docs: add mailbox-first collaboration model

minions/mail/README.md

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+# Mail Packets
+
+Use this folder for primary minion-to-minion communication.
+
+This is the mailbox-style coordination surface. New actionable requests,
+responses, and verdicts should default here rather than going into shared chat
+threads.
+
+## Packet Layout
+
+```text
+minions/mail/
+  YYYY-MM-DD-sender-to-recipient-topic/
+    request.md
+    response.md
+    verdict.md        # optional
+```
+
+## Naming Rule
+
+Use:
+
+`YYYY-MM-DD-<sender>-to-<recipient>-<topic>`
+
+Examples:
+
+- `2026-04-14-pm-to-sm-packet-clarification`
+- `2026-04-14-cm-to-pm-implementation-pressure`
+
+## Ownership Rule
+
+- sender writes `request.md`
+- addressed recipient writes `response.md`
+- gate owner writes `verdict.md` when needed
+- no minion edits another minion's packet file
+
+## Workflow Rule
+
+1. open packet
+2. commit packet request
+3. recipient responds in owned file
+4. gate owner records verdict if needed
+5. `PM` mirrors durable state into shared docs and same-day chat summary
+
+## Staged Rollout Rule
+
+- already-open legacy chat packets may remain where they are until they close
+- any new follow-up packet should open in `minions/mail/`
+- do not mirror one active packet across both chat and mail
+
+## Bootstrap Steps
+
+Before opening or answering a mailbox packet, read:
+
+1. `MEMORY.md`
+2. `docs/project/mailbox-collaboration-model.md`
+3. `minions/mail/README.md`
+4. `minions/mail/packet-template.md`
+
+## Packet Content Rule
+
+Use `packet-template.md` as the default skeleton.
+
+Keep packet files concise, explicit, and owner-labeled.
+
+## Relationship To `minions/chat/`
+
+- `minions/mail/` is the primary coordination surface
+- `minions/chat/` is the PM-owned daily summary and historical continuity
+  surface
+
+See `docs/project/mailbox-collaboration-model.md` for the full repo policy.

minions/mail/packet-template.md

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+# Packet Template
+
+Use this as the default structure for a new mailbox packet.
+
+Recommended path:
+
+`minions/mail/YYYY-MM-DD-sender-to-recipient-topic/`
+
+## `request.md`
+
+```text
+TARGET ROLE:
+
+DECISION:
+
+RATIONALE:
+
+ACTION NEEDED:
+
+### AM
+
+No action needed yet.
+
+### CM
+
+No action needed yet.
+
+### SM
+
+No action needed yet.
+
+### OM-Test / OM
+
+No action needed yet.
+
+### Operator
+
+No action needed until the response is reviewed.
+```
+
+## `response.md`
+
+```text
+DECISION:
+
+RATIONALE:
+
+SCOPE COMPLETED:
+
+OUT OF SCOPE:
+
+EVIDENCE:
+
+BLOCKERS/RISKS:
+
+ACTION NEEDED:
+
+NEXT OWNER:
+
+READY CHECK:
+```
+
+## `verdict.md` (optional)
+
+```text
+DECISION:
+
+RATIONALE:
+
+ACTION NEEDED:
+
+NEXT OWNER:
+
+READY CHECK:
+```