---
title: "Post Task Message"
method: POST
path: "/tasks/{task_id}/messages"
---

# Post Task Message

`POST /tasks/{task_id}/messages`

Append one typed message to the recipient task's mailbox.

The message is DLP-redacted, HMAC-chained onto the mailbox journal,
Ed25519-signed, and mirrored into the audit chain before the response
is returned - the response IS the signed journal entry.

## Path parameters

- `task_id` string, required

## Request body

- TaskMessagePost — Body for POST /tasks/{task_id}/messages (#2357). Typed, size-capped worker mailbox payload. ``kind`` must be one of the closed vocabulary (``finding`` / ``artefact_ref`` / ``question``). The message body is capped by the mailbox chain to 4096 UTF-8 bytes (see ``task_mailbox.MAX_MESSAGE_BODY_BYTES``); the API model mirrors this limit so oversized bodies fail validation up front instead of being rejected downstream. The byte-strict cap remains authoritative in the mailbox for multibyte payloads.
  - `sender` string, required
  - `kind` string, required
  - `body` string, required
  - `sender_card_fingerprint` string, nullable

## Response `201`

Successful Response

- TaskMessageResponse — One delivered mailbox message (chain order = delivery order).
  - `seq` integer, required
  - `task_id` string, required
  - `sender` string, required
  - `sender_card_fingerprint` string, required
  - `kind` string, required
  - `body` string, required
  - `body_hash` string, required
  - `redaction_count` integer, required
  - `timestamp` number, required
  - `prev_entry_hash` string, required
  - `entry_hash` string, required
  - `signature` string, required
  - `signer_public_key_pem` string, required

## Other responses

- `404` — Task not found
- `422` — Unknown message kind or body over the byte cap
- `429` — Recipient task mailbox is full

---

[API](https://skmtc.net/sipyourdrink-ltd/apis/bernstein-task-server.md) · [All operations](https://skmtc.net/sipyourdrink-ltd/apis/bernstein-task-server/llms.txt) · [OpenAPI document](https://skmtc-service-staging.skmtc.workers.dev/v1/apis/sipyourdrink-ltd/bernstein-task-server/versions/86f514b4e920/schema)