Investigate: AskUserQuestion-equivalent Q&A pattern for PAI (not just Claude Code)

[virtualian]

Context

Claude Code ships a built-in AskUserQuestion tool that renders discrete multi-option choices to the user. It's harness-level — not something a hook can force. Two mechanisms exist today in CC:

1. Behavioral default via memory / CLAUDE.md — a rule like "when facing discrete multi-option decisions, use AskUserQuestion" gets loaded every session, making it the default.
2. Hooks — shell commands the harness runs on events (tool calls, Stop, etc.). Hooks cannot force the model to select a specific tool, so they're the wrong mechanism for this.

So in CC: behavior → memory, automation → hooks.

Problem

PAI is multi-harness (primary DA + subagents, plus whatever non-CC surfaces PAI targets). The CC-specific AskUserQuestion tool is not portable. We need a PAI-native pattern so that:

• Structured multi-choice Q&A is available across all PAI modes (NATIVE, ALGORITHM) and subagents, not just the CC primary agent.
• Triggering is consistent — the DA reaches for it automatically for discrete-option decisions, without per-session reminders.
• The rendering/response contract is defined (options, free-text escape, cancel) regardless of the underlying harness.

Investigation scope

• Inventory where discrete-option Q&A would improve PAI flows (Algorithm phases, issue triage, branch/commit confirmations, skill routing).
• Decide: wrap CC's AskUserQuestion behind a PAI-level contract, or define an independent PAI primitive that CC's tool is one implementation of.
• Determine how to trigger it automatically — behavioral rule in PAI/CLAUDE.md / mode headers, or an Algorithm step ("ENUMERATE → OFFER") that formalises the choice point.
• Subagent story: can subagents invoke it, or must they surface choices back to the primary DA?
• Non-CC harness fallback (text-only prompt vs structured tool call).

Out of scope

• Implementation. This issue is investigation only; propose the design, then spin out an implementation issue.

Related

• CC's AskUserQuestion is harness-provided, not hook-triggerable (confirmed in current session).