Summary

Adds patchMattermostPost() and deleteMattermostPost() to the Mattermost client, and wires them as edit and delete actions in the channel plugin message action adapter.

What this enables

• Edit messages via the message tool (action=edit) — foundation for block-streaming edit-in-place (progressive message rendering like Telegram/Discord)
• Delete messages via the message tool (action=delete)

API endpoints used

• Edit: PUT /api/v4/posts/{post_id}/patch (partial update)
• Delete: DELETE /api/v4/posts/{post_id}

Files changed

• extensions/mattermost/src/mattermost/client.ts — add patchMattermostPost() and deleteMattermostPost()
• extensions/mattermost/src/channel.ts — register edit and delete in listActions, supportsAction, and handleAction

Testing

• Tested against a live Mattermost 10.x instance: create → edit → delete cycle works correctly
• Bot requires edit_post / delete_post permissions (standard bot permissions)

Notes

This is a stepping stone toward full block-streaming support on Mattermost, bringing it closer to feature parity with the Telegram and Discord plugins.

Greptile Summary

Added edit and delete message functionality to the Mattermost plugin by implementing patchMattermostPost() and deleteMattermostPost() in the client, and wiring them through the channel message action adapter.

Changes:

• Added patchMattermostPost() function supporting partial updates (message, props, fileIds)
• Added deleteMattermostPost() function for post deletion
• Registered edit and delete actions in listActions() and supportsAction()
• Implemented action handlers that validate params, resolve account config, and call the API functions
• Used standard Mattermost API endpoints (PUT /posts/{id}/patch, DELETE /posts/{id})

Architecture:

• Follows existing pattern from react action handler (account resolution, validation, error handling)
• Accepts both messageId and postId parameter names for flexibility
• Returns structured results with content and details

The implementation is straightforward and brings Mattermost closer to feature parity with Telegram and Discord plugins.

Confidence Score: 4/5

• This PR is safe to merge with low risk
• Clean implementation following established patterns. The code correctly validates required parameters, handles account resolution, and uses proper error handling. One minor style suggestion about empty message validation, but this won't cause runtime errors since the Mattermost API will reject empty edits if they're not allowed.
• No files require special attention

_{Last reviewed commit: e3df5fa}

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