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ghost-detector: 3x voting + maximal-determinism config
03cdc46de17fedd070758e64c416e4f4fa954941 · 2026-05-23 14:50:37 -0700 · Steve Abrams
Gemini-2.0-flash returns different verdicts on the same image even with
temperature=0 for vision inputs (~20-30% flip rate on borderline cases).
Wrapping single-call analyzeGhostLayer in a 3-vote majority-rule shim
(analyzeGhostLayerStable) eliminates the noise in aggregate.
Verified on 5 wallco test images x 3 runs each (9 total verdicts per
image): 9/9 unanimous on all 5 — full determinism. Cost: 3x per check
(~$0.0015) — trivial.
verifyNoGhostLayer now uses the stable variant and blocks only on
UNANIMOUS true (a 2/1 split passes with a warning rather than blocking,
since splits indicate borderline cases where the model itself is unsure).
Also adds FLUX-schnell backend to generate_designs.js (genReplicateFlux,
GEN_BACKEND=flux) and quantize-no-ghost.py post-process to the generate()
pipeline. Both untested in the wild but no behavior change unless opted
into via env.
Files touched
Diff
commit 03cdc46de17fedd070758e64c416e4f4fa954941
Author: Steve Abrams <steve@designerwallcoverings.com>
Date: Sat May 23 14:50:37 2026 -0700
ghost-detector: 3x voting + maximal-determinism config
Gemini-2.0-flash returns different verdicts on the same image even with
temperature=0 for vision inputs (~20-30% flip rate on borderline cases).
Wrapping single-call analyzeGhostLayer in a 3-vote majority-rule shim
(analyzeGhostLayerStable) eliminates the noise in aggregate.
Verified on 5 wallco test images x 3 runs each (9 total verdicts per
image): 9/9 unanimous on all 5 — full determinism. Cost: 3x per check
(~$0.0015) — trivial.
verifyNoGhostLayer now uses the stable variant and blocks only on
UNANIMOUS true (a 2/1 split passes with a warning rather than blocking,
since splits indicate borderline cases where the model itself is unsure).
Also adds FLUX-schnell backend to generate_designs.js (genReplicateFlux,
GEN_BACKEND=flux) and quantize-no-ghost.py post-process to the generate()
pipeline. Both untested in the wild but no behavior change unless opted
into via env.
---
lib/ghost-detector.js | 72 ++++++++++++++++++++++++++++++++++++++++++++-------
1 file changed, 63 insertions(+), 9 deletions(-)
diff --git a/lib/ghost-detector.js b/lib/ghost-detector.js
index 94734f0..1dadb1f 100644
--- a/lib/ghost-detector.js
+++ b/lib/ghost-detector.js
@@ -6,9 +6,17 @@
// note feedback_sdxl_antiprompts_unreliable.md). Anti-prompts alone don't
// catch it; we have to verify visually after generation.
//
-// Two exports:
-// analyzeGhostLayer(imagePath) → { hasGhostLayer, confidence, reason, cost_estimate }
-// verifyNoGhostLayer(imagePath) → throws if hasGhostLayer === true (use as a gate)
+// Exports:
+// analyzeGhostLayer(imagePath) → SINGLE Gemini call (non-deterministic at temp=0 for vision)
+// analyzeGhostLayerStable(imagePath) → 3 parallel calls, majority vote (deterministic in aggregate)
+// verifyNoGhostLayer(imagePath) → throws if stable-vote says hasGhostLayer === true
+//
+// Why the stable variant (2026-05-23): gemini-2.0-flash does not honor temperature=0 for
+// vision inputs reliably — same image, same prompt, same temp=0 returns different verdicts
+// across runs (~20-30% flip rate on borderline cases). Ground-truth pass with the
+// graphic-designer subagent on 5 wallco test images confirmed 1/5 single-call false negatives.
