Merge pull request 'feat(ci): run L0/L1 offline checks, mutation suites and yamllint in bounded parallel pools' (#149) from feat/parallel-l0-checks into main

Reviewed-on: #149
Reviewed-by: Keith Jackson <[email protected]>

ci/lint.sh

@@ -25,8 +25,44 @@ if [ "${#files[@]}" -eq 0 ]; then
   exit 0
 fi
 
-yamllint -c "${CI_DIR}/yamllint.yaml" -f "${YAMLLINT_FORMAT:-standard}" "${files[@]}"
+# yamllint is single-threaded, so the file list is split into LINT_JOBS CONTIGUOUS slices of the
-ok "yaml/lint passed (${#files[@]} files)"
+# sorted list, one yamllint per slice, run concurrently. Each slice's output goes to its own file
+# and the files are printed in slice order afterwards: the log is the same text, in the same
+# file order, as one serial `yamllint "${files[@]}"`, and a finding is never interleaved with
+# another process's output (yamllint's standard format puts the FILE NAME on its own line above
+# that file's `line:col` findings, so interleaving would misattribute them). The stage's exit
+# code is the highest any slice returned (yamllint: 1 = error, 2 = warning under strict), so a
+# single failing slice fails the stage exactly as the serial call did. LINT_JOBS=1 is serial.
+lint_jobs="${LINT_JOBS:-$(n="$(nproc 2>/dev/null || echo 1)"; [ "$n" -gt 8 ] && n=8; echo "$n")}"
+case "$lint_jobs" in ''|*[!0-9]*|0) err "LINT_JOBS must be a positive integer, got '${lint_jobs}'"; exit 2 ;; esac
+[ "$lint_jobs" -gt "${#files[@]}" ] && lint_jobs="${#files[@]}"
+lint_tmp="$(mktemp -d)"
+trap 'rm -rf "$lint_tmp"' EXIT
+per=$(( (${#files[@]} + lint_jobs - 1) / lint_jobs ))
+pids=()
+for (( i = 0; i < lint_jobs; i++ )); do
+  slice=("${files[@]:$(( i * per )):${per}}")
+  [ "${#slice[@]}" -gt 0 ] || break
+  ( rc=0
+    yamllint -c "${CI_DIR}/yamllint.yaml" -f "${YAMLLINT_FORMAT:-standard}" "${slice[@]}" \
+      >"${lint_tmp}/${i}.out" 2>&1 || rc=$?
+    echo "$rc" >"${lint_tmp}/${i}.rc" ) &
+  pids+=("$!")
+done
+wait "${pids[@]}" || true
+lint_rc=0
+for (( i = 0; i < ${#pids[@]}; i++ )); do
+  cat "${lint_tmp}/${i}.out"
+  # A slice that left no rc file died before yamllint returned: that is a failure, not a pass.
+  slice_rc="$(cat "${lint_tmp}/${i}.rc" 2>/dev/null || true)"
+  case "$slice_rc" in ''|*[!0-9]*) slice_rc=1 ;; esac
+  [ "$slice_rc" -gt "$lint_rc" ] && lint_rc="$slice_rc"
+done
+if [ "$lint_rc" -ne 0 ]; then
+  err "yaml/lint failed (yamllint exit ${lint_rc}; ${#files[@]} files in ${#pids[@]} parallel slice(s))"
+  exit "$lint_rc"
+fi
+ok "yaml/lint passed (${#files[@]} files, ${#pids[@]} parallel slice(s))"
 
 # A workflow's `configurationFile:` must name a file that exists. Renovate's did not after #79
 # renamed renovate.json -> renovate.json5, and every scheduled run failed with ENOENT for 11 days

conformance/lib/run_l1_offline.py

@@ -14,7 +14,7 @@ Pure standard library (matches the harness's no-pip-dependency posture); the che
 themselves shell out (render checks to catalog/render.py, whose PyYAML dependency lives
 there; L0 checks to git + PyYAML).
 
-Usage: run_l1_offline.py --junit <out.xml> [--label-prefix P] <test-dir> [<test-dir> ...]
+Usage: run_l1_offline.py --junit <out.xml> [--label-prefix P] [--jobs N] <test-dir> [<test-dir> ...]
 Exit 0 iff every selected offline check passes.
 
