fix: stop const-less anyOf branches from crashing the form, and never select a non-string enum

Closes #2007.

Two things, both surfaced while answering "does #1928's PR also fix #2007?".

**#2007, and why it belongs in this PR.** `z.array(z.union([z.object(…),
z.object(…)]))` gives an `items.anyOf` whose branches carry no top-level
`const`, so every MultiSelect option was `String(item.const ?? "")` — the
empty string, twice. Mantine *throws* on duplicate option values, greying
out the whole tool panel.

That is a pre-existing bug, but this branch makes it reachable from a new
direction: a *nullable* array of object unions previously had no top-level
`type` and fell to the JSON fallback, and now collapses to `type: "array"`
with `items.anyOf` — straight into the crash. Shipping the collapse without
this fix would widen an existing crash, so the two go together. Both shapes
are covered by tests.

`toConstOptions` now returns `null` unless every branch yields a distinct,
non-empty value, and the field falls through to the JSON editor — which is
the honest widget for a union of object shapes anyway. Applied to the
`string`/`oneOf` path as well, which had the identical `?? ""` and the same
duplicate-throw waiting on it.

**Copilot round 2.** Round 1's fix kept "an explicit `type` is
authoritative", so `{ type: "number", enum: [1, 2] }` still collapses with
its enum hoisted. The TUI's dispatcher tests `property.enum` *before* the
type switch, and `toSelectOptions` stringifies, so that reached a select
that submits `"1"` for `1`. The select path is now gated on `isStringEnum`
(exported from core for this), and a typed non-string enum falls through to
its typed field: the enum constraint is lost, the value's type is not,
which is the safer of the two losses. Pre-existing for a plain numeric
enum; the collapse just made the nullable form reachable too.

Signed-off-by: cliffhall <cliff@futurescale.com>

clients/tui/__tests__/schemaToForm.test.ts

@@ -311,6 +311,39 @@ describe("schemaToForm", () => {
       ]);
     });
 
+    // ink-form hands a select's stringified value straight back, so a numeric
+    // enum routed to a select would submit "1" for 1. The typed field loses the
+    // enum constraint but keeps the value's type — the safer loss.
+    it("routes a nullable numeric enum to its typed field, not a select", () => {
+      const form = schemaToForm(
+        {
+          properties: {
+            level: {
+              anyOf: [{ type: "integer", enum: [1, 2] }, { type: "null" }],
+            },
+            ratio: {
+              anyOf: [{ type: "number", enum: [0.5, 1.5] }, { type: "null" }],
+            },
+          },
+        },
+        "numericEnum",
+      );
+      expect(
+        form.sections[0]!.fields.map((f) => ({ name: f.name, type: f.type })),
+      ).toEqual([
+        { name: "level", type: "integer" },
+        { name: "ratio", type: "float" },
+      ]);
+    });
+
+    it("routes a plain numeric enum to its typed field too", () => {
+      const form = schemaToForm(
+        { properties: { level: { type: "integer", enum: [1, 2] } } },
+        "plainNumericEnum",
+      );
+      expect(form.sections[0]!.fields[0]).toMatchObject({ type: "integer" });
+    });
+
     it("leaves a union of two real types as a plain string field", () => {
       const form = schemaToForm(
         {

clients/tui/src/utils/schemaToForm.ts

@@ -3,7 +3,10 @@
  */
 
 import type { FormStructure, FormSection, FormField } from "ink-form";
-import { normalizeNullableUnion } from "@inspector/core/json/nullableUnion.js";
+import {
+  isStringEnum,
+  normalizeNullableUnion,
+} from "@inspector/core/json/nullableUnion.js";
 
 /** Minimal JSON Schema property shape used when building tool parameter forms */
 interface JsonSchemaProperty {
@@ -105,12 +108,17 @@ export function schemaToForm(
         ...baseField,
         options: toSelectOptions(property.items.enum, property.items.enumNames),
       } as FormField;
-    } else if (property.enum) {
-      // Single select
+    } else if (isStringEnum(property.enum)) {
+      // Single select. Gated on the members being strings because
+      // `toSelectOptions` stringifies them and ink-form hands the string
+      // straight back: a numeric `enum: [1, 2]` would submit `"1"` and violate
+      // the schema. A typed non-string enum falls through to its typed field
+      // below, which loses the enum constraint but keeps the value's type —
+      // the safer of the two losses.
       field = {
         type: "select",
         ...baseField,
-        options: toSelectOptions(property.enum, property.enumNames),
+        options: toSelectOptions(property.enum ?? [], property.enumNames),
       } as FormField;
     } else {
       // Map JSON Schema types to ink-form types

clients/web/src/components/groups/SchemaForm/SchemaForm.test.tsx

@@ -971,6 +971,108 @@ describe("SchemaForm nullable unions", () => {
     expect(onChange).toHaveBeenCalledWith({ profile: { nick: "z" } });
   });
 
