diff --git a/goodwe_controller/test_arbitrage.py b/goodwe_controller/test_arbitrage.py
index 9a6e436..e128a26 100644
--- a/goodwe_controller/test_arbitrage.py
+++ b/goodwe_controller/test_arbitrage.py
@@ -109,6 +109,8 @@ from app.validate import validate_startup_config
 
 UTC = timezone.utc
 HERE = os.path.dirname(os.path.abspath(__file__))
+sys.path.insert(0, os.path.join(HERE, "tools"))
+import main_files  # noqa: E402
 
 # PRICE-02: `TariffPlan.arbitrage(now=...)` is required. This instant is before every
 # point these fixtures build, so no period has ended and the whole series counts.
@@ -779,9 +781,7 @@ check("...and cycle() calls it rather than inlining the conjunction, so a "
       "mutation back to a bare `engaged_now` is red rather than silent",
       "arbitrage.guard_state(self.peak_guard)" in
       ast.get_source_segment(
-          open(os.path.join(HERE, "app", "main.py"), encoding="utf-8").read(),
-          _fn(open(os.path.join(HERE, "app", "main.py"),
-                   encoding="utf-8").read(), "cycle")))
+          main_files.source(), _fn(main_files.source(), "cycle")))
 
 
 # --------------------------------------------------------------------------- #
@@ -907,8 +907,8 @@ check("a ZERO headroom does not cap a DISCHARGE. §9.1: 'discharge and export "
 # above calls decide() itself - and a required keyword-only parameter that no
 # caller fills is a TypeError only on the one path a suite does not run. Same
 # pin, same reason, as `weights=` in test_packshare.py part 10.
-_S45_MAIN = open(os.path.join(HERE, "app", "main.py"), encoding="utf-8").read()
-_S45_MAIN_TREE = ast.parse(_S45_MAIN)
+_S45_MAIN = main_files.source()
+_S45_MAIN_TREE = main_files.tree(_S45_MAIN)
 _s45_calls = [n for n in ast.walk(_S45_MAIN_TREE)
               if isinstance(n, ast.Call)
               and ast.unparse(n.func).endswith("arbitrage.decide")]
@@ -2215,8 +2215,7 @@ print()
 print("8. the background refresh - the tick must never await a fetch")
 
 
-_MAIN_SRC = derived(lambda: open(os.path.join(HERE, "app", "main.py"),
-                                 encoding="utf-8").read())
+_MAIN_SRC = derived(main_files.source)
 _cycle = derived(lambda: _fn(_MAIN_SRC, "cycle"))
 _refresh = derived(lambda: _fn(_MAIN_SRC, "run_tariff_refresh"))
 _read_inputs = derived(lambda: _fn(_MAIN_SRC, "read_inputs"))
diff --git a/goodwe_controller/test_clamp.py b/goodwe_controller/test_clamp.py
index f651a2d..e5713e3 100644
--- a/goodwe_controller/test_clamp.py
+++ b/goodwe_controller/test_clamp.py
@@ -1969,9 +1969,11 @@ print("9. SAFETY-40: the integrator bound is not a BUG SIGNAL, and the numbers "
 # The fixtures are chosen so the numbers the old text used DIFFER from the true
 # ones (MUTATION.md habit 4); the PRECONDITION checks pin that.
 import logging
+sys.path.insert(0, os.path.join(os.path.dirname(os.path.abspath(__file__)), "tools"))  # noqa: E402
+import main_files  # noqa: E402
 import app.main as _main_mod
 
-_real_compute = _main_mod.compute
+_real_compute = main_files.live.compute
 
 
 class _LogCap(logging.Handler):
@@ -1995,7 +1997,7 @@ def s40_run(grid, cycles, track, **over):
     cap = _LogCap()
     lg = logging.getLogger("goodwe")
     lg.addHandler(cap)
-    _main_mod.compute = spy
+    main_files.live.compute = spy
 
     async def go():
         hass = _Hass(grid, track=track)
@@ -2024,7 +2026,7 @@ def s40_run(grid, cycles, track, **over):
     try:
         hass, c, red = asyncio.run(go())
     finally:
-        _main_mod.compute = _real_compute
+        main_files.live.compute = _real_compute
         lg.removeHandler(cap)
     return ticks, hass, c, red, cap.records
 
@@ -2104,8 +2106,7 @@ check("...and its ERROR says it is a software fault and that control keeps "
       any(x.levelno == logging.ERROR and "software fault" in x.getMessage()
           and "control runs on" in x.getMessage() for x in log_o)
       and "reached 14 768 W on this project" in
-      open(os.path.join(os.path.dirname(os.path.abspath(__file__)), "app",
-                        "main.py"), encoding="utf-8").read())
+      main_files.source())
 check("...under the over-rating title, quoting a tick's own asked and sent "
       "numbers in that order, with a red status row",
       clamp_notes(hass_o)
diff --git a/goodwe_controller/test_defaults_pin.py b/goodwe_controller/test_defaults_pin.py
index c8acc21..2d43e5c 100644
--- a/goodwe_controller/test_defaults_pin.py
+++ b/goodwe_controller/test_defaults_pin.py
@@ -149,9 +149,15 @@ print("2. the mirrors, DISCOVERED from the tree rather than listed here")
 # `app/` for module-level assignments whose name ends in OPTION_DEFAULTS and
 # grades whatever it finds, so the seventh is covered on the commit that
 # introduces it. That is the property the six hand-written pins cannot have.
-MODULES = sorted(p.name for p in APP.glob("*.py"))
+sys.path.insert(0, str(HERE / "tools"))
+import main_files  # noqa: E402
+
+# MAINT-21: app/main.py stands for itself and the files split from it.
+MODULES = sorted(p.name for p in APP.glob("*.py")
+                 if p.name == "main.py" or p.name not in main_files.files())
 TREES = {name: ast.parse(io.open(APP / name, encoding="utf-8").read(), name)
          for name in MODULES}
+TREES["main.py"] = main_files.tree()
 
 MIRROR = {}          # schema key -> (module, table name, value)
 TABLES = []
diff --git a/goodwe_controller/test_delivery.py b/goodwe_controller/test_delivery.py
index 2688c84..3f6715a 100644
--- a/goodwe_controller/test_delivery.py
+++ b/goodwe_controller/test_delivery.py
@@ -1272,6 +1272,9 @@ check("the operator's START press is the only way out, and it clears the "
 
 print()
 print("8b. SAFETY-34: a Core-only restart - same add-on process, HA's memory wiped")
+import os  # noqa: E402
+sys.path.insert(0, os.path.join(os.path.dirname(os.path.abspath(__file__)), "tools"))  # noqa: E402
+import main_files  # noqa: E402
 import app.main as _main_mod  # noqa: E402
 
 
@@ -1283,8 +1286,8 @@ async def _core_restart():
 
 
 _c = asyncio.run(_core_restart())
-_real_mono, _clock = _main_mod._mono, [_main_mod._mono()]
-_main_mod._mono = lambda: _clock[0]
+_real_mono, _clock = main_files.live._mono, [main_files.live._mono()]
+main_files.live._mono = lambda: _clock[0]
 try:
     _c.hass = _DeliveryHass(b_soc=50.0)
     asyncio.run(_c.check_not_delivering())
@@ -1295,7 +1298,7 @@ try:
     _late = [x for x in _c.hass.calls
              if "not_delivering" in str(x[2].get("notification_id", ""))]
 finally:
-    _main_mod._mono = _real_mono
+    main_files.live._mono = _real_mono
 check("SAFETY-34: the latch tripped in this process",
       _c.inverters[1].delivery_wd.tripped)
 check("SAFETY-34: inside REANNOUNCE_S the same process does not re-raise",
diff --git a/goodwe_controller/test_inverter.py b/goodwe_controller/test_inverter.py
index 4b7281e..217c7fc 100644
--- a/goodwe_controller/test_inverter.py
+++ b/goodwe_controller/test_inverter.py
@@ -75,6 +75,9 @@ from pathlib import Path
 
 from named_absence import first, given, nth, present
 
+import os  # noqa: E402
+sys.path.insert(0, os.path.join(os.path.dirname(os.path.abspath(__file__)), "tools"))  # noqa: E402
+import main_files  # noqa: E402
 from app import main as app_main
 from app.inverter import LINK_STALE_S, UNIT_A, Inverter, build_roster
 from app.main import WRITE_BUDGET_S, Controller
@@ -88,8 +91,10 @@ from app.arbiter import P_LOOP, P_SAFETY, Claim, resolve
 
 fails = []
 HERE = Path(__file__).resolve().parent
-MAIN_SRC = io.open(HERE / "app" / "main.py", encoding="utf-8").read()
-MAIN_AST = ast.parse(MAIN_SRC)
+sys.path.insert(0, str(HERE / "tools"))
+import main_files  # noqa: E402
+MAIN_SRC = main_files.source()
+MAIN_AST = main_files.tree(MAIN_SRC)
 CTRL = [n for n in MAIN_AST.body
         if isinstance(n, ast.ClassDef) and n.name == "Controller"][0]
 
@@ -1097,8 +1102,8 @@ check("...and it is below hass.py's own 10 s HTTP timeout, so the budget is "
 # is healthy. The budget is shortened for the run - the shipped value is graded
 # above - because a 4 s wait per case is 8 s of suite time to measure something
 # that is already a ratio.
-_REAL_BUDGET = app_main.WRITE_BUDGET_S
-app_main.WRITE_BUDGET_S = 0.30
+_REAL_BUDGET = main_files.live.WRITE_BUDGET_S
+main_files.live.WRITE_BUDGET_S = 0.30
 
 
 async def _hung_heartbeat():
@@ -1124,18 +1129,18 @@ async def _hung_heartbeat():
 _c6, _h6, _elapsed, _t0 = run(_hung_heartbeat())
 _b_at = [t - _t0 for e, _v, t in _h6.write_at if e == "number.sp_b"]
 print(f"    A hangs forever, B is healthy: the pair took {_elapsed:.2f} s "
-      f"(budget {app_main.WRITE_BUDGET_S:.2f} s); B's write reached the wire "
+      f"(budget {main_files.live.WRITE_BUDGET_S:.2f} s); B's write reached the wire "
       f"{(_b_at[0] if _b_at else float('nan')):.3f} s in; wire saw "
       f"{_h6.writes}")
 check("⚠️ AC 6. B'S WRITE REACHED THE WIRE WHILE A WAS STILL HANGING. That is "
       "the whole criterion: a hung write to A cannot consume B's layer-1 "
       "budget, because B's write was never behind A's in a queue",
       _h6.writes == [("number.sp_b", 700.0)]
-      and bool(_b_at) and _b_at[0] < app_main.WRITE_BUDGET_S / 2.0)
+      and bool(_b_at) and _b_at[0] < main_files.live.WRITE_BUDGET_S / 2.0)
 check("...and the pair returned in about ONE budget rather than in two, which "
       "is what says the writes were concurrent and not merely bounded. Two "
       "bounded writes in series is still a sibling waiting for a corpse",
-      _elapsed < app_main.WRITE_BUDGET_S * 1.9)
+      _elapsed < main_files.live.WRITE_BUDGET_S * 1.9)
 check("...and the hung inverter is recorded as having FAILED its write, so "
       "`last_write` is not advanced and the next tick re-issues it by itself",
       _c6.inverters[0].last_write is None
@@ -1176,7 +1181,7 @@ check("⚠️ AND THE DEFECT IS REPRODUCED BESIDE THE FIX. Written in series, B'
       "every inverter behind the hung one, and with the unbounded write this "
       "card replaces it was the HTTP stack's timeout - which is what put a "
       "healthy sibling within reach of layer 1's veto",
-      _ser_b_at >= app_main.WRITE_BUDGET_S)
+      _ser_b_at >= main_files.live.WRITE_BUDGET_S)
 
 # AND THE DEADLINE ITSELF IS PER UNIT - graded through the shipped method, for
 # the reason the experiment above is: a `due` list computed in this file is a
@@ -1219,7 +1224,7 @@ check("...and the heartbeat re-emits each unit's OWN share rather than the "
 # heartbeat is not the only place a hung inverter can hold the loop: every cycle
 # writes every unit's share, and in series that is the same defect at the cycle
 # rate rather than at the heartbeat rate.
-app_main.WRITE_BUDGET_S = 0.30
+main_files.live.WRITE_BUDGET_S = 0.30
 
 
 async def _hung_cycle():
@@ -1248,17 +1253,17 @@ check("⚠️ AND A REAL CYCLE DELIVERS B'S SHARE WHILE A HANGS. This is the sam
       "`cycle()` go out together, so a hung inverter costs the loop one budget "
       "and costs its siblings nothing",
       _h6c.writes and _h6c.writes[0][0] == "number.sp_b"
-      and bool(_cyc_b) and _cyc_b[0] < app_main.WRITE_BUDGET_S / 2.0
-      and _cyc_elapsed < app_main.WRITE_BUDGET_S * 1.9)
+      and bool(_cyc_b) and _cyc_b[0] < main_files.live.WRITE_BUDGET_S / 2.0
+      and _cyc_elapsed < main_files.live.WRITE_BUDGET_S * 1.9)
 check("...and the share B was told is the allocator's, not the site target - "
       "the hung sibling does not turn the cycle into a broadcast",
       _h6c.writes[0][1] == float(_c6c.allocation.shares["inverter-b"])
       and _h6c.writes[0][1] != _c6c.target)
 
-app_main.WRITE_BUDGET_S = _REAL_BUDGET
+main_files.live.WRITE_BUDGET_S = _REAL_BUDGET
 check("...and the shipped budget is restored after the experiments, so nothing "
       "below runs against a 0.3 s one",
-      app_main.WRITE_BUDGET_S == WRITE_BUDGET_S)
+      main_files.live.WRITE_BUDGET_S == WRITE_BUDGET_S)
 
 
 # ⚠️ AND THE OPERATOR'S STOP HAS TO MOVE THE SAME TWO THINGS. This is a hazard
diff --git a/goodwe_controller/test_maint10.py b/goodwe_controller/test_maint10.py
index 6025c00..4a109c9 100644
--- a/goodwe_controller/test_maint10.py
+++ b/goodwe_controller/test_maint10.py
@@ -22,6 +22,7 @@ from pathlib import Path
 
 sys.path.insert(0, os.path.join(os.path.dirname(os.path.abspath(__file__)), "tools"))
 
