fix(agents): prevent NOT NULL violation on promoted columns during update

Frontend sent null for empty emoji (emoji.trim() || null), which violated
the NOT NULL constraint on the promoted emoji column (migration 000037).
This caused all agent saves to fail with 500 when emoji was unset.

- Frontend: send empty string instead of null for emoji field
- Backend (PG + SQLite): add null-coercion for all promoted NOT NULL
  columns — TEXT (emoji, agent_description, thinking_level) coerce to "",
  INT (skill_nudge_interval, max_tokens) coerce to 0

internal/store/pg/agents.go

@@ -190,8 +190,17 @@ func (s *PGAgentStore) Update(ctx context.Context, id uuid.UUID, updates map[str
 	}
 
 	// Coerce NOT NULL columns: null → default to prevent constraint violations.
-	if v, ok := updates["skill_nudge_interval"]; ok && v == nil {
-		updates["skill_nudge_interval"] = 0
+	// Promoted TEXT columns (migration 000037): null → empty string.
+	for _, col := range []string{"emoji", "agent_description", "thinking_level"} {
+		if v, ok := updates[col]; ok && v == nil {
+			updates[col] = ""
+		}
+	}
+	// Promoted INT columns: null → 0.
+	for _, col := range []string{"skill_nudge_interval", "max_tokens"} {
+		if v, ok := updates[col]; ok && v == nil {
+			updates[col] = 0
+		}
 	}
 	// NOT NULL JSONB columns: null → empty object.
 	for _, col := range []string{"chatgpt_oauth_routing", "reasoning_config", "workspace_sharing", "shell_deny_groups", "kg_dedup_config"} {

internal/store/sqlitestore/agents.go

@@ -133,9 +133,18 @@ func (s *SQLiteAgentStore) Update(ctx context.Context, id uuid.UUID, updates map
 		return nil
 	}
 
-	// Coerce NOT NULL int columns: null → default to prevent constraint violations.
-	if v, ok := updates["skill_nudge_interval"]; ok && v == nil {
-		updates["skill_nudge_interval"] = 0
+	// Coerce NOT NULL columns: null → default to prevent constraint violations.
+	// Promoted TEXT columns: null → empty string.
+	for _, col := range []string{"emoji", "agent_description", "thinking_level"} {
+		if v, ok := updates[col]; ok && v == nil {
+			updates[col] = ""
+		}
+	}
+	// Promoted INT columns: null → 0.
+	for _, col := range []string{"skill_nudge_interval", "max_tokens"} {
+		if v, ok := updates[col]; ok && v == nil {
+			updates[col] = 0
+		}
 	}
 
 	// Unset existing default before setting a new one (scoped to same tenant).

ui/web/src/pages/agents/agent-detail/agent-overview-tab.tsx

@@ -81,8 +81,8 @@ export function AgentOverviewTab({ agent, onUpdate, heartbeat, onManageCodexPool
         tools_config: toolsEnabled
           ? { profile: tools.profile, allow: tools.allow, deny: tools.deny, alsoAllow: tools.alsoAllow, byProvider: tools.byProvider }
           : {},
-        // Promoted fields sent at top level
-        emoji: emoji.trim() || null,
+        // Promoted fields sent at top level (NOT NULL columns — send "" not null)
+        emoji: emoji.trim(),
         self_evolve: selfEvolve,
         skill_evolve: skillEvolve,
         skill_nudge_interval: skillEvolve ? skillNudgeInterval : 15,