docs: plan the telemetry pool lifecycle rework for issue 15

The design traces the incident to four stacked defects rather than one bad
default: the pool is the only resource in the library that pre-allocates,
the kill switch keys off which step failed instead of what failed, the
degraded state can neither recover nor be observed, and the ownership rules
make the sanctioned sharing path unusable.

The plan sequences the tracker ahead of the pool and failure work so every
commit stays green, and records two facts the implementer needs up front:
the pool-construction path has zero test coverage today, and the commit
gate runs the full suite plus a complexity ceiling.

research-wiki/log.md

@@ -123,3 +123,16 @@
 - [2026-08-20 05:01 UTC] 重建索引: 80 篇页面
 - [2026-08-20 05:01 UTC] 新增 review: 整分支审查: issue #14 熔断等待档 (review:issue14-branch-review)
 - [2026-08-20 05:01 UTC] 重建索引: 81 篇页面
+- [2026-08-24 05:49 UTC] 新增 design: issue #15: 遥测连接池的资源语义与生命周期 (design:issue15-telemetry-pool-lifecycle)
+- [2026-08-24 05:50 UTC] 重建索引: 83 篇页面
+- [2026-08-24 05:50 UTC] 新增边: design:issue15-telemetry-pool-lifecycle --refines--> design:issue9-telemetry-ddl-probe
+- [2026-08-24 05:50 UTC] 新增边: design:issue15-telemetry-pool-lifecycle --depends_on--> design:issue12-telemetry-retention
+- [2026-08-24 05:50 UTC] 重建索引: 83 篇页面
+- [2026-08-24 10:14 UTC] 重建索引: 83 篇页面
+- [2026-08-24 10:15 UTC] design:issue15-telemetry-pool-lifecycle 经 Codex 审查: 3 阻断+3 应改+1 可选,核实后 6 采纳 1 改判,正文补 §9 审查留痕
+- [2026-08-24 10:20 UTC] 最低 Python 提到 3.12(pyproject/ruff/README/CLAUDE.md 四处);design:issue15 §6 版本取舍消解,§7 补两项实施前置
+- [2026-08-24 10:32 UTC] Python 3.12 迁移执行完毕: 环境重建 3.12.13、补装 build/twine、UP047 三处改 PEP 695;make check 绿、973 passed 覆盖率 94%
+- [2026-08-24 12:05 UTC] 新增 plan: 实现计划: 遥测连接池的资源语义与生命周期(issue #15) (plan:plan-issue15-telemetry-pool-lifecycle)
+- [2026-08-24 12:05 UTC] 新增边: plan:plan-issue15-telemetry-pool-lifecycle --implements--> design:issue15-telemetry-pool-lifecycle
+- [2026-08-24 12:05 UTC] 重建索引: 85 篇页面
+- [2026-08-24 12:10 UTC] plan:issue15 经 Codex 审: 2 阻断已修(20 处构造点须同批改、application_name 改走 DSN 查询参数)、_failed 计数修正