tests: realism migration regression coverage

Four gaps from the realism migration plan, plus one flaky test
fixed.

Added:

- tests/deploy/test_orchestrator_unit.py — replaces the dead
  test_emailgen_unit.py. Asserts:
  * decnet-orchestrator.service.j2 carries the DECNET_REALISM_*
    env block (LLM, MODEL, TIMEOUT, PERSONAS) so per-host tuning
    works without editing the .j2.
  * Legacy DECNET_EMAILGEN_* vars are NOT referenced — clean break
    contract from stage 5.
  * decnet.target wants orchestrator + canary, does NOT want
    decnet-emailgen.service. Anti-regression for service-collapse.
  * deploy/decnet-emailgen.service.j2 stays deleted.

- tests/orchestrator/test_worker_integration.py — new
  test_one_tick_email_branch_records_orchestrator_email. Pins the
  action-roll to email, seeds a topology with an IMAP mail decky +
  two personas, stubs LLM + docker-exec write paths, verifies an
  orchestrator_emails row + bus event land. Restores end-to-end
  email coverage that was lost when the pre-collapse
  test_worker_integration.py was deleted.

- tests/realism/test_synthetic_files_truncation.py — pins the 64KB
  last_body cap on create + edit, and documents the consequence:
  edit candidates carry a truncated snapshot of files that exceeded
  the cap. If a future change lifts the cap, _LIMIT in the test
  must lift with it.

Fixed flaky:

- tests/orchestrator/test_scheduler.py — two pick_file tests
  pinned to random.Random(1). Without a seed, the 3% canary gate
  (stage 7) and 10% leave-alone roll occasionally flaked the
  assertions because the _FakeRepo doesn't carry a
  create_canary_token method.

Note: the existing
test_realism_subprocess_import_personas_rejects_in_agent_mode
already covers agent-mode rejection of decnet realism
import-personas; no new gating test needed.

tests/orchestrator/test_scheduler.py

@@ -146,11 +146,15 @@ async def test_pick_file_returns_none_when_topology_has_no_personas():
 
 @pytest.mark.asyncio
 async def test_pick_file_produces_file_action_for_topology_decky():
+    import random as _r
     repo = _FakeRepo(topologies={"t1": _topology_row(_PERSONAS_TWO)})
     deckies = [_decky()]
+    # Pin the RNG so the 3% canary gate (stage 7) and 10% leave-alone
+    # roll don't flake this test.  Seed 1 lands on a vanilla create.
     action = await scheduler.pick_file(
         deckies, repo,
         now=datetime(2026, 4, 27, 12, 0, tzinfo=timezone.utc),
+        rand=_r.Random(1),
     )
     assert isinstance(action, scheduler.FileAction)
     assert action.dst_uuid == "u1"
@@ -178,6 +182,7 @@ async def test_pick_file_skips_decky_when_personas_outside_window():
 @pytest.mark.asyncio
 async def test_pick_file_uses_global_pool_for_fleet_source(tmp_path, monkeypatch):
     import json
+    import random as _r
     pool = tmp_path / "personas.json"
     pool.write_text(json.dumps(_PERSONAS_TWO))
     monkeypatch.setenv("DECNET_REALISM_PERSONAS", str(pool))
@@ -189,9 +194,11 @@ async def test_pick_file_uses_global_pool_for_fleet_source(tmp_path, monkeypatch
     repo = _FakeRepo()  # no topology rows — fleet path
     deckies = [_decky(source="fleet", topology_id=None)]
 
+    # Pin the RNG so the canary / leave-alone rolls don't flake.
     action = await scheduler.pick_file(
         deckies, repo,
         now=datetime(2026, 4, 27, 12, 0, tzinfo=timezone.utc),
+        rand=_r.Random(1),
     )
     assert isinstance(action, scheduler.FileAction)
     assert action.dst_uuid == "u1"