windows-compat

# Windows compatibility (code-graph-mcp) Three defects reached a Windows user from **one** root cause: two spellings of the same path compared unequal. CI already ran `windows-latest` and caught none of them, because nothing asserted on path spellings at all. Closing that gap is what this skill is for. ## The invariant everything hangs off `indexer::merkle::normalize_rel_path` stores every indexed path as a **`/`-separated relative path**, rewriting separators only under `#[cfg(windows)]`. So any path that becomes a lookup key, a dedup key, or stdout must land in *exactly* that spelling. Almost every defect below is one producer handing over a different spelling of the same file. The producer table and the full catalogue are in [references/failure-modes.md](references/failure-modes.md) — read it before changing path-handling code. It is short and every entry is a real defect with its shipped fix. ## The doctrine: platform is a parameter, not a `cfg!` This is the single rule that makes everything else testable. ```rust // NO — the Windows branch only runs on Windows, so the Linux and macOS legs // prove nothing, and a Windows-only CI failure is expensive to debug. fn normalize(path: &str) -> String { if cfg!(windows) { path.replace('\\', "/") } else { path.into() } } // YES — one thin cfg! entry point, all logic in a function taking the platform. fn normalize(path: &str) -> String { normalize_on(path, cfg!(windows)) } fn normalize_on(path: &str, backslash_is_se...