feat: serve message fetches from the cache

Signed-off-by: Sebastian Krupinski <krupinski01@gmail.com>

tests/php/Support/FakeLiveMailService.php

@@ -96,6 +96,15 @@ final class FakeLiveMailService extends LiveMailService
         return $this->found;
     }
 
+    /** @var array<int, array<string, string>> full section content by UID */
+    public array $sections = [];
+
+    public function messageSections(string $collection, int $uid, string ...$partIds): array
+    {
+        $this->calls[] = ['messageSections', [$collection, $uid, $partIds]];
+        return array_intersect_key($this->sections[$uid] ?? [], array_flip($partIds));
+    }
+
     public function entityPatch(string $collection, array $flagsToAdd = [], array $flagsToRemove = [], int ...$uids): void
     {
         $this->calls[] = ['entityPatch', [$collection, $flagsToAdd, $flagsToRemove, $uids]];

tests/php/Support/FakeMessageFileStore.php

@@ -36,6 +36,12 @@ final class FakeMessageFileStore extends MessageFileStore
         $this->files = [];
     }
 
+    /** Direct access for tests */
+    public function content(int $uidValidity, int $uid): ?array
+    {
+        return $this->files[$uidValidity][$uid] ?? null;
+    }
+
     /** @return int[] */
     public function uids(int $uidValidity): array
     {