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/reflexion_gate.py

@@ -16,7 +16,7 @@ Reflexion is a best-effort quality booster, not a hard gate: once the
 budget is spent the workflow proceeds anyway, and the human approval
 step is the final backstop.
 
-Fail-safe (R3): a crash here fails FORWARD to `synthesize` — the same
+Fail-safe: a crash here fails FORWARD to `synthesize` — the same
 direction as the existing malformed-critique PASS default — with a
 PIPELINE-FAULT entry recorded (best-effort preserving existing faults),
 so a broken gate costs the run its automated critique routing, never the