DEV-02: merge release/1.0, and close the two review blockers

PR #43 was rejected on two findings and had gone unmergeable behind SAFETY-28
and the ALLOC-01 fix. This is the merge commit; the conflict resolution and both
fixes are below, because a merge that also changes behaviour has to say so.

THE MERGE, AND WHAT IT COST
===========================
Two conflicts in main.py, both where SAFETY-28 and this card touched the same
method:

  * `write_setpoint()` split into a site entry point plus a per-unit
    `_write_unit()` here, while SAFETY-28 put its record gate in the old
    single-unit body. `write_refusal()` now takes the INVERTER it is about.
    Asking it with `self.unit` - as release/1.0 does - would authorise A's share
    on B's wire, and would also trip test_inverter.py part 1's AST scan, which
    goes red on any read of a Controller N=1 view inside Controller.
  * the SAFETY-28 gate sits above the clamp and below the non-finite coercion,
    exactly where release/1.0 put it, and is now asked about `inv`.

Fallout the merge produced in the checks, re-aimed rather than relaxed:

  * every fixture that calls `write_setpoint()` DIRECTLY - the clamp probe, the
    hung-heartbeat experiment and its serialised counterfactual, the split
    deadline probe - now arms a real allocation record first. test_inverter.py
    grows an `arm()` built through the shipped `resolve()`, the same shape
    test_clamp.py's is: the per-unit envelopes are filed as real `supervised`
    claims and the site target is their sum, so the water-fill has exactly one
    answer and the fixture cannot quietly become its own allocator.
  * test_clamp.py's two-unit failsafe fixture assigned `c.units`, which DEV-02
    made a derived property with no setter. It appends a real `Inverter`.

BLOCKER 1 - AC 4's ARBITER-BOUND EVIDENCE WAS VACUOUS
=====================================================
test_peakguard.py claimed "each unit's `supervised` bound is ITS OWN `max_w` -
give inverter B a different rating and the claim filed on inverter B moves with
it", and compared B's bound against `_b2.max_w`. `second_inverter()` DEFAULTED
B's rating to `LIVE_MAX_W`, which is A's. IT COMPARED (-5000, 5000) AGAINST
(-5000, 5000): a number against itself, unable to observe the failure it named.

Reproduced: filing the per-unit `device`/`supervised` claims from
`self.inverters[0]`'s numbers while leaving `actuator=self.actuator_of(..., inv)`
alone left ALL 19 FILES GREEN. At a roster of two with A=5000/B=3000 that makes
inverter B's planned envelope (-5000, 5000) instead of (-3000, 3000) - a 2000 W
over-command the arbiter believes is supervised. It is a DIFFERENT defect from
the actuator variant the static routing pin catches, and only the actuator
variant was in the mutation table.

  * `second_inverter()` gives B 3000 W - a hypothesis, marked as one - for every
    fixture in the file, so no check there can compare B against A by accident.
  * the claim is asserted against LITERAL numbers rather than against an
    expression that can read the same object twice, for `supervised` AND for
    `device` (whose `dev` had the same defect), plus the envelope the ARBITER
    RESOLVED for B - a claim filed right and resolved wrong is the same defect
    one layer down.
  * a PRECONDITION check fails if the two ratings are ever made equal again.
  * the BOUND mutation is in the table, beside the actuator one, and was
    observed RED (3 checks in test_peakguard.py) via tools/mutation_run.sh.

⚠️ THIRD INSTANCE THIS SESSION of a check whose DATA cannot reach the failure it
names - ARB-03's call-site scan saw 3 of 8 appends, ALLOC-01's replay generator
saw 0 escapes where a widened one saw 39,991. MUTATION.md gains a section for it
beside the stale-bytecode and masking ones, and the rule is written at the line:
ANY CHECK ASSERTING "X DIFFERS FROM Y" MUST BE RUN ONCE WITH X AND Y ACTUALLY
MADE DIFFERENT.

BLOCKER 2 - THE LATCH WAS SILENTLY DISARMED BY THE ROLLBACK ROUND TRIP
======================================================================
store.py's rule 2 keeps the flat keys "so a rollback still finds its latch". The
operator path that rule contemplates is a ROUND TRIP, and this card lost the
latch on it:

  1. install migrates          -> schema_version=1, unit/inverter-a/... = False
  2. operator DOWNGRADES; SAFETY-02 trips inside the downgrade window and the
     old add-on writes only the flat `sign_tripped: true`
  3. operator upgrades again   -> `rep.ran` is False, so `_grade_store_migration()`
     returned early, and `Inverter.__init__` read the namespaced key: False

Observed: the controller came up with `sign_wd.tripped = False` while
/data/state.json said `sign_tripped: true`. That is store.py's own header
sentence - "the file still says sign_tripped: true, the banner is green, and the
controller resumes driving the wrong way" - rebuilt by the version marker. A
firmware version change with a rollback path was performed on this site on
2026-09-02, so this is not hypothetical.

