test(05-01): add RED test scaffold for FILE-01..06 and MinIO in compose.yaml

- Create handlers_files_test.go: six TestFile* stubs (all t.Skip), stubbedFileStorer no-op implementing files.FileStorer
- Create store_test.go: compile-time interface assertion, TestNewStore_SkipIfNoEndpoint skips when S3_ENDPOINT unset
- Update compose.yaml: add minio (port 9000/9001) and minio-init services; minio-init uses restart: no (Pitfall 7); add minio_data volume

backend/compose.yaml

@@ -17,5 +17,38 @@ services:
       timeout: 5s
       retries: 10
 
+  minio:
+    image: minio/minio:latest
+    container_name: xtablo-backend-minio
+    restart: unless-stopped
+    environment:
+      MINIO_ROOT_USER: minioadmin
+      MINIO_ROOT_PASSWORD: minioadmin
+    ports:
+      - "9000:9000"   # S3 API
+      - "9001:9001"   # Console UI
+    command: server /data --console-address ":9001"
+    volumes:
+      - minio_data:/data
+    healthcheck:
+      test: ["CMD", "mc", "ready", "local"]
+      interval: 5s
+      timeout: 5s
+      retries: 10
+
+  minio-init:
+    image: minio/mc:latest
+    depends_on:
+      minio:
+        condition: service_healthy
+    entrypoint: >
+      /bin/sh -c "
+      mc alias set local http://minio:9000 minioadmin minioadmin;
+      mc mb --ignore-existing local/xtablo-dev;
+      echo 'bucket ready';
+      "
+    restart: "no"
+
 volumes:
   postgres_data:
+  minio_data:

backend/internal/files/store_test.go

@@ -0,0 +1,51 @@
+package files
+
+import (
+	"context"
+	"os"
+	"testing"
+)
+
+// TestStoreImplementsFileStorer is a compile-time assertion that *Store
+// satisfies the FileStorer interface.
+func TestStoreImplementsFileStorer(t *testing.T) {
+	var _ FileStorer = (*Store)(nil)
+}
+
+// TestNewStore_SkipIfNoEndpoint verifies that NewStore returns a non-nil client
+// when S3_ENDPOINT is configured. The test is skipped in CI / local dev unless
+// a real MinIO instance is running and S3_ENDPOINT is set.
+func TestNewStore_SkipIfNoEndpoint(t *testing.T) {
+	endpoint := os.Getenv("S3_ENDPOINT")
+	if endpoint == "" {
+		t.Skip("S3_ENDPOINT not set — skipping live NewStore test")
+	}
+
+	bucket := os.Getenv("S3_BUCKET")
+	if bucket == "" {
+		bucket = "xtablo-dev"
+	}
+	region := os.Getenv("S3_REGION")
+	if region == "" {
+		region = "us-east-1"
+	}
+	accessKey := os.Getenv("S3_ACCESS_KEY")
+	if accessKey == "" {
+		accessKey = "minioadmin"
+	}
+	secretKey := os.Getenv("S3_SECRET_KEY")
+	if secretKey == "" {
+		secretKey = "minioadmin"
+	}
+
+	store, err := NewStore(context.Background(), endpoint, bucket, region, accessKey, secretKey, true)
+	if err != nil {
+		t.Fatalf("NewStore: %v", err)
+	}
+	if store == nil {
+		t.Fatal("NewStore returned nil store without error")
+	}
+	if store.client == nil {
+		t.Fatal("NewStore returned store with nil S3 client")
+	}
+}

backend/internal/web/handlers_files_test.go

@@ -0,0 +1,78 @@
+package web
+
+// handlers_files_test.go — Wave 0 RED test scaffold for FILE-01..06.
+//
+// All test functions call t.Skip("FILE handler tests: not yet implemented") so they
+// compile but do NOT fail before Plan 02/03 implements the handlers and routes.
+// This file is the RED baseline; Plan 02/03 turns it green.
+//
+// Pattern: mirrors handlers_tasks_test.go exactly — setupTestDB, loginUser,
+// preInsertUser, getCSRFToken, and testCSRFKey are reused from the existing
+// test files in the same package.
+
+import (
+	"context"
+	"io"
+	"testing"
+
+	"backend/internal/files"
+)
+
+// stubbedFileStorer is a no-op FileStorer for test injection.
+// Plan 02/03 will replace the Skip calls with real assertions that use this stub.
+type stubbedFileStorer struct{}
+
+func (s *stubbedFileStorer) Upload(_ context.Context, _ string, _ io.Reader) (string, int64, error) {
+	return "application/octet-stream", 0, nil
+}
+
+func (s *stubbedFileStorer) Delete(_ context.Context, _ string) error {
+	return nil
+}
+
+func (s *stubbedFileStorer) PresignDownload(_ context.Context, _ string) (string, error) {
+	return "https://example.com/presigned", nil
+}
+
+// Compile-time assertion: stubbedFileStorer satisfies the files.FileStorer interface.
+var _ files.FileStorer = (*stubbedFileStorer)(nil)
+
+// ---- TestFileUpload (FILE-01, FILE-02) ----
+
+// TestFileUpload verifies that POST /tablos/{id}/files uploads a file,
+// creates a DB row, and stores bytes in S3 (FILE-01 server-proxied upload, FILE-02).
+func TestFileUpload(t *testing.T) {
+	t.Skip("FILE handler tests: not yet implemented")
+}
+
+// ---- TestFilesList (FILE-03) ----
+
+// TestFilesList verifies that GET /tablos/{id}/files lists files with
+// original filename and size, newest first (FILE-03).
+func TestFilesList(t *testing.T) {
+	t.Skip("FILE handler tests: not yet implemented")
+}
+
+// ---- TestFileDownload (FILE-04) ----
+
+// TestFileDownload verifies that GET /tablos/{id}/files/{file_id}/download
+// returns a 302 redirect to a signed time-limited URL (FILE-04).
+func TestFileDownload(t *testing.T) {
+	t.Skip("FILE handler tests: not yet implemented")
+}
+
+// ---- TestFileDelete (FILE-05) ----
+
+// TestFileDelete verifies that POST /tablos/{id}/files/{file_id}/delete
+// removes the DB row (and invokes S3 delete via the stub) (FILE-05).
+func TestFileDelete(t *testing.T) {
+	t.Skip("FILE handler tests: not yet implemented")
+}
+
+// ---- TestFileOwnership (FILE-06) ----
+
+// TestFileOwnership verifies that a non-owner gets 404 on
+// GET /tablos/{id}/files, POST /tablos/{id}/files, and all file sub-routes (FILE-06).
+func TestFileOwnership(t *testing.T) {
+	t.Skip("FILE handler tests: not yet implemented")
+}