feat(git): per-key cache invalidation and optional submodule tracking

test/git/helpers.lua

@@ -73,4 +73,25 @@ function M.make_repo(files, opts)
     return dir
 end
 
+---Build an outer repo with one nested submodule at `sub/`. Both the
+---outer and inner repo are committed and registered for cleanup.
+---@return string outer
+---@return string inner
+function M.make_submodule_repo()
+    local inner = M.make_repo({ a = "x\n" })
+    local outer = M.make_repo({ x = "x\n" })
+    vim.system({
+        "git",
+        "-c",
+        "protocol.file.allow=always",
+        "submodule",
+        "add",
+        "--quiet",
+        inner,
+        "sub",
+    }, { cwd = outer, text = true }):wait()
+    M.git(outer, "commit", "-q", "-m", "add submodule")
+    return outer, inner
+end
+
 return M