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/scripts/verify_sources.py

@@ -15,7 +15,7 @@ rendered section when `pipeline_faults` is non-empty and the empty
 string otherwise, keeping the happy-path `{{report}}{{pipeline_notes}}`
 output byte-identical to the pre-hardening `{{report}}`.
 
-Fail-safe (R3): per-URL probes were already guarded; the top level now
+Fail-safe: per-URL probes were already guarded; the top level now
 is too. On a crash the summary says sources were NOT checked, a
 PIPELINE-FAULT is recorded (best-effort preserving existing faults), and
 pipeline_notes still renders — the approval gate remains the backstop.