docs(changelog): link Video Bridge contact-sheet fix

changelog.d/fixes/11350-video-bridge-contact-sheet-labels.md

@@ -0,0 +1 @@
+- **fix(video-bridge):** burn high-contrast timestamps into every bounded contact-sheet cell and add a real-model A/B harness whose promotion verdict stays `HOLD` until token, latency, and quality evidence is actually executed ([#11350](https://github.com/diegosouzapw/OmniRoute/pull/11350))

docs/security/GUARDRAILS.md

@@ -347,10 +347,23 @@ are always retained; comparator or decoder errors fail open and keep coverage.
 The output metadata reports how many frames were dropped.
 
 An explicitly marked video part may request a timestamped contact sheet. The
-bridge builds at most a 4-column, 16-frame JPEG grid and labels the resulting
-observation with every source timestamp. If `sharp` cannot decode or compose
-the grid, the bridge falls back to the individual JPEG frames; a client abort
-still propagates through the sheet operation.
+bridge builds at most a 4-column, 16-frame JPEG grid. Every 512-pixel cell burns
+its source timestamp into a high-contrast bottom band, while the same timestamps
+remain in textual metadata for downstream association and audit. The complete
+JPEG remains capped at 32 MiB. If `sharp` cannot decode or compose the grid, the
+bridge falls back to the individual JPEG frames; a client abort still propagates
+through the sheet operation.
+
+Promotion evidence is deliberately separate from the synthetic composition
+microbenchmark. `scripts/perf/video-bridge-contact-sheet-eval.ts` defines a
+schema-versioned A/B harness for real OpenAI-compatible vision models. It measures
+provider-reported tokens, end-to-end wall latency (including sheet composition),
+model-call count, and manifest-defined fact retention. Raw model responses are not
+written to the report; only SHA-256 digests and matched fact IDs are retained. The
+harness makes no network or paid model call unless `--execute-real` is passed and
+`--model`, `OMNIROUTE_BASE_URL`, and `OMNIROUTE_API_KEY` are configured. Without
+that explicit real run, its machine-readable verdict remains `HOLD`; synthetic
+payload/call-count measurements alone are not promotion evidence.
 
 Callers may attach an optional `transcript.cues` array to a supported video
 part when they already possess aligned text. Each cue must carry `text`, a

scripts/perf/video-bridge-bench.ts

@@ -7,8 +7,10 @@
  *    scene_aware vs segment_aware for growing scene-candidate counts. The
  *    ffmpeg scene-detection pass is shared by both aware policies and is
  *    I/O-bound, so the incremental policy cost is exactly this selection step.
- * 2. Contact sheet: composes synthetic JPEG frames into the timestamped grid
- *    and compares payload bytes + model calls against individual frames.
+ * 2. Contact sheet: composes synthetic JPEG frames into the visually timestamped
+ *    grid and compares payload bytes + structural call counts. This microbenchmark
+ *    does not measure real-model tokens, latency, or quality; use
+ *    video-bridge-contact-sheet-eval.ts before considering promotion.
  */
 import { performance } from "node:perf_hooks";
 
@@ -64,6 +66,9 @@ async function syntheticJpegFrame(index: number): Promise<string> {
 
 async function benchContactSheet(): Promise<void> {
   console.log("\n== Contact sheet vs individual frames (synthetic 512x288 JPEG) ==");
+  console.log(
+    "STRUCTURAL ONLY: real-model tokens/latency/quality are unmeasured; promotion remains HOLD."
+  );
   console.log("frames | sheet_ms sheet_KiB individual_KiB model_calls(sheet/individual)");
   for (const frameCount of [1, 4, 8, 16]) {
     const frames = await Promise.all(

