diff --git a/packages/api/src/features/agent/service.test.ts b/packages/api/src/features/agent/service.test.ts
index a3e30a2aa..6177bc579 100644
--- a/packages/api/src/features/agent/service.test.ts
+++ b/packages/api/src/features/agent/service.test.ts
@@ -1227,7 +1227,7 @@ describe("agentService.attachments.create", () => {
 				select: vi
 					.fn()
 					.mockImplementationOnce(() => ({ from: () => ({ where: () => lockQuery }) }))
-					.mockImplementationOnce(() => {
+					.mockImplementation(() => {
 						quotaRead();
 						return selectWhereResult([{ total, totalBytes: String(totalBytes) }]);
 					}),
@@ -1256,7 +1256,8 @@ describe("agentService.attachments.create", () => {
 			agentService.attachments.create(upload),
 		]);
 		await vi.waitFor(() => expect(storageServiceMock.write).toHaveBeenCalledTimes(1));
-		expect(quotaRead).toHaveBeenCalledTimes(1);
+		// The first upload's two quota reads (unsent count, thread bytes); the second waits on the lock.
+		expect(quotaRead).toHaveBeenCalledTimes(2);
 		storageWrite.resolve();
 		const settled = await results;
 		expect(settled[0]?.status).toBe("fulfilled");
@@ -1266,6 +1267,41 @@ describe("agentService.attachments.create", () => {
 		expect(storageServiceMock.delete).not.toHaveBeenCalled();
 	});
 
+	it("counts only unsent attachments toward the per-message limit", async () => {
+		// Ten files already went out with earlier messages; none is waiting to be sent.
+		const rows = Array.from({ length: 10 }, (_, index) => ({
+			"agent_attachments.thread_id": input.threadId,
+			"agent_attachments.user_id": input.userId,
+			"agent_attachments.message_id": `message-${index}`,
+		}));
+		type Condition = { type: string; conditions?: Condition[]; left?: string; right?: unknown; value?: string };
+		// Evaluates the mocked drizzle conditions, so each count follows the query's own filter.
+		const matches = (row: Record<string, unknown>, condition: Condition): boolean =>
+			condition.type === "and"
+				? (condition.conditions ?? []).every((part) => matches(row, part))
+				: condition.type === "isNull"
+					? row[condition.value ?? ""] == null
+					: row[condition.left ?? ""] === condition.right;
+		dbMock.select
+			.mockReturnValueOnce({ from: () => ({ where: () => ({ for: async () => [{ id: input.threadId }] }) }) })
+			.mockImplementation((columns: Record<string, { type: string }>) => ({
+				from: () => ({
+					where: (condition: Condition) => {
+						const count = rows.filter((row) => matches(row, condition)).length;
+						return Promise.resolve([
+							Object.fromEntries(Object.entries(columns).map(([key, { type }]) => [key, type === "count" ? count : 0])),
+						]);
+					},
+				}),
+			}));
+		dbMock.insert.mockReturnValue({
+			values: (value: object) => ({ returning: async () => [{ ...value, createdAt: new Date() }] }),
+		});
+		const { agentService } = await import("./service");
+
+		await expect(agentService.attachments.create(input)).resolves.toMatchObject({ filename: input.filename });
+	});
+
 	it("requires an owned, active, undeleted thread under the lock", async () => {
 		const where = vi.fn(() => ({ for: vi.fn(async () => []) }));
 		dbMock.select.mockReturnValue({ from: vi.fn(() => ({ where })) });
@@ -1296,7 +1332,7 @@ describe("agentService.attachments.create", () => {
 	it("removes uploaded bytes when metadata insertion fails", async () => {
 		dbMock.select
 			.mockReturnValueOnce({ from: () => ({ where: () => ({ for: async () => [{ id: input.threadId }] }) }) })
-			.mockImplementationOnce(() => selectWhereResult([{ total: 0, totalBytes: 0 }]));
+			.mockImplementation(() => selectWhereResult([{ total: 0, totalBytes: 0 }]));
 		storageServiceMock.write.mockResolvedValue(undefined);
 		storageServiceMock.delete.mockResolvedValue(true);
 		dbMock.insert.mockReturnValue({ values: () => ({ returning: () => Promise.reject(new Error("Insert failed")) }) });
diff --git a/packages/api/src/features/agent/service.ts b/packages/api/src/features/agent/service.ts
index 9a78e4a8e..74f8c4e16 100644
--- a/packages/api/src/features/agent/service.ts
+++ b/packages/api/src/features/agent/service.ts
@@ -1310,16 +1310,25 @@ export const agentService = {
 						.for("update");
 					if (!thread) throw new ORPCError("NOT_FOUND");
 
+					// Files already sent belong to their messages: only unsent ones count toward the next message.
+					const [unsent] = await tx
+						.select({ total: count() })
+						.from(schema.agentAttachment)
+						.where(
+							and(
+								eq(schema.agentAttachment.threadId, input.threadId),
+								eq(schema.agentAttachment.userId, input.userId),
+								isNull(schema.agentAttachment.messageId),
+							),
+						);
+					if ((unsent?.total ?? 0) >= MAX_ATTACHMENTS_PER_MESSAGE) throw new ORPCError("BAD_REQUEST");
+
 					const [stats] = await tx
-						.select({
-							totalBytes: sql<number>`coalesce(sum(${schema.agentAttachment.size}), 0)`,
-							total: count(),
-						})
+						.select({ totalBytes: sql<number>`coalesce(sum(${schema.agentAttachment.size}), 0)` })
 						.from(schema.agentAttachment)
 						.where(
 							and(eq(schema.agentAttachment.threadId, input.threadId), eq(schema.agentAttachment.userId, input.userId)),
 						);
-					if ((stats?.total ?? 0) >= MAX_ATTACHMENTS_PER_MESSAGE) throw new ORPCError("BAD_REQUEST");
 					if (Number(stats?.totalBytes ?? 0) + input.data.byteLength > MAX_THREAD_ATTACHMENT_BYTES) {
 						throw new ORPCError("BAD_REQUEST");
 					}