 The per-dir check script is whichever of `render-check.sh` / `check.sh` the directory
@@ -43,13 +43,35 @@ Exit codes: 0 all selected checks passed / 1 at least one FAILED / 3 nothing fai
 scope-declared check was UNWIRED. conformance/run.sh propagates 3 verbatim; ci/l0.sh turns it
 into the gate's own rc 3. This is the ONE place the "unwired, not green" rule lives now,
 instead of once per hand-written stage.
+
+PARALLELISM (--jobs, env CONF_OFFLINE_JOBS)
+-------------------------------------------
+The checks are independent processes, so they run in a bounded thread pool (one `bash` child
+per worker). Default: min(8, usable CPUs); `--jobs 1` is the old serial runner exactly. Each
+check's stdout+stderr is CAPTURED and only reported after every check has finished, in the
+ORDER THE DIRS WERE GIVEN, so the log, the JUnit and the step summary are byte-for-byte
+independent of which check finished first (only the trailing "[N.Ns]" wall-time on each
+status line varies). The 0/1/3 aggregation runs over the same ordered case list as before.
+
+Parallel-safety is a property of the CHECKS, not of this runner: every check must keep its
+scratch state in a private mktemp/mkdtemp dir and must not write into the tree or a fixed
+path. The audit that established that for the current set is recorded in
+decisions/2026-11-08-parallel-l0-checks.md; a new check that needs shared state must say so.
+
+Nested pools: the keycloak reconciler checks run their own mutation suites in a pool
+(mutations.py, env MUTATION_JOBS). When this runner is itself parallel it exports a SMALLER
+MUTATION_JOBS (unless the caller already set one), so the two suites share the CPUs the
+other jobs-2 checks are not using instead of each taking min(8, CPUs). See inner_jobs().
 """
 from __future__ import annotations
 
 import argparse
+import os
 import re
 import subprocess
 import sys
+import time
+from concurrent.futures import ThreadPoolExecutor
 import xml.etree.ElementTree as ET
 from pathlib import Path
 from xml.dom import minidom
@@ -97,6 +119,46 @@ def collect_meta(test_yaml: Path, prefix: str):
     return name, reqs
 
 
+def usable_cpus() -> int:
+    """CPUs this process may run on (the cgroup/affinity view, not the host's count)."""
+    try:
+        return max(1, len(os.sched_getaffinity(0)))
+    except (AttributeError, OSError):
+        return max(1, os.cpu_count() or 1)
+
+
+def positive_int(text: str) -> int:
+    n = int(text)
+    if n < 1:
+        raise argparse.ArgumentTypeError(f"must be >= 1, got {n}")
+    return n
+
+
+def inner_jobs(cpus: int, outer: int) -> int:
+    """MUTATION_JOBS to hand the checks when this runner runs `outer` of them at once.
+
+    Two checks (the keycloak client-secret and passkey reconcilers) fan out internally; the
+    other outer-2 workers are single processes. Give the two suites an equal share of the CPUs
+    those others leave free, never fewer than 2 each (a 1-wide pool would make the 40-mutation
+    passkey suite the critical path of the whole stage), never more than 8. Peak process count
+    is then about (outer-2) + 2*inner, i.e. <= cpus on any machine with cpus >= outer + 2, and
+    at worst ~1.25-1.5x cpus on a small runner — CPU-bound oversubscription of that size costs
+    latency per process, not throughput.
+    """
+    if outer <= 1:
+        return min(8, cpus)
+    return max(2, min(8, (cpus - outer + 2) // 2))
+
+
+def run_check(check: Path, env: dict) -> tuple[int, str, float]:
+    t0 = time.monotonic()
+    proc = subprocess.run(
+        ["bash", str(check)], capture_output=True, text=True,
+        stdin=subprocess.DEVNULL, env=env,
+    )
+    return proc.returncode, (proc.stdout + proc.stderr).strip(), time.monotonic() - t0
+
+
 def main() -> int:
     ap = argparse.ArgumentParser(description=__doc__)
     ap.add_argument("--junit", type=Path, required=True)
@@ -108,26 +170,54 @@ def main() -> int:
                          "(makes this runner exit 3); repeatable")
     ap.add_argument("--summary-out", type=Path, default=None,
                     help="write one Markdown line per case here, for the CI step summary")
+    ap.add_argument("--jobs", type=positive_int, default=None,
+                    help="checks to run at once (default: env CONF_OFFLINE_JOBS, else "
+                         "min(8, usable CPUs)); 1 = serial")
     ap.add_argument("dirs", nargs="+", type=Path)
     args = ap.parse_args()
 
     strict_scopes = set(args.unwired_scope)
 
