epic CG-1)

Date: 2026-08-04 · New: feature/CG-1 @ edce18f · Baseline: main @ 49c11fc · Harness: scripts/agent-eval/ab-new-vs-baseline.sh, RUNS=3, --model sonnet --effort high on every arm · Both arms codegraph-on.

This is the epic's pass gate. The deterministic probes (CG-6/CG-14) prove the budget moved; only an agent A/B proves the agent stopped reading.

Verdict: the gate does not pass. Bars 2 and 3 hold; bar 1 (Read stays at 0) and bar 4 (no regression on the control) fail on express, with a reproducible, non-agent cause. Per 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.

Method

ab-new-vs-baseline.sh builds and indexes each arm separately (CG-5's generated-file flag is an index-time decision, so each arm must index with its own build), pre-warms a persistent daemon per run, and runs the same flow question 3× per arm. Both arms run with CODEGRAPH_NO_PROMPT_HOOK=1 — the machine's ambient front-load hook resolves to whatever is in dist/ and would inject context through a second, uncontrolled channel.

Each prompt names codegraph as the lookup tool. That is not a forced-Read-0: the agent stays free to Read whenever explore's answer is insufficient, which is exactly what bar 1 measures. It removes the one noise source that would otherwise swamp the signal — in a pre-run without it, one express run made 0 codegraph calls and 3 Reads, measuring adoption (an axis this change does not touch) rather than allocation.

Envelope share is measured with parse-run.mjs --envelope --answer <glob>, which parses the rendered markdown of the responses the agent actually received. The CG-4 diagnostic sidecar only exists on the new build, so it cannot measure the baseline arm; the markdown parse is the only instrument that measures both arms the same way.

Repo	Lang	Files	Generated	Tier	Role
`kubernetes/client-go`	Go	2,454	2,001	medium (2 calls / 28K)	the #1500 shape — generated CRUD beside hand-written machinery
`excalidraw/excalidraw`	TS/React	672	0	medium (2 calls / 28K)	god-file concentration (`App.tsx`, 450 KB)
`expressjs/express`	JS	147	0	small (1 call / 18K)	control

Results

explore = codegraph_explore calls · Read = Read tool calls · answer% = share of the source envelope going to the files that answer the question. Three runs per arm, reported as the range — run-to-run variance is large and a single run means nothing.

client-go — "how does a shared informer keep its cache in sync and deliver events?"

Answer set tools/cache/**; generated set kubernetes/**, listers/**, applyconfigurations/**, informers/**, **/fake/**.

arm	explore	Read	duration	answer%	generated%
new	2 / 2 / 6	0 / 0 / 0	39–61s (med 50)	74.2 / 96.9 / 82.6	4.0 / 0.0 / 5.2
baseline	3 / 2 / 3	0 / 0 / 0	48–52s (med 49)	78.1 / 97.1 / 71.3	10.5 / 0.0 / 5.1

No Read in either arm. The medians overlap: on this query tools/cache/** already dominates graph relevance, so the baseline concentrated well without help. The #1500 signal is visible but small — the generated clientsets and per-resource informers (informers/events/v1beta1/interface.go, kubernetes/typed/events/v1/fake/…) take 10.5% of one baseline run's envelope and never appear in any new run.

excalidraw — "how does updating an element re-render the canvas on screen?"

Answer set: mutateElement.ts, App.tsx, renderer/**, scene/**, components/canvases/**.

arm	explore	Read	duration	answer%
new	2 / 3 / 2	0 / 0 / 0	23–32s (med 24)	74.4 / 67.8 / 84.7
baseline	3 / 3 / 4	0 / 0 / 0	33–39s (med 34)	74.1 / 64.0 / 79.5

The clearest win: 29% faster at the median with one fewer explore call per run, no Read in either arm. Concentration is why — the new arm resolves the flow in 2 calls where the baseline takes 3–4. (One baseline run burned a turn on a hallucinated codegraph_..._explore tool name; counted as-is.)

express — control — "how does res.send decide Content-Type and ETag?"

Answer set lib/** (both arms deliver 100%; the whole answer lives in lib/, so this repo tests concentration within the answer set, not against noise).

arm	explore	Read	duration	answer%
new	1 / 4 / 2	0 / 4 / 0	18 / 52 / 24s	100 / 100 / 100
baseline	2 / 2 / 2	1 / 1 / 1	23 / 28 / 27s	100 / 100 / 100

Two of three new runs are strictly better than every baseline run (0 Reads vs 1, faster). The third is the failure: 4 Reads of lib/utils.js and 52s, a fallback the baseline never made. It is not agent variance — see below.