+import main_files  # noqa: E402
 import app.main as M                                        # noqa: E402
 from app import maintenance as MT                           # noqa: E402
 from app.maintenance import (                               # noqa: E402
@@ -367,7 +368,7 @@ def amain_zone(zone_body, env_tz):
 
     M.load_options = lambda: {"setpoint_entity": "number.sp"}
     M.HomeAssistant = lambda session, **kw: _Hass()
-    M.validate_startup_config = lambda *a, **k: []
+    main_files.live.validate_startup_config = lambda *a, **k: []
     M.mode_announcement = lambda opts, store: ((), ())
     M.Controller = _controller
     M.aiohttp.ClientSession = lambda *a, **k: _Session(zone_body)
diff --git a/goodwe_controller/test_maint13.py b/goodwe_controller/test_maint13.py
index 2e76f48..f510b57 100644
--- a/goodwe_controller/test_maint13.py
+++ b/goodwe_controller/test_maint13.py
@@ -520,9 +520,11 @@ check("a fixed tariff set up counts as a gate: outside its cheap hours a pack "
       "that is not charging is closed, inside them it is open",
       c._price_gated is True
       and c._charge_gate_open(c.inverters[0]) is c.cheap)
+sys.path.insert(0, os.path.join(os.path.dirname(os.path.abspath(__file__)), "tools"))  # noqa: E402
+import main_files  # noqa: E402
 import app.main as main_mod                                     # noqa: E402
-_real_gated, _calls = main_mod.static_gated, []
-main_mod.static_gated = lambda o, now: _calls.append(now) or _real_gated(o, now)
+_real_gated, _calls = main_files.live.static_gated, []
+main_files.live.static_gated = lambda o, now: _calls.append(now) or _real_gated(o, now)
 try:
     c._gated_key = None
     read(c)
@@ -530,7 +532,7 @@ try:
     read(c)
     c._static_gated(c.o, datetime.now(UTC) + timedelta(hours=1))
 finally:
-    main_mod.static_gated = _real_gated
+    main_files.live.static_gated = _real_gated
 check("...worked out once an hour, not on every tick (3 reads in one hour = 1 "
       f"build; a new hour = 1 more): {len(_calls)} builds",
       len(_calls) == 2 and c._price_gated is True)
diff --git a/goodwe_controller/test_messages.py b/goodwe_controller/test_messages.py
index c007134..a4e5a3c 100644
--- a/goodwe_controller/test_messages.py
+++ b/goodwe_controller/test_messages.py
@@ -241,6 +241,27 @@ check("the output-clamp alarm quotes asked before sent",
 # ============================================================================== #
 print("\n2. no notification is worded outside app/messages.py")
 APP = HERE / "app"
+sys.path.insert(0, str(HERE / "tools"))
+import main_files  # noqa: E402
+
+
+class _AppFile:
+    """An app/*.py file. `main.py` stands for itself and the files split from
+    it (MAINT-21), so every scan below still sees the Controller whole."""
+
+    def __init__(self, path):
+        self.name, self.stem, self._path = path.name, path.stem, path
+
+    def read_text(self, encoding="utf-8"):
+        if self.name == "main.py":
+            return main_files.source()
+        return self._path.read_text(encoding=encoding)
+
+
+def _app_py():
+    split = set(main_files.files()) - {"main.py"}
+    return [_AppFile(f) for f in sorted(APP.glob("*.py"))
+            if f.name not in split]
 
 
 # UX-08 2d: a refusal is counted as it is SHOWN. A placeholder that names a
@@ -318,7 +339,7 @@ def notification_calls(tree):
 
 
 bad_calls, n_calls = [], 0
-for f in sorted(APP.glob("*.py")):
+for f in _app_py():
     for call in notification_calls(ast.parse(f.read_text(encoding="utf-8"))):
         n_calls += 1
         payload = call.args[2] if len(call.args) > 2 else None
@@ -368,13 +389,13 @@ def _module_constants(tree):
 
 
 _MODCONST = {f.stem: _module_constants(ast.parse(f.read_text(encoding="utf-8")))
-             for f in sorted(APP.glob("*.py"))}
+             for f in _app_py()}
 
 
 def collect():
     """(kind, where, text) for every user-facing literal of a ratcheted kind."""
     out = []
-    for f in sorted(APP.glob("*.py")):
+    for f in _app_py():
         if f.name == "messages.py":
             continue
         tree = ast.parse(f.read_text(encoding="utf-8"))
@@ -543,7 +564,7 @@ for key, text in messages.hint_samples():
     p = row_problems(messages.GREEN, text)
     check(f"hint   {text!r}{' - ' + '; '.join(p) if p else ''}", not p)
 _calls, _bare = 0, []
-for f in sorted(APP.glob("*.py")):
+for f in _app_py():
     for node in ast.walk(ast.parse(f.read_text(encoding="utf-8"))):
         if (isinstance(node, ast.Call)
                 and ast.unparse(node.func).endswith("log_event")):
@@ -1012,7 +1033,7 @@ def _static(spec):
     the named file (placeholders count as one word, as in part 3)."""
     fname, kind, name = spec
     out = []
-    for f in ([APP / fname] if fname != "*" else sorted(APP.glob("*.py"))):
+    for f in ([_AppFile(APP / fname)] if fname != "*" else _app_py()):
         tree = ast.parse(f.read_text(encoding="utf-8"))
         for node in ast.walk(tree):
             if kind == "call" and isinstance(node, ast.Call) and node.args \
@@ -1201,7 +1222,7 @@ def scan_log_lines(files, text=None, data=None, long_ok=None, long_seen=None):
 
 
 _FILES = [(f.name, ast.parse(f.read_text(encoding="utf-8")))
-          for f in sorted(APP.glob("*.py"))]
+          for f in _app_py()]
 _long_seen = set()
 _unknown, _stale, _bad = scan_log_lines(_FILES, long_seen=_long_seen)
 for k, sample, p in _bad:
@@ -1415,7 +1436,7 @@ def _captured(logger_name, fn):
 
 def _level_of(fname, words_in_line):
     """The level of the log call in `fname` whose literal holds the words."""
-    tree = ast.parse((APP / fname).read_text(encoding="utf-8"))
+    tree = ast.parse(_AppFile(APP / fname).read_text(encoding="utf-8"))
     for node in ast.walk(tree):
         if isinstance(node, ast.Call) and node.args \
                 and re.search(r"_LOG\.\w+$", ast.unparse(node.func)):
@@ -1561,7 +1582,7 @@ check(f"a socket Home Assistant closed is a plain ConnectionResetError, which "
 # words. The keys are found in the code: each `Claim.set(source, ..., reason)`
 # through main.why_key(), plus main.py's own refusal to split ("unsplit").
 _SOURCES = {}
-for _f in sorted(APP.glob("*.py")):
+for _f in _app_py():
     _tree = ast.parse(_f.read_text(encoding="utf-8"))
     _consts = _module_constants(_tree)
     for _n in ast.walk(_tree):
@@ -1781,7 +1802,7 @@ check(f"...and in the action log, which an installer reads at the default "
       and any(e.endswith(messages.NO_REASON_SAVED) for e in _rs_ev))
 
 # UX-11 item 4: the action log's clamp count and the shadow-off entry.
-_main_src = (APP / "main.py").read_text(encoding="utf-8")
+_main_src = _AppFile(APP / "main.py").read_text(encoding="utf-8")
 check("the action log counts 'engagements' with a real plural and the "
       "shadow-off entry is plain, not 'engagement(s)' or 'SHADOW MODE OFF -'",
       "engagement(s)" not in _main_src and "SHADOW MODE OFF" not in _main_src
diff --git a/goodwe_controller/test_modes.py b/goodwe_controller/test_modes.py
index 7f31f9b..026d16a 100644
--- a/goodwe_controller/test_modes.py
+++ b/goodwe_controller/test_modes.py
@@ -32,6 +32,7 @@ sys.path.insert(0, os.path.join(HERE, "tools"))
 
 import opt11_identity as rig                                   # noqa: E402
 from named_absence import nth, present                         # noqa: E402
+import main_files  # noqa: E402
 import app.main as app_main                                    # noqa: E402
 from app import homeview, messages, packmode                   # noqa: E402
 from app.control import MODE_BOUND                             # noqa: E402
@@ -62,24 +63,24 @@ def store_with(**modes):
 
 def spy_claims():
     """Record every claim list main.py's own `resolve` is handed."""
-    seen, real = [], app_main.resolve
+    seen, real = [], main_files.live.resolve
 
     def _spy(claims, **kw):
         seen.append(list(claims))
         return real(claims, **kw)
-    app_main.resolve = _spy
-    return seen, lambda: setattr(app_main, "resolve", real)
+    main_files.live.resolve = _spy
+    return seen, lambda: setattr(main_files.live, "resolve", real)
 
 
 def spy_bounds():
     """Record the `bound` main.py hands `compute()` on every cycle."""
-    seen, real = [], app_main.compute
+    seen, real = [], main_files.live.compute
 
     def _spy(*a, **kw):
         seen.append(kw.get("bound", "absent"))
         return real(*a, **kw)
-    app_main.compute = _spy
-    return seen, lambda: setattr(app_main, "compute", real)
+    main_files.live.compute = _spy
+    return seen, lambda: setattr(main_files.live, "compute", real)
 
 
 def flat(t):
diff --git a/goodwe_controller/test_modes_p4.py b/goodwe_controller/test_modes_p4.py
index 698be67..fb16d90 100644
--- a/goodwe_controller/test_modes_p4.py
+++ b/goodwe_controller/test_modes_p4.py
@@ -37,6 +37,7 @@ sys.path.insert(0, os.path.join(HERE, "tools"))
 logging.disable(logging.WARNING)
 
 from named_absence import nth, present                         # noqa: E402
+import main_files                                              # noqa: E402
 import opt11p3_replay as rp                                    # noqa: E402
 from app import arbitrage, dayplan, homeview, modetrade, packmode  # noqa
 from app import priceruns, solarfc, validate                    # noqa: E402
@@ -777,7 +778,7 @@ check("battery modes off: the forecast sensor is never read", READS[0] == 0)
 print("7. the Batteries screen and the Simple view")
 rows, st_, c = run_day(SF_LS, fc=1.0, soc0={"a": 60.0, "b": 30.0},
                        hours=0.6)
-rp.m.datetime = datetime
+main_files.live.datetime = datetime
 sb = homeview.solar_block(c, c.solar_fc.at)
 check("the forecast line names the forecast, what is counted and when",
       sb["line"].startswith("Solar still to come today:")
@@ -812,14 +813,14 @@ check("a lost forecast says so: no forecast, Leftover solar solar only",
 c._charge_latch = latch
 # the latch ends at its end time; this replay ran in September, so ask at a
 # moment inside it
-_real_dt = rp.m.datetime
-rp.m.datetime = type("_DT", (datetime,), {"now": classmethod(
+_real_dt = main_files.live.datetime
+main_files.live.datetime = type("_DT", (datetime,), {"now": classmethod(
     lambda cls, tz=None: latch[0] - timedelta(hours=1))})
 check("OPT-34: with a charge under way (B charged in this run), the level "
       "stays: plan_targets() gives it (the line: test_opt34.py)",
       latch is not None and c.plan_targets() is not None
       and B in c.plan_targets() and c.plan_targets()[B] == c._plan_targets[B])
-rp.m.datetime = _real_dt
+main_files.live.datetime = _real_dt
 check("the Why line wins over 'saves its power' only while holding",
       homeview.battery_why(modes_on=True, mode="leftover_solar", off=False,
                            reading=True, phase="idle", shadow=False,
diff --git a/goodwe_controller/test_opt27.py b/goodwe_controller/test_opt27.py
index 7f3809d..3670f12 100644
--- a/goodwe_controller/test_opt27.py
+++ b/goodwe_controller/test_opt27.py
@@ -46,6 +46,7 @@ logging.disable(logging.WARNING)
 
 import opt11p3_replay as rp                                    # noqa: E402
 from named_absence import first, nth, present                  # noqa: E402
+import main_files  # noqa: E402
 import app.main as m                                           # noqa: E402
 from app import homeview, modetrade, solarfc                   # noqa: E402
 from app.main import Controller                                # noqa: E402
@@ -404,14 +405,14 @@ def drive27(o, sensors, *, pre, start, minutes=20, restart=None,
 
     async def go():
         c, hass = build(store)
-        real_dt, real_hv = m.datetime, homeview.datetime
+        real_dt, real_hv = main_files.live.datetime, homeview.datetime
 
         class _DT(real_dt):
             @classmethod
             def now(cls, tz=None):
                 return clock[0] if tz is None else clock[0].astimezone(tz)
 
-        m.datetime = homeview.datetime = _DT
+        main_files.live.datetime = homeview.datetime = _DT
         task = None
         try:
             for t_pre in pre:
@@ -477,7 +478,7 @@ def drive27(o, sensors, *, pre, start, minutes=20, restart=None,
                     await task
                 except asyncio.CancelledError:
                     pass
-            m.datetime, homeview.datetime = real_dt, real_hv
+            main_files.live.datetime, homeview.datetime = real_dt, real_hv
         return c
 
     return asyncio.run(go()), rows, pre_rows
diff --git a/goodwe_controller/test_opt34.py b/goodwe_controller/test_opt34.py
index fdb4698..3db53fc 100644
--- a/goodwe_controller/test_opt34.py
+++ b/goodwe_controller/test_opt34.py
@@ -61,6 +61,7 @@ sys.path.insert(0, os.path.join(HERE, "tools"))
 logging.disable(logging.WARNING)
 
 import opt11p3_replay as rp                                    # noqa: E402
+import main_files  # noqa: E402
 import app.main as m                                           # noqa: E402
 from app import homeview, solarfc                              # noqa: E402
 from app.main import Controller                                # noqa: E402
@@ -348,14 +349,14 @@ def run_night(spec):
 
     async def go():
         cur = store
-        real_dt, real_hv = m.datetime, homeview.datetime
+        real_dt, real_hv = main_files.live.datetime, homeview.datetime
 
         class _DT(real_dt):
             @classmethod
             def now(cls, tz=None):
                 return clock[0] if tz is None else clock[0].astimezone(tz)
 
