cypher-codegen: infer nullability for SET-clause params

[jbmusso]

Problem

QueryAnalyzer.extractParams typed query parameters from two sources only:

1. Pass 1 — params inside node-pattern property maps: (n:Label {prop: $p}) (covers CREATE/MATCH constraints).
2. Pass 2 — expr.prop IN $param list expressions.

Params bound via a SET clause — MATCH (n:Label {id: $id}) SET n.prop = $p — were not analyzed. The backend regex scan still surfaced the param name, so it appeared in the generated signature, but with the fallback type { type: "String", nullable: false }.

Net effect: a param assigned to an optional vertex property was typed non-nullable (e.g. prop: string) when it should be prop: string | null — the adapter must be able to persist null to clear such a property.

Fix

Add a Pass 3 to extractParams, mirroring Pass 1 but walking SET items:

• Walks SetItemContext nodes, handling only the propertyExpression ASSIGN expression alternative (<var>.<prop> = $param).
• Resolves <var> → label via the existing buildVarLabelMap, then types the param via lookupParamType exactly as Pass 1 does — emitting the property's type and nullable flag.
• SET n += $map (map-merge) is naturally excluded: that alternative has no propertyExpression(), so it never enters Pass 3 (map params remain a separate feature).
• The shared seenParams set prevents double-counting a param used in both a pattern and a SET.
• Left-hand sides that can't be resolved to a labelled schema property keep the prior non-nullable String fallback, so behaviour is unchanged for untyped params.

Tests

New describe("analyzeQuery — SET-clause param nullability") block in QueryAnalyzer.node.unit.test.ts, written test-first (verified red for the right reason — SET params were absent from analyzer output — before implementing):

• SET param on an optional vertex property → nullable: true.
• SET param on a mandatory vertex property → nullable: false.
• Multi-property SET types each item independently.
• A param constrained in both a MATCH pattern and a SET is not double-counted.

Existing Pass 1 (CREATE/MATCH) and Pass 2 (IN) param typing is unchanged. Full package unit suite: 178/178 green; pnpm check clean.

Release

Changeset included: minor bump for @evryg/effect-cypher-codegen (0.2.0 → 0.3.0).

Commits

• cypher-codegen: infer nullability for SET-clause params — Pass 3 implementation + unit tests
• cypher-codegen: changeset for SET-clause param nullability — release changeset