[pbroom]

Contrast regions keep both solvers, but the caller now selects one and the
engine never switches implicitly.

• Add engine?: 'hybrid' | 'legacy' (default 'hybrid').
  ContrastRegionPathOptions is now a union discriminated by engine
  (ContrastRegionHybridOptions | ContrastRegionLegacyOptions, sharing
  ContrastRegionBaseOptions). The legacy-only options (samplingMode
  'uniform'/'adaptive', edgeInterpolation, adaptiveBaseSteps,
  adaptiveMaxDepth) require engine: 'legacy', and hybridMaxDepth /
  hybridErrorTolerance are hybrid-only. Mixing them is a type error and
  always throws a TypeError at runtime, as do unknown engines. Legacy
  samplingMode defaults to 'adaptive' when adaptive* is set, otherwise
  'uniform'; samplingMode 'hybrid' is gone.
• Plane contrast queries (PlaneContrastQueryOptions and the
  contrastBoundary/contrastRegion query types, now type aliases over the
  union), driver ColorAreaContrastRegionOptions, and inspectPlaneQuery pass
  engine and the engine options through, so invalid combinations are
  rejected the same way instead of being dropped by a field whitelist.
  Scheduler budgets and telemetry signatures follow the selected engine.
• The hybrid engine no longer hands failed queries to the legacy engine.
  It returns its best-effort paths and records
  trace.summary.degradedReason (ContrastHybridFallbackReason is renamed
  ContrastHybridDegradedReason). It bisects lightness intervals whose ends
  are root-free on opposite sides of the threshold, localizes branch ends
  a little past hybridMaxDepth, and keeps splitting (with the extra depth)
  while index-matched roots of neighbouring samples differ by more than
  0.03 chroma, half the branch join distance. Nearly constant-lightness
  contours previously stopped splitting there and left gaps; in a
  720-query brute-force sweep, crossings more than 0.03 from the traced
  path drop from 67 to 0 for about 1.7% more evaluations. Thin regions
  at the top of the lightness range (vertical boundary, no chroma roots)
  still degrade with 'unresolved-sign-change'; the legacy engine finds
  them.
• ContrastRegionLayer passes engine: 'legacy' explicitly (it already ran
  the legacy solver through edgeInterpolation), keeping its fill accuracy
  and speed. Its samplingMode prop is 'uniform' (default) or 'adaptive',
  and the no-op hybridMaxDepth / hybridErrorTolerance props are removed.
• Compute scheduler: only the JS backend exists, so drop the speculative
  webgpu backend kind, preferred-backend selection, warmup, baseline
  probes, circuit breakers, and their options/telemetry fields.
  PlaneComputeBackendKind is 'js' and every run reports 'default-js'.
  Also fix LRU eviction, which evicted the newly created bucket.
• Tests: engine selection and validation (runtime and type level), plane
  query pass-through, regression cases checked against a brute-force
  grid of the public checks, and degraded-reason cases. Docs and benches
  cover both engines.

BREAKING CHANGE: legacy contrast options require engine: 'legacy' and
hybrid options are rejected with it; samplingMode 'hybrid' is removed;
the hybrid solver no longer falls back to the legacy solver; the
ContrastRegionLayer hybridMaxDepth/hybridErrorTolerance props, the
'webgpu' backend kind, and the scheduler's multi-backend options and
circuitBreakers telemetry are removed.

Part of a stacked set of PRs (#204 → #221) from the color-kit assessment. Validated per branch with pnpm build and pnpm test; lint, format, typecheck, size, artifact, preprod and agents checks pass at the top of the stack.

🤖 Generated with Claude Code

[pbroom]

• refactor(react)!: remove UI components; ship state and plane hooks only #249
• docs(react): rebuild the React docs around the plane hooks #248
• feat(react): add plane renderer, geometry and adaptive-quality hooks #247
• feat(docs): syntax highlighting palette for code samples #246
• feat(docs): native API map at /api/map #245
• docs: add concept pages, guides and entry-point narratives #244
• feat(docs): live plane hero on home and the example system #243
• feat(docs): generated API reference from TypeDoc JSON #242
• refactor(core)!: derive plane query budgets from step counts and drop PlaneWithSense #241
• fix(react): render input aria-label once, on the inner input #240
• fix(driver): map absolute percents as range positions and keep tiny-step precision #239
• fix(core): uncap saturate chroma and resolve planeHue as an OKLCH hue #238
• fix(driver): reject unknown gamuts and align validation error types #237
• chore(docs): remove Sandpack, the shadcn kit and the legacy docs shell #236
• docs(core,driver,react): document the public API #235
• chore: pin control-kit to a commit with its own pnpm workspace #234
• docs: update implementation backlog for the contrast solver replacement #232
• refactor(react)!: remove ColorPlane's deprecated edge option and webgl renderer alias #231
• fix(driver): validate the gamut in getColorAreaFallbackPoint #230
• feat(driver,react): keep the previous hue when an achromatic color is entered #229
• refactor(core)!: replace the hybrid contrast solver with chroma-column tracing #228
• perf(core): trim what contrastRatio pulls in #227
• perf(core): pack the named-color table #226
• feat(core): point 'p3' users to 'display-p3' #225
• chore: ignore local .claude files in prettier #224
• refactor(core)!: retire the legacy contrast-region engine #223
• fix(core): keep hybrid contrast contours connected through folds #222
• chore: add changesets for the assessment stack #221
• docs: generated API reference and repo polish #220
• chore: adopt changesets for versioning and release notes #219
• chore: fix facade peers, licensing, and lint ignores #218
• refactor(react): reuse core contrast and transfer functions #217
• refactor(core)!: make the contrast-region engine explicit #216 👈 (View in Graphite)
• refactor(core)!: remove pre-launch aliases and trim the root export surface #215
• refactor!: name the Display P3 space 'display-p3' everywhere #214
• refactor(driver): share pointer drag throttling between slider and area #213
• feat(react): keyboard, ARIA, disabled, and focus support for sliders and areas #212
• fix(react): stable refs, WebGL context loss, and handler composition #211
• fix(react): apply controlled updates against the latest snapshot #210
• feat(core): selectable gamut mapping method #209
• fix(core): compute contrast from unrounded values #208
• fix(core): consistent achromatic hue handling and single transfer function #207
• feat(core): parse CSS Color 4 syntax #206
• fix(core): reject malformed color input instead of producing NaN #205
• chore: add fast-check and axe-core test dependencies #204
• docs: graphics and performance APIs demo page #203
• feat(core): tuple and typed-array interop for GPU and three.js #202
• feat(core): allocation-free *Into variants for hot paths #201
• feat(core): interpolation space option for mix/interpolate/generateScale #200
• main

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[greptile-apps]

Confidence Score: 4/5

[High risk] Refactors the contrast region computation engine and scheduler.

The PR should not merge until the React layer respects adaptive controls supplied without an explicit sampling mode.

Findings

1.  Adaptive controls are ignored ▶
2.  Zero bucket limit is exceeded ▶

Summary

This PR makes contrast-region engine selection explicit, returns trace-marked best-effort hybrid results instead of implicitly switching solvers, and simplifies plane compute scheduling to the JS backend.

• Contrast options, plane queries, the driver, and the React layer now carry the selected engine.
• Hybrid refinement and regression coverage expand; scheduler telemetry and eviction are simplified.
• The React layer’s default suppresses adaptive controls supplied without a sampling mode, and zero-capacity telemetry is not honored.

Diagram

%%{init: {'theme': 'neutral'}}%%
flowchart TD
  A[Contrast region query] --> B{Engine}
  B -->|default hybrid| C[Root tracing]
  B -->|legacy| D{Sampling mode}
  D -->|uniform| E[Fixed grid]
  D -->|adaptive| F[Adaptive grid]
  C --> G[Paths and optional degraded reason]
  E --> H[Paths]
  F --> H

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_{Reviews (1) · Last reviewed commit: "refactor(core)!: make the contrast-regio..."}

[pbroom]

Merge activity

• Oct 10, 6:47 PM UTC: A user started a stack merge that includes this pull request via Graphite.
• Oct 10, 7:22 PM UTC: Graphite rebased this pull request as part of a merge.
• Oct 10, 7:22 PM UTC: @pbroom merged this pull request with Graphite.