diff --git a/tools/release/phpunit.xml.dist b/tools/release/phpunit.xml.dist
index d10c471de14..e0f8f992291 100644
--- a/tools/release/phpunit.xml.dist
+++ b/tools/release/phpunit.xml.dist
@@ -19,6 +19,7 @@
         <!-- Milestone mover: close/create/move + due dates. -->
         <testsuite name="milestones-update">
             <file>tests/MilestoneUpdaterTest.php</file>
+            <file>tests/MilestoneSnapshotTest.php</file>
         </testsuite>
         <!-- Milestone consistency audit. -->
         <testsuite name="milestones-audit">
@@ -27,6 +28,7 @@
         <!-- Repository tagging. -->
         <testsuite name="tagger">
             <file>tests/RepoTaggerTest.php</file>
+            <file>tests/TaggerSnapshotTest.php</file>
         </testsuite>
         <!-- Updater-server release plan + config transforms. -->
         <testsuite name="updater">
diff --git a/tools/release/tests/MilestoneSnapshotTest.php b/tools/release/tests/MilestoneSnapshotTest.php
new file mode 100644
index 00000000000..1f170d34a12
--- /dev/null
+++ b/tools/release/tests/MilestoneSnapshotTest.php
@@ -0,0 +1,110 @@
+<?php
+
+// SPDX-FileCopyrightText: 2026 Nextcloud GmbH and Nextcloud contributors
+// SPDX-License-Identifier: MIT
+
+declare(strict_types=1);
+
+namespace Nextcloud\ReleaseTools\Tests;
+
+use Nextcloud\ReleaseTools\MilestoneUpdater;
+use Nextcloud\ReleaseTools\Tests\Support\FakeGitHubApi;
+use Nextcloud\ReleaseTools\Tests\Support\Journal;
+use Nextcloud\ReleaseTools\Tests\Support\MatchesSnapshots;
+use Nextcloud\ReleaseTools\Version;
+use PHPUnit\Framework\TestCase;
+
+/**
+ * What: golden-file snapshots of the full milestone-update journal per release
+ * scenario (the PHP successor to the old tests/milestone-scripts snapshot
+ * harness).
+ *
+ * Why: alongside the focused assertions in MilestoneUpdaterTest, these pin the
+ * entire mutation sequence as a reviewable artifact - the same "scenario ->
+ * expected" feel as the bash harness, so a behaviour change shows up as a
+ * readable snapshot diff. Update with UPDATE_SNAPSHOTS=1.
+ */
+final class MilestoneSnapshotTest extends TestCase
+{
+    use MatchesSnapshots;
+
+    private const SERVER = 'nextcloud/server';
+    private const ACTIVITY = 'nextcloud/activity';
+
+    private function snapshot(string $description, FakeGitHubApi $api): string
+    {
+        return Journal::snapshot($description, Journal::MILESTONE_LEGEND, $api->journal);
+    }
+
+    public function testPatchRelease(): void
+    {
+        $api = new FakeGitHubApi();
+        $api->seedMilestone(self::SERVER, 10, 'Nextcloud 33.0.4', 'open', 2);
+        $api->seedMilestone(self::SERVER, 11, 'Nextcloud 33.0.5');
+        $api->seedIssue(self::SERVER, 100, 10);
+        $api->seedIssue(self::SERVER, 101, 10);
+
+        (new MilestoneUpdater($api))->run(Version::fromTag('v33.0.4'), [self::SERVER]);
+        $this->assertMatchesSnapshot('milestones/patch-release', $this->snapshot('Patch release v33.0.4: move open issues to 33.0.5, close 33.0.4, open 33.0.6', $api));
+    }
+
+    public function testFirstStable(): void
+    {
+        $api = new FakeGitHubApi();
+        $api->seedMilestone(self::SERVER, 20, 'Nextcloud 34');
+        (new MilestoneUpdater($api))->run(Version::fromTag('v34.0.0'), [self::SERVER]);
+        $this->assertMatchesSnapshot('milestones/first-stable', $this->snapshot('First stable v34.0.0: close the Nextcloud 34 milestone, open 34.0.1 and 34.0.2', $api));
