Redesign the Metric comparison as direction-coloured lift bands

[isuttell]

Summary

The always-visible Metric comparison from #606 was unreadable at a glance: uniform mono numbers, absolute differences with no units, no sense of which moves mattered or which way was good. This replaces it with one line per Treatment per Metric, a colored relative difference as the only loud number, and the confidence interval drawn as a band on a fixed -100% to +100% axis.

Red and green need polarity the Metric contract did not have, so this adds a nullable direction field to the Metric and threads it through D1, the API, and the specs. A Metric without a direction stays neutral in its arm color and says so.

Changes

• New row model (metric-comparison-rows.ts): groups Decision / Guardrails / Exploratory, sorts by size of move, one Treatment per row.
• New lift band (experiment-results-comparison-lift-bar.tsx): 8px band, solid when significant, faded when not, arrow heads past the axis, threshold tick for Guardrails, bounds on hover.
• Row and header rewrite: sole Treatment named in the header with its arm color; several Treatments get a Treatment column with dots and per-row values. Verdict chips: Significant / Disputed / Breached.
• moveTone decides good / bad / breached / neutral from direction, lift, and breach; breach outranks direction.
• Contract: Metric.direction (higher_is_better | lower_is_better | null), exported enum, create/patch body field, contract test.
• D1: metrics.direction column, migration 0034_metric_direction.sql, repo patch type.
• API: direction flows through metricAnalysisConfig and the Metric response.
• Specs: leaf schema, D1 storage schema, and Metric endpoint docs.
• e2e: header assertion now matches vs control.

Risk: HIGH

• Areas touched: control-panel Results tab, @splitch/contracts Metric leaf and envelopes, @splitch/db schema + migration, control-plane-api Metric write path, specs.
• Security: none. No auth, secrets, or PII paths.
• Performance: none. Pure rendering and one nullable column.
• Breaking: additive. direction is optional on write and null on existing rows. Migration is a single ALTER TABLE ADD column.
• Not done here: Panel/CLI controls for direction, and the stats engine's Guardrail bound check still assumes higher-is-better regardless of direction.

Test plan

• pnpm verify:push (knip, format, lint, typecheck, secrets:range, tinybird:local, d1:migrate:local, d1:migrate:populated)
• pnpm verify:commit
• pnpm --filter @splitch/contracts test, @splitch/db test, @splitch/control-plane-api test, @splitch/control-panel test (one unrelated session-resync test timed out under load and passed on rerun)
• pnpm --filter @splitch/control-panel build
• pnpm d1:migrate:local applies 0034 cleanly
• Visual check of 1, 3, and 5 Variant fixtures in light and dark via a scratch Vite build
• Hosted Verify

Issue: SPL-663

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Summary by CodeRabbit

• New Features

  • Added experiment metric comparison rows with relative lift, confidence intervals, significance verdicts, guardrail indicators, and treatment labels.
  • Added a visual lift scale from −100% to +100%, including confidence bands and accessibility labels.
  • Metrics can now specify whether higher or lower values are better, including neutral when unspecified.
  • Comparison results account for missing data, zero observations, and unavailable estimates.

• Documentation

  • Updated metric schemas and API documentation to describe the optional direction setting.

• Tests

  • Expanded coverage for comparison states, metric directions, guardrails, and unavailable results.

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📝 Walkthrough

Walkthrough

The PR redesigns experiment metric comparisons around grouped relative-lift rows and fixed lift bands. It adds direction-aware tones, confidence intervals, verdicts, unavailable-result handling, and nullable metric direction support across contracts, API responses, storage, and documentation.

Changes

Metric comparison redesign

Layer / File(s)	Summary
Metric direction contract and persistence packages/contracts/..., apps/control-plane-api/..., packages/db/..., docs/spec/...	Adds nullable MetricDirection support to schemas, API create and patch handling, metric responses, database storage, and specifications.
Comparison grouping and movement tone apps/control-panel/src/lib/experiments/metric-comparison-rows.ts, apps/control-panel/src/lib/experiments/metric-move-tone.ts, apps/control-panel/src/lib/experiments/metric-move-tone.test.ts	Builds decision, guardrail, and exploratory comparison groups. Preserves missing arm data, orders rows by relative lift, and maps movement to direction-aware tones.
Comparison rows and lift-band rendering apps/control-panel/src/components/experiments/experiment-results-comparison.tsx, apps/control-panel/src/components/experiments/experiment-results-comparison-row.tsx, apps/control-panel/src/components/experiments/experiment-results-comparison-lift-bar.tsx, apps/control-panel/src/components/experiments/experiment-results-comparison-format.ts, apps/control-panel/src/components/experiments/experiment-results-comparison-value.tsx	Replaces the previous value component and table with grouped comparison rows. Adds formatted estimates, relative differences, confidence intervals, guardrail markers, verdicts, accessibility labels, and a fixed −100% to +100% lift axis.
Integration and acceptance coverage apps/control-panel/src/components/experiments/experiment-results-comparison.test.tsx, e2e/control-panel/experiment-results.spec.ts	Covers grouping, ordering, treatment labels, unavailable results, failed intervals, guardrail breaches, and the vs control header.

