fix(cli,sdk,broker): send and receive file attachments (screenshots) over DMs and channels

.agents/skills/using-agent-relay/SKILL.md

@@ -53,6 +53,8 @@ Do not use older category-expanded names such as
 | `send_dm`             | Send a direct message to one agent                 |
 | `send_group_dm`       | Create a group DM and send the first message       |
 | `post_message`        | Post to a channel                                  |
+| `upload_file`         | Upload a local file (e.g. a screenshot) to attach  |
+| `download_file`       | Save a message attachment locally and get its path |
 | `list_messages`       | Read channel history                               |
 | `reply_to_thread`     | Reply to an existing message                       |
 | `get_message_thread`  | Read a thread                                      |

.claude/skills/using-agent-relay/SKILL.md

@@ -77,6 +77,8 @@ Do not use older category-expanded names such as
 | `send_dm`             | Send a direct message to one agent                 |
 | `send_group_dm`       | Create a group DM and send the first message       |
 | `post_message`        | Post to a channel                                  |
+| `upload_file`         | Upload a local file (e.g. a screenshot) to attach  |
+| `download_file`       | Save a message attachment locally and get its path |
 | `list_messages`       | Read channel history                               |
 | `reply_to_thread`     | Reply to an existing message                       |
 | `get_message_thread`  | Read a thread                                      |

CHANGELOG.md

@@ -5,7 +5,20 @@ All notable changes to Agent Relay will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
-## [Unreleased]
+## [Unreleased - Minor]
+
+### Added
+
+- `agent-relay message dm send`, `message post` and `message dm send_group` take a repeatable `--file <path>` that uploads and attaches local files (for example screenshots); `message file upload` accepts `--to <agent>` for a DM.
+- `agent-relay message file download <file_id>` saves a received attachment (default `.agent-relay/attachments/<file_id>/`) and prints its path; `message file get <file_id>` shows it with a short-lived download URL.
+- The `agent-relay mcp` server adds `upload_file` (local path or base64) and `download_file`, and `send_group_dm` accepts `attachments`.
+- Agents spawned by the broker receive message attachments (up to 25 MiB each) as local files: the injected message ends with an `Attachments:` list giving each file's path under `.agent-relay/attachments/` in the agent's working directory, or an `agent-relay message file download <file_id>` command when a file could not be fetched. Messages that carry only attachments are now delivered too.
+- `@agent-relay/sdk` adds `files.upload` / `files.get` / `files.download` on `AgentRelay` and `RelaycastMessagingClient`, plus `uploadRelayFile` / `downloadRelayFile` helpers.
+
+### Fixed
+
+- `agent-relay message file upload` now uploads and attaches the file; it always failed with "Invalid attachments: file ids must exist in workspace and be complete".
+- Broker-managed messages retry failed delivery up to three times, and later sends wait until delivery succeeds.
 
 ## [13.2.0] - 2026-10-08