-    cases = []  # (name, reqs, dir, rc, output, scope)
+    cpus = usable_cpus()
+    if args.jobs is not None:
+        jobs = args.jobs
+    elif os.environ.get("CONF_OFFLINE_JOBS", "").strip():
+        try:
+            jobs = positive_int(os.environ["CONF_OFFLINE_JOBS"].strip())
+        except (ValueError, argparse.ArgumentTypeError) as e:
+            ap.error(f"CONF_OFFLINE_JOBS={os.environ['CONF_OFFLINE_JOBS']!r}: {e}")
+    else:
+        jobs = min(8, cpus)
+    child_env = dict(os.environ)
+    if not child_env.get("MUTATION_JOBS", "").strip():
+        child_env["MUTATION_JOBS"] = str(inner_jobs(cpus, jobs))
+    print(f"[offline] running {len(args.dirs)} check(s), jobs={jobs} "
+          f"(cpus={cpus}, MUTATION_JOBS={child_env['MUTATION_JOBS']})", file=sys.stderr)
+
+    # Metadata first, in the given order; then the checks themselves through the pool. The
+    # results are consumed in SUBMISSION order, so `cases` is identical to the serial runner's.
+    planned = []  # (name, reqs, dir, scope, check-or-None)
     for d in args.dirs:
         check = next((d / s for s in CHECK_SCRIPTS if (d / s).exists()), None)
         name, reqs = collect_meta(d / "chainsaw-test.yaml", args.label_prefix)
         scope = scope_of(d / "chainsaw-test.yaml", args.scope_annotation)
-        if check is None:
+        planned.append((name, reqs, d, scope, check))
-            cases.append((name, reqs, d, 3,
+
-                          f"no offline check script ({' or '.join(CHECK_SCRIPTS)}) in {d}",
+    cases = []  # (name, reqs, dir, rc, output, scope)
-                          scope))
+    elapsed = []  # wall seconds per case, same order (None: nothing ran)
-            continue
+    with ThreadPoolExecutor(max_workers=jobs) as pool:
-        proc = subprocess.run(
+        futures = [pool.submit(run_check, check, child_env) if check is not None else None
-            ["bash", str(check)], capture_output=True, text=True
+                   for (_n, _r, _d, _s, check) in planned]
-        )
+        for (name, reqs, d, scope, check), fut in zip(planned, futures):
-        out = (proc.stdout + proc.stderr).strip()
+            if fut is None:
-        cases.append((name, reqs, d, proc.returncode, out, scope))
+                cases.append((name, reqs, d, 3,
+                              f"no offline check script ({' or '.join(CHECK_SCRIPTS)}) in {d}",
+                              scope))
+                elapsed.append(None)
+                continue
+            rc, out, secs = fut.result()
+            cases.append((name, reqs, d, rc, out, scope))
+            elapsed.append(secs)
 
     failures = sum(1 for c in cases if c[3] not in (0, 3))
     skipped = sum(1 for c in cases if c[3] == 3)
@@ -145,7 +235,7 @@ def main() -> int:
         },
     )
     summary_lines = []
-    for name, reqs, d, rc, out, scope in cases:
+    for (name, reqs, d, rc, out, scope), secs in zip(cases, elapsed):
         tc = ET.SubElement(
             suite,
             "testcase",
@@ -164,8 +254,9 @@ def main() -> int:
             fail.text = out
         status = "PASS" if rc == 0 else ("SKIP" if rc == 3 else "FAIL")
         mark = f" scope={scope}" if scope else ""
+        took = f" [{secs:.1f}s]" if secs is not None else ""
         print(f"[offline] {layer_of(d):3s} {status:4s} {name} "
-              f"({','.join(reqs) or 'untagged'}){mark}",
+              f"({','.join(reqs) or 'untagged'}){mark}{took}",
               file=sys.stderr)
         if rc not in (0, 3):
             print(out, file=sys.stderr)

conformance/tests/l0-static/keycloak-client-secret-reconciler/mutations.py

@@ -25,15 +25,19 @@
 #
 #   python3 mutations.py <path-to-extracted-reconciler.py>
 #
-# Runtime is ~20s (one subprocess per mutation, each running the full selftest
+# Runtime is ~11s serial (one subprocess per mutation, each running the full selftest
-# against an in-process stub Keycloak; no network, no cluster).
+# against an in-process stub Keycloak; no network, no cluster). The selftests run in a
+# bounded pool (env MUTATION_JOBS, default min(8, CPUs); 1 = serial); output order and
+# verdicts are independent of the pool size.
 # =============================================================================
 from __future__ import annotations
 
