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/graph.yaml

@@ -38,6 +38,14 @@ initial_state:
   research_attempts: 0
   local_context: ''
   local_sources: ''
+  # Fault-path defaults (TASK-023 hardening). `questions: []` also keeps the
+  # knowledge_lookup lane alive for one super-step when `plan` dies inside the
+  # static fan-out: research_each_question maps over zero items while the
+  # plan_fault → end_fault route renders the failure sentinel.
+  pipeline_faults: []
+  pipeline_notes: ''
+  fault_text: ''
+  questions: []
 
 start: parse_request
 
@@ -91,8 +99,22 @@ nodes:
           maxItems: 6
           description: 3-5 specific, self-contained sub-questions.
       required: [research_plan, questions]
+    # On success plan_failure holds the node's structured JSON output; on
+    # failure the engine writes "LLM node …failed: <chain>" into it BEFORE
+    # routing to the fallback (schema properties are only merged on success).
+    state_updates:
+      plan_failure: '{{output}}'
+    fallback: plan_fault
     next: research_each_question
 
+  plan_fault:
+    id: plan_fault
+    type: script
+    description: Fail-closed marker for a dead planning stage (reached only via plan's fallback) — normalizes the failure text captured in plan_failure into a PIPELINE-FAULT and continues to end_fault; no plan means nothing to research, so the DEEP_RESEARCH FAILED sentinel always renders. The sibling knowledge_lookup lane survives one more super-step by mapping over the empty initial_state `questions` list.
+    script: scripts/plan_fault.py
+    fallback: end_fault
+    next: end_fault
+
   knowledge_lookup:
     id: knowledge_lookup
     type: rag
@@ -153,6 +175,16 @@ nodes:
     max_attempts: 2
     state_updates:
       finding: '{{output}}'
+    # On failure the engine writes "LLM node …failed: <chain>" into `finding`
+    # via the state_updates above BEFORE routing to the fallback. The marker
+    # is branch-local: a map branch's fallback must stay inside the branch.
+    fallback: question_fault
+
+  question_fault:
+    id: question_fault
+    type: script
+    description: Fail-closed marker for a dead research lane (reached only via research_one_question's fallback route inside the map branch). Normalizes the engine's failure text in `finding` into a PIPELINE-FAULT finding the map collects — one dead lane never sinks the whole map. combine_findings later lifts PIPELINE-FAULT findings into pipeline_faults for the report's Pipeline notes.
+    script: scripts/question_fault.py
 
   combine_findings:
     id: combine_findings
@@ -179,6 +211,15 @@ nodes:
     max_iterations: 15
     state_updates:
       source_assessment: '{{output}}'
+    fallback: vet_fault
+    next: critique
+
+  vet_fault:
+    id: vet_fault
+    type: script
+    description: Degrade-visibly marker for a dead vetting stage (reached only via vet_sources' fallback) — vetting is a quality lane, not the product. Records a PIPELINE-FAULT, rewrites source_assessment to a neutral "unvetted" note, and continues to critique, the stage vet_sources' own next pointed to.
+    script: scripts/vet_fault.py
+    fallback: critique
     next: critique
 
   critique:
@@ -219,6 +260,15 @@ nodes:
     tools: []
     state_updates:
       critique: '{{output}}'
+    fallback: critique_fault
+    next: reflexion_gate
+
+  critique_fault:
+    id: critique_fault
+    type: script
+    description: Degrade-visibly marker for a dead critique stage (reached only via critique's fallback) — critique is a quality lane, not the product. Records a PIPELINE-FAULT and rewrites `critique` to a neutral note with deliberately NO "VERDICT:" line, so reflexion_gate's malformed-critique PASS default proceeds to synthesis; then continues to reflexion_gate, the stage critique's own next pointed to.
+    script: scripts/critique_fault.py
+    fallback: reflexion_gate
     next: reflexion_gate
 
   reflexion_gate:
@@ -245,8 +295,19 @@ nodes:
     max_attempts: 2
     state_updates:
       report: '{{output}}'
+    # On failure the engine writes "Agent node failed: <chain>" into `report`
+    # via the state_updates above BEFORE routing to the fallback.
+    fallback: synth_fault
     next: verify_sources
 
