tools (volt): the fence cell's comment carries the MEASURED pre-fix signature, not an assumed one

Comment only; no behaviour change. The pre-fix census of the first fence cell is
['Q60:CLOSED', 'Q99:CLOSED'] -- the quoted item lands in the census as a closed
record -- not the ['Q60:CLOSED','Q99:OPEN','Q99:CLOSED'] the comment first
asserted. Measured by importing the pre-fix module and running its census on the
fixture strings; the third cell is identical on both sides by design and pins the
FENCE_UNCLOSED diagnostic instead.

tools/queue_claim_check.py

@@ -588,9 +588,11 @@ FIXTURES = [
 
     # The live defect these three cells were written for (2026-10-19): this file
     # had no fence state, so a tick quoting an example record inside a fenced
-    # block opened a phantom item. Pre-fix the first cell reads
+    # block opened a phantom item. Measured pre-fix: the first cell reads
-    # ['Q60:CLOSED', 'Q99:OPEN', 'Q99:CLOSED'] and the second reads two Q61
+    # ['Q60:CLOSED', 'Q99:CLOSED'] -- a quoted item in the open set -- and the
-    # records (the fenced `**Status:` inherited the header, then collided).
+    # second reads two colliding Q61 rows (the fenced `**Status:` inherited the
+    # header). The third is identical on both sides by design: an unclosed fence
+    # fails OPEN, so the cell pins the FENCE_UNCLOSED line, not the masking.
     ('fence: a record inside a ``` block is quoted material, not a record',
      '## Q60 — section\n\n**Q60 — OPEN (lane).**\n\n**Q60 — DONE at 4010b96.**\n\n'
      'Prose quoting a tick:\n\n```\n**Q99 — OPEN (pipe).**\n'