+    }
+
+    public function testFirstBeta(): void
+    {
+        $api = new FakeGitHubApi();
+        (new MilestoneUpdater($api))->run(Version::fromTag('v35.0.0beta1'), [self::SERVER, self::ACTIVITY]);
+        $this->assertMatchesSnapshot('milestones/first-beta', $this->snapshot('First beta v35.0.0beta1: open the next major milestone Nextcloud 36 in each repo', $api));
+    }
+
+    public function testMissingNext(): void
+    {
+        $api = new FakeGitHubApi();
+        $api->seedMilestone(self::SERVER, 10, 'Nextcloud 33.0.4', 'open', 1);
+        $api->seedIssue(self::SERVER, 100, 10);
+        (new MilestoneUpdater($api))->run(Version::fromTag('v33.0.4'), [self::SERVER]);
+        $this->assertMatchesSnapshot('milestones/missing-next', $this->snapshot('Patch v33.0.4 when 33.0.5 is missing: create it first, then move/close/open 33.0.6', $api));
+    }
+
+    public function testDueDates(): void
+    {
+        $api = new FakeGitHubApi();
+        $api->seedMilestone(self::SERVER, 10, 'Nextcloud 33.0.4');
+        $api->seedMilestone(self::SERVER, 11, 'Nextcloud 33.0.5', 'open', 0, '2026-06-25T00:00:00Z');
+        $api->seedMilestone(self::SERVER, 12, 'Nextcloud 33.0.6');
+        (new MilestoneUpdater($api))->run(
+            Version::fromTag('v33.0.4'),
+            [self::SERVER],
+            '2026-07-02T00:00:00Z',
+            '2026-08-27T00:00:00Z',
+        );
+        $this->assertMatchesSnapshot('milestones/due-dates', $this->snapshot('Patch v33.0.4 with due dates: set 33.0.5 and 33.0.6 due dates, close 33.0.4', $api));
+    }
+
+    public function testMultiRepo(): void
+    {
+        $api = new FakeGitHubApi();
+        foreach ([self::SERVER, self::ACTIVITY] as $i => $repo) {
+            $base = ($i + 1) * 10;
+            $api->seedMilestone($repo, $base, 'Nextcloud 33.0.4', 'open', 1);
+            $api->seedMilestone($repo, $base + 1, 'Nextcloud 33.0.5');
+            $api->seedIssue($repo, 500 + $i, $base);
+        }
+        (new MilestoneUpdater($api))->run(Version::fromTag('v33.0.4'), [self::SERVER, self::ACTIVITY]);
+        $this->assertMatchesSnapshot('milestones/multi-repo', $this->snapshot('Patch v33.0.4 across two repos', $api));
+    }
+
+    public function testPrereleaseNoop(): void
+    {
+        $api = new FakeGitHubApi();
+        $api->seedMilestone(self::SERVER, 10, 'Nextcloud 33.0.2');
+        (new MilestoneUpdater($api))->run(Version::fromTag('v33.0.2rc1'), [self::SERVER]);
+        $this->assertMatchesSnapshot('milestones/prerelease-noop', $this->snapshot('Non-first-beta pre-release v33.0.2rc1: nothing happens', $api));
+    }
+}
diff --git a/tools/release/tests/Support/Journal.php b/tools/release/tests/Support/Journal.php
new file mode 100644
index 00000000000..4770de138dc
--- /dev/null
+++ b/tools/release/tests/Support/Journal.php
@@ -0,0 +1,31 @@
+<?php
+
+// SPDX-FileCopyrightText: 2026 Nextcloud GmbH and Nextcloud contributors
+// SPDX-License-Identifier: MIT
+
+declare(strict_types=1);
+
+namespace Nextcloud\ReleaseTools\Tests\Support;
+
+/**
+ * Builds the .snap body for the milestone/tagger snapshot tests: the raw
+ * tab-separated mutation journal (the standard, stable format the assertion
+ * tests also use), preceded by comment lines that say which scenario produced
+ * it and what the columns mean - so a .snap file is understandable on its own.
