RFC: Collaborative multi-participant task sessions

## Primary area

** Cross-cutting / multiple

## Related issue or feature request

_Related: **feature-ide-workspace-context-sync.md**, roadmap **Multi-user nudge**._

## Summary

Explore **multi-participant sessions** where more than one human (or role: PM, engineer, reviewer) can observe and contribute to the same in-flight task context—shared timeline, permissions, and handoff—rather than only single-submitter fire-and-forget.

## Use case and motivation

Background agents are moving from private laptop sessions to **durable cloud objects** teams collaborate around. Use cases: PM starts exploration, engineer takes over; legal/ethics wall boundaries per participant; shared validation before PR.

## Proposal

### Phase 0 (read-heavy)

- Task `participants[]` with roles; all see same `TaskEvents` stream and **Smart progress updates**.
- **Multi-user nudge** (roadmap) as write path.

### Phase 1 (shared session object)

- Session entity linked to `task_id` with join tokens, per-user visibility rules (repo + path ACL).
- Optional live attach to same MicroVM (operator-only pilot).

## Out of scope

- Full collaborative IDE product.
- Replacing GitHub PR review workflow.

## Potential challenges

- AuthZ complexity, data walls between teams, session cost while multiple users attached.
- AgentCore session model may not support multi-attach—may be events-only in v1.

## Dependencies and integrations

- Cognito identities, Cedar policies, `INTERACTIVE_AGENTS.md`, channels

## Alternative solutions

- **Context sync API only**—lighter weight; see separate feature draft.

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**Note:** Non-triaged RFCs may not get timely review. PRs on non-triaged issues might not be accepted.

* RFC PR:
* Approved by:
* Reviewed by:

Start by reading feature-ide-workspace-context-sync.md and INTERACTIVE_AGENTS.md, then review the Cognito identities, Cedar policies, and channels dependencies listed here. This RFC is done when the supported session scope, participant permissions, and phase priorities have been reviewed and decided.

Written by the indexing model from the issue text.