Closes #19264

Enables agents to send messages using channel names (e.g. target: "infra") instead of 26-character Mattermost IDs.

Changes

src/mattermost/directory.ts (new)

• listMattermostDirectoryGroups — scans all enabled bot accounts (deduplicated by token), returns public + private channels
• listMattermostDirectoryPeers — returns team members via first available client
• Multi-account scanning ensures private channels are discoverable regardless of which bot the requesting agent uses

src/channel.ts

• Added directory property with listGroups/listPeers + live variants
• Core's DirectoryCache handles caching; both variants call the same function

src/normalize.ts

• Bare names return undefined → falls through to directory lookup
• Stricter looksLikeId: 26-char alnum + DM format (id__id)

Testing

Tested live with 19 bot accounts across public and private channels.

Greptile Summary

Adds directory adapter for Mattermost to enable channel/user name resolution, allowing agents to send messages using friendly names instead of 26-character IDs.

Major changes:

• New directory.ts implements listMattermostDirectoryGroups and listMattermostDirectoryPeers with multi-account scanning for comprehensive channel discovery
• normalize.ts updated to return undefined for bare names, triggering directory lookup fallback
• looksLikeMattermostTargetId now uses strict 26-char alphanumeric pattern plus DM format validation
• monitor.ts improved to record pending history for messages from non-allowlisted senders, preserving conversation context for future @mentions

Issues found:

• Both directory functions ignore the limit parameter—other channel implementations (msteams, matrix, feishu) apply it via .slice(0, limit)

Confidence Score: 4/5

• Safe to merge after fixing the limit parameter handling
• Well-structured implementation following existing patterns from other channel adapters. The limit parameter bug is straightforward and doesn't affect core functionality—results will just be unbounded when limit is specified. The monitor.ts history recording logic is sound and the normalize.ts changes correctly enable directory fallback.
• Fix limit parameter handling in extensions/mattermost/src/mattermost/directory.ts before merging

_{Last reviewed commit: 67dc87d}

_{(4/5) You can add custom instructions or style guidelines for the agent here!}