diff --git a/common/includes/slack/trac/comment-handler.php b/common/includes/slack/trac/comment-handler.php
index ae47f599eb..8278bd8f99 100644
--- a/common/includes/slack/trac/comment-handler.php
+++ b/common/includes/slack/trac/comment-handler.php
@@ -16,6 +16,13 @@ class Comment_Handler {
 	protected $comment_id;
 	protected $comment_url;
 
+	/**
+	 * The ticket's component, read from the notification's ticket properties table.
+	 *
+	 * @var string
+	 */
+	protected $component;
+
 	/**
 	 * Workflow keywords added to the ticket by this change.
 	 *
@@ -63,6 +70,11 @@ function run() {
 			$this->send->send( $firehose );
 		}
 
+		$component_firehose = $this->trac->get_component_firehose_channel( $this->component );
+		if ( $component_firehose ) {
+			$this->send->send( $component_firehose );
+		}
+
 		// Send notifications for Workflow Keyword additions.
 		$this->send_keyword_notifications();
 	}
@@ -200,9 +212,13 @@ function process_message() {
 		}
 		// Remove top border of table.
 		array_shift( $lines );
-		// Remove ticket properties table.
+		// Remove ticket properties table, keeping the component. It can be in either column.
+		$component = '';
 		while ( $lines && 0 !== strpos( current( $lines ), '------' ) ) {
-			array_shift( $lines );
+			$line = array_shift( $lines );
+			if ( preg_match( '/(?:^|\|)\s*Component:\s+([^|]*?)\s*(?:\||$)/', $line, $matches ) ) {
+				$component = $matches[1];
+			}
 		}
 		// Remove bottom border of table.
 		array_shift( $lines );
@@ -290,6 +306,7 @@ function process_message() {
 		$this->author  = $author;
 		$this->comment = $comment;
 		$this->changes = $changes;
+		$this->component   = $component;
 		$this->ticket_id   = $ticket_id;
 		$this->ticket_url  = $ticket_url;
 		$this->comment_id  = $comment_id;
diff --git a/common/includes/slack/trac/commit-handler.php b/common/includes/slack/trac/commit-handler.php
index cf22dbc45a..492bae15ab 100644
--- a/common/includes/slack/trac/commit-handler.php
+++ b/common/includes/slack/trac/commit-handler.php
@@ -20,9 +20,14 @@ public function __construct( Send $send, $trac, $repo, $rev ) {
 	}
 
 	public function run() {
-		$this->generate_payload();
+		// One payload per commit format, so each channel gets the full message or just the summary.
+		$payloads = array();
 		foreach ( $this->trac->get_commit_channels( $this->svnlook( 'changed' ), $this->svnlook( 'log' ) ) as $channel ) {
-			$this->send->send( $channel );
+			$format = $this->trac->get_commit_format( $channel );
+			if ( ! isset( $payloads[ $format ] ) ) {
+				$payloads[ $format ] = $this->generate_payload( $format );
+			}
+			$payloads[ $format ]->send( $channel );
 		}
 	}
 
@@ -34,9 +39,20 @@ public function set_svnlook_executable( $path ) {
 		$this->svnlook = $path;
 	}
 
-	protected function generate_payload() {
+	/**
+	 * Builds the Slack message for the commit.
+	 *
+	 * @param string $format 'full' for the whole commit message, 'summary' for its first line.
+	 * @return Send A copy of the Send object with the commit attached.
+	 */
+	protected function generate_payload( $format = 'full' ) {
+		$log = $this->svnlook( 'log' );
+		if ( 'summary' === $format ) {
+			$log = Commit::get_summary( $log );
+		}
+
 		$author   = $this->svnlook( 'author' );
-		$message  = Commit::format_commit_for_slack( $this->trac, $this->svnlook( 'log' ) );
+		$message  = Commit::format_commit_for_slack( $this->trac, $log );
 		$date     = $this->svnlook( 'date' );
 		$url      = $this->trac->get_commit_template( $this->rev );
 		$revision = 'r' . $this->rev;
@@ -46,21 +62,26 @@ protected function generate_payload() {
 		$title    = "$username $revision";
 		$fallback = "$username $revision by $author";
 
