docs: add pi provider prd

docs/prds/0058-pi-agent-provider.md

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+# PRD 0058: Add built-in Pi agent provider
+
+- **Status:** Draft
+- **Author:** codex
+- **Created:** 2026-06-09
+- **Issue:** #221
+
+## Summary
+
+Add `pi` as a built-in `agent_provider.template`. The provider runs the Pi
+coding-agent CLI, provisions its agent config under `~/.pi/agent`, and writes a
+provider settings file that targets an unauthenticated Ollama-compatible server.
+
+The default settings assume an Ollama server at `http://ollama:11434/v1`, using
+the `openai-completions` API with a dummy API key because Ollama ignores it.
+Users can override the base URL, model list, API key, API type, and compatibility
+flags through a new `agent_provider.settings` object.
+
+## Problem
+
+bot-bottle currently ships Claude and Codex as built-in agent providers. Pi is a
+useful third harness, but using it today requires a custom provider plugin and a
+custom image. That repeats boilerplate for prompt copying, skill copying,
+provider config, and runtime registration.
+
+Pi's local-model path is also easy to misconfigure: its custom-model docs require
+`~/.pi/agent/models.json`, an API entry, at least one model id, and a dummy
+`apiKey` for Ollama even though the server does not authenticate. bot-bottle
+should generate that shape consistently.
+
+## Goals / Success Criteria
+
+- `agent_provider.template: pi` is accepted as a built-in provider.
+- `bot_bottle/contrib/pi/` provides a Pi image and `PiAgentProvider`.
+- Pi receives the bot-bottle prompt at `~/.bot-bottle-prompt.txt` and starts in
+  print-mode prompt delivery like Codex.
+- Pi skills are copied into `~/.pi/agent/skills/<name>/`.
+- Pi provider settings are configurable from the bottle manifest via
+  `agent_provider.settings`.
+- The default Pi provider settings configure an unauthenticated Ollama-compatible
+  server.
+- Unit tests cover manifest parsing, runtime selection, plan generation, prompt,
+  skills, and provider provisioning.
+
+## Non-goals
+
+- Managing or launching an Ollama server.
+- Authenticating to Ollama or any remote Pi provider.
+- Forwarding host Pi credentials.
+- Implementing Pi extensions or MCP registration.
+- Changing Claude or Codex provider behavior.
+
+## Design
+
+### Manifest
+
+Extend `agent_provider` with an optional `settings` object. It is currently only
+supported for built-in `pi`.
+
+Supported keys:
+
+- `base_url`: string, defaults to `http://ollama:11434/v1`
+- `api`: string, defaults to `openai-completions`
+- `api_key`: string, defaults to `ollama`
+- `models`: non-empty array of strings, defaults to `["qwen2.5-coder:7b"]`
+- `supports_developer_role`: boolean, defaults to `false`
+- `supports_reasoning_effort`: boolean, defaults to `false`
+
+The snake-case manifest keys are converted into Pi's JSON field names:
+`baseUrl`, `apiKey`, `supportsDeveloperRole`, and
+`supportsReasoningEffort`.
+
+### Provider
+
+`PiAgentProvider.provision_plan` writes `models.json` into the per-launch state
+directory and returns an `AgentProvisionPlan` that copies it to
+`~/.pi/agent/models.json`. The provider also declares an unauthenticated egress
+route for the configured base URL host so the egress layer can allow the Ollama
+endpoint.
+
+The Pi runtime uses:
+
+- `command="pi"`
+- `prompt_mode="read_prompt_file"`
+- `image="bot-bottle-pi:latest"`
+- `bypass_args=()`
+- `resume_args=()`
+- `remote_control_args=()`
+
+The Dockerfile installs `@earendil-works/pi-coding-agent` globally from npm and
+keeps the same Debian/node base shape as the existing provider images.
+
+### Supervise MCP
+
+Pi does not have built-in MCP support in the current public docs, so
+`provision_supervise_mcp` is a no-op. This keeps Pi bottles launchable with
+`supervise: true` while preserving the explicit non-goal of implementing Pi
+extensions.
+
+## Merge rule(s)
+
+This PR can merge when the focused unit tests pass and the PRD status is flipped
+from Draft to Active in the final implementation commit.