+  synth_fault:
+    id: synth_fault
+    type: script
+    description: Fail-closed marker for a dead synthesis stage (reached only via synthesize's fallback) — no report means no product. Normalizes the "Agent node failed:" text captured in `report` into a PIPELINE-FAULT and continues to end_fault, which renders the DEEP_RESEARCH FAILED sentinel.
+    script: scripts/synth_fault.py
+    fallback: end_fault
+    next: end_fault
+
   verify_sources:
     id: verify_sources
     type: script
@@ -262,7 +323,7 @@ nodes:
       {{report}}
 
       ----
-      {{source_check}}
+      {{source_check}}{{pipeline_notes}}
       ----
 
       Accept this report? Pick "accept" or "reject", or type specific
@@ -285,9 +346,14 @@ nodes:
   end_accepted:
     id: end_accepted
     type: end
-    output: '{{report}}'
+    output: '{{report}}{{pipeline_notes}}'
 
   end_rejected:
     id: end_rejected
     type: end
     output: "Research on '{{topic}}' was rejected and discarded."
+
+  end_fault:
+    id: end_fault
+    type: end
+    output: 'DEEP_RESEARCH FAILED — PIPELINE-FAULT: {{fault_text}}'

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

@@ -6,6 +6,12 @@ list on this node fans out into two parallel branches (the LLM planner and
 the RAG knowledge lookup) as a single super-step. The validator requires
 declared parallel-branch script outputs, so we emit an empty JSON object
 explicitly here.
+
+Fail-safe (R3): the node reads no state and computes nothing, so its
+happy-path output IS the sane degraded output — the guard emits the same
+empty object on any crash. No PIPELINE-FAULT is recorded: appending one
+would require reading state (the very thing that crashed) or clobbering
+faults recorded upstream by parse_request, and a crash here loses nothing.
 """
 import json
 
@@ -14,5 +20,7 @@ def main():
     print(json.dumps({}))
 
 
-if __name__ == "__main__":
+try:
     main()
+except Exception:  # noqa: BLE001 — the fan-out source must never crash the graph
+    print(json.dumps({}))

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

@@ -6,6 +6,18 @@ one entry per sub-question, in input order). Downstream nodes
 (`vet_sources`, `critique`, `synthesize`) read `{{findings}}` as a
 single block, so this script renders the array as a Markdown document
 with one section per question.
+
+Fault visibility: a research lane that died lands here as a finding
+starting with "PIPELINE-FAULT:" (written by question_fault inside the map
+branch, where `pipeline_faults` itself is out of reach — map branches only
+surface their collected output_key). This script lifts such findings into
+`pipeline_faults` (deduplicated, since a reflexion or feedback loop can
+re-run the map) so dead lanes surface in the report's Pipeline notes.
+
+Fail-safe (R3): on a crash (e.g. malformed GRAPH_STATE), `findings`
+becomes the fault text itself and a PIPELINE-FAULT entry is recorded —
+the pipeline proceeds visibly degraded, and the human approval gate is
+the backstop. Existing faults are preserved best-effort.
 """
 import json
 import os
@@ -19,21 +31,40 @@ 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 main():
     state = load_state()
     questions = state.get("questions") or []
     per_question = state.get("question_findings") or []
+    faults = [f for f in (state.get("pipeline_faults") or []) if isinstance(f, str)]
 
     sections = []
     for idx, q in enumerate(questions):
         body = per_question[idx] if idx < len(per_question) else ""
         if isinstance(body, dict) or isinstance(body, list):
             body = json.dumps(body, indent=2)
+        if isinstance(body, str) and body.startswith("PIPELINE-FAULT:") and body not in faults:
+            faults.append(body)
         sections.append(f"## {q}\n\n{body}")
 
     findings = "\n\n".join(sections) if sections else "No findings gathered."
-    print(json.dumps({"findings": findings}))
+    print(json.dumps({"findings": findings, "pipeline_faults": faults}))
 
