refactor(runtime_validation): 删掉那个从来没人调用的汇总谓词

`has_proven_mismatch()` 在本轮之前就是死的,我只是把它改名成
`has_blocking_failure()` —— 改名的死代码比死代码更糟。

真正的门在 `ninja_backend` 里逐个产物走,因为它要**指名是哪一个**并打印它的解释。
再放一个「有没有失败」的谓词读同一份数据,就是同一个决策两处推导,而没人调用的
那一处正是会悄悄不再一致的那一处。留一条注释说明为什么这里没有它。

Author: speak-agent

src/build/runtime_validation.cppm

@@ -39,15 +39,14 @@ struct ValidatedArtifact {
 struct ValidationReport {
     std::vector<ValidatedArtifact> artifacts;
 
-    // Any artifact PROVEN bad — payloads mixed, or a DT_NEEDED that the
-    // artifact's own loader will not find. Asks the verdict rather than
-    // enumerating states here, so a fifth state cannot be added without this
-    // gate deciding what it means.
-    bool has_blocking_failure() const {
-        return std::ranges::any_of(artifacts, [](auto const& artifact) {
-            return artifact.verdict.blocking();
-        });
-    }
+    // NOTE: there is deliberately no `has_blocking_failure()` here.
+    //
+    // There used to be a `has_proven_mismatch()`, and nothing ever called it —
+    // the real gate walks the artifacts in `ninja_backend` so it can name WHICH
+    // one failed and print its explanation. A second predicate that answers
+    // "did anything fail" from the same data is the same decision in two
+    // places, and the one with no callers is the one that silently stops
+    // agreeing. Ask `verdict.blocking()` per artifact.
 };
 
 struct StoredRuntimeSummary {