fix(codemode): stop leaking undefined into tool arguments

packages/codemode/interpreter-support.md

@@ -19,7 +19,7 @@ ultimate source of truth.
 - [x] Top-level `await` and `return` through the program's implicit async-function scope.
 - [x] Explicit `return`, final top-level expression as a REPL-style result, and `null` when no value is produced.
 - [x] Program results use JSON-like boundaries, with `undefined` and non-finite numbers normalized to `null`. Tool
-      arguments remain subject to their schema and the outbound-handling gap listed below.
+      arguments follow JSON serialization semantics before their schema applies (see the tools section).
 - [x] Live Date, RegExp, Map, Set, URL, and URLSearchParams values inside CodeMode.
 - [x] Tool calls through the host-provided `tools` tree only.
 - [x] The global `search(...)` built-in: synchronous tool discovery that counts as an admitted tool call and is
@@ -157,8 +157,11 @@ ultimate source of truth.
 - [x] Dotted tool names are canonicalized into namespace paths; a path can be both callable and a namespace, and the
       last definition supplied for a canonical path wins.
 - [x] Tool path segments may be named `constructor`, `prototype`, or `__proto__` because paths use inert Map keys.
-- [ ] Reject `undefined` and non-finite numbers in outbound tool arguments before render-only and OpenAPI tools run;
-      retain null normalization for program results and JSON serialization.
+- [x] Outbound tool arguments follow JSON serialization semantics, like `JSON.stringify`: object properties with
+      `undefined` values are dropped, `undefined` array elements and non-finite numbers become `null`, and sparse
+      arrays densify. Tools never receive `undefined` inside their input object, though a bare `tools.t(undefined)`
+      argument still reaches schema decoding as `undefined`. Program results keep the stricter
+      normalization where every `undefined` becomes `null`.
 - [ ] Tokenize and case-fold non-ASCII tool paths, descriptions, and queries for tool search.
 
 ## Objects and properties

packages/codemode/src/interpreter/errors.ts

@@ -44,7 +44,7 @@ export const normalizeError = (error: unknown): Diagnostic => {
       message = (value as { message: string }).message
     } else {
       try {
-        message = JSON.stringify(copyOut(value)) ?? String(value)
+        message = JSON.stringify(copyOut(value, "json")) ?? String(value)
       } catch {
         message = String(value)
       }

packages/codemode/src/interpreter/execute.ts

@@ -52,7 +52,7 @@ export const executeWithLimits = <const Provided extends Record<string, unknown>
             logs,
           )
           const value = yield* interpreter.run(program)
-          const result = copyOut(copyIn(value, "Execution result"), true) as DataValue
+          const result = copyOut(copyIn(value, "Execution result"), "nullify") as DataValue
           returned = { value: result, promises }
           const warnings = yield* promises.interrupt()
           return {

packages/codemode/src/stdlib/console.ts

@@ -89,7 +89,7 @@ const formatConsoleTable = (value: unknown, columnsArgument: unknown): string =>
 const consoleTableColumns = (value: unknown): ReadonlyArray<string> | undefined => {
   if (value === undefined) return undefined
   if (containsRuntimeReference(value)) return undefined
-  const columns = copyOut(copyIn(value, "console.table columns"), true)
+  const columns = copyOut(copyIn(value, "console.table columns"), "nullify")
   return Array.isArray(columns) ? columns.map((column) => String(column)) : undefined
 }
 

packages/codemode/src/stdlib/json.ts

@@ -18,7 +18,7 @@ export const invokeJsonMethod = (name: string, args: Array<unknown>, node: AstNo
       }
       const space = args[2]
       const indent = typeof space === "number" || typeof space === "string" ? space : undefined
-      return JSON.stringify(copyOut(copyIn(args[0], "JSON.stringify value")), null, indent)
+      return JSON.stringify(copyOut(copyIn(args[0], "JSON.stringify value"), "json"), null, indent)
     }
     case "parse": {
       const text = args[0]

packages/codemode/src/tool-runtime.ts

@@ -118,8 +118,7 @@ export class ToolRuntimeError extends Error {
   }
 }
 
-const isDefinition = <R>(value: Definition<R> | Tools<R>): value is Definition<R> =>
-  isToolDefinition<R>(value)
+const isDefinition = <R>(value: Definition<R> | Tools<R>): value is Definition<R> => isToolDefinition<R>(value)
 
 const runHost = <A, E, R>(effect: Effect.Effect<A, E, R>): Effect.Effect<A, ToolError, R> =>
   effect.pipe(
@@ -257,18 +256,31 @@ const copyBounded = (
   return copied
 }
 
-export const copyOut = (value: unknown, undefinedAsNull = false): unknown => {
-  if (value === undefined && undefinedAsNull) return null
+// "json" mirrors JSON.stringify (undefined object values drop, undefined array elements become
+// null, a bare undefined passes through): use it wherever data leaves as JSON, like tool
+// arguments and stringify-style formatting. "nullify" turns every undefined, including a bare
+// one, into null: use it for program results, where the consumer must never see undefined.
+export type CopyOutMode = "json" | "nullify"
+
+export const copyOut = (value: unknown, mode: CopyOutMode): unknown => {
+  if (value === undefined && mode === "nullify") return null
   if (typeof value === "number" && !Number.isFinite(value)) {
     return null
   }
   if (Array.isArray(value)) {
     // Array.from densifies holes so sparse arrays normalize at the boundary like JSON does.
-    return Array.from(value, (item) => copyOut(item, undefinedAsNull))
+    return Array.from(value, (item) => {
+      const copied = copyOut(item, mode)
+      return copied === undefined && mode === "json" ? null : copied
+    })
   }
 
