Make tailwind CLI subprocess handling robust

[vormwald]

Summary

• Switch Open3.popen3 with a shell-joined command string to Open3.capture3 with an argv array — fixes paths containing spaces and removes the pipe-deadlock risk.
• CLI exit status is now checked: on failure, stderr is logged loudly and the converter returns nil instead of silently writing an empty/placeholder stylesheet.
• stderr on success is only warned when non-empty (previously an empty string was warned on every build).
• Shared compile logic is extracted into one module so the two converters can't drift.
• Namespace moved from Tailwindcss::Commands to Jekyll::Tailwindcss::Commands to avoid a constant clash with the tailwindcss-rails gem.

Test plan

• 32 specs pass
• standardrb clean

🤖 Generated with Claude Code

[Copilot]

Pull request overview

Improves Tailwind CLI execution reliability and centralizes compilation behavior.

Changes:

• Uses Open3.capture3 with argv-safe invocation and exit-status handling.
• Moves commands under Jekyll::Tailwindcss to prevent namespace conflicts.
• Updates converter integration and failure-path tests.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
spec/tailwindcss/commands_spec.rb	Removes old namespace tests.
spec/jekyll/tailwindcss/commands_spec.rb	Tests command execution and error handling.
spec/jekyll/converters/tailwindcss_spec.rb	Tests shared compiler integration.
spec/jekyll/converters/css_spec.rb	Updates converter behavior tests.
lib/tailwindcss/commands.rb	Removes old command module.
lib/jekyll/tailwindcss/commands.rb	Adds shared robust compiler implementation.
lib/jekyll/converters/tailwindcss.rb	Delegates compilation to the shared module.
lib/jekyll/converters/css.rb	Delegates CSS compilation to the shared module.
lib/jekyll-tailwindcss.rb	Loads the relocated command module.

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[Copilot]

Pull request overview

Copilot reviewed 9 out of 9 changed files in this pull request and generated 1 comment.

[vormwald]

I checked this against Jekyll 4.4.1's source and a real build, and the TypeError doesn't happen.

• Jekyll::Renderer#run (renderer.rb:84) does convert(output.to_s) and returns the converter's value as-is — there's no type check on the way out.
• Document#write (document.rb:281) does File.write(path, output, mode: "wb"), and IO.write calls to_s on a non-String argument, so nil becomes "".

Verified empirically with a scratch Jekyll site whose .css converter returns nil: the build completes and writes a 0-byte style.css, no exception. I also tested the nil-plus-layout path through place_in_layouts, since that's the one branch that could plausibly choke on nil — also fine.

So "Jekyll's converter contract expects a string" isn't enforced anywhere in this path, and the failure mode is an empty file rather than a crash.

The underlying concern about visibility is fair, but the failure isn't silent: Commands.compile logs Jekyll.logger.error with the CLI's exit status and full stderr before returning nil. An empty stylesheet plus a loud error is also a strict improvement over the previous behavior, which wrote the unresolved @import "tailwindcss" out as if it were real CSS.

Making a CLI failure fatal to the whole build is a reasonable alternative, but it's a behavior change beyond this PR's scope, and it would mean a transient Tailwind hiccup kills jekyll serve in development. Keeping it as-is.