The metric six evidence files reported as 0.0% was never measured.
--shape-budget windows since the last commit, and it is read while
writing the evidence file — right after a commit, when the window holds
one or two responses. SH-1/SH-2 are location statistics and survive n=2.
SH-3 is a rate: at n=2 its only possible values are 0%, 50%, 100%.
cb-cost.py gains sh3_line(), which below a minimum sample prints
"insufficient sample" and no verdict. The floor is derived: if the true
rate were exactly the 20% target, P(zero batched in n) = 0.8^n, and at
n=14 that is 4.4% — so "0 batched in 14" rules out a target-meeting rate
at ~95%. Below that the tool has nothing to say and now says so.
The window was kept rather than split. SH-3 could have been given a
per-pass window, but the budget's purpose is the open remainder since
the last commit, and giving one of three metrics a different window
makes "the window" ambiguous in a tool three specs cite.
Four controls, three mutations, each red for its stated reason —
including the one the evidence files actually hit, where a refusal is
printed as a measured zero.
SessionShape.md §4 carries the correction with the real per-pass figures
(1.1%-6.3%), beside the eighth trusted-arithmetic instance. This is the
ninth, and the second in this same metric. It also shows what the frozen
0.0% hid: against the pinned 7.8%-8.6%, batching has got worse, and six
passes reported a breach that was moving underneath them.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
The task's original premise was wrong and is recorded rather than
deleted. It was written to prescribe one task per session; measurement
says the variable is context, not turn count.
Measured:
- compaction cut context 27x (542,991 -> 19,974) and cost/turn 3.1x;
the 202 turns after C1 cost less than half the 136 before it
- a turn costs $0.010 at 20k context and $0.270 at 540k
- break-even for a compaction is 2-11 turns, so: compact whenever
context exceeds ~300k and work remains
- a fresh session is NOT free -- cold start floors at ~51k and must
then re-read the artifacts a compact summary already holds (~66k).
Prefer compaction to continue work; prefer a fresh session when the
task changes, because then prior context is pure overhead.
cb-cost now emits SH-1..SH-3 so the targets come from the instrument
rather than from analysis, per InnerLoop v1.1. All three are UNMET
(mean context 232,982 vs 200,000; p90 492,042 vs 300,000; batching 7.8%
vs 20%) and are reported unmet rather than retargeted -- retargeting in
the commit that first measures is precisely what T07 exists to prevent.
Eighth error instance found while writing this: CB-WP-0001's claim that
"0 of 330 tool calls were batched" is wrong. 330 was the count of
single-call responses, not the total; 31 responses batched, covering 76
calls. It was carried into this workplan unverified. Trusted-arithmetic
class -- the one the T01 audit flagged as having no executable defence,
confirming that finding within hours of making it.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
