docs: add mailbox-first collaboration model

MEMORY.md

@@ -46,6 +46,35 @@ This project uses multiple AI agents ("minions") that coordinate through git:
 - `OM-Test` — test-environment operations, restarts, runtime verification
 - `OM` — production operations, maintenance, rollback, incident handling
 
+## Communication Model
+
+- actionable role-to-role communication belongs in `minions/mail/`
+- mailbox packets are the default request/response/verdict surface
+- `minions/chat/` is a PM-owned daily summary and continuity surface
+- shared state docs remain single-owner surfaces, usually `PM`
+- the mailbox model is defined in `docs/project/mailbox-collaboration-model.md`
+- mailbox rollout is staged:
+  - already-open legacy chat packets may finish where they started
+  - any new follow-up packet should default to `minions/mail/`
+  - `PM` should leave a transition note in legacy packets when follow-up work
+    moves to mail
+
+## Mailbox Bootstrap
+
+When a minion needs to open or answer a mailbox packet, bootstrap in this
+order:
+
+1. `MEMORY.md`
+2. `docs/project/mailbox-collaboration-model.md`
+3. `minions/mail/README.md`
+4. `minions/mail/packet-template.md`
+
+Current rollout rule:
+
+- existing in-flight chat packets stay in place until they close
+- all new follow-up packets should use `minions/mail/` unless `PM` says
+  otherwise
+
 ## Shared Rules
 
 - Shared truth belongs in `MEMORY.md`
@@ -55,9 +84,10 @@ This project uses multiple AI agents ("minions") that coordinate through git:
 - `CHANGELOG.md` is required and should capture template-impacting and project-impacting changes
 - `ROADMAP.md` is required and should reflect approved direction and upcoming milestones
 - `TODO.md` is required and should track actionable backlog items with current status
+- actionable packet communication belongs in `minions/mail/`
 - Role-specific deltas belong in `minions/roles/`
 - Formal plans belong in `minions/plans/`
-- Informal but durable discussion belongs in `minions/chat/`
+- PM summaries and historical continuity belong in `minions/chat/`
 - Milestone-relevant progress should be mirrored into chat the same day
 
 ## CHANGELOG Maintenance Rule
@@ -130,7 +160,7 @@ These apply to every minion role.
 - Never hide risk, blocker, or incident impact in long status updates; surface it clearly and early.
 - Never perform destructive actions (deletes, forced resets, irreversible migrations) without explicit Operator approval.
 - Never store credentials in the repo, ever. Never store personal data in the repo unless explicitly approved by the Operator.
-- Use environment variables, approved secret managers, or local untracked files for secrets; if personal data is approved, document scope, purpose, and retention in the relevant plan/chat thread.
+- Use environment variables, approved secret managers, or local untracked files for secrets; if personal data is approved, document scope, purpose, and retention in the relevant plan, mail packet, or PM summary.
 - Maintain `.gitignore` proactively so secrets, personal data artifacts, local env files, and machine-specific noise are not committed.
 - Always provide evidence with claims that affect gates, deploy decisions, or incident status.
 - Always update durable context (role file, plan, or chat) the same day when decisions or reality change.
@@ -191,15 +221,23 @@ Interpretation:
 
 ## Communication Conventions
 
-- general daily thread: `minions/chat/YYYY-MM-DD.md`
-- substantive topic thread: `minions/chat/YYYY-MM-DD-topic-name.md`
-- when a minion is bootstrapped, it must announce itself in the current general daily thread
-- chat-thread updates are commit-by-default so discussion remains durable in git history
-- default commit message format for chat-thread updates: `chat: YYYY-MM-DD thread update`
+- primary packet directory: `minions/mail/YYYY-MM-DD-sender-to-recipient-topic/`
+- sender writes `request.md`
+- addressed recipient writes `response.md`
+- gate owner writes `verdict.md` when needed
+- PM daily summary thread: `minions/chat/YYYY-MM-DD.md`
+- PM topic summary thread: `minions/chat/YYYY-MM-DD-topic-name.md`
+- when a minion is bootstrapped or a packet closes, `PM` should mirror a short
+  same-day summary into the current daily summary thread
+- packet and chat updates are commit-by-default so coordination remains durable
+  in git history
+- default commit message format for chat summary updates: `chat: YYYY-MM-DD thread update`
 
 ## Completion Handoff Contract (ADHD-Friendly)
 
-All minions must close work with a clear handoff packet in the active daily thread.
+All minions must close work with a clear handoff packet on the active packet
+surface. Default: `minions/mail/`. During staged rollout, `PM` may allow an
+already-open legacy chat packet to close where it started.
 
 Required structure (in this exact order):