 
-if __name__ == "__main__":
+try:
     main()
+except Exception as e:  # noqa: BLE001 — a crashed join must degrade, not die
+    faults = safe_faults()
+    fault = (
+        f"PIPELINE-FAULT: combining findings crashed — {e}; per-question "
+        "findings may exist in state but could not be joined"
+    )
+    faults.append(fault)
+    print(json.dumps({"findings": fault, "pipeline_faults": faults}))

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

@@ -0,0 +1,61 @@
+#!/usr/bin/env python3
+"""Degrade-visibly marker for a dead critique stage of deep-research.
+
+Reached ONLY via critique's `fallback:` route. Grounded in engine behavior:
+on llm-node failure the engine writes "LLM node …failed: <chain>" into
+`critique` via the node's state_updates BEFORE routing to the fallback.
+Critique is a quality lane, not the product, so this path degrades instead
+of failing closed: it records a PIPELINE-FAULT (surfaced later in the
+report's Pipeline notes) and rewrites `critique` to a neutral note, then
+continues to `reflexion_gate` — the stage critique's own `next` pointed to.
+
+The rewritten note deliberately contains NO "VERDICT:" line:
+reflexion_gate's parse_verdict defaults to PASS when no verdict line is
+found (its documented malformed-critique behavior), so a dead critique
+proceeds to synthesis instead of burning the revision budget on a fault.
+"""
+
+import json
+import os
+
+MAX_DETAIL_CHARS = 500
+
+CRITIQUE_NOTE = (
+    "Critique unavailable — the critique stage failed (pipeline fault); "
+    "proceeding to synthesis without an automated review pass."
+)
+
+
+def load_state():
+    if path := os.environ.get("GRAPH_STATE_FILE"):
+        with open(path) as f:
+            return json.load(f)
+    return json.loads(os.environ.get("GRAPH_STATE", "{}"))
+
+
+def main():
+    state = load_state()
+    faults = [f for f in (state.get("pipeline_faults") or []) if isinstance(f, str)]
+    raw = state.get("critique")
+    detail = raw.strip().replace("\n", " ") if isinstance(raw, str) else ""
+    if not detail.startswith("LLM node"):
+        detail = "the critique stage died without recording a failure detail"
+    if len(detail) > MAX_DETAIL_CHARS:
+        detail = detail[: MAX_DETAIL_CHARS - 1] + "…"
+    faults.append(f"PIPELINE-FAULT: critique failed — {detail}")
+    print(json.dumps({"pipeline_faults": faults, "critique": CRITIQUE_NOTE}))
+
+
+try:
+    main()
+except Exception as e:  # noqa: BLE001 — the fault marker itself must never crash
+    print(
+        json.dumps(
+            {
+                "pipeline_faults": [
+                    f"PIPELINE-FAULT: critique failed — fault-marker script error: {e}"
+                ],
+                "critique": CRITIQUE_NOTE,
+            }
+        )
+    )

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

@@ -10,6 +10,13 @@ reflexion counter is reset so the user-driven pass gets a fresh revision
 budget.
 
 Routing (`_next`): always research_each_question.
+
+Fail-safe (R3): a crash here means the user's feedback text cannot be
+recovered, but their INTENT — another research pass — is unambiguous
+(they chose neither accept nor reject). The degraded route therefore
+still loops to `research_each_question`, with a generic feedback note
+naming the loss and a PIPELINE-FAULT entry (best-effort preserving
+existing faults) that surfaces in the next approval's Pipeline notes.
 """
 import json
 import os
@@ -23,6 +30,14 @@ 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 main():
     state = load_state()
     feedback = (state.get("decision") or "").strip()
@@ -37,5 +52,26 @@ def main():
     print(json.dumps(output))
 
