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-doc-review/SKILL.md

@@ -10,7 +10,7 @@ Review requirements or plan documents through multi-persona analysis. Dispatches
 
 ## Interactive mode rules
 
-- **Pre-load the platform question tool before any question fires.** In Claude Code, `AskUserQuestion` is a deferred tool — its schema is not available at session start. At the start of Interactive-mode work (before the routing question, per-finding walk-through questions, bulk-preview Proceed/Cancel, and Phase 5 terminal question), call `ToolSearch` with query `select:AskUserQuestion` to load the schema. Load it once, eagerly, at the top of the Interactive flow — do not wait for the first question site. On Codex and Gemini this preload is not required.
+- **Pre-load the platform question tool before any question fires.** In Claude Code, `AskUserQuestion` is a deferred tool — its schema is not available at session start. At the start of Interactive-mode work (before the routing question, per-finding walk-through questions, bulk-preview Proceed/Cancel, and Phase 5 terminal question), call `ToolSearch` with query `select:AskUserQuestion` to load the schema. Load it once, eagerly, at the top of the Interactive flow — do not wait for the first question site. On Codex, Gemini, and Pi this preload is not required.
 - **The numbered-list fallback applies only when the harness genuinely lacks a blocking question tool** — `ToolSearch` returns no match, the tool call explicitly fails, or the runtime mode does not expose it (e.g., Codex edit modes where `request_user_input` is unavailable). A pending schema load is not a fallback trigger; call `ToolSearch` first per the pre-load rule. In genuine-fallback cases, present options as a numbered list and wait for the user's reply — never silently skip the question. Rendering a question as narrative text because the tool feels inconvenient, because the model is in report-formatting mode, or because the instruction was buried in a long skill is a bug. A question that calls for a user decision must either fire the tool or fall back loudly.
 
 ## Phase 0: Detect Mode
@@ -22,7 +22,7 @@ If `mode:headless` is present, set **headless mode** for the rest of the workflo
 **Headless mode** changes the interaction model, not the classification boundaries. ce-doc-review still applies the same judgment about which tier each finding belongs in. The only difference is how non-safe_auto findings are delivered:
 
 - `safe_auto` fixes are applied silently (same as interactive)
-- `gated_auto`, `manual`, and FYI findings are returned as structured text for the caller to handle — no AskUserQuestion prompts, no interactive routing
+- `gated_auto`, `manual`, and FYI findings are returned as structured text for the caller to handle — no blocking-question prompts, no interactive routing
 - Phase 5 returns immediately with "Review complete" (no routing question, no terminal question)
 
 The caller receives findings with their original classifications intact and decides what to do with them.
@@ -121,7 +121,7 @@ Add activated conditional personas:
 
 ### Dispatch
 
-Dispatch all agents in **parallel** using the platform's task/agent tool (e.g., Agent tool in Claude Code, spawn in Codex). Omit the `mode` parameter so the user's configured permission settings apply. Each agent receives the prompt built from the subagent template included below with these variables filled:
+Dispatch all agents in **parallel** using the platform's subagent primitive (e.g., `Agent` in Claude Code, `spawn_agent` in Codex, `subagent` in Pi via the `pi-subagents` extension). Omit the `mode` parameter so the user's configured permission settings apply. Each agent receives the prompt built from the subagent template included below with these variables filled:
 
 | Variable | Value |
 |----------|-------|