diff --git a/sds/cli.py b/sds/cli.py
index 35445f7..a95eeea 100644
--- a/sds/cli.py
+++ b/sds/cli.py
@@ -1050,6 +1050,12 @@ def cmd_cluster_table(args: argparse.Namespace) -> int:
     return code
 
 
+def cmd_conformance(args: argparse.Namespace) -> int:
+    from .match import conformance
+
+    return conformance(Path(args.recording), bool(args.bless))
+
+
 def cmd_stand_probe(args: argparse.Namespace) -> int:
     """Record what MegaMek permits a prone, damaged Mek of each chassis."""
     from .match import stand_probe
@@ -2210,6 +2216,29 @@ def main(argv: list[str] | None = None) -> int:
     )
     cluster_table.set_defaults(func=cmd_cluster_table)
 
+    conformance = sub.add_parser(
+        "conformance",
+        help="re-ask MegaMek the questions already asked, and diff the answers",
+        description=(
+            "One JVM, no server, no match. Every fact this repository has probed "
+            "out of MegaMek and then built on - a class relationship, a sentinel, "
+            "a refusal, a step function, a terrain set - re-asked and compared "
+            "against bridge/conformance.txt. --bless re-records; a commit that "
+            "moves a figure has to say why."
+        ),
+    )
+    conformance.add_argument(
+        "--recording",
+        default=str(REPO / "bridge" / "conformance.txt"),
+        help="the committed answers to diff against",
+    )
+    conformance.add_argument(
+        "--bless",
+        action="store_true",
+        help="overwrite the recording with what MegaMek answers now",
+    )
+    conformance.set_defaults(func=cmd_conformance)
+
     club_probe = sub.add_parser(
         "club-probe",
         help="record what MegaMek says a mounted melee weapon does",
diff --git a/sds/match.py b/sds/match.py
index 741afa8..4aa06c1 100644
--- a/sds/match.py
+++ b/sds/match.py
@@ -937,6 +937,73 @@ def cluster_table(out: Path) -> int:
     return _bridge("clustertable", "sds.SdsClusterTable", [], stdout=out)
 
 
+def conformance(out: Path, bless: bool) -> int:
+    """Re-ask MegaMek every question this repository has already asked it.
+
+    One short JVM, no server and no match: `sds.SdsConformance` prints one
+    `key = value` line per pinned fact and this compares that against the
+    committed recording, naming the facts that moved rather than the lines.
+
+    The probes in `bridge/` each settled a question once and then stopped
+    running, and their answers are load-bearing - an `instanceof` rather than a
+    flag, a sentinel a damage reader special-cases, the eight terrains that are
+    cover. A MegaMek upgrade that moved one of those would leave this
+    repository wrong with every test still green. This is what fails instead.
+
+    `bless` re-records. A commit that moves a figure here has to say why.
+    """
+    fresh = REPO / "bridge" / "build" / "conformance.observed.txt"
+    code = _bridge("conformance", "sds.SdsConformance", [], stdout=fresh)
+    if code != 0:
+        print(f"the conformance probe exited {code}; see {fresh}", file=sys.stderr)
+        return code
+
+    observed = _facts(fresh.read_text())
+    if bless:
+        out.parent.mkdir(parents=True, exist_ok=True)
+        out.write_text(fresh.read_text())
+        print(f"recorded {len(observed)} facts -> {out}")
+        return 0
+    if not out.is_file():
+        print(f"no recording at {out}; run `./sds.sh conformance --bless`", file=sys.stderr)
+        return 1
+
+    recorded = _facts(out.read_text())
+    moved = [k for k in recorded if k in observed and recorded[k] != observed[k]]
+    gone = [k for k in recorded if k not in observed]
+    added = [k for k in observed if k not in recorded]
+    if not (moved or gone or added):
+        print(f"conformance: {len(observed)} facts, all as recorded")
+        return 0
+
+    for key in moved:
+        print(f"MOVED   {key}")
+        print(f"  recorded: {recorded[key]}")
+        print(f"  megamek:  {observed[key]}")
+    for key in gone:
+        print(f"GONE    {key}\n  recorded: {recorded[key]}")
+    for key in added:
+        print(f"NEW     {key}\n  megamek:  {observed[key]}")
+    print(
+        f"\nconformance: {len(moved)} moved, {len(gone)} gone, {len(added)} new."
+        "\nMegaMek no longer answers what this repository recorded. Read the facts"
+        "\nabove before blessing them: each one is something the code depends on."
+    )
+    return 1
+
+
+def _facts(text: str) -> dict[str, str]:
+    """`key = value` lines, comments and blanks dropped."""
+    facts = {}
+    for line in text.splitlines():
+        line = line.strip()
+        if not line or line.startswith("#") or " = " not in line:
+            continue
+        key, _, value = line.partition(" = ")
+        facts[key.strip()] = value.strip()
+    return facts
+
+
 def stand_probe(scenario: Path, out: Path) -> int:
     """Ask MegaMek what a prone Mek with each set of destroyed limbs may do.