fix(resolution): C and C++ nesting is never a scope

isLexicallyReachable trusted the graph's nesting for every language. C and
C++ have no nested named functions, so a function shown inside another is an
extraction artifact: tree-sitter-c cannot parse a macro call whose arguments
are designated initializers — betaflight's

    RESET_CONFIG(pidProfile_t, pidProfile, .pid = { … }, …);

— and its error recovery runs the enclosing function_definition (source lines
168–309) to line 1667, nesting the 45 functions after it. That tree has 310
such functions in 73 files. Before this commit exact-match already rejected
them as unreachable and the fuzzy fallback picked them up at 0.5; with the
survivor-side check alone, fuzzy rejected them too and 117 real calls into
pid.c disappeared (base → 4c8f165 on the 2,109-file betaflight fork: LOST
117, GAINED 0, all fuzzy, all pid.c).

With the gate the same tree is LOST 117 fuzzy / GAINED 117 exact-match — the
identical edges, now resolved by the strategy that should have had them, at
0.9. vite (no C) is unchanged.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

__tests__/fuzzy-lexical-reach.test.ts

@@ -138,6 +138,15 @@ describe('fuzzy reachability rejects a unique guess but never manufactures one',
     expect(matchFuzzy(callFrom('vite.config.js', 3), contextWith([closure, method]))).toBeNull();
   });
 
+  it('trusts no nesting in C, where a nested function is an extraction artifact', () => {
+    // betaflight: tree-sitter-c's recovery from `RESET_CONFIG(…, .pid = {…})`
+    // runs resetPidProfile to the end of pid.c, so every function after it is
+    // "nested" in the graph. C has no nested named functions; the call reaches it.
+    const cClosure = node({ ...closure, id: 'f:c', language: 'c' as Node['language'], filePath: 'pid.c' });
+    const cRef = { ...callFrom('core.c', 3), language: 'c' as UnresolvedRef['language'] };
+    expect(matchFuzzy(cRef, contextWith([cClosure]))?.targetNodeId).toBe('f:c');
+  });
+
   it('resolves a lone reachable method as before', () => {
     expect(matchFuzzy(callFrom('vite.config.js', 3), contextWith([method]))?.targetNodeId).toBe('m:resolve');
   });