-		$this->send->set_username( $username );
-		$this->send->set_icon( $icon );
-		$this->send->add_attachment( array(
-			'title'       => $title,
-			'title_link'  => $url,
-			'author_name' => $author,
-			'author_icon' => sprintf( 'https://wordpress.org/grav-redirect.php?user=%s&s=32', $author ),
-			'color'       => $color,
-			'text'        => $message,
-			'fallback'    => $fallback,
-			'mrkdwn_in'   => array( 'text' ),
-			'ts'          => $date,
-			'footer'      => sprintf( '<%s|%s>', $this->trac->get_url(), $this->trac->get_name() ),
-			'footer_icon' => sprintf( '%s/chrome/common/trac.ico', $this->trac->get_url() ),
-		) );
+		$send = clone $this->send;
+		$send->set_username( $username );
+		$send->set_icon( $icon );
+		$send->add_attachment(
+			array(
+				'title'       => $title,
+				'title_link'  => $url,
+				'author_name' => $author,
+				'author_icon' => sprintf( 'https://wordpress.org/grav-redirect.php?user=%s&s=32', $author ),
+				'color'       => $color,
+				'text'        => $message,
+				'fallback'    => $fallback,
+				'mrkdwn_in'   => array( 'text' ),
+				'ts'          => $date,
+				'footer'      => sprintf( '<%s|%s>', $this->trac->get_url(), $this->trac->get_name() ),
+				'footer_icon' => sprintf( '%s/chrome/common/trac.ico', $this->trac->get_url() ),
+			)
+		);
+
+		return $send;
 	}
 
 	protected function svnlook( $subcommand ) {
diff --git a/common/includes/slack/trac/commit.php b/common/includes/slack/trac/commit.php
index 067a6c789a..cef5b5ba3d 100644
--- a/common/includes/slack/trac/commit.php
+++ b/common/includes/slack/trac/commit.php
@@ -92,6 +92,22 @@ function fetch() {
 		return $this->data;
 	}
 
+	/**
+	 * Gets the summary of a commit message: its first non-empty line.
+	 *
+	 * @param string $message Commit message.
+	 * @return string
+	 */
+	public static function get_summary( $message ) {
+		foreach ( explode( "\n", $message ) as $line ) {
+			$line = trim( $line );
+			if ( '' !== $line ) {
+				return $line;
+			}
+		}
+		return '';
+	}
+
 	static function format_commit_for_slack( Trac $trac, $message ) {
 		// Convert ASCII numbers to an UTF-8 character, like ?\226?\128?\148 => — (m-dash).
 		$message = preg_replace_callback( '/(?:\?\\\\(\d{1,3}))/', function( $matches ) {
diff --git a/common/includes/slack/trac/config.php b/common/includes/slack/trac/config.php
index a4e0d1b4b4..cbeef0202e 100644
--- a/common/includes/slack/trac/config.php
+++ b/common/includes/slack/trac/config.php
@@ -12,6 +12,13 @@ class Core extends Trac {
 
 	protected $primary_channel_ticket_format = 'title';
 
+	/**
+	 * Post only the first line of each commit message to #core.
+	 *
+	 * @var string
+	 */
+	protected $primary_channel_commit_format = 'summary';
+
 	/**
 	 * File paths that cause commits to be piped to particular channels.
 	 * Start regex matches with # as your delimiter.
@@ -54,7 +61,7 @@ class Core extends Trac {
 		'webpack.config.js'                => '#core-build-test-tools',
 		'wp-tests-config-sample.php'       => '#core-build-test-tools',
 		'#\.n(v|p)mrc#'                    => '#core-build-test-tools',
-		'#\.version-support-[a-z]+\.json'  => '#core-build-test-tools',
+		'#\.version-support-[a-z]+\.json#' => '#core-build-test-tools',
 		'#^package(-lock)?\.json$#'        => '#core-build-test-tools',
 		'#^php[a-z]+\.xml\.dist$#'         => '#core-build-test-tools',
 	);
@@ -70,34 +77,97 @@ class Core extends Trac {
 	);
 
