fix(rollup): discover git worktrees - .git tested for existence, not directory-ness

The catalog half of a shared gap that was previously PINNED rather than fixed.
This reader of ~/repos tested `.git` with a directory check, so a plain
`git worktree add ~/repos/feature-x` produced a depth-1 sibling that can carry
its own STATE.md and was dropped SILENTLY - no warning, no count,
indistinguishable from a repo with nothing to say. A submodule fails the same
way for the same reason.

It was pinned, not fixed, because diverging would break the very
same-name-from-both-readers invariant discoverRepos exists to hold. ~/repos
answered YES to the gated question and reported their half landed. Verified
here rather than taken on report: board.sh's Discovery block tests `-e`, and
has done since board.sh was introduced (repo-mailbox 61e224c, first released
v0.9.0) - so the released reader has no `-d` era at all, and only this side
was ever the outlier. The two move together from here - change one, change the
other.

THE ACCEPTANCE TRAP, MEASURED RATHER THAN ASSUMED. This changes NO number
against real ~/repos. Old and new builders were run back to back against the
live tree and diffed: stdout and stderr byte-identical, both exit 0. Directly
measured why: 0 directories at depth 1 or 2 currently carry .git as a file.
A number standing still is not ambiguous here, it is the ONLY possible outcome,
and it is why a fixture is not the best way to test this but the only way.

FIXTURE GATED BEFORE BEHAVIOUR. The worktree fixture uses a real `git worktree
add`, not a hand-written `.git` file - faking it would assert against our guess
at git's on-disk format instead of against git. A separate test asserts the
fixture itself: .git exists, is a file, is not a directory. Without it, the day
git stops writing worktree .git as a file the behaviour tests would go green
while measuring nothing, and a green run cannot distinguish that from success.
The gate says which one it was, and says the premise of the -e rule is gone
rather than inviting a test tweak.

Two behaviour tests: a worktree at depth 1, and one under a polyrepo container
at depth 2 - the same rule at both depths board.sh walks.

Suite 90/90 across the six files (rollup 31 -> 34). check-versions 11 OK,
0 WARN, 0 ERROR. Real run unchanged at 8 repos, 17 markers, Output B 0 lines,
1 V6 warning, exit 0.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01KSX2v1m7Fz22BKrGJZuUpQ

scripts/build-rollup-register.mjs

@@ -207,13 +207,20 @@ export function buildRegister({ repos }) {
 //
 // Not descending into a git repo also makes the known nested-name trap
 // (claude-code-100x/claude-code-100x, both git repos) structurally unreachable rather than
-// merely absent. SHARED, DELIBERATE GAP: like board.sh, "is a repo" means `.git` is a
+// merely absent.
-// DIRECTORY, so a git worktree or submodule (where `.git` is a file) is not seen by either
+//
-// reader. Pinned here rather than fixed one-sidedly — diverging would break the very
+// "Is a repo" tests `.git` for EXISTENCE, not directory-ness: a worktree or submodule has
-// same-name-from-both-readers invariant this function exists to hold.
+// `.git` as a FILE. A plain `git worktree add ~/repos/feature-x` lands a depth-1 sibling
+// that can carry its own STATE.md, and a directory test dropped it SILENTLY — no warning,
+// no count, indistinguishable from a repo with nothing to say. This was pinned rather than
+// fixed one-sidedly because diverging would break the very same-name-from-both-readers
+// invariant this function exists to hold. board.sh's side is in place — MEASURED, not
+// reported: its Discovery block tests `-e`, and has since board.sh was introduced
+// (repo-mailbox 61e224c, first released v0.9.0). This is the other half. The two move
+// together or not at all — change one, change the other.
 function isGitRepo(dir) {
   const dotGit = join(dir, '.git');
-  return existsSync(dotGit) && statSync(dotGit).isDirectory();
+  return existsSync(dotGit);
 }
 
