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-ideate/SKILL.md

@@ -18,7 +18,7 @@ This workflow produces a ranked ideation artifact in `docs/ideation/`. It does *
 
 ## Interaction Method
 
-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.
+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 concise single-select choices when natural options exist.
 
@@ -96,7 +96,7 @@ State the inferred approach in one sentence at the top, using plain language the
 
 The correction hints must also be plain language ("actually this is outside the repo", "actually this is about this repo"), not internal labels ("actually elsewhere-software").
 
-**Active confirmation on ambiguity (V16).** When classifier confidence is low — single-keyword or short prompts mapping cleanly to either mode (`/ce-ideate ideas`, `/ce-ideate ideas for the docs`), conflicting CWD/prompt signals, or topic mentioning both repo-internal and external surfaces — ask one confirmation question via the platform's blocking question tool (`AskUserQuestion` in Claude Code, `request_user_input` in Codex, `ask_user` in Gemini) **before dispatching Phase 1 grounding**. For clear cases the one-sentence inferred-mode statement is sufficient; do not ask.
+**Active confirmation on ambiguity (V16).** When classifier confidence is low — single-keyword or short prompts mapping cleanly to either mode (`/ce-ideate ideas`, `/ce-ideate ideas for the docs`), conflicting CWD/prompt signals, or topic mentioning both repo-internal and external surfaces — ask one confirmation question via the platform's blocking question tool (`AskUserQuestion` in Claude Code, `request_user_input` in Codex, `ask_user` in Gemini, `ask_user` in Pi (requires the `pi-ask-user` extension)) **before dispatching Phase 1 grounding**. For clear cases the one-sentence inferred-mode statement is sufficient; do not ask.
 
 Sample wording (refine to fit the prompt at hand; follow the Interactive Question Tool Design rules in the plugin AGENTS.md — self-contained labels, max 4, third person, front-loaded distinguishing word, no leaked internal mode names):
 

plugins/compound-engineering/skills/ce-ideate/references/post-ideation-workflow.md

@@ -136,7 +136,7 @@ When the proof skill returns control:
 
 ## Phase 6: Refine or Hand Off
 
-Ask what should happen next 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.
+Ask what should happen next 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:** "What should the agent do next?"
 

plugins/compound-engineering/skills/ce-ideate/references/universal-ideation.md

@@ -53,7 +53,7 @@ Present survivors before any persistence. For each: title, description, rational
 
 Persistence is opt-in. The terminal review loop is a complete ideation cycle. Refinement happens in conversation with no file or network cost. Persistence triggers only when the user explicitly chooses to save, share, or hand off.
 
-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. Offer four choices:
+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. Offer four choices:
 
 - **Refine the ideation in conversation (or stop here — no save)** — add ideas, re-evaluate, or deepen analysis without writing anything. Ending the conversation at any point after this pick is a valid no-save exit.
 - **Open and iterate in Proof** — invoke the Proof HITL review path per the §6.2 contract in `references/post-ideation-workflow.md`: upload the survivors to Proof (rendered to a temp file since no local file is written in non-software elsewhere mode), iterate via comments, and exit cleanly with the Proof URL as the canonical record on successful return. Proof iteration is typically the terminal act in this mode, so the flow does not force another menu choice afterward. Only an `aborted` status returns to this menu. On persistent Proof failure, apply the §6.5 Proof Failure Ladder from `references/post-ideation-workflow.md` so the iteration attempt is not stranded without recovery.