Fix TS2742 error when inferring exported Config type

[silverwind]

Fixes: #15844
Fixes: #19706
Fixes: #15458

Type aliases get resolved through to UserConfig during declaration emit, which lives in a hashed internal DTS chunk with no stable import path, causing TS2742. Interfaces preserve their named identity, so downstream declaration files reference Config from tailwindcss directly.

🤖 Generated with Claude Code

[coderabbitai]

Walkthrough

The pull request changes the declaration of the Config type from a type alias to an interface in two files. Specifically, export type Config = UserConfig is replaced with export interface Config extends UserConfig {} in both packages/tailwindcss/src/compat/plugin-api.ts and packages/tailwindcss/src/index.ts. This change alters the structural representation of the exported Config type while maintaining the same type semantics through interface extension.

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately describes the main change: converting Config from a type alias to an interface to fix the TS2742 TypeScript error.
Linked Issues check	✅ Passed	The PR directly addresses issue #19706 by converting Config from a type alias to an interface in both index.ts and compat/plugin-api.ts, which resolves the TS2742 error caused by hashed internal type file references.
Out of Scope Changes check	✅ Passed	All changes are narrowly scoped to converting Config declarations from type aliases to interfaces in the two specified files, directly addressing the linked issue with no extraneous modifications.
Description check	✅ Passed	The pull request description clearly explains the issue being fixed (TS2742 error), the solution (converting type alias to interface), and references the related issues.

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[silverwind]

@coderabbitai try again with latest commit.

[coderabbitai]

@silverwind: I'll review the changes with the latest commit.

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[coderabbitai]

Actionable comments posted: 2

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Verify each finding against the current code and only fix it if needed.

Inline comments:
In `@packages/tailwindcss/src/index.ts`:
- Line 37: Replace the type alias export in plugin-api.ts so consumers don't get
TS2742: locate the exported symbol "Config" (currently declared as "export type
Config = UserConfig") and change it to an interface declaration that extends
UserConfig (i.e., "export interface Config extends UserConfig {}") so it matches
the fix in packages/tailwindcss/src/index.ts and avoids re-exporting a type
alias from the public plugin entry point.
- Line 37: The plugin entry's exported Config is still a type alias causing a
public API mismatch; in compat/plugin-api.ts replace the exported type alias for
Config with an exported interface (i.e., export interface Config extends
UserConfig {}) so it matches the change in packages/tailwindcss/src/index.ts and
preserves named type identity; ensure UserConfig is imported/available in
compat/plugin-api.ts and update any re-exports that reference Config to use the
new interface form.