fix: align warning-case blocking semantics across reconcile paths

Co-authored-by: genichin <4282227+genichin@users.noreply.github.com>

trex_core/adapters/persistence/sql/028_preserve_reconcile_warning_cases.sql

@@ -1,7 +1,30 @@
 -- REQ-123 / issue #83:
 -- Preserve simultaneous warning causes by keying warnings per (slot_id, case_code).
+-- NOTE: historical overwritten causes cannot be reconstructed from the prior
+-- slot_id-only schema; this migration enables forward preservation only.
+UPDATE slot_reconcile_warning
+SET case_code = 'B'
+WHERE case_code IS NULL OR case_code = '';
+
+ALTER TABLE slot_reconcile_warning
+    ALTER COLUMN case_code SET NOT NULL;
+
+DELETE FROM slot_reconcile_warning w
+USING (
+    SELECT ctid, ROW_NUMBER() OVER (
+        PARTITION BY slot_id, case_code
+        ORDER BY updated_at DESC, created_at DESC, ctid DESC
+    ) AS rn
+    FROM slot_reconcile_warning
+) ranked
+WHERE w.ctid = ranked.ctid
+  AND ranked.rn > 1;
+
 ALTER TABLE slot_reconcile_warning
     DROP CONSTRAINT IF EXISTS slot_reconcile_warning_pkey;
 
 ALTER TABLE slot_reconcile_warning
     ADD CONSTRAINT slot_reconcile_warning_pkey PRIMARY KEY (slot_id, case_code);
+
+CREATE INDEX IF NOT EXISTS idx_slot_reconcile_warning_slot_id
+    ON slot_reconcile_warning (slot_id);