fix(git): the branch switcher lists and checks out branches only the remote has

GET /api/lanes/:id/git/branches read only refs/heads, so a branch someone
else pushed never showed after a fetch or pull, and `switch` refused it
(ENOBRANCH). It now also returns `remotes`: fetched remote-tracking branches
with no local branch of that name (origin/HEAD left out), listed under
"On the remote"; switching to one runs `git switch -c <b> --track
refs/remotes/<remote>/<b>` with the remote ref looked up, never passed
through (bare name only when exactly one remote has it, else EAMBIGUOUS).
The bar also re-reads the branch list after a fetch or pull instead of
keeping the list it loaded first.

server/__tests__/git-diff-ops.test.js

@@ -138,7 +138,10 @@ describe("collectChanges — work range", () => {
     const out = await collectChanges(LANE, { range: "work" });
     // `--untracked-files=normal` folded these into one "docs/" row that
     // opened nothing; the panel needs the files, like JetBrains and VS Code.
-    assert.deepEqual(out.files.map((f) => f.path).sort(), ["docs/deep/notes.txt", "docs/report.md"]);
+    assert.deepEqual(out.files.map((f) => f.path).sort(), [
+      "docs/deep/notes.txt",
+      "docs/report.md",
+    ]);
     assert.ok(out.files.every((f) => f.untracked && f.added === 1));
     assert.equal((await gitFacts(LANE)).untracked, 2);
   });
@@ -244,10 +247,7 @@ describe("collectChanges — branch range", () => {
 
   it("falls back to the default branch without a base, and refuses a base that is gone", async () => {
     // No recorded base (an adopted folder): what origin/HEAD names.
-    assert.equal(
-      (await collectChanges(LANE, { range: "branch", base: null })).base,
-      "development"
-    );
+    assert.equal((await collectChanges(LANE, { range: "branch", base: null })).base, "development");
     await assert.rejects(() => collectChanges(LANE, { range: "branch", base: "nope" }), {
       code: "ENOBASE",
     });
@@ -374,6 +374,48 @@ describe("runGitAction", () => {
     });
   });
 
+  it("lists a branch only the remote has after a fetch, and switching tracks it", async () => {
+    const { listRemoteBranches } = require("../lib/worktree");
+    // Someone else pushes a new branch; this clone has never seen it.
+    gc(OTHER, "checkout", "-qb", "feat/remote-only");
+    write(OTHER, "r.txt", "remote\n");
+    gc(OTHER, "add", "-A");
+    gc(OTHER, "commit", "-qm", "remote work");
+    gc(OTHER, "push", "-q", "origin", "feat/remote-only");
+    assert.equal(
+      (await listRemoteBranches(LANE)).some((r) => r.name === "origin/feat/remote-only"),
+      false
+    );
+    await runGitAction(LANE, "fetch");
+    const remote = await listRemoteBranches(LANE);
+    assert.ok(remote.some((r) => r.name === "origin/feat/remote-only"));
+    // origin/HEAD and branches that already have a local one are left out.
+    assert.ok(!remote.some((r) => r.branch === "HEAD" || r.branch === "development"));
+
+    const result = await runGitAction(LANE, "switch", { branch: "origin/feat/remote-only" });
+    assert.equal(result.branch, "feat/remote-only");
+    assert.equal(g(LANE, "rev-parse", "--abbrev-ref", "HEAD").trim(), "feat/remote-only");
+    assert.equal(
+      g(LANE, "rev-parse", "--abbrev-ref", "--symbolic-full-name", "@{upstream}").trim(),
+      "origin/feat/remote-only"
+    );
+    assert.ok(!(await listRemoteBranches(LANE)).some((r) => r.branch === "feat/remote-only"));
+    gc(LANE, "checkout", "-q", "development");
+  });
+
+  it("switches to a bare remote branch name when exactly one remote has it", async () => {
+    gc(OTHER, "checkout", "-qb", "feat/bare");
+    gc(OTHER, "push", "-q", "origin", "feat/bare");
+    await runGitAction(LANE, "fetch");
+    const result = await runGitAction(LANE, "switch", { branch: "feat/bare" });
+    assert.equal(result.branch, "feat/bare");
+    assert.equal(
+      g(LANE, "rev-parse", "--abbrev-ref", "--symbolic-full-name", "@{upstream}").trim(),
+      "origin/feat/bare"
+    );
+    gc(LANE, "checkout", "-q", "development");
+  });
+
   it("refuses a branch another worktree holds", async () => {
     const wt = path.join(ROOT, "sibling");
     g(LANE, "worktree", "add", "-q", wt, "development");

server/__tests__/lanes-api.test.js

@@ -1122,6 +1122,7 @@ describe("the lane git surface: changes, branches, actions (issue #34)", () => {
     const r = await request("GET", `/api/lanes/${laneId}/git/branches`);
     assert.equal(r.status, 200);
     assert.deepEqual(r.body.branches, ["feat/api-changes"]);
+    assert.deepEqual(r.body.remotes, []); // no remote at all
     assert.equal(r.body.current, "feat/api-changes");
   });