externals/.loom/published/externals.md

Externals

How a repository records what it depends on, and finds out when it changes.

Pull what you use

You fetch a copy of somebody's document and keep it at .loom/externals/<host>/<path>.md.

The path says where it came from, so nothing has to record an origin. This was false and it was load-bearing. A stored path is short enough to read and therefore too short to resolve: it drops the host's routing, the branch, and — worst — the published/ segment, which is the whole contract.

The path is for a person. The origin is recorded in the lock, resolved: host, route, branch, and full path.

Record the resolved URL and not the short form. A host may redirect a short form to whatever the default branch is at the time you ask — so a lock holding one is locked to a moving target, and a rename of the branch reports as a change in the document.

Pull what you need to understand, not everything it depends on. A document you fetch may refer to others; follow one when you hit something you do not know. Pre-resolving that is how you get a node_modules.

Two facets beside it

• .usages.md — what we use, and which of our artifacts depend on it
• .gaps.md — what we expected here and did not find

A usage that does not name what it justifies is half a usage. "We use the tailnet approach" is weak. "We use the tailnet approach — see manifests/ingress.yaml" is the whole value, because it answers the only question reconciliation asks.

What a lock holds

One record per adopted document, in .loom/externals/.locks:

• where it was fetched from — resolved, as above
• the publisher's ETag — verbatim

It is committed, because the thing it locks is committed, and a lock that travels separately from what it locks is the drift this is meant to prevent.

A document with no lock is not broken; it is unlocked. Report it and fetch again. Do not adopt whatever the remote currently serves as the lock — that asserts your copy is the one being served, which is the thing you were going to check.

Freshness is a conditional request

Locked on the publisher's ETag, verbatim — never a hash you compute. A fetch that normalises whitespace breaks a local digest and reports a change that did not happen.

304	nothing changed
200	changed — the new copy is a candidate, not a replacement
410	gone — follow whatever the response points at
404	unresolved. Report both readings; do not pick one

404 is two different answers wearing one status. The document was withdrawn, or you no longer have access — and over HTTP they are indistinguishable, because a host that distinguished them would leak the existence of things you may not see.

Say both. Do not guess. They want different actions — re-pull elsewhere, versus ask somebody for access — and a tool that picks one will be wrong half the time silently.

Over ssh they are distinguishable — permission denied against repository not found — so a client that has both transports should say which it used.

Reconciliation runs the other way

You cannot fold your facets back into their document. So the question is not what do we rewrite here:

Given what changed in theirs, what do we change in ours?

The facets usually survive unchanged. What moves is the manifests, the config, the code that a usage named — which is why a usage names them.

And gaps reconcile too, which is the half nobody builds for: a new version may have filled one, and nothing will tell you.

A facet describes the local pair. A gap is true of the copy you hold, not of the document upstream — so a publisher fixing their end does not close it. It closes when you fetch the new copy and replace the pair, and until then it is still true of what is in your tree.

What survives a closed gap is not the gap. It is what the gap justified. If you recorded a local workaround, ask whether it is retired or merely no longer provisional — the second is the common case and it is invisible in the code, which is why it is an entry in your own log. Somebody inheriting your workaround will go looking for the gap that justified it, and find nothing.

A closed gap is not a decline. A decline is what you considered and did not do; a closed gap is what you needed and got.

The new copy replaces the old pair wholesale. There is no merging a document you do not own.

Venues, for things you cannot fetch

.loom/venues/<name>.md — Kafka, React, HTTP. Choices we made about something with no document to hang them on.

If there is a document, hang it there instead: put a choice where reconciliation will look for it.

Gaps that belong to nobody

.loom/gaps/ — a need with no owner. The test: could you say whose job this is? If yes, it is a claim against them and belongs in their .gaps.md.

Moving a file from gaps/ into an external's .gaps.md is how a gap gets homed. The position is the claim.

A gap records the local workaround beside the need. "We are using Docker Hub for now." Forgetting it was provisional is the disease; the provisional answer is fine — and when the gap is finally homed, every workaround that should be retired is findable.