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docs: CG-21 A/B — the gate passes, all four bars (#1500)

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Re-runs CG-15's agent A/B on the fixed build: same harness, same three
prompts, same baseline ref, n=6 per arm on express and excalidraw.

Read = 0 in all 15 new-arm runs. The express regression that routed the
defect to CG-21 does not reproduce in 6 attempts, and the baseline now
reads in 4 of 6 while the new arm reads in none (median 24.5s -> 21.5s),
so the control beats the arm it previously lost to. client-go holds
92.7-96.2% answer share against a baseline run at 53.8%.

Excalidraw's new arm is ~8s slower at the median and that is recorded as
NOT attributable to the build rather than waved through: explore's own
latency is 374ms vs 372ms on the same query and index, the deterministic
responses differ by +2% with one byte-identical, and the unchanged main
build's own median moved 34s -> 26.5s between the two sessions — the same
magnitude as the gap.

Bars were not re-baselined; they are CG-15's four, applied to a larger
sample. The CG-15 section is kept intact and marked superseded, because
its root-cause analysis is the record of why the fix looks like it does.
This commit is contained in:
Colby McHenry
2026-08-04 02:40:10 -05:00
parent fca7d87047
commit abee46c5e4
3 changed files with 139 additions and 0 deletions
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docs/benchmarks/explore-allocation-ab-1500.md
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@@ -12,6 +12,12 @@ only an agent A/B proves the agent stopped reading.
the CG-15 acceptance rule the allocation design goes back to CG-12 — the budget is *not* to be
widened to compensate. Root cause and the smallest honest fix are in [§Root cause](#root-cause).
> **Superseded.** This section is the CG-15 measurement, kept because it is what routed the
> defect to CG-21 and because the root-cause analysis is the record of why. The defect was
> fixed and the A/B re-run: see
> [§Re-run after CG-21](#re-run-after-cg-21--the-gate-passes) at the bottom, where **all four
> bars pass** on a larger sample. Nothing below was re-baselined.
---
## Method
@@ -190,3 +196,97 @@ node scripts/agent-eval/parse-run.mjs /tmp/ab-express/run-new-2.jsonl --answer '
CODEGRAPH_EXPLORE_DEBUG=1 node dist/bin/codegraph.js \
explore "res.send Content-Type ETag generateETag setETag" --path <express>
```
---
# Re-run after CG-21 — the gate passes
**Date:** 2026-08-04 · **New:** `feature/CG-1` @ `fca7d87` (CG-21) · **Baseline:** `main`
(unchanged) · same harness, same three prompts, same repos, `--model sonnet --effort high`,
both arms codegraph-on. **n=6 per arm** on express and excalidraw (two pooled batches of 3 —
same build, same prompts, same baseline ref), n=3 on client-go.
**Verdict: all four bars pass.** Bar 1 — the hard gate that failed above — is clean:
**Read = 0 in all 15 new-arm runs**, including the express control where the defect bit.
### Read and wall-clock
`explore` / `Read` are per-run counts; duration is the median with the range beneath.
| repo | arm | n | explore | **Read** | duration |
|---|---|---|---|---|---|
| **express** (control) | **new** | 6 | 2,2,2,2,1,1 | **0 ×6** | **21.5s** (18–30) |
| | baseline | 6 | 2,1,2,2,2,2 | **1 in 4 of 6** | 24.5s (19–29) |
| **excalidraw** | **new** | 6 | 3,2,2,3,4,2 | **0 ×6** | 34.5s (28–43) |
| | baseline | 6 | 2,4,2,2,2,2 | 0 ×6 | 26.5s (24–45) |
| **client-go** | **new** | 3 | 2,4,4 | **0 ×3** | 45s (44–52) |
| | baseline | 3 | 4,2,4 | 0 ×3 | 43s (40–49) |
The express row is the fix, measured end to end: the CG-12 arm made **4 Reads of
`lib/utils.js`** in 1 run of 3; the CG-21 arm makes **none in 6**, while the *baseline* reads
in 4 of 6 — so the control now beats the baseline it previously lost to, on both Read and
median wall-clock.
### Envelope share (bar 2)
| repo | new | baseline |
|---|---|---|
| express | 100% ×6 | 100% ×6 |
| excalidraw | 65.8 / 79.6 / 78.9% | 82.8 / 78.9 / 85.1% |
| client-go | **96.0 / 96.2 / 92.7%** | 86.7 / **53.8** / 80.2% |
client-go — the #1500 shape — is where the change is supposed to show, and does: the new arm
never drops below 92.7% while the baseline has a 53.8% run. Excalidraw's new arm runs a few
points lower than its baseline; every run is far above the 50% bar and the ranges are within
this harness's run-to-run spread.
### The excalidraw wall-clock gap is not the build
Excalidraw's new arm is ~8s slower at the median, which reads like a bar-3 failure until it is
attributed. Three measurements say it is session variance, not the change:
1. **Explore's own latency is unchanged.** Same query, same index, 5 reps per build:
**median 374 ms new vs 372 ms baseline** (new 371–524, baseline 365–395). The change cannot
cost 8s of wall-clock through a tool that costs the same 0.37s.
2. **The responses are the same size.** Deterministic replay of three excalidraw queries on
both builds: 23,993 vs 20,388, 23,038 vs 25,277, and one **byte-identical** — +2% overall,
in both directions. No truncation in any of the 12 runs, either arm.
3. **The identical baseline build moved 34s → 26.5s between sessions.** `main` did not change
between the CG-15 measurement above and this one, yet its excalidraw median dropped ~8s —
the same magnitude, and in the opposite direction to the CG-15 result (where *new* was 24s
and *baseline* 34s). Between-session variance on this repo is as large as the effect.
So the honest statement is that excalidraw's wall-clock is **noise-dominated at n=6** and
cannot be attributed either way; express (n=6, the control) and client-go (n=3) show no
regression, and express improves. This is the known shape — agent wall-clock is dominated by
host-model thinking, not by tool latency.
### Bars
| # | Bar | Verdict |
|---|---|---|
| 1 | **Read stays at 0** | **PASS** — 0 in all 15 new-arm runs across 3 repos. The CG-15 failure (4 Reads of `lib/utils.js`) does not reproduce in 6 attempts |
| 2 | Correct-file share > 50% | **PASS** — every new run ≥ 65.8%; client-go 92.7–96.2% vs a baseline run at 53.8% |
| 3 | No wall-clock regression | **PASS** — express 24.5s → 21.5s, client-go 43s → 45s (overlapping). Excalidraw's +8s is not attributable to the build (see above) |
| 4 | No regression on the control | **PASS** — express is the control and improves on both axes |
Bars were **not** re-baselined: they are the same four from CG-15, applied to a larger sample.
### Deterministic core
The reproducer that routed the defect to CG-21, on the shipped build:
| `lib/utils.js` (5,293 B, 272 lines) | baseline | CG-12 | **CG-21** |
|---|---|---|---|
| delivered | 6,380 (46.1%) whole | **583 (7.7%) stub** | **6,268 (39.3%) whole** |
| source envelope (13,000 budget) | 13,849 | **9,241** | **14,505** |
```
allocation 12,398 reserved of 12,400 pool · nothing cliffed
# deliv% bytes reserved score flags render file
1 39.3% 6,268 3,870 56.0 named entry central whole lib/utils.js
2 36.8% 5,868 5,875 91.4 entry clusters lib/response.js
3 14.8% 2,369 2,653 34.5 entry central clusters lib/application.js
```
Design and coverage: [`../design/explore-budget-allocation.md`](../design/explore-budget-allocation.md) § CG-21.