fix(mcp): resolve module-qualified symbol lookups (#173) (#179)

`codegraph_callees stage_apply::run` (and `_node`, `_impact`, ...)
returned "not found" against a repo with 7-9 sibling Rust modules,
each exporting `pub async fn run`. Two underlying issues:

1. The FTS5 query builder stripped `:` as a special char without
   splitting on `::`, so `stage_apply::run` collapsed to the literal
   `stage_applyrun` which matches nothing. Treat `::` as whitespace
   before the strip step so both halves become FTS tokens.

2. `matchesSymbol` only understood `Parent.child` qualifiers and
   relied on `qualifiedName` carrying the module path. Rust file-
   level functions don't have their module name in `qualifiedName`
   (it's encoded in the file path instead), so even dot-style
   lookups failed. Accept `::`, `.`, `/` as separators; multi-level
   forms compose; Rust `crate::`/`super::`/`self::` prefixes get
   stripped before path matching. Fall back to file-path containment
   when the qualified-name suffix doesn't match — `stage_apply::run`
   matches a `run` in any file whose path has a `stage_apply` segment.

Also tightens the no-match branch: qualified lookups no longer fall
through to a fuzzy text match. `stage_apply::nonexistent_fn` returns
`null` instead of silently resolving to an unrelated `rollback` in
the same file.

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/db/queries.ts

@@ -696,8 +696,14 @@ export class QueryBuilder {
     const { kinds, languages, limit = 100, offset = 0 } = options;
 
     // Add prefix wildcard for better matching (e.g., "auth" matches "AuthService", "authenticate")
-    // Escape special FTS5 characters and add prefix wildcard
+    // Escape special FTS5 characters and add prefix wildcard.
+    //
+    // `::` is a qualifier separator in Rust/C++/Ruby, not a token char,
+    // so treat it as whitespace before the strip step. Otherwise queries
+    // like `stage_apply::run` collapse to `stage_applyrun` (the colons
+    // are stripped without splitting) and find nothing. See #173.
     const ftsQuery = query
+      .replace(/::/g, ' ') // Rust/C++/Ruby qualifier separator
       .replace(/['"*():^]/g, '') // Remove FTS5 special chars
       .split(/\s+/)
       .filter(term => term.length > 0)