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
2026-09-08 18:08:16 +02:00
parent d1b7e3f113
commit f6d7bfcb04
4 changed files with 126 additions and 31 deletions
@@ -0,0 +1,10 @@
+{
+ "_comment": "SAFETY-44 SYNTHETIC FIXTURE - not a copy of any live state file; this session cannot read that one and did not try. It exists for ONE control: a store in which TWO ROSTER UNITS ARE LATCHED AT THE SAME VALUE. `state-legacy.json` cannot serve it - it is pre-DEV-02 and flat, so after migration only the FIRST roster entry is ever latched, and a rule that suppresses a vanished key when another key holds the same value can never be exercised against it. That is exactly how M12's first draft came to pass on the UNMUTATED tree. Both units are latched by ONE site event, so the reasons match too, which is the arrangement in which the suppression is most dangerous.",
+ "schema_version": 1,
+ "maint_schema_version": 1,
+ "auto": true,
+ "unit/garage/sign_tripped": true,
+ "unit/garage/sign_reason": "SIGN_DISAGREEMENT: grid meter reversed, both units",
+ "unit/shed/sign_tripped": true,
+ "unit/shed/sign_reason": "SIGN_DISAGREEMENT: grid meter reversed, both units"
+}
@@ -545,6 +545,19 @@ def diff(before: Snapshot, after: Snapshot) -> list:
    # name and whose roster start writes them under another reported two
    # VANISHED findings about a pair of defaults, and CONTROL-C went red on a
    # build that was CORRECT.
+    # ⚠️ `claimed` MAKES THE MOVE **INJECTIVE**, WHICH IT WAS NOT. `moved_to` is
+    # "any machine-read key with the same bare name and the same value", so N
+    # vanished keys could all claim the SAME destination. Review measured it: a
+    # rename that carries `inverter-a` -> `garage` correctly and DROPS
+    # `inverter-b` -> `shed`, both latched by one event, reported
+    #
+    #   migrated  unit/inverter-a/sign_tripped = True -> unit/garage/sign_tripped
+    #   migrated  unit/inverter-b/sign_tripped = True -> unit/garage/sign_tripped
+    #
+    # with ZERO store-key findings, on a run where `shed` came up unlatched. Two
+    # keys cannot both have become one key. A destination is claimable once; the
+    # second claimant has not moved anywhere and is reported as what it is.
+    claimed = set()
    for key in sorted(set(before.data) - set(after.data)):
        value = before.data[key]
        bare = key.rsplit("/", 1)[-1]
@@ -598,8 +611,10 @@ def diff(before: Snapshot, after: Snapshot) -> list:
        # own unit is still on the roster has not been renamed - it has been
        # LOST - and no amount of the same value elsewhere makes that untrue.
        vanished_unit = key.split("/")[1] if key.startswith("unit/") else None
+        moved_to = [k for k in moved_to if k not in claimed]
        if vanished_unit is not None and vanished_unit not in after.units \
                and moved_to:
+            claimed.add(moved_to[0])
            after.vanished_but_migrated.append(
                f"{key} = {value!r} -> {moved_to[0]}")
            continue