scripts/perf/video-bridge-contact-sheet-eval.ts

@@ -0,0 +1,578 @@
+#!/usr/bin/env node
+
+import { createHash } from "node:crypto";
+import { readFile } from "node:fs/promises";
+import path from "node:path";
+import { performance } from "node:perf_hooks";
+import { fileURLToPath } from "node:url";
+
+import { z } from "zod";
+
+import {
+  buildVideoContactSheet,
+  type ContactSheetFrame,
+} from "../../src/lib/guardrails/videoBridgeContactSheet";
+
+export type VideoContactSheetEvalConfigurationState = "configured-not-executed" | "not-configured";
+
+export interface VideoContactSheetEvalHoldReportInput {
+  caseCount: number;
+  configurationState: VideoContactSheetEvalConfigurationState;
+  missingConfiguration?: string[];
+}
+
+export interface VideoContactSheetEvalHoldReport {
+  caseCount: number;
+  execution: {
+    realModel: false;
+    state: VideoContactSheetEvalConfigurationState;
+  };
+  kind: "video-contact-sheet-ab-eval";
+  missingConfiguration: string[];
+  promotion: {
+    reasons: ["REAL_MODEL_CONFIGURATION_MISSING" | "REAL_MODEL_EVAL_NOT_EXECUTED"];
+    status: "HOLD";
+  };
+  results: [];
+  schemaVersion: 1;
+  summary: null;
+}
+
+export interface VideoContactSheetEvalThresholds {
+  minLatencyReductionRatio: number;
+  minQualityRetention: number;
+  minQualityScore: number;
+  minTokenReductionRatio: number;
+}
+
+export interface VideoContactSheetEvalAggregate {
+  latencyMs: number;
+  qualityScore: number;
+  totalTokens: number | null;
+}
+
+export type VideoContactSheetPromotionReason =
+  | "LATENCY_REDUCTION_BELOW_THRESHOLD"
+  | "QUALITY_RETENTION_BELOW_THRESHOLD"
+  | "QUALITY_SCORE_BELOW_THRESHOLD"
+  | "TOKEN_REDUCTION_BELOW_THRESHOLD"
+  | "TOKEN_USAGE_UNAVAILABLE";
+
+export interface VideoContactSheetPromotionDecision {
+  metrics: {
+    latencyReductionRatio: number;
+    qualityRetention: number;
+    tokenReductionRatio: number | null;
+  };
+  reasons: VideoContactSheetPromotionReason[];
+  status: "ELIGIBLE" | "HOLD";
+}
+
+const MAX_EVAL_FRAME_BASE64_CHARS = 5_592_408;
+
+const evalThresholdsSchema = z
+  .object({
+    minLatencyReductionRatio: z.number().positive().max(1),
+    minQualityRetention: z.number().min(0).max(1),
+    minQualityScore: z.number().min(0).max(1),
+    minTokenReductionRatio: z.number().positive().max(1),
+  })
+  .strict();
+
+const evalManifestSchema = z
+  .object({
+    cases: z
+      .array(
+        z
+          .object({
+            expectedFacts: z
+              .array(
+                z
+                  .object({
+                    id: z.string().min(1),
+                    requiredTerms: z.array(z.string().min(1)).min(1),
+                    timestampSeconds: z.number().finite().nonnegative(),
+                  })
+                  .strict()
+              )
+              .min(1),
+            frames: z
+              .array(
+                z
+                  .object({
+                    dataUri: z
+                      .string()
+                      .max("data:image/jpeg;base64,".length + MAX_EVAL_FRAME_BASE64_CHARS)
+                      .regex(
+                        /^data:image\/jpeg;base64,[A-Za-z0-9+/=]{4,5592408}$/i,
+                        "expected a bounded JPEG data URI"
+                      ),
+                    timestampSeconds: z.number().finite().nonnegative(),
+                  })
+                  .strict()
+              )
+              .min(1)
+              .max(16),
+            id: z.string().min(1),
+            prompt: z.string().min(1),
+          })
+          .strict()
+      )
+      .min(1),
+    id: z.string().min(1),
+    schemaVersion: z.literal(1),
+    thresholds: evalThresholdsSchema,
+  })
+  .strict();
+
+const chatCompletionSchema = z
+  .object({
+    choices: z
+      .array(
+        z
+          .object({
+            message: z.object({ content: z.string() }).passthrough(),
+          })
+          .passthrough()
+      )
+      .min(1),
+    usage: z
+      .object({
+        completion_tokens: z.number().nonnegative().optional(),
+        prompt_tokens: z.number().nonnegative().optional(),
+        total_tokens: z.number().nonnegative().optional(),
+      })
+      .passthrough()
+      .optional(),
+  })
+  .passthrough();
+
+export type VideoContactSheetEvalManifest = z.infer<typeof evalManifestSchema>;
+
+export interface VideoContactSheetEvalConfig {
+  apiKey: string;
+  endpoint: string;
+  model: string;
+}
+
+interface EvalFactScore {
+  matchedFactIds: string[];
+  qualityScore: number;
+}
+
+interface EvalPathResult extends EvalFactScore {
+  latencyMs: number;
+  modelCalls: number;
+  responseDigest: string;
+  totalTokens: number | null;
+}
+
+export interface VideoContactSheetEvalCaseResult {
+  caseId: string;
+  individual: EvalPathResult;
+  sheet: EvalPathResult;
+}
