fix: broaden retrospective nudge to cover all terminal transition paths

The retrospective nudge previously only fired after complete_tree, missing
single-item runs that reach terminal via advance_item. Updated the nudge
condition to trigger on any terminal transition during an /implement run,
with single-item, multi-item, and fallback detection rules.

Also: minor AdvanceItemTool optimization — derive existingKeys from
notesByKey instead of a separate .map() pass.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: jpicklyk

claude-plugins/task-orchestrator/output-styles/workflow-orchestrator.md

@@ -129,7 +129,13 @@ During any implementation run (triggered by `/implement` or `post-plan-workflow`
 
 ## Retrospective Nudge
 
-After `complete_tree` completes, or when 3+ items transition to terminal during a session, append a one-line suggestion:
+When **any** item that was part of an `/implement` run reaches terminal — whether via `advance_item`, `complete_tree`, or auto-cascade — check if the run is complete:
+
+- **Single-item run:** The item reaching terminal = run complete.
+- **Multi-item run (manifest exists):** All items in `scope.preExistingItems` are terminal = run complete.
+- **No manifest fallback:** 3+ items transition to terminal during a session = likely run complete.
+
+When the run is complete, append a one-line suggestion:
 
 ```
 ↳ Implementation run complete. Consider running `/session-retrospective` to capture learnings.

current/src/main/kotlin/io/github/jpicklyk/mcptask/current/application/tools/workflow/AdvanceItemTool.kt

@@ -387,8 +387,8 @@ Trigger-based role transitions for WorkItems with validation, cascade detection,
                     is Result.Success -> notesResult.data
                     is Result.Error -> emptyList()
                 }
-                val existingKeys = existingNotes.map { it.key }.toSet()
                 val notesByKey = existingNotes.associateBy { it.key }
+                val existingKeys = notesByKey.keys
 
                 // Build expectedNotes: schema entries matching the new role (tool-specific, includes "exists")
                 val forNewRole = schema.filter { it.role == newRoleStr }