feat(TASK-029): review-gauntlet fault-only lane re-run loop

Give the review gauntlet a deterministic retry loop for lanes that FAULT
(PIPELINE-FAULT marker, missing verdict sentinel, or a nested graph's own
degraded-run wording) without ever re-running a lane that reached a real
verdict.

- graph.yaml: the four lane maps route to a new `retry_gate` script node
  (static `next: verdict_gate`; emits `_next: build_items` to retry).
  initial_state gains lane_attempts / kept_results / retry_lanes /
  review_incomplete / gauntlet_started_at. settings.timeout 24000 -> 69600
  (3 passes x 2 attempts x 11400 + 1200 margin).
- scripts/retry_gate.py (new): stashes every lane report that ran
  (completed and faulted alike) and restores reports a re-run pass
  overwrote with []; classifies with verdict_gate.py's sentinel regexes
  verbatim; counts attempts; retries while attempts < 3 and inside a
  45600 s wall-clock budget; otherwise records the lane in
  review_incomplete and falls through. Crash guard appends to
  signals_error and never retries.
- scripts/signals.py: stamps gauntlet_started_at before the git work so a
  failed diff still starts the clock.
- scripts/build_items.py: retry pass emits items only for retry_lanes
  (with attempt numbers), adds a `retried:` note to lanes_summary, resets
  retry_lanes; falsy-guarded stamp fallback; crash guard appends to
  signals_error and preserves lanes_summary.
- Tests: hermetic python3-guarded script tests for retry_gate /
  build_items / signals, graph wiring + initial_state pins, sentinel and
  LANE_KEYS cross-pins, retry-budget envelope vs settings.timeout, a
  first-pass golden payload, and an engine-level executor test proving a
  script `_next` back-edge re-fires a static fan-out and an empty map
  re-run clears its collect_into.

Plan: PLAN-review-retry section A items 1-3 and 5. Verdict/report surface
(section A items 4 and 6) is TASK-032.

assets/agents/review-gauntlet/scripts/build_items.py

@@ -9,6 +9,10 @@ skip mechanism — no dynamic routing anywhere.
 The LLM's add_* flags can only ADD lanes. A flag that is false never
 removes a lane the hard rules selected.
 
+A re-run pass (retry_gate emitted `retry_lanes`) skips selection: only the
+named lanes get an item, stamped with their attempt number, and every other
+lane maps over nothing — retry_gate restores their earlier reports.
+
 Fail-closed: a builder crash emits all four lists empty plus a
 PIPELINE-FAULT in signals_error — verdict_gate blocks on it and the crash
 never kills the graph.
@@ -16,6 +20,7 @@ never kills the graph.
 
 import json
 import os
+import time
 
 # Keep in sync with default_lanes.ALIASES — a caller-forced lane must
 # canonicalize the same way on the degraded path as it does here.
@@ -35,6 +40,18 @@ ALIASES = {
     "usage-pattern-testing": "probe",
 }
 
+# Keep in sync with retry_gate.LANES
+LANE_KEYS = {
+    "code-review": "code_review_items",
+    "adversary": "adversary_items",
+    "security": "security_items",
+    "probe": "probe_items",
+}
+
+# Filled by main() so the crash guard can append to an upstream fault
+# instead of overwriting it, and keep the first pass's lanes_summary.
+crash_context = {"signals_error": "", "lanes_summary": ""}
+
 
 def load_state():
     if path := os.environ.get("GRAPH_STATE_FILE"):
@@ -45,11 +62,38 @@ def load_state():
 
 def main():
     state = load_state()
+    prior = state.get("signals_error")
+    crash_context["signals_error"] = prior if isinstance(prior, str) else ""
+    # retry_gate's wall-clock budget is measured from this stamp; signals.py
+    # is the normal stamper, this is the defensive fallback.
+    stamp = {} if state.get("gauntlet_started_at") else {"gauntlet_started_at": time.time()}
 
     def text(key):
         v = state.get(key)
         return v.strip() if isinstance(v, str) else ""
 