-        m.datetime = homeview.datetime = _DT
+        main_files.live.datetime = homeview.datetime = _DT
         try:
             # TEST-37: built under the scenario's clock, not the real one:
             # Controller.__init__ checks a stored latch's end against now().
@@ -420,7 +421,7 @@ def run_night(spec):
             out["soc"] = (hass.plants["a"].soc, hass.plants["b"].soc)
             out["latch"] = getattr(c, "_charge_latch", None) is not None
         finally:
-            m.datetime, homeview.datetime = real_dt, real_hv
+            main_files.live.datetime, homeview.datetime = real_dt, real_hv
         return out
 
     return asyncio.run(go())
@@ -722,7 +723,7 @@ from types import SimpleNamespace                              # noqa: E402
 from app import modetrade, priceruns                           # noqa: E402
 
 CLOCK = [at(4, 1, 0)]
-_dt0 = m.datetime
+_dt0 = main_files.live.datetime
 
 
 class _FixedDT(_dt0):
@@ -731,7 +732,7 @@ class _FixedDT(_dt0):
         return CLOCK[0] if tz is None else CLOCK[0].astimezone(tz)
 
 
-m.datetime = homeview.datetime = _FixedDT
+main_files.live.datetime = homeview.datetime = _FixedDT
 _tmp = tempfile.mkdtemp(prefix="o34-")
 lc = Controller(dict(opts()), rp.Hass(("a", "b"), lambda t: 300.0,
                                       {"a": 40.0, "b": 40.0}),
@@ -858,7 +859,7 @@ lc._charge_latch = (at(4, 6, 10), {A: 80.0}, at(4, 1, 0))
 lt, _s = latch_step(None, resting, None, now=at(4, 6, 5), runs=r3)
 check("F4: a run that starts AT the bell (06:00-09:00) does carry it on, "
       "to its end + one slot", lt is not None and lt[0] == at(4, 9, 15))
-m.datetime = homeview.datetime = _dt0
+main_files.live.datetime = homeview.datetime = _dt0
 
 print()
 if fails:
diff --git a/goodwe_controller/test_opt36.py b/goodwe_controller/test_opt36.py
index 331f6ed..1b1d3da 100644
--- a/goodwe_controller/test_opt36.py
+++ b/goodwe_controller/test_opt36.py
@@ -49,6 +49,7 @@ logging.disable(logging.WARNING)
 from named_absence import nth, present                          # noqa: E402
 import ux54_scenarios as S                                      # noqa: E402
 import opt11p3_replay as rp                                     # noqa: E402
+import main_files  # noqa: E402
 import app.main as m                                            # noqa: E402
 from app import dayplan, homeview, modetrade, packmode          # noqa: E402
 from app import priceruns, solarfc, uitext                      # noqa: E402
@@ -662,14 +663,14 @@ def run_night(spec):
                           for d in ("2026-10-31", "2026-11-01", "2026-11-02")})
 
     async def go():
-        real_dt, real_hv = m.datetime, homeview.datetime
+        real_dt, real_hv = main_files.live.datetime, homeview.datetime
 
         class _DT(real_dt):
             @classmethod
             def now(cls, tz=None):
                 return clock[0] if tz is None else clock[0].astimezone(tz)
 
-        m.datetime = homeview.datetime = _DT
+        main_files.live.datetime = homeview.datetime = _DT
         try:
             for t_pre in EVENING:
                 clock[0] = t_pre
@@ -722,7 +723,7 @@ def run_night(spec):
             out["soc"] = (hass.plants["a"].soc, hass.plants["b"].soc)
             out["latch"] = getattr(c, "_charge_latch", None) is not None
         finally:
-            m.datetime, homeview.datetime = real_dt, real_hv
+            main_files.live.datetime, homeview.datetime = real_dt, real_hv
         return out
 
     return asyncio.run(go())
diff --git a/goodwe_controller/test_packshare.py b/goodwe_controller/test_packshare.py
index 561e9ad..b4e3893 100644
--- a/goodwe_controller/test_packshare.py
+++ b/goodwe_controller/test_packshare.py
@@ -34,6 +34,8 @@ import sys
 from datetime import datetime, timedelta, timezone
 from math import inf
 from pathlib import Path
+sys.path.insert(0, str(Path(__file__).resolve().parent / "tools"))
+import main_files  # noqa: E402
 
 from app import arbitrage, packshare
 from named_absence import first, nth, present
@@ -1132,8 +1134,7 @@ check("...and misfiling it ON THE SITE is caught and REFUSED, not consumed. A "
 # main.py's own AST, the way test_peakguard.py part 12i pins the arguments of
 # `arbitrage.decide()`, and for the same reason: a call site that stopped
 # passing it is invisible to every fixture.
-_main_src = (Path(__file__).resolve().parent / "app" / "main.py").read_text(
-    encoding="utf-8")
+_main_src = main_files.source()
 _resolve_calls = [n for n in ast.walk(ast.parse(_main_src))
                   if isinstance(n, ast.Call) and isinstance(n.func, ast.Name)
                   and n.func.id == "resolve"]
@@ -1158,9 +1159,7 @@ check("⚠️ MAIN.PY ACTUALLY PASSES `weights=`, AND IT PASSES THE METHOD RATHE
 # cycle's value, and logs. What it does NOT grade is the sentence it logs or
 # that a real cycle reaches it; that is stated here rather than implied.
 _cycle_src = first(
-    f for cls in ast.walk(ast.parse(
-        (Path(__file__).resolve().parent / "app" / "main.py")
-        .read_text(encoding="utf-8")))
+    f for cls in ast.walk(main_files.tree())
     if isinstance(cls, ast.ClassDef) and cls.name == "Controller"
     for f in cls.body
     if isinstance(f, (ast.FunctionDef, ast.AsyncFunctionDef)) and f.name == "cycle")
diff --git a/goodwe_controller/test_peak_margin.py b/goodwe_controller/test_peak_margin.py
index 19f09d9..97aae45 100644
--- a/goodwe_controller/test_peak_margin.py
+++ b/goodwe_controller/test_peak_margin.py
@@ -22,6 +22,7 @@ import sys
 
 HERE = os.path.dirname(os.path.abspath(__file__))
 sys.path.insert(0, os.path.join(HERE, "tools"))
+import main_files  # noqa: E402
 
 import safety79_identity as rig                               # noqa: E402
 from named_absence import nth, present                        # noqa: E402
@@ -207,9 +208,8 @@ check("...and the user-facing peak notice built from the decision's limit "
 
 # ============================================================================ #
 print("\n4. each call site in main.py")
-with open(os.path.join(HERE, "app", "main.py"), encoding="utf-8") as f:
-    _src = f.read()
-_tree = ast.parse(_src)
+_src = main_files.source()
+_tree = main_files.tree(_src)
 
 
 def calls(name):
diff --git a/goodwe_controller/test_peakguard.py b/goodwe_controller/test_peakguard.py
index 42e2f52..f64701b 100644
--- a/goodwe_controller/test_peakguard.py
+++ b/goodwe_controller/test_peakguard.py
@@ -135,6 +135,9 @@ from app.arbiter import (
 )
 from app.control import Tuning, compute, peak_at_risk
 from app.freeze import FreezeWatchdogConfig, looks_frozen, rail_w
+import os  # noqa: E402
+sys.path.insert(0, os.path.join(os.path.dirname(os.path.abspath(__file__)), "tools"))  # noqa: E402
+import main_files  # noqa: E402
 from app import main as app_main
 from app.inverter import Inverter, build_roster
 from app.main import Controller
@@ -1295,7 +1298,7 @@ print("   the wiring's own mutations - a default install, maintenance charging")
 # `peak_at_risk()` answers False forever. That is the whole point - it is the
 # configuration on which the old suspension could not fire.
 MAINT_CHARGING = {"phase": "charge"}
-_mainsrc = (HERE / "app" / "main.py").read_text(encoding="utf-8")
+_mainsrc = main_files.source()
 
 
 def maint_cycle(tag, want_floor_w=LIVE_MAX_W * 0.3, **kw):
@@ -2709,7 +2712,7 @@ CLAIM_SOURCES = {"device", "supervised", "failsafe", "safety", "peak",
 # silent gap in the scan.
 CLAIM_BUILDERS = {"peak_claim": "peak", "arb_claim": "arbitrage"}
 
-_main_tree = ast.parse((HERE / "app" / "main.py").read_text(encoding="utf-8"))
+_main_tree = main_files.tree()
 _cycle_def = first((
     f
     for cls in ast.walk(_main_tree)
@@ -2762,7 +2765,7 @@ def cycle_claims(run):
     call site and nowhere else.
     """
     seen = []
-    real = app_main.resolve
+    real = main_files.live.resolve
 
     def _spy(claims, **kw):
         # ⚠️ `**kw` PASSES THE ROSTER THROUGH UNREAD, AND THAT IS THE WHOLE
@@ -2776,11 +2779,11 @@ def cycle_claims(run):
         seen.append(list(claims))
         return real(claims, **kw)
 
-    app_main.resolve = _spy
+    main_files.live.resolve = _spy
     try:
         out = run()
     finally:
-        app_main.resolve = real
+        main_files.live.resolve = real
     return out, (seen[-1] if seen else [])
 
 
@@ -4977,7 +4980,11 @@ check("⚠️ AND THE SECOND CONSUMER OF THE SAME REDUCTION. `arbitrage.decide()
 # written, at every roster length, in every configuration, and with no fixture
 # required.
 _APP_SRC = {p.stem: p.read_text(encoding="utf-8")
-            for p in sorted((HERE / "app").glob("*.py"))}
+            for p in sorted((HERE / "app").glob("*.py"))
+            if p.name == "main.py" or p.name not in main_files.files()}
+# MAINT-21: main.py and the files split from it, the mixins read as Controller.
+_APP_SRC["main"] = re.sub(r"^class \w+Mixin:", "class Controller:",
+                          main_files.source(), flags=re.M)
 _ROSTER_OPTION = "inverters"        # the ONE seed. Everything else is closure.
 _WRAPPERS = {"list", "tuple", "sorted", "enumerate", "zip", "reversed",
              "filter", "iter", "set", "dict"}
diff --git a/goodwe_controller/test_price_history.py b/goodwe_controller/test_price_history.py
index 33827f9..ce04bff 100644
--- a/goodwe_controller/test_price_history.py
+++ b/goodwe_controller/test_price_history.py
@@ -118,6 +118,8 @@ from app.static_tariff import resolve_tariff
 
 UTC = timezone.utc
 HERE = os.path.dirname(os.path.abspath(__file__))
+sys.path.insert(0, os.path.join(HERE, "tools"))
+import main_files  # noqa: E402
 
 # PRICE-02: `TariffPlan.arbitrage(now=...)` is required. This instant is before every
 # point these fixtures build, so no period has ended and the whole series counts.
@@ -2015,8 +2017,8 @@ check("...so calling it without one is a TypeError, not a quiet regression",
                                         transport=transport_for(_body_today),
                                         now=NOW)), TypeError))
 
-_MAIN = open(os.path.join(_APP, "main.py"), encoding="utf-8").read()
-_main_tree = ast.parse(_MAIN)
+_MAIN = main_files.source()
+_main_tree = main_files.tree(_MAIN)
 _refresh = first((n for n in ast.walk(_main_tree)
                   if isinstance(n, ast.AsyncFunctionDef)
                   and n.name == "run_tariff_refresh"), "run_tariff_refresh in main.py")
diff --git a/goodwe_controller/test_price_service.py b/goodwe_controller/test_price_service.py
index bfe94ae..6b0d1c6 100644
--- a/goodwe_controller/test_price_service.py
+++ b/goodwe_controller/test_price_service.py
@@ -44,6 +44,8 @@ import tempfile
 from datetime import date, datetime, timedelta, timezone
 
 from named_absence import nth
+sys.path.insert(0, os.path.join(os.path.dirname(os.path.abspath(__file__)), "tools"))  # noqa: E402
+import main_files  # noqa: E402
 from app import main as _main
 from app import messages, price as P, price_chain as C
 from app.price import (
@@ -686,8 +688,8 @@ def controller(clock, o, tmp=None):
     return ctl
 
 
-_REAL_DT, _REAL_GET = _main.datetime, P.https_get
-_real_resolve = _main.resolve_tariff
+_REAL_DT, _REAL_GET = main_files.live.datetime, P.https_get
+_real_resolve = main_files.live.resolve_tariff
 
 
 class Wired:
@@ -701,7 +703,7 @@ class Wired:
         self.refreshes = 0
 
     def __enter__(self):
-        _main.datetime = FakeDT
+        main_files.live.datetime = FakeDT
         P.https_get = self.net
         W = self
 
@@ -709,12 +711,12 @@ class Wired:
             r = await _real_resolve(*a, **k)
             W.refreshes += 1
             return r
-        _main.resolve_tariff = counting
+        main_files.live.resolve_tariff = counting
         return self
 
     def __exit__(self, *exc):
-        _main.datetime, P.https_get = _REAL_DT, _REAL_GET
-        _main.resolve_tariff = _real_resolve
+        main_files.live.datetime, P.https_get = _REAL_DT, _REAL_GET
+        main_files.live.resolve_tariff = _real_resolve
 
     async def refresh(self, now=None):
         if now is not None:
diff --git a/goodwe_controller/test_pv.py b/goodwe_controller/test_pv.py
index ad71ba7..090575a 100644
--- a/goodwe_controller/test_pv.py
+++ b/goodwe_controller/test_pv.py
@@ -692,7 +692,13 @@ def touches(src: str) -> bool:
         or "from .pv import" in src
 
