Fix ambiguous git worktree start points

apps/server/src/vcs/GitVcsDriverCore.test.ts

@@ -310,6 +310,49 @@ it.layer(TestLayer)("GitVcsDriver core integration", (it) => {
         assert.equal(yield* fileSystem.exists(worktreePath), false);
       }),
     );
+
+    it.effect("creates a new worktree when the base branch name is also a remote ref", () =>
+      Effect.gen(function* () {
+        const cwd = yield* makeTmpDir();
+        const remote = yield* makeTmpDir("git-vcs-driver-remote-");
+        const { initialBranch } = yield* initRepoWithCommit(cwd);
+        const pathService = yield* Path.Path;
+        const worktreePath = pathService.join(
+          yield* makeTmpDir("git-worktrees-"),
+          "feature-ambiguous-worktree",
+        );
+        const driver = yield* GitVcsDriver.GitVcsDriver;
+
+        yield* git(remote, ["init", "--bare"]);
+        yield* git(cwd, ["remote", "add", initialBranch, remote]);
+        yield* git(cwd, ["push", initialBranch, `${initialBranch}:${initialBranch}`]);
+        yield* git(cwd, [
+          "fetch",
+          initialBranch,
+          `${initialBranch}:refs/remotes/${initialBranch}/${initialBranch}`,
+        ]);
+
+        const refs = yield* git(cwd, ["show-ref", initialBranch]);
+        assert.include(refs, `refs/heads/${initialBranch}`);
+        assert.include(refs, `refs/remotes/${initialBranch}/${initialBranch}`);
+
+        const created = yield* driver.createWorktree({
+          cwd,
+          path: worktreePath,
+          refName: initialBranch,
+          newRefName: "feature/ambiguous-worktree",
+        });
+
+        assert.equal(created.worktree.path, worktreePath);
+        assert.equal(created.worktree.refName, "feature/ambiguous-worktree");
+        assert.equal(
+          yield* git(worktreePath, ["branch", "--show-current"]),
+          "feature/ambiguous-worktree",
+        );
+
+        yield* driver.removeWorktree({ cwd, path: worktreePath });
+      }),
+    );
   });
 
   describe("commit context", () => {

apps/server/src/vcs/GitVcsDriverCore.ts

@@ -992,6 +992,35 @@ export const makeGitVcsDriverCore = Effect.fn("makeGitVcsDriverCore")(function*
       Effect.map(parseRemoteNamesInGitOrder),
     );
 
+  const qualifyWorktreeStartPoint = Effect.fn("qualifyWorktreeStartPoint")(function* (
+    cwd: string,
+    refName: string,
+  ) {
+    if (refName.startsWith("refs/")) {
+      return refName;
+    }
+
+    const isLocalBranch = yield* branchExists(cwd, refName);
+    if (isLocalBranch) {
+      return `refs/heads/${refName}`;
+    }
+
+    const remoteNames = yield* listRemoteNames(cwd).pipe(Effect.catch(() => Effect.succeed([])));
+    const parsedRemoteRef = parseRemoteRefWithRemoteNames(refName, remoteNames);
+    if (parsedRemoteRef) {
+      const isRemoteBranch = yield* remoteBranchExists(
+        cwd,
+        parsedRemoteRef.remoteName,
+        parsedRemoteRef.branchName,
+      );
+      if (isRemoteBranch) {
+        return `refs/remotes/${parsedRemoteRef.remoteName}/${parsedRemoteRef.branchName}`;
+      }
+    }
+
+    return refName;
+  });
+
   const resolvePublishBranchName = Effect.fn("resolvePublishBranchName")(function* (
     cwd: string,
     branchName: string,
@@ -2063,9 +2092,10 @@ export const makeGitVcsDriverCore = Effect.fn("makeGitVcsDriverCore")(function*
     const sanitizedBranch = targetBranch.replace(/\//g, "-");
     const repoName = path.basename(input.cwd);
     const worktreePath = input.path ?? path.join(worktreesDir, repoName, sanitizedBranch);
+    const startPoint = yield* qualifyWorktreeStartPoint(input.cwd, input.refName);
     const args = input.newRefName
-      ? ["worktree", "add", "-b", input.newRefName, worktreePath, input.refName]
-      : ["worktree", "add", worktreePath, input.refName];
+      ? ["worktree", "add", "-b", input.newRefName, worktreePath, startPoint]
+      : ["worktree", "add", worktreePath, startPoint];
 
     yield* executeGit("GitVcsDriver.createWorktree", input.cwd, args, {
       fallbackErrorMessage: "git worktree add failed",