docs: one entry point for the three feedback metrics, and how to run them (CG-11)

Three per-metric docs told a maintainer what each number means; none said
which one answers which question, which harness produces it, or how to read
the arm table. agent-eval-feedback-metrics.md is that page — the metric →
question map, when to reach for ab-new-vs-baseline.sh (isolates a change,
both arms codegraph-on) versus run-all.sh (with vs without, a different
question) versus bench-readme.sh, the worked CG-22 express table where all
three read together, and the bucket → fix mapping. Not a fourth restatement:
the derivations stay where they are and each doc now points here.

The caveats that change how the summary table is read are carried over rather
than dropped — allocation efficiency is relative (attribution is by citation,
so same-question builds only, and never "codegraph wastes N%"), occupancy
shares are Claude Code / 200k and do not transfer between hosts while the arm
ratio does, sufficient is not correct, small-n throughout. Plus the
contamination row, which means different things in the two harnesses and is
the first thing to look at in both.

Also records that the CG-8 7-repo bucket block no longer re-derives:
bench-readme.sh overwrites /tmp/ab-readme, so the swept logs are gone. The
current logs give a different distribution over the same 62 calls, and the
CG-8-era and current classifiers agree exactly on them — so nothing moved
under the metric, the corpus did. CG-13 re-establishes the baseline.

.claude/skills/agent-eval/SKILL.md

@@ -58,6 +58,12 @@ scripts/agent-eval/audit.sh <VERSION> <repo-name> <repo-url> "<question>" <MODE>
   codegraph-tool calls, duration, **total cost**.
 - Interactive (`parse-session.mjs`): the `VERDICT: codegraph_explore used Nx |
   Read N | Grep/Bash N` and `TOKENS:` lines.
+- Both paths also print the three feedback metrics — residual context occupancy,
+  explore sufficiency, allocation efficiency — and a headless A/B ends with a
+  side-by-side `ARM COMPARISON` table. Report that table, and check its
+  contamination row first: `CLI calls that RETURNED output` > 0 means the arm
+  reached codegraph through Bash and its numbers are void. How to read the rest:
+  `docs/benchmarks/agent-eval-feedback-metrics.md`.
 
 Lead with cost + tool/Read counts — they are the reliable signals; raw token
 in/out are confounded by subagent delegation and prompt caching. State whether