 
-_touch = sorted(f.name for f in APP if touches(f.read_text(encoding="utf-8")))
+sys.path.insert(0, str(HERE / "tools"))
+import main_files  # noqa: E402
+
+# MAINT-21: the files split from app/main.py are counted as main.py.
+_SPLIT = set(main_files.files()) - {"main.py"}
+_touch = sorted({"main.py" if f.name in _SPLIT else f.name for f in APP
+                 if touches(f.read_text(encoding="utf-8"))})
 print(f"    {len(APP)} modules under app/; TEL-11 material is in: {_touch}")
 check(f"PRECONDITION: the scan found the whole package, not a subset - "
       f"{len(APP)} modules", len(APP) >= 25 and "control.py" in
diff --git a/goodwe_controller/test_refusal.py b/goodwe_controller/test_refusal.py
index a396727..04ddf02 100644
--- a/goodwe_controller/test_refusal.py
+++ b/goodwe_controller/test_refusal.py
@@ -142,8 +142,11 @@ def run(load, cut, dur, cap=lambda t: 1e9, old=False, events=None):
             **LIVE), hass, _Store(), _Pub(), stop=asyncio.Event())
         c.auto = True
         c.dev_min, c.dev_max = -LIVE["max_w"], LIVE["max_w"]
+        import os  # noqa: E402
+        sys.path.insert(0, os.path.join(os.path.dirname(os.path.abspath(__file__)), "tools"))  # noqa: E402
+        import main_files  # noqa: E402
         import app.main as m
-        real, real_dt = m.compute, m.datetime
+        real, real_dt = main_files.live.compute, main_files.live.datetime
         clock = [0.0]
 
         class _DT(real_dt):
@@ -153,9 +156,9 @@ def run(load, cut, dur, cap=lambda t: 1e9, old=False, events=None):
             def now(cls, tz=None):
                 return BASE + timedelta(seconds=clock[0])
 
-        m.datetime = _DT
+        main_files.live.datetime = _DT
         if old:
-            m.compute = lambda *a, **k: real(*a, **dict(k, refused=None))
+            main_files.live.compute = lambda *a, **k: real(*a, **dict(k, refused=None))
         rows, trips, was = [], 0, False
         try:
             t = 0.0
@@ -174,7 +177,7 @@ def run(load, cut, dur, cap=lambda t: 1e9, old=False, events=None):
                              hass.cmd, c.i_w, c.loop_reason, c.batt_refused))
                 t += TICK
         finally:
-            m.compute, m.datetime = real, real_dt
+            main_files.live.compute, main_files.live.datetime = real, real_dt
         return rows, trips, c
     return asyncio.run(go())
 
diff --git a/goodwe_controller/test_refusal_units.py b/goodwe_controller/test_refusal_units.py
index 4366a7a..a6e689b 100644
--- a/goodwe_controller/test_refusal_units.py
+++ b/goodwe_controller/test_refusal_units.py
@@ -50,6 +50,9 @@ from app import control
 from app.control import PROBE_EVERY_S, PROBE_S, PROBE_W
 from app.main import Controller
 from app.arbiter import P_LOOP, P_PEAK, P_SAFETY, Claim, resolve
+import os  # noqa: E402
+sys.path.insert(0, os.path.join(os.path.dirname(os.path.abspath(__file__)), "tools"))  # noqa: E402
+import main_files  # noqa: E402
 import app.main as m
 
 fails = []
@@ -177,7 +180,7 @@ def run(load, cut, dur, *, soc=None, jitter=False, old=False, events=None,
         c.auto = True
         if old:
             _off(c)
-        real_dt = m.datetime
+        real_dt = main_files.live.datetime
         clock = [0.0]
 
         class _DT(real_dt):
@@ -185,7 +188,7 @@ def run(load, cut, dur, *, soc=None, jitter=False, old=False, events=None,
             def now(cls, tz=None):
                 return BASE + timedelta(seconds=clock[0])
 
-        m.datetime = _DT
+        main_files.live.datetime = _DT
         rows = []
         trips = {u: 0 for u in UNITS}
         was = {u: False for u in UNITS}
@@ -211,7 +214,7 @@ def run(load, cut, dur, *, soc=None, jitter=False, old=False, events=None,
                     db=c.inverters[1].delivery_wd.tripped))
                 t += dt
         finally:
-            m.datetime = real_dt
+            main_files.live.datetime = real_dt
         return rows, trips, c
     return asyncio.run(go())
 
diff --git a/goodwe_controller/test_rehearse.py b/goodwe_controller/test_rehearse.py
index ded905a..4387c72 100644
--- a/goodwe_controller/test_rehearse.py
+++ b/goodwe_controller/test_rehearse.py
@@ -73,6 +73,7 @@ def check(name, cond):
 print("1. the harness's own preconditions")
 # --------------------------------------------------------------------------- #
 sys.path.insert(0, str(HERE / "tools"))
+import main_files  # noqa: E402
 import rehearse_roster as RR  # noqa: E402
 
 check("the tool refuses rather than passing when it cannot run: its four exit "
@@ -210,6 +211,11 @@ def mutant_tree(edits) -> str:
                     dest / "tools" / "predeploy_check.py")
     shutil.copyfile(HERE / "config.yaml", dest / "config.yaml")
     for rel, old, new in edits:
+        if rel == "app/main.py":
+            # MAINT-21: app/main.py stands for the files split from it.
+            where = [n for n in main_files.files() if (dest / "app" / n)
+                     .read_text(encoding="utf-8").count(old) == 1]
+            rel = f"app/{where[0]}" if len(where) == 1 else rel
         path = dest / rel
         text = path.read_text(encoding="utf-8")
         hits = text.count(old)
diff --git a/goodwe_controller/test_safety107.py b/goodwe_controller/test_safety107.py
index e3f7516..e58c71f 100644
--- a/goodwe_controller/test_safety107.py
+++ b/goodwe_controller/test_safety107.py
@@ -35,6 +35,7 @@ logging.disable(logging.WARNING)
 import opt11_identity as rig                                   # noqa: E402
 import safety79_identity as s79                                # noqa: E402
 import app.main as app_main                                    # noqa: E402
+import main_files                                              # noqa: E402
 from app import control                                        # noqa: E402
 from app.arbiter import Claim, P_ARBITRAGE                     # noqa: E402
 from app.main import Controller                                # noqa: E402
@@ -61,7 +62,7 @@ def run(n=1, *, plant, house, dur=QUARTER, tick=5.0, maint=True,
     (a writer above the loop), or None."""
     log, rows, now = [], [], [0.0]
     real_power, real_tick = rig._Hass.power, rig.TICK
-    real_log, real_resolve, real_c = (Controller.log_event, app_main.resolve,
+    real_log, real_resolve, real_c = (Controller.log_event, main_files.live.resolve,
                                       rig.Controller)
 
     def power(self, u):
@@ -108,7 +109,7 @@ def run(n=1, *, plant, house, dur=QUARTER, tick=5.0, maint=True,
         extra.update(s79.P1, peak_cap_w=cap)
     db = os.path.join(tempfile.mkdtemp(prefix="s107-"), "tariff.db")
     rig._Hass.power, rig.TICK = power, tick
-    Controller.log_event, app_main.resolve = log_event, resolve
+    Controller.log_event, main_files.live.resolve = log_event, resolve
     rig.Controller = functools.partial(real_c, peak_db_path=db)
     try:
         _, c = rig.run(n, extra=extra, dur=dur, load=house,
@@ -117,7 +118,7 @@ def run(n=1, *, plant, house, dur=QUARTER, tick=5.0, maint=True,
                        store=s79.store_charging(n) if maint else rig._Store())
     finally:
         rig._Hass.power, rig.TICK = real_power, real_tick
-        Controller.log_event, app_main.resolve = real_log, real_resolve
+        Controller.log_event, main_files.live.resolve = real_log, real_resolve
         rig.Controller = real_c
     return rows, log, c
 
diff --git a/goodwe_controller/test_safety118.py b/goodwe_controller/test_safety118.py
index 30058a6..f6fe602 100644
--- a/goodwe_controller/test_safety118.py
+++ b/goodwe_controller/test_safety118.py
@@ -19,6 +19,10 @@ import asyncio
 import logging
 from pathlib import Path
 
+import os  # noqa: E402
+import sys  # noqa: E402
+sys.path.insert(0, os.path.join(os.path.dirname(os.path.abspath(__file__)), "tools"))  # noqa: E402
+import main_files  # noqa: E402
 from app import main as _main
 from app import messages, pv, validate
 from app.main import Controller
@@ -217,7 +221,7 @@ check(f"one read of the forecast entity per read_inputs() ({h.reads})",
 
 print("4. maintenance headroom and the charge-only clamp use watts")
 seen = []
-_real = _main.maintenance_charge_floor
+_real = main_files.live.maintenance_charge_floor
 
 
 def spy(charge_w, fc, cap):
@@ -226,7 +230,7 @@ def spy(charge_w, fc, cap):
     return out
 
 
-_main.maintenance_charge_floor = spy
+main_files.live.maintenance_charge_floor = spy
 try:
     def cycle(fc, **kw):
         c, h = make(fc, store={"phase": "charge"},
@@ -264,7 +268,7 @@ try:
     check("no unit: forecast unused, clamp in place, as with the option empty",
           clamp(st(6000)) is False)
 finally:
-    _main.maintenance_charge_floor = _real
+    main_files.live.maintenance_charge_floor = _real
 
 print("5. validator and strings")
 def notes(unit, key="peak_forecast_entity"):
diff --git a/goodwe_controller/test_safety119.py b/goodwe_controller/test_safety119.py
index 069ddc6..91e1204 100644
--- a/goodwe_controller/test_safety119.py
+++ b/goodwe_controller/test_safety119.py
@@ -59,6 +59,7 @@ logging.disable(logging.WARNING)
 import opt11_identity as rig                                   # noqa: E402
 import safety79_identity as s79                                # noqa: E402
 import safety84_identity as s84                                # noqa: E402
+import main_files  # noqa: E402
 import app.main as app_main                                    # noqa: E402
 from app import messages                                       # noqa: E402
 from app.main import Controller                                # noqa: E402
@@ -413,8 +414,8 @@ _rg = {t: never(t, hw, seed=1, delay=0) for t, hw in RIG.items()}
 _rg_old = {t: never(t, hw, fix=False, seed=1, delay=0)
            for t, hw in RIG.items()}
 # SAFETY-119 as merged (bee7431) at 5 s: a settle of 12 cycles, budget 8.
-_rg_119 = patched(app_main, "HANDBACK_CYCLES", app_main.SHORT_CYCLES)(
-    lambda: patched(app_main, "ROLLING_BOUND_CYCLES", 8)(
+_rg_119 = patched(main_files.live, "HANDBACK_CYCLES", app_main.SHORT_CYCLES)(
+    lambda: patched(main_files.live, "ROLLING_BOUND_CYCLES", 8)(
         lambda: never(5.0, 5100.0, seed=1, delay=0)))
 for _t in _rg:
     print(f"    rig shape, {_t:.0f} s meter, house {RIG[_t]:.0f} W: per "
@@ -464,10 +465,10 @@ check("...every command the same as without the fix; without it the false "
 # the rig's shape (1 s, house 5050 W, seed 1).
 rig.TICK = 2.0
 _q25 = (run(house(25), delay=2),
-        patched(app_main, "ROLLING_BOUND_CYCLES", 8)(
+        patched(main_files.live, "ROLLING_BOUND_CYCLES", 8)(
             lambda: run(house(25), delay=2)))
 rig.TICK = 1.0
-_m14 = patched(app_main, "ROLLING_BOUND_CYCLES", 14)(
+_m14 = patched(main_files.live, "ROLLING_BOUND_CYCLES", 14)(
     lambda: never(1.0, 5050.0, seed=1, delay=0))
 _m11 = never(1.0, 5050.0, seed=1, delay=0)
 print(f"    2 s, quarter edge, seed 25: {notes(_q25[0][1])}, budget 8 "
@@ -480,7 +481,7 @@ check("...the budget's margins: 11 is silent at 2 s seed 25 and warns every "
       and every_quarter(_m11[1]) and not every_quarter(_m14[1]))
 check("the rule is the one the sweep chose. Changing it means re-running "
       "the sweep in DECISIONS/SAFETY-121-bound-every-quarter.md",
-      app_main.HANDBACK_CYCLES == 4 and app_main.ROLLING_BOUND_CYCLES == 11
+      main_files.live.HANDBACK_CYCLES == 4 and main_files.live.ROLLING_BOUND_CYCLES == 11
       and app_main.ROLLING_S == 900.0 and app_main.SHORT_SPAN_S == 22.0)
 
