Colby McHenry
10f1ac601a
The issue blamed the density tiebreak; both real cases lost on maxImportance, so ranking was left alone. Full before/after table, the one cost (okhttp's rank-6 file, squeezed out by reservations that were already structurally over-subscribed), and what ships to keep it measurable.
99 lines
6.0 KiB
Markdown
99 lines
6.0 KiB
Markdown
# Epic resolution — explore response noise (CG-24)
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Worked 2026-08-05 → 2026-08-06. Started from one bad `codegraph_explore` response
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in a real session and ended with four shipped fixes, one open defect, and five
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issues closed because measurement contradicted them.
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**The headline: the reported symptom was not an explore bug.** It was a degraded
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index. The explore defects the investigation found are real and were fixed, but
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none of them caused the report.
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## The report
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A prose flow query returned an unusable response: the symbol the agent had named
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never rendered, and a 12k-line generated Cloudflare ambient-types file took 60.7%
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of the output envelope.
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```
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# deliv% bytes reserved score pen flags file
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1 1.0% 251 10,970 87.0 1.00 named entry central <the named file>
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2 60.7% 15,043 6,484 49.0 1.00 entry central worker-configuration.d.ts
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4 — — — 19.9 1.00 dropped: budget <a third file>
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```
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## Root cause
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**Index drift ([CG-33](index-drift-cg33.md)).** The live incrementally-synced index
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diverged from a clean rebuild by 4.3% of distinct edges, bidirectionally,
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overwhelmingly `calls`. RWR graph mass is relative and normalized, so call edges
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missing elsewhere inflate an unaffected file's share — the `.d.ts` carried mass
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0.24750 drifted vs 0.13119 rebuilt (~1.9×), score 49.0 vs 27.0.
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Two causes, both fixed: incremental sync re-resolved only references *in* changed
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files, and `getNodesByName` had no `ORDER BY`, so ties broke by rowid — i.e. by
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the order files happened to be **written**. The second is why scope alone could
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never converge. Stale edges dropped 671 → 2 across an 80-commit replay.
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On a freshly rebuilt index the reported query answers correctly **with no explore
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change at all**.
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## Shipped
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| | what |
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|---|---|
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| **CG-30** | Bounded how far an oversize cluster member may overshoot; windows on whole lines past 1.5× instead of emitting whole — or, when larger than the response ceiling, dropping the file silently. |
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| **CG-31** | Gave the cluster path the `owedBelow` displacement guard the whole-file BUY arm always had, holding back only the prefix of what is owed below that the response can actually pay. |
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| **CG-26** | Closed the remaining holes: whole-file arms had no displacement guard at all, section overhead was charged at a flat 200 against a real 300–500, and `owedPayableBelow` held all-or-nothing. |
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| **CG-25** | Recognize `Generated by <tool> by running <command>` banners. Precision held by requiring two `by` clauses, so ordinary prose does not match. |
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| **CG-28** | Damp declaration-only files that nothing in the index depends on. Does not stack with the generated penalty (`Math.min`), and naming a declaration symbol exempts its file. |
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| **CG-33 / CG-35** | Incremental sync converges with a rebuild, plus a regression suite that fails when the fix is disabled. |
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| **CG-36** | A later cluster is shrunk into the remainder rather than dropped whole — at selection, and again in the ceiling trim. All 8 starvation flags across the suite clear; +1,012 source chars net. `explore-cluster-starvation-cg36.md`. |
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Deterministic across the 6-repo suite: no repo truncates, none loses a file,
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okhttp gains one, every repo lands at or under the 25,000 hard ceiling.
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## Open
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Nothing. CG-36, the last one, shipped 2026-08-06.
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Its own measurement is worth carrying forward, because the issue named the wrong
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fix point: both real cases (`query.py`, `RealInterceptorChain.kt`) lost on
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`maxImportance`, **not** on the density tiebreak the issue suspected. Ranking was
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left alone; the never-shrink rule was the lever. Full numbers and the one cost
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(okhttp trades its rank-6 file for +7,196 chars in the two that answer the
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question) in `explore-cluster-starvation-cg36.md`.
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## Closed because measurement contradicted them
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Five, which is the story of this epic as much as the fixes are.
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| | why |
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| **CG-32** | Named file "didn't render first." Drift artifact; on a clean index it renders first and takes 89%. |
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| **CG-34** | "Allocator over-reserves for low-scoring files." Filed on a runner's diagnosis without checking the numbers. The file was never over-reserved (4,314 in both arms) — it was over-*spending*, which is CG-31. |
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| **CG-27** | Adding `function`/`method` to `ENVELOPE_KINDS` measured as a **large regression** — rank #1 fell from 7,539 delivered chars to 397, 7 of 11 inner closures to 0. The enclosing range was holding the file together as one cluster, inside which `shrinkCluster` already did the per-symbol ranking the issue wanted. A careful version was noise (69 vs 68 across nine queries). |
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| **CG-29** | Prose-vs-symbol query gap. Inverted on measurement: prose matches symbol on django and delivers 63% more source on okhttp. The founding observation was drift. |
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| **CG-37** | Duplicate of CG-36, filed without seeing it. |
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## What this epic is actually a lesson in
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**A confident diagnosis is worth less than a cheap measurement.** Every issue
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above was filed by someone — human or agent — who had read the code and had a
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plausible mechanism. Five were wrong. The ones that survived did so because a
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deterministic probe disagreed with them and the probe won.
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Two specific traps this cost real time on, both now guarded in tooling:
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- **`.codegraph/graph.db` does not exist** — the index is `codegraph.db`, and
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`sqlite3` against a mistyped path *creates* an empty database rather than
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failing. An empty schema reads exactly like a stale pre-migration index. This
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produced a wrong root cause. `diff-index-drift.mjs` refuses a missing path.
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- **`ab-new-vs-baseline.sh` checks the engine out at the baseline ref mid-run.**
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A commit made while it runs captures baseline sources and silently reverts the
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fix under test. This happened during CG-30. Check the `changed:` line before
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believing any A/B result.
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And one measurement discipline worth keeping: **compare sets, not totals.** The
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drift that started all of this shows up as +0.7% on raw edge counts, because it
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is bidirectional and nets out. On distinct edge triples it is 4.3%.
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