+
+export interface VideoContactSheetEvalExecutedReport {
+  caseCount: number;
+  execution: {
+    realModel: true;
+    state: "executed";
+  };
+  generatedAt: string;
+  kind: "video-contact-sheet-ab-eval";
+  manifestDigest: string;
+  manifestId: string;
+  model: string;
+  promotion: VideoContactSheetPromotionDecision;
+  results: VideoContactSheetEvalCaseResult[];
+  schemaVersion: 1;
+  summary: {
+    individual: VideoContactSheetEvalAggregate & { modelCalls: number };
+    sheet: VideoContactSheetEvalAggregate & { modelCalls: number };
+  };
+  thresholds: VideoContactSheetEvalThresholds;
+}
+
+type FetchLike = (input: string | URL | Request, init?: RequestInit) => Promise<Response>;
+
+export function createVideoContactSheetEvalHoldReport(
+  input: VideoContactSheetEvalHoldReportInput
+): VideoContactSheetEvalHoldReport {
+  const reason =
+    input.configurationState === "not-configured"
+      ? "REAL_MODEL_CONFIGURATION_MISSING"
+      : "REAL_MODEL_EVAL_NOT_EXECUTED";
+  return {
+    caseCount: input.caseCount,
+    execution: {
+      realModel: false,
+      state: input.configurationState,
+    },
+    kind: "video-contact-sheet-ab-eval",
+    missingConfiguration: [...(input.missingConfiguration ?? [])],
+    promotion: {
+      reasons: [reason],
+      status: "HOLD",
+    },
+    results: [],
+    schemaVersion: 1,
+    summary: null,
+  };
+}
+
+function reductionRatio(baseline: number, candidate: number): number {
+  if (baseline <= 0) return 0;
+  return (baseline - candidate) / baseline;
+}
+
+export function assessVideoContactSheetPromotion(input: {
+  individual: VideoContactSheetEvalAggregate;
+  sheet: VideoContactSheetEvalAggregate;
+  thresholds: VideoContactSheetEvalThresholds;
+}): VideoContactSheetPromotionDecision {
+  const latencyReductionRatio = reductionRatio(input.individual.latencyMs, input.sheet.latencyMs);
+  const qualityRetention =
+    input.individual.qualityScore > 0
+      ? input.sheet.qualityScore / input.individual.qualityScore
+      : 0;
+  const tokenReductionRatio =
+    input.individual.totalTokens === null || input.sheet.totalTokens === null
+      ? null
+      : reductionRatio(input.individual.totalTokens, input.sheet.totalTokens);
+  const reasons: VideoContactSheetPromotionReason[] = [];
+  const requiredLatencyReduction = Math.max(
+    Number.EPSILON,
+    input.thresholds.minLatencyReductionRatio
+  );
+  const requiredTokenReduction = Math.max(Number.EPSILON, input.thresholds.minTokenReductionRatio);
+  if (latencyReductionRatio < requiredLatencyReduction) {
+    reasons.push("LATENCY_REDUCTION_BELOW_THRESHOLD");
+  }
+  if (input.sheet.qualityScore < input.thresholds.minQualityScore) {
+    reasons.push("QUALITY_SCORE_BELOW_THRESHOLD");
+  }
+  if (qualityRetention < input.thresholds.minQualityRetention) {
+    reasons.push("QUALITY_RETENTION_BELOW_THRESHOLD");
+  }
+  if (tokenReductionRatio === null) {
+    reasons.push("TOKEN_USAGE_UNAVAILABLE");
+  } else if (tokenReductionRatio < requiredTokenReduction) {
+    reasons.push("TOKEN_REDUCTION_BELOW_THRESHOLD");
+  }
+  return {
+    metrics: {
+      latencyReductionRatio,
+      qualityRetention,
+      tokenReductionRatio,
+    },
+    reasons,
+    status: reasons.length === 0 ? "ELIGIBLE" : "HOLD",
+  };
+}
+
+function normalizeEvalText(value: string): string {
+  return value
+    .normalize("NFD")
+    .replace(/[\u0300-\u036f]/g, "")
+    .toLowerCase();
+}
+
+function formatEvalTimestamp(timestampSeconds: number): string {
+  const totalMilliseconds = Math.max(0, Math.round(timestampSeconds * 1000));
+  const minutes = Math.floor(totalMilliseconds / 60_000);
+  const seconds = Math.floor((totalMilliseconds % 60_000) / 1000);
+  const milliseconds = totalMilliseconds % 1000;
+  return `${String(minutes).padStart(2, "0")}:${String(seconds).padStart(2, "0")}.${String(milliseconds).padStart(3, "0")}`;
+}
+
+function scoreFacts(
+  response: string,
+  expectedFacts: VideoContactSheetEvalManifest["cases"][number]["expectedFacts"]
+): EvalFactScore {
+  const normalizedResponse = normalizeEvalText(response);
+  const matchedFactIds = expectedFacts
+    .filter((fact) => {
+      const timestamp = normalizeEvalText(formatEvalTimestamp(fact.timestampSeconds));
+      const timestampIndex = normalizedResponse.indexOf(timestamp);
+      if (timestampIndex < 0) return false;
+      const factWindow = normalizedResponse.slice(
+        Math.max(0, timestampIndex - 160),
+        Math.min(normalizedResponse.length, timestampIndex + timestamp.length + 160)
+      );
+      return fact.requiredTerms.every((term) => factWindow.includes(normalizeEvalText(term)));
+    })
+    .map((fact) => fact.id);
+  return {
+    matchedFactIds,
+    qualityScore: matchedFactIds.length / expectedFacts.length,
+  };
+}
+
+function digestResponse(response: string): string {