 # A start, or a blind cycle, is not a hand-back: the loop at its rail after
diff --git a/goodwe_controller/test_safety123.py b/goodwe_controller/test_safety123.py
index 2708594..00827cd 100644
--- a/goodwe_controller/test_safety123.py
+++ b/goodwe_controller/test_safety123.py
@@ -37,6 +37,7 @@ sys.path.insert(0, os.path.join(HERE, "tools"))
 logging.disable(logging.WARNING)
 
 import opt11_identity as rig                                    # noqa: E402
+import main_files  # noqa: E402
 import app.main as M                                            # noqa: E402
 from app import dayplan, modetrade, packmode, priceruns, solarfc  # noqa: E402
 from app.price import PricePoint, PriceProduct, PriceRead, brussels  # noqa
@@ -492,13 +493,13 @@ for iso in ("2027-03-27T21:00:05+00:00", "2027-03-27T23:45:05+00:00",
             "2027-03-28T00:00:05+00:00"):
     now = datetime.fromisoformat(iso)
     c, hass = controller(MODES["Leftover solar"], now)
-    real_dt = M.datetime
+    real_dt = main_files.live.datetime
 
     class _DT(real_dt):
         @classmethod
         def now(cls, tz=None, _n=now):
             return _n if tz is None else _n.astimezone(tz)
-    M.datetime = _DT
+    main_files.live.datetime = _DT
     try:
         async def one():
             await c.read_inputs(now_mono=0.0)
@@ -510,7 +511,7 @@ for iso in ("2027-03-27T21:00:05+00:00", "2027-03-27T23:45:05+00:00",
         except Slow:
             ok = False
     finally:
-        M.datetime = real_dt
+        main_files.live.datetime = real_dt
     check(f"a whole control cycle at {iso[:16]}Z (three forecast sensors a "
           "day) returns with a day plan", ok)
 
diff --git a/goodwe_controller/test_safety125.py b/goodwe_controller/test_safety125.py
index 0769255..9ca5fa2 100644
--- a/goodwe_controller/test_safety125.py
+++ b/goodwe_controller/test_safety125.py
@@ -48,6 +48,7 @@ logging.disable(logging.WARNING)
 import opt11_identity as rig                                   # noqa: E402
 import opt11p3_replay as rp                                    # noqa: E402
 import safety84_identity as s84                                # noqa: E402
+import main_files  # noqa: E402
 import app.main as m                                           # noqa: E402
 import app.p1 as p1mod                                         # noqa: E402
 from named_absence import first, nth, present                  # noqa: E402
@@ -164,14 +165,14 @@ def drive(o, *, peak=None, late=0.0, minutes=31, every=0, start=None,
         c.inverters[0].dev_min, c.inverters[0].dev_max = -5000.0, 5000.0
         c.inverters[1].dev_min, c.inverters[1].dev_max = -4600.0, 4600.0
         c.auto = True
-        real = m.datetime, homeview.datetime, p1mod.time
+        real = main_files.live.datetime, homeview.datetime, p1mod.time
         clock, simt = [t0], [0.0]
 
         class _DT(real[0]):
             @classmethod
             def now(cls, tz=None):
                 return clock[0] if tz is None else clock[0].astimezone(tz)
-        m.datetime = homeview.datetime = _DT
+        main_files.live.datetime = homeview.datetime = _DT
         p1mod.time = types.SimpleNamespace(monotonic=lambda: 1e6 + simt[0])
         real_load = _price.load_prices, _st.load_prices
         _price.load_prices = _st.load_prices = _no_fetch
@@ -223,7 +224,7 @@ def drive(o, *, peak=None, late=0.0, minutes=31, every=0, start=None,
                 await task
             except asyncio.CancelledError:
                 pass
-            m.datetime, homeview.datetime, p1mod.time = real
+            main_files.live.datetime, homeview.datetime, p1mod.time = real
             _price.load_prices, _st.load_prices = real_load
         return c
     c = asyncio.run(go())
diff --git a/goodwe_controller/test_safety126.py b/goodwe_controller/test_safety126.py
index 5d3275c..87834da 100644
--- a/goodwe_controller/test_safety126.py
+++ b/goodwe_controller/test_safety126.py
@@ -43,6 +43,7 @@ sys.path.insert(0, os.path.join(HERE, "tools"))
 
 import opt11p3_replay as rp                                    # noqa: E402
 from named_absence import first, nth, present                  # noqa: E402
+import main_files  # noqa: E402
 import app.main as m                                           # noqa: E402
 import app.p1 as p1mod                                         # noqa: E402
 from app import homeview, messages, peakguard, tariff          # noqa: E402
@@ -179,14 +180,14 @@ def drive(o, *, modes=OWNER, socs=(10.0, 10.0), house=600.0, minutes=46,
         c.inverters[0].dev_min, c.inverters[0].dev_max = -5000.0, 5000.0
         c.inverters[1].dev_min, c.inverters[1].dev_max = -4600.0, 4600.0
         c.auto = True
-        real = m.datetime, homeview.datetime, p1mod.time
+        real = main_files.live.datetime, homeview.datetime, p1mod.time
         clock, simt = [t0], [0.0]
 
         class _DT(real[0]):
             @classmethod
             def now(cls, tz=None):
                 return clock[0] if tz is None else clock[0].astimezone(tz)
-        m.datetime = homeview.datetime = _DT
+        main_files.live.datetime = homeview.datetime = _DT
         p1mod.time = types.SimpleNamespace(monotonic=lambda: 1e6 + simt[0])
         real_load = _price.load_prices, _st.load_prices
         _price.load_prices = _st.load_prices = _no_fetch
@@ -237,7 +238,7 @@ def drive(o, *, modes=OWNER, socs=(10.0, 10.0), house=600.0, minutes=46,
                     await task
                 except asyncio.CancelledError:
                     pass
-            m.datetime, homeview.datetime, p1mod.time = real
+            main_files.live.datetime, homeview.datetime, p1mod.time = real
             _price.load_prices, _st.load_prices = real_load
         return c
     out["c"] = asyncio.run(go())
diff --git a/goodwe_controller/test_safety85.py b/goodwe_controller/test_safety85.py
index ed70653..9e4798f 100644
--- a/goodwe_controller/test_safety85.py
+++ b/goodwe_controller/test_safety85.py
@@ -38,6 +38,7 @@ logging.disable(logging.WARNING)
 import opt11_identity as rig                                   # noqa: E402
 import safety79_identity as s79                                # noqa: E402
 import safety84_identity as s84                                # noqa: E402
+import main_files  # noqa: E402
 import app.main as app_main                                    # noqa: E402
 from app import clamp, messages                                # noqa: E402
 from app.main import Controller                                # noqa: E402
@@ -202,7 +203,7 @@ check("⭐ N=2, A in its HOLD and B, which the loop drives, gives nothing: the "
 check("...it starts no earlier than the saturation cycles allow (3 x 5 s)",
       all(e.split(" ", 1)[0] >= "11:10:10" for c in (_c1, _c2)
           for e in c.events if "OUTPUT_CLAMP" in e))
-_quiet = patched(app_main, "delivery_short", lambda *a: False)(
+_quiet = patched(main_files.live, "delivery_short", lambda *a: False)(
     lambda: run(1, "drain", 1000.0, 20000, dur=1200.0, cut=gone(600, 1200)))
 check("non-vacuous: without the delivery rule the N=1 drain that gives "
       "nothing is silent (the loop's clamp never reaches its rail here)",
@@ -214,7 +215,7 @@ check("a dip of two cycles is not an alarm", warned(_dip[1]) == (0, 0, 0))
 print("\n3. control coming back from maintenance does not jump")
 END = {"maintenance_hold_min": 10}
 _bounds = []
-_real_compute = app_main.compute
+_real_compute = main_files.live.compute
 
 
 def _spy_compute(*a, **kw):
@@ -222,11 +223,11 @@ def _spy_compute(*a, **kw):
     return _real_compute(*a, **kw)
 
 
-app_main.compute = _spy_compute
+main_files.live.compute = _spy_compute
 try:
     _h2 = run(2, "hold", 4500.0, 20000, dur=900.0, extra=END)
 finally:
-    app_main.compute = _real_compute
+    main_files.live.compute = _real_compute
 _h2_old = no_bound(lambda: run(2, "hold", 4500.0, 20000, dur=900.0,
                                extra=END))
 _h1 = run(1, "hold", 4500.0, 20000, dur=900.0, extra=END)
@@ -380,8 +381,8 @@ def lag_runs():
 
 
 _lag = lagging(lag_runs)
-_lag_old = patched(app_main, "SHORT_CYCLES", 1)(
-    lambda: patched(app_main, "SHORT_SPAN_S", 0.0)(
+_lag_old = patched(main_files.live, "SHORT_CYCLES", 1)(
+    lambda: patched(main_files.live, "SHORT_SPAN_S", 0.0)(
         lambda: lagging(lag_runs)))
 _lag_dead = lagging(lambda: run(1, "drain", 1000.0, 20000, dur=900.0,
                                 cut=gone(600, 900)))
@@ -432,7 +433,7 @@ def both_ways(asked, given, margin):
 
 
 _tp = taper(charge_runs)
-_tp_old = patched(app_main, "delivery_short", both_ways)(
+_tp_old = patched(main_files.live, "delivery_short", both_ways)(
     lambda: taper(charge_runs))
 print(f"    a charge that tapers: {[warned(c) for _r, c in _tp]}, grading "
       f"charges too {[warned(c) for _r, c in _tp_old]}")
diff --git a/goodwe_controller/test_safety87.py b/goodwe_controller/test_safety87.py
index 71c70c6..d2be66c 100644
--- a/goodwe_controller/test_safety87.py
+++ b/goodwe_controller/test_safety87.py
@@ -38,6 +38,7 @@ import types
 HERE = os.path.dirname(os.path.abspath(__file__))
 sys.path.insert(0, HERE)
 sys.path.insert(0, os.path.join(HERE, "tools"))
+import main_files  # noqa: E402
 logging.disable(logging.WARNING)
 
 import opt11_identity as rig                                   # noqa: E402
@@ -703,8 +704,11 @@ check("⭐ the reserve alarm is graded on the real limit, not the aim: a "
 
 _runs_src = {}
 for _f in ("main.py", "homeview.py"):
-    with open(os.path.join(HERE, "app", _f), encoding="utf-8") as _fh:
-        _src = _fh.read()
+    if _f == "main.py":
+        _src = main_files.source()
+    else:
+        with open(os.path.join(HERE, "app", _f), encoding="utf-8") as _fh:
+            _src = _fh.read()
     for _part in _src.split('out.append({')[1:]:
         if '"runs": True' in _part.split("})", 1)[0]:
             _runs_src.setdefault(_f, []).append(
diff --git a/goodwe_controller/test_safety91.py b/goodwe_controller/test_safety91.py
index cd7ce12..6f477bb 100644
--- a/goodwe_controller/test_safety91.py
+++ b/goodwe_controller/test_safety91.py
@@ -127,16 +127,17 @@ def without_fix(fn):
     """release/1.0 8c438ab: held only for the peak, a drain stays pinned, the
     quarter's edge is not rolled over."""
     real = (Controller._held_back, Controller._drain_rise)
+    import main_files  # noqa: E402
     import app.main as m
-    real_nq = m.next_quarter
+    real_nq = main_files.live.next_quarter
     Controller._held_back = lambda self: self._peak_reserve()
     Controller._drain_rise = lambda self, claims, results: None
-    m.next_quarter = lambda p, max_hold_s: p
+    main_files.live.next_quarter = lambda p, max_hold_s: p
     try:
         return fn()
     finally:
         Controller._held_back, Controller._drain_rise = real
-        m.next_quarter = real_nq
+        main_files.live.next_quarter = real_nq
 
 
 def cmd(r):
diff --git a/goodwe_controller/test_safety94.py b/goodwe_controller/test_safety94.py
index 512834c..bae8300 100644
--- a/goodwe_controller/test_safety94.py
+++ b/goodwe_controller/test_safety94.py
@@ -37,6 +37,7 @@ logging.disable(logging.CRITICAL)
 
 import safety94_rig as rig                                    # noqa: E402
 import app.inverter as app_inverter                            # noqa: E402
+import main_files  # noqa: E402
 import app.main as app_main                                    # noqa: E402
 from app import control                                        # noqa: E402
 from app.freshness import BOUNDS, Freshness                    # noqa: E402
@@ -59,19 +60,19 @@ class Before94(Freshness):
 
 def without_fix(fn):
     """Run `fn` with the gate's old clock and the old refusal evidence."""
-    real_f, real_c = app_inverter.Freshness, app_main.compute
-    real_p = app_main.REFUSED_PROGRESS_W
+    real_f, real_c = app_inverter.Freshness, main_files.live.compute
+    real_p = main_files.live.REFUSED_PROGRESS_W
     real_l = app_main.Controller._readings_late
     # SAFETY-128: that tree had no late-readings gate either.
     app_main.Controller._readings_late = lambda self, standing_w: None
     app_inverter.Freshness = Before94
-    app_main.compute = lambda *a, **k: real_c(*a, **dict(k, gave_nothing=None))
-    app_main.REFUSED_PROGRESS_W = float("inf")
+    main_files.live.compute = lambda *a, **k: real_c(*a, **dict(k, gave_nothing=None))
+    main_files.live.REFUSED_PROGRESS_W = float("inf")
     try:
         return fn()
     finally:
-        app_inverter.Freshness, app_main.compute = real_f, real_c
-        app_main.REFUSED_PROGRESS_W = real_p
+        app_inverter.Freshness, main_files.live.compute = real_f, real_c
+        main_files.live.REFUSED_PROGRESS_W = real_p
         app_main.Controller._readings_late = real_l
 
 
@@ -315,7 +316,7 @@ check("compute(): a frozen loop at SETTLE_CYCLES reading -20 W engages with "
       and control.compute(**args, gave_nothing=False).refused == 0)
 
 # The evidence restarts on progress towards the ask, not on jitter.
-print(f"    REFUSED_PROGRESS_W {app_main.REFUSED_PROGRESS_W:.0f} W, span "
+print(f"    REFUSED_PROGRESS_W {main_files.live.REFUSED_PROGRESS_W:.0f} W, span "
       f"{app_main.REFUSED_SPAN_S:.0f} s")
 
 
@@ -356,7 +357,7 @@ check("a command that swaps direction every cycle is never evidence, and a "
       not any(flap) and 1 in away and away.index(1) == 22)
 check("REFUSED_PROGRESS_W is under the band's width and over the live "
       "readings' rest wander (25 W)",
-      25.0 < app_main.REFUSED_PROGRESS_W < 2 * control.REFUSED_BELOW_W)
+      25.0 < main_files.live.REFUSED_PROGRESS_W < 2 * control.REFUSED_BELOW_W)
 
 print()
 if fails:
diff --git a/goodwe_controller/test_safety95.py b/goodwe_controller/test_safety95.py
index acc1965..a1fdab7 100644
--- a/goodwe_controller/test_safety95.py
+++ b/goodwe_controller/test_safety95.py
@@ -36,6 +36,7 @@ logging.disable(logging.WARNING)
 
 import opt11_identity as rig                                   # noqa: E402
 import safety79_identity as s79                                # noqa: E402
+import main_files  # noqa: E402
 from app import main as app_main, packmode                     # noqa: E402
 from app.arbiter import Claim, P_MAINTENANCE, P_SAFETY         # noqa: E402
 from app.main import Controller                                # noqa: E402
@@ -149,13 +150,13 @@ def run(n, house, *, store, extra=None, soc=None, reject=None, dead=None,
         for i in c.inverters:
             i.dev_min, i.dev_max = -5000.0, 5000.0
         c.auto = True
-        real_dt, clock = app_main.datetime, [0.0]
+        real_dt, clock = main_files.live.datetime, [0.0]
 
         class _DT(real_dt):
             @classmethod
             def now(cls, tz=None):
                 return rig.BASE + timedelta(seconds=clock[0])
-        app_main.datetime = _DT
+        main_files.live.datetime = _DT
         rows = []
         try:
             t = 0.0
@@ -182,7 +183,7 @@ def run(n, house, *, store, extra=None, soc=None, reject=None, dead=None,
                              else g.floor_w))
                 t += 2.0
         finally:
-            app_main.datetime = real_dt
+            main_files.live.datetime = real_dt
         return rows, c
     return asyncio.run(go())
 
diff --git a/goodwe_controller/test_sma10_two_idle_states.py b/goodwe_controller/test_sma10_two_idle_states.py
index b395333..d338938 100644
--- a/goodwe_controller/test_sma10_two_idle_states.py
+++ b/goodwe_controller/test_sma10_two_idle_states.py
@@ -32,6 +32,7 @@ from pathlib import Path
 
