fix: guard empty MiniMax Anthropic messages (#74731)

Fixes #74589. Thanks @neeravmakwana and @DerekEXS.

CHANGELOG.md

@@ -60,6 +60,7 @@ Docs: https://docs.openclaw.ai
 ### Fixes
 
 - Bonjour/Gateway: treat active ciao probing and fresh name-conflict renames as in-progress so the mDNS watchdog waits for probe settlement before retrying, preventing rapid re-advertise loops on Windows, WSL, and other multicast-hostile hosts. (#74778) Refs #74242. Thanks @fuller-stack-dev.
+- Providers/MiniMax: send a minimal Anthropic-compatible user fallback when message conversion filters a turn to an empty payload, so MiniMax M2.7 no longer returns `chat content is empty` after tool-heavy sessions. Fixes #74589. Thanks @neeravmakwana and @DerekEXS.
 - Cron: keep long manual cron runs active in the task registry until completion, preventing transient `lost` markers before durable recovery reconciles. Fixes #78233. (#78243) Thanks @Feelw00.
 - Doctor/GitHub CLI: surface a `GH_CONFIG_DIR` hint when the GitHub skill is usable but `gh` auth lives under a different operator HOME than the agent process, without warning for disabled or filtered skills. Fixes #78063. (#78095) Thanks @tmimmanuel.
 - Gateway: dedupe concurrent `send`, `poll`, and `message.action` requests while delivery is still in flight, preventing duplicate outbound work for the same idempotency key. (#68341) Thanks @thesomewhatyou.

src/agents/anthropic-transport-stream.test.ts

@@ -718,6 +718,61 @@ describe("anthropic transport stream", () => {
     expect(toolUse.input).toEqual({});
   });
 
+  it.each([
+    {
+      name: "empty history",
+      context: { messages: [] } as AnthropicStreamContext,
+    },
+    {
+      name: "blank user content",
+      context: {
+        messages: [
+          {
+            role: "user",
+            content: " \n\t ",
+            timestamp: 0,
+          },
+        ],
+      } as AnthropicStreamContext,
+    },
+  ])(
+    "sends a minimal user fallback when Anthropic message conversion has no content: $name",
+    async ({ context }) => {
+      await runTransportStream(
+        makeAnthropicTransportModel({
+          id: "MiniMax-M2.7",
+          name: "MiniMax M2.7",
+          provider: "minimax",
+          baseUrl: "https://api.minimax.io/anthropic",
+        }),
+        context,
+        {
+          apiKey: "sk-minimax-test",
+        } as AnthropicStreamOptions,
+      );
+
+      expect(latestAnthropicRequest().payload).toMatchObject({
+        model: "MiniMax-M2.7",
+        messages: [
+          {
+            role: "user",
+            content: [
+              {
+                type: "text",
+                text: ".",
+                cache_control: { type: "ephemeral" },
+              },
+            ],
+          },
+        ],
+      });
+      expect(guardedFetchMock).toHaveBeenCalledWith(
+        "https://api.minimax.io/anthropic/v1/messages",
+        expect.objectContaining({ method: "POST" }),
+      );
+    },
+  );
+
   it.each([
     ["empty", ""],
     ["whitespace-only", " \n\t "],

src/agents/anthropic-transport-stream.ts

@@ -108,6 +108,8 @@ type MutableAssistantOutput = {
   errorMessage?: string;
 };
 
+const EMPTY_ANTHROPIC_MESSAGES_FALLBACK_TEXT = ".";
+
 function isClaudeOpus47Model(modelId: string): boolean {
   return modelId.includes("opus-4-7") || modelId.includes("opus-4.7");
 }
@@ -425,6 +427,12 @@ function convertAnthropicMessages(
   return params;
 }
 
+function ensureNonEmptyAnthropicMessages(messages: Array<Record<string, unknown>>) {
+  return messages.length > 0
+    ? messages
+    : [{ role: "user", content: EMPTY_ANTHROPIC_MESSAGES_FALLBACK_TEXT }];
+}
+
 function convertAnthropicTools(tools: Context["tools"], isOAuthToken: boolean) {
   if (!tools) {
     return [];
@@ -754,7 +762,9 @@ function buildAnthropicParams(
   });
   const params: Record<string, unknown> = {
     model: model.id,
-    messages: convertAnthropicMessages(context.messages, model, isOAuthToken),
+    messages: ensureNonEmptyAnthropicMessages(
+      convertAnthropicMessages(context.messages, model, isOAuthToken),
+    ),
     max_tokens: maxTokens,
     stream: true,
   };