Address code review feedback: simplify type guards and use direct toString()

Co-authored-by: bcho <1975118+bcho@users.noreply.github.com>

Author: Copilot

sdks/typescript/src/sqlite.ts

@@ -8,7 +8,6 @@ import type {
 import {
   isInstant,
   instantFromEpochMilliseconds,
-  instantToDate,
 } from "./temporal-types";
 
 export class SqliteConnection implements Queryable {
@@ -178,9 +177,9 @@ function decodeColumnValue<V = any>(
 }
 
 function encodeColumnValue(value: any): any {
-  // Handle Temporal.Instant - convert to ISO string
+  // Handle Temporal.Instant - use built-in toString() for ISO string
   if (isInstant(value)) {
-    return instantToDate(value).toISOString();
+    return value.toString();
   }
   // Handle legacy Date objects
   if (value instanceof Date) {

sdks/typescript/src/temporal-types.ts

@@ -85,11 +85,7 @@ export function instantToEpochMilliseconds(instant: Instant): number {
  * @returns True if the value is a Temporal.Instant
  */
 export function isInstant(value: unknown): value is Instant {
-  return (
-    value !== null &&
-    typeof value === "object" &&
-    value instanceof Temporal.Instant
-  );
+  return value instanceof Temporal.Instant;
 }
 
 /**
@@ -98,9 +94,5 @@ export function isInstant(value: unknown): value is Instant {
  * @returns True if the value is a Temporal.Duration
  */
 export function isDuration(value: unknown): value is Duration {
-  return (
-    value !== null &&
-    typeof value === "object" &&
-    value instanceof Temporal.Duration
-  );
+  return value instanceof Temporal.Duration;
 }