 	/**
-	 * Components or focuses that cause new tickets to be piped to particular channels.
+	 * Maps each Core Trac component to its component specific channel.
+	 *
+	 * Notifications for a component go to that channel's -firehose, -newtickets and -commits
+	 * channels, not to the channel itself.
+	 *
+	 * Subcomponents map to their parent's channel, unless they have their own.
+	 *
+	 * Some components have no discussion channel, or an archived one, but still have
+	 * -firehose, -newtickets and -commits channels.
+	 *
+	 * Retired components have an empty value, and only post to the global channels.
+	 *
+	 * @var array
 	 */
-	protected $ticket_component_filters = array(
+	protected $component_channels = array(
+		'AI'                     => '#core-ai',
 		'Build/Test Tools'       => '#core-build-test-tools',
 		'Bundled Theme'          => '#core-themes',
-		'Customize'              => '#core-customize',
-		'Date/Time'              => '#core-datetime',
-		'Press This'             => '#core-pressthis',
-		'multisite'              => '#core-multisite',
-		'Networks and Sites'     => '#core-multisite',
-		'REST API'               => '#core-restapi',
-		'rest-api'               => '#core-restapi',
+		'Editor'                 => '#core-editor',
+		'HTML API'               => '#core-html-api',
 		'I18N'                   => '#core-i18n',
+		'Import'                 => '#core-importers',
+		'Interactivity API'      => '#core-interactivity-api',
 		'Media'                  => '#core-media',
-		'docs'                   => '#core-docs',
-		'css'                    => '#core-css',
-		'javascript'             => '#core-js',
-		'coding-standards'       => '#core-coding-standards',
-		'performance'            => '#core-performance',
+		'Networks and Sites'     => '#core-multisite',
 		'Privacy'                => '#core-privacy',
-		'privacy'                => '#core-privacy',
-		'Site Health'            => '#core-site-health',
-		'Sitemaps'               => '#core-sitemaps',
+		'REST API'               => '#core-restapi',
+		'Themes'                 => '#core-themes',
 		'Upgrade/Install'        => '#core-upgrade-install',
-		'Application Passwords'  => [ '#core-passwords' => true, '#core-restapi' => true ],
+
+		// Subcomponents.
+		'Abilities API'          => '#core-ai',
+		'Application Passwords'  => '#core-restapi',
+		'Autosave'               => '#core-editor',
+		'Canonical'              => '#core-permalinks',
+		'Charset'                => '#core-formatting',
+		'Embeds'                 => '#core-media',
+		'Emoji'                  => '#core-formatting',
+		'Gallery'                => '#core-media',
 		'Login and Registration' => '#core-passwords',
-		'HTML API'               => '#core-html-api',
-		'Interactivity API'      => '#core-interactivity-api',
+		'Menus'                  => '#core-themes',
+		'Multisite'              => '#core-multisite',
+		'Notes'                  => '#core-notes',
+		'Pings/Trackbacks'       => '#core-comments',
+		'Post Formats'           => '#core-posts-post-types',
+		'Post Thumbnails'        => '#core-posts-post-types',
+		'Quick/Bulk Edit'        => '#core-editor',
+		'Revisions'              => '#core-posts-post-types',
+		'Rewrite Rules'          => '#core-permalinks',
+		'Role/Capability'        => '#core-users',
+		'Shortcodes'             => '#core-formatting',
+		'TinyMCE'                => '#core-editor', // #core-tinymce has been archived since 2025-06-24.
+		'Upload'                 => '#core-media',
+		'Widgets'                => '#core-themes',
+
+		// Components with an archived component specific channel.
+		'Bootstrap/Load'         => '#core-bootstrap',
+		'Comments'               => '#core-comments',
+		'Customize'              => '#core-customize',
+		'Date/Time'              => '#core-datetime',
+		'HTTP API'               => '#core-http-api',
+		'Site Health'            => '#core-site-health',
+		'Sitemaps'               => '#core-sitemaps',
+
+		// Components that have never had a component specific channel.
+		'Administration'         => '#core-administration',
+		'Cache API'              => '#core-cache-api',
+		'Cron API'               => '#core-cron-api',
+		'Database'               => '#core-database',
+		'Export'                 => '#core-export',
+		'External Libraries'     => '#core-external-libraries',
+		'Feeds'                  => '#core-feeds',
+		'Filesystem API'         => '#core-filesystem-api',
+		'Formatting'             => '#core-formatting',
+		'General'                => '#core-general',
+		'Help/About'             => '#core-help-about',
+		'Mail'                   => '#core-mail',
+		'Options, Meta APIs'     => '#core-options-meta-apis',
+		'Permalinks'             => '#core-permalinks',
+		'Plugins'                => '#core-plugins',
+		'Posts, Post Types'      => '#core-posts-post-types',
+		'Query'                  => '#core-query',
+		'Script Loader'          => '#core-script-loader',
+		'Security'               => '#core-security',
+		'Taxonomy'               => '#core-taxonomy',
+		'Toolbar'                => '#core-toolbar',
+		'Users'                  => '#core-users',
+		'XML-RPC'                => '#core-xml-rpc',
+
+		// Retired components.
+		'Press This'             => '', // #core-pressthis is archived.
 	);
 }
 
