SAFETY-44: give the moved-not-lost branch a control that reaches it, and make the move injective

⚠️ THE CONTROL I WROTE LAST ROUND WAS INERT, AND REVIEW MEASURED IT. M12 ran its
mutant over `state-legacy.json` and the findings diff against the UNMUTATED tree
was EMPTY. It "passed" because that fixture's STAGED leg is already exit 1 on
pre-existing litter, and `"migrated  unit/shed/" not in out` was trivially true
because a pre-DEV-02 FLAT store has no shed latch to lose - after migration only
the FIRST roster entry is ever latched.

The decisive measurement is the one it could not make: reverting the
`vanished_unit not in after.units` narrowing - restoring exactly the rule that
hides a real latch loss - left 28/28 GREEN.

⚠️ SO IT WAS HABIT 4 WEARING THE CLOTHES OF ITS OWN FIX, AND WORSE THAN THE
"NO CONTROL" IT REPLACED, because it reads as checked. That is this commit's
own argument about the M3 mis-citation, turned on the thing I wrote to answer it.

⭐ THE FIXTURE CAME FIRST THIS TIME. `state-both-latched.json` is a store at
SCHEMA_VERSION with `unit/garage/*` AND `unit/shed/*` both latched by ONE site
event, so the reasons match too - the arrangement in which same-value
suppression is most dangerous, and the one no existing fixture could produce.
M12's mutant then makes ONE roster unit's latch key VANISH while its sibling's
survives at the same value:

    shipped tree, both-latched fixture      exit 0, no findings
    one unit's latch key deleted            exit 1, ADDS
                                            VANISHED STORE KEY unit/shed/sign_tripped
    narrowing reverted                      ⚠️ RED  (was 28/28 green)

And it asserts the PRECONDITION - the fixture is clean on the shipped tree -
plus that the mutation ADDS findings rather than coinciding with ones the
fixture already had. An empty diff there is exactly what made the last draft
inert, and nothing said so.

⭐ AND THE MOVE IS NOW INJECTIVE, which is the narrower hole review found still
open. `moved_to` is "any machine-read key with the same bare name and the same
value", and `DEFAULTS["sign_tripped"] is False` means `True` is the ONLY
non-default value a latch can hold - so N vanished keys could all claim the SAME
destination, by construction rather than by coincidence. Measured on a rename
carrying `inverter-a` -> `garage` correctly while DROPPING `inverter-b` -> `shed`:

    migrated  unit/inverter-a/sign_tripped = True -> unit/garage/sign_tripped
    migrated  unit/inverter-b/sign_tripped = True -> unit/garage/sign_tripped

Zero store-key findings, on a run where `shed` came up UNLATCHED. Two keys
cannot both have become one key. `diff()` claims each destination once.

⚠️ AND THE CHECK FOR IT IS ANCHORED TO A RUN THAT ACTUALLY PRODUCES MIGRATED
LINES. A dedicated mutant was written first and asserted over an EMPTY list -
vacuous, passing, indistinguishable from working, the same defect twice in one
sitting. These fixtures cannot produce two claimants (`migrate_unit_keys()`
moves FLAT keys only, so one flat latch yields one migration), so rather than
build a fiction to grade, injectivity is asserted over part 5's real migrations,
with a PRECONDITION that there are at least two of them. THE TWO-CLAIMANT
ARRANGEMENT IS A STATED RESIDUAL: bounded in `diff()` by construction, not
measured end-to-end.

Finding 4, and my correction to it was also wrong. The comment cited "line 315"
and "two hundred lines below"; the fix I wrote said "~54 lines down", which was
review's distance to the WRONG line, carried to a new referent without
re-measuring - inside the sentence apologising for a wrong number. Recomputed at
5e382f5: 327-261 = 66, 327-252 = 75, and 54 was neither. There is no distance
now, because a distance is a coordinate and the sentence already names the thing.

And the residual gains its second half, which review noticed and I had not: the
reason re-armed from is the FLAT mirror, carrying whatever tripped LAST, so this
path can print one inverter's evidence under another's name. The latch is right
and the explanation may not be. `test_maintenance.py`'s check that the reason is
not the removed unit's is guaranteed by that fixture's flat string, NOT by the
code, and now says so.

28/28 files pass.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BwRLw7eKYj2byVdwB6kbjU

goodwe_controller/app/main.py

@@ -251,11 +251,14 @@ class Controller:
         # WRITES FOR THEM. This line used to read `migrate_unit_keys(store,
         # UNIT_A)`, and the constant was wrong in exactly the way the
         # `maint_migration` call below says the SAME constant would be wrong -
-        # ⚠️ this comment used to cite "line 315" and "two hundred lines below",
-        # and BOTH numbers were wrong (315 is the CFG-03 defaults note; the
-        # comment meant is ~54 lines down, and line numbers move). Cite the
-        # thing, not its coordinates. On a declared roster the flat latch
-        # landed under
+        # ⚠️ this comment used to cite "line 315" and "two hundred lines
+        # below", and both were wrong. The correction I wrote for them was
+        # wrong too: it said "~54 lines down", which was review's distance to
+        # the WRONG line, carried to a new referent without re-measuring -
+        # inside the sentence apologising for a wrong number. There is no
+        # distance here now, because a distance is a coordinate and the
+        # sentence above already names the thing. On a declared roster the flat
+        # latch landed under
         # `unit/inverter-a/`, which is on no roster, was read back under the
         # name it was handed, and stamped the marker. `roster_names()` is the
         # naming rule itself and returns `[UNIT_A]` on the flat shape, so the
@@ -830,6 +833,15 @@ class Controller:
         # held at 0 W until an operator clears it, which is the conservative
         # direction; SAFETY-44's is a site DRIVING on a state file that says it
         # is latched.
+        #
+        # ⚠️ AND THE SECOND HALF OF THAT RESIDUAL IS THE **SENTENCE**, NOT THE
+        # BOOLEAN. The reason re-armed from is the FLAT mirror, which carries
+        # whatever tripped LAST - so on a multi-unit site this path can print
+        # one inverter's evidence under another inverter's name. The latch is
+        # right and the explanation may not be. It is disclosed here because the
+        # banner is what an operator acts on, and `test_maintenance.py`'s check
+        # that the reason is not the removed unit's is guaranteed by that
+        # fixture's choice of flat string, NOT by this code.
         # ⚠️ AND THE THREE CASES ARE THREE VARIABLES, NOT ONE SHARED FLAG.
         # THIS IS WHERE THE FIRST VERSION OF THIS FIX WAS DEFEATED, BY ONE KEY.
         # It wrote `namespaced_latched = True` for BOTH "on the roster" and "off