+  return createHash("sha256").update(response).digest("hex");
+}
+
+function sumTokens(values: Array<number | null>): number | null {
+  if (values.some((value) => value === null)) return null;
+  return values.reduce<number>((sum, value) => sum + (value ?? 0), 0);
+}
+
+async function callVisionModel(input: {
+  config: VideoContactSheetEvalConfig;
+  dataUri: string;
+  fetchImpl: FetchLike;
+  prompt: string;
+}): Promise<{ content: string; totalTokens: number | null }> {
+  const response = await input.fetchImpl(input.config.endpoint, {
+    body: JSON.stringify({
+      messages: [
+        {
+          content: [
+            { text: input.prompt, type: "text" },
+            { image_url: { url: input.dataUri }, type: "image_url" },
+          ],
+          role: "user",
+        },
+      ],
+      model: input.config.model,
+      temperature: 0,
+    }),
+    headers: {
+      authorization: `Bearer ${input.config.apiKey}`,
+      "content-type": "application/json",
+    },
+    method: "POST",
+  });
+  if (!response.ok) {
+    throw new Error(`Video contact-sheet eval request failed with HTTP ${response.status}`);
+  }
+  const parsed = chatCompletionSchema.parse(await response.json());
+  const usage = parsed.usage;
+  const totalTokens =
+    usage?.total_tokens ??
+    (usage?.prompt_tokens !== undefined && usage.completion_tokens !== undefined
+      ? usage.prompt_tokens + usage.completion_tokens
+      : null);
+  return {
+    content: parsed.choices[0].message.content,
+    totalTokens,
+  };
+}
+
+async function evaluateIndividualFrames(input: {
+  evalCase: VideoContactSheetEvalManifest["cases"][number];
+  config: VideoContactSheetEvalConfig;
+  fetchImpl: FetchLike;
+}): Promise<EvalPathResult> {
+  const startedAt = performance.now();
+  const calls: Array<{ content: string; totalTokens: number | null }> = [];
+  for (const frame of input.evalCase.frames) {
+    calls.push(
+      await callVisionModel({
+        config: input.config,
+        dataUri: frame.dataUri,
+        fetchImpl: input.fetchImpl,
+        prompt: `${input.evalCase.prompt}\nAnalyze only the frame at ${formatEvalTimestamp(frame.timestampSeconds)}. Associate every observation with that exact timestamp label.`,
+      })
+    );
+  }
+  const content = calls.map((call) => call.content).join("\n");
+  return {
+    ...scoreFacts(content, input.evalCase.expectedFacts),
+    latencyMs: performance.now() - startedAt,
+    modelCalls: calls.length,
+    responseDigest: digestResponse(content),
+    totalTokens: sumTokens(calls.map((call) => call.totalTokens)),
+  };
+}
+
+async function evaluateContactSheet(input: {
+  evalCase: VideoContactSheetEvalManifest["cases"][number];
+  config: VideoContactSheetEvalConfig;
+  fetchImpl: FetchLike;
+}): Promise<EvalPathResult> {
+  const startedAt = performance.now();
+  const sheet = await buildVideoContactSheet(input.evalCase.frames as ContactSheetFrame[], {
+    columns: 4,
+    timeoutMs: 30_000,
+  });
+  if (!sheet.used || !sheet.dataUri) {
+    throw new Error("Video contact-sheet eval could not compose the bounded JPEG grid");
+  }
+  const call = await callVisionModel({
+    config: input.config,
+    dataUri: sheet.dataUri,
+    fetchImpl: input.fetchImpl,
+    prompt: `${input.evalCase.prompt}\nAnalyze every cell in the contact sheet. Timestamp labels are burned into each cell. Associate every observation with its visible timestamp.`,
+  });
+  return {
+    ...scoreFacts(call.content, input.evalCase.expectedFacts),
+    latencyMs: performance.now() - startedAt,
+    modelCalls: 1,
+    responseDigest: digestResponse(call.content),
+    totalTokens: call.totalTokens,
+  };
+}
+
+function aggregatePathResults(
+  results: VideoContactSheetEvalCaseResult[],
+  path: "individual" | "sheet"
+): VideoContactSheetEvalAggregate & { modelCalls: number } {
+  const pathResults = results.map((result) => result[path]);
+  return {
+    latencyMs: pathResults.reduce((sum, result) => sum + result.latencyMs, 0),
+    modelCalls: pathResults.reduce((sum, result) => sum + result.modelCalls, 0),
+    qualityScore:
+      pathResults.reduce((sum, result) => sum + result.qualityScore, 0) / pathResults.length,
+    totalTokens: sumTokens(pathResults.map((result) => result.totalTokens)),
+  };
+}
+
+export async function runVideoContactSheetEval(input: {
+  config: VideoContactSheetEvalConfig;
+  fetchImpl?: FetchLike;
+  manifest: VideoContactSheetEvalManifest;
+}): Promise<VideoContactSheetEvalExecutedReport> {
+  const manifest = evalManifestSchema.parse(input.manifest);
+  const endpoint = z.string().url().parse(input.config.endpoint);
+  const config = {
+    apiKey: z.string().min(1).parse(input.config.apiKey),
+    endpoint,
+    model: z.string().min(1).parse(input.config.model),
+  };
