diff --git a/.changeset/cypher-codegen-typecheck-generated-output.md b/.changeset/cypher-codegen-typecheck-generated-output.md
new file mode 100644
index 0000000..6ad02a8
--- /dev/null
+++ b/.changeset/cypher-codegen-typecheck-generated-output.md
@@ -0,0 +1,15 @@
+---
+"@evryg/effect-cypher-codegen": patch
+---
+
+Make generated query code type-check under Effect v4.
+
+- Row decoding no longer emits an untyped `Neo4jRecordToObject` schema transform.
+  `record.toObject()` is called in the Effect pipeline and each row is validated
+  directly with `Schema.Array(Row)`, so the row struct fully type-checks the
+  decoded shape.
+- The generated `TemporalString` transform now carries explicit
+  `SchemaTransformation.transform<string, unknown>` type parameters, matching its
+  `Schema.Unknown` source so it satisfies `decodeTo`'s getter signature.
+- Single-file modules now annotate query parameters with their types instead of
+  relying on an implicit `any`, the same way the barrel output already did.
diff --git a/packages/cypher-codegen/package.json b/packages/cypher-codegen/package.json
index 51f5003..076b4c2 100644
--- a/packages/cypher-codegen/package.json
+++ b/packages/cypher-codegen/package.json
@@ -51,6 +51,7 @@
     "@evryg/effect-vitest-neo4j": "workspace:^",
     "antlr-ng": "^1.0.10",
     "effect": "4.0.0-beta.78",
-    "neo4j-driver": "^6.0.1"
+    "neo4j-driver": "^6.0.1",
+    "typescript": "5.9.3"
   }
 }
diff --git a/packages/cypher-codegen/src/Register.ts b/packages/cypher-codegen/src/Register.ts
index b57822e..197a76f 100644
--- a/packages/cypher-codegen/src/Register.ts
+++ b/packages/cypher-codegen/src/Register.ts
@@ -26,11 +26,11 @@ registerHooks({
   load(url, context, nextLoad) {
     if (context.format === "cypher" || url.endsWith(".cypher")) {
       const source = readFileSync(fileURLToPath(url), "utf-8").trim()
-      const columns = schema ? analyzeQuery(source, schema).columns : undefined
+      const analysis = schema ? analyzeQuery(source, schema) : undefined
       return {
         format: "module",
         shortCircuit: true,
-        source: generateModule(source, columns)
+        source: generateModule(source, analysis?.columns, analysis?.params)
       }
     }
     return nextLoad(url, context)
diff --git a/packages/cypher-codegen/src/VitePlugin.ts b/packages/cypher-codegen/src/VitePlugin.ts
index 87bf09f..918f273 100644
--- a/packages/cypher-codegen/src/VitePlugin.ts
+++ b/packages/cypher-codegen/src/VitePlugin.ts
@@ -13,8 +13,8 @@ export const cypherPlugin = (opts?: { schema?: GraphSchema }) => ({
   transform(_code: string, id: string) {
     if (id.endsWith(".cypher")) {
       const content = readFileSync(id, "utf-8").trim()
-      const columns = opts?.schema ? analyzeQuery(content, opts.schema).columns : undefined
-      return { code: generateModule(content, columns), map: null }
+      const analysis = opts?.schema ? analyzeQuery(content, opts.schema) : undefined
+      return { code: generateModule(content, analysis?.columns, analysis?.params), map: null }
     }
   }
 })
diff --git a/packages/cypher-codegen/src/backend/CypherCodegen.node.unit.test.ts b/packages/cypher-codegen/src/backend/CypherCodegen.node.unit.test.ts
index bca4407..7a88850 100644
--- a/packages/cypher-codegen/src/backend/CypherCodegen.node.unit.test.ts
+++ b/packages/cypher-codegen/src/backend/CypherCodegen.node.unit.test.ts
@@ -81,26 +81,28 @@ describe("generateModule with columns (typed codegen)", () => {
     expect(source).toContain("Schema.String")
   })
 
-  it("emits Neo4jRecordToObject transform with toObject()", () => {
+  it("maps records through .toObject() in the query pipeline (no record-level schema transform)", () => {
     const source = generateModule("MATCH (c:Class) RETURN c.fqcn AS fqcn", [
       col("fqcn", S("String"), false)
     ])
-    expect(source).toContain("Neo4jRecordToObject")
-    expect(source).toContain(".toObject()")
+    expect(source).not.toContain("Neo4jRecordToObject")
+    expect(source).toContain("records.map((r) => r.toObject())")
   })
 
-  it("composes Neo4jRecordToObject with Row via decodeTo", () => {
+  it("decodes rows directly against the struct via Schema.Array(Row)", () => {
     const source = generateModule("MATCH (c:Class) RETURN c.fqcn AS fqcn", [
       col("fqcn", S("String"), false)
     ])
-    expect(source).toContain("Schema.Array(Neo4jRecordToObject.pipe(Schema.decodeTo(Row)))")
+    expect(source).toContain("Schema.decodeUnknownSync(Schema.Array(Row))")
   })
 
-  it("passes decoder directly to Effect.map (no lambda)", () => {
+  it("maps records through .toObject() before decoding", () => {
     const source = generateModule("MATCH (c:Class) RETURN c.fqcn AS fqcn", [
       col("fqcn", S("String"), false)
     ])
-    expect(source).toContain("Effect.map(neo4j.query(cypher), decodeRows)")
+    expect(source).toContain(
+      "Effect.map(neo4j.query(cypher), (records) => decodeRows(records.map((r) => r.toObject())))"
+    )
   })
 
   it("imports Neo4jInt from effect-neo4j for Long columns", () => {
@@ -134,12 +136,23 @@ describe("generateModule with columns (typed codegen)", () => {
   })
 