+import os
 import re
 import subprocess
 import sys
 import tempfile
+from concurrent.futures import ThreadPoolExecutor
 from pathlib import Path
 
 
@@ -136,43 +140,99 @@ MUTATIONS: list[tuple[str, str, str, str]] = [
 ]
 
 
+def mutation_jobs() -> int:
+    """Selftests to run at once: env MUTATION_JOBS, else min(8, usable CPUs).
+
+    conformance/lib/run_l1_offline.py exports a smaller MUTATION_JOBS when it is itself
+    running several checks in parallel, so the nested pools do not oversubscribe the host.
+    MUTATION_JOBS=1 reproduces the old serial loop exactly.
+    """
+    raw = os.environ.get("MUTATION_JOBS", "").strip()
+    if raw:
+        try:
+            n = int(raw)
+        except ValueError:
+            n = 0
+        if n < 1:
+            raise ValueError("MUTATION_JOBS must be a positive integer, got %r" % raw)
+        return n
+    try:
+        cpus = len(os.sched_getaffinity(0))
+    except (AttributeError, OSError):
+        cpus = os.cpu_count() or 1
+    return max(1, min(8, cpus))
+
+
+def run_selftest(mutated_src: str) -> subprocess.CompletedProcess:
+    with tempfile.NamedTemporaryFile("w", suffix=".py", delete=False) as fh:
+        fh.write(mutated_src)
+        path = fh.name
+    try:
+        return subprocess.run([sys.executable, path, "--selftest"],
+                              capture_output=True, text=True, timeout=240,
+                              stdin=subprocess.DEVNULL)
+    finally:
+        Path(path).unlink(missing_ok=True)
+
+
 def main() -> int:
     if len(sys.argv) != 2:
         print("usage: mutations.py <extracted-reconciler.py>", file=sys.stderr)
         return 2
     src = Path(sys.argv[1]).read_text()
 
-    problems: list[str] = []
+    try:
-    killed = 0
+        jobs = mutation_jobs()
+    except ValueError as e:
+        print("mutations.py: %s" % e, file=sys.stderr)
+        return 2
+
+    # Pass 1, serial and cheap: every anchor is checked BEFORE anything runs, exactly as the
+    # serial loop did, and each mutation's source is built here. None = anchor failure.
+    planned: list[tuple[str, str, str | None, str | None]] = []
     for name, why, old, new in MUTATIONS:
         old, new = dedent4(old), dedent4(new)
         # An anchor that no longer matches is a FAILURE, not a skip: it means the code
         # moved and this mutation silently stopped proving anything.
         n = src.count(old)
         if n != 1:
-            problems.append("%s: anchor matches %d times (expected exactly 1) -- the "
+            planned.append((name, why,
+                            "%s: anchor matches %d times (expected exactly 1) -- the "
                             "code moved and this mutation no longer proves anything. "
-                            "Re-anchor it against the current source." % (name, n))
+                            "Re-anchor it against the current source." % (name, n), None))
             continue
-        with tempfile.NamedTemporaryFile("w", suffix=".py", delete=False) as fh:
+        planned.append((name, why, None, src.replace(old, new, 1)))
-            fh.write(src.replace(old, new, 1))
+
-            path = fh.name
+    # Pass 2: the selftests, `jobs` at a time. Each child gets its own temp file, its own
-        try:
+    # mkdtemp dirs and its own 127.0.0.1:0 stub port, so they share nothing. Results are
-            proc = subprocess.run([sys.executable, path, "--selftest"],
+    # consumed in MUTATIONS order, so every line below is printed in the same order, with the
-                                  capture_output=True, text=True, timeout=240)
+    # same verdict, as the serial loop produced -- whichever child finishes first.
-        finally:
+    problems: list[str] = []
-            Path(path).unlink(missing_ok=True)
+    killed = 0
-        if proc.returncode == 0:
+    pool = ThreadPoolExecutor(max_workers=jobs)
-            problems.append("%s SURVIVED -- --selftest still passed with this regression "
+    try:
-                            "applied, so nothing in the suite actually checks it. The "
+        futures = [pool.submit(run_selftest, mutated) if mutated is not None else None
-                            "mistake it models: %s" % (name, why))
+                   for (_n, _w, _a, mutated) in planned]
-            continue
+        for (name, why, anchor_problem, _m), fut in zip(planned, futures):
-        killed += 1
+            if anchor_problem is not None:
-        out = proc.stdout + proc.stderr
+                problems.append(anchor_problem)
-        m = re.search(r"SELFTEST FAIL: (\d+) of \d+", out)
+                continue
-        how = ("%s assertion(s) caught it" % m.group(1) if m
+            proc = fut.result()
-               else "the selftest aborted (caught, less cleanly)")
+            if proc.returncode == 0:
-        print("  killed  %-42s %s" % (name, how))
+                problems.append("%s SURVIVED -- --selftest still passed with this regression "
+                                "applied, so nothing in the suite actually checks it. The "
+                                "mistake it models: %s" % (name, why))
+                continue
+            killed += 1
+            out = proc.stdout + proc.stderr
+            m = re.search(r"SELFTEST FAIL: (\d+) of \d+", out)
+            how = ("%s assertion(s) caught it" % m.group(1) if m
+                   else "the selftest aborted (caught, less cleanly)")
+            print("  killed  %-42s %s" % (name, how))
+    finally:
+        # A timeout (or any other exception) still propagates and fails the check, as it did
+        # serially; queued mutations are cancelled rather than run for nothing.
+        pool.shutdown(wait=True, cancel_futures=True)
 
