CollaborativeMarkdownView: deleting a comment throws "Node not found" when the comment was already deleted #4668

What is failing

The CollaborativeMarkdownView component's comment-deletion handler fails with System.InvalidOperationException: Node not found when it attempts to delete a comment node that the mesh no longer holds. The comment shown in the UI could not be deleted because it was already gone server-side.

Probable cause

The delete handler operates on stale view state: the comment node (here CollaborationClientG/PrereadToNotus20260918/_Comment/b1bbf6a2) was already deleted — by a double-click of the delete button, a concurrent delete from another session, or a stale UI list after the node was removed underneath the view — and the handler then calls the mesh Delete unconditionally and surfaces the resulting Node not found as a user-facing failure instead of treating it as already-deleted (idempotent success). Confidence: medium — the single sample clearly shows the delete arriving for a non-existent node, but with only one occurrence the exact stale-state path is unproven.

Impact

Minimal: a single occurrence on one pod — a one-off failed comment deletion for one document. No systemic impact, but any user who deletes an already-removed comment would hit the same error.

Where to look

MeshWeaver.Blazor.Components.CollaborativeMarkdownView — the comment delete handler that logs Deleting comment on {path}. It should verify the node still exists / reconcile its comment list on failure, or swallow Node not found as success. Related context: the noisy "Comment failed" bursts around 2026-09-09 in Ops/Logs (incidents e1e996b2610f3272, 782ef3ac96819798, d4c8f6f74ecfa422) suggest comment CRUD in this component has other failure modes worth a look at the same time.

Evidence

2026-09-17 16:54:55Z memex-portal-deployment-6c967c7c4c-kdff5 fail: MeshWeaver.Blazor.Components.CollaborativeMarkdownView[0]
      Deleting comment on CollaborationClientG/PrereadToNotus20260918/_Comment/b1bbf6a2 in Area Overview/2/1/2
      System.InvalidOperationException: Node not found: CollaborationClientG/PrereadToNotus20260918/_Comment/b1bbf6a2

_{Opened automatically from Admin/_LogIncident/8f99d92ba56c4c4c. Recurrences are folded into this issue rather than opening new ones.}