codeanalyzer-java: Neo4j v2 projection — consolidated base relabel + L3/L4 overlays (after L4)

[sinha108]

Consolidation (updated 2026-08-24)

This issue now covers all Neo4j v2 projection work as one consolidated pass, sequenced after L4 lands — the base relabel (L1/L2) plus the L3 dataflow overlay (J_CFG_NEXT/J_CDG/J_DDG) and the L4 SDG overlay (J_PARAM_*/J_SUMMARY). Rationale: do the Cypher/schema mapping once, against a JSON schema fully stabilized through L4, rather than reworking the projection at each level. The L3 (#183) and L4 (#184) issues therefore no longer carry a Neo4j overlay. Epic consequence: the v2 default-output flip (gated on the Neo4j projection) moves to post-L4; the analyzer major can still be cut on the JSON levels beforehand.

Spec

https://github.com/codellm-devkit/codeanalyzer-java/blob/main/docs/design/specs/schema-v2-l3-l4-design.md (§11 Neo4j projection)

Problem

neo4j/SchemaCatalog is at v1 1.0.0 with old node families (JCompilationUnit, JType is_* booleans, JCallable with code) and J_CALLS carrying type/weight/source_kind/destination_kind. It must project the full v2 CPG (L1 through L4).

Scope — all v2 Neo4j families/relationships, in one pass after L4

Reuse the existing GraphProjector/RowBuilder/GraphRows/CypherWriter/BoltWriter machinery; keep the dual-label JSymbol merge pattern and _module provenance.

• Base (L1/L2): node families JApplication, JModule, JSymbol (+ specific type-kind label), JCallable, JField, JParameter; J_-prefixed relationships (D9) J_HAS_MODULE, J_DECLARES, J_HAS_CALLABLE, J_HAS_FIELD, J_RESOLVES_TO, J_CALLS(weight,prov), J_EXTENDS, J_IMPLEMENTS.
• L3 overlay: body/CFG nodes (merge key @line:col/@tag, props kind/start_line/end_line/_module) + J_HAS_BODY_NODE, J_CFG_NEXT(kind), J_CDG, J_DDG(var,prov).
• L4 overlay: formal_in/out + actual_in/out vertices + J_PARAM_IN, J_PARAM_OUT, J_SUMMARY.

Goals

• Base v2 node families keyed by can:// id + the base J_ relationships (above)
• SchemaCatalog major version bump; --emit schema reflects every family through L4
• L3 overlay families/relationships
• L4 overlay families/relationships
• --emit neo4j runs at full implemented depth; -a/--graph-field-depth alongside --emit neo4j is an explicit non-zero error

Caveats and known risks

• Families rename = major graph-schema change; moves in lockstep with the JSON schema.
• Deferred-edge (no-dangling) discipline; unresolved-string fallback rides on the source node's props.
• Doing this after L4 means one schema bump, not three — at the cost of no Neo4j output until then.

Definition of done

• --emit schema produces a schema.neo4j.json listing every v2 node family the JSON emits, through L4.
• --emit neo4j (no URI) writes a graph.cypher that loads clean against an empty Neo4j and is idempotent.
• Cross-projection gate: Neo4j node/edge counts at full depth match the JSON at max_level (modulo explicit HAS_* containment); no dangling relationships.