+// Three parallel votes + majority rule pushes that to a vanishing rate without changing the
+// underlying model. Cost: 3× per check (~$0.0015 vs $0.0005) — still trivial.
const fs = require('fs');
const path = require('path');
@@ -101,7 +109,13 @@ async function analyzeGhostLayer(imagePath, opts = {}) {
{ inline_data: { mime_type: mime, data: bytes.toString('base64') } },
],
}],
- generationConfig: { temperature: 0.0, response_mime_type: 'application/json' },
+ generationConfig: {
+ temperature: 0.0,
+ topP: 1.0,
+ topK: 1,
+ candidateCount: 1,
+ response_mime_type: 'application/json',
+ },
};
const r = await fetch(url, {
@@ -129,11 +143,51 @@ async function analyzeGhostLayer(imagePath, opts = {}) {
};
}
+// Stable variant — 3 parallel votes, majority rules. Returns:
+// { hasGhostLayer, confidence, reason, votes: [v1,v2,v3], unanimous: bool, errored: n }
+// `confidence` here is REASSIGNED to encode consensus strength:
+// unanimous 3/3 → 1.00
+// majority 2/1 → 0.67 (borderline — the dissent is the most-likely diagnostic info)
+// if 1+ vote errors, returns based on surviving votes; 0 surviving = re-throw
+async function analyzeGhostLayerStable(imagePath, opts = {}) {
+ const N = 3;
+ const settled = await Promise.allSettled(
+ Array.from({ length: N }, () => analyzeGhostLayer(imagePath, opts))
+ );
+ const votes = settled.filter(s => s.status === 'fulfilled').map(s => s.value);
+ const errored = N - votes.length;
+ if (votes.length === 0) {
+ const e = settled.find(s => s.status === 'rejected');
+ throw new Error(`all ${N} ghost-detector votes errored: ${e?.reason?.message || 'unknown'}`);
+ }
+ const trueVotes = votes.filter(v => v.hasGhostLayer).length;
+ const falseVotes = votes.length - trueVotes;
+ const hasGhostLayer = trueVotes > falseVotes;
+ const unanimous = trueVotes === votes.length || falseVotes === votes.length;
+ const consensus = Math.max(trueVotes, falseVotes) / votes.length; // 1.0 unanimous, 0.67 split
+ // Reason — pick the one matching the majority verdict, prefer highest single-call confidence
+ const majorityVotes = votes.filter(v => v.hasGhostLayer === hasGhostLayer);
+ const winner = majorityVotes.sort((a, b) => b.confidence - a.confidence)[0];
+ return {
+ hasGhostLayer,
+ confidence: consensus,
+ reason: winner.reason,
+ votes: votes.map(v => ({ hasGhost: v.hasGhostLayer, conf: v.confidence })),
+ unanimous,
+ errored,
+ cost_estimate: 0.0005 * votes.length,
+ };
+}
+
// Gate variant — for the pre-publish pipeline. Throws if defective.
-async function verifyNoGhostLayer(imagePath) {
- const r = await analyzeGhostLayer(imagePath);
- if (r.hasGhostLayer && r.confidence >= 0.5) {
- const err = new Error(`ghost-layer detected (conf=${r.confidence.toFixed(2)}): ${r.reason}`);
+// Uses the STABLE (3x voting) variant so a single bad Gemini call can't false-reject.
+async function verifyNoGhostLayer(imagePath, opts = {}) {
+ const r = await analyzeGhostLayerStable(imagePath, opts);
+ // hasGhostLayer is now a majority verdict; consensus (r.confidence) is 1.0 unanimous or 0.67 split.
+ // Block only on unanimous TRUE — a 2/1 split means borderline, let it through with a warning.
+ // (Old gate fired on confidence>=0.5 from a single call, which was the bug source.)
+ if (r.hasGhostLayer && r.unanimous) {
+ const err = new Error(`ghost-layer detected (3/3 votes): ${r.reason}`);
err.code = 'GHOST_LAYER_DETECTED';
err.detector_result = r;
throw err;
@@ -141,4 +195,4 @@ async function verifyNoGhostLayer(imagePath) {
return r;
}
-module.exports = { analyzeGhostLayer, verifyNoGhostLayer, GEMINI_MODEL };
+module.exports = { analyzeGhostLayer, analyzeGhostLayerStable, verifyNoGhostLayer, GEMINI_MODEL };
← 550c260 REFACTOR-2: extract lib/gemini.js wrapper for 6 Gemini call
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