Fix Bedrock blank text blocks

closes #4975

packages/ai/test/bedrock-convert-messages.test.ts

@@ -117,7 +117,7 @@ describe("bedrock convertMessages skips unknown content types", () => {
 		expect(p.messages[0].content[0]).toEqual({ text: "hello" });
 	});
 
-	it("skips user messages with only unknown content blocks", async () => {
+	it("replaces user messages with only unknown content blocks with a placeholder", async () => {
 		const messages: Message[] = [
 			{
 				role: "user",
@@ -128,9 +128,95 @@ describe("bedrock convertMessages skips unknown content types", () => {
 		const payload = await capturePayload({ messages });
 		expect(payload).toBeDefined();
 		const p = payload as { messages: Array<{ role: string; content: unknown[] }> };
+		expect(p.messages).toHaveLength(1);
+		expect(p.messages[0].content).toEqual([{ text: "<empty>" }]);
+	});
+
+	it("replaces blank user string content with a placeholder", async () => {
+		const payload = await capturePayload({
+			messages: [{ role: "user", content: "   ", timestamp: Date.now() }],
+		});
+		expect(payload).toBeDefined();
+		const p = payload as { messages: Array<{ role: string; content: unknown[] }> };
+		expect(p.messages).toHaveLength(1);
+		expect(p.messages[0].content).toEqual([{ text: "<empty>" }]);
+	});
+
+	it("filters blank user text blocks when other content remains", async () => {
+		const payload = await capturePayload({
+			messages: [
+				{
+					role: "user",
+					content: [
+						{ type: "text", text: "" },
+						{ type: "text", text: "hello" },
+					],
+					timestamp: Date.now(),
+				},
+			],
+		});
+		expect(payload).toBeDefined();
+		const p = payload as { messages: Array<{ role: string; content: unknown[] }> };
+		expect(p.messages).toHaveLength(1);
+		expect(p.messages[0].content).toEqual([{ text: "hello" }]);
+	});
+
+	it("replaces user content emptied by surrogate sanitization with a placeholder", async () => {
+		const payload = await capturePayload({
+			messages: [{ role: "user", content: String.fromCharCode(0xd83d), timestamp: Date.now() }],
+		});
+		expect(payload).toBeDefined();
+		const p = payload as { messages: Array<{ role: string; content: unknown[] }> };
+		expect(p.messages).toHaveLength(1);
+		expect(p.messages[0].content).toEqual([{ text: "<empty>" }]);
+	});
+
+	it("skips assistant text blocks emptied by surrogate sanitization", async () => {
+		const messages: Message[] = [
+			{
+				role: "assistant",
+				content: [{ type: "text", text: String.fromCharCode(0xd83d) }],
+				api: "bedrock-converse-stream",
+				provider: "amazon-bedrock",
+				model: baseModel.id,
+				usage: {
+					input: 0,
+					output: 0,
+					cacheRead: 0,
+					cacheWrite: 0,
+					totalTokens: 0,
+					cost: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0, total: 0 },
+				},
+				stopReason: "stop",
+				timestamp: Date.now(),
+			},
+		];
+		const payload = await capturePayload({ messages });
+		expect(payload).toBeDefined();
+		const p = payload as { messages: Array<{ role: string; content: unknown[] }> };
 		expect(p.messages).toHaveLength(0);
 	});
 
+	it("replaces blank tool result content with a placeholder", async () => {
+		const messages: Message[] = [
+			{
+				role: "toolResult",
+				toolCallId: "tool-1",
+				toolName: "tool",
+				content: [{ type: "text", text: "" }],
+				isError: false,
+				timestamp: Date.now(),
+			},
+		];
+		const payload = await capturePayload({ messages });
+		expect(payload).toBeDefined();
+		const p = payload as {
+			messages: Array<{ role: string; content: Array<{ toolResult: { content: unknown[] } }> }>;
+		};
+		expect(p.messages).toHaveLength(1);
+		expect(p.messages[0].content[0].toolResult.content).toEqual([{ text: "<empty>" }]);
+	});
+
 	it("skips assistant messages with only unknown content blocks", async () => {
 		const messages: Message[] = [
 			{