docs: add multi-agent development paradigm README

docs/superpowers/MULTI-AGENT.md

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+# Multi-Agent Development Paradigm
+
+This repo uses a three-terminal workflow for large development lifts: one Claude Code session acts as **PM** and two act as **senior developers** (Dev-A, Dev-B), each working in their own git worktree on a parallel feature branch.
+
+A local relay MCP server eliminates manual message copying between terminals — agents call `post_message`/`read_messages` instead of asking the user to copy-paste.
+
+---
+
+## Overview
+
+| Role | Terminal | Branch | Responsibilities |
+|------|----------|--------|-----------------|
+| PM | 1 | `main` (read-only) | Drive doc-audit follow-ups, review PRs, write CHANGELOG, authorize merges and tagging |
+| Dev-A | 2 | `feature/<release>-plan-a-*` | Implement Plan A tasks in their own worktree |
+| Dev-B | 3 | `feature/<release>-plan-b-*` | Implement Plan B tasks in their own worktree |
+| Relay server | 4 | — | Message bus; Ctrl-C to stop at end of lift |
+
+**User's job:** authorize merges (the PM asks), resolve escalations the PM can't handle, and watch the streams. You are no longer the message bus.
+
+---
+
+## Starting a lift
+
+### Prerequisites
+
+- [ ] Kickoff prompts exist in `docs/superpowers/coordination/` (generate with the `multi-agent-kickoff` skill if not)
+- [ ] No uncommitted changes in main that would confuse the devs
+- [ ] `tools/relay/` is present (run `ls tools/relay/` to confirm)
+
+### Launch sequence
+
+```bash
+# 1. Start the relay server (this terminal becomes the relay log)
+tools/relay/start.sh           # prints copy-paste instructions, then starts server
+
+# Optional: use a multiplexer to auto-open all four terminals
+tools/relay/start.sh --tmux    # creates tmux session "relay-lift" with 4 windows
+tools/relay/start.sh --kitty   # creates kitty tab "relay" + 3 windows
+```
+
+`start.sh` prints the paths to the three kickoff prompt files. In each Claude Code terminal, run `cat <path>` and paste everything below the `---` line as the first message.
+
+---
+
+## Coordination protocol
+
+Agents communicate by posting structured blocks to each other's inboxes. Four message kinds:
+
+| Kind | Block header | When used |
+|------|-------------|-----------|
+| `status` | `## STATUS UPDATE — DEV-*` | After completing a task, getting blocked, or reaching a review-ready state |
+| `question` | `## QUESTION TO PM — DEV-*` | When a dev needs PM input mid-task |
+| `directive` | `## DIRECTIVE TO DEV-*` | When PM instructs a dev to proceed, hold, rescope, or approve a PR |
+| `free` | (none) | Ad-hoc messages not covered by the above |
+
+A well-formed `status` block:
+
+```
+## STATUS UPDATE — DEV-B
+Time: 2026-05-02T14:30:00-07:00
+Branch: feature/v0.5.0-plan-b-extension-ux
+Task: P4 / error-copy map
+Status: DONE
+Last commit: abc1234 feat(extension): centralize ERROR_COPY map
+Tests: green
+Notes: No issues. Ready for PM review of P4 before starting B1.
+```
+
+---
+
+## Using the relay tools
+
+All three Claude Code sessions have these tools available when the relay server is running:
+
+```
+post_message(from, to, kind, body)   → { id }
+read_messages(for)                   → RelayMessage[]   (drains inbox)
+list_pending(for)                    → { count, kinds } (non-destructive)
+```
+
+Typical dev flow per task:
+
+```
+1. read_messages(for="dev-b")           # check for directives before starting
+2. ... do the work ...
+3. post_message(from="dev-b", to="pm", kind="status", body="## STATUS UPDATE...")
+```
+
+Typical PM flow:
+
+```
+1. read_messages(for="pm")             # see what devs posted
+2. ... review ...
+3. post_message(from="pm", to="dev-b", kind="directive", body="## DIRECTIVE TO DEV-B...")
+```
+
+---
+
+## If the relay server isn't running
+
+Claude Code will show a yellow MCP connection warning for the `relay` server. The tools will be unavailable.
+
+Agents fall back to the manual protocol: they emit the structured blocks as text and ask the user to copy-paste them to the relevant terminal. This is slower but fully functional — the coordination protocol works either way.
+
+To restart a crashed server mid-lift:
+
+```bash
+tools/relay/start.sh
+```
+
+In-flight messages are lost on restart. Any agent with unread messages should re-post them.
+
+---
+
+## Generating kickoff prompts
+
+Use the `multi-agent-kickoff` skill (in the `superpowers` plugin). It auto-discovers the spec and plans for the release, substitutes all placeholders including the relay paragraph, and writes files to `docs/superpowers/coordination/`.
+
+The skill reminder: run `tools/relay/start.sh` **before** opening the three Claude Code sessions — the MCP tools need the server to be up when each session initializes.
+
+---
+
+## Ending a lift
+
+1. PM emits `REVIEW-COMPLETE` and `MERGE-APPROVED` for each dev's PR
+2. User merges each PR (the PM session does `gh pr merge` with user authorization)
+3. PM tags the release (only after explicit user `yes`)
+4. Ctrl-C the relay terminal — all in-memory messages are discarded
+
+---
+
+## Roles and boundaries (quick reference)
+
+**PM must not:** write feature code, merge without user authorization, tag without user approval, run `git push --force` / `git reset --hard` without asking.
+
+**Devs must not:** merge their branch to main, push `--force`, run `git reset --hard` without asking.
+
+**User must:** authorize all merges and the release tag. Everything else is delegated.