   it("handles params AND columns together", () => {
-    const source = generateModule("MATCH (c:Class {fqcn: $fqcn}) RETURN c.name AS name", [
-      col("name", S("String"), false)
-    ])
+    const source = generateModule(
+      "MATCH (c:Class {fqcn: $fqcn}) RETURN c.name AS name",
+      [col("name", S("String"), false)],
+      [{ name: "fqcn", type: "String", nullable: false }]
+    )
     expect(source).toContain("{ fqcn }")
     expect(source).toContain("Schema.Struct")
-    expect(source).toContain("Neo4jRecordToObject.pipe(Schema.decodeTo(Row")
+    expect(source).toContain("Schema.decodeUnknownSync(Schema.Array(Row))")
+  })
+
+  it("annotates module params with their types (no implicit any)", () => {
+    const source = generateModule(
+      "MATCH (c:Class {fqcn: $fqcn}) RETURN c.name AS name",
+      [col("name", S("String"), false)],
+      [{ name: "fqcn", type: "String", nullable: false }]
+    )
+    expect(source).toContain("export const query = ({ fqcn }: { fqcn: string }) =>")
   })
 
   it("emits Neo4jValue for UnknownType columns (escape hatch)", () => {
@@ -247,7 +260,7 @@ describe("generateBarrel — typed params", () => {
     expect(source).toContain("{ note }: { note: string | null }")
   })
 
-  it("emits shared Neo4jRecordToObject transform once", () => {
+  it("does not emit a record-level schema transform (toObject() happens in the pipeline)", () => {
     const entry: BarrelEntry = {
       filename: "Foo.cypher",
       cypher: "MATCH (c:Class) RETURN c.fqcn AS fqcn",
@@ -255,12 +268,11 @@ describe("generateBarrel — typed params", () => {
       params: []
     }
     const source = generateBarrel([entry])
-    const matches = source.match(/Neo4jRecordToObject = Schema\.Unknown\.pipe\(Schema\.decodeTo/g)
-    expect(matches).toHaveLength(1)
-    expect(source).toContain(".toObject()")
+    expect(source).not.toContain("Neo4jRecordToObject")
+    expect(source).toContain("records.map((r) => r.toObject())")
   })
 
-  it("composes Neo4jRecordToObject with row schema via decodeTo", () => {
+  it("decodes rows directly against the row struct via Schema.Array(Row)", () => {
     const entry: BarrelEntry = {
       filename: "Foo.cypher",
       cypher: "MATCH (c:Class) RETURN c.fqcn AS fqcn",
@@ -268,10 +280,10 @@ describe("generateBarrel — typed params", () => {
       params: []
     }
     const source = generateBarrel([entry])
-    expect(source).toContain("Schema.Array(Neo4jRecordToObject.pipe(Schema.decodeTo(fooQueryRow)))")
+    expect(source).toContain("Schema.decodeUnknownSync(Schema.Array(fooQueryRow))")
   })
 
-  it("passes decoder directly to Effect.map (no lambda)", () => {
+  it("maps records through .toObject() before decoding", () => {
     const entry: BarrelEntry = {
       filename: "Foo.cypher",
       cypher: "MATCH (c:Class) RETURN c.fqcn AS fqcn",
@@ -279,7 +291,9 @@ describe("generateBarrel — typed params", () => {
       params: []
     }
     const source = generateBarrel([entry])
-    expect(source).toContain("Effect.map(neo4j.query(fooQueryCypher), decodeFooQuery)")
+    expect(source).toContain(
+      "Effect.map(neo4j.query(fooQueryCypher), (records) => decodeFooQuery(records.map((r) => r.toObject())))"
+    )
   })
 
   it("emits Neo4jValue for UnknownType columns in barrel", () => {
@@ -319,7 +333,7 @@ describe("generateBarrel — no any in generated code", () => {
 })
 
 describe("generateModule — no any in generated code", () => {
-  it("Neo4jRecordToObject decode param is not typed as any", () => {
+  it("typed row decoder does not emit an any-typed param", () => {
     const source = generateModule("MATCH (c:Class) RETURN c.fqcn AS fqcn", [
       col("fqcn", S("String"), false)
     ])
diff --git a/packages/cypher-codegen/src/backend/CypherCodegen.ts b/packages/cypher-codegen/src/backend/CypherCodegen.ts
index bf95796..ceb30d4 100644
--- a/packages/cypher-codegen/src/backend/CypherCodegen.ts
+++ b/packages/cypher-codegen/src/backend/CypherCodegen.ts
@@ -142,21 +142,50 @@ function tsTypeFor(type: Neo4jType): string {
   }
 }
 
+// ── Parameter signatures ──
+
+/**
+ * The parameter signature for a generated query function: the declaration
+ * (typed when param types are known, so the generated code never relies on an
+ * implicit `any`) and the call-site destructure. `undefined` when the query
+ * takes no parameters.
+ */
+function queryParams(
+  cypher: string,
+  params?: ReadonlyArray<ResolvedParam>
+): { readonly decl: string; readonly call: string } | undefined {
+  if (params && params.length > 0) {
+    const call = `{ ${params.map((p) => p.name).join(", ")} }`
+    const annotation = params
+      .map((p) => `${p.name}: ${tsTypeFor(p.type)}${p.nullable ? " | null" : ""}`)
+      .join("; ")
+    return { decl: `${call}: { ${annotation} }`, call }
+  }
+  const names = extractParams(cypher)
+  if (names.length === 0) return undefined
+  const destructure = `{ ${names.join(", ")} }`
+  return { decl: destructure, call: destructure }
+}
+
 // ── Module generation ──
 
 /**
  * @since 0.0.1
  * @category codegen
  */
-export function generateModule(cypher: string, columns?: ReadonlyArray<ResolvedColumn>): string {
+export function generateModule(
+  cypher: string,
+  columns?: ReadonlyArray<ResolvedColumn>,
+  params?: ReadonlyArray<ResolvedParam>
+): string {
   if (!columns || columns.length === 0) {
-    return generateUntypedModule(cypher)
+    return generateUntypedModule(cypher, params)
   }
-  return generateTypedModule(cypher, columns)
+  return generateTypedModule(cypher, columns, params)
 }
 
-function generateUntypedModule(cypher: string): string {
-  const params = extractParams(cypher)
+function generateUntypedModule(cypher: string, params?: ReadonlyArray<ResolvedParam>): string {
+  const sig = queryParams(cypher, params)
   const lines = [
     `import { Effect } from "effect";`,
     `import { Neo4jClient } from "@evryg/effect-neo4j";`,
@@ -165,25 +194,30 @@ function generateUntypedModule(cypher: string): string {
     ``
   ]
 
