feat(FN-4518): complete Step 3 — use rebase range in done-task diff fallback

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

packages/dashboard/src/__tests__/routes-diff.test.ts

@@ -285,6 +285,65 @@ describe("FN-4308 multi-commit done task aggregation", () => {
     expect(response.body.files[0].path).toBe("healed.ts");
   });
 
+  it("uses rebaseBaseSha..commitSha fallback range for done task diff", async () => {
+    const store = new MockStore();
+    store.addTask(createTask({ column: "done", mergeDetails: { commitSha: "head-sha", rebaseBaseSha: "base-sha", filesChanged: 2 } }));
+
+    gitResponses({
+      "merge-base --is-ancestor head-sha HEAD": "",
+      "merge-base --is-ancestor base-sha head-sha": "",
+      "diff --name-status -M base-sha..head-sha": "A\tone.ts\nA\ttwo.ts",
+      "diff -M base-sha..head-sha -- one.ts": "+1\n",
+      "diff -M base-sha..head-sha -- two.ts": "+2\n",
+    });
+
+    const app = createServer(store as any);
+    const response = await requestDiff(app);
+    expect(response.status).toBe(200);
+    expect(response.body.stats.filesChanged).toBe(2);
+    expect(response.body.files.map((f: any) => f.path).sort()).toEqual(["one.ts", "two.ts"]);
+  });
+
+  it("falls back to single-commit range when rebaseBaseSha is unreachable", async () => {
+    const store = new MockStore();
+    store.addTask(createTask({ column: "done", mergeDetails: { commitSha: "head-sha", rebaseBaseSha: "base-sha" } }));
+
+    runGitCommandMock.mockImplementation(async (args: string[]) => {
+      const key = args.join(" ");
+      if (key === "merge-base --is-ancestor head-sha HEAD") return "";
+      if (key === "merge-base --is-ancestor base-sha head-sha") throw new Error("unreachable");
+      if (key === "rev-list --parents -n 1 head-sha") return "head-sha parent";
+      if (key === "diff --name-status -M parent..head-sha") return "A\tfallback.ts";
+      if (key === "diff -M parent..head-sha -- fallback.ts") return "+f\n";
+      throw new Error(`Unexpected git command: ${key}`);
+    });
+
+    const app = createServer(store as any);
+    const response = await requestDiff(app);
+    expect(response.status).toBe(200);
+    expect(response.body.files).toHaveLength(1);
+    expect(response.body.files[0].path).toBe("fallback.ts");
+  });
+
+  it("uses rebaseBaseSha..commitSha fallback range for done task file-diffs", async () => {
+    const store = new MockStore();
+    store.addTask(createTask({ column: "done", mergeDetails: { commitSha: "head-sha", rebaseBaseSha: "base-sha", filesChanged: 2 } }));
+
+    gitResponses({
+      "merge-base --is-ancestor head-sha HEAD": "",
+      "merge-base --is-ancestor base-sha head-sha": "",
+      "diff --name-status -M base-sha..head-sha": "A\tone.ts\nA\ttwo.ts",
+      "diff -M base-sha..head-sha -- one.ts": "+1\n",
+      "diff -M base-sha..head-sha -- two.ts": "+2\n",
+    });
+
+    const app = createServer(store as any);
+    const response = await requestFileDiffs(app);
+    expect(response.status).toBe(200);
+    expect(response.body).toHaveLength(2);
+    expect(response.body.map((f: any) => f.path).sort()).toEqual(["one.ts", "two.ts"]);
+  });
+
   it("uses parent-to-parent range for merge commits", async () => {
     const store = new MockStore();
     store.addTask(createTask({ column: "done", mergeDetails: { commitSha: "merge-sha" } }));

packages/dashboard/src/routes/register-session-diff-routes.ts

@@ -224,7 +224,13 @@ async function isReachableFromHead(sha: string, rootDir: string): Promise<boolea
 type DoneTaskAggregationTask = {
   id: string;
   lineageId?: string | null;
-  mergeDetails?: { commitSha?: string; filesChanged?: number; insertions?: number; deletions?: number } | null;
+  mergeDetails?: {
+    commitSha?: string;
+    rebaseBaseSha?: string;
+    filesChanged?: number;
+    insertions?: number;
+    deletions?: number;
+  } | null;
 };
 
 type DoneTaskAggregationStore = {
@@ -252,6 +258,19 @@ async function resolveCommitDiffSpec(sha: string, rootDir: string): Promise<
   return { mode: "single-parent", base: parents[0]!, range: `${parents[0]}..${sha}` };
 }
 
