fix(plugins): guard legacy zod schemas without toJSONSchema

src/channels/plugins/config-schema.test.ts

@@ -0,0 +1,17 @@
+import { describe, expect, it } from "vitest";
+import { z } from "zod";
+import { buildChannelConfigSchema } from "./config-schema.js";
+
+describe("buildChannelConfigSchema", () => {
+  it("builds json schema when toJSONSchema is available", () => {
+    const schema = z.object({ enabled: z.boolean().default(true) });
+    const result = buildChannelConfigSchema(schema);
+    expect(result.schema).toMatchObject({ type: "object" });
+  });
+
+  it("falls back when toJSONSchema is missing (zod v3 plugin compatibility)", () => {
+    const legacySchema = {} as unknown as Parameters<typeof buildChannelConfigSchema>[0];
+    const result = buildChannelConfigSchema(legacySchema);
+    expect(result.schema).toEqual({ type: "object", additionalProperties: true });
+  });
+});

src/channels/plugins/config-schema.ts

@@ -1,11 +1,27 @@
 import type { ZodTypeAny } from "zod";
 import type { ChannelConfigSchema } from "./types.plugin.js";
 
+type ZodSchemaWithToJsonSchema = ZodTypeAny & {
+  toJSONSchema?: (params?: Record<string, unknown>) => unknown;
+};
+
 export function buildChannelConfigSchema(schema: ZodTypeAny): ChannelConfigSchema {
+  const schemaWithJson = schema as ZodSchemaWithToJsonSchema;
+  if (typeof schemaWithJson.toJSONSchema === "function") {
+    return {
+      schema: schemaWithJson.toJSONSchema({
+        target: "draft-07",
+        unrepresentable: "any",
+      }) as Record<string, unknown>,
+    };
+  }
+
+  // Compatibility fallback for plugins built against Zod v3 schemas,
+  // where `.toJSONSchema()` is unavailable.
   return {
-    schema: schema.toJSONSchema({
-      target: "draft-07",
-      unrepresentable: "any",
-    }) as Record<string, unknown>,
+    schema: {
+      type: "object",
+      additionalProperties: true,
+    },
   };
 }