Fix TS2742 error when inferring exported Config type

[silverwind]

Change Config exports from type aliases (type Config = UserConfig) to interfaces (interface Config extends UserConfig {}) in both index.ts and compat/plugin-api.ts.

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.

Fixes #19706

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[coderabbitai]

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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.
Description check	✅ Passed	The description clearly explains the technical change (type alias to interface), the rationale (preserving Config name in declaration emit), and links to the relevant issue.
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.

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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.