feat(pi): first-class support via pi-subagents + pi-ask-user (#651)

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

plugins/compound-engineering/skills/ce-plan/SKILL.md

@@ -16,7 +16,7 @@ This workflow produces a durable implementation plan. It does **not** implement
 
 ## Interaction Method
 
-When asking the user a question, use the platform's blocking question tool: `AskUserQuestion` in Claude Code (call `ToolSearch` with `select:AskUserQuestion` first if its schema isn't loaded), `request_user_input` in Codex, `ask_user` in Gemini. Fall back to numbered options in chat only when no blocking tool exists in the harness or the call errors (e.g., Codex edit modes) — not because a schema load is required. Never silently skip the question.
+When asking the user a question, use the platform's blocking question tool: `AskUserQuestion` in Claude Code (call `ToolSearch` with `select:AskUserQuestion` first if its schema isn't loaded), `request_user_input` in Codex, `ask_user` in Gemini, `ask_user` in Pi (requires the `pi-ask-user` extension). Fall back to numbered options in chat only when no blocking tool exists in the harness or the call errors (e.g., Codex edit modes) — not because a schema load is required. Never silently skip the question.
 
 Ask one question at a time. Prefer a concise single-select choice when natural options exist.
 
@@ -832,7 +832,7 @@ When deepening is warranted, read `references/deepening-workflow.md` for confide
 
 **Load `references/plan-handoff.md` now.** It contains the full instructions for 5.3.8 (document review), 5.3.9 (final checks and cleanup), and 5.4 (post-generation handoff, including the Proof HITL flow, post-HITL re-review, and Issue Creation branching). Document review is mandatory — do not skip it even if the confidence check already ran.
 
-After document review and final checks, present this menu using the platform's blocking question tool: `AskUserQuestion` in Claude Code (call `ToolSearch` with `select:AskUserQuestion` first if its schema isn't loaded), `request_user_input` in Codex, `ask_user` in Gemini. Fall back to numbered options in chat only when no blocking tool exists in the harness or the call errors (e.g., Codex edit modes) — not because a schema load is required. Never silently skip the question.
+After document review and final checks, present this menu using the platform's blocking question tool: `AskUserQuestion` in Claude Code (call `ToolSearch` with `select:AskUserQuestion` first if its schema isn't loaded), `request_user_input` in Codex, `ask_user` in Gemini, `ask_user` in Pi (requires the `pi-ask-user` extension). Fall back to numbered options in chat only when no blocking tool exists in the harness or the call errors (e.g., Codex edit modes) — not because a schema load is required. Never silently skip the question.
 
 **Question:** "Plan ready at `docs/plans/YYYY-MM-DD-NNN-<type>-<name>-plan.md`. What would you like to do next?"
 

plugins/compound-engineering/skills/ce-plan/references/plan-handoff.md

@@ -31,7 +31,7 @@ If artifact-backed mode was used:
 
 **Pipeline mode:** If invoked from an automated workflow such as LFG, SLFG, or any `disable-model-invocation` context, skip the interactive menu below and return control to the caller immediately. The plan file has already been written, the confidence check has already run, and ce-doc-review has already run — the caller (e.g., lfg, slfg) determines the next step.
 
-After document-review completes, present the options using the platform's blocking question tool: `AskUserQuestion` in Claude Code (call `ToolSearch` with `select:AskUserQuestion` first if its schema isn't loaded), `request_user_input` in Codex, `ask_user` in Gemini. Fall back to numbered options in chat only when no blocking tool exists in the harness or the call errors (e.g., Codex edit modes) — not because a schema load is required. Never silently skip the question.
+After document-review completes, present the options using the platform's blocking question tool: `AskUserQuestion` in Claude Code (call `ToolSearch` with `select:AskUserQuestion` first if its schema isn't loaded), `request_user_input` in Codex, `ask_user` in Gemini, `ask_user` in Pi (requires the `pi-ask-user` extension). Fall back to numbered options in chat only when no blocking tool exists in the harness or the call errors (e.g., Codex edit modes) — not because a schema load is required. Never silently skip the question.
 