+  // #2007: `z.array(z.union([z.object(…), z.object(…)]))` gives an `items.anyOf`
+  // whose branches carry no top-level `const`, so every MultiSelect option was
+  // the empty string — and Mantine *throws* on duplicate option values, greying
+  // out the whole tool panel. The nullable form below is reachable only because
+  // this PR now collapses it into `type: "array"`, so it has to be safe too.
+  it("falls back to the JSON input for an array of object-union items", () => {
+    const objectBranch = (name: string): InspectorFormSchema => ({
+      type: "object",
+      properties: { type: { type: "string", const: name } },
+      required: ["type"],
+    });
+    const schema: InspectorFormSchema = {
+      type: "object",
+      properties: {
+        items: {
+          title: "Items",
+          type: "array",
+          items: { anyOf: [objectBranch("A"), objectBranch("B")] },
+        },
+      },
+    };
+    renderWithMantine(
+      <SchemaForm schema={schema} values={{}} onChange={vi.fn()} />,
+    );
+    expect(screen.getByLabelText(/Items/).tagName).toBe("TEXTAREA");
+  });
+
+  it("falls back to the JSON input for a nullable array of object-union items", () => {
+    const objectBranch = (name: string): InspectorFormSchema => ({
+      type: "object",
+      properties: { type: { type: "string", const: name } },
+      required: ["type"],
+    });
+    const schema: InspectorFormSchema = {
+      type: "object",
+      properties: {
+        items: {
+          title: "Items",
+          anyOf: [
+            { type: "array", items: { anyOf: [objectBranch("A")] } },
+            { type: "null" },
+          ],
+        },
+      },
+    };
+    renderWithMantine(
+      <SchemaForm schema={schema} values={{}} onChange={vi.fn()} />,
+    );
+    expect(screen.getByLabelText(/Items/).tagName).toBe("TEXTAREA");
+  });
+
+  it("falls back to the JSON input when two anyOf branches share a const", () => {
+    const schema: InspectorFormSchema = {
+      type: "object",
+      properties: {
+        items: {
+          title: "Items",
+          type: "array",
+          items: { anyOf: [{ const: "dup" }, { const: "dup" }] },
+        },
+      },
+    };
+    renderWithMantine(
+      <SchemaForm schema={schema} values={{}} onChange={vi.fn()} />,
+    );
+    expect(screen.getByLabelText(/Items/).tagName).toBe("TEXTAREA");
+  });
+
+  it("falls back to a text input for a string oneOf with no consts", () => {
+    const schema: InspectorFormSchema = {
+      type: "object",
+      properties: {
+        mode: {
+          title: "Mode",
+          type: "string",
+          oneOf: [{ type: "string" }, { type: "string" }],
+        },
+      },
+    };
+    renderWithMantine(
+      <SchemaForm schema={schema} values={{}} onChange={vi.fn()} />,
+    );
+    expect(screen.getByLabelText(/Mode/).tagName).toBe("INPUT");
+  });
+
+  it("still renders a MultiSelect when every anyOf branch has a distinct const", () => {
+    const schema: InspectorFormSchema = {
+      type: "object",
+      properties: {
+        items: {
+          title: "Items",
+          type: "array",
+          items: { anyOf: [{ const: "a", title: "Alpha" }, { const: "b" }] },
+        },
+      },
+    };
+    renderWithMantine(
+      <SchemaForm schema={schema} values={{}} onChange={vi.fn()} />,
+    );
+    expect(screen.getByRole("textbox", { name: "Items" })).toBeInTheDocument();
+  });
+
   it("still falls back to the JSON input for a union of two real types", () => {
     const schema: InspectorFormSchema = {
       type: "object",

clients/web/src/components/groups/SchemaForm/SchemaForm.tsx

@@ -11,7 +11,10 @@ import {
 import { useState } from "react";
 import { ClearButton } from "../../elements/ClearButton/ClearButton";
 import { useValueChange } from "../../../hooks/useValueChange";
-import type { InspectorFormSchema } from "../../../utils/jsonUtils";
+import type {
+  InspectorFormSchema,
+  JsonSchemaConst,
+} from "../../../utils/jsonUtils";
 import { normalizeNullableUnion } from "@inspector/core/json/nullableUnion.js";
 
 const FieldLabel = Text.withProps({
@@ -52,6 +55,44 @@ function toEnumData(
   return values;
 }
 