+    crash_context["lanes_summary"] = text("lanes_summary")
+    retry_lanes = [lane for lane in (state.get("retry_lanes") or []) if lane in LANE_KEYS]
+    if retry_lanes:
+        attempts = state.get("lane_attempts") or {}
+        retried = [(lane, int(attempts.get(lane) or 0) + 1) for lane in retry_lanes]
+        note = "- retried: [" + ", ".join(f"{lane} (attempt {n})" for lane, n in retried) + "]"
+        summary = text("lanes_summary")
+        print(
+            json.dumps(
+                {
+                    **{key: [] for key in LANE_KEYS.values()},
+                    **{
+                        LANE_KEYS[lane]: [{"lane": lane, "attempt": n}] for lane, n in retried
+                    },
+                    "lanes_summary": f"{summary}\n{note}" if summary else note,
+                    "retry_lanes": [],
+                    **stamp,
+                }
+            )
+        )
+        return
+
     forced_raw = state.get("forced_lanes") or []
     forced, unknown = [], []
     for lane in forced_raw:
@@ -126,6 +170,7 @@ def main():
                 "security_items": [{"lane": "security"}] if "security" in lanes else [],
                 "probe_items": [{"lane": "probe"}] if "probe" in lanes else [],
                 "lanes_summary": "\n".join(f"- {r}" for r in reasons),
+                **stamp,
             }
         )
     )
@@ -134,6 +179,9 @@ def main():
 try:
     main()
 except Exception as e:  # noqa: BLE001 — a builder crash must never kill the graph
+    fault = f"PIPELINE-FAULT: lane builder crashed — {e}; no lanes were run"
+    if crash_context["signals_error"]:
+        fault = f"{crash_context['signals_error']}; {fault}"
     print(
         json.dumps(
             {
@@ -141,8 +189,8 @@ except Exception as e:  # noqa: BLE001 — a builder crash must never kill the g
                 "adversary_items": [],
                 "security_items": [],
                 "probe_items": [],
-                "lanes_summary": "",
-                "signals_error": f"PIPELINE-FAULT: lane builder crashed — {e}; no lanes were run",
+                "lanes_summary": crash_context["lanes_summary"],
+                "signals_error": fault,
             }
         )
     )