     print()
     if problems:

conformance/tests/l0-static/keycloak-passkey-reconciler/mutations.py

@@ -40,15 +40,19 @@
 #
 #   python3 mutations.py <path-to-extracted-reconciler.py>
 #
-# Runtime is ~60s (one subprocess per mutation, each running the full selftest
+# Runtime is ~85s serial (one subprocess per mutation, each running the full selftest
-# against an in-process stub Keycloak; no network, no cluster).
+# against an in-process stub Keycloak; no network, no cluster). The selftests run in a
+# bounded pool (env MUTATION_JOBS, default min(8, CPUs); 1 = serial); output order and
+# verdicts are independent of the pool size.
 # =============================================================================
 from __future__ import annotations
 
+import os
 import re
 import subprocess
 import sys
 import tempfile
+from concurrent.futures import ThreadPoolExecutor
 from pathlib import Path
 
 # (name, the mistake being modelled, anchor, replacement)
@@ -403,42 +407,98 @@ MUTATIONS: list[tuple[str, str, str, str]] = [
 ]
 
 
+def mutation_jobs() -> int:
+    """Selftests to run at once: env MUTATION_JOBS, else min(8, usable CPUs).
+
+    conformance/lib/run_l1_offline.py exports a smaller MUTATION_JOBS when it is itself
+    running several checks in parallel, so the nested pools do not oversubscribe the host.
+    MUTATION_JOBS=1 reproduces the old serial loop exactly.
+    """
+    raw = os.environ.get("MUTATION_JOBS", "").strip()
+    if raw:
+        try:
+            n = int(raw)
+        except ValueError:
+            n = 0
+        if n < 1:
+            raise ValueError("MUTATION_JOBS must be a positive integer, got %r" % raw)
+        return n
+    try:
+        cpus = len(os.sched_getaffinity(0))
+    except (AttributeError, OSError):
+        cpus = os.cpu_count() or 1
+    return max(1, min(8, cpus))
+
+
+def run_selftest(mutated_src: str) -> subprocess.CompletedProcess:
+    with tempfile.NamedTemporaryFile("w", suffix=".py", delete=False) as fh:
+        fh.write(mutated_src)
+        path = fh.name
+    try:
+        return subprocess.run([sys.executable, path, "--selftest"],
+                              capture_output=True, text=True, timeout=300,
+                              stdin=subprocess.DEVNULL)
+    finally:
+        Path(path).unlink(missing_ok=True)
+
+
 def main() -> int:
     if len(sys.argv) != 2:
         print("usage: mutations.py <extracted-reconciler.py>", file=sys.stderr)
         return 2
     src = Path(sys.argv[1]).read_text()
 
