Greptile Summary

This PR fixes a bug where Mattermost DM replies could create thread roots by passing a root_id to the API. The fix adds a kind: ChatType parameter to resolveMattermostReplyRootId, canFinalizeMattermostPreviewInPlace, and deliverMattermostReplyWithDraftPreview, and moves the kind === "direct" early-return in resolveMattermostEffectiveReplyToId to before the threadRootId check so that existing thread context on a DM channel is properly suppressed. All three call sites in monitorMattermostProvider are updated, and the new test cases cover the DM suppression path for both functions and the preview finalization check.

Confidence Score: 5/5

This PR is safe to merge; the fix is narrow, well-tested, and all call sites are updated consistently.

No P0 or P1 issues found. The logic change is correct: moving the kind === 'direct' early-return before the threadRootId check in resolveMattermostEffectiveReplyToId closes the regression, and kind is forwarded at every call site of the two affected public functions. New tests cover the DM suppression path in both resolveMattermostReplyRootId and resolveMattermostEffectiveReplyToId, and the canFinalizeMattermostPreviewInPlace DM case.

No files require special attention.

_{Reviews (2): Last reviewed commit: "fix(mattermost): prevent DM replies from..." | Re-trigger Greptile}

ProjectClownfish could not safely update this branch, so it opened a narrow replacement PR instead.

Replacement PR: #72659
Source PR: #72659
Contributor credit is preserved in the replacement PR body and changelog plan.

ProjectClownfish pushed a narrow repair to this branch so the original contributor path can stay canonical.

Source PR: #72659
Validation: pnpm check:changed
Contributor credit is preserved in the branch history and PR context.

🔒 Aisle Security Analysis

We found 1 potential security issue(s) in this PR:

const channelInfo = await resolveChannelInfo(channelId);
const kind = resolveMattermostTrustedChatKind({
  channelType: channelInfo?.type,
});
...
const accessDecision = resolveDmGroupAccessWithLists({
  isGroup: kind !== "direct",
  dmPolicy,
  groupPolicy,
  ...
});

const channelInfo = await resolveChannelInfo(channelId);
const channelType = channelInfo?.type?.trim();
if (!channelType) {
  logVerboseMessage(`mattermost: drop post (cannot resolve channel type for ${channelId})`);
  return;
}
const kind = mapMattermostChannelTypeToChatType(channelType);

const channelType = channelInfo?.type ?? payload.data?.channel_type;
const kind = resolveMattermostTrustedChatKind({
  channelType,
  ​// optionally: fallback: "channel" (explicit)
});

Analyzed PR: #72659 at commit 47ee191

_{Last updated on: 2026-04-27T09:36:31Z}

ProjectClownfish pushed a narrow repair to this branch so the original contributor path can stay canonical.

Source PR: #72659
Validation: pnpm check:changed
Contributor credit is preserved in the branch history and PR context.