-  if (params.length === 0) {
+  if (sig === undefined) {
     lines.push(`export const query = () =>`)
     lines.push(`  Effect.flatMap(Neo4jClient, (neo4j) => neo4j.query(cypher));`)
   } else {
-    const destructure = `{ ${params.join(", ")} }`
-    lines.push(`export const query = (${destructure}) =>`)
-    lines.push(`  Effect.flatMap(Neo4jClient, (neo4j) => neo4j.query(cypher, ${destructure}));`)
+    lines.push(`export const query = (${sig.decl}) =>`)
+    lines.push(`  Effect.flatMap(Neo4jClient, (neo4j) => neo4j.query(cypher, ${sig.call}));`)
   }
 
   return lines.join("\n") + "\n"
 }
 
-function generateTypedModule(cypher: string, columns: ReadonlyArray<ResolvedColumn>): string {
+function generateTypedModule(
+  cypher: string,
+  columns: ReadonlyArray<ResolvedColumn>,
+  params?: ReadonlyArray<ResolvedParam>
+): string {
   // UnknownType columns emit Neo4jValue (escape hatch for unlabeled nodes)
-  const params = extractParams(cypher)
+  const sig = queryParams(cypher, params)
   const lines: Array<string> = []
 
   // Imports
-  lines.push(`import { Effect, Schema, SchemaTransformation } from "effect";`)
+  lines.push(
+    `import { Effect, Schema${needsTemporalString(columns) ? ", SchemaTransformation" : ""} } from "effect";`
+  )
   const neo4jImports = neo4jSchemaImports(columns)
   if (neo4jImports.length > 0) {
     lines.push(`import { Neo4jClient, ${neo4jImports.join(", ")} } from "@evryg/effect-neo4j";`)
@@ -196,20 +230,13 @@ function generateTypedModule(cypher: string, columns: ReadonlyArray<ResolvedColu
   lines.push(`const cypher = ${JSON.stringify(cypher)};`)
   lines.push(``)
 
-  // Neo4j Record → plain object transform
-  lines.push(`const Neo4jRecordToObject = Schema.Unknown.pipe(Schema.decodeTo(`)
-  lines.push(`  Schema.Unknown,`)
-  lines.push(
-    `  SchemaTransformation.transform({ decode: (rec) => (rec as { toObject(): Record<string, unknown> }).toObject(), encode: (obj) => obj }),`
-  )
-  lines.push(`));`)
-  lines.push(``)
-
   // Temporal string transform (only if needed)
   if (needsTemporalString(columns)) {
     lines.push(`const TemporalString = Schema.Unknown.pipe(Schema.decodeTo(`)
     lines.push(`  Schema.String,`)
-    lines.push(`  SchemaTransformation.transform({ decode: (v) => (v).toString(), encode: (s) => s }),`)
+    lines.push(
+      `  SchemaTransformation.transform<string, unknown>({ decode: (v) => (v as { toString(): string }).toString(), encode: (s) => s }),`
+    )
     lines.push(`));`)
     lines.push(``)
   }
@@ -222,26 +249,20 @@ function generateTypedModule(cypher: string, columns: ReadonlyArray<ResolvedColu
   lines.push(`});`)
   lines.push(``)
 
-  // Decoder (compose transform + struct, wrap in array)
-  lines.push(`const decodeRows = Schema.decodeUnknownSync(`)
-  lines.push(`  Schema.Array(Neo4jRecordToObject.pipe(Schema.decodeTo(Row)))`)
-  lines.push(`);`)
+  // Decoder: validate each row's plain object against the struct
+  lines.push(`const decodeRows = Schema.decodeUnknownSync(Schema.Array(Row));`)
   lines.push(``)
 
   // Query export
-  if (params.length === 0) {
-    lines.push(`export const query = () =>`)
-  } else {
-    const destructure = `{ ${params.join(", ")} }`
-    lines.push(`export const query = (${destructure}) =>`)
-  }
+  lines.push(`export const query = (${sig?.decl ?? ""}) =>`)
   lines.push(`  Effect.flatMap(Neo4jClient, (neo4j) =>`)
 
-  if (params.length === 0) {
-    lines.push(`    Effect.map(neo4j.query(cypher), decodeRows));`)
+  if (sig === undefined) {
+    lines.push(`    Effect.map(neo4j.query(cypher), (records) => decodeRows(records.map((r) => r.toObject()))));`)
   } else {
-    const destructure = `{ ${params.join(", ")} }`
-    lines.push(`    Effect.map(neo4j.query(cypher, ${destructure}), decodeRows));`)
+    lines.push(
+      `    Effect.map(neo4j.query(cypher, ${sig.call}), (records) => decodeRows(records.map((r) => r.toObject()))));`
+    )
   }
   lines.push(``)
 
@@ -273,10 +294,10 @@ export interface BarrelEntry {
 export function generateBarrel(entries: ReadonlyArray<BarrelEntry>): string {
   const lines: Array<string> = []
 
-  const anyHasColumns = entries.some((e) => e.columns.length > 0)
+  const anyNeedTemporal = entries.some((e) => needsTemporalString(e.columns))
 
   lines.push(`// Auto-generated by cypher-codegen — do not edit`)
-  lines.push(`import { Effect, Schema${anyHasColumns ? ", SchemaTransformation" : ""} } from "effect"`)
+  lines.push(`import { Effect, Schema${anyNeedTemporal ? ", SchemaTransformation" : ""} } from "effect"`)
 
   // Collect all neo4j schema imports needed across all entries
   const allColumns = entries.flatMap((e) => e.columns)
@@ -288,24 +309,12 @@ export function generateBarrel(entries: ReadonlyArray<BarrelEntry>): string {
   }
   lines.push(``)
 
