fix: preserve cascading order for @container queries (#1798)

[hum4nBeing]

Fixes #1798

Description

Currently, @container queries do not preserve their cascading order because the lastMediaQueryWinsTransform logic in @stylexjs/shared strictly looks for @media prefixes, completely bypassing container queries.

This PR fixes the issue by:

1. Expanding the Parser (style-value-parser): Updated atRuleNameParser in media-query.js to accept the @container keyword alongside @media. (The existing range-syntax machinery already natively handles >= and <= operators).
2. Fixing Serialization: Updated the AST formatter to preserve the original at-rule name so it serializes back to @container instead of rewriting to @media.
3. Refactoring the Transformer (shared): Extracted the sorting, negation, and range-slicing logic into a reusable helper function (applyQueryOrder) inside media-query-transform.js, and applied it sequentially to both @media and @container query families.

By routing container queries through this deterministic pipeline, they are correctly converted into mutually exclusive ranges. This guarantees that container rules never collide, making physical CSS injection order irrelevant—which aligns perfectly with StyleX's atomic CSS architecture.

Test Plan

• Added new regression tests to parse-media-query-test.js verifying that @container (width >= 360px) successfully parses into a valid AST shape.
• Added regression test cases to media-query-transform-test.js verifying that multiple container queries are correctly sorted and transformed into mutually exclusive ranges.
• Ran test suites to confirm all existing and new tests pass successfully.

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1 Skipped Deployment

Project	Deployment	Actions	Updated (UTC)
stylex	Ignored		Aug 9, 2026 9:11pm