-    problems: list[str] = []
+    try:
-    killed = 0
+        jobs = mutation_jobs()
+    except ValueError as e:
+        print("mutations.py: %s" % e, file=sys.stderr)
+        return 2
+
+    # Pass 1, serial and cheap: every anchor is checked BEFORE anything runs, exactly as the
+    # serial loop did, and each mutation's source is built here. None = anchor failure.
+    planned: list[tuple[str, str, str | None, str | None]] = []
     for name, why, old, new in MUTATIONS:
         # An anchor that no longer matches is a FAILURE, not a skip: it means the code
         # moved and this mutation silently stopped proving anything.
         n = src.count(old)
         if n != 1:
-            problems.append("%s: anchor matches %d times (expected exactly 1) -- the "
+            planned.append((name, why,
+                            "%s: anchor matches %d times (expected exactly 1) -- the "
                             "code moved and this mutation no longer proves anything. "
-                            "Re-anchor it against the current source." % (name, n))
+                            "Re-anchor it against the current source." % (name, n), None))
             continue
-        with tempfile.NamedTemporaryFile("w", suffix=".py", delete=False) as fh:
+        planned.append((name, why, None, src.replace(old, new, 1)))
-            fh.write(src.replace(old, new, 1))
+
-            path = fh.name
+    # Pass 2: the selftests, `jobs` at a time. Each child gets its own temp file, its own
-        try:
+    # mkdtemp dirs and its own 127.0.0.1:0 stub port, so they share nothing. Results are
-            proc = subprocess.run([sys.executable, path, "--selftest"],
+    # consumed in MUTATIONS order, so every line below is printed in the same order, with the
-                                  capture_output=True, text=True, timeout=300)
+    # same verdict, as the serial loop produced -- whichever child finishes first.
-        finally:
+    problems: list[str] = []
-            Path(path).unlink(missing_ok=True)
+    killed = 0
-        if proc.returncode == 0:
+    pool = ThreadPoolExecutor(max_workers=jobs)
-            problems.append("%s SURVIVED -- --selftest still passed with this regression "
+    try:
-                            "applied, so nothing in the suite actually checks it. The "
+        futures = [pool.submit(run_selftest, mutated) if mutated is not None else None
-                            "mistake it models: %s" % (name, why))
+                   for (_n, _w, _a, mutated) in planned]
-            continue
+        for (name, why, anchor_problem, _m), fut in zip(planned, futures):
-        killed += 1
+            if anchor_problem is not None:
-        out = proc.stdout + proc.stderr
+                problems.append(anchor_problem)
-        m = re.search(r"SELFTEST FAIL: (\d+) of \d+", out)
+                continue
-        how = ("%s assertion(s) caught it" % m.group(1) if m
+            proc = fut.result()
-               else "the selftest aborted (caught, less cleanly)")
+            if proc.returncode == 0:
-        print("  killed  %-54s %s" % (name, how))
+                problems.append("%s SURVIVED -- --selftest still passed with this regression "
+                                "applied, so nothing in the suite actually checks it. The "
+                                "mistake it models: %s" % (name, why))
+                continue
+            killed += 1
+            out = proc.stdout + proc.stderr
+            m = re.search(r"SELFTEST FAIL: (\d+) of \d+", out)
+            how = ("%s assertion(s) caught it" % m.group(1) if m
+                   else "the selftest aborted (caught, less cleanly)")
+            print("  killed  %-54s %s" % (name, how))
+    finally:
+        # A timeout (or any other exception) still propagates and fails the check, as it did
+        # serially; queued mutations are cancelled rather than run for nothing.
+        pool.shutdown(wait=True, cancel_futures=True)
 
     print()
     if problems:

