fix(extraction): index nested repos recorded as gitlinks (#1031, #1033) (#1038)

A nested git repo tracked as a gitlink (mode 160000) — a clone `git add`ed
into the super-repo without a `.gitmodules` entry, or a submodule that
isn't active/initialized in this checkout — fell through both file-collection
passes: it's tracked, so the untracked `-o` listing skips it, but it's not
an active submodule, so `--recurse-submodules` won't expand it. Indexing the
top level therefore pulled in only the outer repo's own files and stopped at
the nested repo's boundary (one report: ~10 files at the root).

Switch the tracked scan to `ls-files -s` to expose file modes, collect the
unexpanded 160000 entries, and recurse into each that has a real working tree
on disk as its own embedded repo. Mirror the same discovery in
discoverEmbeddedRepoRoots so the watcher's scope stays equal to the indexer's.

Active submodules (#147) and untracked nested clones (#193) are unchanged;
gitlinks under default-ignored dirs (vendor/, node_modules/) stay excluded
(#407); an uninitialized submodule with no checkout on disk is left alone.
Adds four-shape coverage in extraction.test.ts.

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

CHANGELOG.md

@@ -9,6 +9,10 @@ and adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased]
 
+### Fixes
+
+- CodeGraph now indexes nested repositories that git records as gitlinks, so a workspace built by stacking several repos inside one another indexes completely from a single `codegraph init` at the top. When a repo contains another git repo that was `git add`ed into it — so git tracks it as a `160000` "commit" pointer rather than a folder of files — or a submodule that isn't an active, initialized submodule in your checkout, that nested repo's source used to be skipped entirely: indexing the top level stopped at the nested repo's boundary and pulled in only the outer repo's own files, so a stacked-repo project came up nearly empty (one report saw ~10 files indexed at the root). CodeGraph now descends into each such nested repo that has a real working tree on disk and indexes it as its own embedded repository, recursively, so every layer of a stacked workspace is covered. Active submodules (already handled) and plain untracked nested clones are unchanged; a nested repo under a dependency directory such as `vendor/` or `node_modules/` stays excluded; and a submodule with nothing checked out on disk is correctly left alone rather than reported as empty. Thanks @ofergr and @kun-yx for the reports. (#1031, #1033)
+
 
 ## [1.1.2] - 2026-06-28