Priority: ➖ Normal

Estimated code review effort: 4 (Complex) | ~60 minutes

Change: Feature

Sequence Diagram(s)

sequenceDiagram
  participant ExperimentResultsComparison
  participant metricComparisonGroups
  participant ExperimentResultsComparisonRow
  participant ExperimentResultsLiftBar
  ExperimentResultsComparison->>metricComparisonGroups: Build grouped comparison rows
  metricComparisonGroups->>ExperimentResultsComparison: Return metric groups and treatments
  ExperimentResultsComparison->>ExperimentResultsComparisonRow: Render comparison row
  ExperimentResultsComparisonRow->>ExperimentResultsLiftBar: Render lift and confidence interval

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Merge Risk: 🔵 Low · up to 14d2c

Unsupported direction values could enter storage outside validated API paths. Adding the localized database constraint is recommended before merge.

🚥 Pre-merge checks | ✅ 3 | ❌ 2

❌ Failed checks (1 warning, 1 inconclusive)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 50.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 30 functions across 17 files. (4 skipped:…	Write docstrings for the functions missing them to satisfy the coverage threshold.
Linked Issues check	❓ Inconclusive	The changes implement the coding objectives in SPL-663. They add the grouped lift-band comparison, direction-aware tones, treatment labels, confidence bands, verdict handling, direction contract/API/D…	Provide evidence that pnpm d1:migrate:local applies migration 0034 cleanly, or provide equivalent migration execution test evidence.

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the primary change: redesigning metric comparison with direction-coloured lift bands.
Out of Scope Changes check	✅ Passed	The reviewed changes support SPL-663. The UI, comparison modeling, tests, contract/API/D1 direction support, migration, specifications, and E2E header update all map to the linked issue. No unrelated …

Full details: Linked Issues check

Explanation

The changes implement the coding objectives in SPL-663. They add the grouped lift-band comparison, direction-aware tones, treatment labels, confidence bands, verdict handling, direction contract/API/D1 support, migration 0034, specifications, and the listed unit and E2E coverage. The evidence does not show that pnpm d1:migrate:local applied migration 0034 cleanly, which is an explicit acceptance criterion.

Full details: Docstring Coverage

Explanation

Docstring coverage is 50.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 30 functions across 17 files. (4 skipped: 4 unsupported.)

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Actionable comments posted: 1

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Inline comments:
In `@packages/db/migrations/0034_metric_direction.sql`:
- Line 1: Update the metrics table migration’s direction column definition to
add a CHECK constraint allowing only NULL, higher_is_better, or lower_is_better,
without rebuilding the table.

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📥 Commits

Reviewing files that changed from the base of the PR and between 4ccab72 and 14d2c2a.

⛔ Files ignored due to path filters (1)

• apps/cli/src/__snapshots__/cli-help.test.ts.snap is excluded by !**/*.snap

📒 Files selected for processing (22)

• apps/control-panel/src/components/experiments/experiment-results-comparison-format.ts
• apps/control-panel/src/components/experiments/experiment-results-comparison-lift-bar.tsx
• apps/control-panel/src/components/experiments/experiment-results-comparison-row.tsx
• apps/control-panel/src/components/experiments/experiment-results-comparison-value.tsx
• apps/control-panel/src/components/experiments/experiment-results-comparison.test.tsx
• apps/control-panel/src/components/experiments/experiment-results-comparison.tsx
• apps/control-panel/src/lib/experiments/metric-comparison-rows.ts
• apps/control-panel/src/lib/experiments/metric-move-tone.test.ts
• apps/control-panel/src/lib/experiments/metric-move-tone.ts
• apps/control-plane-api/src/metric-analysis-config.ts
• apps/control-plane-api/src/metric-segment-shared.ts
• docs/spec/contracts/leaf-schemas-experiment.md
• docs/spec/contracts/storage-schemas-d1-experiment.md
• docs/spec/control-plane/endpoints-metric.md
• e2e/control-panel/experiment-results.spec.ts
• packages/contracts/src/index.ts
• packages/contracts/src/leaf-schemas-experiment-metric.test.ts
• packages/contracts/src/leaf-schemas-experiment.ts
• packages/contracts/src/resource-envelopes-account.ts
• packages/db/migrations/0034_metric_direction.sql
• packages/db/src/repo/experiments.ts
• packages/db/src/schema/experiments.ts

💤 Files with no reviewable changes (1)

• apps/control-panel/src/components/experiments/experiment-results-comparison-value.tsx

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