fix(events): Handle nullable label and milestone in resource events

GitLab returns null for the label/milestone fields on resource_label_events
and resource_milestone_events when the referenced label or milestone has
been deleted. This caused deserialization failures during sync.

- Add migration 012 to recreate both event tables with nullable
  label_name, milestone_title, and milestone_id columns (SQLite
  requires table recreation to alter NOT NULL constraints)
- Change GitLabLabelEvent.label and GitLabMilestoneEvent.milestone
  to Option<> in the Rust types
- Update upsert functions to pass through None values correctly
- Add tests for null label and null milestone deserialization

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

migrations/012_nullable_label_milestone.sql

@@ -0,0 +1,65 @@
+-- Migration 012: Make label_name and milestone_title nullable
+-- GitLab returns null for these when the referenced label/milestone has been deleted.
+
+-- Recreate resource_label_events with nullable label_name
+CREATE TABLE resource_label_events_new (
+    id INTEGER PRIMARY KEY,
+    gitlab_id INTEGER NOT NULL,
+    project_id INTEGER NOT NULL REFERENCES projects(id) ON DELETE CASCADE,
+    issue_id INTEGER REFERENCES issues(id) ON DELETE CASCADE,
+    merge_request_id INTEGER REFERENCES merge_requests(id) ON DELETE CASCADE,
+    action TEXT NOT NULL CHECK (action IN ('add', 'remove')),
+    label_name TEXT,
+    actor_gitlab_id INTEGER,
+    actor_username TEXT,
+    created_at INTEGER NOT NULL,
+    CHECK (
+        (issue_id IS NOT NULL AND merge_request_id IS NULL) OR
+        (issue_id IS NULL AND merge_request_id IS NOT NULL)
+    )
+);
+
+INSERT INTO resource_label_events_new
+SELECT * FROM resource_label_events;
+
+DROP TABLE resource_label_events;
+ALTER TABLE resource_label_events_new RENAME TO resource_label_events;
+
+CREATE UNIQUE INDEX uq_label_events_gitlab ON resource_label_events(gitlab_id, project_id);
+CREATE INDEX idx_label_events_issue ON resource_label_events(issue_id) WHERE issue_id IS NOT NULL;
+CREATE INDEX idx_label_events_mr ON resource_label_events(merge_request_id) WHERE merge_request_id IS NOT NULL;
+CREATE INDEX idx_label_events_created ON resource_label_events(created_at);
+
+-- Recreate resource_milestone_events with nullable milestone_title
+CREATE TABLE resource_milestone_events_new (
+    id INTEGER PRIMARY KEY,
+    gitlab_id INTEGER NOT NULL,
+    project_id INTEGER NOT NULL REFERENCES projects(id) ON DELETE CASCADE,
+    issue_id INTEGER REFERENCES issues(id) ON DELETE CASCADE,
+    merge_request_id INTEGER REFERENCES merge_requests(id) ON DELETE CASCADE,
+    action TEXT NOT NULL CHECK (action IN ('add', 'remove')),
+    milestone_title TEXT,
+    milestone_id INTEGER,
+    actor_gitlab_id INTEGER,
+    actor_username TEXT,
+    created_at INTEGER NOT NULL,
+    CHECK (
+        (issue_id IS NOT NULL AND merge_request_id IS NULL) OR
+        (issue_id IS NULL AND merge_request_id IS NOT NULL)
+    )
+);
+
+INSERT INTO resource_milestone_events_new
+SELECT * FROM resource_milestone_events;
+
+DROP TABLE resource_milestone_events;
+ALTER TABLE resource_milestone_events_new RENAME TO resource_milestone_events;
+
+CREATE UNIQUE INDEX uq_milestone_events_gitlab ON resource_milestone_events(gitlab_id, project_id);
+CREATE INDEX idx_milestone_events_issue ON resource_milestone_events(issue_id) WHERE issue_id IS NOT NULL;
+CREATE INDEX idx_milestone_events_mr ON resource_milestone_events(merge_request_id) WHERE merge_request_id IS NOT NULL;
+CREATE INDEX idx_milestone_events_created ON resource_milestone_events(created_at);
+
+-- Update schema version
+INSERT INTO schema_version (version, applied_at, description)
+VALUES (12, strftime('%s', 'now') * 1000, 'Make label_name and milestone_title nullable for deleted labels/milestones');

src/core/db.rs

@@ -39,6 +39,10 @@ const MIGRATIONS: &[(&str, &str)] = &[
         "011",
         include_str!("../../migrations/011_resource_events.sql"),
     ),
+    (
+        "012",
+        include_str!("../../migrations/012_nullable_label_milestone.sql"),
+    ),
 ];
 
