port: correct a check that asserted an absence of measurement as a finding

The pair I shipped this iteration -- focus_persists on for main_menu, off
everywhere else -- reported both halves as agreement with the contract. Nothing
measured that extras does not persist. The corpus has EXTRAS' opening item from
one entry and (B) restoring the PARENT's focus 4/4; neither says what a submenu's
own cursor does on re-entry. Caught by the Decoder.

It is the mirror of the trap it was written to avoid. I refused to let a derived
menu-wide rule overwrite a measured value, then let 'not measured here' become a
positive assertion of the negative. Both treat a gap in the corpus as if it
carried information and differ only in which direction they fill it. And the
failure mode was the bad one: if the game does persist EXTRAS, the check holds
the port to the wrong behaviour and passes while doing it.

check_focus_persists now asserts only the measured half. The scope became a
separate guard with its own outcome word -- 'only main_menu, AUTHORED DEFAULT,
unmeasured elsewhere' -- which still fails if widened, since that should be a
deliberate edit, but can no longer be read as the game being known to reset.
focus_persists_why records the correction rather than being rewritten.

It also weakens a label. EXTRAS' initial_focus is marked measured and was taken
on a single entry; now that the main menu is known to remember its cursor, a
one-entry reading of any screen may be measuring history rather than what the
screen opens on -- the same objection that reframed the TUTORIAL/NEW GAME
disagreement. The observation stands, its reading as an initial focus does not.
Caveat attached, kind left as measured with a note that it changes if EXTRAS
turns out to persist.

Not building on the non-persistence half until their EXTRAS re-entry run returns.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01N7FiFFFwbvG2uxdcEh8HyF

tools/port/contract-check

@@ -219,17 +219,46 @@ def flow_buttons(screen):
 
 
 def check_focus_persists(h):
-    """The menu remembers its cursor -- measured on the MAIN MENU, one screen.
+    """The menu remembers its cursor -- MEASURED, on the main menu, one screen.
 
-    Checked as a pair: the behaviour must be on where it was measured and off
-    everywhere else. A one-sided check would pass a port that had quietly made it
-    a menu-wide rule, which would override `extras`' measured initial focus.
+    🔴 This checked a PAIR until 2026-08-30: on for `main_menu`, off everywhere
+    else. The second half asserted that `extras` does NOT persist, and **nothing
+    measured that**. What the corpus has is EXTRAS' initial focus from a single
+    entry and Ⓑ restoring the PARENT's focus 4/4 — neither says what a submenu's
+    own cursor does on re-entry. So one measured behaviour and one absence of a
+    measurement were being reported identically, and if the game does persist
+    EXTRAS the check would have held the port to the wrong behaviour AND PASSED.
+
+    The mirror of the trap it was written to avoid: refusing to let a derived
+    rule overwrite a measured value, then letting "not measured here" become a
+    positive assertion of the negative. Now only the measured half is asserted
+    against the contract; the scope is a guard, below.
     """
     want = bool(re.search(r"the main menu remembers its cursor; re-entry is not a reset", h))
-    scr = (jload("authored/flow.json") or {}).get("screens") or {}
-    on = [n for n, v in scr.items() if isinstance(v, dict) and v.get("focus_persists")]
-    report("menu remembers its cursor", want or None, on == ["main_menu"] and on,
-           want and on == ["main_menu"])
+    got = (((jload("authored/flow.json") or {}).get("screens") or {})
+           .get("main_menu", {}).get("focus_persists"))
+    report("menu remembers its cursor", want or None, got, want and got is True)
+
+
+def guard_focus_scope(_h):
+    """NOT a contract check. A regression guard on an AUTHORED DEFAULT.
+
+    No screen but `main_menu` persists its cursor in this port, and that is the
+    port's choice, not a finding: it preserves EXTRAS' measured opening item and
+    invents the least. Guarded so that widening it is a deliberate edit with a
+    `why`, and labelled so a passing run cannot be read as the game being known
+    to reset.
+    """
+    global FAIL
+    on = sorted(n for n, v in ((jload("authored/flow.json") or {}).get("screens") or {}).items()
+                if isinstance(v, dict) and v.get("focus_persists"))
+    if on == ["main_menu"]:
+        print(f"  {'focus_persists scope':<30} guard     only main_menu"
+              f"  -- AUTHORED DEFAULT, unmeasured elsewhere")
+    else:
+        FAIL += 1
+        print(f"  {'focus_persists scope':<30} 🔴 GUARD  {on} -- widened past the"
+              f" one screen measured; needs a why and a measurement")
 
 
 def check_menu_labels(_h):
@@ -295,7 +324,7 @@ def main():
     for fn in (check_fade_quads, check_fade_out, check_plate_period,
                check_bgm_window, check_black_hold, check_menu_bank,
                check_splash_dwell, check_menu_labels, check_extras_labels,
-               check_wrap, check_focus_persists):
+               check_wrap, check_focus_persists, guard_focus_scope):
         fn(h)
     print()
     print("  A passing run means the port agrees with the contract ON THESE VALUES.")