-  // Shared transforms (emit once)
-  if (anyHasColumns) {
-    lines.push(`const Neo4jRecordToObject = Schema.Unknown.pipe(Schema.decodeTo(`)
-    lines.push(`  Schema.Unknown,`)
-    lines.push(
-      `  SchemaTransformation.transform({ decode: (rec) => (rec as { toObject(): Record<string, unknown> }).toObject(), encode: (obj) => obj }),`
-    )
-    lines.push(`))`)
-    lines.push(``)
-  }
-
-  const anyNeedTemporal = entries.some((e) => needsTemporalString(e.columns))
-
+  // Shared temporal transform (emit once, only if needed)
   if (anyNeedTemporal) {
     lines.push(`const TemporalString = Schema.Unknown.pipe(Schema.decodeTo(`)
     lines.push(`  Schema.String,`)
     lines.push(
-      `  SchemaTransformation.transform({ decode: (v) => (v as { toString(): string }).toString(), encode: (s: string) => s }),`
+      `  SchemaTransformation.transform<string, unknown>({ decode: (v) => (v as { toString(): string }).toString(), encode: (s) => s }),`
     )
     lines.push(`))`)
     lines.push(``)
@@ -327,6 +336,8 @@ export function generateBarrel(entries: ReadonlyArray<BarrelEntry>): string {
     lines.push(`const ${name}Cypher = ${JSON.stringify(entry.cypher)}`)
     lines.push(``)
 
+    const sig = queryParams(entry.cypher, entry.params)
+
     if (hasColumns) {
       const decodeName = `decode${name.charAt(0).toUpperCase() + name.slice(1)}`
 
@@ -338,33 +349,26 @@ export function generateBarrel(entries: ReadonlyArray<BarrelEntry>): string {
       lines.push(``)
       lines.push(`export type ${name.charAt(0).toUpperCase() + name.slice(1)}Row = typeof ${name}Row.Type`)
       lines.push(``)
-      lines.push(`const ${decodeName} = Schema.decodeUnknownSync(`)
-      lines.push(`  Schema.Array(Neo4jRecordToObject.pipe(Schema.decodeTo(${name}Row)))`)
-      lines.push(`)`)
+      lines.push(`const ${decodeName} = Schema.decodeUnknownSync(Schema.Array(${name}Row))`)
       lines.push(``)
 
-      if (entry.params.length === 0) {
-        lines.push(`export const ${name} = () =>`)
-        lines.push(`  Effect.flatMap(Neo4jClient, (neo4j) =>`)
-        lines.push(`    Effect.map(neo4j.query(${name}Cypher), ${decodeName}))`)
+      lines.push(`export const ${name} = (${sig?.decl ?? ""}) =>`)
+      lines.push(`  Effect.flatMap(Neo4jClient, (neo4j) =>`)
+      if (sig === undefined) {
+        lines.push(
+          `    Effect.map(neo4j.query(${name}Cypher), (records) => ${decodeName}(records.map((r) => r.toObject()))))`
+        )
       } else {
-        const destructure = `{ ${entry.params.map((p) => p.name).join(", ")} }`
-        const typeAnnotation = entry.params.map((p) => `${p.name}: ${tsTypeFor(p.type)}${p.nullable ? " | null" : ""}`)
-          .join("; ")
-        lines.push(`export const ${name} = (${destructure}: { ${typeAnnotation} }) =>`)
-        lines.push(`  Effect.flatMap(Neo4jClient, (neo4j) =>`)
-        lines.push(`    Effect.map(neo4j.query(${name}Cypher, ${destructure}), ${decodeName}))`)
+        lines.push(
+          `    Effect.map(neo4j.query(${name}Cypher, ${sig.call}), (records) => ${decodeName}(records.map((r) => r.toObject()))))`
+        )
       }
     } else {
-      if (entry.params.length === 0) {
-        lines.push(`export const ${name} = () =>`)
+      lines.push(`export const ${name} = (${sig?.decl ?? ""}) =>`)
+      if (sig === undefined) {
         lines.push(`  Effect.flatMap(Neo4jClient, (neo4j) => neo4j.query(${name}Cypher))`)
       } else {
-        const destructure = `{ ${entry.params.map((p) => p.name).join(", ")} }`
-        const typeAnnotation = entry.params.map((p) => `${p.name}: ${tsTypeFor(p.type)}${p.nullable ? " | null" : ""}`)
-          .join("; ")
-        lines.push(`export const ${name} = (${destructure}: { ${typeAnnotation} }) =>`)
-        lines.push(`  Effect.flatMap(Neo4jClient, (neo4j) => neo4j.query(${name}Cypher, ${destructure}))`)
+        lines.push(`  Effect.flatMap(Neo4jClient, (neo4j) => neo4j.query(${name}Cypher, ${sig.call}))`)
       }
     }
 