diff --git a/common/includes/slack/trac/trac.php b/common/includes/slack/trac/trac.php
index 34314412eb..1eb4829e5e 100644
--- a/common/includes/slack/trac/trac.php
+++ b/common/includes/slack/trac/trac.php
@@ -23,6 +23,15 @@ class Trac implements User {
 	// 'title', 'fields', 'description'
 	protected $primary_channel_ticket_format = 'description';
 
+	/**
+	 * How much of the commit message to post to the primary channel.
+	 *
+	 * 'full' posts the whole commit message, 'summary' only its first line.
+	 *
+	 * @var string
+	 */
+	protected $primary_channel_commit_format = 'full';
+
 	protected $bypass_primary_channel_for_commit_filter_matches = false;
 	protected $bypass_primary_channel_for_ticket_filter_matches = false;
 
@@ -36,6 +45,19 @@ class Trac implements User {
 	 */
 	protected $ticket_keyword_filters = array();
 
+	/**
+	 * Maps Trac components (or commit message prefixes) to component specific channels.
+	 *
+	 * Notifications for a component go to that channel's -firehose, -newtickets and -commits
+	 * channels, not to the channel itself. This includes commits that $commit_path_filters
+	 * sends to one of these channels.
+	 *
+	 * Components with an empty value have no component channels.
+	 *
+	 * @var array
+	 */
+	protected $component_channels = array();
+
 	protected $color = '#0073aa';
 	protected $icon  = ':wordpress:';
 
@@ -250,6 +272,21 @@ function get_commit_channels( $changed_files = null, $log_text = null ) {
 			}
 		}
 
+		foreach ( $this->component_channels as $component => $channel ) {
+			if ( $channel && 0 === stripos( $log_text, $component ) ) {
+				$channels[ $channel ] = true;
+			}
+		}
+
+		// Commits for a component go to its -commits and -firehose channels rather than the component channel itself.
+		foreach ( array_unique( array_filter( $this->component_channels ) ) as $channel ) {
+			if ( ! empty( $channels[ $channel ] ) ) {
+				unset( $channels[ $channel ] );
+				$channels[ $channel . '-commits' ]  = true;
+				$channels[ $channel . '-firehose' ] = true;
+			}
+		}
+
 		if ( $this->firehose_channel ) {
 			$channels[ $this->firehose_channel ] = true;
 		}
@@ -291,6 +328,14 @@ function get_ticket_channels( $ticket = null ) {
 			}
 		}
 
