programs.vscode.profiles.<name>.userSettings accepts either JSON settings or a path to a settings.json file. The update-check defaults were merged into userSettings before deciding whether to generate JSON or link a source file, so path values failed when Nix tried to apply // to them.
Skip those merges for path-like values and use the shared isPathLike helper for VS Code's source-or-generated JSON options so Nix paths, store path strings, and derivation outputs are handled consistently.
Fixes#7726
f96f717a47