docs(changelog): note the sync cross-file caller-edge fix (#899)

PR #927 (merged to main) fixed `sync()` dropping incoming cross-file
calls/references edges on callee re-index but did not add a CHANGELOG
entry; add it to [Unreleased] so it lands in the next release notes.

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

CHANGELOG.md

@@ -32,6 +32,7 @@ and adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 - React components declared with `forwardRef`, `memo`, or styled-components / emotion (`const Button = forwardRef(...)`, `const Card = memo(...)`, `const Box = styled.button\`…\``) are now recognized as components, so finding where they're used works. Before, they were indexed as plain constants, so `codegraph callers` and impact analysis reported "no callers found" even when the component was rendered across dozens of files — a dangerous false "safe to change" right before refactoring a shared component. Now every `<Button/>` usage links back to the component, so callers and blast radius are complete. This is the standard shadcn/ui declaration style, so for typical React design systems the whole UI layer is no longer invisible to impact analysis. Thanks @Arlandaren for the report and @maxmilian for the root-cause. (#841)
 - React Router and Next.js routes defined in `.tsx` / `.jsx` files are now indexed. Routes written as JSX — `<Route path="/users" element={<UsersPage/>}/>`, `createBrowserRouter([...])`, and Next.js `app/`/`pages/` page files — were being skipped entirely (only routes that happened to live in plain `.ts`/`.js` were picked up), so "what renders at this path?" and the route → page-component link were missing for most React apps. Now those routes show up in `codegraph search`/`codegraph_explore` and connect to the component they render, just like the backend route → handler links on other frameworks.
+- `codegraph sync` (and the file-watcher auto-sync behind always-on / MCP use) no longer drops a function's callers when you edit the file that function lives in. Re-indexing a file after an edit — even a docstring-only change — was severing the `calls` / `references` edges coming from *other, unchanged* files (e.g. `from pkg import mod; mod.fn()` callers, or any cross-file reference), so `codegraph callers` / `impact` would abruptly report "no callers" for a function that's used throughout the codebase, until the next full re-index. Sync now preserves those incoming cross-file edges across the re-index, re-matching them to the symbol even when the edit shifted its line number. Most visible in large Python package trees, but it applies to every language. Thanks @JosefAschauer. (#899)
 - `codegraph index` now rebuilds the full graph from scratch, so it produces the same result as a fresh `codegraph init` instead of reporting "0 nodes, 0 edges" and looking like it wiped your index. Previously, re-running `index` on an unchanged project skipped every file (their contents hadn't changed) and showed an empty-looking summary; it now clears and re-indexes for an honest, complete rebuild every time. Use `codegraph sync` for fast incremental updates between full rebuilds. Thanks @Arc-univer. (#874)
 - The file watcher that auto-syncs the graph now fails cleanly when live watching can no longer be trusted, instead of looking healthy while the index quietly goes stale. If the operating system runs out of file-watch resources, or another process holds the write lock far longer than a normal save, CodeGraph now disables auto-sync once — with a single clear message telling you to run `codegraph sync` (or rely on the git sync hooks) to refresh — rather than retrying forever or repeating the same error on a loop. And while auto-sync is disabled, CodeGraph's tool responses (and `codegraph status`) now say so plainly, so your AI agent knows to read files directly instead of trusting a frozen index. This mostly matters for long-running MCP/daemon sessions, which could otherwise keep serving stale results while appearing to work. Thanks @thismilktea. (#876)
 - On Linux, hitting the kernel's inotify watch limit on a large project no longer silently leaves half the tree unwatched. CodeGraph now tells you once — naming the exact setting to raise (`fs.inotify.max_user_watches`, e.g. `sudo sysctl fs.inotify.max_user_watches=1048576`) — and keeps live-watching the directories it could register while `codegraph sync` (or the git sync hooks) covers the rest. (#876)