diff --git a/packages/cypher-codegen/src/backend/CypherCodegen.typecheck.node.unit.test.ts b/packages/cypher-codegen/src/backend/CypherCodegen.typecheck.node.unit.test.ts
new file mode 100644
index 0000000..9197678
--- /dev/null
+++ b/packages/cypher-codegen/src/backend/CypherCodegen.typecheck.node.unit.test.ts
@@ -0,0 +1,110 @@
+import { describe, expect, it } from "@effect/vitest"
+import * as path from "node:path"
+import { fileURLToPath } from "node:url"
+import ts from "typescript"
+import type { ResolvedColumn, ResolvedParam } from "../frontend/QueryAnalyzer.js"
+import { type CypherType, ListType, MapType, ScalarType, UnknownType } from "../types/CypherType.js"
+import { type BarrelEntry, generateBarrel, generateModule } from "./CypherCodegen.js"
+
+// Type-checks generated query source against the repo's real compiler options.
+//
+// The unit tests in CypherCodegen.node.unit.test.ts only assert on the emitted
+// *string*; they never compile it. The regression these guards exist for —
+// generated `queries.ts` failing to type-check under Effect v4 — therefore could
+// not surface as a string assertion. These tests close that gap by running the
+// TypeScript checker over the generator's output and asserting zero diagnostics.
+
+const here = path.dirname(fileURLToPath(import.meta.url))
+const repoRoot = path.resolve(here, "../../../..")
+const virtualPath = path.join(here, "__codegen_typecheck__.ts")
+
+const compilerOptions = (): ts.CompilerOptions => {
+  const configFile = ts.readConfigFile(path.join(repoRoot, "tsconfig.base.json"), ts.sys.readFile)
+  const parsed = ts.parseJsonConfigFileContent(configFile.config, ts.sys, repoRoot)
+  return {
+    ...parsed.options,
+    // Single in-memory file: drop build-mode flags and emit. tsBuildInfoFile is
+    // omitted rather than set to undefined (exactOptionalPropertyTypes forbids it).
+    composite: false,
+    incremental: false,
+    noEmit: true,
+    skipLibCheck: true,
+    types: []
+  }
+}
+
+const typeCheck = (source: string): ReadonlyArray<string> => {
+  const options = compilerOptions()
+  const host = ts.createCompilerHost(options, true)
+  const getSourceFile = host.getSourceFile.bind(host)
+  host.getSourceFile = (fileName, languageVersion, onError, shouldCreate) =>
+    path.resolve(fileName) === virtualPath
+      ? ts.createSourceFile(fileName, source, languageVersion, true)
+      : getSourceFile(fileName, languageVersion, onError, shouldCreate)
+
+  const program = ts.createProgram([virtualPath], options, host)
+  const sourceFile = program.getSourceFile(virtualPath)!
+  return [...program.getSyntacticDiagnostics(sourceFile), ...program.getSemanticDiagnostics(sourceFile)]
+    .map((d) => ts.flattenDiagnosticMessageText(d.messageText, "\n"))
+}
+
+// ── Helpers ──
+
+const scalar = (t: string): ScalarType => new ScalarType({ scalarType: t as ScalarType["scalarType"] })
+
+const col = (name: string, type: CypherType, nullable: boolean): ResolvedColumn => ({ name, type, nullable })
+
+const param = (name: string, type: ResolvedParam["type"], nullable: boolean): ResolvedParam => ({
+  name,
+  type,
+  nullable
+})
+
+// Columns covering every schema-emitting branch: scalars, Neo4jInt (Long),
+// nullable, temporal (TemporalString + SchemaTransformation), list, map, and
+// the Neo4jValue escape hatch.
+const allColumns: ReadonlyArray<ResolvedColumn> = [
+  col("fqcn", scalar("String"), false),
+  col("count", scalar("Long"), false),
+  col("ratio", scalar("Double"), false),
+  col("active", scalar("Boolean"), true),
+  col("createdAt", scalar("DateTime"), false),
+  col("tags", ListType(scalar("String")), false),
+  col("meta", MapType([{ name: "label", value: scalar("String") }]), false),
+  col("blob", new UnknownType(), false)
+]
+
+describe("generated source type-checks under Effect v4", () => {
+  it("generateModule output compiles with no type errors", () => {
+    const source = generateModule(
+      "MATCH (c:Class {fqcn: $fqcn}) WHERE c.count > $min RETURN c.fqcn AS fqcn",
+      allColumns,
+      [param("fqcn", "String", false), param("min", "Long", true)]
+    )
+    expect(typeCheck(source)).toEqual([])
+  })
+
+  it("generateBarrel output compiles with no type errors", () => {
+    const entries: ReadonlyArray<BarrelEntry> = [
+      {
+        filename: "Classes.cypher",
+        cypher: "MATCH (c:Class) WHERE c.label = $label RETURN c.fqcn AS fqcn, count(c) AS count",
+        columns: [col("fqcn", scalar("String"), false), col("count", scalar("Long"), false)],
+        params: [param("label", "String", false)]
+      },
+      {
+        filename: "Raw.cypher",
+        cypher: "MATCH (c:Class) RETURN c",
+        columns: [],
+        params: []
+      },
+      {
+        filename: "Events.cypher",
+        cypher: "MATCH (e:Event) RETURN e.at AS at",
+        columns: [col("at", scalar("DateTime"), false)],
+        params: []
+      }
+    ]
+    expect(typeCheck(generateBarrel(entries))).toEqual([])
+  })
+})
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index fbf5862..9ef01c3 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -177,6 +177,9 @@ importers:
       neo4j-driver:
         specifier: ^6.0.1
         version: 6.0.1
+      typescript:
+        specifier: 5.9.3
+        version: 5.9.3
     publishDirectory: dist
 
   packages/demo:
@@ -282,7 +285,7 @@ importers:
     dependencies:
       vitest:
         specifier: ^3.2.4
-        version: 3.2.4(@edge-runtime/vm@4.0.3)(@types/node@24.12.2)(@vitest/browser@3.2.4)(msw@2.12.10(@types/node@24.12.2)(typescript@5.9.3))(terser@5.32.0)(tsx@4.17.0)(yaml@2.8.3)
+        version: 3.2.4(@edge-runtime/vm@4.0.3)(@types/node@24.13.0)(@vitest/browser@3.2.4)(msw@2.12.10(@types/node@24.13.0)(typescript@5.9.3))(terser@5.32.0)(tsx@4.17.0)(yaml@2.9.0)
     devDependencies:
       '@evryg/effect-neo4j':
         specifier: workspace:^
@@ -7531,6 +7534,14 @@ snapshots:
       '@types/node': 24.12.2
     optional: true
 
+  '@inquirer/confirm@5.1.21(@types/node@24.13.0)':
+    dependencies:
+      '@inquirer/core': 10.3.2(@types/node@24.13.0)
+      '@inquirer/type': 3.0.10(@types/node@24.13.0)
+    optionalDependencies:
+      '@types/node': 24.13.0
+    optional: true
+
   '@inquirer/core@10.3.2(@types/node@24.12.2)':
     dependencies:
       '@inquirer/ansi': 1.0.2
@@ -7545,6 +7556,20 @@ snapshots:
       '@types/node': 24.12.2
     optional: true
 