+		// New tickets in a component with a channel go to that channel's -newtickets and -firehose channels.
+		if ( isset( $ticket->component ) && ! empty( $this->component_channels[ $ticket->component ] ) ) {
+			$channel = $this->component_channels[ $ticket->component ];
+
+			$channels[ $channel . '-newtickets' ] = true;
+			$channels[ $channel . '-firehose' ]   = true;
+		}
+
 		if ( $this->firehose_channel ) {
 			$channels[ $this->firehose_channel ] = true;
 		}
@@ -302,6 +347,19 @@ function get_firehose_channel() {
 		return $this->firehose_channel;
 	}
 
+	/**
+	 * Gets the firehose channel for a component.
+	 *
+	 * @param string $component Trac component name.
+	 * @return string|false Channel name, or false if the component has no channels.
+	 */
+	public function get_component_firehose_channel( $component ) {
+		if ( ! empty( $this->component_channels[ $component ] ) ) {
+			return $this->component_channels[ $component ] . '-firehose';
+		}
+		return false;
+	}
+
 	/**
 	 * Gets the channels a ticket update should be posted to when a workflow keyword is added.
 	 *
@@ -323,6 +381,19 @@ function get_ticket_format( $channel ) {
 		return 'description';
 	}
 
+	/**
+	 * Gets how much of the commit message to post to a channel.
+	 *
+	 * @param string $channel Channel name.
+	 * @return string 'full' or 'summary'.
+	 */
+	public function get_commit_format( $channel ) {
+		if ( $channel === $this->primary_channel ) {
+			return $this->primary_channel_commit_format;
+		}
+		return 'full';
+	}
+
 	/**
 	 * Stop message text people typed from being read as Slack markup.
 	 *
diff --git a/common/includes/tests/slack/trac/channels.php b/common/includes/tests/slack/trac/channels.php
new file mode 100644
index 0000000000..84c66e045f
--- /dev/null
+++ b/common/includes/tests/slack/trac/channels.php
@@ -0,0 +1,141 @@
+<?php
+/**
+ * Tests for routing Core Trac notifications to Slack channels.
+ *
+ * @package WordPressdotorg\Slack\Trac
+ */
+
+declare( strict_types = 1 );
+
+require_once dirname( dirname( dirname( __DIR__ ) ) ) . '/slack/autoload.php';
+
+use Dotorg\Slack\Trac\Trac;
+
+/**
+ * Tests for the component channels of Dotorg\Slack\Trac\Trac.
+ */
+class Test_Slack_Trac_Channels extends \PHPUnit\Framework\TestCase {
+
+	/**
+	 * Core commits post to the global channels and the component's channels.
+	 *
+	 * @dataProvider data_core_commit_channels
+	 *
+	 * @param string   $changed_files Changed file paths, one per line.
+	 * @param string   $log           Commit message.
+	 * @param string[] $expected      Expected channels.
+	 */
+	public function test_core_commit_channels( string $changed_files, string $log, array $expected ): void {
+		$channels = Trac::get( 'core' )->get_commit_channels( $changed_files, $log );
+
+		sort( $channels );
+		sort( $expected );
+		$this->assertSame( $expected, $channels );
+	}
+
+	/**
+	 * Data provider for test_core_commit_channels().
+	 *
+	 * @return array[]
+	 */
+	public static function data_core_commit_channels(): array {
+		$global = array( '#core', '#core-commits', '#core-firehose' );
+
+		return array(
+			'component prefix'                       => array(
+				'trunk/src/wp-admin/import.php',
+				"Import: Check the file type.\n\nFixes #12345.",
+				array_merge( $global, array( '#core-importers-commits', '#core-importers-firehose' ) ),
+			),
+			'component without a discussion channel' => array(
+				'trunk/src/wp-includes/class-wp-query.php',
+				'Query: Cache the results.',
+				array_merge( $global, array( '#core-query-commits', '#core-query-firehose' ) ),
+			),
+			'archived channel path filter'           => array(
+				'trunk/src/wp-includes/sitemaps/class-wp-sitemaps.php',
