fix(task): cancel registered statements once

[HandSonic]

Related issue

N/A - no matching issue was found.

Summary

When cancellation raced with JDBC statement registration, both requestCancellation and registerCancelable could schedule cancellation for the same resource. A previously retained synchronous compensation also risked blocking the task thread in a driver cancel call. This change linearizes token/resource publication under one lifecycle lock, claims one cancellation snapshot, and performs Future.cancel and driver cancellation outside the lock.

Affected surfaces

• Frontend / Web
• Backend / API / Storage
• Database plugin / Driver
• JCEF / Desktop packaging
• CI / Build / Release
• Documentation only

Verification

• Commands and results:
  • RunningTaskTest: 3 tests passed.
  • Related task lifecycle suite: 22 tests passed.
  • Domain-core module tests after rebase: 228 passed; dependency modules passed.
  • git diff --check origin/main...HEAD: passed.
  • Latest-main revalidation: focused 3/3 and full domain-core module 228/228 passed; related combined domain-core suite 250/250 and 45/45 pairwise merge simulations passed.
• Manual verification: N/A - controlled executors and latches deterministically reproduce the registration/cancellation interleaving.
• UI evidence: N/A

Risk and compatibility

• Public API or stored data: No API or storage changes.
• Database or driver compatibility: JDBC Statement.cancel remains asynchronous and is now scheduled exactly once per registration.
• Network, privacy, or security: N/A.
• Community / Local / Pro boundary: Shared Community task runtime.
• Backward compatibility: Existing cancellation tokens and Future interruption behavior are preserved.

Reviewer map

• Start here: RunningTask.requestCancellation/registerCancelable and RunningTaskTest.
• Failure condition: one registration queues two driver cancels, driver cancellation executes while holding the lifecycle lock, or clearCancelable removes a replacement resource.
• Rollback or disable path: Revert commit 5441ff5; no migration is required.

Contributor declaration

• I linked the Issue that defines this change.
• I tested the affected behavior and reported the actual results above.
• I did not include credentials, private data, or generated build output.
• I disclosed substantial AI assistance below, or this PR contains no substantial AI-generated code.

AI assistance: OpenAI Codex assisted with diagnosis, implementation, automated tests, verification, and adversarial review.

[HandSonic]

Exhaustive cross-PR integration update: combined this PR with #2802 in an isolated tree by preserving both cancellation-executor ownership and retryable input cleanup in RunningTask. The resulting full 9-module reactor passed: tools 68, domain-api 27, SPI 142, domain-core 256, storage 64, web 95 (1 environment skip), with 0 failures/errors.