feat(FN-4518): complete Step 4 — carry rebase base through self-healing

Fusion-Task-Id: FN-4518
Fusion-Task-Lineage: 48749dec-b2c9-484b-a13e-ffacc1fa9014

packages/engine/src/__tests__/self-healing.test.ts

@@ -5443,6 +5443,108 @@ describe("recoverDoneTaskMergeMetadata", () => {
     manager.stop();
   });
 
+  it("populates rebaseBaseSha from landed commit when missing", async () => {
+    const store = createMockStore();
+    const manager = new SelfHealingManager(store, { rootDir: "/tmp/test-project" });
+
+    (store.listTasks as ReturnType<typeof vi.fn>).mockResolvedValue([
+      {
+        id: "FN-4518-A",
+        column: "done",
+        paused: false,
+        mergeDetails: { commitSha: "merge1", mergeConfirmed: false },
+      },
+    ]);
+
+    vi.spyOn(manager as any, "findLandedTaskCommit").mockResolvedValue({
+      sha: "merge1",
+      subject: "fix(FN-4518): landed",
+      filesChanged: 2,
+      insertions: 4,
+      deletions: 1,
+      rebaseBaseSha: "base1",
+    });
+
+    const repaired = await manager.recoverDoneTaskMergeMetadata();
+
+    expect(repaired).toBe(1);
+    expect(store.updateTask).toHaveBeenCalledWith("FN-4518-A", {
+      mergeDetails: expect.objectContaining({
+        commitSha: "merge1",
+        rebaseBaseSha: "base1",
+      }),
+    });
+
+    manager.stop();
+  });
+
+  it("does not overwrite existing rebaseBaseSha during reconciliation", async () => {
+    const store = createMockStore();
+    const manager = new SelfHealingManager(store, { rootDir: "/tmp/test-project" });
+
+    (store.listTasks as ReturnType<typeof vi.fn>).mockResolvedValue([
+      {
+        id: "FN-4518-B",
+        column: "done",
+        paused: false,
+        mergeDetails: { commitSha: "merge1", mergeConfirmed: false, rebaseBaseSha: "existing-base" },
+      },
+    ]);
+
+    vi.spyOn(manager as any, "findLandedTaskCommit").mockResolvedValue({
+      sha: "merge1",
+      subject: "fix(FN-4518): landed",
+      filesChanged: 2,
+      insertions: 4,
+      deletions: 1,
+      rebaseBaseSha: "incoming-base",
+    });
+
+    const repaired = await manager.recoverDoneTaskMergeMetadata();
+
+    expect(repaired).toBe(1);
+    expect(store.updateTask).toHaveBeenCalledWith("FN-4518-B", {
+      mergeDetails: expect.objectContaining({
+        rebaseBaseSha: "existing-base",
+      }),
+    });
+
+    manager.stop();
+  });
+
+  it("keeps rebaseBaseSha undefined when neither stored nor landed provides it", async () => {
+    const store = createMockStore();
+    const manager = new SelfHealingManager(store, { rootDir: "/tmp/test-project" });
+
+    (store.listTasks as ReturnType<typeof vi.fn>).mockResolvedValue([
+      {
+        id: "FN-4518-C",
+        column: "done",
+        paused: false,
+        mergeDetails: { commitSha: "merge1", mergeConfirmed: false },
+      },
+    ]);
+
+    vi.spyOn(manager as any, "findLandedTaskCommit").mockResolvedValue({
+      sha: "merge1",
+      subject: "fix(FN-4518): landed",
+      filesChanged: 2,
+      insertions: 4,
+      deletions: 1,
+    });
+
+    const repaired = await manager.recoverDoneTaskMergeMetadata();
+
+    expect(repaired).toBe(1);
+    expect(store.updateTask).toHaveBeenCalledWith("FN-4518-C", {
+      mergeDetails: expect.not.objectContaining({
+        rebaseBaseSha: expect.any(String),
+      }),
+    });
+
+    manager.stop();
+  });
+
   it("FN-3862: confirmed task with unreachable stored SHA is preserved with warning", async () => {
     const store = createMockStore();
     const manager = new SelfHealingManager(store, { rootDir: "/tmp/test-project" });

packages/engine/src/self-healing.ts

@@ -238,6 +238,7 @@ interface LandedTaskCommit {
   filesChanged?: number;
   insertions?: number;
   deletions?: number;
+  rebaseBaseSha?: string;
 }
 
 type AlreadyMergedDetectionStrategy = "trailer" | "ancestry" | "patch-id" | "tree-equal";
@@ -2580,6 +2581,7 @@ export class SelfHealingManager {
           if (landedCommit) {
             const mergeDetails: MergeDetails = {
               commitSha: landedCommit.sha,
+              rebaseBaseSha: landedCommit.rebaseBaseSha,
               filesChanged: landedCommit.filesChanged,
               insertions: landedCommit.insertions,
               deletions: landedCommit.deletions,
@@ -2704,6 +2706,7 @@ export class SelfHealingManager {
                 insertions: nextInsertions,
                 deletions: nextDeletions,
                 mergeCommitMessage: task.mergeDetails?.mergeCommitMessage ?? landed.subject,
+                rebaseBaseSha: task.mergeDetails?.rebaseBaseSha ?? landed.rebaseBaseSha,
                 mergedAt: task.mergeDetails?.mergedAt ?? new Date().toISOString(),
                 prNumber: task.prInfo?.number,
               },
@@ -2756,6 +2759,7 @@ export class SelfHealingManager {
               insertions: landedStats.insertions,
               deletions: landedStats.deletions,
               mergeCommitMessage: landed.subject,
+              rebaseBaseSha: task.mergeDetails?.rebaseBaseSha ?? landed.rebaseBaseSha,
               mergedAt: task.mergeDetails?.mergedAt ?? new Date().toISOString(),
               mergeConfirmed: true,
               prNumber: task.prInfo?.number,
@@ -2898,6 +2902,7 @@ export class SelfHealingManager {
           if (landedCommit) {
             const mergeDetails: MergeDetails = {
               commitSha: landedCommit.sha,
+              rebaseBaseSha: landedCommit.rebaseBaseSha,
               filesChanged: landedCommit.filesChanged,
               insertions: landedCommit.insertions,
               deletions: landedCommit.deletions,