+  '@inquirer/core@10.3.2(@types/node@24.13.0)':
+    dependencies:
+      '@inquirer/ansi': 1.0.2
+      '@inquirer/figures': 1.0.15
+      '@inquirer/type': 3.0.10(@types/node@24.13.0)
+      cli-width: 4.1.0
+      mute-stream: 2.0.0
+      signal-exit: 4.1.0
+      wrap-ansi: 6.2.0
+      yoctocolors-cjs: 2.1.3
+    optionalDependencies:
+      '@types/node': 24.13.0
+    optional: true
+
   '@inquirer/external-editor@1.0.3(@types/node@24.12.2)':
     dependencies:
       chardet: 2.1.1
@@ -7560,6 +7585,11 @@ snapshots:
       '@types/node': 24.12.2
     optional: true
 
+  '@inquirer/type@3.0.10(@types/node@24.13.0)':
+    optionalDependencies:
+      '@types/node': 24.13.0
+    optional: true
+
   '@ioredis/commands@1.10.0': {}
 
   '@isaacs/cliui@9.0.0': {}
@@ -8154,16 +8184,16 @@ snapshots:
   '@unrs/resolver-binding-win32-x64-msvc@1.11.1':
     optional: true
 
-  '@vitest/browser@3.2.4(msw@2.12.10(@types/node@24.12.2)(typescript@5.9.3))(playwright@1.58.2)(vite@6.4.2(@types/node@24.12.2)(terser@5.32.0)(tsx@4.17.0)(yaml@2.8.3))(vitest@3.2.4)':
+  '@vitest/browser@3.2.4(msw@2.12.10(@types/node@24.12.2)(typescript@5.9.3))(playwright@1.58.2)(vite@6.4.2(@types/node@24.12.2)(terser@5.32.0)(tsx@4.17.0)(yaml@2.9.0))(vitest@3.2.4)':
     dependencies:
       '@testing-library/dom': 10.4.0
       '@testing-library/user-event': 14.6.1(@testing-library/dom@10.4.0)
-      '@vitest/mocker': 3.2.4(msw@2.12.10(@types/node@24.12.2)(typescript@5.9.3))(vite@6.4.2(@types/node@24.12.2)(terser@5.32.0)(tsx@4.17.0)(yaml@2.8.3))
+      '@vitest/mocker': 3.2.4(msw@2.12.10(@types/node@24.12.2)(typescript@5.9.3))(vite@6.4.2(@types/node@24.12.2)(terser@5.32.0)(tsx@4.17.0)(yaml@2.9.0))
       '@vitest/utils': 3.2.4
       magic-string: 0.30.21
       sirv: 3.0.2
       tinyrainbow: 2.0.0
-      vitest: 3.2.4(@edge-runtime/vm@4.0.3)(@types/node@24.12.2)(@vitest/browser@3.2.4)(msw@2.12.10(@types/node@24.12.2)(typescript@5.9.3))(terser@5.32.0)(tsx@4.17.0)(yaml@2.8.3)
+      vitest: 3.2.4(@edge-runtime/vm@4.0.3)(@types/node@24.12.2)(@vitest/browser@3.2.4)(msw@2.12.10(@types/node@24.12.2)(typescript@5.9.3))(terser@5.32.0)(tsx@4.17.0)(yaml@2.9.0)
       ws: 8.20.0
     optionalDependencies:
       playwright: 1.58.2
@@ -8172,18 +8202,17 @@ snapshots:
       - msw
       - utf-8-validate
       - vite
-    optional: true
 
-  '@vitest/browser@3.2.4(msw@2.12.10(@types/node@24.12.2)(typescript@5.9.3))(playwright@1.58.2)(vite@6.4.2(@types/node@24.12.2)(terser@5.32.0)(tsx@4.17.0)(yaml@2.9.0))(vitest@3.2.4)':
+  '@vitest/browser@3.2.4(msw@2.12.10(@types/node@24.13.0)(typescript@5.9.3))(playwright@1.58.2)(vite@6.4.2(@types/node@24.13.0)(terser@5.32.0)(tsx@4.17.0)(yaml@2.9.0))(vitest@3.2.4)':
     dependencies:
       '@testing-library/dom': 10.4.0
       '@testing-library/user-event': 14.6.1(@testing-library/dom@10.4.0)
-      '@vitest/mocker': 3.2.4(msw@2.12.10(@types/node@24.12.2)(typescript@5.9.3))(vite@6.4.2(@types/node@24.12.2)(terser@5.32.0)(tsx@4.17.0)(yaml@2.9.0))
+      '@vitest/mocker': 3.2.4(msw@2.12.10(@types/node@24.13.0)(typescript@5.9.3))(vite@6.4.2(@types/node@24.13.0)(terser@5.32.0)(tsx@4.17.0)(yaml@2.9.0))
       '@vitest/utils': 3.2.4
       magic-string: 0.30.21
       sirv: 3.0.2
       tinyrainbow: 2.0.0
-      vitest: 3.2.4(@edge-runtime/vm@4.0.3)(@types/node@24.12.2)(@vitest/browser@3.2.4)(msw@2.12.10(@types/node@24.12.2)(typescript@5.9.3))(terser@5.32.0)(tsx@4.17.0)(yaml@2.9.0)
+      vitest: 3.2.4(@edge-runtime/vm@4.0.3)(@types/node@24.13.0)(@vitest/browser@3.2.4)(msw@2.12.10(@types/node@24.13.0)(typescript@5.9.3))(terser@5.32.0)(tsx@4.17.0)(yaml@2.9.0)
       ws: 8.20.0
     optionalDependencies:
       playwright: 1.58.2
@@ -8192,6 +8221,7 @@ snapshots:
       - msw
       - utf-8-validate
       - vite
+    optional: true
 
   '@vitest/coverage-v8@3.2.4(@vitest/browser@3.2.4)(vitest@3.2.4)':
     dependencies:
@@ -8222,23 +8252,23 @@ snapshots:
       chai: 5.3.3
       tinyrainbow: 2.0.0
 