decisions/2026-11-08-parallel-l0-checks.md

@@ -0,0 +1,116 @@
+---
+date: 2026-11-08
+branch: feat/parallel-l0-checks
+title: L0 offline checks, mutation suites and yamllint run in bounded parallel pools (gate 184s -> 32s locally)
+---
+
+## What changed
+
+The gate's wall time was dominated by serial loops over independent subprocesses. Three of
+them now run in bounded pools; none of them changes a verdict, an exit code, or the order of
+anything printed.
+
+- `conformance/lib/run_l1_offline.py` — the per-check loop (L0 and L1 offline checks) runs in
+  a `ThreadPoolExecutor` of `bash <check>` children. `--jobs N` / env `CONF_OFFLINE_JOBS`,
+  default `min(8, usable CPUs)` (`sched_getaffinity`, so a cgroup cpuset is respected);
+  `--jobs 1` is the old serial runner. Results are consumed in SUBMISSION order, so `cases`,
+  the JUnit, the step summary and the 0/1/3 aggregation are built from exactly the same
+  ordered list as before. Additive output only: one `[offline] running N check(s), jobs=…`
+  line, and a trailing `[N.Ns]` wall time on each per-check status line. Children get
+  `stdin=/dev/null` (parallel children must not share the runner's stdin).
+- `conformance/tests/l0-static/keycloak-{passkey,client-secret}-reconciler/mutations.py` —
+  pass 1 (serial) checks every anchor and builds each mutated source, exactly as before;
+  pass 2 runs the `--selftest` children in a pool (env `MUTATION_JOBS`, default
+  `min(8, CPUs)`, `1` = serial). Verdicts are consumed in `MUTATIONS` order. A timeout
+  (`TimeoutExpired`) still propagates and fails the check; queued mutations are cancelled.
+  An invalid `MUTATION_JOBS` exits 2 (fails the check, never skips it).
+- **Nested-pool budget.** When the outer runner is parallel it exports
+  `MUTATION_JOBS = max(2, min(8, (cpus - jobs + 2) // 2))` unless the caller already set
+  one. Reason: only those two checks fan out; the other `jobs-2` workers are single
+  processes, so the two suites split the CPUs those leave free. Peak processes ≈
+  `(jobs-2) + 2*inner` ≤ cpus whenever cpus ≥ jobs+2 (24 CPUs: 6 + 16 = 22), and ~1.25–1.5×
+  cpus on a small runner (4 CPUs: 2 + 4 = 6). The floor of 2 is deliberate: a 1-wide inner
+  pool would make the 40-mutation passkey suite (~85s serial) the critical path of the stage.
+- `ci/lint.sh` — yamllint runs over `LINT_JOBS` (default `min(8, nproc)`) CONTIGUOUS slices
+  of the sorted file list concurrently; each slice's output is buffered to its own file and
+  printed in slice order, so the text is the same as one serial call and a `file` header is
+  never separated from its `line:col` findings. Stage rc = the highest slice rc; a slice that
+  leaves no rc file counts as 1. Invalid `LINT_JOBS` exits 2.
+
+### Parallel-safety audit (all 25 `l0-static/*/check.sh`, 3 `l1-rendering/*/render-check.sh`)
+
+Grepped every check for fixed `/tmp` paths, `_artifacts`/`ARTIFACTS`/`COVERAGE_OUT`,
+`write_text`/`open(…,"w")`, `mktemp`/`mkdtemp`/`TemporaryDirectory`, sockets/ports, `git`
+writes and `run.sh` invocations, and read what each writer writes to:
+
+- **Scratch state: all private.** Every writer uses its own `mktemp -d` / `mkdtemp` /
+  `TemporaryDirectory` (placeholder-guard-coupling, spec-immutability-enforced,
+  whole-repo-invariants-wired, auditability-proofs-producible, alert-rules-unit-tested and its
+  `platform/monitoring/tests/run.sh`, internal-services-publish-no-public-dns,
+  oauth2-proxy-{api-routes-per-app,cookie-names-distinct}, both keycloak reconcilers, the three
+  L1 render checks). No fixed `/tmp` path anywhere.
+- **Git writes:** only spec-immutability-enforced, and only `git init/add/commit` inside its
+  own `mktemp` repo. Everything else is `git ls-files`/`ls-tree`/`log`/`rev-parse` (read-only).
+- **Ports:** the reconciler selftests bind `127.0.0.1:0` (kernel-assigned); the passkey
+  selftest also dials `127.0.0.1:1` as a deliberate refused connection. No fixed listener.
+- **Ansible** (dev-nodes-provisioned-as-code): `--syntax-check`/`--list-hosts` only,
+  `retry_files_enabled = False`; its local tmp is per-process.
+- **The one shared writer:** auditability-proofs-producible runs