+ */
+final class Journal
+{
+    public const MILESTONE_LEGEND =
+        'columns (tab): <action> <repo> <args> -- '
+        . 'create: title, due=<date|-> | setdue: #ms, date | move: #issue, #ms | close: #ms';
+
+    public const TAG_LEGEND =
+        'tags (tab): <action> <repo> <tag> <sha> -- tag | retag adds force=<bool>';
+
+    /** @param list<string> $lines raw journal lines */
+    public static function snapshot(string $description, string $legend, array $lines): string
+    {
+        $body = $lines === [] ? '(no changes)' : implode("\n", $lines);
+        return "# {$description}\n# {$legend}\n{$body}";
+    }
+}
diff --git a/tools/release/tests/Support/MatchesSnapshots.php b/tools/release/tests/Support/MatchesSnapshots.php
new file mode 100644
index 00000000000..22567523ac8
--- /dev/null
+++ b/tools/release/tests/Support/MatchesSnapshots.php
@@ -0,0 +1,38 @@
+<?php
+
+// SPDX-FileCopyrightText: 2026 Nextcloud GmbH and Nextcloud contributors
+// SPDX-License-Identifier: MIT
+
+declare(strict_types=1);
+
+namespace Nextcloud\ReleaseTools\Tests\Support;
+
+/**
+ * Tiny golden-file snapshot helper. A test produces a string (e.g. the journal
+ * of GitHub mutations or a rendered file) and compares it to a committed
+ * `tests/snapshots/<name>.snap`. Missing snapshots are written on first run;
+ * re-run with `UPDATE_SNAPSHOTS=1` to regenerate after an intended change.
+ */
+trait MatchesSnapshots
+{
+    protected function assertMatchesSnapshot(string $name, string $actual): void
+    {
+        $file = __DIR__ . '/../snapshots/' . $name . '.snap';
+        $actual = rtrim($actual, "\n") . "\n";
+
+        if (getenv('UPDATE_SNAPSHOTS') === '1' || !is_file($file)) {
+            if (!is_dir(dirname($file))) {
+                mkdir(dirname($file), 0o777, true);
+            }
+            file_put_contents($file, $actual);
+            $this->addToAssertionCount(1);
+            return;
+        }
+
+        $this->assertSame(
+            file_get_contents($file),
+            $actual,
+            "Snapshot '{$name}' differs. Re-run with UPDATE_SNAPSHOTS=1 if the change is intended.",
+        );
+    }
+}
diff --git a/tools/release/tests/TaggerSnapshotTest.php b/tools/release/tests/TaggerSnapshotTest.php
new file mode 100644
index 00000000000..9e9d932bd80
--- /dev/null
+++ b/tools/release/tests/TaggerSnapshotTest.php
@@ -0,0 +1,93 @@
+<?php
+
+// SPDX-FileCopyrightText: 2026 Nextcloud GmbH and Nextcloud contributors
+// SPDX-License-Identifier: MIT
+
+declare(strict_types=1);
+
+namespace Nextcloud\ReleaseTools\Tests;
+
+use Nextcloud\ReleaseTools\RepoTagger;
+use Nextcloud\ReleaseTools\Tests\Support\FakeGitHubApi;
+use Nextcloud\ReleaseTools\Tests\Support\Journal;
+use Nextcloud\ReleaseTools\Tests\Support\MatchesSnapshots;
+use PHPUnit\Framework\TestCase;
+
+/**
+ * What: golden-file snapshots of the tagger's per-repo decisions and the tags
+ * it writes, across a representative mix of repositories.
