Preserve source maps through ESM specifier rewriting

[woksin]

Problem

The build rewrites relative ESM specifiers after TypeScript/Rollup emit so Node can load published modules directly. A pre-rewrite source map would be dishonest, so maps for rewritten modules are currently removed. Consumers consequently lose source-level debugging across much of the package.

Direction

Make the specifier rewrite source-map-aware rather than retaining stale mappings:

• apply rewrites through a mapping-preserving transform;
• compose the transform map with Rollup/TypeScript maps;
• retain correct sourceMappingURL references;
• verify sources, names, line/column mappings, and declaration maps from the packed archive;
• keep direct Node ESM import behavior unchanged.

Acceptance criteria

• Every emitted JavaScript file that declares a source map references an existing packed map.
• Representative stack frames and breakpoints map to the correct TypeScript source line/column.
• Rewritten import/export/dynamic-import/import-type specifiers remain Node-loadable.
• A planted stale/pre-rewrite map fails the package gate.
• Archive budgets are reviewed after map restoration.