docs(19-02): complete item and thread service COALESCE merge plan

- SUMMARY.md with task commits, decisions, and verification results
- STATE.md updated with position, progress, and decisions
- ROADMAP.md updated with plan progress

.planning/STATE.md

@@ -2,16 +2,16 @@
 gsd_state_version: 1.0
 milestone: v1.3
 milestone_name: Research & Decision Tools
-status: planning
-stopped_at: Completed 19-01-PLAN.md
-last_updated: "2026-04-05T11:22:25.312Z"
+status: executing
+stopped_at: Completed 19-02-PLAN.md
+last_updated: "2026-04-05T18:51:11.895Z"
 last_activity: 2026-04-05
 progress:
-  total_phases: 12
+  total_phases: 13
   completed_phases: 11
-  total_plans: 33
-  completed_plans: 31
-  percent: 0
+  total_plans: 36
+  completed_plans: 33
+  percent: 3
 ---
 
 # Project State
@@ -26,8 +26,8 @@ See: .planning/PROJECT.md (updated 2026-04-03)
 ## Current Position
 
 Phase: 19 of 19 (Reference Item Model & Tags Schema)
-Plan: 1 of 3
-Status: Executing
+Plan: 2 of 3
+Status: Ready to execute
 Last activity: 2026-04-05
 
 Progress: [#---------] 3% (v2.0 milestone)
@@ -58,6 +58,7 @@ Key decisions made during v2.0 planning:
 - [Phase 19]: Direct globalItemId FK on items replaces itemGlobalLinks junction table
 - [Phase 19]: Data migration SQL: UPDATE items before DROP TABLE item_global_links
 - [Phase 19]: Flat tags system without type categorization per D-16
+- [Phase 19-reference-item-model-tags-schema]: COALESCE merge pattern for transparent reference item data in item/thread services
 
 ### Pending Todos
 
@@ -70,6 +71,6 @@ None active.
 
 ## Session Continuity
 
-Last session: 2026-04-05T18:28:00Z
-Stopped at: Completed 19-01-PLAN.md
+Last session: 2026-04-05T18:51:11.893Z
+Stopped at: Completed 19-02-PLAN.md
 Resume file: None