diff --git a/CHANGELOG.md b/CHANGELOG.md
index c59515830..e3bdbdba8 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -129,6 +129,7 @@ Docs: https://docs.openclaw.ai
 - Agents/Subagents: restore announce-chain delivery to agent injection, defer nested announce output until descendant follow-up content is ready, and prevent descendant deferrals from consuming announce retry budget so deep chains do not drop final completions. (#22223) Thanks @tyler6204.
 - Agents/System Prompt: label allowlisted senders as authorized senders to avoid implying ownership. Thanks @thewilloftheshadow.
 - Agents/Tool display: fix exec cwd suffix inference so `pushd ... && popd ... && <command>` does not keep stale `(in <dir>)` context in summaries. (#21925) Thanks @Lukavyi.
+- Agents/Google: flatten residual nested `anyOf`/`oneOf` unions in Gemini tool-schema cleanup so Cloud Code Assist no longer rejects unsupported union keywords that survive earlier simplification. (#22825) Thanks @Oceanswave.
 - Tools/web_search: handle xAI Responses API payloads that emit top-level `output_text` blocks (without a `message` wrapper) so Grok web_search no longer returns `No response` for those results. (#20508) Thanks @echoVic.
 - Agents/Failover: treat non-default override runs as direct fallback-to-configured-primary (skip configured fallback chain), normalize default-model detection for provider casing/whitespace, and add regression coverage for override/auth error paths. (#18820) Thanks @Glucksberg.
 - Docker/Build: include `ownerDisplay` in `CommandsSchema` object-level defaults so Docker `pnpm build` no longer fails with `TS2769` during plugin SDK d.ts generation. (#22558) Thanks @obviyus.
diff --git a/src/agents/schema/clean-for-gemini.ts b/src/agents/schema/clean-for-gemini.ts
index e18d2e8c1..b416c3216 100644
--- a/src/agents/schema/clean-for-gemini.ts
+++ b/src/agents/schema/clean-for-gemini.ts
@@ -339,9 +339,63 @@ function cleanSchemaForGeminiWithDefs(
     }
   }
 
+  // Cloud Code Assist API rejects anyOf/oneOf in nested schemas even after
+  // simplifyUnionVariants runs above. Flatten remaining unions as a fallback:
+  // pick the common type or use the first variant's type so the tool
+  // declaration is accepted by Google's validation layer.
+  if (cleaned.anyOf && Array.isArray(cleaned.anyOf)) {
+    const flattened = flattenUnionFallback(cleaned, cleaned.anyOf);
+    if (flattened) {
+      return flattened;
+    }
+  }
+  if (cleaned.oneOf && Array.isArray(cleaned.oneOf)) {
+    const flattened = flattenUnionFallback(cleaned, cleaned.oneOf);
+    if (flattened) {
+      return flattened;
+    }
+  }
+
   return cleaned;
 }
 
+/**
+ * Last-resort flattening for anyOf/oneOf arrays that could not be simplified
+ * by `simplifyUnionVariants`. Picks a representative type so the schema is
+ * accepted by Google's restricted JSON Schema validation.
+ */
+function flattenUnionFallback(
+  obj: Record<string, unknown>,
+  variants: unknown[],
+): Record<string, unknown> | undefined {
+  const objects = variants.filter(
+    (v): v is Record<string, unknown> => !!v && typeof v === "object",
+  );
+  if (objects.length === 0) {
+    return undefined;
+  }
+  const types = new Set(objects.map((v) => v.type).filter(Boolean));
+  if (objects.length === 1) {
+    const merged: Record<string, unknown> = { ...objects[0] };
+    copySchemaMeta(obj, merged);
+    return merged;
+  }
+  if (types.size === 1) {
+    const merged: Record<string, unknown> = { type: Array.from(types)[0] };
+    copySchemaMeta(obj, merged);
+    return merged;
+  }
+  const first = objects[0];
+  if (first?.type) {
+    const merged: Record<string, unknown> = { type: first.type };
+    copySchemaMeta(obj, merged);
+    return merged;
+  }
+  const merged: Record<string, unknown> = {};
+  copySchemaMeta(obj, merged);
+  return merged;
+}
+
 export function cleanSchemaForGemini(schema: unknown): unknown {
   if (!schema || typeof schema !== "object") {
     return schema;