+				'Fix a typo.',
+				array_merge( $global, array( '#core-sitemaps-commits', '#core-sitemaps-firehose' ) ),
+			),
+			'subcomponent prefix'                    => array(
+				'trunk/src/wp-includes/embed.php',
+				'Embeds: Fix the iframe title.',
+				array_merge( $global, array( '#core-media-commits', '#core-media-firehose' ) ),
+			),
+			'bundled themes'                         => array(
+				'trunk/src/wp-includes/theme.php',
+				'Bundled Themes: Fix a typo.',
+				array_merge( $global, array( '#core-themes-commits', '#core-themes-firehose' ) ),
+			),
+			'path filter'                            => array(
+				'trunk/src/wp-includes/html-api/class-wp-html-processor.php',
+				'Fix a typo.',
+				array_merge( $global, array( '#core-html-api-commits', '#core-html-api-firehose' ) ),
+			),
+			'path filter and prefix'                 => array(
+				'trunk/src/wp-includes/media.php',
+				'I18N: Add context to a string.',
+				array_merge( $global, array( '#core-i18n-commits', '#core-i18n-firehose', '#core-media-commits', '#core-media-firehose' ) ),
+			),
+			'no component'                           => array(
+				'trunk/src/wp-includes/formatting.php',
+				'Docs: Correct a parameter type.',
+				$global,
+			),
+		);
+	}
+
+	/**
+	 * New Core tickets post to the global channels and the component's channels.
+	 */
+	public function test_core_new_ticket_channels(): void {
+		$ticket = (object) array(
+			'component' => 'Gallery',
+			'focuses'   => 'css, javascript',
+			'keywords'  => 'has-patch needs-testing',
+		);
+
+		$channels = Trac::get( 'core' )->get_ticket_channels( $ticket );
+
+		sort( $channels );
+		$this->assertSame(
+			array( '#core', '#core-firehose', '#core-media-firehose', '#core-media-newtickets', '#core-newtickets', '#core-test' ),
+			$channels
+		);
+	}
+
+	/**
+	 * New Core tickets in a component that isn't listed post only to the global channels.
+	 */
+	public function test_core_new_ticket_unlisted_component(): void {
+		$channels = Trac::get( 'core' )->get_ticket_channels( (object) array( 'component' => 'Text Changes' ) );
+
+		sort( $channels );
+		$this->assertSame( array( '#core', '#core-firehose', '#core-newtickets' ), $channels );
+	}
+
+	/**
+	 * Core ticket updates post to the component's firehose.
+	 */
+	public function test_core_component_firehose_channel(): void {
+		$trac = Trac::get( 'core' );
+
+		$this->assertSame( '#core-passwords-firehose', $trac->get_component_firehose_channel( 'Login and Registration' ) );
+		$this->assertSame( '#core-formatting-firehose', $trac->get_component_firehose_channel( 'Shortcodes' ) );
+		$this->assertFalse( $trac->get_component_firehose_channel( 'Text Changes' ) );
+		$this->assertFalse( $trac->get_component_firehose_channel( 'Not A Component' ) );
+	}
+
+	/**
+	 * Meta has no component channels, so its routing is unchanged.
+	 */
+	public function test_meta_commit_channels_are_unchanged(): void {
+		$channels = Trac::get( 'meta' )->get_commit_channels(
+			'sites/trunk/wordpress.org/public_html/wp-content/plugins/plugin-directory/class-plugin-directory.php',
+			'Plugin Directory: Fix a thing.'
+		);
+
+		sort( $channels );
+		$this->assertSame( array( '#meta', '#meta-commits', '#meta-firehose', '#pluginreview' ), $channels );
+	}
+}
diff --git a/common/includes/tests/slack/trac/comment-handler.php b/common/includes/tests/slack/trac/comment-handler.php
index 9cf7faf8a0..c4dbbe764c 100644
--- a/common/includes/tests/slack/trac/comment-handler.php
+++ b/common/includes/tests/slack/trac/comment-handler.php
@@ -60,6 +60,32 @@ public function test_last_line_is_kept( array $body, string $comment, array $cha
 		$this->assertSame( $changes, $handler->changes );
 	}
 
