Add a Program-owned validation pass that walks the final AST and reports TS1206 once per decorated parameter, using the full decorator-list span for the diagnostic range.

Invoke that validation from compile after transforms have had their afterInitialize window, so transformers can still remove parameter decorators before any diagnostics are emitted.

Add a dedicated compiler rejection fixture covering regular, rest, explicit-this, constructor-property, function-type, function-expression, and arrow-parameter cases.

Add a dedicated transform input containing the same invalid parameter-decorator forms exercised by the compiler rejection fixture.

Introduce ESM and CommonJS afterInitialize transforms that walk the AST and strip parameter decorators, including explicit-this decorators on function signatures.

Extend the transform test scripts to compile that input with the stripping transforms, proving no TS1206 diagnostics are emitted once transforms remove the decorators in time.

Replace the bespoke parameter-decorator validation pass in Program with a small validator built on top of a shared AST walker.

The previous implementation worked, but it reimplemented a near-complete AST traversal inside program.ts for one feature. That made Program responsible for AST topology, duplicated traversal logic, and created exactly the kind of ad hoc pass review feedback called out: every AST shape change would have to remember to update this validator as well.

This change separates three concerns more cleanly:

- parser.ts records which source-level statements actually preserved parameter decorators while parsing
- ast.ts owns subtree traversal through a generic NodeWalker utility
- program.ts only performs the parameter-specific check after afterInitialize

In other words, the parser decides what roots are relevant, the walker decides how to descend the tree, and the validator decides what to report.

This is better because it keeps AST traversal knowledge in one place, removes a large one-off recursive pass from Program, and makes future AST validation/analysis passes much smaller if they need to inspect subtrees later.

The validator still runs after afterInitialize so transforms can inspect or remove preserved parameter decorators first, and the tests continue to cover parser round-tripping, compiler rejection, and transform-time removal.

Also add a namespace regression case to ensure preserved parameter decorators nested under a tracked source-level statement are still validated and can still be stripped by transforms.

Drop AST imports from src/program.ts that became unused after moving subtree traversal into NodeWalker. This fixes the lint warnings reported in CI and keeps the parameter decorator refactor clean.

Follow the existing AST convention that Range is the last constructor field and the last factory/helper parameter. This updates ParameterNode and Node.createParameter accordingly, and adjusts all call sites.

Account for explicit-this parameter decorators in the same way as parameter decorators: wire explicitThisDecorators through FunctionTypeNode and Node.createFunctionType, keep it adjacent to explicitThisType, and leave range as the last constructor/helper parameter. Update all call sites accordingly.

Remove the duplicate parameter-decorator serializer in ASTBuilder and fold the inline formatting case into serializeDecorator with an optional flag. This keeps decorator serialization in one place while preserving the spacing differences between declaration decorators and parameter decorators.

Rename the parser helper that consumes and reports decorators found after a parameter has already started from reportInvalidParameterDecorators to tryParseParameterDecorators, matching its behavior more closely and aligning with the review suggestion.