   if (value !== null && typeof value === "object" && !(value instanceof ToolReference)) {
-    return Object.fromEntries(Object.entries(value).map(([key, item]) => [key, copyOut(item, undefinedAsNull)]))
+    return Object.fromEntries(
+      Object.entries(value)
+        .map(([key, item]) => [key, copyOut(item, mode)] as const)
+        .filter(([, item]) => !(item === undefined && mode === "json")),
+    )
   }
 
   return value
@@ -696,13 +708,13 @@ export const make = <R>(
         invokeDefinition(
           "search",
           searchTool,
-          args.map((arg) => copyOut(copyIn(arg, "Arguments for tool 'search'"))),
+          args.map((arg) => copyOut(copyIn(arg, "Arguments for tool 'search'"), "json")),
         ),
       ),
     invoke: (path, args) =>
       Effect.gen(function* () {
         const name = canonicalSegments(path).join(".")
-        const externalArgs = args.map((arg) => copyOut(copyIn(arg, `Arguments for tool '${name}'`)))
+        const externalArgs = args.map((arg) => copyOut(copyIn(arg, `Arguments for tool '${name}'`), "json"))
         const tool = resolve(root, path)
         return yield* invokeDefinition(name, tool, externalArgs)
       }),

packages/codemode/test/codemode.test.ts

@@ -453,6 +453,56 @@ describe("CodeMode schema flexibility", () => {
     expect(observed).toStrictEqual([{ id: 42 }])
   })
 
+  test("outbound tool arguments follow JSON serialization semantics", async () => {
+    const observed: Array<unknown> = []
+    const call = Tool.make({
+      description: "Observe raw input",
+      input: { type: "object" },
+      run: (input) =>
+        Effect.sync(() => {
+          observed.push(input)
+          return "ok"
+        }),
+    })
+    const runtime = CodeMode.make({ tools: { adapter: { call } } })
+
+    const result = await Effect.runPromise(
+      runtime.execute(
+        `return await tools.adapter.call({ q: undefined, limit: 0 / 0, rate: 1 / 0, items: [1, undefined, 2], holes: [1, , 3] })`,
+      ),
+    )
+    expect(result.ok).toBe(true)
+    const received = observed[0] as Record<string, unknown>
+    expect(received).toStrictEqual({ limit: null, rate: null, items: [1, null, 2], holes: [1, null, 3] })
+    // The undefined-valued property is dropped like JSON.stringify, not delivered as undefined.
+    expect(Object.hasOwn(received, "q")).toBe(false)
+  })
+
+  test("dropping undefined values lets optionalKey schemas accept conditional arguments", async () => {
+    const observed: Array<unknown> = []
+    const find = Tool.make({
+      description: "Find things",
+      input: Schema.Struct({ query: Schema.optionalKey(Schema.String), limit: Schema.optionalKey(Schema.Number) }),
+      run: (input) =>
+        Effect.sync(() => {
+          observed.push(input)
+          return "ok"
+        }),
+    })
+    const runtime = CodeMode.make({ tools: { things: { find } } })
+
+    // The `cond ? value : undefined` idiom: optionalKey rejects a present undefined, so the
+    // JSON boundary must drop the key before the schema decodes.
+    const result = await Effect.runPromise(
+      runtime.execute(`return await tools.things.find({ query: undefined, limit: 5 })`),
+    )
+    expect(result.ok).toBe(true)
+    expect(observed).toStrictEqual([{ limit: 5 }])
+
+    const search = await Effect.runPromise(runtime.execute(`return (await search({ query: undefined })).items.length`))
+    expect(search.ok).toBe(true)
+  })
+
   test("renders JSON Schema outputs and $defs references", async () => {
     const lookup = Tool.make({
       description: "Look up a user",

packages/codemode/test/parity.test.ts

@@ -258,11 +258,23 @@ describe("H1: NaN/Infinity flow as intermediates and normalize to null at the bo
 
   test("copyOut normalizes non-finite numbers to null (the shared return + tool-arg boundary)", () => {
     // Tool-call arguments funnel through copyOut too, so this one function pins both boundaries.
-    expect(ToolRuntime.copyOut(NaN)).toBeNull()
-    expect(ToolRuntime.copyOut(Infinity)).toBeNull()
-    expect(ToolRuntime.copyOut(-Infinity)).toBeNull()
-    expect(ToolRuntime.copyOut(42)).toBe(42)
-    expect(ToolRuntime.copyOut({ a: NaN, b: [Infinity, 1] })).toEqual({ a: null, b: [null, 1] })
+    expect(ToolRuntime.copyOut(NaN, "json")).toBeNull()
+    expect(ToolRuntime.copyOut(Infinity, "json")).toBeNull()
+    expect(ToolRuntime.copyOut(-Infinity, "nullify")).toBeNull()
+    expect(ToolRuntime.copyOut(42, "json")).toBe(42)
+    expect(ToolRuntime.copyOut({ a: NaN, b: [Infinity, 1] }, "json")).toEqual({ a: null, b: [null, 1] })
+  })
+})
+
+describe("copyOut undefined handling per boundary mode", () => {
+  test("json mode mirrors JSON.stringify for undefined", () => {
+    expect(ToolRuntime.copyOut({ q: undefined, keep: 1 }, "json")).toStrictEqual({ keep: 1 })
+    expect(ToolRuntime.copyOut([1, undefined, 2], "json")).toStrictEqual([1, null, 2])
+    expect(ToolRuntime.copyOut({ nested: { a: undefined, b: [undefined] } }, "json")).toStrictEqual({
+      nested: { b: [null] },
+    })
+    expect(ToolRuntime.copyOut(undefined, "json")).toBeUndefined()
+    expect(ToolRuntime.copyOut({ a: undefined }, "nullify")).toStrictEqual({ a: null })
   })
 })