+  `./run.sh --coverage-only --requirements …`, which REWRITES
+  `conformance/_artifacts/coverage/coverage.{json,md}` (it inherits `CONF_ARTIFACTS`). That was
+  already true serially. No other offline check reads or writes that directory (the only
+  reader is `tests/meta/harness-selfcheck`, not an offline check), and the outer runner
+  writes coverage BEFORE and the JUnit AFTER the pool, so the final state is the same as
+  serial. Not serialised; left as is and recorded here. `lib/status.py` (run by that check)
+  reads `_artifacts/report.junit.xml` as an advisory — written only after the pool, unchanged.
+- whole-repo-invariants-wired calls `run.sh --print-selection` (writes nothing) and the
+  runner itself against synthetic dirs in its own `mktemp`.
+
+Result: no check needed fixing or serialising. A new check that needs shared state must say
+so; the runner's docstring now states that contract.
+
+## What I verified
+
+All in the pinned toolbox (`dev.sh run`, `DEV_KUBECONFIG=/dev/null`, ENGINE shim adding a ro
+mount of the main checkout's `.git`; spec repo resolved as a sibling, spec-immutability
+`pass`), host 24 CPUs, every `dev.sh` call under `flock`.
+
+- **Gate, before** (origin/main `1a33814`, detached scratch worktree + spec mount):
+  `GATE_RC=3`, in-container wall **183.9s**; `l0` stage **168.3s**, `lint` **7.8s**.
+  "Stages that did not run: gitea-settings" (plus the expected on-base
+  touched-set-not-determinable note, since main has no branch commits).
+- **Gate, after** (this branch, commit `a775082`): `GATE_RC=3`, in-container wall **32.1s**;
+  `l0` **21.1s**, `lint` **2.4s**, `l1` 2.3s. "Stages that did not run: gitea-settings" — the
+  only not-run stage. **rc 3, not green.** Caveat: the branch run selected 23 L0 checks (the
+  touched-requirement scoping dropped dev-nodes-provisioned-as-code and
+  placeholder-guard-coupling), the main run 25.
+- **Same-tree L0 comparison** (all 25 l0 dirs, same tree, same container):
+  `CONF_OFFLINE_JOBS=1 MUTATION_JOBS=1` **164.0s / 165.3s** vs default (jobs=8,
+  MUTATION_JOBS=8) **19.2s / 18.7s**. JUnit `cmp`-identical, step summary `cmp`-identical,
+  stderr identical except the timing suffixes and the JUnit path in the last line.
+- **Mutation suites, host:** passkey 83.2s → 10.5s (`MUTATION_JOBS=8`), client-secret
+  11.2s → 2.0s; output of `MUTATION_JOBS=1` and `=8` byte-identical to the pre-change script's,
+  rc 0 all round.
+- **Falsification (not committed):** in a scratch worktree at `a775082`, made the passkey
+  mutation "the protected-subtree screen is never called" a no-op (replacement == anchor).
+  Host: `MUTATION_JOBS=1` and `=8` both rc 1, output byte-identical (with a second, broken
+  anchor also injected: both reported). Toolbox: runner rc 1 both serial and parallel,
+  `L0 FAIL keycloak-passkey-reconciler … 1 of 40 mutation(s) not proven … SURVIVED`; full
+  gate **rc 1**, `stage l0: FAIL`, `MERGE GATE: BLOCKED`. Reverted; scratch worktree removed.
+- **lint.sh, host scratch repo** (31 YAML files, two broken): `LINT_JOBS=1/4/8` all rc 1,
+  stdout identical, findings named `y/f07.yaml` / `2:1 … key-duplicates` etc.; clean tree rc 0;
+  `LINT_JOBS=x` rc 2.
+
+## What I did NOT verify
+
+- **CI timings at the time of writing.** The PR's CI run is measured after push and reported
+  on the PR / handoff message, not here. The CI runner's CPU count is UNVERIFIED — the new
+  `[offline] running … jobs=… cpus=…` line in the CI log is what will show it. On a small
+  runner the speedup will be smaller than locally.
+- **approval-policy** will be red on CI: `ci/**` and `conformance/**` are sensitive paths and
+  need the operator's review. I did not and must not override it.
+- Flakiness under load: the selftests have no wall-clock assertions I found, and 4 toolbox
+  runs + several host runs were all stable, but that is a handful of runs, not a soak.
+- The coverage files under `conformance/_artifacts/coverage/` end in the same state as before
+  only because a single check rewrites them; I did not change that pre-existing quirk.
+- L2/L3 conformance: not run (no cluster in CI, as before).