Add PDF archive store, raw-body IPC and export file helpers

The searchable PDF can be archived content-addressed under the local data
dir with its sha256 and layout fingerprint; a different PDF for an archived
invoice is refused and reads verify the hash. Export writes go through a
raw-body command that remembers the last folder; reveal-in-folder and open
fall back to xdg-open / explorer. Adds a Windows-safe export file name
builder. Migration M4 adds the archive columns and last export dir.

src-tauri/src/db.rs

@@ -10,7 +10,7 @@ const MAX_BACKUPS: usize = 10;
 const BACKUP_PREFIX: &str = "voiced-pre-v";
 
 /// Highest schema version, i.e. the number of entries in `migrations()`.
-const LATEST_VERSION: i64 = 3;
+const LATEST_VERSION: i64 = 4;
 
 #[derive(Debug, thiserror::Error)]
 pub enum DbError {
@@ -174,8 +174,15 @@ const M3: &str = r#"
 ALTER TABLE app_settings ADD COLUMN render_prefs TEXT NOT NULL DEFAULT '';
 "#;
 
+/// Version 4: the archived PDF's layout fingerprint and time, and the last export folder.
+const M4: &str = r#"
+ALTER TABLE invoices ADD COLUMN archived_fingerprint TEXT;
+ALTER TABLE invoices ADD COLUMN archived_at TEXT;
+ALTER TABLE app_settings ADD COLUMN last_export_dir TEXT NOT NULL DEFAULT '';
+"#;
+
 fn migrations() -> Migrations<'static> {
-    Migrations::new(vec![M::up(SCHEMA), M::up(M2), M::up(M3)])
+    Migrations::new(vec![M::up(SCHEMA), M::up(M2), M::up(M3), M::up(M4)])
 }
 
 /// Open (creating if needed) the database at `path` and bring it to the latest schema.
@@ -541,6 +548,27 @@ CREATE INDEX IF NOT EXISTS idx_invoices_created ON invoices(created_at DESC);
         assert!(backups_in(&backups).is_empty());
     }
 
+    #[test]
+    fn m4_adds_archive_and_export_dir_columns() {
+        let conn = open_in_memory().unwrap();
+        let dir: String = conn
+            .query_row("SELECT last_export_dir FROM app_settings WHERE id = 1", [], |r| r.get(0))
+            .unwrap();
+        assert_eq!(dir, "");
+        // The columns exist and are nullable on invoices (no rows needed to prove it).
+        conn.prepare("SELECT archived_pdf_sha256, archived_fingerprint, archived_at FROM invoices")
+            .unwrap();
+        let notnull: i64 = conn
+            .query_row(
+                "SELECT SUM(\"notnull\") FROM pragma_table_info('invoices')
+                 WHERE name IN ('archived_fingerprint', 'archived_at')",
+                [],
+                |r| r.get(0),
+            )
+            .unwrap();
+        assert_eq!(notnull, 0);
+    }
+
     #[test]
     fn render_prefs_column_defaults_to_empty_and_round_trips() {
         let conn = open_in_memory().unwrap();