Fix foreign key constraints and improve snapshot tracking

- Add unified compression/encryption package in internal/blobgen
- Update DATAMODEL.md to reflect current schema implementation
- Refactor snapshot cleanup into well-named methods for clarity
- Add snapshot_id to uploads table to track new blobs per snapshot
- Fix blob count reporting for incremental backups
- Add DeleteOrphaned method to BlobChunkRepository
- Fix cleanup order to respect foreign key constraints
- Update tests to reflect schema changes

internal/database/schema.sql

@@ -24,13 +24,13 @@ CREATE TABLE IF NOT EXISTS file_chunks (
     idx INTEGER NOT NULL,
     chunk_hash TEXT NOT NULL,
     PRIMARY KEY (file_id, idx),
-    FOREIGN KEY (file_id) REFERENCES files(id) ON DELETE CASCADE
+    FOREIGN KEY (file_id) REFERENCES files(id) ON DELETE CASCADE,
+    FOREIGN KEY (chunk_hash) REFERENCES chunks(chunk_hash)
 );
 
 -- Chunks table: stores unique content-defined chunks
 CREATE TABLE IF NOT EXISTS chunks (
     chunk_hash TEXT PRIMARY KEY,
-    sha256 TEXT NOT NULL,
     size INTEGER NOT NULL
 );
 
@@ -52,7 +52,8 @@ CREATE TABLE IF NOT EXISTS blob_chunks (
     offset INTEGER NOT NULL,
     length INTEGER NOT NULL,
     PRIMARY KEY (blob_id, chunk_hash),
-    FOREIGN KEY (blob_id) REFERENCES blobs(id)
+    FOREIGN KEY (blob_id) REFERENCES blobs(id) ON DELETE CASCADE,
+    FOREIGN KEY (chunk_hash) REFERENCES chunks(chunk_hash)
 );
 
 -- Chunk files table: reverse mapping of chunks to files
@@ -62,6 +63,7 @@ CREATE TABLE IF NOT EXISTS chunk_files (
     file_offset INTEGER NOT NULL,
     length INTEGER NOT NULL,
     PRIMARY KEY (chunk_hash, file_id),
+    FOREIGN KEY (chunk_hash) REFERENCES chunks(chunk_hash),
     FOREIGN KEY (file_id) REFERENCES files(id) ON DELETE CASCADE
 );
 
@@ -91,7 +93,7 @@ CREATE TABLE IF NOT EXISTS snapshot_files (
     file_id TEXT NOT NULL,
     PRIMARY KEY (snapshot_id, file_id),
     FOREIGN KEY (snapshot_id) REFERENCES snapshots(id) ON DELETE CASCADE,
-    FOREIGN KEY (file_id) REFERENCES files(id) ON DELETE CASCADE
+    FOREIGN KEY (file_id) REFERENCES files(id)
 );
 
 -- Snapshot blobs table: maps snapshots to blobs
@@ -101,13 +103,16 @@ CREATE TABLE IF NOT EXISTS snapshot_blobs (
     blob_hash TEXT NOT NULL,
     PRIMARY KEY (snapshot_id, blob_id),
     FOREIGN KEY (snapshot_id) REFERENCES snapshots(id) ON DELETE CASCADE,
-    FOREIGN KEY (blob_id) REFERENCES blobs(id) ON DELETE CASCADE
+    FOREIGN KEY (blob_id) REFERENCES blobs(id)
 );
 
 -- Uploads table: tracks blob upload metrics
 CREATE TABLE IF NOT EXISTS uploads (
     blob_hash TEXT PRIMARY KEY,
+    snapshot_id TEXT NOT NULL,
     uploaded_at INTEGER NOT NULL,
     size INTEGER NOT NULL,
-    duration_ms INTEGER NOT NULL
+    duration_ms INTEGER NOT NULL,
+    FOREIGN KEY (blob_hash) REFERENCES blobs(blob_hash),
+    FOREIGN KEY (snapshot_id) REFERENCES snapshots(id)
 );