fix(tools): harden asynchronous JDBC downloads

[HandSonic]

Summary

• Use daemon workers for asynchronous JDBC driver downloads so they cannot keep the JVM alive.
• Publish completed downloads atomically and isolate concurrent temporary-file cleanup.

Validation

• Focused tests: 9/9
• Tools module tests: 72/72
• Maven package

Fixes #2684

Latest-main verification (2026-09-04)

• Rebased onto 144a04ee2; full tools suite passed (73 tests).n- The Linux CI-only race was traced to OkHttp temporarily renaming a daemon worker during its callback. The test now separates stable factory naming from actual callback daemon status; the focused suite passed 10 consecutive runs before the full suite.n- Combined with fix(jdbc): use configured driver download URLs #2695 using a semantic conflict resolution; full combined tools suite passed (76 tests), covering daemon workers, atomic publication, and dynamic runtime paths.

[openai0229]

The daemon dispatcher and unique temporary-file plus atomic publish flow fix both reported failure modes, including cleanup after interrupted writes. Approved.\n\nNon-blocking follow-up: the response stream still has no maximum byte limit, so a future hardening change should cap driver downloads and delete the temporary file on overflow. Merge this before #2695, then rebase #2695 so its configured-URL changes retain this atomic-write behavior.

Superseded by a corrected review because shell quoting corrupted the submitted text.

[openai0229]

The daemon dispatcher and unique temporary-file plus atomic publish flow fix both reported failure modes, including cleanup after interrupted writes. Approved.

Non-blocking follow-up: the response stream still has no maximum byte limit, so a future hardening change should cap driver downloads and delete the temporary file on overflow. Merge this before #2695, then rebase #2695 so its configured-URL changes retain this atomic-write behavior.