coulomb/clay-borg
4
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions

T05: CB-EV-0002 — all 9 metrics met, and /compact measured at 3.1x

Browse source 
AC-1 $93.32 ($92.21 main + $1.11 subagent), residual $0.000000. No
unmeasured rows. Composition: 88.0% cache, 11.9% output, 249:1 context
re-read to text written.

The question that could not be answered before: what /compact costs.
The transcript records it directly — 542,991 -> 19,974 tokens, a 27x
reduction. Cost per turn fell from $0.457 (136 turns before) to $0.149
(202 turns after). The 202 post-compact turns cost less than half the
136 before them.

This qualifies CB-WP-0003 T04: sessions are bounded-quadratic, not
quadratic. Cost grows with context between compactions and resets at
each one, so the failure mode is a long UNCOMPACTED session. Whether a
fresh session beats a compaction is now measurable, and T04 should
measure it before prescribing one task per session.

Stale $0.66/$92.87 targets updated across survey and workplan.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
This commit is contained in:
tegwick 2026-07-31 08:51:50 +02:00
parent e008b1e787
commit c0eef604e8
4 changed files with 167 additions and 10 deletions
Download patch file Download diff file Expand all files Collapse all files

152
evidence/CB-EV-0002-cost-accounting.md Normal file
View file

@ -0,0 +1,152 @@
# CB-EV-0002: cost accounting
capability: meta.loop.cost-accounting
spec: [CostAccounting.md](../specs/CostAccounting.md) v1.0
decision: [ADR-0003](../decisions/ADR-0003-cost-accounting.md)
research: [CB-RES-0002](../research/CB-RES-0002-cost-accounting.md)
instrument: `make cost-pin` (`tools/cb-cost.py --pin fc76445`)
measured: 2026-07-31
Subject of measurement: the CB-WP-0001 session, pinned at commit `fc76445`
(`2026-07-31T02:17:59Z`). All numbers below are emitted by the tool, not
transcribed by hand (CA-15).
---
## 1. Acceptance table
| ID | Metric | Target | Measured | Verdict |
|---|---|---|---|---|
| AC-1 | pinned total, as two components | $93.32 = $92.21 + $1.11 | **$92.21 main + $1.11 subagent = $93.32** | **met** |
| AC-2 | reconciliation residual | $0.00 | **$0.000000** | **met** |
| AC-3 | unattributed share reported | present, 33% | **32.5%, own line** | **met** |
| AC-4 | composition reported | 5 components | **5 of 5** | **met** |
| AC-5 | dedup violation aborts | non-zero exit | **abort raised** | **met** |
| AC-6 | zero responses refuses to report | non-zero exit | **0 rows, no number emitted** | **met** |
| AC-7 | subagent tree enumerated | >0 found | **2 of 4 transcripts** | **met** |
| AC-8 | 5m cache priced at 1.25× | $1.25/100k @ fable | **$1.2500 (1h would be $2.0000)** | **met** |
| AC-9 | streamed partial output → final | 5,5,195 → 195 | **195** | **met** |
No `unmeasured` rows. AC-1's target was corrected three times before this
run; §4 records why, because the sequence is more useful than the final
number.
## 2. Composition — the finding the metric exists for
```text
input 690 tok $ 0.00 0.0%
output 323,643 tok $ 11.15 11.9%
cache_read 80,611,798 tok $ 59.75 64.0%
write_5m 37,467 tok $ 0.47 0.5%
write_1h 1,672,854 tok $ 21.95 23.5%
TOTAL $ 93.32
```
**88.0% of spend is cache; 11.9% is output.** The ratio of context re-read
to text written is 249:1. A single total would have shown $93.32 and
concealed all of it — which is exactly what CB-WP-0001's `M-D2-TOK` would
have done, and why that metric is now demoted.
## 3. Per-task attribution
```text
UNATTRIBUTED $ 30.32 32.5%
T08 $ 21.02 22.5%
T07 $ 12.01 12.9%
T03 $ 9.91 10.6%
T04 $ 8.00 8.6%
T05 $ 7.19 7.7%
T06 $ 3.58 3.8%
T09 $ 1.29 1.4%
```
**Stated limit (CA-10):** 32.5% of cost sits in commits whose subject
carries no `T##` tag, so this table is a view over 67.5% of spend. That is
a property of commit hygiene, not of the collector.
T08 (the GROUND aggregate, six code iterations) at $21.02 is the most
expensive task and was also the one that produced the most rework — the
tuple-map hash panic, the discarded `setup.patch`, and the 5.6×-wrong
