FABRIC-2.md Section Q: heartbeat-tick ACL-TTL remeasurement finds the

instrument blind to the effect, not a corrected number

Per Captain Bob's correction (heartbeat tick counter is the sole
canonical clock, not wall-clock), added HEARTBEAT-TICKS@ and re-ran the
ACL-TTL overhead measurement using tick deltas. Diagnostics confirmed
the counter is a FORTH-level colon-word-dispatch counter (frozen at
idle, jumps with real work) -- not a wall-clock proxy. A pilot pair
(amd64, seed 12345, 30 reps, ACL disabled vs enabled) produced
byte-identical deltas (261064 ticks both runs): acl_recheck() runs at
the C dispatch level and doesn't change which/how many colon words
execute, so it's invisible to a counter gated on colon-word-entry
count. Root-caused, not proceeding to the full 18-cell campaign --
every cell would read +0.00% by construction. Section P's wall-clock
numbers stand as the best estimate on record pending a instrument that
can see per-dispatch cost rather than control-flow shape.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

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