Problem

Agents must use 26-character Mattermost channel IDs to send messages (e.g. target: "uygoe35x3idumqo5mb5jfbqrdh"). This is error-prone and requires maintaining external ID mappings.

Solution

Add a directory adapter to the Mattermost channel plugin that enables name-based resolution. Agents can now use target: "infra" or target: "off-topic" and core's built-in resolveMessagingTarget handles the lookup.

Changes

src/mattermost/directory.ts (new, ~130 lines)

• listMattermostDirectoryGroups — scans ALL enabled bot accounts (deduplicated by token) and returns public + private channels. Multi-account scanning is essential because private channels are only visible to bots that are members.
• listMattermostDirectoryPeers — returns team members via first available client (all bots see the same user list).
• Graceful error handling: invalid/expired tokens are skipped with debug logging.

src/channel.ts (+15 lines)

• Added directory property with listGroups/listGroupsLive/listPeers/listPeersLive. Core's DirectoryCache handles caching at the resolver level.

src/normalize.ts (3 lines changed)

• normalizeMattermostMessagingTarget: bare names (no prefix) now return undefined instead of channel:${name}, allowing fallthrough to directory lookup.
• looksLikeMattermostTargetId: stricter regex — /^[a-z0-9]{26}$/i for standard IDs + /^[a-z0-9]{26}__[a-z0-9]{26}$/i for DM channel IDs. Previously /^[a-z0-9]{8,}$/i matched channel names like "infra" as IDs.

Known limitations

• per_page=200 for channel/member listing — covers most instances but very large ones may see incomplete results.
• Peers use first team only (teams[0]) — multi-team setups would need iteration.

Testing

Tested live with 19 bot accounts, successfully resolves both public and private channel names.