-  '@vitest/mocker@3.2.4(msw@2.12.10(@types/node@24.12.2)(typescript@5.9.3))(vite@6.4.2(@types/node@24.12.2)(terser@5.32.0)(tsx@4.17.0)(yaml@2.8.3))':
+  '@vitest/mocker@3.2.4(msw@2.12.10(@types/node@24.12.2)(typescript@5.9.3))(vite@6.4.2(@types/node@24.12.2)(terser@5.32.0)(tsx@4.17.0)(yaml@2.9.0))':
     dependencies:
       '@vitest/spy': 3.2.4
       estree-walker: 3.0.3
       magic-string: 0.30.21
     optionalDependencies:
       msw: 2.12.10(@types/node@24.12.2)(typescript@5.9.3)
-      vite: 6.4.2(@types/node@24.12.2)(terser@5.32.0)(tsx@4.17.0)(yaml@2.8.3)
+      vite: 6.4.2(@types/node@24.12.2)(terser@5.32.0)(tsx@4.17.0)(yaml@2.9.0)
 
-  '@vitest/mocker@3.2.4(msw@2.12.10(@types/node@24.12.2)(typescript@5.9.3))(vite@6.4.2(@types/node@24.12.2)(terser@5.32.0)(tsx@4.17.0)(yaml@2.9.0))':
+  '@vitest/mocker@3.2.4(msw@2.12.10(@types/node@24.13.0)(typescript@5.9.3))(vite@6.4.2(@types/node@24.13.0)(terser@5.32.0)(tsx@4.17.0)(yaml@2.9.0))':
     dependencies:
       '@vitest/spy': 3.2.4
       estree-walker: 3.0.3
       magic-string: 0.30.21
     optionalDependencies:
-      msw: 2.12.10(@types/node@24.12.2)(typescript@5.9.3)
-      vite: 6.4.2(@types/node@24.12.2)(terser@5.32.0)(tsx@4.17.0)(yaml@2.9.0)
+      msw: 2.12.10(@types/node@24.13.0)(typescript@5.9.3)
+      vite: 6.4.2(@types/node@24.13.0)(terser@5.32.0)(tsx@4.17.0)(yaml@2.9.0)
 
   '@vitest/pretty-format@3.2.4':
     dependencies:
@@ -10599,6 +10629,32 @@ snapshots:
       - '@types/node'
     optional: true
 
+  msw@2.12.10(@types/node@24.13.0)(typescript@5.9.3):
+    dependencies:
+      '@inquirer/confirm': 5.1.21(@types/node@24.13.0)
+      '@mswjs/interceptors': 0.41.9
+      '@open-draft/deferred-promise': 2.2.0
+      '@types/statuses': 2.0.6
+      cookie: 1.1.1
+      graphql: 16.14.1
+      headers-polyfill: 4.0.3
+      is-node-process: 1.2.0
+      outvariant: 1.4.3
+      path-to-regexp: 6.3.0
+      picocolors: 1.1.1
+      rettime: 0.10.1
+      statuses: 2.0.2
+      strict-event-emitter: 0.5.1
+      tough-cookie: 6.0.1
+      type-fest: 5.7.0
+      until-async: 3.0.2
+      yargs: 17.7.2
+    optionalDependencies:
+      typescript: 5.9.3
+    transitivePeerDependencies:
+      - '@types/node'
+    optional: true
+
   multipasta@0.2.7: {}
 
   mute-stream@2.0.0:
@@ -12043,13 +12099,13 @@ snapshots:
       spdx-correct: 3.2.0
       spdx-expression-parse: 3.0.1
 
-  vite-node@3.2.4(@types/node@24.12.2)(terser@5.32.0)(tsx@4.17.0)(yaml@2.8.3):
+  vite-node@3.2.4(@types/node@24.12.2)(terser@5.32.0)(tsx@4.17.0)(yaml@2.9.0):
     dependencies:
       cac: 6.7.14
       debug: 4.4.3
       es-module-lexer: 1.7.0
       pathe: 2.0.3
-      vite: 6.4.2(@types/node@24.12.2)(terser@5.32.0)(tsx@4.17.0)(yaml@2.8.3)
+      vite: 6.4.2(@types/node@24.12.2)(terser@5.32.0)(tsx@4.17.0)(yaml@2.9.0)
     transitivePeerDependencies:
       - '@types/node'
       - jiti
@@ -12064,13 +12120,13 @@ snapshots:
       - tsx
       - yaml
 
-  vite-node@3.2.4(@types/node@24.12.2)(terser@5.32.0)(tsx@4.17.0)(yaml@2.9.0):
+  vite-node@3.2.4(@types/node@24.13.0)(terser@5.32.0)(tsx@4.17.0)(yaml@2.9.0):
     dependencies:
       cac: 6.7.14
       debug: 4.4.3
       es-module-lexer: 1.7.0
       pathe: 2.0.3
-      vite: 6.4.2(@types/node@24.12.2)(terser@5.32.0)(tsx@4.17.0)(yaml@2.9.0)
+      vite: 6.4.2(@types/node@24.13.0)(terser@5.32.0)(tsx@4.17.0)(yaml@2.9.0)
     transitivePeerDependencies:
       - '@types/node'
       - jiti
@@ -12085,7 +12141,7 @@ snapshots:
       - tsx
       - yaml
 
-  vite@6.4.2(@types/node@24.12.2)(terser@5.32.0)(tsx@4.17.0)(yaml@2.8.3):
+  vite@6.4.2(@types/node@24.12.2)(terser@5.32.0)(tsx@4.17.0)(yaml@2.9.0):
     dependencies:
       esbuild: 0.25.12
       fdir: 6.5.0(picomatch@4.0.4)
@@ -12098,9 +12154,9 @@ snapshots:
       fsevents: 2.3.3
       terser: 5.32.0
       tsx: 4.17.0
-      yaml: 2.8.3
+      yaml: 2.9.0
 
-  vite@6.4.2(@types/node@24.12.2)(terser@5.32.0)(tsx@4.17.0)(yaml@2.9.0):
+  vite@6.4.2(@types/node@24.13.0)(terser@5.32.0)(tsx@4.17.0)(yaml@2.9.0):
     dependencies:
       esbuild: 0.25.12
       fdir: 6.5.0(picomatch@4.0.4)
@@ -12109,17 +12165,17 @@ snapshots:
       rollup: 4.57.1
       tinyglobby: 0.2.16
     optionalDependencies:
-      '@types/node': 24.12.2
+      '@types/node': 24.13.0
       fsevents: 2.3.3
       terser: 5.32.0
       tsx: 4.17.0
       yaml: 2.9.0
 
