fix(core): tolerate missing tool input schemas (#39130)

Co-authored-by: Dax Raad <d@ironbay.co>

packages/core/test/session-runner-tool-registry.test.ts

@@ -140,6 +140,22 @@ describe("Tool", () => {
     }),
   )
 
+  it.effect("snapshots external tools with missing input schemas", () =>
+    Effect.gen(function* () {
+      const service = yield* Tool.Service
+      yield* service.transform((draft) =>
+        draft.add({
+          ...make(),
+          input: undefined,
+        } as unknown as Info),
+      )
+
+      const snapshot = yield* service.snapshot()
+      expect(snapshot.definitions.map((tool) => tool.name)).toEqual(["execute"])
+      expect(snapshot.codeModeCatalog?.[0]?.signature).toContain("tools.echo")
+    }),
+  )
+
   it.effect("keeps execute available without Code Mode tools unless explicitly denied", () =>
     Effect.gen(function* () {
       const service = yield* Tool.Service

packages/core/test/tool-schema.test.ts

@@ -143,3 +143,18 @@ test("raw JSON schemas are render-only and omitted output means model-only", asy
     content: [{ type: "text", text: '{"value":1}' }],
   })
 })
+
+test("missing external input schemas fall back to an empty schema", () => {
+  const tool = {
+    name: "external",
+    description: "External tool",
+    input: undefined,
+    execute: () => Effect.succeed({ content: "unused" }),
+  } as unknown as Info
+
+  expect(definition(tool)).toEqual({
+    name: "external",
+    description: "External tool",
+    inputSchema: {},
+  })
+})