fix(transform): synthetic map params leak

[seefeldb]

Replaces fragile heuristic-based detection of map callbacks with explicit
marking using a shared WeakSet registry. This fixes bugs where synthetic
identifiers (element, index, array) leaked into outer scope derives.

Problem:

• ClosureTransformer creates synthetic identifiers without symbols for map params
• OpaqueRefJSXTransformer analyzes transformed AST and needs to distinguish:
  1. Synthetic params INSIDE map callbacks (keep)
  2. Synthetic params that leaked to outer scope (filter out)
• Previous heuristics based on counting dataflows were brittle and error-prone

Solution:

1. Add mapCallbackRegistry: WeakSet<ts.Node> to TransformationOptions
2. ClosureTransformer marks arrow functions when creating map callbacks
3. OpaqueRefJSXTransformer checks marking to detect map callback scopes
4. Filter logic:
   • Only synthetic dataflows → inside callback (keep all)
   • Mixed synthetic + non-synthetic → check if in marked callback
   • If not in marked callback → filter out synthetic params

Benefits:

• Direct knowledge instead of heuristics (no more magic thresholds)
• Clear contract between transformers via shared registry
• More maintainable - reduced from ~130 lines to ~100 lines
• Fixes "element is not defined" runtime errors

🤖 Generated with Claude Code

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Summary by cubic

Prevents synthetic map params (element, index, array) from leaking into outer derives by explicitly tracking map callbacks with a shared WeakSet. Fixes “element is not defined” errors and removes brittle heuristics.

• Bug Fixes

  • Filter synthetic params when they appear outside a marked map callback.
  • Fix runtime errors in JSX map expressions.
  • Add test fixture for a single capture in JSX map.

• Refactors

  • Add mapCallbackRegistry: WeakSet<ts.Node> to TransformationOptions and pipeline.
  • Mark map callbacks in ClosureTransformer and check with context.isMapCallback in OpaqueRefJSXTransformer.
  • Simplify dataflow filtering: keep pure synthetic inside callbacks; filter synthetic when outside.

[cubic-dev-ai]

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