Three changes, each graded by a mutation observed RED:

  * THE OPERATOR'S CLEAR CLEARS BOTH SPELLINGS. That is what removes the
    "re-arm forever" objection the `rep.ran` gate existed to answer: with the
    fossil cleared, `flat True + namespaced False` is unambiguously a
    downgrade-window latch.
  * A TRIP MIRRORS THE FLAT PAIR. Rule 2 only ever covered the latch present AT
    MIGRATION TIME - nothing flat was written for a trip taken afterwards, so an
    operator who downgraded found `sign_tripped: false` and came up DRIVING.
    store.py claimed the staleness could only fail toward a SPURIOUS latch. It
    could not; that sentence is corrected rather than left standing.
  * THE GUARD RUNS ON EVERY START, and asks the STORE - not the roster - whether
    anything namespaced is latched. A mirrored trip on B must not re-arm a
    healthy A, and the store is the right place to ask because it holds every
    `unit/*/sign_tripped` this install has written, including one belonging to a
    unit that is not in today's roster.

Graded by the three-step scenario itself, run end to end in test_inverter.py
part 2, with all three preconditions asserted - including that the catching
start did NOT migrate anything, which is what used to skip the guard. Part 2's
idempotence check now PRESSES the button instead of hand-writing the store,
because the state it used to construct is not one the shipped clear path can
produce. Part 3 grades the mirror and the clear on a real roster of two.

test_watchdog.py's "the flat key is NOT written" assertion is re-aimed rather
than deleted: its argument was right about the READ and wrong about the WRITE.
Nothing at runtime reads that key, and the one thing that does ignores it
whenever any namespaced latch is set - which a sibling's trip always leaves.
What its absence actually cost was the rollback.

HANDOVER.md and DOCS.md said the flat key "is never read again", which was the
instruction an operator clearing a trip by hand would follow. Both corrected: it
is a maintained rollback view, it IS read on every start, and clearing a trip by
hand means clearing both spellings.

MUTATIONS THIS ROUND, each applied on a purged tree via tools/mutation_run.sh
and observed RED:
  * per-unit `device`/`supervised` BOUNDS from `self.inverters[0]`, actuator
    left correct                                   -> test_peakguard.py 10g
  * `_grade_store_migration()` gated on `rep.ran`   -> test_inverter.py part 2
  * the operator's clear leaving the flat keys set  -> test_inverter.py part 2/3
  * a trip not mirroring the flat pair              -> test_inverter.py part 3
  * the guard asking only `self.inverters[0]`       -> test_inverter.py part 3

19/19 files green on the merged tree. No hardware was touched.

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

HANDOVER.md

@@ -85,15 +85,22 @@ rejected.
 add-on will not clear a trip.** That is the point of it; use the *Start / stop
 control* button twice, or delete the trip from `/data/state.json`.
 
-⚠️ **DEV-02 renamed that key and the old name is now a fossil.** There is one
-`SignWatchdog` per inverter, so the latch lives under
-`unit/<inverter>/sign_tripped` — `unit/inverter-a/sign_tripped` on a
-single-inverter site. The pre-DEV-02 flat `sign_tripped` is still written in
-the file on purpose (so a rollback finds its latch) and is **never read again**,
-so deleting it clears nothing. An install upgrading is migrated on first start,
-and if the latch cannot be made to survive that migration the controller
-re-arms it from the old key and says so in the log rather than coming up
-disarmed.
+⚠️ **DEV-02 renamed that key. There is one `SignWatchdog` per inverter, so the
+LIVE latch lives under `unit/<inverter>/sign_tripped`** —
+`unit/inverter-a/sign_tripped` on a single-inverter site. **That is the one to
+delete if you are clearing a trip by hand**; deleting the flat one alone clears
+nothing.
+
+⚠️ **The flat `sign_tripped` is still maintained, though — it is the ROLLBACK
+VIEW, not a fossil.** It is written alongside the namespaced key on a trip and
+cleared alongside it when you press *Start / stop control*, so an add-on you
+**downgrade** past this version still finds the latch it should. It is also read
+on **every** start, and the one disagreement it can produce is acted on: *the
+flat key says tripped and no inverter came up latched* means the latch was
+written by an older add-on while this install was rolled back — or the migration
+lost it — and the controller **re-arms the latch and shouts in the log** rather
+than coming up disarmed with a green banner. So if you edit `/data/state.json`
+by hand, clear **both** spellings or the next start will put the trip back.
 
 ⚠️ `test_loop.py` takes about **95 seconds** (measured 93 s) and that is not a bug. It
 drives the real control loop, which sleeps 1 s a tick, eight times over, to prove a