Fix DuckDB connection pool with database path validation

[jfrench9]

Summary

Fixes a bug in the DuckDB connection pool by adding path validation logic. The DuckDBConnectionPool now validates the database file path before attempting to establish connections, preventing errors caused by invalid or missing paths.

Key Accomplishments

• Added path validation: Introduced validation checks for the DuckDB database file path within the connection pool, ensuring the path is verified before connections are created
• Improved error resilience: Prevents the pool from entering a broken state when initialized with an invalid or nonexistent database path
• Proactive failure handling: Connections now fail fast with clear errors rather than producing cryptic downstream failures

Breaking Changes

None. This is a purely additive fix that adds validation guards without altering existing public interfaces or behavior for valid paths.

Testing Notes

• Verify that the connection pool correctly initializes when provided with a valid DuckDB database path
• Confirm that an appropriate error is raised when an invalid or nonexistent path is supplied
• Test pool behavior under concurrent access to ensure the validation does not introduce race conditions or performance regressions
• Validate that existing workflows relying on the DuckDB connection pool continue to function as expected

Infrastructure Considerations

• No new dependencies or configuration changes required
• The fix is contained within the connection pool module and does not affect deployment or infrastructure setup
• Environments that rely on dynamically resolved database paths should ensure those paths are valid at pool initialization time

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Branch Info:

• Source: bugfix/duckdb-pool-bug
• Target: main
• Type: bugfix

Co-Authored-By: Claude noreply@anthropic.com