fix: return 0 completion tokens for empty content

apps/gateway/src/chat/tools/estimate-tokens-from-content.ts

@@ -2,5 +2,8 @@
  * Estimates tokens from content length using simple division
  */
 export function estimateTokensFromContent(content: string): number {
+	if (!content) {
+		return 0;
+	}
 	return Math.max(1, Math.round(content.length / 4));
 }

apps/gateway/src/lib/prompt-tokens.spec.ts

@@ -8,16 +8,19 @@ describe("Prompt token calculation", () => {
 	describe("estimateTokensFromContent", () => {
 		it("should estimate tokens from content length", () => {
 			expect(estimateTokensFromContent("Hello world")).toBe(3); // 11 chars / 4 = 2.75, rounded to 3
-			expect(estimateTokensFromContent("")).toBe(1); // Always at least 1
+			expect(estimateTokensFromContent("")).toBe(0); // Empty content = 0 tokens
 			expect(
 				estimateTokensFromContent(
 					"A very long message that should result in more tokens",
 				),
 			).toBe(13); // 53 chars / 4 = 13.25, rounded to 13
 		});
 
-		it("should always return at least 1 token", () => {
-			expect(estimateTokensFromContent("")).toBe(1);
+		it("should return 0 for empty content", () => {
+			expect(estimateTokensFromContent("")).toBe(0);
+		});
+
+		it("should return at least 1 token for non-empty content", () => {
 			expect(estimateTokensFromContent("A")).toBe(1);
 		});
 	});