+  const fetchImpl = input.fetchImpl ?? fetch;
+  const results: VideoContactSheetEvalCaseResult[] = [];
+  for (const evalCase of manifest.cases) {
+    const individual = await evaluateIndividualFrames({ config, evalCase, fetchImpl });
+    const sheet = await evaluateContactSheet({ config, evalCase, fetchImpl });
+    results.push({ caseId: evalCase.id, individual, sheet });
+  }
+  const individual = aggregatePathResults(results, "individual");
+  const sheet = aggregatePathResults(results, "sheet");
+  const promotion = assessVideoContactSheetPromotion({
+    individual,
+    sheet,
+    thresholds: manifest.thresholds,
+  });
+  return {
+    caseCount: manifest.cases.length,
+    execution: { realModel: true, state: "executed" },
+    generatedAt: new Date().toISOString(),
+    kind: "video-contact-sheet-ab-eval",
+    manifestDigest: createHash("sha256").update(JSON.stringify(manifest)).digest("hex"),
+    manifestId: manifest.id,
+    model: config.model,
+    promotion,
+    results,
+    schemaVersion: 1,
+    summary: { individual, sheet },
+    thresholds: manifest.thresholds,
+  };
+}
+
+function readArgument(name: string): string | undefined {
+  const index = process.argv.indexOf(`--${name}`);
+  if (index < 0) return undefined;
+  const value = process.argv[index + 1];
+  return value && !value.startsWith("--") ? value : undefined;
+}
+
+function printUsage(): void {
+  console.log(
+    [
+      "Usage:",
+      "  node --import tsx/esm scripts/perf/video-bridge-contact-sheet-eval.ts --manifest <manifest.json> --model <vision-model>",
+      "  node --import tsx/esm scripts/perf/video-bridge-contact-sheet-eval.ts --manifest <manifest.json> --model <vision-model> --execute-real",
+      "",
+      "The default command validates configuration and emits HOLD without calling a model.",
+      "A real paid/networked run requires --execute-real, --model, and the documented variables:",
+      "  OMNIROUTE_BASE_URL",
+      "  OMNIROUTE_API_KEY",
+      "",
+      "Manifest v1: id, thresholds, and 1+ cases. Each case has 1-16 bounded JPEG data URIs,",
+      "timestamps, a prompt, and expectedFacts with timestampSeconds + requiredTerms.",
+    ].join("\n")
+  );
+}
+
+async function loadManifest(manifestPath: string): Promise<VideoContactSheetEvalManifest> {
+  const raw = await readFile(path.resolve(manifestPath), "utf8");
+  return evalManifestSchema.parse(JSON.parse(raw));
+}
+
+function resolveChatCompletionsEndpoint(baseUrl: string): string {
+  const normalized = baseUrl.replace(/\/{1,8}$/u, "");
+  if (normalized.endsWith("/v1/chat/completions")) return normalized;
+  if (normalized.endsWith("/v1")) return `${normalized}/chat/completions`;
+  return `${normalized}/v1/chat/completions`;
+}
+
+async function main(): Promise<void> {
+  if (process.argv.includes("--help") || process.argv.includes("-h")) {
+    printUsage();
+    return;
+  }
+  const manifestPath = readArgument("manifest");
+  const model = readArgument("model");
+  const missingConfiguration: string[] = [];
+  if (!manifestPath) missingConfiguration.push("--manifest");
+  if (!model) missingConfiguration.push("--model");
+  const baseUrl = process.env.OMNIROUTE_BASE_URL;
+  const apiKey = process.env.OMNIROUTE_API_KEY;
+  if (!baseUrl) missingConfiguration.push("OMNIROUTE_BASE_URL");
+  if (!apiKey) missingConfiguration.push("OMNIROUTE_API_KEY");
+
+  let manifest: VideoContactSheetEvalManifest | null = null;
+  if (manifestPath) manifest = await loadManifest(manifestPath);
+  if (missingConfiguration.length > 0) {
+    console.log(
+      JSON.stringify(
+        createVideoContactSheetEvalHoldReport({
+          caseCount: manifest?.cases.length ?? 0,
+          configurationState: "not-configured",
+          missingConfiguration,
+        }),
+        null,
+        2
+      )
+    );
+    return;
+  }
+  if (!process.argv.includes("--execute-real")) {
+    console.log(
+      JSON.stringify(
+        createVideoContactSheetEvalHoldReport({
+          caseCount: manifest?.cases.length ?? 0,
+          configurationState: "configured-not-executed",
+        }),
+        null,
+        2
+      )
+    );
+    return;
+  }
+  if (!manifest || !baseUrl || !apiKey || !model) {
+    throw new Error("Video contact-sheet eval configuration was not resolved");
+  }
+  console.log(
+    JSON.stringify(
+      await runVideoContactSheetEval({
+        config: { apiKey, endpoint: resolveChatCompletionsEndpoint(baseUrl), model },
+        manifest,
+      }),
+      null,
+      2
+    )
+  );
+}
+
+const isMainModule =
+  typeof process.argv[1] === "string" &&
+  path.resolve(process.argv[1]) === fileURLToPath(import.meta.url);
+if (isMainModule) {
+  main().catch(() => {
+    console.error("Video contact-sheet eval failed validation or execution.");
+    process.exitCode = 1;
+  });
+}