+ *
+ * Why: pins the whole tag run (status + chosen branch + the create/recreate/skip
+ * journal) as one reviewable artifact, covering create, skip-existing,
+ * force-recreate, server-repo immutability, default-branch fallback and
+ * no-branch failure together. Update with UPDATE_SNAPSHOTS=1.
+ */
+final class TaggerSnapshotTest extends TestCase
+{
+    use MatchesSnapshots;
+
+    private function render(string $description, array $results, FakeGitHubApi $api): string
+    {
+        $lines = [
+            "# {$description}",
+            '# results (tab): <repo> <status> <branch> <detail>',
+            '# ' . Journal::TAG_LEGEND,
+        ];
+        foreach ($results as $r) {
+            $lines[] = sprintf("%s\t%s\t%s\t%s", $r->repo, $r->status, $r->branch === '' ? '-' : $r->branch, $r->detail);
+        }
+        $lines[] = '';
+        $lines[] = $api->journal === [] ? '(no tags written)' : implode("\n", $api->journal);
+        return implode("\n", $lines);
+    }
+
+    public function testMixedRun(): void
+    {
+        $api = new FakeGitHubApi();
+        // a normal app on the release branch
+        $api->seedBranch('nextcloud/activity', 'stable34', 'sha-activity', true);
+        // an app where the tag already exists (will skip without force)
+        $api->seedBranch('nextcloud/notes', 'stable34', 'sha-notes', true);
+        $api->seedTag('nextcloud/notes', 'v34.0.1', 'old-notes');
+        // an app with no stable34, only a default branch (fallback)
+        $api->seedBranch('nextcloud/photos', 'main', 'sha-photos', true);
+        // the server repo, tag exists - must never be recreated even with force
+        $api->seedBranch('nextcloud/server', 'stable34', 'sha-server', true);
+        $api->seedTag('nextcloud/server', 'v34.0.1', 'old-server');
+        // a repo with no branch at all (fails)
+        // (nextcloud/ghost: nothing seeded)
+
+        $repos = ['nextcloud/activity', 'nextcloud/notes', 'nextcloud/photos', 'nextcloud/server', 'nextcloud/ghost'];
+        $tagger = new RepoTagger($api);
+        $results = array_map(
+            static fn (string $repo) => $tagger->tag($repo, 'stable34', 'v34.0.1', false),
+            $repos,
+        );
+
+        $this->assertMatchesSnapshot('tagger/mixed', $this->render('Tag v34.0.1 across a mixed set: new, already-tagged, default-branch fallback, server (immutable), and a repo with no branch', $results, $api));
+    }
+
+    public function testForceRun(): void
+    {
+        $api = new FakeGitHubApi();
+        $api->seedBranch('nextcloud/activity', 'stable34', 'sha-activity', true);
+        $api->seedTag('nextcloud/activity', 'v34.0.1', 'old');
+        $api->seedBranch('nextcloud/server', 'stable34', 'sha-server', true);
+        $api->seedTag('nextcloud/server', 'v34.0.1', 'old-server');
+
+        $tagger = new RepoTagger($api);
+        $results = [
+            $tagger->tag('nextcloud/activity', 'stable34', 'v34.0.1', true),
+            $tagger->tag('nextcloud/server', 'stable34', 'v34.0.1', true),
+        ];
+        $this->assertMatchesSnapshot('tagger/force', $this->render('Tag v34.0.1 with --force: a normal repo is recreated, the server repo is still skipped', $results, $api));
+    }
+
+    public function testDryRun(): void
+    {
