feat(FN-4476): complete Step 2 — add patch-id unique commit helper

Fusion-Task-Id: FN-4476
Fusion-Task-Lineage: 8673c1d9-f47e-4d02-89e6-646040b9be32

packages/engine/src/__tests__/branch-conflicts.test.ts

@@ -48,6 +48,7 @@ import {
   assertCleanBranchAtBase,
   inspectBranchConflict,
   listBranchRecoveryCandidates,
+  listUniqueBranchCommits,
 } from "../branch-conflicts.js";
 
 const mockedExecSync = vi.mocked(execSync);
@@ -185,6 +186,92 @@ describe("branch-conflicts", () => {
     expect(result.error.message).toContain("Run branch recovery");
   });
 
+  it("lists zero unique commits when git cherry has no plus entries", async () => {
+    mockedExecSync.mockImplementation((cmd: string | string[]) => {
+      const command = typeof cmd === "string" ? cmd : cmd[0];
+      if (command.includes("git rev-parse --verify 'main^{commit}'")) {
+        return Buffer.from("mainsha\n");
+      }
+      if (command === "git merge-base 'main' 'fusion/fn-4068'") {
+        return Buffer.from("base123\n");
+      }
+      if (command === "git cherry 'main' 'fusion/fn-4068' 'base123'") {
+        return Buffer.from("- abc111\n");
+      }
+      throw new Error(`Unexpected command: ${command}`);
+    });
+
+    const result = await listUniqueBranchCommits("/tmp/repo", "main", "fusion/fn-4068");
+
+    expect(result).toEqual({ commits: [], mainRef: "main", degraded: false });
+  });
+
+  it("lists patch-id-unique commits from git cherry plus lines", async () => {
+    mockedExecSync.mockImplementation((cmd: string | string[]) => {
+      const command = typeof cmd === "string" ? cmd : cmd[0];
+      if (command.includes("git rev-parse --verify 'main^{commit}'")) {
+        return Buffer.from("mainsha\n");
+      }
+      if (command === "git merge-base 'main' 'fusion/fn-4068'") {
+        return Buffer.from("base123\n");
+      }
+      if (command === "git cherry 'main' 'fusion/fn-4068' 'base123'") {
+        return Buffer.from("+ abc111\n+ def222\n");
+      }
+      if (command.includes("git rev-parse --verify 'abc111^{commit}'")) {
+        return Buffer.from("abc111full\n");
+      }
+      if (command.includes("git rev-parse --verify 'def222^{commit}'")) {
+        return Buffer.from("def222full\n");
+      }
+      if (command === "git log -1 --format=%s 'abc111'") {
+        return Buffer.from("First unique\n");
+      }
+      if (command === "git log -1 --format=%s 'def222'") {
+        return Buffer.from("Second unique\n");
+      }
+      throw new Error(`Unexpected command: ${command}`);
+    });
+
+    const result = await listUniqueBranchCommits("/tmp/repo", "main", "fusion/fn-4068");
+
+    expect(result).toEqual({
+      commits: [
+        { sha: "abc111full", subject: "First unique" },
+        { sha: "def222full", subject: "Second unique" },
+      ],
+      mainRef: "main",
+      degraded: false,
+    });
+  });
+
+  it("falls back to rev-list stranded commits when git cherry fails", async () => {
+    mockedExecSync.mockImplementation((cmd: string | string[]) => {
+      const command = typeof cmd === "string" ? cmd : cmd[0];
+      if (command.includes("git rev-parse --verify 'main^{commit}'")) {
+        return Buffer.from("mainsha\n");
+      }
+      if (command === "git merge-base 'main' 'fusion/fn-4068'") {
+        return Buffer.from("base123\n");
+      }
+      if (command === "git cherry 'main' 'fusion/fn-4068' 'base123'") {
+        throw new Error("cherry failed");
+      }
+      if (command.includes("git log --reverse --format=%H%x09%s 'main..fusion/fn-4068'")) {
+        return Buffer.from("aaa111\tFallback one\n");
+      }
+      throw new Error(`Unexpected command: ${command}`);
+    });
+
+    const result = await listUniqueBranchCommits("/tmp/repo", "main", "fusion/fn-4068");
+
+    expect(result).toEqual({
+      commits: [{ sha: "aaa111", subject: "Fallback one" }],
+      mainRef: "main",
+      degraded: true,
+    });
+  });
+
   it("assertCleanBranchAtBase passes when no foreign task commits exist", async () => {
     mockedExecSync.mockImplementation((cmd: string | string[]) => {
       const command = typeof cmd === "string" ? cmd : cmd[0];

packages/engine/src/branch-conflicts.ts

@@ -104,6 +104,12 @@ export type BranchConflictInspectionResult =
   | { kind: "reclaimable"; livePath: string; tipSha: string; taskAttributedCommitCount: number; strandedCommits: BranchConflictCommit[] }
   | { kind: "live-foreign"; livePath: string; error: BranchConflictError };
 
+interface UniqueBranchCommitListResult {
+  commits: BranchConflictCommit[];
+  mainRef: string;
+  degraded: boolean;
+}
+
 export interface ListBranchRecoveryCandidatesInput {
   repoDir: string;
   branchName: string;
@@ -148,6 +154,58 @@ async function listStrandedCommits(repoDir: string, startPoint: string, branchNa
   }
 }
 
+async function resolveBranchComparisonRef(repoDir: string, startPoint: string, branchName: string): Promise<string> {
+  try {
+    await revParse(repoDir, startPoint);
+    await runGit(repoDir, `git merge-base ${quoteShellArg(startPoint)} ${quoteShellArg(branchName)}`);
+    return startPoint;
+  } catch {
+    return "main";
+  }
+}
+
+export async function listUniqueBranchCommits(
+  repoDir: string,
+  startPoint: string,
+  branchName: string,
+): Promise<UniqueBranchCommitListResult> {
+  const mainRef = await resolveBranchComparisonRef(repoDir, startPoint, branchName);
+  try {
+    const comparisonBase = await runGit(repoDir, `git merge-base ${quoteShellArg(mainRef)} ${quoteShellArg(branchName)}`);
+    const cherryOutput = await runGit(
+      repoDir,
+      `git cherry ${quoteShellArg(mainRef)} ${quoteShellArg(branchName)} ${quoteShellArg(comparisonBase)}`,
+    );
+    const plusTokens = cherryOutput
+      .split("\n")
+      .map((line) => line.trim())
+      .filter((line) => line.startsWith("+ "))
+      .map((line) => line.slice(2).trim())
+      .filter(Boolean);
+
+    const commits: BranchConflictCommit[] = [];
+    for (const token of plusTokens) {
+      const [sha, subject] = await Promise.all([
+        runGit(repoDir, `git rev-parse --verify ${quoteShellArg(`${token}^{commit}`)}`).catch(() => token),
+        runGit(repoDir, `git log -1 --format=%s ${quoteShellArg(token)}`).catch(() => ""),
+      ]);
+      commits.push({ sha, subject });
+    }
+
+    return {
+      commits,
+      mainRef,
+      degraded: false,
+    };
+  } catch {
+    return {
+      commits: await listStrandedCommits(repoDir, mainRef, branchName),
+      mainRef,
+      degraded: true,
+    };
+  }
+}
+
 async function getWorktreeBranchMap(repoDir: string): Promise<Map<string, string>> {
   const output = await runGit(repoDir, "git worktree list --porcelain");
   const map = new Map<string, string>();