 HERE = Path(__file__).resolve().parent
 sys.path.insert(0, str(HERE / "tools"))
+import main_files  # noqa: E402
 
 fails = []
 
@@ -336,7 +337,7 @@ def run(coro):
     return asyncio.run(coro)
 
 
-_real_time = M.time
+_real_time = main_files.live.time
 
 
 class _FakeTime:
@@ -891,9 +892,9 @@ check("the units that raised, failed or hung are NOT marked handed back, so "
                                       for i in (1, 2, 4)))
 fb_raise.mode = "ok"
 FT.t = _real_time.monotonic() + 11.0                   # one heartbeat later
-M.time = FT
+main_files.live.time = FT
 run(c.send_heartbeats(60_000.0, 10.0))
-M.time = _real_time
+main_files.live.time = _real_time
 check("...and the next idle write (a heartbeat later) retries the one that "
       "raised (now answers): released, and the healthy unit is not released a "
       "second time",
@@ -955,7 +956,7 @@ for mode in ("false", "raise", "hang"):
 
 # the cadence and the log, over N failed retries on a clock we move
 c, h, f = failing_site("false")
-M.time = FT
+main_files.live.time = FT
 FT.t = 5000.0
 _cap.clear()
 run(c.handle_action("auto_toggle"))              # Stop: try 1 (forced)
@@ -997,7 +998,7 @@ _cap.clear()
 run(c.handle_action("auto_toggle"))               # Stop, fails again
 check("a NEW failure streak is logged again, once",
       len([1 for lv, m in _cap if lv >= logging.ERROR]) == 1)
-M.time = _real_time
+main_files.live.time = _real_time
 
 # shutdown with a failed release: the one 0 W still goes out inside the bound
 c, h, f = failing_site("hang")
@@ -1098,7 +1099,7 @@ check("the two new Last-event hints exist and are plain",
       .endswith("trying again"))
 
 # --- 3j. the call sites -------------------------------------------------------
-src = (HERE / "app" / "main.py").read_text(encoding="utf-8")
+src = main_files.source()
 ss = src.splitlines()
 
 
@@ -1115,7 +1116,8 @@ check("main.py: the Stop button and shutdown() call command_site_release(); "
       "the two maintenance-abort paths keep command_site_zero() (a third call "
       "is the all-GoodWe branch inside command_site_release itself)",
       len(rel) == 2 and len(zer) == 3
-      and "async def command_site_release" in "\n".join(ss[zer[1] - 30:zer[1]]))
+      and any("async def command_site_release" in "\n".join(ss[i - 30:i])
+              for i in zer))
 
 # =============================================================================
 print()
diff --git a/goodwe_controller/test_split_patches.py b/goodwe_controller/test_split_patches.py
new file mode 100644
index 0000000..7bd26bb
--- /dev/null
+++ b/goodwe_controller/test_split_patches.py
@@ -0,0 +1,181 @@
+"""MAINT-21 tripwire: a test must patch a Controller global where it is read.
+
+The Controller's code lives in app/main.py and in the files split from it
+(app/ctl_*.py, app/rows.py). A function reads a module global from its own
+file, so `app.main.NAME = fake` changes only the code that is still in
+main.py. This file fails when a test or tool still does that:
+
+  1. it patches an `app.main` attribute that main.py's own functions no
+     longer read (a stale patch, silently inert), or
+  2. it patches an `app.main` attribute that another file also reads (the
+     patch reaches only part of the code).
+
+The way to patch is `tools/main_files.py`: `main_files.live.NAME = fake` sets
+NAME in every file that reads it and raises when none does.
+
+Part 3 runs the scan on spoilt sources and the patch helper on the real tree.
+Read MUTATION.md for the habit this follows.  `python3 test_split_patches.py`
+"""
+
+import ast
+import glob
+import os
+import sys
+
+HERE = os.path.dirname(os.path.abspath(__file__))
+sys.path.insert(0, HERE)
+sys.path.insert(0, os.path.join(HERE, "tools"))
+import main_files  # noqa: E402
+
+fails = []
+ALIASES = {"m", "M", "main", "app_main", "_main", "_main_mod", "main_mod"}
+
+
+def check(name, cond):
+    print(f"  {'ok  ' if cond else 'FAIL'} {name}")
+    if not cond:
+        fails.append(name)
+
+
+def main_aliases(tree):
+    """Names bound to the module app.main in one file."""
+    al = set()
+    for n in ast.walk(tree):
+        if isinstance(n, ast.Import):
+            al.update(a.asname for a in n.names
+                      if a.name == "app.main" and a.asname)
+        elif isinstance(n, ast.ImportFrom) and n.module == "app":
+            al.update(a.asname or a.name for a in n.names if a.name == "main")
+    for n in ast.walk(tree):
+        if (isinstance(n, ast.Assign) and isinstance(n.value, ast.Name)
+                and n.value.id in al):
+            al.update(t.id for t in n.targets if isinstance(t, ast.Name))
+        # `for mod in (app_main, homeview): mod.datetime = fake`
+        if (isinstance(n, ast.For) and isinstance(n.target, ast.Name)
+                and isinstance(n.iter, (ast.Tuple, ast.List))
+                and any(isinstance(e, ast.Name) and e.id in al
+                        for e in n.iter.elts)):
+            al.add(n.target.id)
+    return al
+
+
+def flat(targets):
+    """The assignment targets, tuples and lists taken apart."""
+    for t in targets:
+        if isinstance(t, (ast.Tuple, ast.List)):
+            yield from flat(t.elts)
+        else:
+            yield t
+
+
+def patches(src):
+    """[(line, name)]: every attribute of app.main a file assigns, or hands to
+    setattr / a patching helper as `(app.main alias, "name", value)`."""
+    tree = ast.parse(src)
+    al = main_aliases(tree)
+    out = []
+    for n in ast.walk(tree):
+        targets = []
+        if isinstance(n, ast.Assign):
+            targets = n.targets
+        elif isinstance(n, (ast.AugAssign, ast.AnnAssign)):
+            targets = [n.target]
+        for t in flat(targets):
+            # `app_main.NAME = x`, or `rig.m.NAME = x` where rig did
+            # `import app.main as m`
+            if isinstance(t, ast.Attribute) and (
+                    (isinstance(t.value, ast.Name) and t.value.id in al)
+                    or (isinstance(t.value, ast.Attribute)
+                        and t.value.attr in ALIASES)):
+                out.append((n.lineno, t.attr))
+        if (isinstance(n, ast.Call) and len(n.args) >= 3
+                and isinstance(n.args[0], ast.Name) and n.args[0].id in al
+                and isinstance(n.args[1], ast.Constant)
+                and isinstance(n.args[1].value, str)
+                and ast.unparse(n.func) != "getattr"):
+            out.append((n.lineno, n.args[1].value))
+    return out
+
+
+def problems(src, where="<source>", readers=main_files.reading):
+    """Messages for each patch in `src` that the rule above rejects."""
+    out = []
+    for line, name in patches(src):
+        who = readers(name)
+        if "main" not in who:
+            out.append(f"{where}:{line} patches main.{name}, which main.py "
+                       f"does not read" + (f" (read by {who})" if who else ""))
+        elif who != ["main"]:
+            out.append(f"{where}:{line} patches main.{name}, which "
+                       f"{[w for w in who if w != 'main']} also read: use "
+                       f"main_files.live.{name}")
+    return out
+
+
+# --------------------------------------------------------------------------- #
+print("1. no test and no tool patches a main global the code reads elsewhere")
+sites = bad = 0
+for path in sorted(glob.glob(os.path.join(HERE, "test_*.py"))
+                   + glob.glob(os.path.join(HERE, "tools", "*.py"))):
+    if os.path.basename(path) == "test_split_patches.py":
+        continue
+    with open(path, encoding="utf-8") as fh:
+        src = fh.read()
+    found = problems(src, os.path.relpath(path, HERE))
+    sites += len(patches(src))
+    for msg in found:
+        print("       " + msg)
+    bad += len(found)
+check(f"{sites} patches of an app.main attribute found, {bad} stale or partial",
+      sites > 0 and bad == 0)
+
+# --------------------------------------------------------------------------- #
+print("\n2. the scan is not blind: spoilt sources are caught")
+HEAD = "import app.main as m\n"
+check("main.<a name nothing reads> is stale",
+      len(problems(HEAD + "m.no_such_global_anywhere = 1\n")) == 1)
+check("main.datetime is partial (the clock is read in more than one file)"
+      if len(main_files.reading("datetime")) > 1 else
+      "main.datetime (one reader here, so nothing to catch yet)",
+      len(problems(HEAD + "m.datetime = 1\n")) ==
+      (1 if len(main_files.reading("datetime")) > 1 else 0))
+check("the same through setattr, a helper and an alias",
+      len(problems(HEAD + "k = m\nsetattr(k, 'no_such_global_anywhere', 1)\n"
+                   "patched(m, 'no_such_global_anywhere', 1)(f)\n")) == 2)
+check("a patch through main_files.live is not flagged",
+      problems(HEAD + "import main_files\n"
+               "main_files.live.datetime = 1\n") == [])
+check("a name only main reads may still be patched on main",
+      problems(HEAD + "m.load_options = 1\n") == [])
+
+# --------------------------------------------------------------------------- #
+print("\n3. main_files.live sets a global in every file that reads it")
+import importlib  # noqa: E402
+
+live = main_files.live
+for name in ("datetime", "compute", "_mono"):
+    readers = main_files.reading(name)
+    mods = [importlib.import_module("app." + r) for r in readers]
+    before = [getattr(m, name) for m in mods]
+    sentinel = object()
+    setattr(live, name, sentinel)
+    try:
+        hit = all(getattr(m, name) is sentinel for m in mods)
+        read_back = getattr(live, name) is sentinel
+    finally:
+        for m, old in zip(mods, before):
+            setattr(m, name, old)
+    check(f"{name}: set in all {len(mods)} reading file(s) {readers}, and "
+          f"read back", bool(mods) and hit and read_back)
+try:
+    live.no_such_global_anywhere = 1
+    raised = False
+except AttributeError:
+    raised = True
+check("a name no file reads raises instead of patching nothing", raised)
+
+print()
+if fails:
+    print(f"FAILED: {len(fails)}")
+    sys.exit(1)
+print("all ok")
diff --git a/goodwe_controller/test_static_tariff.py b/goodwe_controller/test_static_tariff.py
index 2537ac3..378a73d 100644
--- a/goodwe_controller/test_static_tariff.py
+++ b/goodwe_controller/test_static_tariff.py
@@ -81,6 +81,8 @@ from app.static_tariff import (
 from app.validate import validate_startup_config
 
 HERE = Path(__file__).resolve().parent
+sys.path.insert(0, str(HERE / "tools"))
+import main_files  # noqa: E402
 UTC = timezone.utc
 
 # PRICE-02: `TariffPlan.arbitrage(now=...)` is required. This instant is before every
@@ -893,7 +895,7 @@ check("the new module holds no option-defaults dict of its own, so this ticket "
 check("...and it reads the option through price.price_option(), the framework's "
       "single read path, rather than through opts.get(key, <a number>)",
       "price_option(opts" in _SRC and 'opts.get("static_profile"' not in _SRC)
-_MAIN = (HERE / "app" / "main.py").read_text(encoding="utf-8")
+_MAIN = main_files.source()
 check("...and main.py grew no `o.get(\"static_profile\", <a default>)` fallback "
       "either - it calls static_status(o, now), and the option is read once, "
       "inside the framework",
diff --git a/goodwe_controller/test_tariff24.py b/goodwe_controller/test_tariff24.py
index f5b74a4..abf6110 100644
--- a/goodwe_controller/test_tariff24.py
+++ b/goodwe_controller/test_tariff24.py
@@ -40,6 +40,7 @@ logging.disable(logging.WARNING)
 
 import opt11p3_replay as rp                                    # noqa: E402
 from named_absence import first, nth, present                  # noqa: E402
+import main_files  # noqa: E402
 import app.main as m                                           # noqa: E402
 from app import homeview, modetrade, packmode                  # noqa: E402
 from app import price as _price, static_tariff as _st          # noqa: E402
@@ -196,7 +197,7 @@ def drive(o, *, start=NIGHT, minutes=20, soc0=None, choice=CHOICE,
         for i in c.inverters:
             i.dev_min, i.dev_max = -5000.0, 5000.0
         c.auto = True
-        real_dt, real_hv = m.datetime, homeview.datetime
+        real_dt, real_hv = main_files.live.datetime, homeview.datetime
         clock = [start]
 
         class _DT(real_dt):
@@ -204,7 +205,7 @@ def drive(o, *, start=NIGHT, minutes=20, soc0=None, choice=CHOICE,
             def now(cls, tz=None):
                 return clock[0] if tz is None else clock[0].astimezone(tz)
 
