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/index.md

@@ -1,12 +1,12 @@
 ---
 title: Durable Agent Runtime
-description: State & durability lens of agent infrastructure — durable objects (celld), actors (rivet), multi-hypervisor VM runtimes (hypeman, E2B/Amp Orbs), scale-to-zero/hibernation — and what they mean for building a self-hosted orb-like runtime on hermes-vm. Sibling of harness-engineering under the agent-infra umbrella.
+description: State & durability lens of agent infrastructure — durable objects (celld), actors (rivet), multi-hypervisor VM runtimes (hypeman, E2B/Amp Orbs), durable harness libraries (pi-durable), scale-to-zero/hibernation — and what they mean for building a self-hosted orb-like runtime on hermes-vm. Sibling of harness-engineering under the agent-infra umbrella.
 status: active
 category: technical
-tags: [durable-objects, actors, agent-runtime, agent-infra, sandbox, microvm, self-hosting, orbs, stateful, durable-execution]
+tags: [durable-objects, actors, agent-runtime, agent-infra, sandbox, microvm, self-hosting, orbs, stateful, durable-execution, pi-durable]
 draft: true
 created: 2026-08-07
-updated: 2026-08-11
+updated: 2026-10-20
 origin: buzz://d8a718be-031f-4a6e-9f5c-a55466641654/4123d35532d0b2cbfb80a0a34f79fb3e4e63c16c25b77d43bc0f10bb178e4f1b
 ---
 
@@ -14,7 +14,7 @@ origin: buzz://d8a718be-031f-4a6e-9f5c-a55466641654/4123d35532d0b2cbfb80a0a34f79
 
 ## Summary
 
-Research into how modern agent execution environments achieve **durability and statefulness** — where agent state lives, what compute primitive runs the agent, and how the environment hibernates and wakes. Covers durable objects / durable execution (celld, rivet, Durable Objects), actor runtimes, and microVM sandboxes (hypeman, E2B/Amp Orbs). The harness/loop lens (nanocodex, pi, Code Mode) now lives in [[harness-engineering/index|Harness Engineering]]. Goal: derive a build plan for a self-hosted, orb-like runtime on our NixOS VM (hermes-vm) without overbuilding.
+Research into how modern agent execution environments achieve **durability and statefulness** — where agent state lives, what compute primitive runs the agent, and how the environment hibernates and wakes. Covers durable objects / durable execution (celld, rivet, Durable Objects), actor runtimes, durable harness libraries (pi-durable), and microVM sandboxes (hypeman, E2B/Amp Orbs). The harness/loop lens (nanocodex, pi, Code Mode) now lives in [[harness-engineering/index|Harness Engineering]]. Goal: derive a build plan for a self-hosted, orb-like runtime on our NixOS VM (hermes-vm) without overbuilding.
 
 ## Research Question
 
@@ -36,6 +36,7 @@ What are the architectural primitives for a durable, stateful agent runtime (san
 - **Scale-to-zero / hibernation is universal**: Amp orbs pause after 5 min idle; celld cells hibernate; rivet actors hibernate when idle; hypeman standby = snapshot VM to disk, resume in milliseconds; E2B snapshot reuse gives sub-30ms cold starts.
 - **Two hard problems everyone solves**: (a) cold start latency (actor ~20ms vs VM ~30s, mitigated by snapshot/pooling), (b) state checkpointing and recovery (SQLite replication, thread JSONL, VM snapshots, actor state persistence).
 - **For our stack**: hermes-vm is already a durable compute host (systemd services, kanban DB, session DBs, herdr panes). The real gap is a per-task disposable environment contract + event wake, not a distributed state layer. celld/rivet solve problems we don't have on a single box; hypeman is interesting for per-task VMs but likely overkill.
+- **A new primitive family emerged (2026-10-01): the durable harness library.** `@earendil-works/pi-durable` commits the agent loop itself — transcript entries, documents, tasks, submissions — and resumes unfinished work on reopen. It is substrate-agnostic: Node + SQLite/JSONL, or one Session per Cloudflare Durable Object. Its semantics are the interesting part: phases are at-least-once, tool effects are opt-in replay (`safe` vs `interrupted`), and only submission admission is exactly-once (`requestId`). See [[durable-agent-runtime/pi-durable|pi-durable]].
 
 ## Sources
 
@@ -45,6 +46,7 @@ For the full reference list see [[durable-agent-runtime/sources|Sources]].
 
 - [[durable-agent-runtime/sources|Sources]] — full reference list
 - [[durable-agent-runtime/analysis|Analysis]] — taxonomy, comparison matrix, implications for our build
+- [[durable-agent-runtime/pi-durable|pi-durable]] — deep dive + crash/replay experiments on `@earendil-works/pi-durable` 1.3.0 (2026-10-20)
 - [[durable-agent-runtime/agent-collaboration|Agent-Native Collaboration]] — agents as first-class signed participants (Radicle COBs / delegates / namespaces)
 - [[durable-agent-runtime/next-steps|Next Steps]] — follow-up questions and build plan
 
@@ -64,6 +66,7 @@ Triggered from the Amp Orbs thread (2026-08-07). User connected the dots: orbs,
 
 - [ ] Decide Phase 1 scope: per-repo `.agents/setup`-style contracts + AGENTS.md per repo on hermes-vm
 - [ ] Evaluate hypeman as an opt-in per-task VM runtime (snapshot/standby) vs NixOS containers
+- [ ] Decide whether to prototype pi-durable (Node/SQLite) for one long-running multi-client agent service, or only borrow its semantics for Hermes core (see [[durable-agent-runtime/pi-durable|pi-durable]] §Implications)
 
 ## Conclusion