 
-if __name__ == "__main__":
+try:
     main()
+except Exception as e:  # noqa: BLE001 — a crashed feedback fold must degrade, not die
+    faults = safe_faults()
+    faults.append(
+        f"PIPELINE-FAULT: feedback incorporation crashed — {e}; the reviewer's "
+        "feedback text could not be recovered"
+    )
+    print(
+        json.dumps(
+            {
+                "_next": "research_each_question",
+                "research_attempts": 0,
+                "research_feedback": (
+                    "The user reviewed the report and asked for changes, but "
+                    "the feedback text could not be recovered (pipeline "
+                    "fault). Re-run the research pass with extra care and "
+                    "note this loss."
+                ),
+                "pipeline_faults": faults,
+            }
+        )
+    )

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

@@ -9,6 +9,13 @@ supply one interactively.
 Routing (`_next`):
   - prompt present -> (no _next; static next: plan)
   - prompt empty   -> ask_topic
+
+Fail-safe (R3): a crash here (e.g. malformed GRAPH_STATE) means the
+caller's prompt cannot be read at all, so proceeding silently is
+meaningless — the degraded route is `ask_topic`, which asks the user for
+the topic directly, plus a PIPELINE-FAULT entry so the loss is visible in
+the final report's Pipeline notes. Clobbering `pipeline_faults` is safe
+here: this is the start node, so the list can only hold its initial [].
 """
 import json
 import os
@@ -31,5 +38,17 @@ def main():
         print(json.dumps({"_next": "ask_topic"}))
 
 
-if __name__ == "__main__":
+try:
     main()
+except Exception as e:  # noqa: BLE001 — a crashed entry router must degrade, not die
+    print(
+        json.dumps(
+            {
+                "_next": "ask_topic",
+                "pipeline_faults": [
+                    f"PIPELINE-FAULT: request parsing crashed — {e}; asked the "
+                    "user for the research topic instead"
+                ],
+            }
+        )
+    )

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

@@ -0,0 +1,58 @@
+#!/usr/bin/env python3
+"""Fail-closed marker for a dead planning stage of the deep-research graph.
+
+Reached ONLY via plan's `fallback:` route. Grounded in engine behavior: on
+llm-node failure the engine writes "LLM node …failed: <chain>" into
+`plan_failure` via the node's state_updates BEFORE routing to the fallback
+(on success the same key holds the node's structured JSON output, which
+never starts with the "LLM node" prefix). No plan means no sub-questions —
+there is nothing to research — so this path is fail-closed: record the
+PIPELINE-FAULT and continue to `end_fault`, which renders the
+DEEP_RESEARCH FAILED sentinel.
+
+The planner runs inside the static fan-out [plan, knowledge_lookup]. While
+this marker routes to end_fault, the sibling branch proceeds one more
+super-step into `research_each_question`, whose `{{questions}}` resolves to
+the initial_state [] — the doomed lane maps over zero items and the graph
+returns end_fault's output at the next join.
+"""
+
+import json
+import os
+
+MAX_DETAIL_CHARS = 500
+
+
+def load_state():
+    if path := os.environ.get("GRAPH_STATE_FILE"):
+        with open(path) as f:
+            return json.load(f)
+    return json.loads(os.environ.get("GRAPH_STATE", "{}"))
+
+
+def main():
+    state = load_state()
+    faults = [f for f in (state.get("pipeline_faults") or []) if isinstance(f, str)]
+    raw = state.get("plan_failure")
+    detail = raw.strip().replace("\n", " ") if isinstance(raw, str) else ""
+    if not detail.startswith("LLM node"):
+        detail = "the planning stage died without recording a failure detail"
+    if len(detail) > MAX_DETAIL_CHARS:
+        detail = detail[: MAX_DETAIL_CHARS - 1] + "…"
+    fault_text = f"planning failed — nothing to research: {detail}"
+    faults.append(f"PIPELINE-FAULT: {fault_text}")
+    print(json.dumps({"fault_text": fault_text, "pipeline_faults": faults}))
+
+
+try:
+    main()
+except Exception as e:  # noqa: BLE001 — the fault marker itself must never crash
+    fault_text = f"planning failed — fault-marker script error: {e}"
+    print(
+        json.dumps(
+            {
+                "fault_text": fault_text,
+                "pipeline_faults": [f"PIPELINE-FAULT: {fault_text}"],
+            }
+        )
+    )

