diff --git a/src/adapters/openai-responses.ts b/src/adapters/openai-responses.ts
index b03561c2d..d6f6227bc 100644
--- a/src/adapters/openai-responses.ts
+++ b/src/adapters/openai-responses.ts
@@ -354,6 +354,61 @@ function isPlainObject(v: unknown): v is Record<string, unknown> {
   return !!v && typeof v === "object" && !Array.isArray(v);
 }
 
+/**
+ * Ensure every function tool exposes a valid object JSON Schema at its
+ * `parameters` root. Strict validators (e.g. DeepSeek) reject schemas whose
+ * root `type` is `null`, missing, or non-`"object"` with HTTP 400.
+ *
+ * Codex tools such as `codex_app__automation_update` arrive without a
+ * `parameters` field, which would otherwise serialize to a schema lacking the
+ * root `type`. Walks both top-level `tools` and Responses Lite
+ * `additional_tools[].tools`. Namespace grouping is flattened by earlier strip
+ * steps, so any function tool seen here is already top-level.
+ */
+function normalizeToolSchemas(body: unknown): unknown {
+  if (!isPlainObject(body)) return body;
+
+  const fixFunctionParams = (tool: unknown): unknown => {
+    if (!isPlainObject(tool) || tool.type !== "function") return tool;
+    const params = isPlainObject(tool.parameters) ? { ...tool.parameters } : {};
+    let changed = false;
+    if (params.type !== "object") { params.type = "object"; changed = true; }
+    if (!isPlainObject(params.properties)) { params.properties = {}; changed = true; }
+    return changed ? { ...tool, parameters: params } : tool;
+  };
+
+  let changed = false;
+
+  // Top-level tools array.
+  if (Array.isArray(body.tools)) {
+    const tools = body.tools.map((t) => {
+      const fixed = fixFunctionParams(t);
+      if (fixed !== t) changed = true;
+      return fixed;
+    });
+    if (changed) body = { ...body, tools };
+  }
+
+  // Responses Lite `additional_tools` items embed their own tools arrays.
+  if (Array.isArray(body.input)) {
+    let inputChanged = false;
+    const input = body.input.map((item) => {
+      if (!isPlainObject(item) || item.type !== "additional_tools" || !Array.isArray(item.tools)) return item;
+      let innerChanged = false;
+      const innerTools = item.tools.map((t) => {
+        const fixed = fixFunctionParams(t);
+        if (fixed !== t) innerChanged = true;
+        return fixed;
+      });
+      if (innerChanged) { inputChanged = true; return { ...item, tools: innerTools }; }
+      return item;
+    });
+    if (inputChanged) { changed = true; body = { ...body, input }; }
+  }
+
+  return body;
+}
+
 const MAX_RESPONSES_CALL_ID_LENGTH = 64;
 const REPAIRED_CALL_ID_PREFIX = "call_ocx_";
 const REPAIRED_CALL_ID_DIGEST_LENGTH = MAX_RESPONSES_CALL_ID_LENGTH - REPAIRED_CALL_ID_PREFIX.length;
@@ -938,7 +993,7 @@ export function createResponsesPassthroughAdapter(provider: OcxProviderConfig):
       if (parsed._compactionRequest === true && !isCanonicalOpenAiForwardProvider(provider)) {
         outBody = buildRoutedCompactionBody(outBody);
       }
-      const sanitizedBody = stripSparkCompatibility(stripUnsupportedReasoningParams(stripItemIdsWhenUnstored(stripInvalidItemIds(stripUnsupportedHostedTools(sanitizeReasoningInputContent(scrubOcxCompactionItems(outBody)))))));
+      const sanitizedBody = normalizeToolSchemas(stripSparkCompatibility(stripUnsupportedReasoningParams(stripItemIdsWhenUnstored(stripInvalidItemIds(stripUnsupportedHostedTools(sanitizeReasoningInputContent(scrubOcxCompactionItems(outBody))))))));
       return {
         url,
         method: "POST",
diff --git a/src/responses/parser.ts b/src/responses/parser.ts
index 1a3d3e49c..3740b0386 100644
--- a/src/responses/parser.ts
+++ b/src/responses/parser.ts
@@ -137,11 +137,24 @@ function allowedToolName(tool: unknown): string | undefined {
 function buildTools(tools: unknown[] | undefined): OcxTool[] | undefined {
   if (!tools) return undefined;
   const out: OcxTool[] = [];
+  // Some tool definitions (e.g. Codex `codex_app__automation_update`) arrive
+  // without a `parameters` field or with `parameters: null`. When serialized,
+  // that produces a JSON Schema whose root `type` is `null` (or missing).
+  // Strict validators reject such schemas with HTTP 400
+  // ("schema must be a JSON Schema of 'type: \"object\"', got 'type: null'").
+  // Coerce every function tool's `parameters` to a valid object-schema root
+  // so all downstream adapters pass through cleanly.
+  const normalizeParameters = (raw: unknown): Record<string, unknown> => {
+    const p = isObj(raw) ? { ...raw } : {};
+    if (p.type !== "object") p.type = "object";
+    if (!isObj(p.properties)) p.properties = {};
+    return p;
+  };
   const pushFn = (t: Record<string, unknown>, namespace?: string) => {
     const tool: OcxTool = {
       name: t.name as string,
       description: (t.description as string) ?? "",
-      parameters: (t.parameters ?? {}) as Record<string, unknown>,
+      parameters: normalizeParameters(t.parameters),
     };
     if (t.strict !== undefined) tool.strict = t.strict as boolean;
     if (namespace) tool.namespace = namespace;