-  vitest@3.2.4(@edge-runtime/vm@4.0.3)(@types/node@24.12.2)(@vitest/browser@3.2.4)(msw@2.12.10(@types/node@24.12.2)(typescript@5.9.3))(terser@5.32.0)(tsx@4.17.0)(yaml@2.8.3):
+  vitest@3.2.4(@edge-runtime/vm@4.0.3)(@types/node@24.12.2)(@vitest/browser@3.2.4)(msw@2.12.10(@types/node@24.12.2)(typescript@5.9.3))(terser@5.32.0)(tsx@4.17.0)(yaml@2.9.0):
     dependencies:
       '@types/chai': 5.2.3
       '@vitest/expect': 3.2.4
-      '@vitest/mocker': 3.2.4(msw@2.12.10(@types/node@24.12.2)(typescript@5.9.3))(vite@6.4.2(@types/node@24.12.2)(terser@5.32.0)(tsx@4.17.0)(yaml@2.8.3))
+      '@vitest/mocker': 3.2.4(msw@2.12.10(@types/node@24.12.2)(typescript@5.9.3))(vite@6.4.2(@types/node@24.12.2)(terser@5.32.0)(tsx@4.17.0)(yaml@2.9.0))
       '@vitest/pretty-format': 3.2.4
       '@vitest/runner': 3.2.4
       '@vitest/snapshot': 3.2.4
@@ -12137,13 +12193,13 @@ snapshots:
       tinyglobby: 0.2.16
       tinypool: 1.1.1
       tinyrainbow: 2.0.0
-      vite: 6.4.2(@types/node@24.12.2)(terser@5.32.0)(tsx@4.17.0)(yaml@2.8.3)
-      vite-node: 3.2.4(@types/node@24.12.2)(terser@5.32.0)(tsx@4.17.0)(yaml@2.8.3)
+      vite: 6.4.2(@types/node@24.12.2)(terser@5.32.0)(tsx@4.17.0)(yaml@2.9.0)
+      vite-node: 3.2.4(@types/node@24.12.2)(terser@5.32.0)(tsx@4.17.0)(yaml@2.9.0)
       why-is-node-running: 2.3.0
     optionalDependencies:
       '@edge-runtime/vm': 4.0.3
       '@types/node': 24.12.2
-      '@vitest/browser': 3.2.4(msw@2.12.10(@types/node@24.12.2)(typescript@5.9.3))(playwright@1.58.2)(vite@6.4.2(@types/node@24.12.2)(terser@5.32.0)(tsx@4.17.0)(yaml@2.8.3))(vitest@3.2.4)
+      '@vitest/browser': 3.2.4(msw@2.12.10(@types/node@24.12.2)(typescript@5.9.3))(playwright@1.58.2)(vite@6.4.2(@types/node@24.12.2)(terser@5.32.0)(tsx@4.17.0)(yaml@2.9.0))(vitest@3.2.4)
     transitivePeerDependencies:
       - jiti
       - less
@@ -12158,11 +12214,11 @@ snapshots:
       - tsx
       - yaml
 
-  vitest@3.2.4(@edge-runtime/vm@4.0.3)(@types/node@24.12.2)(@vitest/browser@3.2.4)(msw@2.12.10(@types/node@24.12.2)(typescript@5.9.3))(terser@5.32.0)(tsx@4.17.0)(yaml@2.9.0):
+  vitest@3.2.4(@edge-runtime/vm@4.0.3)(@types/node@24.13.0)(@vitest/browser@3.2.4)(msw@2.12.10(@types/node@24.13.0)(typescript@5.9.3))(terser@5.32.0)(tsx@4.17.0)(yaml@2.9.0):
     dependencies:
       '@types/chai': 5.2.3
       '@vitest/expect': 3.2.4
-      '@vitest/mocker': 3.2.4(msw@2.12.10(@types/node@24.12.2)(typescript@5.9.3))(vite@6.4.2(@types/node@24.12.2)(terser@5.32.0)(tsx@4.17.0)(yaml@2.9.0))
+      '@vitest/mocker': 3.2.4(msw@2.12.10(@types/node@24.13.0)(typescript@5.9.3))(vite@6.4.2(@types/node@24.13.0)(terser@5.32.0)(tsx@4.17.0)(yaml@2.9.0))
       '@vitest/pretty-format': 3.2.4
       '@vitest/runner': 3.2.4
       '@vitest/snapshot': 3.2.4
@@ -12180,13 +12236,13 @@ snapshots:
       tinyglobby: 0.2.16
       tinypool: 1.1.1
       tinyrainbow: 2.0.0
-      vite: 6.4.2(@types/node@24.12.2)(terser@5.32.0)(tsx@4.17.0)(yaml@2.9.0)
-      vite-node: 3.2.4(@types/node@24.12.2)(terser@5.32.0)(tsx@4.17.0)(yaml@2.9.0)
+      vite: 6.4.2(@types/node@24.13.0)(terser@5.32.0)(tsx@4.17.0)(yaml@2.9.0)
+      vite-node: 3.2.4(@types/node@24.13.0)(terser@5.32.0)(tsx@4.17.0)(yaml@2.9.0)
       why-is-node-running: 2.3.0
     optionalDependencies:
       '@edge-runtime/vm': 4.0.3
-      '@types/node': 24.12.2
-      '@vitest/browser': 3.2.4(msw@2.12.10(@types/node@24.12.2)(typescript@5.9.3))(playwright@1.58.2)(vite@6.4.2(@types/node@24.12.2)(terser@5.32.0)(tsx@4.17.0)(yaml@2.9.0))(vitest@3.2.4)
+      '@types/node': 24.13.0
+      '@vitest/browser': 3.2.4(msw@2.12.10(@types/node@24.13.0)(typescript@5.9.3))(playwright@1.58.2)(vite@6.4.2(@types/node@24.13.0)(terser@5.32.0)(tsx@4.17.0)(yaml@2.9.0))(vitest@3.2.4)
     transitivePeerDependencies:
       - jiti
       - less