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

@@ -0,0 +1,52 @@
+#!/usr/bin/env python3
+"""Fail-closed marker for a dead research lane of the deep-research graph.
+
+Reached ONLY via research_one_question's `fallback:` route inside the
+`research_each_question` map branch (branch-local — a map branch's fallback
+must stay inside the branch subgraph). Grounded in engine behavior: on
+llm-node failure the engine writes "LLM node …failed: <chain>" into
+`finding` via the node's state_updates BEFORE routing to the fallback (on
+success the same key holds the researched findings, which never start with
+the "LLM node" prefix). This node normalizes the failure text into a
+PIPELINE-FAULT finding and the chain ends here — the map collects the fault
+as the lane's `finding`, so one dead research lane never sinks the whole
+map. combine_findings later lifts PIPELINE-FAULT findings into
+`pipeline_faults` so the fault also surfaces in the report's Pipeline notes.
+"""
+
+import json
+import os
+
+MAX_DETAIL_CHARS = 500
+
+
+def load_state():
+    if path := os.environ.get("GRAPH_STATE_FILE"):
+        with open(path) as f:
+            return json.load(f)
+    return json.loads(os.environ.get("GRAPH_STATE", "{}"))
+
+
+def fault_finding(detail):
+    return {
+        "finding": (
+            f"PIPELINE-FAULT: question research failed — finding unavailable — {detail}"
+        )
+    }
+
+
+def main():
+    state = load_state()
+    raw = state.get("finding")
+    detail = raw.strip().replace("\n", " ") if isinstance(raw, str) else ""
+    if not detail.startswith("LLM node"):
+        detail = "the research lane died without recording a failure detail"
+    if len(detail) > MAX_DETAIL_CHARS:
+        detail = detail[: MAX_DETAIL_CHARS - 1] + "…"
+    print(json.dumps(fault_finding(detail)))
+
+
+try:
+    main()
+except Exception as e:  # noqa: BLE001 — the fault marker itself must never crash
+    print(json.dumps(fault_finding(f"fault-marker script error: {e}")))

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

@@ -15,6 +15,12 @@ Routing (`_next`):
 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
+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
+run itself.
 """
 import json
 import os
@@ -33,6 +39,14 @@ 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 as_int(value, default=0):
     try:
         return int(value)
@@ -72,5 +86,12 @@ def main():
     print(json.dumps(output))
 
 
-if __name__ == "__main__":
+try:
     main()
+except Exception as e:  # noqa: BLE001 — a crashed gate fails forward, never dies
+    faults = safe_faults()
+    faults.append(
+        f"PIPELINE-FAULT: reflexion gate crashed — {e}; proceeded to synthesis "
+        "without automated critique routing"
+    )
+    print(json.dumps({"_next": "synthesize", "pipeline_faults": faults}))