+	/**
+	 * The ticket's component is read from either column of the properties table.
+	 */
+	public function test_component_is_read(): void {
+		$body = array(
+			'',
+			'Comment (by desrosj):',
+			'',
+			' Does anyone have any idea why Nacin would make this change?',
+		);
+
+		$handler = new \Dotorg\Slack\Trac\Comment_Handler( new \Dotorg\Slack\Send( '' ), $this->get_email( $body ) );
+		$handler->process_message();
+		$this->assertSame( 'Trac', $handler->component );
+
+		$email = str_replace(
+			array( 'Component:  Trac             |  Resolution:', '     Type:  defect (bug)     |      Status:  new' ),
+			array( '     Type:  defect (bug)     |  Resolution:', ' Priority:  normal          |   Component:  Build/Test Tools' ),
+			$this->get_email( $body )
+		);
+
+		$handler = new \Dotorg\Slack\Trac\Comment_Handler( new \Dotorg\Slack\Send( '' ), $email );
+		$handler->process_message();
+		$this->assertSame( 'Build/Test Tools', $handler->component );
+	}
+
 	/**
 	 * Data provider for test_last_line_is_kept().
 	 *
diff --git a/common/includes/tests/slack/trac/commit-handler.php b/common/includes/tests/slack/trac/commit-handler.php
new file mode 100644
index 0000000000..6d9756f528
--- /dev/null
+++ b/common/includes/tests/slack/trac/commit-handler.php
@@ -0,0 +1,160 @@
+<?php
+/**
+ * Tests for posting Trac commits to Slack.
+ *
+ * @package WordPressdotorg\Slack\Trac
+ */
+
+declare( strict_types = 1 );
+
+require_once dirname( dirname( dirname( __DIR__ ) ) ) . '/slack/autoload.php';
+
+use Dotorg\Slack\Send;
+use Dotorg\Slack\Trac\Commit;
+use Dotorg\Slack\Trac\Commit_Handler;
+use Dotorg\Slack\Trac\Trac;
+
+/**
+ * Tests for Dotorg\Slack\Trac\Commit_Handler.
+ */
+class Test_Slack_Trac_Commit_Handler extends \PHPUnit\Framework\TestCase {
+
+	/**
+	 * A Core commit message with a summary line, a description, props and a ticket reference.
+	 *
+	 * @var string
+	 */
+	const LOG = "Media: Add a missing alt attribute.\n\nThe image in the media modal had no alt text.\n\nProps desrosj.\nFixes #12345.";
+
+	/**
+	 * Runs a commit through Commit_Handler without svnlook or the Slack webhook.
+	 *
+	 * @param string $trac          Trac slug.
+	 * @param string $changed_files Changed file paths, one per line.
+	 * @param string $log           Commit message.
+	 * @return string[] Attachment text sent to each channel, keyed by channel.
+	 */
+	private function run_handler( string $trac, string $changed_files, string $log ): array {
+		$sent = new ArrayObject();
+
+		$send = new class( 'https://example.com/webhook', $sent ) extends Send {
+			private $sent;
+
+			public function __construct( $webhook, ArrayObject $sent ) {
+				parent::__construct( $webhook );
+				$this->sent = $sent;
+			}
+
+			public function send( $channel, $thread = false ) {
+				$attachments            = $this->get_attachments();
+				$this->sent[ $channel ] = $attachments[0]['text'];
+			}
+		};
+
+		$handler = new class( $send, $trac, '/repo', 1 ) extends Commit_Handler {
+			public $svnlook_output = array();
+
+			protected function svnlook( $subcommand ) {
+				return $this->svnlook_output[ $subcommand ];
+			}
+		};
+
+		$handler->svnlook_output = array(
+			'changed' => $changed_files,
+			'log'     => $log,
+			'author'  => 'desrosj',
+			'date'    => '1762732800',
+		);
+		$handler->run();
