Fixes #23501

Problem

oxfmt drops the load-bearing outer parentheses in export default (fn as T) when the cast is chained:

// input
export default (function foo() {} as unknown as Foo);

// oxfmt output (wrong — parens lost)
export default function foo() {} as unknown as Foo;

Without the parens the leading function/class token makes export default parse the right-hand side as a declaration, so the trailing as … cast is no longer attached to anything. Downstream new defaultExport(...) then fails with TS7009.

Cause

The ExportDefaultDeclaration arm of ts_as_or_satisfies_needs_parens only inspected the direct inner expression:

AstNodes::ExportDefaultDeclaration(_) =>
    matches!(inner, Expression::FunctionExpression(_) | Expression::ClassExpression(_)),

A single as worked, but for a chained cast the outer as node's inner is another TSAsExpression, so the FunctionExpression/ClassExpression check failed and the parens were dropped.

Fix

Walk to the leftmost descendant via ExpressionLeftSide::leftmost before checking for FunctionExpression/ClassExpression — mirroring the existing CallExpression handler, which already does this for the same export default scenario. This matches the ECMAScript grammar: export default forbids a right-hand side whose leading token is function/async function/class, so parens are needed exactly when the leftmost leaf is a function/class expression.

Tests

• New fixture tests/fixtures/ts/parenthesis/export-default-as.ts.
• Full oxc_formatter fixture suite passes (290 tests).
• Verified no over-parenthesization: identifiers, calls, object literals, and non-export-default contexts get no parens; function/class as leftmost (even chained or via member access) keep them.

🤖 Generated with Claude Code