Add event id validation

docs/DATA_MODEL.md

@@ -462,7 +462,7 @@ Conditions may include `after_event` to stay inactive until a one-shot event has
 
 `post_battle_choices` are shown on the victory result panel after first-time scenario rewards are applied. Each choice needs a unique stable lowercase `id`, a non-empty `label`, and a `set_flags` object whose keys are stable lowercase flag ids. Choices may also grant positive `gold`, known `items`, `join_officers`, and `leave_officers`. When rewards are saved but the player has not selected a choice yet, `CampaignState.pending_post_battle_choice_scenario_id` records that scenario id so reloading the game returns to the victory choice panel instead of skipping the branch. The selected choice is saved to `CampaignState.flags`, `CampaignState.applied_post_battle_choices`, and campaign membership only when the player presses its result-panel button; completed-scenario replays do not show choices again. Save-load migration for older saves uses flags as a conservative choice signal, so avoid designing multiple choices in one scenario that can all match the same saved flag state.
 
-Scenario `events` support `battle_start`, `battle_begin`, `turn_start`, and movement-triggered `unit_reaches_tile` triggers. `battle_begin` runs after the briefing is closed. `unit_reaches_tile` events run when a moved unit enters the zero-based `pos` cell; use `team`, `unit_ids`, or `officer_ids` to limit who can trigger the event. Actions currently include `log`, `dialogue`, `set_objective`, `grant_item`, `grant_items`, `spawn_deployment`, and `spawn_deployments`. Event `dialogue` actions use the same dialogue line format, portrait default rules, and optional `side` placement as `post_battle_dialogue`. Event item grants add to the battle inventory immediately; they persist to the campaign save only when the battle is won.
+Scenario `events` support `battle_start`, `battle_begin`, `turn_start`, and movement-triggered `unit_reaches_tile` triggers. Each event needs a stable lowercase `id` that is unique within the scenario; `after_event` conditions can only reference those explicit ids. `battle_begin` runs after the briefing is closed. `unit_reaches_tile` events run when a moved unit enters the zero-based `pos` cell; use `team`, `unit_ids`, or `officer_ids` to limit who can trigger the event. Actions currently include `log`, `dialogue`, `set_objective`, `grant_item`, `grant_items`, `spawn_deployment`, and `spawn_deployments`. Event `dialogue` actions use the same dialogue line format, portrait default rules, and optional `side` placement as `post_battle_dialogue`. Event item grants add to the battle inventory immediately; they persist to the campaign save only when the battle is won.
 
 ```json
 {

tools/validate_data.ps1

@@ -1408,6 +1408,35 @@ function Check-Post-Battle-Choices($Choices, [string]$ScenarioId) {
     }
 }
 
+function Check-Event-Ids($Events, [string]$ScenarioId) {
+    $eventIds = New-Object System.Collections.Generic.HashSet[string]
+    if ($null -eq $Events) {
+        return ,$eventIds
+    }
+    if (-not ($Events -is [System.Array])) {
+        Fail "Scenario $ScenarioId events must be an array."
+    }
+    foreach ($event in @($Events)) {
+        if ($event -is [string] -or $event -is [System.Array]) {
+            Fail "Scenario $ScenarioId has malformed event."
+        }
+        if (-not (Has-Prop $event "id")) {
+            Fail "Scenario $ScenarioId event has empty id."
+        }
+        $eventId = [string](Get-Prop $event "id" "")
+        if ([string]::IsNullOrWhiteSpace($eventId)) {
+            Fail "Scenario $ScenarioId event has empty id."
+        }
+        if (-not ($eventId -match "^[a-z0-9_]+$")) {
+            Fail "Scenario $ScenarioId event has unstable id: $eventId"
+        }
+        if (-not $eventIds.Add($eventId)) {
+            Fail "Scenario $ScenarioId has duplicate event id: $eventId"
+        }
+    }
+    return ,$eventIds
+}
+
 function Check-Required-Flags($RequiredFlags, [string]$ScenarioId, [string]$Context) {
     if ($null -eq $RequiredFlags) {
         return
@@ -1602,12 +1631,7 @@ foreach ($scenario in $campaign.scenarios) {
         }
     }
 
-    $eventIds = New-Object System.Collections.Generic.HashSet[string]
-    foreach ($event in (Get-Prop $scenarioData "events" @())) {
-        if (Has-Prop $event "id") {
-            $eventIds.Add([string]$event.id) | Out-Null
-        }
-    }
+    $eventIds = Check-Event-Ids (Get-Prop $scenarioData "events" $null) $scenarioId
     $knownUnitIds = Collect-Scenario-Unit-Ids $scenarioData
 
     if (Has-Prop $scenarioData "conditions") {