Serve engine CSS via tailwindcss-rails engine support

[thomasgallagher]

Replace the copy-based CSS install with tailwindcss-rails' Rails engine support: the engine's stylesheet is now imported straight from the gem, so it stays in sync with the installed version instead of being copied into the host app at install time.

• Move app/assets/tailwind/layered/ui/styles.css to the convention path app/assets/tailwind/layered_ui/engine.css (engine_name is layered_ui)
• Remove CopyAssetsGenerator; ImportCssGenerator now injects @import "../builds/tailwind/layered_ui";
• Switch the engine layout to stylesheet_link_tag "tailwind" so propshaft's :app glob no longer emits a stray link to the generated intermediate file
• Update README, gemspec post-install message, SKILL.md, AGENTS.md, dummy install docs, and CHANGELOG (flagging the breaking install-flow change)

Compiled output is byte-identical to the previous build; fonts and masked SVG icons resolve unchanged. All tests pass.

[claude]

Review

Switches the engine's CSS delivery from a copied file ( generated into the host app) to tailwindcss-rails' engine support, so the engine CSS is compiled directly from the gem on each build. The install generator, layout link tag, documentation, and tests are all updated consistently.

Issues

No issues found. A few things checked:

• **** (layout line 23): matches tailwindcss-rails' own convention for its compiled output file; the previous Sprockets bundle could have linked the engine's intermediate build file as a side effect, so this is an improvement.
• ****: idempotency is preserved - the new import line is checked before insertion, and the overrides import is only added when absent. The generator does not remove the now-obsolete from existing files, but the CHANGELOG migration note covers this explicitly and it is a deliberate hand-off to the developer.
• **** in : raises on a missing gem; is a test-suite dependency via , so generator tests won't hit the guard.
• Builds directory in CI: is gitignored and no Tailwind build step runs in CI, but the test suite is Ruby-only (no CSS compilation needed for the test cases).

Verdict

✅ Ship - Clean, well-scoped change with thorough documentation and consistent test updates.

[claude]

Review

Migrates engine CSS delivery from copying assets into the host app to using tailwindcss-rails' engine support, so the engine stylesheet stays in sync with the installed gem version automatically. Also removes the now-redundant CopyAssetsGenerator and updates all docs, tests, and the dummy app accordingly.

No issues found - the implementation is clean.

Notes (not blocking):

• The migration guide correctly tells users to manually remove the old @import "./layered_ui"; line; the install generator does not do this automatically. That is a reasonable choice for a Rails generator, but worth verifying the CHANGELOG makes the manual step obvious. It does.
• stylesheet_link_tag "tailwind" in the engine layout assumes the host app's tailwindcss-rails output is named tailwind.css (the framework default). Since tailwindcss-rails ~> 4.0 is a hard gem dependency, this assumption is sound.

Verdict

✅ Ship - clean, well-tested migration with clear breaking-change documentation.

[claude]

This PR replaces the copy-based CSS install with tailwindcss-rails' engine support, moving the engine stylesheet from app/assets/tailwind/layered/ui/styles.css to app/assets/tailwind/layered_ui/engine.css, removing CopyAssetsGenerator, and updating the engine layout to link tailwind.css directly.

No issues found. The migration guide in CHANGELOG is clear, the Rakefile task addition is correctly motivated, tests are updated throughout, and the SKILL.md/AGENTS.md/README updates are consistent with the implementation change.

✅ Ship