-        m.datetime = homeview.datetime = _DT
+        main_files.live.datetime = homeview.datetime = _DT
         _real_load = _price.load_prices, _st.load_prices
         _price.load_prices = _st.load_prices = _no_fetch
         started = task_started(o)
@@ -246,7 +247,7 @@ def drive(o, *, start=NIGHT, minutes=20, soc0=None, choice=CHOICE,
                     await task
                 except asyncio.CancelledError:
                     pass
-            m.datetime, homeview.datetime = real_dt, real_hv
+            main_files.live.datetime, homeview.datetime = real_dt, real_hv
             _price.load_prices, _st.load_prices = _real_load
         return c, started
 
diff --git a/goodwe_controller/test_tariff24_weather.py b/goodwe_controller/test_tariff24_weather.py
index 5d69662..10c6322 100644
--- a/goodwe_controller/test_tariff24_weather.py
+++ b/goodwe_controller/test_tariff24_weather.py
@@ -47,6 +47,7 @@ logging.disable(logging.WARNING)
 
 import opt11p3_replay as rp                                    # noqa: E402
 from named_absence import first, nth, present                  # noqa: E402
+import main_files  # noqa: E402
 import app.main as m                                           # noqa: E402
 from app import arbitrage, homeview, modetrade, solarfc        # noqa: E402
 from app.main import Controller                                # noqa: E402
@@ -175,7 +176,7 @@ def drive(o, *, fc="fresh", points=None, minutes=20, tick=5.0,
         # forecast IS lost, so it runs with a hold that never covers
         # (test_opt27.py tests the cover).
         c.fc_hold = _NoHold()
-        real_dt, real_hv = m.datetime, homeview.datetime
+        real_dt, real_hv = main_files.live.datetime, homeview.datetime
         clock = [t0]
 
         class _DT(real_dt):
@@ -183,7 +184,7 @@ def drive(o, *, fc="fresh", points=None, minutes=20, tick=5.0,
             def now(cls, tz=None):
                 return clock[0] if tz is None else clock[0].astimezone(tz)
 
-        m.datetime = homeview.datetime = _DT
+        main_files.live.datetime = homeview.datetime = _DT
         pts = None if points is None else points
         task = None
         if pts is None:
@@ -248,7 +249,7 @@ def drive(o, *, fc="fresh", points=None, minutes=20, tick=5.0,
                     await task
                 except asyncio.CancelledError:
                     pass
-            m.datetime, homeview.datetime = real_dt, real_hv
+            main_files.live.datetime, homeview.datetime = real_dt, real_hv
         return c
 
     return asyncio.run(go()), rows
diff --git a/goodwe_controller/test_ux54_dst.py b/goodwe_controller/test_ux54_dst.py
index 850873b..288ce97 100644
--- a/goodwe_controller/test_ux54_dst.py
+++ b/goodwe_controller/test_ux54_dst.py
@@ -36,6 +36,7 @@ logging.disable(logging.WARNING)
 
 import ux54_scenarios as S                                        # noqa: E402
 import app.main as M                                              # noqa: E402
+import main_files                                              # noqa: E402
 from app import arbitrage, dayplan, dayview, homeview, solarfc    # noqa: E402
 from app import tariff                                            # noqa: E402
 from app.daycurve import SolarToday                               # noqa: E402
@@ -90,7 +91,8 @@ class FakeDT(datetime):
         return NOW[0].astimezone(tz) if tz else NOW[0].replace(tzinfo=None)
 
 
-for _mod in (M, homeview, dayview):         # what reads the wall clock
+main_files.live.datetime = FakeDT           # the Controller's clock
+for _mod in (homeview, dayview):            # the other readers of the clock
     _mod.datetime = FakeDT
 
 TZ_MODULES = (tariff, dayplan, homeview, solarfc)
diff --git a/goodwe_controller/test_watchdog.py b/goodwe_controller/test_watchdog.py
index 7389bf3..0d9e172 100644
--- a/goodwe_controller/test_watchdog.py
+++ b/goodwe_controller/test_watchdog.py
@@ -1161,9 +1161,12 @@ check("...and it does not raise the same card on every cycle - a per-PROCESS "
 
 # SAFETY-34: a Core-ONLY restart. The add-on process lives on (measured on
 # TEST-23), HA's memory is wiped, so the SAME process must re-assert the card.
+import os  # noqa: E402
+sys.path.insert(0, os.path.join(os.path.dirname(os.path.abspath(__file__)), "tools"))  # noqa: E402
+import main_files  # noqa: E402
 import app.main as _main_mod  # noqa: E402
-_real_mono, _clock = _main_mod._mono, [_main_mod._mono()]
-_main_mod._mono = lambda: _clock[0]
+_real_mono, _clock = main_files.live._mono, [main_files.live._mono()]
+main_files.live._mono = lambda: _clock[0]
 try:
     _h3 = _CircHass(a_w=0.0, b_w=0.0)
     _b.hass = _h3
@@ -1173,7 +1176,7 @@ try:
     asyncio.run(_b.check_circulating())
     _late = [c for c in _h3.calls if c[0] == "persistent_notification"]
 finally:
-    _main_mod._mono = _real_mono
+    main_files.live._mono = _real_mono
 check("SAFETY-34: inside REANNOUNCE_S the same process does not re-raise - no "
       "storm on the event bus", len(_early) == 0)
 check("SAFETY-34: a Core-only restart wipes the card and the add-on process "
diff --git a/goodwe_controller/tools/main_files.py b/goodwe_controller/tools/main_files.py
new file mode 100644
index 0000000..4ef7056
--- /dev/null
+++ b/goodwe_controller/tools/main_files.py
@@ -0,0 +1,98 @@
+"""MAINT-21: the Controller lives in app/main.py and the files split from it.
+
+A test that reads `app/main.py` for a call, a comment or a def reads
+`source()` instead; a test that replaces a global that `main` used to read
+calls `patch_global()`, which sets it in each file whose code reads it. A name
+no file reads is an error: a stale patch cannot pass unnoticed.
+"""
+import ast
+import glob
+import importlib
+import os
+import symtable
+
+APP = os.path.join(os.path.dirname(os.path.abspath(__file__)), "..", "app")
+
+
+def files():
+    """main.py, rows.py and ctl_*.py, in that order, as bare file names."""
+    split = ["rows.py"] + sorted(os.path.basename(p)
+                                 for p in glob.glob(os.path.join(APP, "ctl_*.py")))
+    return ["main.py"] + [f for f in split
+                          if os.path.exists(os.path.join(APP, f))]
+
+
+def text(name):
+    with open(os.path.join(APP, name), encoding="utf-8") as fh:
+        return fh.read()
+
+
+def source():
+    """All the files' text, one after the other."""
+    return "\n".join(text(f) for f in files())
+
+
+def tree(src=None):
+    """`ast.parse(source())` with every `*Mixin` class folded into
+    `Controller`, so `Controller` has all its methods. Positions refer to
+    `source()`."""
+    src = source() if src is None else src
+    mod = ast.parse(src)
+    ctl = next(n for n in mod.body
+               if isinstance(n, ast.ClassDef) and n.name == "Controller")
+    keep = []
+    for n in mod.body:
+        if isinstance(n, ast.ClassDef) and n.name.endswith("Mixin"):
+            ctl.body.extend(n.body)
+        else:
+            keep.append(n)
+    mod.body = keep
+    return mod
+
+
+def _function_reads(table, acc):
+    for s in table.get_symbols():
+        if (table.get_type() == "function" and s.is_global()
+                and s.is_referenced()):
+            acc.add(s.get_name())
+    for child in table.get_children():
+        _function_reads(child, acc)
+
+
+def reading(name):
+    """The bare module names (`main`, `ctl_cycle` ...) whose functions read
+    `name` as a global."""
+    out = []
+    for f in files():
+        acc = set()
+        _function_reads(symtable.symtable(text(f), f, "exec"), acc)
+        if name in acc:
+            out.append(f[:-3])
+    return out
+
+
+class _Live:
+    """The globals the Controller's code reads, wherever they are read.
+
+    `live.NAME = value` sets NAME in every file whose functions read it;
+    `live.NAME` reads it. A name no file reads is an AttributeError, so a
+    patch that changes nothing cannot pass unnoticed.
+    """
+
+    def __getattr__(self, name):
+        mods = reading(name)
+        if not mods:
+            raise AttributeError(f"no file under app/ reads the global "
+                                 f"{name!r}")
+        return getattr(importlib.import_module("app." + mods[0]), name)
+
+    def __setattr__(self, name, value):
+        mods = reading(name)
+        if not mods:
+            raise AttributeError(f"no file under app/ reads the global "
+                                 f"{name!r}: a patch of it changes nothing")
+        for stem in mods:
+            setattr(importlib.import_module("app." + stem), name, value)
+
+
+live = _Live()
diff --git a/goodwe_controller/tools/maint21_same_ast.py b/goodwe_controller/tools/maint21_same_ast.py
new file mode 100644
index 0000000..7564a42
--- /dev/null
+++ b/goodwe_controller/tools/maint21_same_ast.py
@@ -0,0 +1,142 @@
+#!/usr/bin/env python3
+"""MAINT-21: prove that splitting app/main.py moved code and changed none.
+
+    python3 goodwe_controller/tools/maint21_same_ast.py [BASE_REF] [--docstrings]
+
+Every module-level def, class and assignment of app/main.py at BASE_REF
+(default release/1.0), and every method of its `Controller`, is looked up by
+qualified name in the working tree: app/main.py, app/rows.py and the mixin
+classes of app/ctl_*.py (a mixin's methods count as `Controller.<name>`).
+Each must be found exactly once with an identical `ast.dump()`, docstrings
+removed unless --docstrings. Allowed extras: the `Controller` class header,
+`_LOG = logging.getLogger("goodwe")` in a module that logs, and import lines.
+Prints one line per file and `OK` or the differences. The diff against
+BASE_REF may touch only goodwe_controller/app, DECISIONS, test_*.py and
+tools. Run from the repository root on a clean checkout (untracked files are
+read, but the diff check only sees tracked ones). Exit 1 on any difference.
+"""
+import ast
+import collections
+import glob
+import os
+import re
+import subprocess
+import sys
+
+APP = "goodwe_controller/app"
+MIXIN = re.compile(r"^[A-Z][A-Za-z]*Mixin$")
+
+
+def git(*a):
+    return subprocess.run(["git", *a], check=True, capture_output=True,
+                          text=True).stdout
+
+
+def bare(n, docstrings):
+    if not docstrings:
+        for x in ast.walk(n):
+            if isinstance(x, (ast.FunctionDef, ast.AsyncFunctionDef,
+                              ast.ClassDef)) and x.body:
+                e = x.body[0]
+                if (isinstance(e, ast.Expr) and isinstance(e.value, ast.Constant)
+                        and isinstance(e.value.value, str)):
+                    x.body = x.body[1:] or [ast.Pass()]
+    return ast.dump(n)
+
+
+def key_of(n):
+    if isinstance(n, (ast.FunctionDef, ast.AsyncFunctionDef, ast.ClassDef)):
+        return n.name
+    if isinstance(n, ast.Assign):
+        return "=" + ",".join(ast.unparse(t) for t in n.targets)
+    if isinstance(n, ast.AnnAssign):
+        return "=" + ast.unparse(n.target)
+    return "?" + ast.unparse(n)[:60]
+
+
+def units(src, docstrings, mixins):
+    """{qualified name: [dump, ...]} for one file's text."""
+    out = collections.defaultdict(list)
+    tree = ast.parse(src)
+    for n in tree.body:
+        if isinstance(n, (ast.Import, ast.ImportFrom)):
+            continue
+        if (isinstance(n, ast.Expr) and isinstance(n.value, ast.Constant)
+                and isinstance(n.value.value, str)):
+            continue
+        if isinstance(n, ast.ClassDef) and (
+                n.name == "Controller" or (mixins and MIXIN.match(n.name))):
+            for m in n.body:
+                out["Controller." + key_of(m)].append(bare(m, docstrings))
+            continue
+        out[key_of(n)].append(bare(n, docstrings))
+    return out
+
+
+def main(argv):
+    docstrings = "--docstrings" in argv
+    argv = [a for a in argv if not a.startswith("--")]
+    base = argv[0] if argv else "release/1.0"
+    bad = 0
+    print(f"base {base} = {git('rev-parse', base).strip()}")
+    for f in git("diff", "--name-only", base).split():
+        if not re.match(r"^goodwe_controller/(app/[^/]+|DECISIONS/[^/]+|"
+                        r"test_[^/]+\.py|tools/[^/]+)$", f):
+            print(f"FAIL: diff touches {f}")
+            bad += 1
+    old = units(git("show", f"{base}:{APP}/main.py"), docstrings, False)
+    files = ["main.py", "rows.py"] + sorted(
+        os.path.basename(p) for p in glob.glob(f"{APP}/ctl_*.py"))
+    where = collections.defaultdict(list)       # key -> [(file, dump)]
+    for fn in files:
+        p = f"{APP}/{fn}"
+        if not os.path.exists(p):
+            continue
+        for k, dumps in units(open(p, encoding="utf-8").read(), docstrings,
+                              True).items():
+            for d in dumps:
+                where[k].append((fn, d))
+    found = collections.Counter()
+    problems = collections.defaultdict(list)
+    for k, dumps in old.items():
+        if k == "Controller":
+            continue
+        got = where.get(k, [])
+        if k == "=_LOG":        # one per module that logs, all the same
+            got = got[:1] * len(dumps) if all(
+                d == dumps[0] for _, d in got) else []
+        if len(got) != len(dumps):
+            problems["?"].append(f"{k}: {len(dumps)} in base, "
+                                 f"{len(got)} in head")
+            continue
+        for (fn, d), want in zip(got, dumps):
+            if d != want:
+                problems[fn].append(f"{k}: AST differs")
+            else:
+                found[fn] += 1
+    for k, got in where.items():
+        if k not in old and k != "=_LOG":
+            for fn, _ in got:
+                problems[fn].append(f"{k}: not in base")
+    for fn in files:
+        if not os.path.exists(f"{APP}/{fn}"):
+            continue
+        if problems.get(fn):
+            print(f"DIFFERS  {fn}")
+            for line in problems[fn]:
+                print("   ", line)
+            bad += len(problems[fn])
+        else:
+            print(f"OK       {fn}  {found[fn]} units identical")
+    for line in problems.get("?", []):
+        print("DIFFERS ", line)
+        bad += 1
+    total = sum(found.values())
+    print(f"base units {sum(len(v) for k, v in old.items() if k != 'Controller')}"
+          f", identical in head {total}")
+    print("OK: code moved, none changed" if not bad else f"FAIL: {bad} problem(s)")
+    return 1 if bad else 0
+
+
+if __name__ == "__main__":
+    sys.exit(main(sys.argv[1:]))
diff --git a/goodwe_controller/tools/opt11_identity.py b/goodwe_controller/tools/opt11_identity.py
index f775816..4bf29be 100644
--- a/goodwe_controller/tools/opt11_identity.py
+++ b/goodwe_controller/tools/opt11_identity.py
@@ -26,6 +26,7 @@ from datetime import datetime, timedelta, timezone
 
 sys.path.insert(0, os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
 
+import main_files  # noqa: E402
 import app.main as m                                      # noqa: E402
 from app.main import Controller                           # noqa: E402
 
