durable-agent-runtime: add pi-durable deep dive + crash/replay experiments

- new pi-durable.md: architecture (session/entry/document/task/submission),
  effect-sandwich semantics, structured concurrency, storage backends,
  maturity/adoption, taxonomy placement, implications for hermes-vm
- empirical tests on @earendil-works/pi-durable 1.3.0 (Node 22.22.2):
  kill -9 mid-phase (memo vs plain), kill -9 mid-tool (safe vs unsafe),
  SQLite schema; noted cold-open waitForTask race and the main-vs-1.3.0
  version gap (sleepUntil/onWake/restartLimit/sleeping not published)
- taxonomy: durable harness library added as a new primitive family
- sources + next-steps updated

durable-agent-runtime/next-steps.md

@@ -7,6 +7,8 @@
 - [ ] Which repos get the `.agents/setup`-style contract first (clan-private, law retrieval, idx-cli)?
 - [ ] Should the dev-server + ports-file pattern be a shared script library in clan-private or per-repo?
 - [ ] Is hypeman worth an evaluation build on hermes-vm (per-task VM with standby) vs NixOS containers?
+- [ ] pi-durable: prototype one long-running service on Node/SQLite, or borrow only its semantics? (see [[durable-agent-runtime/pi-durable|pi-durable]])
+- [ ] pi-durable open questions: no Postgres/KV adapter; multi-client transport is app-owned; default Node env has no sandbox; no published recovery/latency benchmarks; `sleeping`/`onWake`/`restartLimit` not yet in a published release
 - [ ] Does the Forgejo webhook → kanban wake need a new service, or does an existing cron/webhook path cover it?
 - [ ] Code Mode pattern for our Effect TS stack now tracked in [[harness-engineering/index|Harness Engineering]]