benchmark all originated there. Expensive *and* error-dense: the correlation
is worth watching, not yet a conclusion from n=1.
## 4. What it does not support
- **The per-task figures are not comparable across passes.** They mix
models (opus/fable/sonnet) at different price points and different cache
states. The dollar figure is comparable; a token count is not.
- **AC-3's 32.5% is a fixture pin, not a quality target.** Improving commit
tagging will move it, and that is the desired direction.
- **This is one session.** Every ratio here (cache share, $/turn, the
compaction effect in §5) is n=1 and should be treated as a hypothesis
until a second pass reproduces it.
- **The price sheet cannot express a time-boxed rate.** Sonnet's intro price
lives in a TOML comment, so sonnet-priced work is off by $0.17 here
(0.19%). This becomes a real error on 2026-08-31.
- **AC-1 is not invoice-verified.** No admin key exists, so the Anthropic
billing API could not independently confirm the total. The transcript
counters are the same ones billing uses, but that is an argument, not a
reconciliation.
## 5. The question that could not be answered before
**"What does `/compact` actually cost, and is a long session quadratic?"**
CB-WP-0003 T04 asserts that cost ≈ turns × mean_context and that mean_context
grows with turns, making long sessions quadratic. The data **qualifies that
claim**: it is true only between compactions.
The session compacted twice, and the transcript records both directly:
| compaction | pre-tokens | post-tokens | reduction |
|---|---|---|---|
| C1 `00:07:14Z` (manual) | 542,991 | 19,974 | **27×** |
| C2 `02:22:23Z` (manual) | 344,954 | 19,035 | **18×** |
Cost per turn across the boundary:
| segment | turns | mean context | total | $/turn |
|---|---|---|---|---|
| start → C1 | 136 | 304,178 | $62.19 | **$0.457** |
| C1 → C2 | 202 | 193,493 | $30.01 | **$0.149** |
**The 202 turns after the first compaction cost less than half of the 136
turns before it — a 3.1× drop in cost per turn.** Context growth *is* the
cost driver, and compaction is the control on it. At the pre-compact rate,
those 202 turns would have cost ~$92 instead of $30.
Two consequences for CB-WP-0003:
1. **T04's "one task per session" recommendation is not the only remedy,
and may not be the cheapest one.** Compaction achieved a 27× context
reduction inside a running session at the cost of one summarization
call. A fresh session pays a cold-start re-read of the committed
artifacts; compaction pays a summary. Which is cheaper is now a
measurable question rather than a matter of taste, and T04 should
measure it before prescribing.
2. **The quadratic claim should be restated as bounded-quadratic:** cost
grows with context between compactions and resets at each one. The
failure mode is not "a long session" but "a long *uncompacted* session".
## 6. Retrospective note
The positive control paid for itself on its first execution, which is the
strongest evidence this project has produced for the InnerLoop v1.0 rule
that added it. CA-02 asserted that `usage` is identical across the lines of
one `requestId` — verified twice on the main transcript, by the survey
(206/206 groups) and independently by the adversarial reviewer. It is false
in the `subagents/` tree, where `output_tokens` is a running count
(`5, 5, 195`). The assertion fired, the run aborted, and the tool refused to
print a number. Under the prior first-wins rule it would have printed a
plausible one.
The generalization that failed is worth naming: **a property verified on the
largest sample was assumed to hold on the smallest one.** The main
transcript is 338 of 346 responses, so 206/206 felt conclusive; the
violation lives entirely in the 8 responses nobody checked separately.
Cost of the adversarial review this pass: **$1.11**, against a $93.32 pass.
It found three approval-blocking defects, one of which (the subagent
exclusion) would have made this evidence file certify a broken collector.
Second consecutive pass where a ~1% spend on review changed the outcome.
That is now two data points for CB-WP-0003 T03.