@@ -157,7 +158,7 @@ def run(n, *, extra=None, dur=2700.0, store=None, on_cycle=None, load=house,
         for i in c.inverters:
             i.dev_min, i.dev_max = -5000.0, 5000.0
         c.auto = True
-        real_dt = m.datetime
+        real_dt = main_files.live.datetime
         clock = [0.0]
 
         class _DT(real_dt):
@@ -165,7 +166,7 @@ def run(n, *, extra=None, dur=2700.0, store=None, on_cycle=None, load=house,
             def now(cls, tz=None):
                 return BASE + timedelta(seconds=clock[0])
 
-        m.datetime = _DT
+        main_files.live.datetime = _DT
         rows = []
         try:
             t = 0.0
@@ -186,7 +187,7 @@ def run(n, *, extra=None, dur=2700.0, store=None, on_cycle=None, load=house,
                     on_cycle(c, t)
                 t += TICK
         finally:
-            m.datetime = real_dt
+            main_files.live.datetime = real_dt
         return rows, c
     return asyncio.run(go())
 
diff --git a/goodwe_controller/tools/opt11p3_replay.py b/goodwe_controller/tools/opt11p3_replay.py
index a9eac56..589c22f 100644
--- a/goodwe_controller/tools/opt11p3_replay.py
+++ b/goodwe_controller/tools/opt11p3_replay.py
@@ -41,6 +41,7 @@ from datetime import datetime, timedelta, timezone
 HERE = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
 sys.path.insert(0, HERE)
 
+import main_files  # noqa: E402
 import app.main as m                                      # noqa: E402
 from app.main import Controller                           # noqa: E402
 from app.p1 import make_sample, split_signed               # noqa: E402
@@ -348,7 +349,7 @@ def run(variant, house, pts, start, dur, *, check=None, stride=1, n=2,
         if patch is not None:
             patch(c)
         c.auto = True
-        real_dt = m.datetime
+        real_dt = main_files.live.datetime
         clock = [start]
 
         class _DT(real_dt):
@@ -356,7 +357,7 @@ def run(variant, house, pts, start, dur, *, check=None, stride=1, n=2,
             def now(cls, tz=None):
                 return clock[0] if tz is None else clock[0].astimezone(tz)
 
-        m.datetime = _DT
+        main_files.live.datetime = _DT
         plan_hour = None
         try:
             t = 0.0
@@ -416,7 +417,7 @@ def run(variant, house, pts, start, dur, *, check=None, stride=1, n=2,
                     check(c, hass, now, pr)
                 t += tick
         finally:
-            m.datetime = real_dt
+            main_files.live.datetime = real_dt
         return c
     c = asyncio.run(go())
     return stats, c
diff --git a/goodwe_controller/tools/safety103_plant.py b/goodwe_controller/tools/safety103_plant.py
index 122f939..544b0df 100644
--- a/goodwe_controller/tools/safety103_plant.py
+++ b/goodwe_controller/tools/safety103_plant.py
@@ -22,6 +22,7 @@ sys.path.insert(0, HERE)
 sys.path.insert(0, os.path.join(HERE, "tools"))
 
 import opt11_identity as rig                                   # noqa: E402
+import main_files  # noqa: E402
 from app import main as app_main, packmode                     # noqa: E402
 from app.main import Controller                                # noqa: E402
 from app.store import unit_key                                 # noqa: E402
@@ -127,13 +128,13 @@ def run(n, house, *, before=off, dur=T + 90.0, tick=1.0, reg_s=10.0,
         for i in c.inverters:
             i.dev_min, i.dev_max = -5000.0, 5000.0
         c.auto = True
-        real_dt, clock = app_main.datetime, [0.0]
+        real_dt, clock = main_files.live.datetime, [0.0]
 
         class _DT(real_dt):
             @classmethod
             def now(cls, tz=None):
                 return rig.BASE + timedelta(seconds=clock[0])
-        app_main.datetime = _DT
+        main_files.live.datetime = _DT
         rows = []
         try:
             t = 0.0
@@ -161,7 +162,7 @@ def run(n, house, *, before=off, dur=T + 90.0, tick=1.0, reg_s=10.0,
                     reason=c.loop_reason))
                 t += tick
         finally:
-            app_main.datetime = real_dt
+            main_files.live.datetime = real_dt
         return rows, c
     return asyncio.run(go())
 
diff --git a/goodwe_controller/tools/safety128_rig.py b/goodwe_controller/tools/safety128_rig.py
index 3d97eec..1e8898d 100644
--- a/goodwe_controller/tools/safety128_rig.py
+++ b/goodwe_controller/tools/safety128_rig.py
@@ -33,6 +33,7 @@ from datetime import datetime, timedelta, timezone
 
 sys.path.insert(0, os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
 
+import main_files  # noqa: E402
 import app.main as m                                      # noqa: E402
 from app.main import Controller                           # noqa: E402
 from app.p1 import make_sample, split_signed              # noqa: E402
@@ -222,7 +223,7 @@ class Rig:
                 i.dev_min, i.dev_max = -MAXW[i.name[-1]], MAXW[i.name[-1]]
             c.auto = True
             self.c = c
-            real_dt = m.datetime
+            real_dt = main_files.live.datetime
             clock = [self.start]
 
             class _DT(real_dt):
@@ -230,7 +231,7 @@ class Rig:
                 def now(cls, tz=None):
                     return clock[0] if tz is None else clock[0].astimezone(tz)
 
-            m.datetime = _DT
+            main_files.live.datetime = _DT
             floor = float(self.o.get("cycle_floor_s", 15))
             last_grid, last_cycle, last_n = object(), None, None
             try:
@@ -260,7 +261,7 @@ class Rig:
                         sample(self, c, t)
                     t += 1.0
             finally:
-                m.datetime = real_dt
+                main_files.live.datetime = real_dt
             return c
         return asyncio.run(go())
 
diff --git a/goodwe_controller/tools/safety78_identity.py b/goodwe_controller/tools/safety78_identity.py
index 06af703..8815a2f 100644
--- a/goodwe_controller/tools/safety78_identity.py
+++ b/goodwe_controller/tools/safety78_identity.py
@@ -33,6 +33,7 @@ sys.path.insert(0, os.path.dirname(os.path.abspath(__file__)))
 import opt11_identity as rig                               # noqa: E402
 import opt11p3_identity as p3                              # noqa: E402
 import safety79_identity as s79                            # noqa: E402
+import main_files  # noqa: E402
 import app.main as m                                       # noqa: E402
 from app import packmode                                  # noqa: E402
 from app.store import unit_key                            # noqa: E402
@@ -76,7 +77,7 @@ def run(n, *, modes=False, dur=DUR, load=load, extra=None):
     if modes:
         extra.update(p3.ARB, battery_modes_enabled=True)
     seen, extra_rows = [], []
-    real_resolve = m.resolve
+    real_resolve = main_files.live.resolve
 
     def spy(claims, **kw):
         seen.append(tuple((c.source, c.priority, c.kind, c.value, c.lo, c.hi,
@@ -96,7 +97,7 @@ def run(n, *, modes=False, dur=DUR, load=load, extra=None):
     db = os.path.join(tempfile.mkdtemp(prefix="s78-"), "tariff.db")
     real = rig.Controller
     rig.Controller = functools.partial(real, peak_db_path=db)
-    m.resolve = spy
+    main_files.live.resolve = spy
     try:
         rows, c = rig.run(n, extra=extra, dur=dur, load=load, soc=s79.soc,
                           cut=lambda u, t: False,
@@ -105,7 +106,7 @@ def run(n, *, modes=False, dur=DUR, load=load, extra=None):
                           store=store_cheap(n) if modes else None)
     finally:
         rig.Controller = real
-        m.resolve = real_resolve
+        main_files.live.resolve = real_resolve
     return [r + (x,) for r, x in zip(rows, extra_rows)], c
 
 
diff --git a/goodwe_controller/tools/safety81_sim.py b/goodwe_controller/tools/safety81_sim.py
index a0accfc..c3dcc12 100644
--- a/goodwe_controller/tools/safety81_sim.py
+++ b/goodwe_controller/tools/safety81_sim.py
@@ -29,6 +29,7 @@ from datetime import timedelta
 sys.path.insert(0, os.path.dirname(os.path.abspath(__file__)))
 
 import opt11_identity as rig                               # noqa: E402
+import main_files  # noqa: E402
 import app.main as m                                       # noqa: E402
 from app import packmode                                   # noqa: E402
 from app.main import Controller                            # noqa: E402
@@ -140,13 +141,13 @@ def run(load, *, margin=50, dur=2700.0, rating=2000.0, cap=3500.0,
         for i in c.inverters:
             i.dev_min, i.dev_max = -5000.0, 5000.0
         c.auto = True
-        real_dt, clock = m.datetime, [0.0]
+        real_dt, clock = main_files.live.datetime, [0.0]
 
         class _DT(real_dt):
             @classmethod
             def now(cls, tz=None):
                 return rig.BASE + timedelta(seconds=clock[0])
-        m.datetime = _DT
+        main_files.live.datetime = _DT
         rows, late = [], random.Random(8100)
         errors = []
 
@@ -173,7 +174,7 @@ def run(load, *, margin=50, dur=2700.0, rating=2000.0, cap=3500.0,
                 rows.append((t, c.target, round(plant.hist[-1][1], 6)))
                 t += TICK
         finally:
-            m.datetime = real_dt
+            main_files.live.datetime = real_dt
             logging.getLogger("goodwe").removeHandler(h)
         return plant, c, rows, errors
     plant, c, rows, errors = asyncio.run(go())
diff --git a/goodwe_controller/tools/safety84_identity.py b/goodwe_controller/tools/safety84_identity.py
index 87730c0..ff1675c 100644
--- a/goodwe_controller/tools/safety84_identity.py
+++ b/goodwe_controller/tools/safety84_identity.py
@@ -23,6 +23,7 @@ sys.path.insert(0, os.path.dirname(os.path.abspath(__file__)))
 
 import opt11_identity as rig                               # noqa: E402
 import safety79_identity as s79                            # noqa: E402
+import main_files  # noqa: E402
 import app.main as m                                       # noqa: E402
 from app import tariff                                     # noqa: E402
 
@@ -71,7 +72,7 @@ def run(n, *, cheap=True, month_peak=None, dur=DUR, load=load, soc=None,
     """Rows (opt11_identity's fields plus every claim, the guard and the
     phases) and the controller. `month_peak` banks that peak this month."""
     seen, extra_rows = [], []
-    real_resolve = m.resolve
+    real_resolve = main_files.live.resolve
 
     def spy(claims, **kw):
         seen.append(tuple((c.source, c.priority, c.kind, c.value, c.lo, c.hi,
@@ -93,7 +94,7 @@ def run(n, *, cheap=True, month_peak=None, dur=DUR, load=load, soc=None,
              "2026-09-02T10:00:00+00:00")).connection.commit()
     real = rig.Controller
     rig.Controller = functools.partial(real, peak_db_path=db)
-    m.resolve = spy
+    main_files.live.resolve = spy
     try:
         rows, c = rig.run(n, extra=dict(s79.P1, **OPT, **(extra or {})),
                           dur=dur, load=load, soc=soc or s79.soc,
@@ -102,7 +103,7 @@ def run(n, *, cheap=True, month_peak=None, dur=DUR, load=load, soc=None,
                           store=store or s79.store_charging(n))
     finally:
         rig.Controller = real
-        m.resolve = real_resolve
+        main_files.live.resolve = real_resolve
     return [r + (x,) for r, x in zip(rows, extra_rows)], c
 
 
diff --git a/goodwe_controller/tools/safety94_rig.py b/goodwe_controller/tools/safety94_rig.py
index f832c5e..9e4bc65 100644
--- a/goodwe_controller/tools/safety94_rig.py
+++ b/goodwe_controller/tools/safety94_rig.py
@@ -25,6 +25,7 @@ from datetime import datetime, timedelta, timezone
 
 sys.path.insert(0, os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
 
+import main_files  # noqa: E402
 import app.main as m                                      # noqa: E402
 from app.main import Controller                           # noqa: E402
 
@@ -169,7 +170,7 @@ def run(n, load, dur, *, tau=10.0, tick=1.0, soc=None, cut=None,
         for i in c.inverters:
             i.dev_min, i.dev_max = -5000.0, 5000.0
         c.auto = True
-        real_dt = m.datetime
+        real_dt = main_files.live.datetime
         clock = [0.0]
 
         class _DT(real_dt):
@@ -177,7 +178,7 @@ def run(n, load, dur, *, tau=10.0, tick=1.0, soc=None, cut=None,
             def now(cls, tz=None):
                 return BASE + timedelta(seconds=clock[0])
 
-        m.datetime = _DT
+        main_files.live.datetime = _DT
         out = {"stale": [], "refused": [], "rows": [], "c": c}
         was = {i.name: False for i in c.inverters}
         was_ref = {i.name: 0 for i in c.inverters}
@@ -213,7 +214,7 @@ def run(n, load, dur, *, tau=10.0, tick=1.0, soc=None, cut=None,
                         dict(plant.reg), [mm.phase for mm in c.maints]))
                 t += 1.0
         finally:
-            m.datetime = real_dt
+            main_files.live.datetime = real_dt
         return out
     return asyncio.run(go())