test(episodes): characterize mixed admission boundaries

docs/adr/0001-episode-semantics-boundaries.md

@@ -309,6 +309,29 @@ algorithm and strict format-version binding. Rollback is removal of the v2
 algorithm branch, schema definitions, and v2 golden; the v1 writer and artifacts
 do not require migration.
 
+### Mixed contrast means whole-selection rejection, not missing evidence
+
+A focused three-candidate control resolves the first admission-atomicity
+question without changing the v2 schema. The first and second threshold cores
+have an `18x` bridge contrast, while the second and third have a `1x` contrast.
+All three candidates remain selected; the adjacent decisions are therefore
+`[pass, fail]` and the segment-level `admitted` value is false.
+
+The aggregate means only that the complete v1 selection cannot be adopted
+unchanged. It does not mean that every selected candidate or every boundary is
+invalid. V2 must retain both local contrast records, including the passing
+boundary, when the aggregate rejects the selection. Changing the aggregate from
+`all` to `any` makes this control fail, so the test observes whole-selection
+admission rather than merely counting contrasts.
+
+This accepts the conservative all-adjacencies gate for the current research
+oracle. It does not authorize dropping all findings in a runtime projection.
+Partial adoption would require a separate boundary-driven partition contract:
+how failed boundaries merge evidence, how an interior candidate with one pass
+and one fail is assigned, and how resulting finding identities remain stable.
+The first mixed control answers the aggregate-semantics question, so no cadence,
+ratio, or candidate-count sweep is warranted in this slice.
+
 Together, the two fixtures and focused tie/shared-evidence/background controls
 accept the recovery, null-control, deterministic tie-break, and publication
 single-consumption hypotheses for their bounded cases. The background control

tests/test_episode_candidate.py

@@ -16,6 +16,7 @@
     validate_oracle,
 )
 from scripts.episode_candidate_core import (  # noqa: E402
+    activity_segments,
     enumerate_candidate_windows,
     parse_timestamp,
     select_window_separated_candidates,
@@ -38,6 +39,22 @@
 )
 
 
+def make_events(offsets: list[int]) -> list[dict[str, object]]:
+    origin = parse_timestamp("2026-03-10T09:00:00Z")
+    return [
+        {
+            "event_id": f"line:{index}",
+            "line_number": index,
+            "timestamp": (origin + timedelta(seconds=offset))
+            .isoformat()
+            .replace("+00:00", "Z"),
+            "event_type": "ssh_failed_password",
+            "source_ip": "203.0.113.77",
+        }
+        for index, offset in enumerate(offsets, start=1)
+    ]
+
+
 class ContinuousBackgroundFixtureTests(unittest.TestCase):
     def setUp(self) -> None:
         self.fixture = json.loads(
@@ -202,19 +219,7 @@ def test_v2_materializes_core_contrast_admission_without_changing_selection(
     def test_v2_materializes_uniform_background_rejection_without_hiding_selection(
         self,
     ) -> None:
-        origin = parse_timestamp("2026-03-10T09:00:00Z")
-        events = [
-            {
-                "event_id": f"line:{index}",
-                "line_number": index,
-                "timestamp": (origin + timedelta(seconds=150 * (index - 1)))
-                .isoformat()
-                .replace("+00:00", "Z"),
-                "event_type": "ssh_failed_password",
-                "source_ip": "203.0.113.77",
-            }
-            for index in range(1, 15)
-        ]
+        events = make_events([150 * offset for offset in range(14)])
         selected = select_window_separated_candidates(
             enumerate_candidate_windows(events, 5, 600), 600
         )
@@ -232,6 +237,101 @@ def test_v2_materializes_uniform_background_rejection_without_hiding_selection(
         )
         self.assertFalse(admission["adjacent_contrasts"][0]["passes"])
 
+    def test_v2_mixed_contrasts_reject_unchanged_selection_and_keep_boundaries(
+        self,
+    ) -> None:
+        events = make_events(
+            [
+                0,
+                30,
+                60,
+                90,
+                120,
+                660,
+                1200,
+                1740,
+                2280,
+                2820,
+                3360,
+                3390,
+                3420,
+                3450,
+                3480,
+                *range(3630, 5581, 150),
+            ]
+        )
+        selected = select_window_separated_candidates(
+            enumerate_candidate_windows(events, 5, 600), 600
+        )
+
+        admission = materialize_core_contrast_admission(events, selected, 5)
+
+        self.assertEqual(len(activity_segments(events, 600)), 1)
+        self.assertEqual(
+            [candidate.candidate_id for candidate in selected],
+            [
+                "candidate:line:1..line:5",
+                "candidate:line:11..line:18",
+                "candidate:line:23..line:27",
+            ],
+        )
+        self.assertFalse(admission["admitted"])
+        self.assertEqual(
+            admission["reason_code"], "adjacent_core_contrast_below_minimum"
+        )
+        self.assertEqual(
+            [core["event_ids"] for core in admission["threshold_cores"]],
+            [
+                [f"line:{index}" for index in range(1, 6)],
+                [f"line:{index}" for index in range(11, 16)],
+                [f"line:{index}" for index in range(23, 28)],
+            ],
+        )
+        self.assertEqual(
+            [
+                (
+                    contrast["left_candidate_id"],
+                    contrast["right_candidate_id"],
+                    contrast["passes"],
+                    contrast["reason_code"],
+                )
+                for contrast in admission["adjacent_contrasts"]
+            ],
+            [
+                (
+                    "candidate:line:1..line:5",
+                    "candidate:line:11..line:18",
+                    True,
+                    "minimum_core_gap_contrast_met",
+                ),
+                (
+                    "candidate:line:11..line:18",
+                    "candidate:line:23..line:27",
+                    False,
+                    "minimum_core_gap_contrast_below_minimum",
+                ),
+            ],
+        )
+        self.assertEqual(
+            [
+                (
+                    contrast["bridge_mean_gap_microseconds"],
+                    contrast["required_bridge_mean_gap_microseconds"],
+                )
+                for contrast in admission["adjacent_contrasts"]
+            ],
+            [
+                (
+                    {"numerator": 540_000_000, "denominator": 1},
+                    {"numerator": 60_000_000, "denominator": 1},
+                ),
+                (
+                    {"numerator": 150_000_000, "denominator": 1},
+                    {"numerator": 300_000_000, "denominator": 1},
+                ),
+            ],
+        )
+
 
 class IsolatedDenseBurstsFixtureTests(unittest.TestCase):
     def setUp(self) -> None: