feat(TASK-023): deep-research hardening — fail-safe scripts, fault fallbacks, pipeline notes

R3 guards: parse_request (crash → ask_topic), bootstrap_research,
combine_findings (crash → fault-text findings; also lifts branch-local
PIPELINE-FAULT findings into pipeline_faults, deduped), reflexion_gate
(crash fails forward to synthesize), incorporate_feedback (crash still
loops with a generic feedback note), verify_sources (top-level guard +
pipeline_notes fold).

Fallbacks per the plan's naming pins: plan → plan_fault → end_fault
(fail-closed; gains state_updates plan_failure per the TASK-016 rule);
research_one_question → branch-local question_fault (map collects the
fault finding); vet_sources/critique → degrade-visibly markers that
continue to the stage each node's own next pointed to; synthesize →
synth_fault → end_fault. end_fault renders
'DEEP_RESEARCH FAILED — PIPELINE-FAULT: <fault text>'.

Accepted-path visibility: verify_sources folds pipeline_faults into
pipeline_notes ('' when fault-free), appended to end_accepted's output
and the approval question — happy-path output stays byte-identical.
initial_state seeds questions: [] so a dying plan inside the static
fan-out leaves the sibling knowledge_lookup lane mapping over zero
items while end_fault renders.

R5: 19 python3-guarded regression tests + GraphParser wiring test;
bundled warning baseline unchanged.

assets/agents/deep-research/scripts/verify_sources.py

@@ -6,6 +6,19 @@ request, and writes a `source_check` summary into state so the human
 reviewer sees broken citations at the approval step.
 
 Times out per request so a slow source cannot stall the graph.
+
+Pipeline-notes fold: end-node templates render unconditionally, so the
+conditional "## Pipeline notes" section of the accepted report is built
+HERE — the last stop before the approval gate on every accepted path,
+including reflexion and feedback re-loops. `pipeline_notes` is the
+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
+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.
 """
 import json
 import os
@@ -25,6 +38,21 @@ def load_state():
     return json.loads(os.environ.get("GRAPH_STATE", "{}"))
 
 
+def safe_faults():
+    try:
+        state = load_state()
+        return [f for f in (state.get("pipeline_faults") or []) if isinstance(f, str)]
+    except Exception:  # noqa: BLE001 — best-effort preservation only
+        return []
+
+
+def render_notes(faults):
+    entries = [f for f in (faults or []) if isinstance(f, str) and f.strip()]
+    if not entries:
+        return ""
+    return "\n\n## Pipeline notes\n\n" + "\n".join(f"- {e}" for e in entries)
+
+
 def reachable(url, timeout=5.0):
     req = urllib.request.Request(url, method="HEAD")
     try:
@@ -62,8 +90,27 @@ def main():
             + "\n".join(results)
         )
 
-    print(json.dumps({"source_check": summary}))
+    notes = render_notes(state.get("pipeline_faults"))
+    print(json.dumps({"source_check": summary, "pipeline_notes": notes}))
 
 
-if __name__ == "__main__":
+try:
     main()
+except Exception as e:  # noqa: BLE001 — a crashed source check must degrade, not die
+    faults = safe_faults()
+    faults.append(
+        f"PIPELINE-FAULT: source verification crashed — {e}; cited sources "
+        "were not checked for reachability"
+    )
+    print(
+        json.dumps(
+            {
+                "source_check": (
+                    "Source verification crashed (pipeline fault) — cited "
+                    "sources were NOT checked for reachability."
+                ),
+                "pipeline_notes": render_notes(faults),
+                "pipeline_faults": faults,
+            }
+        )
+    )