Fix filing taxonomy schema mismatch by adding explicit column verification

The filing_taxonomy_snapshot table was missing parser_engine and related columns
on databases created before the taxonomy surface sidecar migration. This caused
filing sync workflows to fail with 'table has no column named parser_engine'.

Changes:
- Add TAXONOMY_SNAPSHOT_REQUIRED_COLUMNS constant for required columns
- Add verifyCriticalSchema() to fail fast at startup if schema is incompatible
- Reorder ensureTaxonomySnapshotCompat to check table existence before column ops
- Add explicit column verification after ALTER TABLE attempts
- Add regression tests for missing column detection

Fixes #2

lib/server/db/sqlite-schema-compat.ts

@@ -296,7 +296,23 @@ function ensureResearchWorkspaceSchema(client: Database) {
   `);
 }
 
+const TAXONOMY_SNAPSHOT_REQUIRED_COLUMNS = [
+  'parser_engine',
+  'parser_version',
+  'taxonomy_regime',
+  'fiscal_pack',
+  'faithful_rows',
+  'surface_rows',
+  'detail_rows',
+  'kpi_rows',
+  'normalization_summary'
+] as const;
+
 function ensureTaxonomySnapshotCompat(client: Database) {
+  if (!hasTable(client, 'filing_taxonomy_snapshot')) {
+    return;
+  }
+
   ensureColumns(client, 'filing_taxonomy_snapshot', [
     { name: 'parser_engine', sql: "ALTER TABLE `filing_taxonomy_snapshot` ADD `parser_engine` text NOT NULL DEFAULT 'fiscal-xbrl';" },
     { name: 'parser_version', sql: "ALTER TABLE `filing_taxonomy_snapshot` ADD `parser_version` text NOT NULL DEFAULT 'unknown';" },
@@ -309,8 +325,13 @@ function ensureTaxonomySnapshotCompat(client: Database) {
     { name: 'normalization_summary', sql: 'ALTER TABLE `filing_taxonomy_snapshot` ADD `normalization_summary` text;' }
   ]);
 
-  if (!hasTable(client, 'filing_taxonomy_snapshot')) {
-    return;
+  for (const columnName of TAXONOMY_SNAPSHOT_REQUIRED_COLUMNS) {
+    if (!hasColumn(client, 'filing_taxonomy_snapshot', columnName)) {
+      throw new Error(
+        `Schema compat failed: filing_taxonomy_snapshot missing required column '${columnName}'. ` +
+          `Delete the database file and restart to rebuild schema.`
+      );
+    }
   }
 
   client.exec(`
@@ -451,6 +472,10 @@ export function ensureLocalSqliteSchema(client: Database) {
 
   client.exec('CREATE INDEX IF NOT EXISTS `task_user_updated_idx` ON `task_run` (`user_id`, `updated_at`);');
 
+  client.exec(`CREATE UNIQUE INDEX IF NOT EXISTS task_active_resource_uidx 
+ON task_run (user_id, task_type, resource_key) 
+WHERE resource_key IS NOT NULL AND status IN ('queued', 'running');`);
+
   ensureColumns(client, 'watchlist_item', [
     { name: 'category', sql: 'ALTER TABLE `watchlist_item` ADD `category` text;' },
     { name: 'tags', sql: 'ALTER TABLE `watchlist_item` ADD `tags` text;' },
@@ -529,5 +554,8 @@ export const __sqliteSchemaCompatInternals = {
   applyBaseSchemaCompat,
   applySqlFile,
   hasColumn,
-  hasTable
+  hasTable,
+  TAXONOMY_SNAPSHOT_REQUIRED_COLUMNS
 };
+
+export { TAXONOMY_SNAPSHOT_REQUIRED_COLUMNS };