SSS Postal System

Inspiration

When AI work is split across multiple tasks, a handoff can disappear into scheduling gaps. The sender sees no response, the recipient sees no durable message, and retrying the same native channel does not change the failure mode. The Owner described a simpler model: tasks need addresses, and a post office should accept, store, route, and trace letters.

What it does

SSS Postal System is an installable local Codex plugin. A task registers a stable task-stage address. Another task posts a complete letter to that address. The post office stores it durably, routes it when possible, surfaces it at the recipient's next safe work boundary, and preserves an append-only receipt from acceptance through handling.

The recipient sees deterministic [LETTER][信件] text without losing current work. Delivery never becomes automatic construction authority. DELIVERED, PRESENTED, READ, and HANDLED remain distinct, and HANDLED requires a concrete disposition note.

How we built it

The plugin combines a local Node.js MCP service, six tool contracts, a Codex Skill, optional lifecycle hooks, atomic JSON persistence, lock fencing, and deterministic tests. The Owner supplied the postal-service concept, product name, and coordination pain. GPT-5.6 and Codex translated that into the state model, implementation, tests, plugin packaging, and live two-task validation.

Challenges

The first live trial revealed that model instructions alone could summarize away the mail marker and could mark a letter handled too early. We moved the bilingual display block into deterministic tool output and made a concrete handling note mandatory.

We also preserved an important platform boundary: the plugin can store mail while a task is dormant, but it does not claim that public plugin surfaces can force-wake a fully dormant task.

Accomplishments

Real desktop sender/receiver path without native inter-task messaging. Durable receipt: ACCEPTED → DELIVERED → PRESENTED → READ → HANDLED. Exact envelope and append-only event history preservation. Mail does not interrupt current work or grant authority. 12/12 product tests plus official plugin and Skill validation. Judge installation and smoke-test path with no build step.

What we learned

Reliable agent coordination needs more than a send call. It needs stable addresses, store-and-forward persistence, explicit state transitions, safe pickup boundaries, and evidence that separates arrived from acted on.

Owner's lifecycle assessment

The Owner does not assume that this platform gap will exist forever. If Codex later provides native durable cross-task delivery, explicit receipt states, and reliable safe-boundary pickup, SSS Postal System should evolve into a compatibility and audit layer or be retired. Being made unnecessary by a stronger native platform would also validate the coordination problem this project identified.

What's next

Potential follow-ups include expiration policy, administrative mailbox views, stronger multi-process storage, and supported wake notifications when Codex exposes a public lifecycle mechanism. These are outside the Build Week MVP.

Built With

• codex
• codex-hooks
• codex-skills
• gpt-5.6
• mcp
• node.js
• powershell