FN-5920: prefer mission detail event count for activity tab

Use mission detail event counts as the authoritative pre-load source for mission activity.

- add mission hierarchy eventCount support in core and dashboard mission types
- return mission eventCount from mission detail APIs and document the field
- prefer the detail eventCount over stale list summaries before activity events load
- add coverage for store, API, and MissionManager pre-load count behavior

Files changed:
 docs/missions.md                                   |  2 +-
 packages/core/src/__tests__/mission-store.test.ts  | 18 +++++++++
 packages/core/src/mission-store.ts                 |  6 +++
 packages/core/src/mission-types.ts                 |  2 +
 packages/dashboard/app/api/legacy.ts               |  2 +
 packages/dashboard/app/components/MissionManager.tsx    | 12 +++++-
 packages/dashboard/app/components/__tests__/MissionManager.test.tsx   | 46 +++++++++++++++++++++-
 packages/dashboard/app/components/mission-types.ts |  1 +
 packages/dashboard/src/__tests__/mission-e2e.test.ts    |  2 +
 9 files changed, 86 insertions(+), 5 deletions(-)

Fusion-Task-Id: FN-5920

Fusion-Task-Lineage: a0269499-d34a-495d-89fc-0534bb62a94e

packages/core/src/__tests__/mission-store.test.ts

@@ -1920,6 +1920,24 @@ describe("MissionStore", () => {
 
       expect(withHierarchy.linkedGoals).toEqual([]);
     });
+
+    it("reports detail eventCount consistently with mission summaries", () => {
+      const mission = store.createMission({ title: "Hierarchy event counts" });
+
+      const emptyHierarchy = store.getMissionWithHierarchy(mission.id)!;
+      const emptySummary = store.getMissionSummary(mission.id);
+      expect(emptyHierarchy.eventCount).toBe(0);
+      expect(emptyHierarchy.eventCount).toBe(emptySummary.eventCount);
+
+      store.logMissionEvent(mission.id, "mission_started", "started");
+      store.logMissionEvent(mission.id, "warning", "warning");
+      store.logMissionEvent(mission.id, "error", "error");
+
+      const populatedHierarchy = store.getMissionWithHierarchy(mission.id)!;
+      const populatedSummary = store.getMissionSummary(mission.id);
+      expect(populatedHierarchy.eventCount).toBe(3);
+      expect(populatedHierarchy.eventCount).toBe(populatedSummary.eventCount);
+    });
   });
 
   // ── Transaction Tests ────────────────────────────────────────────────

packages/core/src/mission-store.ts

@@ -723,9 +723,15 @@ export class MissionStore extends EventEmitter<MissionStoreEvents> {
       };
     });
 
+    const eventCountRow = this.db
+      .prepare("SELECT COUNT(*) AS count FROM mission_events WHERE missionId = ?")
+      .get(id) as { count?: number | bigint } | undefined;
+    const eventCount = Number(eventCountRow?.count ?? 0);
+
     return {
       ...mission,
       linkedGoals,
+      eventCount,
       milestones: milestonesWithSlices,
     };
   }

packages/core/src/mission-types.ts

@@ -461,6 +461,8 @@ export interface SliceWithFeatures extends Slice {
 export interface MissionWithHierarchy extends Mission {
   /** Goals linked to this mission */
   linkedGoals?: Goal[];
+  /** Unfiltered total of all mission lifecycle events, matching `MissionSummary.eventCount` and `getMissionEvents` `total` with no `eventType` filter */
+  eventCount?: number;
   /** Milestones belonging to this mission, each with their slices */
   milestones: Array<MilestoneWithSlices & {
     /** Slices with their features loaded */