Support popular Pi extensions through per-extension adapters (#5309)

* refactor(server): give Pi extension handling a registry

* feat(server): map Pi task extensions to Paseo task lists

* feat(server): map Pi subagent extensions to the Subagents track

* refactor(server): hydrate Pi child sessions asynchronously through the extension host

Child session JSONL reads blocked the daemon during live events and replay. The extension host now prepares immediate upserts and bounded async timeline hydration; replay awaits it, and closed sessions discard it. Preserve claimed notification text so completion details remain visible in the parent conversation.

* feat(server): present Pi question extensions as one question form

Keep the extension questionnaire in one Paseo permission while Pi walks its RPC dialogs. The host defers an early dialog until the form is answered, then replies to each dialog using the collected choices.

* fix(server): satisfy Pi extension start hook contract

The server build checks the session interface more strictly than the fast typecheck. Return the optional permission explicitly so the adapter satisfies the published extension contract.

* docs: document Pi extension adapters

* chore(server): format Pi subagent captures

These real RPC fixtures were added before the formatter ran over the captured JSON. Normalize whitespace so repository format checks pass without changing the captured data.

* test(server): resolve Pi child fixtures as local paths on Windows

File URL pathnames retain a leading slash before a Windows drive letter. Convert fixture URLs to filesystem paths and escape those paths when inserting them into captured JSON, so child timeline assertions exercise the real file on every CI platform.

* refactor(server): remove Oh My Pi handling from the Pi provider

* fix(server): keep Pi extension adapter failures out of core session handling

* fix(server): bound Pi child-session hydration during history replay

docs/providers.md

@@ -79,6 +79,8 @@ A provider that can register runtime tools directly should set `supportsNativePa
 
 Pi is a process-backed provider. Paseo requires the user to have the `pi` binary installed and talks to it through `pi --mode rpc`; the server package does not embed Pi's SDK/runtime packages.
 
+Pi extension adapters live under `packages/server/src/server/agent/providers/pi/extensions/<extension>/`. Each adapter turns Pi RPC facts into Paseo tool, timeline, subagent, or question mappings through the [extension contract](../packages/server/src/server/agent/providers/pi/extensions/contract.ts). To add one, create its directory, add one entry to `extensions/registry.ts`, and test it with fixtures captured from the real extension in Pi that record package, version, source commit, Pi version, and capture date. `agent.ts`, `history-mapper.ts`, and `tool-call-mapper.ts` never name an extension.
+
 Paseo's per-agent and daemon-wide system prompts are appended by its generated Pi integration extension. Paseo deliberately does not pass `--append-system-prompt`, because that flag replaces Pi's automatic `APPEND_SYSTEM.md` discovery instead of composing with it.
 
 Pi model records expose input capabilities through `model.input`. Only send raw RPC `images` when the current model explicitly includes `"image"` in that list. Text-only Pi/OMP models reject image content and persist the rejected image in JSONL history, so image prompts for those models must be materialized to a local file and passed as a text path hint instead.