fix(extraction): C# produces references edges for type annotations (#381) (#470)

Indexing any C# project produced zero `references` edges, so
`codegraph_callers SomeDto` returned no hits even when the DTO was used
as a param/return type across the codebase, and `codegraph_callees` on
a service class only saw its `using` imports — the headline structural
query silently degraded to text-search on half of every typical backend
stack.

Two root causes:

1. `csharp.ts` was missing `returnField` (default `'return_type'` doesn't
   exist on C# AST; the field is `'type'`) AND had
   `paramsField:'parameter_list'` (the node TYPE, not the field NAME
   `'parameters'`) — so parameter type extraction silently no-op'd.
2. `extractTypeRefsFromSubtree` only emitted refs for `type_identifier`
   leaves. C# tree-sitter doesn't produce `type_identifier` — it uses
   `identifier`, `predefined_type`, `qualified_name`, `generic_name`,
   `array_type`, `nullable_type`, `tuple_type`, etc.

Fix:

- `csharp.ts`: `paramsField:'parameters'`, `returnField:'type'`.
- Route C# through a dedicated `extractCsharpTypeRefs` +
  `walkCsharpTypePosition`. Descends ONLY into known type fields
  (`parameter.type`, `method.type`, `property.type`,
  `variable_declaration.type`, `tuple_element.type`), so parameter
  NAMES like `request` in `Build(UserDto request)` never leak as type
  refs.
- Hook `extractField` and `extractProperty` to call
  `extractTypeAnnotations` so property/field type refs land in the graph.

Validation on dotnet/eShop (527 .cs files):
  C# `references` edges: 35 -> 925 (+26x)
  No regression in calls/imports/instantiates/extends/implements.

Closes #381.

CHANGELOG.md

@@ -16,6 +16,7 @@ and adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
   - **Field-injected concrete-bean trace.** A Spring controller's `@Resource(name="userBO") private UserBO userbo;` followed by `this.userbo.toLogin2(...)` now resolves through to `UserBO.toLogin2` even when the field type is a concrete class whose name doesn't match the field by Java naming convention (`userbo` → `UserBO`). The fix is two layered changes in the language layer (Java only): (a) the call extractor unwraps `this.<field>` receivers (previously surfaced as `this.userbo.toLogin2` and dropped through every name-matcher strategy); (b) the resolver looks up the receiver name in the enclosing class's field declarations and uses the declared type to resolve the method. This generalizes beyond Spring — any Java code using `this.field.method()` now resolves correctly.
 
 ### Fixed
+- **C# now produces `references` edges for parameter, return, property, and field types (#381).** Indexing any C# project used to yield **zero** `references` edges, so `codegraph_callers SomeDto` returned no results even when the DTO was used as a parameter or return type across the codebase, and `codegraph_callees` on a service class only saw its `using` imports. Two root causes: `csharp.ts` was missing `returnField`, and the type-leaf walker only matched `type_identifier` nodes — but C# tree-sitter emits `identifier`/`predefined_type`/`qualified_name`/`generic_name` instead. The fix adds the missing extractor field, routes C# through a dedicated type walker that only descends into known type-position fields (so parameter NAMES like `request` in `Build(UserDto request)` never mis-emit as type refs), and hooks `extractField`/`extractProperty` to invoke the walker. Measured on dotnet/eShop (527 `.cs` files): C# `references` edges go from **35 → 925** (+26x), with no regression in `calls`/`imports`/`instantiates`/`extends`/`implements`.
 - **Go cross-package qualified calls (`pkga.FuncX(...)`) now resolve to the right package (#388).** On a Go monorepo with a layered package layout (handler/service/domain/dao), `codegraph_callers`, `_callees`, `_impact`, and `_trace` used to return ~0-1 results where grep finds hundreds to thousands of real call sites — the central value proposition of CodeGraph silently degraded on entire Go codebases. Root cause: the import resolver flagged every Go import path without `/internal/` as third-party (because it had no idea what the project's own module path was), so cross-package calls fell through to name-matching with path-proximity scoring, which on real codebases picks ~one accidental candidate per call site. The Go branch now reads the project's `go.mod`, treats `<module-path>/...` imports as in-module, and looks up the qualified symbol in the imported package's directory; same-name functions in *different* packages no longer collide. As a side fix, Go nodes now correctly carry `is_exported=1` for capitalized identifiers (the resolver needs this to filter candidates). Measured on gRPC-Go (1,031 `.go` files, layered packages): cross-package `calls` edges go from 10,880 → 19,929 (**+83%**), total `calls` from 23,803 → 34,105 (**+43%**), with no false-positive resolution of stdlib calls (`fmt.Println` etc. stay external).
 - **`codegraph_files` now returns the whole project when an agent passes `path="/"`, `"."`, `"./"`, `""`, or a Windows-style `"\\"` — instead of "No files found matching the criteria."** Indexed file paths are stored as project-relative POSIX (e.g. `src/foo.ts`), but the path filter used a plain `startsWith`, so a leading slash or any of the other root-ish shapes an agent might guess matched nothing and pushed the agent back to Read/Glob — the exact opencode + Gemini Flash regression reported on Windows 11. Subdirectory filters are now equally forgiving: `"/src"`, `"./src"`, `"src/"`, `"src\\components"`, etc. all resolve correctly. Sibling-prefix bleed (`"src"` was previously matching `src-utils/...`) is also fixed — the filter now requires either an exact match or a `<filter>/` boundary. Closes #426.
 - **File watcher no longer marks edited files as fresh when another process holds the index lock.** When a second writer (concurrent `codegraph index`, a git hook, another MCP daemon) held `.codegraph/codegraph.lock`, `CodeGraph.sync()` returned a zero-shape no-op instead of throwing. The file watcher took that as a successful sync and cleared `pendingFiles` — so the per-file staleness signal MCP tools surface to agents (issue #403) dropped immediately, even though the edit was never indexed. `CodeGraph.watch()` now converts that no-op into a typed `LockUnavailableError` thrown into the watcher; the existing retry path preserves `pendingFiles` and reschedules until the lock becomes available. The error is logged at debug only (no `onSyncError` callback) so a long-running external indexer doesn't spam stderr every debounce cycle. Closes #449.