refactor: structured SQLResult.messages (DatabaseMessage[])

[tianzhou]

Summary

Follow-up to #307. That PR added SQLResult.messages?: string[] to surface SQL Server informational output (SET STATISTICS TIME/IO, PRINT, warnings) to MCP clients. This PR promotes that field from a bare string[] to a structured DatabaseMessage[] so per-message metadata is preserved instead of flattened away.

Why

string[] is lossy. The mssql info event carries message, class (severity), number, and lineNumber — all discarded by the string form. Most importantly, severity lets a client tell a benign PRINT from an actual warning.

It's also a genuinely cross-database concept, not a SQL-Server quirk: PostgreSQL emits NOTICE/WARNING and MySQL/MariaDB emit warnings. Doing the structured shape now — while there's exactly one producer — means those connectors can populate the same type later without a breaking interface change.

Changes

• src/connectors/interface.ts: add DatabaseMessage { text; severity?; code?; line? }; SQLResult.messages is now DatabaseMessage[]. Only text is guaranteed — the rest are populated when the driver exposes them.
• src/connectors/sqlserver/index.ts: map the info event into DatabaseMessage (text/severity/code/line) instead of pushing the raw string.
• src/tools/execute-sql.ts: unchanged — it already forwards result.messages as-is, so clients now receive the structured objects automatically.
• src/connectors/__tests__/sqlserver.integration.test.ts: assertions updated to read .text.

Notes

• Backward-compatible at the wire level only in spirit — the messages field shape changes from string[] to objects, but feat(sqlserver): surface informational messages (STATISTICS, PRINT) in query results #307 has not shipped in a release yet, so no consumers depend on the old form.
• severity is intentionally a general string (PG level name vs. SQL Server numeric class as a string), documented per-engine, rather than a SQL-Server-specific field name.

Verification

• npx tsc --noEmit: zero new errors (135 pre-existing on both main and this branch; CI builds via tsup).
• pnpm run build: ✓
• Unit tests: 668/668 pass.
• SQL Server integration tests require Docker and were not run here.

🤖 Generated with Claude Code

[Copilot]

Pull request overview

This PR refactors SQLResult.messages from a lossy string[] into a structured DatabaseMessage[] so database informational output can carry per-message metadata (severity/code/line) rather than being flattened to plain text.

Changes:

• Introduces DatabaseMessage in the connector interface and updates SQLResult.messages to DatabaseMessage[].
• Updates the SQL Server connector to map mssql info events into { text, severity, code, line }.
• Adjusts SQL Server integration tests to assert on msg.text instead of raw string messages.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
src/connectors/interface.ts	Adds DatabaseMessage type and updates SQLResult.messages to use it.
src/connectors/sqlserver/index.ts	Collects SQL Server info events into structured DatabaseMessage objects.
src/connectors/tests/sqlserver.integration.test.ts	Updates assertions to use DatabaseMessage.text.