epic(ux): interactive task UX Phase 2

**Context:** ROADMAP.md → Interactive task UX (section)
**Related:** #53 (hydration follow-up, not ask), `docs/design/INTERACTIVE_AGENTS.md`

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## Component

API or orchestration

## Describe the feature

Epic for **Phase 2 interactive UX** beyond shipped `bgagent status`, `watch`, and `nudge`: manager-style progress, mid-run `bgagent ask`, and optional LLM-synthesized status.

## Use case

Deterministic status snapshots answer ops questions but not "what did you decide and what's next?" Operators want consistent, auditable progress across CLI and notification channels.

## Proposed solution

Child issues:

| Draft | Capability |
|-------|------------|
| [smart-progress-updates.md](./smart-progress-updates.md) | Manager-style progress events |
| [bgagent-ask-phase2.md](./bgagent-ask-phase2.md) | `bgagent ask` + REST API |
| [llm-synthesized-status-summary.md](./llm-synthesized-status-summary.md) | Optional LLM status mode |

Design authority: `docs/design/INTERACTIVE_AGENTS.md` (Phase 2 section).

## Other information

- Fanout already forward-compat subscribes to `status_response` (not yet emitted).
- Distinct from **LLM-assisted trace analysis** (post-mortem).

- [ ] This might be a breaking change

Start with the Interactive task UX section of ROADMAP.md and the Phase 2 section of docs/design/INTERACTIVE_AGENTS.md, then review smart-progress-updates.md, bgagent-ask-phase2.md, and llm-synthesized-status-summary.md. This is an epic rather than a self-contained change; done means implementing and validating the selected child capabilities against the design.

Written by the indexing model from the issue text.