+
+		return $sent->getArrayCopy();
+	}
+
+	/**
+	 * #core gets the commit summary; every other channel gets the full message.
+	 */
+	public function test_core_commit_summary_only_goes_to_core(): void {
+		$sent = $this->run_handler( 'core', 'trunk/src/wp-includes/media.php', self::LOG );
+
+		$this->assertSame(
+			array( '#core', '#core-commits', '#core-firehose', '#core-media-commits', '#core-media-firehose' ),
+			$this->sorted_keys( $sent )
+		);
+
+		$this->assertSame( 'Media: Add a missing alt attribute.', $sent['#core'] );
+
+		foreach ( array( '#core-commits', '#core-firehose', '#core-media-commits', '#core-media-firehose' ) as $channel ) {
+			$this->assertStringContainsString( 'Props desrosj.', $sent[ $channel ], "$channel should get the full commit message." );
+		}
+	}
+
+	/**
+	 * Meta posts the full commit message everywhere, including its primary channel.
+	 */
+	public function test_meta_commit_is_unchanged(): void {
+		$sent = $this->run_handler(
+			'meta',
+			'sites/trunk/wordpress.org/public_html/wp-content/plugins/plugin-directory/class-plugin-directory.php',
+			"Plugin Directory: Fix a thing.\n\nProps desrosj."
+		);
+
+		$this->assertNotEmpty( $sent );
+		foreach ( $sent as $channel => $text ) {
+			$this->assertStringContainsString( 'Props desrosj.', $text, "$channel should get the full commit message." );
+		}
+	}
+
+	/**
+	 * Only Core's primary channel uses the summary format.
+	 */
+	public function test_get_commit_format(): void {
+		$core = Trac::get( 'core' );
+
+		$this->assertSame( 'summary', $core->get_commit_format( '#core' ) );
+		$this->assertSame( 'full', $core->get_commit_format( '#core-commits' ) );
+		$this->assertSame( 'full', $core->get_commit_format( '#core-media-commits' ) );
+		$this->assertSame( 'full', Trac::get( 'meta' )->get_commit_format( '#meta' ) );
+	}
+
+	/**
+	 * The summary is the first non-empty line of the commit message.
+	 */
+	public function test_get_summary(): void {
+		$this->assertSame( 'Media: Add a missing alt attribute.', Commit::get_summary( self::LOG ) );
+		$this->assertSame( 'Docs: Fix a typo.', Commit::get_summary( "\n  Docs: Fix a typo.  \n\nProps someone." ) );
+		$this->assertSame( 'One line.', Commit::get_summary( 'One line.' ) );
+		$this->assertSame( '', Commit::get_summary( '' ) );
+	}
+
+	/**
+	 * Every -newtickets channel gets the same format as #core-newtickets: the full ticket.
+	 * Only #core gets the title alone.
+	 */
+	public function test_newtickets_channels_match_core_newtickets_format(): void {
+		$core = Trac::get( 'core' );
+		$map  = ( new ReflectionProperty( $core, 'component_channels' ) )->getValue( $core );
+
+		$this->assertSame( 'title', $core->get_ticket_format( '#core' ) );
+		$this->assertSame( 'description', $core->get_ticket_format( '#core-newtickets' ) );
+
+		foreach ( array_unique( array_filter( $map ) ) as $channel ) {
+			$this->assertSame(
+				$core->get_ticket_format( '#core-newtickets' ),
+				$core->get_ticket_format( $channel . '-newtickets' ),
+				"$channel-newtickets should match #core-newtickets."
+			);
+		}
+	}
+
+	/**
+	 * Returns an array's keys, sorted.
+	 *
+	 * @param array $array Array.
+	 * @return string[]
+	 */
+	private function sorted_keys( array $array ): array {
+		$keys = array_keys( $array );
+		sort( $keys );
+		return $keys;
+	}
+}