 **Question:** "Plan ready at `docs/plans/YYYY-MM-DD-NNN-<type>-<name>-plan.md`. What would you like to do next?"
 
@@ -82,7 +82,7 @@ When the user selects "Create Issue", detect their project tracker:
    linear issue create --title "<title>" --description "$(cat <plan_path>)"
    ```
 
-4. If no tracker is configured, ask the user which tracker they use with the platform's blocking question tool: `AskUserQuestion` in Claude Code (call `ToolSearch` with `select:AskUserQuestion` first if its schema isn't loaded), `request_user_input` in Codex, `ask_user` in Gemini. Fall back to asking in chat only when no blocking tool exists or the call errors (e.g., Codex edit modes) — not because a schema load is required. Never silently skip. Options: `GitHub`, `Linear`, `Skip`. Then:
+4. If no tracker is configured, ask the user which tracker they use with the platform's blocking question tool: `AskUserQuestion` in Claude Code (call `ToolSearch` with `select:AskUserQuestion` first if its schema isn't loaded), `request_user_input` in Codex, `ask_user` in Gemini, `ask_user` in Pi (requires the `pi-ask-user` extension). Fall back to asking in chat only when no blocking tool exists or the call errors (e.g., Codex edit modes) — not because a schema load is required. Never silently skip. Options: `GitHub`, `Linear`, `Skip`. Then:
    - Proceed with the chosen tracker's command above
    - Offer to persist the choice by adding `project_tracker: <value>` to `AGENTS.md`, where `<value>` is the lowercase tracker key (`github` or `linear`) — not the display label — so future runs match the detector in step 1 and skip this prompt
    - If `Skip`, return to the options without creating an issue

plugins/compound-engineering/skills/ce-plan/references/universal-planning.md

@@ -44,7 +44,7 @@ Example for "plan a date night in Seattle this Saturday":
 
 ## Step 1b: Focused Q&A
 
-Ask up to 3 questions targeting the unknowns that would most change the plan. Use the platform's blocking question tool: `AskUserQuestion` in Claude Code (call `ToolSearch` with `select:AskUserQuestion` first if its schema isn't loaded), `request_user_input` in Codex, `ask_user` in Gemini. Fall back to numbered options in chat only when no blocking tool exists or the call errors (e.g., Codex edit modes) — not because a schema load is required. Never silently skip the question.
+Ask up to 3 questions targeting the unknowns that would most change the plan. Use the platform's blocking question tool: `AskUserQuestion` in Claude Code (call `ToolSearch` with `select:AskUserQuestion` first if its schema isn't loaded), `request_user_input` in Codex, `ask_user` in Gemini, `ask_user` in Pi (requires the `pi-ask-user` extension). Fall back to numbered options in chat only when no blocking tool exists or the call errors (e.g., Codex edit modes) — not because a schema load is required. Never silently skip the question.
 
 **How to ask well:**
 - Offer informed options, not open-ended blanks. Instead of "When are you going?", try "Mid-week visits have 30-40% shorter lines — are you flexible on timing?" The question should give the user a frame of reference, not just extract information.
@@ -93,7 +93,7 @@ Example: A date night plan should present 2-3 restaurant options, 2-3 activity o
 
 ## Step 3: Save or Share
 
-After structuring the plan, ask the user how they want to receive it using the platform's blocking question tool: `AskUserQuestion` in Claude Code (call `ToolSearch` with `select:AskUserQuestion` first if its schema isn't loaded), `request_user_input` in Codex, `ask_user` in Gemini. Fall back to numbered options in chat only when no blocking tool exists or the call errors (e.g., Codex edit modes) — not because a schema load is required. Never silently skip the question.
+After structuring the plan, ask the user how they want to receive it using the platform's blocking question tool: `AskUserQuestion` in Claude Code (call `ToolSearch` with `select:AskUserQuestion` first if its schema isn't loaded), `request_user_input` in Codex, `ask_user` in Gemini, `ask_user` in Pi (requires the `pi-ask-user` extension). Fall back to numbered options in chat only when no blocking tool exists or the call errors (e.g., Codex edit modes) — not because a schema load is required. Never silently skip the question.
 
 **Question:** "Plan ready. How would you like to receive it?"