 /// Create a database connection with production-grade pragmas.

src/core/events_db.rs

@@ -82,7 +82,7 @@ pub fn upsert_label_events(
             issue_id,
             merge_request_id,
             event.action,
-            event.label.name,
+            event.label.as_ref().map(|l| l.name.as_str()),
             actor_id,
             actor_username,
             created_at,
@@ -123,8 +123,8 @@ pub fn upsert_milestone_events(
             issue_id,
             merge_request_id,
             event.action,
-            event.milestone.title,
-            event.milestone.id,
+            event.milestone.as_ref().map(|m| m.title.as_str()),
+            event.milestone.as_ref().map(|m| m.id),
             actor_id,
             actor_username,
             created_at,

src/gitlab/types.rs

@@ -230,7 +230,7 @@ pub struct GitLabLabelEvent {
     pub created_at: String,
     pub resource_type: String,
     pub resource_id: i64,
-    pub label: GitLabLabelRef,
+    pub label: Option<GitLabLabelRef>,
     pub action: String,
 }
 
@@ -242,7 +242,7 @@ pub struct GitLabMilestoneEvent {
     pub created_at: String,
     pub resource_type: String,
     pub resource_id: i64,
-    pub milestone: GitLabMilestoneRef,
+    pub milestone: Option<GitLabMilestoneRef>,
     pub action: String,
 }
 

tests/gitlab_types_tests.rs

@@ -729,10 +729,11 @@ fn deserializes_label_event_add() {
 
     assert_eq!(event.id, 2001);
     assert_eq!(event.action, "add");
-    assert_eq!(event.label.id, 100);
-    assert_eq!(event.label.name, "bug");
-    assert_eq!(event.label.color, Some("#FF0000".to_string()));
-    assert_eq!(event.label.description, Some("Bug label".to_string()));
+    let label = event.label.expect("label should be Some");
+    assert_eq!(label.id, 100);
+    assert_eq!(label.name, "bug");
+    assert_eq!(label.color, Some("#FF0000".to_string()));
+    assert_eq!(label.description, Some("Bug label".to_string()));
 }
 
 #[test]
@@ -760,8 +761,57 @@ fn deserializes_label_event_remove_null_color() {
         serde_json::from_str(json).expect("Failed to deserialize label remove event");
 
     assert_eq!(event.action, "remove");
-    assert!(event.label.color.is_none());
-    assert!(event.label.description.is_none());
+    let label = event.label.expect("label should be Some");
+    assert!(label.color.is_none());
+    assert!(label.description.is_none());
+}
+
+#[test]
+fn deserializes_label_event_null_label() {
+    let json = r#"{
+        "id": 2003,
+        "user": {
+            "id": 42,
+            "username": "developer",
+            "name": "Dev User"
+        },
+        "created_at": "2024-03-15T10:30:00.000Z",
+        "resource_type": "Issue",
+        "resource_id": 999,
+        "label": null,
+        "action": "remove"
+    }"#;
+
+    let event: GitLabLabelEvent =
+        serde_json::from_str(json).expect("Failed to deserialize label event with null label");
+
+    assert_eq!(event.id, 2003);
+    assert_eq!(event.action, "remove");
+    assert!(event.label.is_none());
+}
+
+#[test]
+fn deserializes_milestone_event_null_milestone() {
+    let json = r#"{
+        "id": 3002,
+        "user": {
+            "id": 42,
+            "username": "developer",
+            "name": "Dev User"
+        },
+        "created_at": "2024-03-15T10:30:00.000Z",
+        "resource_type": "Issue",
+        "resource_id": 999,
+        "milestone": null,
+        "action": "remove"
+    }"#;
+
+    let event: GitLabMilestoneEvent = serde_json::from_str(json)
+        .expect("Failed to deserialize milestone event with null milestone");
+
+    assert_eq!(event.id, 3002);
+    assert_eq!(event.action, "remove");
+    assert!(event.milestone.is_none());
 }
 
 #[test]
@@ -789,9 +839,10 @@ fn deserializes_milestone_event() {
 
     assert_eq!(event.id, 3001);
     assert_eq!(event.action, "add");
-    assert_eq!(event.milestone.id, 200);
-    assert_eq!(event.milestone.iid, 5);
-    assert_eq!(event.milestone.title, "v1.0");
+    let milestone = event.milestone.expect("milestone should be Some");
+    assert_eq!(milestone.id, 200);
+    assert_eq!(milestone.iid, 5);
+    assert_eq!(milestone.title, "v1.0");
 }
 
 #[test]