test(ida): expect direction in combined call coverage

Keep the ARM64 dossier boundary assertion aligned with caller/callee coverage ownership while preserving unknown coverage, diagnostics, and observed callee assertions.

Validation: recorded IDA protocol and callee relationship boundary tests (22 passed). Live IDA was not exercised.

tests/boundary/providers/ida/calleeRelationships.test.ts

@@ -37,7 +37,8 @@ it("keeps unknown caller coverage and callee diagnostics in an ARM64 dossier", a
     if (!result.ok) throw result.error;
     expect(result.value.relationshipCoverage).toMatchObject({
       status: "unknown",
-      reason: "Upstream xrefs do not establish direct caller relationships.",
+      reason:
+        "Callers: Upstream xrefs do not establish direct caller relationships.",
       diagnostics: expect.arrayContaining([
         expect.stringContaining("targets IDA does not recognize as functions"),
       ]),