fix(gate): correct max_breaking/max_dangerous threshold semantics

src/api_contract_guardian/cli.py

@@ -124,8 +124,8 @@ def check(
     fail_on_dangerous: bool = typer.Option(
         False, "--fail-on-dangerous/--allow-dangerous", help="Fail on dangerous changes",
     ),
-    max_breaking: int = typer.Option(0, "--max-breaking", help="Max allowed breaking changes (default 0)"),
-    max_dangerous: int = typer.Option(-1, "--max-dangerous", help="Max allowed dangerous changes (-1=unlimited)"),
+    max_breaking: int = typer.Option(-1, "--max-breaking", help="Max allowed breaking changes (-1=defer to flag, 0=none)"),
+    max_dangerous: int = typer.Option(-1, "--max-dangerous", help="Max allowed dangerous changes (-1=defer to flag, 0=none)"),
     output: str | None = typer.Option(None, "--output", "-o", help="Output file path"),
 ) -> None:
     """Gate CI pipeline on breaking changes. Returns exit code 1 if gate fails."""

src/api_contract_guardian/gate.py

@@ -33,7 +33,7 @@ def check_gate(
     *,
     fail_on_breaking: bool = True,
     fail_on_dangerous: bool = False,
-    max_breaking: int = 0,
+    max_breaking: int = -1,
     max_dangerous: int = -1,
 ) -> GateResult:
     """Check if a diff result passes the CI gate.
@@ -52,21 +52,17 @@ def check_gate(
     dangerous_count = len(result.dangerous_changes)
 
     # Determine effective thresholds
+    # max_breaking >= 0 is an explicit ceiling — always honour it.
+    # When absent (-1, the default), fall back to fail_on_breaking flag.
     if max_breaking >= 0:
-        if fail_on_breaking or max_breaking > 0:  # noqa: SIM108
-            effective_max_breaking = max_breaking
-        else:
-            effective_max_breaking = -1 # unlimited
+        effective_max_breaking = max_breaking
     elif fail_on_breaking:
         effective_max_breaking = 0   # default: zero tolerance
     else:
         effective_max_breaking = -1  # unlimited
 
     if max_dangerous >= 0:
-        if fail_on_dangerous or max_dangerous > 0:  # noqa: SIM108
-            effective_max_dangerous = max_dangerous
-        else:
-            effective_max_dangerous = -1 # unlimited
+        effective_max_dangerous = max_dangerous
     elif fail_on_dangerous:
         effective_max_dangerous = 0   # default: zero tolerance
     else:

tests/test_gate.py

@@ -125,3 +125,15 @@ def test_fail_on_breaking_false_max_breaking_exceeded(self):
         result = _make_result(breaking=3)
         gate = check_gate(result, fail_on_breaking=False, max_breaking=1)
         assert not gate.passed
+
+    def test_fail_on_breaking_false_max_breaking_zero_enforced(self):
+        """max_breaking=0 should still fail even when fail_on_breaking=False."""
+        result = _make_result(breaking=1)
+        gate = check_gate(result, fail_on_breaking=False, max_breaking=0)
+        assert not gate.passed
+
+    def test_fail_on_dangerous_false_max_dangerous_zero_enforced(self):
+        """max_dangerous=0 should still fail even when fail_on_dangerous=False."""
+        result = _make_result(dangerous=1)
+        gate = check_gate(result, fail_on_breaking=False, max_dangerous=0)
+        assert not gate.passed