| 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:
- Read the teammate's output artifact.
- Read
mailbox.md for any new messages since the last check.
- If a
HOLD_REQUEST message exists, forward the question to the user via a numbered-options markdown question before dispatching downstream work.
- If an
INTERFACE_CHANGE message exists, include the change details in the dispatch prompt for any affected downstream teammate.
- 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.