+/**
+ * Build `Select`/`MultiSelect` option data from a list of `oneOf`/`anyOf`
+ * branches that are expected to be constants.
+ *
+ * Returns `null` when the branches are not usable as options, which sends the
+ * field to the JSON fallback instead. Three ways that happens, all of which
+ * Mantine reacts to badly:
+ *
+ * - **No `const`.** An `anyOf` of *object* schemas — what
+ *   `z.array(z.union([z.object(…), z.object(…)]))` compiles to — has no
+ *   top-level `const` on any branch, so every option would be the empty
+ *   string. Mantine **throws** on duplicate option values, which greys out the
+ *   whole tool panel rather than degrading (#2007).
+ * - **Duplicate values.** Two branches sharing a `const` throw the same way.
+ * - **An empty option value**, which Mantine cannot render as selectable.
+ *
+ * A union of object shapes has no faithful dropdown anyway, so the JSON editor
+ * is the honest widget for it rather than a lossy or crashing one.
+ */
+function toConstOptions(
+  branches: (InspectorFormSchema | JsonSchemaConst)[],
+): { value: string; label: string }[] | null {
+  const options: { value: string; label: string }[] = [];
+  const seen = new Set<string>();
+  for (const branch of branches) {
+    if (branch.const === undefined || branch.const === null) {
+      return null;
+    }
+    const value = String(branch.const);
+    if (value === "" || seen.has(value)) {
+      return null;
+    }
+    seen.add(value);
+    options.push({ value, label: branch.title ?? value });
+  }
+  return options.length > 0 ? options : null;
+}
+
 /**
  * Whether an enum `Select` should offer a clear affordance. Only a schema that
  * admits `null` does: clearing emits `null`, and an enum without a null branch
@@ -248,11 +289,11 @@ export function SchemaForm({
     }
 
     // string with oneOf
-    if (fieldSchema.type === "string" && fieldSchema.oneOf) {
-      const data = fieldSchema.oneOf.map((item) => ({
-        value: String(item.const ?? ""),
-        label: item.title ?? String(item.const ?? ""),
-      }));
+    const oneOfData = fieldSchema.oneOf
+      ? toConstOptions(fieldSchema.oneOf)
+      : null;
+    if (fieldSchema.type === "string" && oneOfData) {
+      const data = oneOfData;
       return (
         <Select
           key={fieldName}
@@ -352,11 +393,11 @@ export function SchemaForm({
     }
 
     // array with items having anyOf
-    if (fieldSchema.type === "array" && fieldSchema.items?.anyOf) {
-      const data = fieldSchema.items.anyOf.map((item) => ({
-        value: String(item.const ?? ""),
-        label: item.title ?? String(item.const ?? ""),
-      }));
+    const itemsAnyOfData = fieldSchema.items?.anyOf
+      ? toConstOptions(fieldSchema.items.anyOf)
+      : null;
+    if (fieldSchema.type === "array" && itemsAnyOfData) {
+      const data = itemsAnyOfData;
       return (
         <MultiSelect
           key={fieldName}

core/json/nullableUnion.ts

@@ -53,8 +53,7 @@ function toBranch(value: unknown): Record<string, unknown> | null {
 }
 
 /**
- * Whether a branch's `enum` is one a *typeless* branch can be read as a string
- * enum.
+ * Whether an `enum` is one that can be rendered as a string-valued dropdown.
  *
  * JSON Schema's `enum` is untyped — `[1, 2]`, `[true, false]`, and `[null]` are
  * all legal — so a bare `{ enum: [...] }` does **not** imply strings. Guessing
@@ -63,8 +62,12 @@ function toBranch(value: unknown): Record<string, unknown> | null {
  * would `String(...)` them and submit `"1"` where the server expects `1`. So
  * only an all-string enum earns the inference; anything else stays on the
  * fallback path, which renders the value honestly as JSON.
+ *
+ * Exported because the same question decides whether a *dispatcher* may route
+ * an enum to a select at all. The TUI's does, and its options are stringified,
+ * so an unguarded numeric enum there submits `"1"` where the server wants `1`.
  */
-function isStringEnum(value: unknown): boolean {
+export function isStringEnum(value: unknown): boolean {
   return (
     Array.isArray(value) &&
     value.length > 0 &&