src/lib/guardrails/videoBridgeContactSheet.ts

@@ -21,6 +21,9 @@ export interface VideoContactSheetResult {
 
 const MAX_FRAMES = 16;
 const MAX_SHEET_BYTES = 32 * 1024 * 1024;
+const LABEL_FONT_SIZE = 32;
+const LABEL_HEIGHT = 64;
+const LABEL_PADDING = 16;
 const TILE_SIZE = 512;
 
 function fallback(frames: readonly ContactSheetFrame[]): VideoContactSheetResult {
@@ -33,11 +36,31 @@ function fallback(frames: readonly ContactSheetFrame[]): VideoContactSheetResult
 }
 
 function decodeFrame(dataUri: string): Buffer {
-  const match = /^data:image\/jpeg;base64,([A-Za-z0-9+/=]+)$/i.exec(dataUri);
+  const match = /^data:image\/jpeg;base64,([A-Za-z0-9+/=]{4,5592408})$/i.exec(dataUri);
   if (!match) throw new Error("Contact sheet requires JPEG data URIs");
   return Buffer.from(match[1], "base64");
 }
 
+function formatContactSheetTimestamp(timestampSeconds: number): string {
+  const totalMilliseconds = Math.max(0, Math.round(timestampSeconds * 1000));
+  const minutes = Math.floor(totalMilliseconds / 60_000);
+  const seconds = Math.floor((totalMilliseconds % 60_000) / 1000);
+  const milliseconds = totalMilliseconds % 1000;
+  if (minutes > 999) return `t=${timestampSeconds.toExponential(3)}s`;
+  return `${String(minutes).padStart(2, "0")}:${String(seconds).padStart(2, "0")}.${String(milliseconds).padStart(3, "0")}`;
+}
+
+function buildTimestampLabel(timestampSeconds: number): Buffer {
+  const label = formatContactSheetTimestamp(timestampSeconds);
+  const labelTop = TILE_SIZE - LABEL_HEIGHT;
+  return Buffer.from(
+    `<svg xmlns="http://www.w3.org/2000/svg" width="${TILE_SIZE}" height="${TILE_SIZE}" viewBox="0 0 ${TILE_SIZE} ${TILE_SIZE}">
+      <rect x="0" y="${labelTop}" width="${TILE_SIZE}" height="${LABEL_HEIGHT}" fill="#000000" fill-opacity="0.82" />
+      <text x="${LABEL_PADDING}" y="${labelTop + 42}" fill="#ffffff" font-family="DejaVu Sans Mono, monospace" font-size="${LABEL_FONT_SIZE}" font-weight="700">${label}</text>
+    </svg>`
+  );
+}
+
 /** Build an optional bounded JPEG grid; every failure except abort is fail-safe to individual frames. */
 export async function buildVideoContactSheet(
   frames: readonly ContactSheetFrame[],
@@ -69,6 +92,7 @@ export async function buildVideoContactSheet(
       frames.map(async (frame) =>
         sharp(decodeFrame(frame.dataUri))
           .resize(TILE_SIZE, TILE_SIZE, { fit: "contain", background: "#000000" })
+          .composite([{ input: buildTimestampLabel(frame.timestampSeconds), left: 0, top: 0 }])
           .jpeg({ quality: 80 })
           .toBuffer()
       )
@@ -101,7 +125,7 @@ export async function buildVideoContactSheet(
       used: true,
       width: columns * TILE_SIZE,
     };
-  } catch (error) {
+  } catch {
     if (signal.aborted) throw new Error("Video contact sheet was aborted");
     return fallback(frames);
   } finally {

tests/unit/guardrails/videoBridgeContactSheet.test.ts

@@ -15,6 +15,12 @@ async function frame(color: string, timestampSeconds: number) {
   return { dataUri: `data:image/jpeg;base64,${bytes.toString("base64")}`, timestampSeconds };
 }
 