 function subdirs(dir) {

scripts/build-rollup-register.test.mjs

@@ -11,7 +11,8 @@
 // and to make the V4 "no em-dash in carrier" axis unambiguous.
 import { test } from 'node:test';
 import assert from 'node:assert/strict';
-import { mkdtempSync, mkdirSync, writeFileSync } from 'node:fs';
+import { mkdtempSync, mkdirSync, writeFileSync, statSync, existsSync } from 'node:fs';
+import { execFileSync } from 'node:child_process';
 import { join } from 'node:path';
 import { tmpdir } from 'node:os';
 import {
@@ -350,3 +351,80 @@ test('D1: a basename collision fails LOUDLY instead of silently overwriting', ()
     'two STATE.md files resolving to one name must stop the build',
   );
 });
+
+// --- D1 discovery: git worktrees, where .git is a FILE and not a directory -------------
+// Closes a gap that was previously PINNED rather than fixed: both readers tested `.git`
+// with a directory check, so `git worktree add ~/repos/feature-x` produced a depth-1
+// sibling that can carry its own STATE.md and was dropped SILENTLY here. board.sh's
+// Discovery block tests `-e` (measured: repo-mailbox 61e224c, first released v0.9.0); this
+// is the catalog half. Diverging would break the one invariant the mirroring exists to
+// hold, so the two move together or not at all.
+//
+// This cannot be faked with mkdirSync: a fixture that writes `.git` as a file by hand
+// would assert against our own guess at git's on-disk format rather than against git.
+// Hence a REAL `git worktree add` -- and hence the fixture gate below.
+function gitWorktreeTree() {
+  const root = mkdtempSync(join(tmpdir(), 'rollup-worktree-'));
+  const main = join(root, 'main');
+  mkdirSync(main, { recursive: true });
+  const git = (args, cwd) => execFileSync('git', args, { cwd, stdio: 'pipe' });
+  git(['init', '-q', '-b', 'main'], main);
+  git(['config', 'user.email', 'test@example.invalid'], main);
+  git(['config', 'user.name', 'test'], main);
+  writeFileSync(join(main, 'seed.txt'), 'seed\n');
+  git(['add', 'seed.txt'], main);
+  git(['commit', '-q', '-m', 'seed'], main);
+  // A worktree needs a commit to attach to, which is why the seed above exists.
+  const worktree = join(root, 'feature-x');
+  git(['worktree', 'add', '-q', '-b', 'feature-x', worktree], main);
+  writeFileSync(join(main, 'STATE.md'), MARKER);
+  writeFileSync(join(worktree, 'STATE.md'), MARKER);
+  return { root, main, worktree };
+}
+
+test('D1 fixture gate: git really does write a worktree .git as a FILE', () => {
+  // Gate the fixture BEFORE gating the behaviour. Without this, the day git starts
+  // writing worktree `.git` as a directory, the test below would go green while
+  // measuring nothing -- passing for the wrong reason is the failure mode that a
+  // green run cannot distinguish from success. This assertion says which one it was.
+  const { worktree } = gitWorktreeTree();
+  const dotGit = join(worktree, '.git');
+  assert.ok(existsSync(dotGit), 'a worktree must carry a .git entry at all');
+  assert.ok(
+    statSync(dotGit).isFile(),
+    'git no longer writes a worktree .git as a file -- the premise of the -e rule is gone, '
+      + 'and both this builder and board.sh need re-deciding, not a test tweak',
+  );
+  assert.ok(!statSync(dotGit).isDirectory(), 'a file and a directory must not both be true');
+});
+
+test('D1: a git worktree at depth 1 is discovered (.git is a file, not a directory)', () => {
+  const { root } = gitWorktreeTree();
+  const repos = discoverRepos(root);
+  assert.deepEqual(
+    repos.map((r) => r.name).sort(),
+    ['feature-x', 'main'],
+    'the worktree carries its own STATE.md and must not be dropped for having a .git FILE',
+  );
+});
+
+test('D1: a git worktree under a polyrepo container (depth 2) is discovered', () => {
+  // Same rule at the depth board.sh also walks: a container is not itself a repo, so a
+  // worktree parked inside one is reached by the same child pass as an ordinary repo.
+  const { root, main, worktree } = gitWorktreeTree();
+  const outer = mkdtempSync(join(tmpdir(), 'rollup-worktree-outer-'));
+  const container = join(outer, 'container');
+  mkdirSync(container, { recursive: true });
+  execFileSync('git', ['worktree', 'add', '-q', '-b', 'nested-x', join(container, 'nested-x')], {
+    cwd: main,
+    stdio: 'pipe',
+  });
+  writeFileSync(join(container, 'nested-x', 'STATE.md'), MARKER);
+  assert.ok(statSync(join(container, 'nested-x', '.git')).isFile(), 'fixture gate: .git is a file');
+  assert.deepEqual(
+    discoverRepos(outer).map((r) => r.name),
+    ['nested-x'],
+    'a container holding only a worktree still contributes that worktree',
+  );
+  assert.ok(existsSync(join(root, 'main')) && existsSync(worktree), 'fixture roots intact');
+});