Root cause

Deterministic replay of the divergent run's own query on both builds, same index, no agent:

codegraph explore "res.send Content-Type ETag generateETag setETag" --path <express>

file	baseline	new
`lib/utils.js` (5,293 B, 272 lines)	6,380 (46.1%) — whole	583 (7.7%) — cluster stub
`lib/response.js`	3,935 (28.4%)	6,001 (64.9%)
`lib/application.js`	1,607 (11.6%)	2,532 (27.4%)
`lib/express.js`	1,927 (13.9%)	—
source envelope	13,849	9,241

lib/utils.js is where compileETag, createETagGenerator, etag and wetag live — half the answer. The CG-4 diagnostic on the new build:

envelope 10,295 delivered · 10,292 allocated of 13,000 budget
allocation 12,398 reserved of 12,400 pool · cliff at weight 10.00 · nothing cliffed
 #  deliv%   bytes  reserved  score   flags                render     file
 1    5.7%     583     3,870   56.0   named entry central  clusters   lib/utils.js
 2   57.0%   5,868     5,875   91.4   entry                clusters*  lib/response.js
 3   23.0%   2,369     2,653   34.5   entry central        clusters*  lib/application.js

utils.js is the top-ranked file (score 56.0, named + entry + central) and was reserved 3,870 chars — and spent 583 of them. Nothing was cliffed. The allocator did its job; the render loop threw the reservation away.

The mechanism is the whole-file bound at src/mcp/tools.ts:4008:

const WHOLE_FILE_MAX_CHARS = allowance + Math.min(WHOLE_FILE_GRACE_MAX,
                                                  round(allowance * WHOLE_FILE_GRACE_FRACTION));

= 3,870 + min(800, 580) = 4,450 < the file's 5,293 bytes, so the whole-file render is declined. Pre-CG-12 the bound was maxCharsPerFile * 3 = 11,400, which the file cleared comfortably. The fallback cluster render only has 3 matched symbols to work with, so it emits 583 chars and 3,287 chars of the reservation are simply lost — which is also why the whole response shrank from 13.8K to 9.2K against an unchanged 13,000-char budget.

This is CG-12's own acceptance criterion — "no file that was previously unclipped becomes clipped" — failing, and here it is the direct cause of an agent Read. CG-14 recorded one instance of it (memory-budget.ts) as a documented exception; this is the same defect observed in the wild, where it costs a round-trip.

Not systemic. On both medium repos the render loop saturates ([over budget] [TRUNCATED], 23,599 of a 23,600 pool reserved), so there is no unspent budget to lose. The failure needs a file whose proportional reservation lands below its own size while its matched-symbol set is thin — likelier on small repos, where per-file reservations are smallest.

The fix belongs in CG-12, not here

Per this task's acceptance rule the budget must not be widened to compensate. The defect is that a reservation can go unspent, so the fix is one of:

Let a large-enough reservation buy the whole file. If allowance >= k * fileSize for some k < 1 (utils.js: 3,870 / 5,293 = 0.73), render whole and let the bounded overshoot the ceiling already tolerates absorb it — the bytes were reserved for this file anyway.
Redistribute what a file cannot spend. After the render loop knows a file's realised size, hand the shortfall to the next-ranked file instead of dropping it. This also fixes the shrinking-envelope symptom directly.

(1) is the smaller change and matches the observed shape; (2) is the more complete invariant ("the pool is spent"). They compose.

Bars

#	Bar	Verdict
1	Read stays at 0	FAIL — client-go 0/0/0 and excalidraw 0/0/0 both arms, but express run 2 makes 4 Reads the baseline never made, from a reproducible non-agent cause
2	Correct-file share > 50%	PASS — new 67.8–100% across all 9 runs; self-query fixture 16% → 59.9%. (Caveat: on these three repos the baseline was already above 50%; the ~16% figure is the self-query fixture, not these repos)
3	No wall-clock regression	PASS at the median — excalidraw 34s → 24s, express 27s → 24s, client-go 49s → 50s. The 52s express outlier is the failing run
4	No regression on the control	FAIL — express, 1 run of 3

Bar 1 is the hard gate and it fails, so the epic does not pass on this measurement regardless of bars 2 and 3.

Reproduce

# clone fresh (never eval on a private repo), index, then:
RUNS=3 AGENT_EVAL_OUT=/tmp/ab-express \
  scripts/agent-eval/ab-new-vs-baseline.sh <express> "<question>" main

node scripts/agent-eval/parse-run.mjs /tmp/ab-express/run-new-2.jsonl --answer 'lib/**'

# the deterministic core of the failure, no agent needed:
CODEGRAPH_EXPLORE_DEBUG=1 node dist/bin/codegraph.js \
  explore "res.send Content-Type ETag generateETag setETag" --path <express>

explore-allocation-ab-1500.md 9.8 KB Historique Raw