Add post image storage

internal/store/migrate_posts_test.go

@@ -75,6 +75,12 @@ CREATE TABLE users (
 	if err := migratePostAuthorIndex(ctx, conn); err != nil {
 		t.Fatalf("post author index migration is not idempotent: %v", err)
 	}
+	if err := migratePostImages(ctx, conn); err != nil {
+		t.Fatal(err)
+	}
+	if err := migratePostImages(ctx, conn); err != nil {
+		t.Fatalf("post images migration is not idempotent: %v", err)
+	}
 	if _, err := conn.ExecContext(ctx, `
 INSERT INTO users (id, name, role)
 VALUES ('homeowner', 'Home Owner', 'user'), ('plumber', 'The Plumber', 'admin');
@@ -104,6 +110,39 @@ VALUES ('homeowner', 'root-1', 1);`); err != nil {
 	if postCount != 2 || voteCount != 1 {
 		t.Fatalf("counts posts=%d votes=%d", postCount, voteCount)
 	}
+	imageQueries := sqlc.New(conn)
+	for _, image := range []sqlc.CreatePostImageParams{
+		{ID: "root-image-1", PostID: "root-1", ObjectKey: "posts/root-1/1.jpg", PublicUrl: "https://cdn.example/root-1.jpg", Description: "Valve", Position: 0, Width: 1200, Height: 900, CreatedAt: "2026-08-26T08:00:00Z"},
+		{ID: "root-image-2", PostID: "root-1", ObjectKey: "posts/root-1/2.png", PublicUrl: "https://cdn.example/root-2.png", Position: 1, Width: 900, Height: 1200, CreatedAt: "2026-08-26T08:00:00Z"},
+		{ID: "reply-image-1", PostID: "reply-1", ObjectKey: "posts/reply-1/1.jpg", PublicUrl: "https://cdn.example/reply-1.jpg", Description: "Cartridge", Position: 0, Width: 1000, Height: 1000, CreatedAt: "2026-08-26T09:00:00Z"},
+	} {
+		if err := imageQueries.CreatePostImage(ctx, image); err != nil {
+			t.Fatal(err)
+		}
+	}
+	rootImages, err := imageQueries.ListPostImages(ctx, "root-1")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(rootImages) != 2 ||
+		rootImages[0].ID != "root-image-1" ||
+		rootImages[1].ID != "root-image-2" {
+		t.Fatalf("root images = %+v", rootImages)
+	}
+	threadImages, err := imageQueries.ListPostThreadImages(ctx, "root-1")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(threadImages) != 3 {
+		t.Fatalf("thread images = %+v", threadImages)
+	}
+	if err := imageQueries.CreatePostImage(ctx, sqlc.CreatePostImageParams{
+		ID: "too-many", PostID: "root-1", ObjectKey: "posts/root-1/5.jpg",
+		PublicUrl: "https://cdn.example/root-5.jpg", Position: 4,
+		Width: 100, Height: 100, CreatedAt: "2026-08-26T08:00:00Z",
+	}); err == nil {
+		t.Fatal("fifth image position unexpectedly succeeded")
+	}
 	var postVoteIndexCount int
 	if err := conn.QueryRowContext(ctx, `
 SELECT count(*)