assets/agents/review-gauntlet/scripts/retry_gate.py

@@ -0,0 +1,159 @@
+#!/usr/bin/env python3
+"""Deterministic fault-only re-run gate for the review gauntlet.
+
+Sits between the four lane maps and the verdict gate. Every lane map runs
+on every pass — a lane that is not being re-run maps over [] — so a re-run
+pass overwrites the untouched lanes' collected results with []. The gate's
+hard rules:
+
+  - every lane that ran this pass is stashed in kept_results, completed
+    and faulted alike, and a lane whose map ran nothing this pass gets
+    its stashed report restored — the verdict gate always sees each
+    lane's LAST report;
+  - a lane is FAULTED only when its report is missing, non-string, the
+    lane_fault.py marker, sentinel-less, or carries the nested graph's own
+    degraded-run wording; a real verdict (DIVERGES, FAIL, INCONCLUSIVE,
+    NEEDS-HUMAN, …) is never re-run — the review's judgment stands;
+  - a faulted lane is re-run only while it has attempts left AND the
+    gauntlet is inside its wall-clock budget; otherwise it is recorded in
+    review_incomplete and its fault flows to the verdict gate as-is;
+  - the gate itself must never retry by accident: any internal error
+    records a PIPELINE-FAULT in signals_error and falls through to the
+    verdict gate, which blocks on it.
+"""
+
+import json
+import os
+import re
+import time
+
+MAX_RETRY_ELAPSED_SECS = 45600
+MAX_ATTEMPTS = 3
+
+# lane name -> (items key, results key)
+LANES = {
+    "code-review": ("code_review_items", "code_review_results"),
+    "adversary": ("adversary_items", "adversary_results"),
+    "security": ("security_items", "security_results"),
+    "probe": ("probe_items", "probe_results"),
+}
+
+# Must stay identical to verdict_gate.py's sentinel regexes: a lane this
+# gate calls completed must be one the verdict gate can parse, or a drift
+# would re-run lanes the verdict gate accepts (or accept lanes it cannot
+# read). A cross-pin test compares the literals in both files.
+SENTINELS = {
+    "code-review": r"Verdict:\**\s*\**\s*(MERGE-READY|NEEDS-HUMAN)",
+    "adversary": r"ADVERSARIAL_REVIEW:\s*(CONFORMS|DIVERGES)",
+    "security": r"SECURITY_REVIEW:\s*(PASS|FAIL)",
+    "probe": r"USAGE_PROBE:\s*(PASS|FAIL|INCONCLUSIVE)",
+}
+
+# Filled by main() so the crash guard can append to an upstream fault
+# instead of overwriting it, and report the lanes it had already declined.
+crash_context = {"signals_error": "", "review_incomplete": []}
+
+
+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 nested_degraded(lane, report):
+    # The nested graphs complete with a sentinel even when a stage inside
+    # them died; their own degraded-run wording marks a partial review,
+    # which is not a completed one. Same anchoring as verdict_gate.py.
+    if lane == "code-review":
+        verdict_line = re.search(r"^\*\*Verdict: .*$", report, re.MULTILINE)
+        return bool(
+            verdict_line
+            and re.search(
+                r"^\*\*Verdict: NEEDS-HUMAN\*\* — .*"
+                r"(pipeline fault\(s\) recorded|PIPELINE-FAULT:|report rendering error)",
+                verdict_line.group(0),
+            )
+        )
+    if lane == "adversary":
+        return bool(
+            re.search(
+                r"^Criteria: .*degraded run: pipeline fault recorded",
+                report,
+                re.MULTILINE,
+            )
+        )
+    return False
+
+
+def is_faulted(lane, report):
+    if not isinstance(report, str):
+        return True
+    if report.strip().startswith("PIPELINE-FAULT:"):
+        return True
+    if not re.search(SENTINELS[lane], report):
+        return True
+    return nested_degraded(lane, report)
+
+
+def main():
+    state = load_state()
+    prior = state.get("signals_error")
+    crash_context["signals_error"] = prior if isinstance(prior, str) else ""
+    incomplete = list(state.get("review_incomplete") or [])
+    crash_context["review_incomplete"] = incomplete
+    attempts = dict(state.get("lane_attempts") or {})
+    kept = dict(state.get("kept_results") or {})
+    out = {}
+    faulted = []
+
+    for lane, (items_key, results_key) in LANES.items():
+        results = state.get(results_key) or []
+        if not state.get(items_key):
+            if not results and lane in kept:
+                out[results_key] = [kept[lane]]
+            continue
+        report = results[0] if results else None
+        if report is not None:
+            kept[lane] = report
+        if is_faulted(lane, report):
+            faulted.append(lane)
+        attempts[lane] = int(attempts.get(lane) or 0) + 1
+
+    # A missing/zero stamp reads as an ancient start and declines every
+    # retry — the safe direction when the clock's origin is unknown.
+    started = state.get("gauntlet_started_at") or 0
+    within_budget = (time.time() - float(started)) <= MAX_RETRY_ELAPSED_SECS
+    retry = [lane for lane in faulted if within_budget and attempts[lane] < MAX_ATTEMPTS]
+    declined = [lane for lane in faulted if lane not in retry]
+    incomplete = sorted(set(incomplete) | set(declined))
+    crash_context["review_incomplete"] = incomplete
+
+    out.update(
+        {
+            "lane_attempts": attempts,
+            "kept_results": kept,
+            "retry_lanes": retry,
+            "review_incomplete": incomplete,
+        }
+    )
+    if retry:
+        out["_next"] = "build_items"
+    print(json.dumps(out))
+
+
+try:
+    main()
+except Exception as e:  # noqa: BLE001 — a gate crash must fall through, never retry
+    fault = f"PIPELINE-FAULT: retry gate crashed — {e}"
+    if crash_context["signals_error"]:
+        fault = f"{crash_context['signals_error']}; {fault}"
+    print(
+        json.dumps(
+            {
+                "retry_lanes": [],
+                "review_incomplete": crash_context["review_incomplete"],
+                "signals_error": fault,
+            }
+        )
+    )

assets/agents/review-gauntlet/scripts/signals.py

@@ -12,6 +12,7 @@ import json
 import os
 import re
 import subprocess
+import time
 
 def load_state():
     if path := os.environ.get("GRAPH_STATE_FILE"):
@@ -37,6 +38,10 @@ def git(*args):
 
 
 out = {"project_dir": proj}
+# retry_gate measures its wall-clock budget from this stamp; it is set
+# before the git work so a failed diff still starts the clock.
+if not state.get("gauntlet_started_at"):
+    out["gauntlet_started_at"] = time.time()
 try:
     if spec in ("", "worktree"):
         names = git("diff", "--name-only", "HEAD")