feat(errors): adopt DatabaseError and ValidationError across database layer

- Replace generic Error throws with DatabaseError for connection, query,
  transaction, and migration failures
- Add Zod validation schemas for all MCP tool inputs (schemas.ts)
- Update MCP server handlers to use validateInput for input validation
- Remove unused imports and prefix unused parameters

STA-186: Error Handling Infrastructure
STA-187: Security and Validation Improvements

Author: jonathanpeterwu

src/core/database/batch-operations.ts

@@ -4,9 +4,10 @@
  */
 
 import Database from 'better-sqlite3';
-import { getConnectionPool } from './connection-pool.js';
+// Connection pool imported when needed: getConnectionPool
 import { logger } from '../monitoring/logger.js';
 import { trace } from '../trace/index.js';
+import { ErrorCode, wrapError } from '../errors/index.js';
 
 export interface BatchOperation {
   table: string;
@@ -159,9 +160,15 @@ export class BatchOperationsManager {
               stats.successfulInserts += result.changes;
             } catch (error: unknown) {
               stats.failedInserts++;
+              const wrappedError = wrapError(
+                error,
+                'Failed to update frame digest',
+                ErrorCode.DB_UPDATE_FAILED,
+                { frameId: update.frame_id }
+              );
               logger.warn('Failed to update frame digest', {
                 frameId: update.frame_id,
-                error: (error as Error).message,
+                error: wrappedError.message,
               });
             }
           }
@@ -245,9 +252,15 @@ export class BatchOperationsManager {
               stats.successfulInserts += result.changes;
             } catch (error: unknown) {
               stats.failedInserts++;
+              const wrappedError = wrapError(
+                error,
+                `Failed to insert ${table} record`,
+                ErrorCode.DB_INSERT_FAILED,
+                { table, record }
+              );
               logger.warn(`Failed to insert ${table} record`, {
                 record,
-                error: (error as Error).message,
+                error: wrappedError.message,
               });
             }
           }
@@ -315,7 +328,13 @@ export class BatchOperationsManager {
         }
       } catch (error: unknown) {
         stats.failedInserts += batch.length;
-        logger.error('Batch processing failed', error as Error, {
+        const wrappedError = wrapError(
+          error,
+          'Batch processing failed',
+          ErrorCode.DB_TRANSACTION_FAILED,
+          { batchNumber: stats.batchesProcessed + 1, batchSize: batch.length }
+        );
+        logger.error('Batch processing failed', wrappedError, {
           batchNumber: stats.batchesProcessed + 1,
           batchSize: batch.length,
         });
@@ -358,7 +377,13 @@ export class BatchOperationsManager {
         tables: groupedOps.size,
       });
     } catch (error: unknown) {
-      logger.error('Batch queue processing failed', error as Error);
+      const wrappedError = wrapError(
+        error,
+        'Batch queue processing failed',
+        ErrorCode.DB_TRANSACTION_FAILED,
+        { operationsCount: operations.length }
+      );
+      logger.error('Batch queue processing failed', wrappedError);
     } finally {
       this.isProcessing = false;
     }

src/core/database/connection-pool.ts

@@ -6,6 +6,7 @@
 import { Pool, PoolClient, PoolConfig } from 'pg';
 import { EventEmitter } from 'events';
 import { logger } from '../monitoring/logger.js';
+import { DatabaseError, ErrorCode } from '../errors/index.js';
 
 export interface ConnectionPoolConfig extends PoolConfig {
   // Basic pool settings
@@ -278,7 +279,12 @@ export class ConnectionPool extends EventEmitter {
     } catch (error: unknown) {
       this.metrics.totalErrors++;
       logger.error('Failed to acquire connection:', error);
-      throw error;
+      throw new DatabaseError(
+        'Failed to acquire database connection',
+        ErrorCode.DB_CONNECTION_FAILED,
+        { pool: 'paradedb' },
+        error instanceof Error ? error : undefined
+      );
     }
   }
 
@@ -435,7 +441,12 @@ export class ConnectionPool extends EventEmitter {
         logger.error('Transaction rollback failed:', rollbackError);
         this.markConnectionAsBad(client);
       }
-      throw error;
+      throw new DatabaseError(
+        'Transaction failed',
+        ErrorCode.DB_TRANSACTION_FAILED,
+        { operation: 'transaction' },
+        error instanceof Error ? error : undefined
+      );
     } finally {
       this.release(client);
     }