+function decodeJpegDataUri(dataUri: string): Buffer {
+  const prefix = "data:image/jpeg;base64,";
+  assert.ok(dataUri.toLowerCase().startsWith(prefix), "expected a JPEG data URI");
+  return Buffer.from(dataUri.slice(prefix.length), "base64");
+}
+
 test("builds a bounded contact sheet and preserves timestamp labels", async () => {
   const result = await buildVideoContactSheet([
     await frame("red", 1),
@@ -28,6 +34,61 @@ test("builds a bounded contact sheet and preserves timestamp labels", async () =
   assert.equal(result.frames.length, 3);
 });
 
+test("renders a high-contrast timestamp label inside every contact-sheet cell", async () => {
+  const result = await buildVideoContactSheet([
+    await frame("white", 1),
+    await frame("white", 65.25),
+    await frame("white", 130.5),
+    await frame("white", 600),
+  ]);
+
+  assert.equal(result.used, true);
+  assert.equal(result.width, 1024);
+  assert.equal(result.height, 1024);
+  const { data, info } = await sharp(decodeJpegDataUri(result.dataUri ?? ""))
+    .removeAlpha()
+    .raw()
+    .toBuffer({ resolveWithObject: true });
+  assert.equal(info.channels, 3);
+
+  const tileSize = 512;
+  const labelTop = 448;
+  const labelBottom = 512;
+  const labelFingerprints: string[] = [];
+  for (let index = 0; index < 4; index++) {
+    const tileLeft = (index % 2) * tileSize;
+    const tileTop = Math.floor(index / 2) * tileSize;
+    let darkPixels = 0;
+    let lightPixels = 0;
+    let contentLightPixels = 0;
+    const labelBytes: number[] = [];
+
+    for (let y = labelTop; y < labelBottom; y++) {
+      for (let x = 0; x < tileSize; x++) {
+        const offset = ((tileTop + y) * info.width + tileLeft + x) * info.channels;
+        const luminance = (data[offset] + data[offset + 1] + data[offset + 2]) / 3;
+        if (luminance < 48) darkPixels += 1;
+        if (luminance > 208) lightPixels += 1;
+        labelBytes.push(Math.round(luminance));
+      }
+    }
+    for (let y = 128; y < 384; y++) {
+      for (let x = 64; x < 448; x++) {
+        const offset = ((tileTop + y) * info.width + tileLeft + x) * info.channels;
+        const luminance = (data[offset] + data[offset + 1] + data[offset + 2]) / 3;
+        if (luminance > 208) contentLightPixels += 1;
+      }
+    }
+
+    assert.ok(darkPixels > tileSize * 48, `cell ${index} should have a dark label band`);
+    assert.ok(lightPixels > 40, `cell ${index} should have light timestamp glyphs`);
+    assert.ok(contentLightPixels > 90_000, `cell ${index} should preserve visible frame content`);
+    labelFingerprints.push(Buffer.from(labelBytes).toString("base64"));
+  }
+
+  assert.equal(new Set(labelFingerprints).size, 4, "each timestamp should render a distinct label");
+});
+
 test("contact sheet falls back to individual frames when decoding fails", async () => {
   const frames = [{ dataUri: "data:image/jpeg;base64,QQ==", timestampSeconds: 2 }];
   const result = await buildVideoContactSheet(frames);