+        $api = new FakeGitHubApi();
+        $api->seedBranch('nextcloud/activity', 'stable34', 'sha-activity', true);
+        $results = [(new RepoTagger($api, dryRun: true))->tag('nextcloud/activity', 'stable34', 'v34.0.1', false)];
+        $this->assertMatchesSnapshot('tagger/dry-run', $this->render('Tag v34.0.1 in dry-run: reports what it would do, writes nothing', $results, $api));
+    }
+}
diff --git a/tools/release/tests/snapshots/milestones/due-dates.snap b/tools/release/tests/snapshots/milestones/due-dates.snap
new file mode 100644
index 00000000000..cc9be4a82a0
--- /dev/null
+++ b/tools/release/tests/snapshots/milestones/due-dates.snap
@@ -0,0 +1,5 @@
+# Patch v33.0.4 with due dates: set 33.0.5 and 33.0.6 due dates, close 33.0.4
+# columns (tab): <action> <repo> <args> -- create: title, due=<date|-> | setdue: #ms, date | move: #issue, #ms | close: #ms
+setdue	nextcloud/server	11	2026-07-02T00:00:00Z
+close	nextcloud/server	10
+setdue	nextcloud/server	12	2026-08-27T00:00:00Z
diff --git a/tools/release/tests/snapshots/milestones/first-beta.snap b/tools/release/tests/snapshots/milestones/first-beta.snap
new file mode 100644
index 00000000000..4db44a776ca
--- /dev/null
+++ b/tools/release/tests/snapshots/milestones/first-beta.snap
@@ -0,0 +1,4 @@
+# First beta v35.0.0beta1: open the next major milestone Nextcloud 36 in each repo
+# columns (tab): <action> <repo> <args> -- create: title, due=<date|-> | setdue: #ms, date | move: #issue, #ms | close: #ms
+create	nextcloud/server	Nextcloud 36	due=-
+create	nextcloud/activity	Nextcloud 36	due=-
diff --git a/tools/release/tests/snapshots/milestones/first-stable.snap b/tools/release/tests/snapshots/milestones/first-stable.snap
new file mode 100644
index 00000000000..7e938682c64
--- /dev/null
+++ b/tools/release/tests/snapshots/milestones/first-stable.snap
@@ -0,0 +1,5 @@
+# First stable v34.0.0: close the Nextcloud 34 milestone, open 34.0.1 and 34.0.2
+# columns (tab): <action> <repo> <args> -- create: title, due=<date|-> | setdue: #ms, date | move: #issue, #ms | close: #ms
+create	nextcloud/server	Nextcloud 34.0.1	due=-
+close	nextcloud/server	20
+create	nextcloud/server	Nextcloud 34.0.2	due=-
diff --git a/tools/release/tests/snapshots/milestones/missing-next.snap b/tools/release/tests/snapshots/milestones/missing-next.snap
new file mode 100644
index 00000000000..3cbfc1e9642
--- /dev/null
+++ b/tools/release/tests/snapshots/milestones/missing-next.snap
@@ -0,0 +1,6 @@
+# Patch v33.0.4 when 33.0.5 is missing: create it first, then move/close/open 33.0.6
+# columns (tab): <action> <repo> <args> -- create: title, due=<date|-> | setdue: #ms, date | move: #issue, #ms | close: #ms
+create	nextcloud/server	Nextcloud 33.0.5	due=-
+move	nextcloud/server	100	11
+close	nextcloud/server	10
+create	nextcloud/server	Nextcloud 33.0.6	due=-
diff --git a/tools/release/tests/snapshots/milestones/multi-repo.snap b/tools/release/tests/snapshots/milestones/multi-repo.snap
new file mode 100644
index 00000000000..93f37134f4d
--- /dev/null
+++ b/tools/release/tests/snapshots/milestones/multi-repo.snap
@@ -0,0 +1,8 @@
+# Patch v33.0.4 across two repos
+# columns (tab): <action> <repo> <args> -- create: title, due=<date|-> | setdue: #ms, date | move: #issue, #ms | close: #ms
+move	nextcloud/server	500	11
