fix(ui): TrendChart renders a gap for null points instead of a fabricated 0

[bitfathers94]

fix(ui): TrendChart renders a gap for null points instead of a fabricated 0

Sparkline already breaks its line on a null TrendPoint via connectNulls={false};
TrendChart's plain-SVG values prop only accepted number[], so the calibration and
slop/duplicate trend cards coerced a null (below-sample-floor) point to 0 before
handing it off, plotting a fake 0% right above a "—" in the same card. TrendChart
now accepts nullable values and splits the path into a fresh sub-path per
contiguous run, and the two model helpers keep nulls instead of substituting 0.
Also gives each of the four TrendChart instances its own aria-label instead of
the shared "Trend chart" string.

Closes #9674

UI Evidence

Viewport · Theme	Before	After
Desktop · Dark	before	after
Tablet · Dark	before	after
Mobile · Dark	before	after

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✅ LoopOver review result - approve/merge recommended

_{Review updated: 2026-07-29 22:26:24 UTC}

12 files · 1 AI reviewer · no blockers · readiness 93/100 · CI green · clean

✅ Suggested Action - Approve/Merge

• safe to merge

Review summary
This fixes a real bug: TrendChart previously coerced null (below-sample-floor) points to 0, so calibration and slop/duplicate cards plotted a fabricated 0% next to a "—" label in the same card. The fix correctly threads `number | null` through TrendChart, splits the path/area into per-run sub-paths on null so the line and fill both break instead of interpolating, and the two model helpers now preserve nulls instead of substituting 0. It also fixes a real a11y bug by giving each of the four TrendChart call sites a distinct aria-label instead of the shared "Trend chart" string, with solid test coverage across both changes (empty/all-null/leading/trailing-null edge cases, per-run area closing, and label uniqueness).

Nits — 6 non-blocking

• apps/loopover-ui/src/components/site/trend-chart.tsx:32 — `runs.length` in `prevIndex === i - 1 && runs.length` is redundant since `prevIndex` starts at -1 and can't equal `i-1` before a run exists; harmless but could be simplified to just `prevIndex === i - 1`.
• Several TrendChart height/width literals (96, 80, 40) are pre-existing style, not introduced by this diff's logic change, but a named constant would help readability per the external brief.
• apps/loopover-ui/src/components/site/trend-chart.tsx — the two block comments explaining sub-path/area splitting are a bit verbose for the non-obviousness of the logic; could be tightened to one line each.
• Consider extracting the run-splitting logic in trend-chart.tsx into a small named helper (e.g. `splitIntoRuns`) to make the useMemo body easier to scan, though current inline form is not incorrect.
• The screenshot evidence provided shows unrelated sign-in page images with no visible diff — worth flagging to the contributor that the attached UI evidence doesn't actually demonstrate the fix; the code change itself is what should be judged here.
• Possible screenshot-table issue: pair 1 — Advisory only — verify the screenshot-table images against the stated change before deciding.

Decision drivers

• ✅ Code review — No blockers (1 reviewer)
• ✅ Gate result — Passing (No configured blocker found.)

Context & advisory signals — never blocks the verdict

Signal	Result	Evidence
Linked issue	✅ Linked	#9674
Related work	✅ No active overlap found	No same-issue or scoped active PR overlap found.
Change scope	✅ 20/20	Low review scope from cached public metadata (1 linked issue).
Validation posture	⚠️ 20/25	Preflight is ready, but the PR body does not name the validation run.
Contributor workload	✅ 10/10	Author activity: 101 registered-repo PR(s), 69 merged, 1 issue(s).
Contributor context	✅ Confirmed Gittensor contributor	bitfathers94; Gittensor profile; 101 PR(s), 1 issue(s).
Improvement	✅ Minor	risk: clean · value: minor · LLM: moderate

Linked issue satisfaction

Addressed
The diff implements TrendChart with a required label prop and nullable ReadonlyArray<number|null> values that split into multiple M sub-paths per contiguous run, excludes nulls from min/max, and renders empty d/area for all-null input; both model helpers (calibrationTrendValues, chartValuesForSeries) now preserve null instead of coercing to 0, and all four call sites pass distinct labels, matching

Review context

• Author: bitfathers94
• Role context: outside_contributor
• Public audience mode: oss maintainer
• Lane context: Repository is configured for direct PR review.
• Public profile languages: TypeScript
• Official Gittensor activity: 101 PR(s), 1 issue(s).
• PR-specific overlap: none found.

Contributor next steps

• Start here: Add validation command/output.

Signal definitions

• Related work = same linked issue, overlapping active PRs, or title/path similarity.
• Change scope = cached public metadata such as size labels, draft state, and review-burden hints.
• Validation posture = whether the PR provides enough public validation/test evidence for maintainer review.
• Contributor workload = public contributor activity and cleanup pressure, not a repo-wide quality failure.
• Contributor context = public GitHub/Gittensor identity context; non-Gittensor status is not a blocker.

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Visual preview

Route	Viewport	Before (production)	After (this PR's preview)	Diff
/app/analytics/test	desktop	before /app/analytics/test	after /app/analytics/test	—
/app/analytics/test	mobile	before /app/analytics/test (mobile)	after /app/analytics/test (mobile)	—
/app/analytics	desktop	before /app/analytics	after /app/analytics	—
/app/analytics	mobile	before /app/analytics (mobile)	after /app/analytics (mobile)	—

Click any thumbnail to open the full-size screenshot. Before = production · After = this PR's preview deploy.

Scroll preview

Route	Before (production)	After (this PR's preview)
/app/analytics/test	before /app/analytics/test (scroll)	after /app/analytics/test (scroll)
/app/analytics	before /app/analytics (scroll)	after /app/analytics (scroll)

A short scroll-through clip (desktop) — click either thumbnail to open the full animation. Evidence for scroll-linked behavior a single screenshot can't show.

_{🟩 Safe / merged · 🟦 Advisory · 🟨 Held for review · 🟥 Blocked / closed}

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[superagent-security]

Superagent didn't find any vulnerabilities or security issues in this PR.

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LoopOver approves — the gate is satisfied and CI is green.