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

@@ -0,0 +1,51 @@
+#!/usr/bin/env python3
+"""Fail-closed marker for a dead synthesis stage of the deep-research graph.
+
+Reached ONLY via synthesize's `fallback:` route. Grounded in engine
+behavior: on agent-node failure the engine writes "Agent node failed:
+{e:#}" into `report` via the node's state_updates BEFORE routing to the
+fallback (on success the same key holds the report-writer's report, which
+never starts with that prefix). No report means no product, so this path is
+fail-closed: normalize the failure text, record the PIPELINE-FAULT, and
+continue to `end_fault`, which renders the DEEP_RESEARCH FAILED sentinel.
+"""
+
+import json
+import os
+
+MAX_DETAIL_CHARS = 500
+
+
+def load_state():
+    if path := os.environ.get("GRAPH_STATE_FILE"):
+        with open(path) as f:
+            return json.load(f)
+    return json.loads(os.environ.get("GRAPH_STATE", "{}"))
+
+
+def main():
+    state = load_state()
+    faults = [f for f in (state.get("pipeline_faults") or []) if isinstance(f, str)]
+    raw = state.get("report")
+    detail = raw.strip().replace("\n", " ") if isinstance(raw, str) else ""
+    if not detail.startswith("Agent node failed:"):
+        detail = "the synthesis stage died without recording a failure detail"
+    if len(detail) > MAX_DETAIL_CHARS:
+        detail = detail[: MAX_DETAIL_CHARS - 1] + "…"
+    fault_text = f"report synthesis failed — no report was produced: {detail}"
+    faults.append(f"PIPELINE-FAULT: {fault_text}")
+    print(json.dumps({"fault_text": fault_text, "pipeline_faults": faults}))
+
+
+try:
+    main()
+except Exception as e:  # noqa: BLE001 — the fault marker itself must never crash
+    fault_text = f"report synthesis failed — fault-marker script error: {e}"
+    print(
+        json.dumps(
+            {
+                "fault_text": fault_text,
+                "pipeline_faults": [f"PIPELINE-FAULT: {fault_text}"],
+            }
+        )
+    )

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,
+            }
+        )
+    )

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

@@ -0,0 +1,60 @@
+#!/usr/bin/env python3
+"""Degrade-visibly marker for a dead source-vetting stage of deep-research.
+
+Reached ONLY via vet_sources' `fallback:` route. Grounded in engine
+behavior: on llm-node failure the engine writes "LLM node …failed: <chain>"
+into `source_assessment` via the node's state_updates BEFORE routing to the
+fallback. Vetting is a quality lane, not the product, so this path degrades
+instead of failing closed: it records a PIPELINE-FAULT (surfaced later in
+the report's Pipeline notes) and rewrites `source_assessment` to a neutral
+"unvetted" note so downstream prompts (critique, synthesize) never carry
+raw engine error text, then continues to `critique` — the stage
+vet_sources' own `next` pointed to.
+"""
+
+import json
+import os
+
+MAX_DETAIL_CHARS = 500
+
+UNVETTED_NOTE = (
+    "Source credibility assessment unavailable — the vetting stage failed "
+    "(pipeline fault); treat every cited source as unvetted and needing "
+    "corroboration."
+)
+
+
+def load_state():
+    if path := os.environ.get("GRAPH_STATE_FILE"):
+        with open(path) as f:
+            return json.load(f)
+    return json.loads(os.environ.get("GRAPH_STATE", "{}"))
+
+
+def main():
+    state = load_state()
+    faults = [f for f in (state.get("pipeline_faults") or []) if isinstance(f, str)]
+    raw = state.get("source_assessment")
+    detail = raw.strip().replace("\n", " ") if isinstance(raw, str) else ""
+    if not detail.startswith("LLM node"):
+        detail = "the vetting stage died without recording a failure detail"
+    if len(detail) > MAX_DETAIL_CHARS:
+        detail = detail[: MAX_DETAIL_CHARS - 1] + "…"
+    faults.append(f"PIPELINE-FAULT: source vetting failed — {detail}")
+    print(json.dumps({"pipeline_faults": faults, "source_assessment": UNVETTED_NOTE}))
+
+
+try:
+    main()
+except Exception as e:  # noqa: BLE001 — the fault marker itself must never crash
+    print(
+        json.dumps(
+            {
+                "pipeline_faults": [
+                    f"PIPELINE-FAULT: source vetting failed — "
+                    f"fault-marker script error: {e}"
+                ],
+                "source_assessment": UNVETTED_NOTE,
+            }
+        )
+    )