fix(init): surface and offer to opt in gitignored child repos on an empty index (#1156) (#1208)

A Git super-repo whose `.gitignore` excludes its child repositories indexed
~nothing at the parent: CodeGraph respects `.gitignore` by default (#970,
#1065), so the excluded children were skipped and `codegraph init` printed
"Done" with 0 nodes — even though `init` inside each child worked fine. The
empty index was silent and unexplained.

`init`/`index` now detect the gitignored child repos they skipped when an
index comes up empty of symbols, name them, and — in an interactive terminal
— offer to index them (writing an `includeIgnored` entry to codegraph.json and
re-indexing on the spot); non-interactive runs print the exact codegraph.json
snippet to add. Gated on nodesCreated === 0, so a project that deliberately
keeps gitignored reference clones out of a working index is never nagged.

- extraction: findUnindexedIgnoredRepos — the inverse of discoverEmbeddedRepoRoots
  (bounded, skips default-ignored dirs, respects existing includeIgnored)
- project-config: addIncludeIgnoredPatterns — create/merge codegraph.json,
  idempotent, refuses to clobber malformed JSON
- cli: wire the detect-name-offer flow into both `init` and `index`
- tests: +13 covering detection, config writing, and the no-nag gate

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

__tests__/multi-repo-workspace.test.ts

@@ -26,7 +26,7 @@ import * as path from 'path';
 import * as os from 'os';
 import { execFileSync } from 'child_process';
 import CodeGraph from '../src/index';
-import { scanDirectory, buildScopeIgnore, discoverEmbeddedRepoRoots } from '../src/extraction';
+import { scanDirectory, buildScopeIgnore, discoverEmbeddedRepoRoots, findUnindexedIgnoredRepos } from '../src/extraction';
 import { clearProjectConfigCache } from '../src/project-config';
 
 function git(cwd: string, ...args: string[]): void {
@@ -361,4 +361,81 @@ describe('multi-repo workspaces (#514) + .gitignore-respect default (#970, #976)
       expect(discoverEmbeddedRepoRoots(child)).toEqual([]);
     });
   });
+
+  describe('findUnindexedIgnoredRepos: the skipped-child-repos hint (#1156)', () => {
+    // The reported layout: a super-repo whose `.gitignore` excludes its child
+    // repos, so `init` at the parent correctly indexes ~nothing. This detector
+    // is the inverse of `discoverEmbeddedRepoRoots` — it names exactly the repos
+    // the default scan skipped so the CLI can offer to opt them in.
+    it('names the gitignored child repos a default index skipped', () => {
+      write(path.join(ws, 'mtc-activity/src/a.ts'), 'export const a = 1;\n');
+      write(path.join(ws, 'mtc-admin/src/b.ts'), 'export const b = 2;\n');
+      makeRepo(path.join(ws, 'mtc-activity'));
+      makeRepo(path.join(ws, 'mtc-admin'));
+      write(path.join(ws, '.gitignore'), 'mtc-*/\n');
+      write(path.join(ws, 'AGENTS.md'), '# docs\n');
+      makeRepo(ws);
+
+      // Nothing of the child repos indexes by default — the symptom being fixed.
+      expect(scanDirectory(ws).some((f) => f.startsWith('mtc-'))).toBe(false);
+      // ...but the detector names them (trailing-slashed, valid includeIgnored patterns).
+      expect(findUnindexedIgnoredRepos(ws).sort()).toEqual(['mtc-activity/', 'mtc-admin/']);
+    });
+
+    it('excludes repos already opted in via includeIgnored (only the rest remain)', () => {
+      write(path.join(ws, 'mtc-activity/src/a.ts'), 'export const a = 1;\n');
+      write(path.join(ws, 'mtc-admin/src/b.ts'), 'export const b = 2;\n');
+      makeRepo(path.join(ws, 'mtc-activity'));
+      makeRepo(path.join(ws, 'mtc-admin'));
+      write(path.join(ws, '.gitignore'), 'mtc-*/\n');
+      writeConfig({ includeIgnored: ['mtc-activity/'] });
+      makeRepo(ws);
+
+      expect(findUnindexedIgnoredRepos(ws)).toEqual(['mtc-admin/']);
+    });
+
+    it('returns [] when every gitignored repo is already opted in (nothing to nag)', () => {
+      write(path.join(ws, 'pkgs/a/src/a.ts'), 'export const a = 1;\n');
+      makeRepo(path.join(ws, 'pkgs/a'));
+      write(path.join(ws, '.gitignore'), '/pkgs/\n');
+      writeConfig({ includeIgnored: ['pkgs/'] });
+      makeRepo(ws);
+
+      expect(findUnindexedIgnoredRepos(ws)).toEqual([]);
+    });
+
+    it('does NOT report nested repos that are NOT gitignored (they already index)', () => {
+      // Scenario A: an untracked, non-ignored nested repo is indexed via the
+      // untracked-embedded path, so there is nothing to hint about.
+      write(path.join(ws, 'sub/src/a.ts'), 'export const a = 1;\n');
+      makeRepo(path.join(ws, 'sub'));
+      write(path.join(ws, 'app.ts'), 'export const app = 0;\n');
+      makeRepo(ws); // sub/ stays untracked, not ignored
+
+      expect(findUnindexedIgnoredRepos(ws)).toEqual([]);
+    });
+
+    it('skips a gitignored node_modules even when it holds a git repo', () => {
+      write(path.join(ws, 'node_modules/dep/index.js'), 'module.exports = 1;\n');
+      makeRepo(path.join(ws, 'node_modules/dep'));
+      write(path.join(ws, '.gitignore'), 'node_modules/\n');
+      makeRepo(ws);
+
+      expect(findUnindexedIgnoredRepos(ws)).toEqual([]);
+    });
+
+    it('finds repos nested inside a gitignored data dir, not just top-level ones', () => {
+      write(path.join(ws, 'refs/lib-a/x.ts'), 'export const x = 1;\n');
+      makeRepo(path.join(ws, 'refs/lib-a'));
+      write(path.join(ws, '.gitignore'), '/refs/\n');
+      makeRepo(ws);
+
+      expect(findUnindexedIgnoredRepos(ws)).toEqual(['refs/lib-a/']);
+    });
+
+    it('returns [] for a non-git directory', () => {
+      write(path.join(ws, 'a.ts'), 'export const a = 1;\n'); // no git init at all
+      expect(findUnindexedIgnoredRepos(ws)).toEqual([]);
+    });
+  });
 });