diff --git a/src/config/config.test.ts b/src/config/config.test.ts
index f271fd211..9d49b5416 100644
--- a/src/config/config.test.ts
+++ b/src/config/config.test.ts
@@ -1685,3 +1685,46 @@ describe("multi-agent agentDir validation", () => {
     });
   });
 });
+
+describe("config preservation on validation failure", () => {
+  it("preserves unknown fields via passthrough", async () => {
+    vi.resetModules();
+    const { validateConfigObject } = await import("./config.js");
+    const res = validateConfigObject({
+      agents: { list: [{ id: "pi" }] },
+      customUnknownField: { nested: "value" },
+    });
+    expect(res.ok).toBe(true);
+    expect(
+      (res as { config: Record<string, unknown> }).config.customUnknownField,
+    ).toEqual({
+      nested: "value",
+    });
+  });
+
+  it("preserves config data when validation fails", async () => {
+    await withTempHome(async (home) => {
+      const configDir = path.join(home, ".clawdbot");
+      await fs.mkdir(configDir, { recursive: true });
+      await fs.writeFile(
+        path.join(configDir, "clawdbot.json"),
+        JSON.stringify({
+          agents: { list: [{ id: "pi" }] },
+          routing: { allowFrom: ["+15555550123"] },
+          customData: { preserved: true },
+        }),
+        "utf-8",
+      );
+
+      vi.resetModules();
+      const { readConfigFileSnapshot } = await import("./config.js");
+      const snap = await readConfigFileSnapshot();
+
+      expect(snap.valid).toBe(false);
+      expect(snap.legacyIssues.length).toBeGreaterThan(0);
+      expect((snap.config as Record<string, unknown>).customData).toEqual({
+        preserved: true,
+      });
+    });
+  });
+});
diff --git a/src/config/io.ts b/src/config/io.ts
index af86cdc7e..b6388acc6 100644
--- a/src/config/io.ts
+++ b/src/config/io.ts
@@ -296,7 +296,7 @@ export function createConfigIO(overrides: ConfigIoDeps = {}) {
           raw,
           parsed: parsedRes.parsed,
           valid: false,
-          config: {},
+          config: resolved as ClawdbotConfig,
           issues: validated.issues,
           legacyIssues,
         };
diff --git a/src/config/zod-schema.ts b/src/config/zod-schema.ts
index b6a912e54..d72b855f4 100644
--- a/src/config/zod-schema.ts
+++ b/src/config/zod-schema.ts
@@ -1757,6 +1757,7 @@ export const ClawdbotSchema = z
       })
       .optional(),
   })
+  .passthrough()
   .superRefine((cfg, ctx) => {
     const agents = cfg.agents?.list ?? [];
     if (agents.length === 0) return;