fix(site-publish): refuse to record a contract a scoped run did not publish

Review found the hole in the first commit's claim. render_site_manifests
advances the stored route contract for every route in site.yaml, and
`access` there is a replacement, not a union the way immutable_paths is.
So a catalogue-only publish could write `protected` for the distributions
bucket that nothing published — and validate_route_migrations then
refuses to put that bucket back public. Unpublished intent became an
irreversible fact.

Reproduced from the repo's own fixture: after a whole publish the record
reads public; after a catalogue-only publish with the route flipped it
reads protected, with nothing written to baseline-dist, and reverting
fails with "artifact distributions cannot become public while reusing
protected bucket baseline-dist".

A scoped run now refuses before the first bucket is touched when an
unselected artifact's path, access or artifact name differs from what is
recorded, naming both contracts. It also refuses an unselected artifact
with no published history, which is the same defect at time zero. Publish
the artifact in the same run.

Three tests: the reviewer's flip scenario (and the same change published
in the same run, which proceeds), the no-history case, and one proving
deploy_static reaches the guard before publish_route_immutables,
reconcile_artifact_cors or s3_sync. Disabling the call site alone turns
the last one red.

The README sentence is narrowed to what the code actually guarantees, and
gains the CORS consequence: a scoped run holds no credential for the
other bucket, so a cors_origins change lands with that artifact's next
publish rather than on the merge that edits site.yaml.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UjQqc4qFmdpAWaYfy2Aypb

README.md

@@ -255,9 +255,24 @@ Selection scopes the build and the S3 publication only. Ingresses, Services,
 Certificates and the immutable-path history are always rendered from the whole
 `site.yaml`, so a scoped run cannot retire another artifact's route or delete
 its bucket contents. Credentials are resolved for the selected artifacts alone,
-so a workflow need not carry secrets for artifacts it does not publish. An
-undeclared name fails before the first bucket is touched, and `enabled: false`
-refuses a selection because decommissioning is whole-site.
+so a workflow need not carry secrets for artifacts it does not publish.
+
+What a scoped run may **not** do is move an artifact it is not publishing. The
+generated route contract in `site-publish-history.yaml` is written from the
+whole `site.yaml`, and `access` there is a replacement rather than a union — so
+recording a change nothing published would turn intent into a fact that
+`validate_route_migrations` then refuses to undo. A run whose `site.yaml`
+changes an unselected artifact's route path, access or artifact name is refused
+before the first bucket is touched, naming both contracts: publish that artifact
+in the same run. For the same reason a scoped run cannot introduce an artifact
+that has no published history yet.
+
+Two more refusals, both before any bucket changes: an undeclared name, and
+`enabled: false` with a selection, because decommissioning is whole-site.
+
+One consequence to know: CORS reconciliation is scoped too, since a scoped run
+holds no credential for the other bucket. A `cors_origins:` change lands with
+that artifact's next publish, not on the merge that edits `site.yaml`.
 
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