FR: dependency override (replace) — redirect a metadata dependency to a local path or fork

[dmealing]

Gap

No way to redirect a declared metadata dependency to a different location — a local checkout, or a patched fork — without editing the declaration itself.

Every enterprise eventually needs "we are running a patched shared model while the fix lands upstream," and needs it to be a local, uncommitted override rather than a change to the shared declaration.

Prior art (open source)

Go modules — the replace directive redirects a module to a local path or a fork, and is understood to be a local/temporary concern. https://go.dev/ref/mod

Notes

• Not needed while only path sources exist: a path source is an override, since it names a location directly.
• Becomes necessary once package sources land (FR-023 — Metadata packages: cross-repo distribution + reuse #9), where the location is resolved by an ecosystem rather than named.
• Should compose with the set semantics in the source-resolution design: an override replaces a member of the source set, it does not add one.
• Worth deciding whether overrides live in the committed config or in a local, gitignored sidecar. Go puts them in the committed go.mod, which is arguably the wrong default for this case.