From 33e3d1ebca05c640b654640c5fdfc7b210a8748b Mon Sep 17 00:00:00 2001
From: "opencode-agent[bot]"
 <219766164+opencode-agent[bot]@users.noreply.github.com>
Date: Mon, 27 Jul 2026 11:21:47 -0400
Subject: [PATCH] fix(core): tolerate missing tool input schemas (#39130)

Co-authored-by: Dax Raad <d@ironbay.co>
---
 packages/core/src/tool/runtime.ts                |  4 +++-
 .../test/session-runner-tool-registry.test.ts    | 16 ++++++++++++++++
 packages/core/test/tool-schema.test.ts           | 15 +++++++++++++++
 3 files changed, 34 insertions(+), 1 deletion(-)

diff --git a/packages/core/src/tool/runtime.ts b/packages/core/src/tool/runtime.ts
index 80872798e02..5c5b767c8c8 100644
--- a/packages/core/src/tool/runtime.ts
+++ b/packages/core/src/tool/runtime.ts
@@ -58,7 +58,8 @@ const encodeOutput = (schema: Tool.ValueSchema<any>, value: unknown) => {
 
 const isStandardSchema = (
   schema: Tool.ValueSchema<any>,
-): schema is StandardSchemaV1<any, any> & StandardJSONSchemaV1<any, any> => "~standard" in schema
+): schema is StandardSchemaV1<any, any> & StandardJSONSchemaV1<any, any> =>
+  typeof schema === "object" && schema !== null && "~standard" in schema
 
 const validateStandard = (
   schema: StandardSchemaV1<any, any> & StandardJSONSchemaV1<any, any>,
@@ -85,6 +86,7 @@ const standardFailure = (prefix: string, error: unknown) =>
   new Tool.Error({ message: `${prefix}: ${error instanceof Error ? error.message : String(error)}` })
 
 const inputJsonSchema = (schema: Tool.ValueSchema<any>): JsonSchema.JsonSchema => {
+  if (schema === undefined || schema === null) return {}
   if (isStandardSchema(schema))
     return schema["~standard"].jsonSchema.input({ target: "draft-2020-12" }) as JsonSchema.JsonSchema
   return Schema.isSchema(schema) ? toJsonSchema(schema) : (schema as JsonSchema.JsonSchema)
diff --git a/packages/core/test/session-runner-tool-registry.test.ts b/packages/core/test/session-runner-tool-registry.test.ts
index 37a32fa4c7a..1398a749791 100644
--- a/packages/core/test/session-runner-tool-registry.test.ts
+++ b/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
diff --git a/packages/core/test/tool-schema.test.ts b/packages/core/test/tool-schema.test.ts
index 72e053ab8bb..4008e0a8c44 100644
--- a/packages/core/test/tool-schema.test.ts
+++ b/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: {},
+  })
+})