refactor(tests): derive the two duplicated test helpers into tests/helpers.py (#4276)

Derive-first, ahead of the tests shape pay-down. An AST pass over all 2628
definitions under `tests/` found exactly three helper bodies duplicated
across files. Two are real copies and are consolidated here; the third is
not, and is left alone.

`need_tools(*tools)` — byte-identical in three hook-test modules, each
skipping when `jq`/`awk`/`git` is absent from PATH. Now snippet #4277. The
`import shutil` each file carried existed only to serve it and goes with it.

`rule_row(rule_id)` — byte-identical in two integration modules, reading a
Rule back through a SEPARATE session so the assertion is about what Postgres
holds rather than what the writing session's identity map remembers. Now
snippet #4278. Its imports are lazy, because `tests/helpers.py` is imported
by unit tests that have no database, which is the same reason
`plugin_config` defers its service imports.

NOT consolidated: `_side(uid, k, d="")` in test_services_plugin_context and
test_write_path_trigger. The body is identical but it closes over a
module-local `stored` dict, so it is not self-contained and "moving" it
would mean inventing a parameter neither call site wants. That is convention
plumbing — two tests independently writing the same one-line side_effect —
and it is dismissed in the ledger rather than lifted.

Worth recording for the next pass: a repeated NAME is not a family. `_row`
is defined in five modules and only two of those share a body; the other
three (test_list_rows_brief, test_calibration_stamp, test_shape_ledger)
build entirely different objects. Grouping by name would have consolidated
three things that have nothing in common.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01821k5B3Ysecp9fNYs92Kuy

tests/test_integration_rule_move.py

@@ -20,7 +20,7 @@ from scribe.models.rulebook import Rule
 from scribe.services import canonical_systems as canonical_svc
 from scribe.services import rule_versions as rv_svc
 from scribe.services import rulebooks as rulebooks_svc
-from tests.helpers import ensure_user
+from tests.helpers import ensure_user, rule_row
 
 pytestmark = [pytest.mark.integration, pytest.mark.usefixtures("_dispose_engine")]
 
@@ -69,17 +69,12 @@ async def homes():
     return ids
 
 
-async def _row(rule_id: int) -> Rule:
-    async with async_session() as s:
-        return await s.get(Rule, rule_id)
-
-
 async def test_a_project_rule_becomes_global_and_keeps_everything(homes):
     owner, rule_id = homes["owner"], homes["rule"]
     moved = await rulebooks_svc.move_rule(rule_id, owner, topic_id=homes["topic"])
 
     assert moved.id == rule_id
-    row = await _row(rule_id)
+    row = await rule_row(rule_id)
     assert (row.topic_id, row.project_id) == (homes["topic"], None)
     assert len(await rv_svc.list_versions(rule_id)) == 1, "the move must not drop history"
     areas = await rulebooks_svc.list_rule_systems([rule_id])
@@ -100,7 +95,7 @@ async def test_a_global_rule_can_move_onto_a_project(homes):
     owner, rule_id = homes["owner"], homes["rule"]
     await rulebooks_svc.move_rule(rule_id, owner, topic_id=homes["topic"])
     await rulebooks_svc.move_rule(rule_id, owner, project_id=homes["other"])
-    row = await _row(rule_id)
+    row = await rule_row(rule_id)
     assert (row.topic_id, row.project_id) == (None, homes["other"])
 
 
@@ -126,7 +121,7 @@ async def test_refusals_happen_before_anything_is_written(homes):
     with pytest.raises(ValueError, match=f"rule {clash.id}"):
         await rulebooks_svc.move_rule(rule_id, owner, topic_id=homes["topic"])
 
-    row = await _row(rule_id)
+    row = await rule_row(rule_id)
     assert (row.topic_id, row.project_id) == (None, homes["home"])