closes #209

[mairas]

Code review — PR #210 (strictNullChecks slice 2: instrument widgets + #209)

Scope: 11 source files + a spec vs main (base 027c6bdd). Mode: interactive, 5 persona reviewers (correctness, adversarial, testing, maintainability, project-standards), each in its own fresh context. Security/api-contract/reliability were not selected — this display-widget diff touches no auth, contract, or error-handling surface.

Headline: no bugs — every null-guard replaces a path where the original code dereferenced undefined and crashed, so the guarded paths are strictly safer, and fallback values were confirmed to match each widget's own DEFAULT_CONFIG. #209 was verified unbreakable (adversarial tried to construct misrouting and couldn't). The findings are four behavior deltas the null-safety work pulled in (two flagged in the PR, two more found here) that need conscious sign-off, one scope-creep config change to revert, and the expected test gap.

P2 — behavior changes to accept or revert

#	File	Change	Reviewers	Conf
1	gauge-steel.component.ts	Open-ended metadata zones now render as full colored bands. A zone with an unset bound + a recognized unit produced an invisible/NaN steelseries section on base; it now clamps to min/max and paints a band (e.g. a battery low-alarm {upper: 11.5} now shows a red band from gauge-floor→11.5). Open-ended zones are the common SK alarm case, so this is visible on real configs. Also changes zone sort order (base's NaN comparator was non-deterministic). Correct/safety-relevant (alarm zones were silently invisible), but not behavior-preserving.	adversarial (0.80), correctness (0.85)	0.85
2	widget-numeric.component.ts	Min/Max survives null sensor dropouts. Base wiped Min or Max (by sign) to -- on every null delta (null < 3 → 0 < 3 → true → minValue = null); the new if (dataValue !== null) skip preserves the tracked extremes. More correct, but the Min/Max readout visibly differs after any dropout.	correctness (0.90), adversarial (0.82), testing (0.82)	0.90
3	widget-numeric / gauge-steel	No tests for #1 and #2. The widgets ship no specs; these are exactly the class of behavior change that slipped past type-checking last slice and was caught only by vitest. #209 has good coverage; these don't.	testing (0.82), correctness, adversarial, maintainability	0.82
4	widget-simple-linear / widget-gauge-ng-*	displayScale fallback solved three ways. widget-slider centralizes it in getScaleBounds(); simple-linear and the gauge-ng widgets inline magic literals (?? 15, ?? 100) that duplicate each widget's DEFAULT_CONFIG.displayScale. Values verified correct today, but nothing links them — editing the config leaves the fallbacks stale.	maintainability (0.72)	0.72

P3 — smaller

#	File	Issue	Reviewers	Conf
5	widget-slider.component.ts	Scope creep: convertUnitTo: null deleted from DEFAULT_CONFIG.paths.gaugePath. IWidgetPath.convertUnitTo is typed `string	null`, so strictNullChecks did not require it, and the streams directive treats null/undefined identically (inert). An unrelated shipped-default change in a type-safety PR. → revert.	maintainability (0.65), project-standards
6	gauge-steel.component.ts	theme-null divergence: most widgets early-return if (!theme) return; gauge-steel keeps rendering with a transparent ?? "rgba(0,0,0,0)" fallback. Arguably intentional (draw zones without a theme) but undocumented. → one-line note.	maintainability (0.60)	0.60

Verified clean (adversarial + correctness)

#209 setPathContext fold — foreign/self routing identical to base; only empty/undefined context changes (the intended fix); _selfUrn-mutation path preserved. minichart verticalChart — pure type widening. setMiniChart ?? 1/0/10 — matches DEFAULT_CONFIG. boolean-SVG guards — replace crashes only. No any/!/casts/suppressions; version-bump exempt; serving-path untouched.

Coverage

5/5 reviewers returned. No P0/P1. Suppressed: a couple of pre-existing awareness notes (cfg.paths?.['x'].y guards paths not the entry — pre-existing). Residual: setMiniChart differs only for configs omitting numDecimal/yScale* (low likelihood; fallbacks are the sensible defaults).

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Verdict: Ready with decisions. No defects. Decide whether to keep the two behavior improvements (#1 gauge zones, #2 numeric min/max) — both are more correct and #1 is safety-relevant (visible alarm zones) — or preserve base behavior and file them separately. Revert the scope-creep config change (#5). Tests for #1/#2 recommended (extract the numeric min/max reducer to a pure function is the cheap path; gauge-steel zones via a steelseries.Section spy).

[mairas]

Review addressed (commit d66b2141)

Decision: kept both behavior improvements, with tests (they're more correct; the gauge fix makes marine alarm zones visible).

All four behavior deltas (two were flagged in the PR, two surfaced by review — now all documented):

1. gauge-steel: open-ended metadata zones (unset bound) render as a band clamped to min/max instead of an invisible NaN section.
2. gauge-steel: zone sort order is now deterministic (base's a.lower - b.lower was NaN for unset lowers).
3. widget-numeric: Min/Max survive null sensor dropouts (base wiped min-or-max to -- on every null via null < x → 0 < x).
4. minichart.verticalChart: boolean | null type (pure type widening, no runtime change).

Tests added:

• reduceMinMax() extracted to a pure util + unit test, including the null-preserves-extremes regression guard.
• gauge-steel spec drives buildOptions() with an open-ended low-alarm zone and asserts the clamped band Section(10, 11.5, …).

Finding #5 (convertUnitTo scope creep) — dismissed after verification. Restoring convertUnitTo: null breaks the build: the governing IWidgetPath.convertUnitTo is typed string (the string | null at widgets-interface.ts:386 is a different interface). The agent's removal was a required strict fix, not scope creep.

Deferred: finding #4 (three widgets inline ?? 15/?? 100 displayScale fallbacks vs slider's getScaleBounds() helper). Values verified to match each widget's DEFAULT_CONFIG today; it's a drift-risk, not a bug, so consolidating is left out to keep this PR scoped. #6 theme-null divergence got a one-line note on gauge-steel.

All gates green: lint, build:dev (AOT/strictTemplates), betterer:ci (574), and the affected specs (numeric-util, gauge-steel, data.service — 21 tests).