feat(sdks): client sandbox pool implementation

[ninan-nn]

Summary

• Implement Kotlin SDK SandboxPool with client-side idle buffer management and configurable acquire policy (FAIL_FAST / DIRECT_CREATE).
• Add pool domain model and extensibility points: PoolConfig, PoolCreationSpec, PoolSnapshot, PoolState, PoolStateStore, and InMemoryPoolStateStore.
• Add reconcile loop with leader-gated replenish behavior for distributed deployments, including:
  • primary lock acquire/renew flow
  • stale idle fallback handling
  • degraded state/backoff tracking
  • lock-loss guard during putIdle
  • best-effort orphan cleanup callback on lock-loss window
• Improve lifecycle/concurrency safety in SandboxPool:
  • periodic reconcile tick exception guard (prevents scheduler from silently stopping)
  • resize vs shutdown race handling (RejectedExecutionException safe path)
  • graceful shutdown waits for local in-flight operations (bounded by drainTimeout)
• Remove @Deprecated annotation from SandboxPool to align with README guidance while keeping feature marked experimental in docs.
• Update Kotlin SDK README (EN/ZH) with pool usage and distributed-store expectations.
• Add/extend tests:
  • Kotlin unit tests for reconciler/store/pool behavior (including distributed-lock edge cases)
  • Java pool E2E coverage:
    • existing single-node pool suite
    • new pseudo-distributed suite with shared in-process distributed-like store

Testing

• Not run (explain why)
• Unit tests
• Integration tests
• e2e / manual verification

Executed:

• cd sdks/sandbox/kotlin && ./gradlew spotlessApply build
• cd tests/java && ./gradlew test --tests "*SandboxPool*E2ETest"

Result summary:

• SandboxPoolSingleNodeE2ETest: 15/15 passed
• SandboxPoolPseudoDistributedE2ETest: 7/7 passed

Breaking Changes

• None
• Yes (describe impact and migration path)

Checklist

• Linked Issue or clearly described motivation
• Added/updated docs (if needed)
• Added/updated tests (if needed)
• Security impact considered
• Backward compatibility considered

[chatgpt-codex-connector]

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[hittyt]

@codex review

[chatgpt-codex-connector]

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Reviewed commit:75ca5a84db

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[hittyt]

LGTM

[Pangjiping]

LGTM

[Pangjiping]

LGTM

[jwx0925]

@codex review

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit:9c776ed674

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Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

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• Comment "@codex review".

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[Pangjiping]

LGTM

[hittyt]

LGTM