fix(retrieval-gate): row 5 reads git for the half a registration cannot assert

PM's J1. Three of row 5's ten checks now read the repository's history instead
of the registration's own fields:

- the registration is COMMITTED and unmodified against HEAD -- a file written
  in a working tree is not a pre-registration;
- the commit that ADDED it is not itself a change to the ranking -- a
  threshold and the change it is supposed to bind, in one commit, is neither;
- a change to the ranking landed AFTER it. This is the one that cannot be
  self-attested: it is satisfied only in the order a pre-registration actually
  happens, and it is red today because neither half has happened.

The three come from `git_provenance`, a `Provenance` the row receives the way
it already receives a path, so both directions are driven from the test and
the default is the real git. Outside a git tree, or with no git on PATH, the
fields come back in their REFUSING form with the reason printed -- unknown is
not unknown-and-therefore-fine.

WHAT GIT CANNOT PROVE IS STATED IN THE ROW, not implied: history shows ORDER,
never that nobody read the number before writing the threshold -- a number can
be read from an uncommitted tree. Order is what these three checks are.

Row 5 is unchanged where it matters today: `0 of 1 RED`, no registration. The
two existing direction tests move 7 -> 10 checks and a third arm is added that
drives each git check red on its own. 54 passed.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

tests/test_retrieval_gate.py

@@ -329,6 +329,21 @@ def test_a_covered_question_that_came_back_marked_would_fail_the_same_row(
 # --- row 5 --------------------------------------------------------------------
 
 
+def _carried_by_git(
+    *, tracked: bool = True, same_commit: bool = False, after: int = 1
+) -> gate.Provenance:
+    """A history row 5 reads instead of believing the registration. The three
+    git checks are driven from HERE, never from a file the test writes, which
+    is the whole point of the row."""
+    return gate.Provenance(
+        tracked=tracked,
+        unmodified=tracked,
+        commit="0" * 40 if tracked else "",
+        commit_touches_ranking=same_commit,
+        ranking_commits_after=after,
+    )
+
+
 def test_row_five_is_red_while_no_hold_out_is_registered(tmp_path: Path) -> None:
     row = gate.row_five(tmp_path / "absent.json")
     assert (row.k, row.m, row.status) == (0, 1, gate.RED)
@@ -352,8 +367,8 @@ def test_row_five_is_green_for_a_registration_that_carries_all_seven(tmp_path: P
         ),
         encoding="utf-8",
     )
-    row = gate.row_five(registration)
-    assert (row.k, row.m, row.status) == (7, 7, gate.GREEN)
+    row = gate.row_five(registration, provenance=lambda _: _carried_by_git())
+    assert (row.k, row.m, row.status) == (10, 10, gate.GREEN)
 
 
 def test_row_five_falls_on_a_number_read_before_its_threshold_was_written(
@@ -375,11 +390,44 @@ def test_row_five_falls_on_a_number_read_before_its_threshold_was_written(
         ),
         encoding="utf-8",
     )
-    row = gate.row_five(registration)
-    assert (row.k, row.m, row.status) == (6, 7, gate.RED)
+    row = gate.row_five(registration, provenance=lambda _: _carried_by_git())
+    assert (row.k, row.m, row.status) == (9, 10, gate.RED)
     assert any("no reading predates the threshold: NO" in detail for detail in row.details)
 
 
+def test_row_five_falls_when_the_registration_rides_in_on_the_ranking_change(
+    tmp_path: Path,
+) -> None:
+    """The three git checks, each driven red on its own: a file nobody
+    committed, a threshold committed together with the ranking change, and a
+    registration no ranking change has come after."""
+    held = tmp_path / "held.json"
+    held.write_text('{"questions": []}', encoding="utf-8")
+    registration = tmp_path / "registration.json"
+    registration.write_text(
+        json.dumps(
+            {
+                "set": str(held),
+                "sha256": gate.sha256_of(held),
+                "threshold": "hit@payload at unit granularity >= 0.8",
+                "threshold_written_at": "2026-09-19T10:00:00Z",
+                "written_by": "somebody",
+                "readings": [],
+            }
+        ),
+        encoding="utf-8",
+    )
+    arms = {
+        "uncommitted": (_carried_by_git(tracked=False), "committed"),
+        "same commit as the ranking": (_carried_by_git(same_commit=True), "same commit"),
+        "nothing changed since": (_carried_by_git(after=0), "0 commit(s) touching"),
+    }
+    for label, (history, expected) in arms.items():
+        row = gate.row_five(registration, provenance=lambda _, h=history: h)
+        assert row.status == gate.RED, label
+        assert any(expected in detail for detail in row.details), (label, row.details)
+
+
 # --- row 6 --------------------------------------------------------------------