Remove sprite-generator color helper APIs

[andorthehood]

Problem Description

The @8f4e/sprite-generator package currently exposes a small set of color derivation helpers:

• lighten
• darken
• alpha
• mix

These helpers are implemented in packages/editor/packages/sprite-generator/src/color-helpers.ts, re-exported from the package entrypoint, documented in the package README, and used by the example file packages/editor/packages/sprite-generator/examples/derived-color-scheme.ts.

If the project no longer wants to support helper-driven derived color schemes as part of the sprite-generator package surface, these exports and their supporting materials should be removed completely.

Important context:

• the software is not released yet
• backward compatibility is not a constraint for this cleanup
• sprite generation itself does not depend on these helpers

Proposed Solution

Remove the color-helper API surface from @8f4e/sprite-generator and clean up all package-local references.

Scope of removal:

• remove the public re-exports from the package entrypoint
• delete the helper implementation file
• delete helper-specific tests
• remove or rewrite helper-focused docs
• remove or rewrite the derived color-scheme example that imports these helpers

Preferred outcome:

• @8f4e/sprite-generator exposes only the sprite/color-scheme functionality that is still intended to ship
• no documentation or examples imply that helper-based derived palettes are part of the package

Anti-Patterns

• Do not leave dead exports in the public API.
• Do not keep the example file importing removed helpers.
• Do not leave README sections advertising helper functions that no longer exist.
• Do not add compatibility shims unless there is a concrete migration need.

Implementation Plan

Step 1: Remove the helper exports

• Update packages/editor/packages/sprite-generator/src/index.ts to stop exporting lighten, darken, alpha, and mix.
• Confirm no other package entrypoints re-export them indirectly.

Step 2: Remove implementation and tests

• Delete packages/editor/packages/sprite-generator/src/color-helpers.ts.
• Delete packages/editor/packages/sprite-generator/tests/color-helpers.test.ts.

Step 3: Clean up examples and docs

• Remove or rewrite packages/editor/packages/sprite-generator/examples/derived-color-scheme.ts.
• Update packages/editor/packages/sprite-generator/README.md to remove:
  • the Color Helpers section
  • helper usage examples
  • helper API reference entries
• Clean up any references in repo docs that still describe these helpers as active functionality.

Step 4: Verify package integrity

• Run package tests and typecheck after the cleanup.
• Confirm there are no remaining imports of the removed helpers.

Validation Checkpoints

• rg -n "lighten|darken|alpha|mix" packages/editor/packages/sprite-generator docs
• npx nx run sprite-generator:test
• npx nx run sprite-generator:typecheck

Success Criteria

• @8f4e/sprite-generator no longer exports lighten, darken, alpha, or mix.
• The helper implementation and its tests are removed.
• The derived color-scheme example is removed or rewritten so it does not rely on helper APIs.
• Package docs no longer describe helper-based color derivation as supported behavior.
• Package tests and typecheck pass after the cleanup.

Affected Components

• packages/editor/packages/sprite-generator/src/index.ts - remove helper re-exports
• packages/editor/packages/sprite-generator/src/color-helpers.ts - remove implementation
• packages/editor/packages/sprite-generator/tests/color-helpers.test.ts - remove helper tests
• packages/editor/packages/sprite-generator/examples/derived-color-scheme.ts - remove or rewrite helper-based example
• packages/editor/packages/sprite-generator/README.md - remove helper documentation
• docs/todos/_index.md - optional cleanup if active TODO index text still references color helpers as current package scope

Risks & Considerations

• Doc drift: README, examples, and todo index references can easily get out of sync if only code is removed.
• Hidden imports: verify there are no remaining internal imports of lighten, darken, alpha, or mix.
• Intent clarity: if derived color schemes are still desirable later, reintroduce them deliberately under a different API instead of leaving partial remnants now.

Related Items

• docs/todos/303-dedupe-font-atlas-rows-for-identical-text-colors.md
• docs/todos/archived/204-expose-color-helpers-sprite-generator.md

Notes

• hueRotate is not currently implemented in the codebase, so there is nothing to remove for that name.
• This cleanup is expected to be low-risk because sprite generation uses resolved color strings and does not depend on helper functions internally.

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Source TODO: docs/todos/304-remove-sprite-generator-color-helper-apis.md
Priority: Medium
Effort: 0.5-1h