+async function resolveRebaseDiffSpec(
+  rebaseBaseSha: string,
+  commitSha: string,
+  rootDir: string,
+): Promise<{ mode: "rebase-range"; base: string; range: string } | null> {
+  try {
+    await runGitCommand(["merge-base", "--is-ancestor", rebaseBaseSha, commitSha], rootDir, 5000);
+    return { mode: "rebase-range", base: rebaseBaseSha, range: `${rebaseBaseSha}..${commitSha}` };
+  } catch {
+    return null;
+  }
+}
+
 function parseStatusCode(statusCode: string): DoneTaskFileStatus {
   if (statusCode.startsWith("A")) return "added";
   if (statusCode.startsWith("D")) return "deleted";
@@ -637,12 +656,28 @@ export function registerSessionDiffRoutes(router: Router, deps: SessionDiffRoute
         const rootDir = scopedStore.getRootDir();
         const sha = resolvedMergeSha;
 
-        let diffSpec: Awaited<ReturnType<typeof resolveCommitDiffSpec>>;
-        try {
-          diffSpec = await resolveCommitDiffSpec(sha, rootDir);
-        } catch {
-          res.json({ files: [], stats: { filesChanged: 0, additions: 0, deletions: 0 } });
-          return;
+        let diffSpec: Awaited<ReturnType<typeof resolveCommitDiffSpec>> | { mode: "rebase-range"; base: string; range: string };
+        const rebaseBaseSha = task.mergeDetails?.rebaseBaseSha?.trim();
+        if (rebaseBaseSha) {
+          const rebaseDiffSpec = await resolveRebaseDiffSpec(rebaseBaseSha, sha, rootDir);
+          if (rebaseDiffSpec) {
+            diffSpec = rebaseDiffSpec;
+          } else {
+            console.warn(`[diff] done task ${task.id}: mergeDetails.rebaseBaseSha ${rebaseBaseSha} is not ancestor of ${sha}; falling back to single-commit diff`);
+            try {
+              diffSpec = await resolveCommitDiffSpec(sha, rootDir);
+            } catch {
+              res.json({ files: [], stats: { filesChanged: 0, additions: 0, deletions: 0 } });
+              return;
+            }
+          }
+        } else {
+          try {
+            diffSpec = await resolveCommitDiffSpec(sha, rootDir);
+          } catch {
+            res.json({ files: [], stats: { filesChanged: 0, additions: 0, deletions: 0 } });
+            return;
+          }
         }
 
         const doneFiles = await collectDoneRangeFiles(diffSpec.range, rootDir).catch(() => []);
@@ -836,13 +871,29 @@ export function registerSessionDiffRoutes(router: Router, deps: SessionDiffRoute
         const rootDir = scopedStore.getRootDir();
         const sha = resolvedMergeSha;
 
-        let diffSpec: Awaited<ReturnType<typeof resolveCommitDiffSpec>>;
+        let diffSpec: Awaited<ReturnType<typeof resolveCommitDiffSpec>> | { mode: "rebase-range"; base: string; range: string };
+        const rebaseBaseSha = task.mergeDetails?.rebaseBaseSha?.trim();
 
-        try {
-          diffSpec = await resolveCommitDiffSpec(sha, rootDir);
-        } catch {
-          res.json([]);
-          return;
+        if (rebaseBaseSha) {
+          const rebaseDiffSpec = await resolveRebaseDiffSpec(rebaseBaseSha, sha, rootDir);
+          if (rebaseDiffSpec) {
+            diffSpec = rebaseDiffSpec;
+          } else {
+            console.warn(`[file-diffs] done task ${task.id}: mergeDetails.rebaseBaseSha ${rebaseBaseSha} is not ancestor of ${sha}; falling back to single-commit diff`);
+            try {
+              diffSpec = await resolveCommitDiffSpec(sha, rootDir);
+            } catch {
+              res.json([]);
+              return;
+            }
+          }
+        } else {
+          try {
+            diffSpec = await resolveCommitDiffSpec(sha, rootDir);
+          } catch {
+            res.json([]);
+            return;
+          }
         }
 
         try {