feat(FN-4219): complete Step 4 — add experiment executor runtime

Fusion-Task-Id: FN-4219
Fusion-Task-Lineage: 8d9a9ba6-6729-4376-b935-549e28a7fa35

packages/core/src/__tests__/experiment-session-store.test.ts

@@ -158,6 +158,23 @@ describe("ExperimentSessionStore", () => {
     expect(onRecord).not.toHaveBeenCalled();
   });
 
+  it("updates run payload patch additively", () => {
+    const session = store.createSession({ name: "p", metric: { name: "x", direction: "maximize" } });
+    const run = store.appendRecord(session.id, {
+      type: "run",
+      payload: { primaryMetric: 9, secondaryMetrics: [], status: "keep" },
+    });
+
+    const updated = store.updateRecordPayload(run.id, { commit: "abc123" });
+    expect(updated.payload).toEqual({
+      primaryMetric: 9,
+      secondaryMetrics: [],
+      status: "keep",
+      commit: "abc123",
+    });
+    expect(store.getRecord(run.id)?.payload).toEqual(updated.payload);
+  });
+
   it("recordKept is idempotent", () => {
     const session = store.createSession({ name: "k", metric: { name: "x", direction: "maximize" } });
     const run = store.appendRecord(session.id, {

packages/core/src/experiment-session-store.ts

@@ -270,6 +270,28 @@ export class ExperimentSessionStore extends EventEmitter<ExperimentSessionStoreE
     return this.updateSession(session.id, { bestRunId: runRecordId });
   }
 
+  updateRecordPayload(recordId: string, patch: Partial<ExperimentSessionRecord["payload"]>): ExperimentSessionRecord {
+    const record = this.getRecord(recordId);
+    if (!record) throw new Error(`Experiment record not found: ${recordId}`);
+
+    const updated = {
+      ...record,
+      payload: {
+        ...record.payload,
+        ...patch,
+      },
+    } as ExperimentSessionRecord;
+
+    this.db.prepare(`
+      UPDATE experiment_session_records
+      SET payload = ?
+      WHERE id = ?
+    `).run(toJson(updated.payload), recordId);
+
+    this.db.bumpLastModified();
+    return updated;
+  }
+
   recordKept(sessionId: string, runRecordId: string): ExperimentSession {
     const session = this.assertRunRecordOwnership(sessionId, runRecordId);
     const keptRunIds = session.keptRunIds.includes(runRecordId)