Fix: externalize database drivers to prevent dynamic require error

[tianzhou]

Summary

• Commit 1eefec4 moved database drivers to optionalDependencies with dynamic import(), but tsup bundled their CJS code into ESM chunks
• At runtime, the bundled CJS require("events") calls fail with "Dynamic require of 'events' is not supported"
• Adding the driver packages to tsup's external list ensures they're loaded from node_modules at runtime via standard ES imports

Changes

• Add external: ['pg', 'mysql2', 'mariadb', 'mssql', 'better-sqlite3'] to tsup.config.ts

Closes #288

Test plan

• pnpm run build:backend succeeds
• Built output uses import pg from "pg" (external) instead of inlining pg internals
• No Dynamic require / __require / createRequire shims in output
• Runtime smoke test: no "Dynamic require" error loading dist/index.js
• load-connectors.test.ts passes (10/10)

🤖 Generated with Claude Code

[Copilot]

Pull request overview

Updates the backend build configuration to ensure DB driver packages remain unbundled so DBHub can dynamically load optional connector drivers at runtime without triggering Node ESM “Dynamic require” failures.

Changes:

• Mark common database driver packages as external in tsup.config.ts to prevent bundling their CJS internals into ESM chunks.

[Copilot]

external: ['mysql2', ...] does not externalize the subpath import used by the MySQL connector (import mysql from "mysql2/promise"). With esbuild/tsup, externals are exact-match unless you add patterns, so mysql2/promise may still get bundled and reintroduce the CJS-in-ESM require() runtime failure for the MySQL connector. Add mysql2/promise (or use a wildcard like mysql2/*) to the external list.

Suggested change

	external: ['pg', 'mysql2', 'mariadb', 'mssql', 'better-sqlite3'],
	external: ['pg', 'mysql2', 'mysql2/promise', 'mariadb', 'mssql', 'better-sqlite3'],

[tianzhou]

Verified — esbuild (which tsup uses) treats external entries as prefix matches, not exact matches. external: ['mysql2'] already externalizes mysql2/promise.

Evidence from the current build output:

# dist/mysql-I35IQ2GH.js line 16:
import mysql from "mysql2/promise";

The mysql chunk is 469 lines (just connector code), not the thousands of lines mysql2 would add if bundled. No change needed here.