+close	nextcloud/server	10
+create	nextcloud/server	Nextcloud 33.0.6	due=-
+move	nextcloud/activity	501	21
+close	nextcloud/activity	20
+create	nextcloud/activity	Nextcloud 33.0.6	due=-
diff --git a/tools/release/tests/snapshots/milestones/patch-release.snap b/tools/release/tests/snapshots/milestones/patch-release.snap
new file mode 100644
index 00000000000..e7667157165
--- /dev/null
+++ b/tools/release/tests/snapshots/milestones/patch-release.snap
@@ -0,0 +1,6 @@
+# Patch release v33.0.4: move open issues to 33.0.5, close 33.0.4, open 33.0.6
+# columns (tab): <action> <repo> <args> -- create: title, due=<date|-> | setdue: #ms, date | move: #issue, #ms | close: #ms
+move	nextcloud/server	100	11
+move	nextcloud/server	101	11
+close	nextcloud/server	10
+create	nextcloud/server	Nextcloud 33.0.6	due=-
diff --git a/tools/release/tests/snapshots/milestones/prerelease-noop.snap b/tools/release/tests/snapshots/milestones/prerelease-noop.snap
new file mode 100644
index 00000000000..48fb0f2bd1c
--- /dev/null
+++ b/tools/release/tests/snapshots/milestones/prerelease-noop.snap
@@ -0,0 +1,3 @@
+# Non-first-beta pre-release v33.0.2rc1: nothing happens
+# columns (tab): <action> <repo> <args> -- create: title, due=<date|-> | setdue: #ms, date | move: #issue, #ms | close: #ms
+(no changes)
diff --git a/tools/release/tests/snapshots/tagger/dry-run.snap b/tools/release/tests/snapshots/tagger/dry-run.snap
new file mode 100644
index 00000000000..834c71c706a
--- /dev/null
+++ b/tools/release/tests/snapshots/tagger/dry-run.snap
@@ -0,0 +1,6 @@
+# Tag v34.0.1 in dry-run: reports what it would do, writes nothing
+# results (tab): <repo> <status> <branch> <detail>
+# tags (tab): <action> <repo> <tag> <sha> -- tag | retag adds force=<bool>
+nextcloud/activity	OK	stable34	would create v34.0.1 @ sha-activity
+
+(no tags written)
diff --git a/tools/release/tests/snapshots/tagger/force.snap b/tools/release/tests/snapshots/tagger/force.snap
new file mode 100644
index 00000000000..c96adf11cae
--- /dev/null
+++ b/tools/release/tests/snapshots/tagger/force.snap
@@ -0,0 +1,7 @@
+# Tag v34.0.1 with --force: a normal repo is recreated, the server repo is still skipped
+# results (tab): <repo> <status> <branch> <detail>
+# tags (tab): <action> <repo> <tag> <sha> -- tag | retag adds force=<bool>
+nextcloud/activity	OK	stable34	recreated v34.0.1
+nextcloud/server	SKIPPED	stable34	already tagged
+
+retag	nextcloud/activity	v34.0.1	sha-activity	force=true
diff --git a/tools/release/tests/snapshots/tagger/mixed.snap b/tools/release/tests/snapshots/tagger/mixed.snap
new file mode 100644
index 00000000000..8ecda7c0511
--- /dev/null
+++ b/tools/release/tests/snapshots/tagger/mixed.snap
@@ -0,0 +1,11 @@
+# Tag v34.0.1 across a mixed set: new, already-tagged, default-branch fallback, server (immutable), and a repo with no branch
+# results (tab): <repo> <status> <branch> <detail>
+# tags (tab): <action> <repo> <tag> <sha> -- tag | retag adds force=<bool>
+nextcloud/activity	OK	stable34	created v34.0.1
+nextcloud/notes	SKIPPED	stable34	already tagged
+nextcloud/photos	OK	main	created v34.0.1
+nextcloud/server	SKIPPED	stable34	already tagged
+nextcloud/ghost	FAILED	-	no branch found
+
+tag	nextcloud/activity	v34.0.1	sha-activity
+tag	nextcloud/photos	v34.0.1	sha-photos