Neo4j: scope destructive statements on the can:// id prefix; retire _module #219

Spec: 2026-09-02-prune-scope-on-can-id-prefix.md · Epic: codellm-devkit/.github#50

Problem

#213 anchored the purge on java-owned labels, stopping it reaching other languages. It is still application-blind — see #218, which is the narrow immediate fix. This issue is the full change: the prefix subsumes both the label anchor from #213 and _module itself.

Java has no _module indexes to remove (#217 asked for them; deleting the property resolves it instead) and no --eager gate.

What to do

• Scope the per-module purge and the orphan prune on the application's can:// id prefix (can://java/<app>), replacing the _module predicate and the label-list anchor.
• Drop _module from the projection, from the graph catalog, and from any index on it.
• Add a JCanNode marker label to every node keyed by a can:// id, as an index anchor only — Neo4j property indexes are label-scoped, so MATCH (n) WHERE n.id STARTS WITH $p scans the whole store without one. STARTS WITH is index-backed on a range index; CONTAINS/ENDS WITH are not.
• MAJOR graph-contract bump: a property is removed.
• Grep this analyzer's SDK Neo4j backend for _module so a consumer is updated in the same train. The removal is not conditional on the answer — that was decided — but a surprise later is worse than a check now.

Two things not to get wrong

• Prefix boundary. can://java/<app> also prefixes can://java/<app>Xtra. Match descendants on prefix + '/' and the node itself by equality.
• Empty prefix. STARTS WITH '' matches every node in the database. Refuse a null or empty application id rather than falling through.

Goals

• Both destructive statements scoped by id prefix
• _module gone from projection, catalog and indexes
• Marker label added and used as the index anchor
• A test showing a second application in this same language, with a colliding module path, survives a push
• The null/empty application id case is refused
• Graph contract MAJOR bump

Definition of done

• A test that fails before and passes after
• The emitted graph is unchanged apart from _module's removal and the added marker label, shown by diffing a fixture projection
• Full test suite green