test(suite): replace plan-label references with self-contained wording

Rust test comments/assert messages and deep-research script docstrings
cited numbered requirement labels (R3/R5) and task labels (TASK-016,
TASK-021) that are defined only in an external plan document. Reword
each to say what it means on its own: fail-safe crash guards, the
validator's fallback-capture warning, task-queue anchors.

assets/agents/deep-research/README.md

@@ -263,7 +263,7 @@ pass — every fault is visible to the reviewer or the caller — and some
 end node always renders its sentinel, so the graph degrades instead of
 dying.
 
-All 11 scripts also carry a top-level crash guard (R3): a script that
+All 11 scripts also carry a top-level crash guard: a script that
 throws records a fault and fails forward where the flow allows it (a
 crashed `reflexion_gate` proceeds to `synthesize`; a crashed
 `verify_sources` reports that sources were NOT checked) instead of