fix(plugin): preserve cross-zod tool arg metadata

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-opencode)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/plugin/normalize-tool-arg-schemas.ts

@@ -0,0 +1,42 @@
+import { tool } from "@opencode-ai/plugin"
+import type { ToolDefinition } from "@opencode-ai/plugin"
+
+type ToolArgSchema = ToolDefinition["args"][string]
+
+type SchemaWithJsonSchemaOverride = ToolArgSchema & {
+  _zod: ToolArgSchema["_zod"] & {
+    toJSONSchema?: () => unknown
+  }
+}
+
+function stripRootJsonSchemaFields(jsonSchema: Record<string, unknown>): Record<string, unknown> {
+  const { $schema: _schema, ...rest } = jsonSchema
+  return rest
+}
+
+function attachJsonSchemaOverride(schema: SchemaWithJsonSchemaOverride): void {
+  if (schema._zod.toJSONSchema) {
+    return
+  }
+
+  schema._zod.toJSONSchema = (): Record<string, unknown> => {
+    const originalOverride = schema._zod.toJSONSchema
+    delete schema._zod.toJSONSchema
+
+    try {
+      return stripRootJsonSchemaFields(tool.schema.toJSONSchema(schema))
+    } finally {
+      schema._zod.toJSONSchema = originalOverride
+    }
+  }
+}
+
+export function normalizeToolArgSchemas<TDefinition extends Pick<ToolDefinition, "args">>(
+  toolDefinition: TDefinition,
+): TDefinition {
+  for (const schema of Object.values(toolDefinition.args)) {
+    attachJsonSchemaOverride(schema)
+  }
+
+  return toolDefinition
+}