fix(extraction): detect a plain struct Derived : Base base clause in .h headers as C++ (#1592) (#1593)

Fixes #1592.

## What was wrong

A `.h` header whose only C++ construct is a plain derived type —

```cpp
struct Base {};
struct Derived : Base {};
```

— was classified as C. The `.h` language check (`looksLikeCpp`) recognizes `class`, `namespace`, `template`, access sections, `virtual`, `using`, and — since #1159/#1207 — the export-macro form `struct ENGINE_API Derived : Base`. The plain form has none of those signals. Routed through the C extractor, `Derived` vanished from the index and the base clause was read as a K&R-style declaration, minting a phantom `function Base` with `returnType=Derived` (the exact output in the issue).

A second, independent miss the reporter called out: the check only read the first 8192 characters, so a large header with a long C-compatible preamble (include guards, `#define`s, plain typedefs) hid the signal even when it was there.

## What this does

`looksLikeCpp()` now runs two passes:

1. The existing 8 KB sample regex, unchanged.
2. A scan of the **whole file** (comments stripped) for a class/struct **base clause**: `class`/`struct` + tag + optional `final` + `:` + optional `public`/`protected`/`private`/`virtual` + a base name (scoped, optionally templated) followed by the body's `{` or a `,` introducing the next base.

That shape has no valid C reading, so widening it to the whole file can't drag a C header over to C++:

- a bit-field's `:` follows a member *name* inside the body (`unsigned a : 3;`), not the tag;
- a ternary's `:` is separated from the tag by `)` / `*` / a declarator (`sizeof(struct foo) : 0`);
- a label or identifier like `struct_end:` has no whitespace after `struct`;
- comments are removed before the scan, so doc-comment prose (`/* struct timeval: seconds, microseconds */`) can't match; and the `{`/`,` terminator keeps a string literal's prose from matching too.

Detection only — the C++ extractor already handles the header correctly once it's routed there (renaming to `.hpp`, as the issue notes, already worked).

## Tests

`__tests__/extraction.test.ts`:

- plain / `: public Base` / `: ns::Base` / `: Base<int, Foo<T>>` / `final : Base` / multi-base with `{` on the next line / `: virtual Base` → `cpp`;
- a base clause placed **after** 8192 characters of C-compatible preamble → `cpp`;
- controls that must stay `c`: a bit-field struct, `sizeof(struct foo) : 0` + a cast ternary, a `struct_end:` label and `struct_a` identifiers, doc-comment prose shaped like a base clause, and the two pre-existing C controls;
- end-to-end `extractFromSource('src/min.h', …)` on the issue's header: a `struct` node `Derived` (language `cpp`), exactly one `Base` node and it is a `struct` — no phantom function.

Issue repro re-run against this build: `codegraph init` → `query Derived` returns the `cpp` struct; `query Base` returns only the struct; the files table records `src/min.h` as `cpp`.

Full suite: `npm test` → 174 files passed, 3010 tests passed, 179 skipped.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

https://claude.ai/code/session_01LxZj6W6Y1SHXwvpT3uwJpK

CHANGELOG.md

@@ -73,6 +73,7 @@ and adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 - Files skipped because they are too large or repeatedly fail to parse are now recorded with the reason, so unchanged rejected files are no longer rediscovered and retried on every status check and sync — and a later successful parse of such a file replaces the record with its real symbols. Thanks @netbrah for the exceptional failure analysis behind this batch, and @danusha2345 for the fixes. (#1557)
 - C/C++ function-pointer analysis now bounds its compiled-pattern caches, so very large repositories can no longer exhaust the JavaScript engine's regular-expression code space during indexing. (#1559)
 - JSX rendering analysis now runs only on JavaScript-family files, so JSX-looking strings in C/C++ (or any other language) no longer create impossible call edges — in pure-C projects and in mixed-language monorepos alike. (#1560)
+- A C++ `.h` header whose only C++ construct is a plain derived type — `struct Derived : Base` with no export macro, `class` keyword, or access section — is now recognized as C++ (previously only the export-macro form was). Such a header was read as C, so the derived struct vanished from the index and a phantom function named after the base type appeared in its place. The check now also covers the whole file rather than its first few kilobytes, so a long C-compatible preamble no longer hides the signal. Re-index after upgrading to pick up affected headers. Thanks @Jaysenpeng. (#1592)
 - Editing `codegraph.json`'s `exclude` or `include` (or a `.gitignore`) while the MCP server is running now takes effect immediately. Previously the running file watcher kept the scope it had when it started, so a newly excluded file was removed by `codegraph sync` and then quietly re-added by the watcher seconds later — which looked like `exclude` not working at all — until the server was restarted. A scope change now refreshes the watcher and triggers a full reconcile, and a changed file the watcher hands to sync is re-checked against the current scope first, so the CLI and the live server can no longer disagree about what belongs in the index. Thanks @K1nG11. (#1590)
 - Indexing no longer crashes the whole process — a segmentation fault with no message and no partial index — on a C/C++ (or any other) file with extremely deep nesting, such as the parser stress-test fixtures in the clang and gcc test suites or a fuzzer corpus. Such a file is now handed to the fallback parser and recorded with a parse warning while the rest of the repository indexes normally. Thanks @apollo600 for the exact diagnosis. (#1581)
 - Calls to the methods of an exported object-literal constant — `export const api = { call() { … } }` used as a module's namespace, a common way to organize a TypeScript API surface — now resolve to the method, both in the defining file and through imports. Previously such a call linked to nothing (or to the constant itself), so `codegraph callers` and impact analysis reported zero callers for methods that are called from everywhere. Re-index after upgrading to pick up the edges. Thanks @IAliceBobI for the precise report and root-cause. (#1573)