mailbox

name	mailbox
description	[Internal protocol — leader-only. Not a user-invocable skill; do NOT trigger from user input.] Inter-agent mailbox protocol. Specifies how teammates drop HOLD_REQUEST / BLOCK / STATUS messages into the shared mailbox and how leader drains it on every transition.

Shared Skill: Mailbox Communication Protocol

This protocol governs how teammates communicate with each other and with leader through the shared mailbox during a run.

---

Location

The mailbox for each run lives at:

.repos/workspace/<repo-name>/runs/<request-id>/mailbox.md

Leader creates this file when the run starts. If it does not exist when a teammate needs to write, the teammate creates it.

---

Append-Only Rule

The mailbox is append-only. Teammates may only add new messages to the end of the file. They MUST NOT:

• Delete existing messages
• Edit existing messages
• Reorder messages
• Overwrite the file

This ensures a reliable audit trail of cross-teammate communication.

---

Message Format

Each message follows this exact format:

---
**Timestamp:** YYYY-MM-DD HH:MM UTC
**From:** <agent-name>
**Type:** INFO | HOLD_REQUEST | INTERFACE_CHANGE
**Subject:** <one-line summary>

<message body — as concise as possible>

Message Types

Type	Meaning	Action Required
INFO	Non-blocking observation or note for downstream teammates	Leader reads and forwards if relevant
HOLD_REQUEST	The sender cannot continue without user input — corresponds to a HOLD signal	Leader must ask the user the specific question before dispatching downstream work
INTERFACE_CHANGE	A function signature, file path, export, or API surface changed in a way that affects other teammates	Leader must notify affected downstream teammates in their dispatch prompt

Relationship to Workflow Signals

Mailbox message types are not workflow signals. They are communication records. The mapping:

Mailbox Type	Corresponding Signal	Who Acts
HOLD_REQUEST	HOLD (raised by the teammate)	Leader asks user, re-dispatches teammate
INFO	(none — no signal raised)	Leader reads and optionally forwards
INTERFACE_CHANGE	(none — no signal raised)	Leader includes in downstream dispatch

Note: BLOCK and STOP are NOT mailbox types. They are verdicts written directly in audit.md (BLOCK) and review.md (STOP). The mailbox is for inter-teammate communication, not for verdict delivery.

---

When to Use the Mailbox

Teammates SHOULD write to the mailbox when:

• They need user input to continue (type: HOLD_REQUEST)
• They change a function signature, file name, or export that downstream teammates depend on (type: INTERFACE_CHANGE)
• They discover an upstream artifact is incomplete but can work around it (type: INFO)
• They make a judgment call not covered by the spec and want to document it for reviewer (type: INFO)
• They notice an out-of-scope issue for a future run (type: INFO)

Teammates SHOULD NOT use the mailbox for:

• Routine progress updates (the output artifact covers this)
• Duplicating information already in their output artifact
• Communicating directly with the user (only leader talks to the user)
• Delivering BLOCK or STOP verdicts (those go in audit.md and review.md)

---

Leader Responsibilities

After each teammate completes, leader MUST:

1. Read the teammate's output artifact.
2. Read mailbox.md for any new messages since the last check.
3. If a HOLD_REQUEST message exists, forward the question to the user via a numbered-options markdown question before dispatching downstream work.
4. If an INTERFACE_CHANGE message exists, include the change details in the dispatch prompt for any affected downstream teammate.
5. If an INFO message is relevant to downstream work, summarize it in the next dispatch prompt.

---

Example

---
**Timestamp:** 2026-03-13 14:22 UTC
**From:** builder
**Type:** INTERFACE_CHANGE
**Subject:** Renamed `calc_stats()` to `compute_statistics()`

The function `calc_stats()` in `src/stats.R` was renamed to `compute_statistics()` to match the naming convention used elsewhere in the package. All internal callers have been updated. Scriber should update any documentation or examples that reference the old name.

---
**Timestamp:** 2026-03-13 14:45 UTC
**From:** planner
**Type:** HOLD_REQUEST
**Subject:** Undefined symbol in equation (3)

In equation (3) of the uploaded PDF, the symbol $\hat\Sigma$ is used but never defined. Is this: (a) the sample covariance matrix $X'X/N$, (b) the residual covariance $\hat{e}\hat{e}'/N$, or (c) something else? Its dimension ($N \times N$ vs $T \times T$) also needs clarification.