FR: meta why <fqn> — query per-node source provenance (attribution already tracked, no query surface)

[dmealing]

Gap

Once a collection can be assembled from multiple sources, "where did this node come from?" stops being obvious. Today it is answerable only when something fails.

What we already have

The loader already tracks per-node source attribution and surfaces it in diagnostics (resolvedSource(failure.source, failure.nodeFqn, failure.ref) in meta-data-loader.ts). The data exists; there is no way to query it on demand.

Prior art (open source)

Go — go mod why explains why a dependency is in the graph. https://go.dev/ref/mod

Direction

meta why <fqn> reporting, for a resolved node: which source contributed it, which sources contributed overlays onto it, what it resolved its extends against, and (once package sources land) which package and version.

Notes

• Low priority precisely because attribution is already in error messages — this is a convenience for the working case, not a fix for a broken one.
• Value rises sharply with package sources (FR-023 — Metadata packages: cross-repo distribution + reuse #9) and with overlays across collection boundaries, where a node's final shape may have several contributors.