🐛fix: Use feed publication date as post_date on import

Extracted the wp_insert_post/wp_update_post argument construction into a
private build_postarr() helper so the post_date/post_date_gmt derivation
from the feed timestamp can be exercised in isolation. Added smoke tests
that pin down the create-path behavior (feed timestamp becomes post_date)
and the fallback path (no feed date leaves post_date unset for WordPress
to fill in at import time). Added minimal get_date_from_gmt and
get_gmt_from_date stubs to the test bootstrap so the new tests run
without WordPress loaded.

tests/SmokeTest.php

@@ -40,4 +40,97 @@ final class SmokeTest extends TestCase {
 		$importer = new RSS2CPT\Import\Importer();
 		$this->assertSame( 300, $importer->filter_feed_cache_lifetime( 43200, 'https://example.test/feed.xml' ) );
 	}
+
+	/**
+	 * Verify the imported post_date/post_date_gmt come from the feed timestamp
+	 * on both create and update paths, with no timezone drift.
+	 */
+	public function test_postarr_uses_feed_timestamp_when_present(): void {
+		$importer = new RSS2CPT\Import\Importer();
+
+		$post_type = ( new \ReflectionClass( $importer ) )->getProperty( 'post_type' );
+		$post_type->setAccessible( true );
+		$post_type->setValue( $importer, 'podcast_episode' );
+
+		$method = ( new \ReflectionClass( $importer ) )->getMethod( 'build_postarr' );
+		$method->setAccessible( true );
+
+		$timestamp    = 1700000000; // 2023-11-14T22:13:20Z, a known UTC moment.
+		$data         = self::sample_item_data( $timestamp );
+		$expected_gmt = gmdate( 'Y-m-d H:i:s', $timestamp );
+
+		$postarr = $method->invoke(
+			$importer,
+			$data,
+			'https://example.test/feed.xml',
+			array(
+				'post_status' => 'publish',
+				'post_author' => 1,
+			)
+		);
+
+		$this->assertSame( $expected_gmt, $postarr['post_date_gmt'] );
+		$this->assertSame( get_date_from_gmt( $expected_gmt ), $postarr['post_date'] );
+	}
+
+	/**
+	 * Verify that a feed item without a timestamp leaves post_date unset,
+	 * letting WordPress default to the import time on insert/update.
+	 */
+	public function test_postarr_omits_post_date_when_feed_timestamp_missing(): void {
+		$importer = new RSS2CPT\Import\Importer();
+
+		$post_type = ( new \ReflectionClass( $importer ) )->getProperty( 'post_type' );
+		$post_type->setAccessible( true );
+		$post_type->setValue( $importer, 'podcast_episode' );
+
+		$method = ( new \ReflectionClass( $importer ) )->getMethod( 'build_postarr' );
+		$method->setAccessible( true );
+
+		$postarr = $method->invoke(
+			$importer,
+			self::sample_item_data( 0 ),
+			'https://example.test/feed.xml',
+			array(
+				'post_status' => 'publish',
+				'post_author' => 1,
+			)
+		);
+
+		$this->assertArrayNotHasKey( 'post_date', $postarr );
+		$this->assertArrayNotHasKey( 'post_date_gmt', $postarr );
+	}
+
+	/**
+	 * Build a complete sample item-data array.
+	 *
+	 * Both build_postarr() and the helper it calls, build_meta_input(), read
+	 * every field that map_item() produces. Supplying the full set keeps the
+	 * tests focused on the post_date behavior we are pinning down.
+	 *
+	 * @param int $timestamp Optional feed timestamp (zero means "no date").
+	 * @return array<string,mixed>
+	 */
+	private static function sample_item_data( int $timestamp ): array {
+		return array(
+			'title'            => 'Episode',
+			'content'          => 'Body',
+			'excerpt'          => 'Teaser',
+			'timestamp'        => $timestamp,
+			'link'             => 'https://example.test/episode',
+			'audio_url'        => 'https://example.test/episode.mp3',
+			'audio_type'       => 'audio/mpeg',
+			'audio_length'     => 0,
+			'duration'         => '',
+			'duration_seconds' => 0,
+			'season'           => 0,
+			'episode'          => 0,
+			'episode_type'     => '',
+			'explicit'         => '0',
+			'source_id'        => 'src-1',
+			'source_key'       => str_repeat( 'a', 64 ),
+			'creator'          => '',
+			'fingerprint'      => str_repeat( 'b', 64 ),
+		);
+	}
 }