tests/unit/guardrails/videoBridgeContactSheetEval.test.ts

@@ -0,0 +1,177 @@
+import assert from "node:assert/strict";
+import test from "node:test";
+
+import sharp from "sharp";
+
+import {
+  assessVideoContactSheetPromotion,
+  createVideoContactSheetEvalHoldReport,
+  runVideoContactSheetEval,
+} from "../../../scripts/perf/video-bridge-contact-sheet-eval.ts";
+
+async function evalFrame(color: string, timestampSeconds: number) {
+  const bytes = await sharp({
+    create: { background: color, channels: 3, height: 32, width: 32 },
+  })
+    .jpeg()
+    .toBuffer();
+  return {
+    dataUri: `data:image/jpeg;base64,${bytes.toString("base64")}`,
+    timestampSeconds,
+  };
+}
+
+test("contact-sheet A/B eval remains HOLD when real-model configuration is missing", () => {
+  const report = createVideoContactSheetEvalHoldReport({
+    caseCount: 0,
+    configurationState: "not-configured",
+    missingConfiguration: ["OMNIROUTE_API_KEY", "--model"],
+  });
+
+  assert.equal(report.schemaVersion, 1);
+  assert.equal(report.kind, "video-contact-sheet-ab-eval");
+  assert.deepEqual(report.execution, {
+    realModel: false,
+    state: "not-configured",
+  });
+  assert.deepEqual(report.promotion, {
+    reasons: ["REAL_MODEL_CONFIGURATION_MISSING"],
+    status: "HOLD",
+  });
+  assert.deepEqual(report.missingConfiguration, ["OMNIROUTE_API_KEY", "--model"]);
+  assert.deepEqual(report.results, []);
+  assert.equal(report.summary, null);
+});
+
+test("contact-sheet A/B eval becomes eligible only with measured cost gains and retained quality", () => {
+  const decision = assessVideoContactSheetPromotion({
+    individual: { latencyMs: 1_000, qualityScore: 0.9, totalTokens: 1_000 },
+    sheet: { latencyMs: 600, qualityScore: 0.9, totalTokens: 600 },
+    thresholds: {
+      minLatencyReductionRatio: 0.01,
+      minQualityRetention: 1,
+      minQualityScore: 0.8,
+      minTokenReductionRatio: 0.01,
+    },
+  });
+
+  assert.deepEqual(decision, {
+    metrics: {
+      latencyReductionRatio: 0.4,
+      qualityRetention: 1,
+      tokenReductionRatio: 0.4,
+    },
+    reasons: [],
+    status: "ELIGIBLE",
+  });
+});
+
+test("contact-sheet A/B promotion remains HOLD for quality loss or absent token evidence", () => {
+  const decision = assessVideoContactSheetPromotion({
+    individual: { latencyMs: 1_000, qualityScore: 1, totalTokens: 1_000 },
+    sheet: { latencyMs: 500, qualityScore: 0.7, totalTokens: null },
+    thresholds: {
+      minLatencyReductionRatio: 0.01,
+      minQualityRetention: 0.95,
+      minQualityScore: 0.8,
+      minTokenReductionRatio: 0.01,
+    },
+  });
+
+  assert.equal(decision.status, "HOLD");
+  assert.deepEqual(decision.reasons, [
+    "QUALITY_SCORE_BELOW_THRESHOLD",
+    "QUALITY_RETENTION_BELOW_THRESHOLD",
+    "TOKEN_USAGE_UNAVAILABLE",
+  ]);
+  assert.equal(decision.metrics.tokenReductionRatio, null);
+});
+
+test("contact-sheet A/B promotion rejects zero cost gain even with permissive thresholds", () => {
+  const decision = assessVideoContactSheetPromotion({
+    individual: { latencyMs: 1_000, qualityScore: 1, totalTokens: 1_000 },
+    sheet: { latencyMs: 1_000, qualityScore: 1, totalTokens: 1_000 },
+    thresholds: {
+      minLatencyReductionRatio: 0,
+      minQualityRetention: 1,
+      minQualityScore: 1,
+      minTokenReductionRatio: 0,
+    },
+  });
+
+  assert.equal(decision.status, "HOLD");
+  assert.deepEqual(decision.reasons, [
+    "LATENCY_REDUCTION_BELOW_THRESHOLD",
+    "TOKEN_REDUCTION_BELOW_THRESHOLD",
+  ]);
+});
+
+test("contact-sheet A/B harness measures real-model calls without storing raw responses", async () => {
+  const responses = [
+    "At 00:01.000 there is a red square.",
+    "At 00:05.000 there is a blue circle.",
+    "At 00:01.000 there is a red square; at 00:05.000 there is a blue circle.",
+  ];
+  let requestCount = 0;
+  const report = await runVideoContactSheetEval({
+    config: {
+      apiKey: "test-only-key",
+      endpoint: "https://eval.invalid/v1/chat/completions",
+      model: "vision-eval-model",
+    },
+    fetchImpl: async () => {
+      const content = responses[requestCount];
+      requestCount += 1;
+      return new Response(
+        JSON.stringify({
+          choices: [{ message: { content } }],
+          usage: { completion_tokens: 20, prompt_tokens: 80, total_tokens: 100 },
+        }),
+        { headers: { "content-type": "application/json" }, status: 200 }
+      );
+    },
+    manifest: {
+      cases: [
+        {
+          expectedFacts: [
+            {
+              id: "red-square",
+              requiredTerms: ["red", "square"],
+              timestampSeconds: 1,
+            },
+            {
+              id: "blue-circle",
+              requiredTerms: ["blue", "circle"],
+              timestampSeconds: 5,
+            },
+          ],
+          frames: [await evalFrame("red", 1), await evalFrame("blue", 5)],
+          id: "two-scenes",
+          prompt: "Describe the visible shape and color at each timestamp.",
+        },
+      ],
+      id: "contact-sheet-fixture-v1",
+      schemaVersion: 1,
+      thresholds: {
+        minLatencyReductionRatio: 0.01,
+        minQualityRetention: 1,
+        minQualityScore: 1,
+        minTokenReductionRatio: 0.01,
+      },
+    },
+  });
+
+  assert.equal(requestCount, 3);
+  assert.deepEqual(report.execution, { realModel: true, state: "executed" });
+  assert.equal(report.results[0].individual.modelCalls, 2);
+  assert.equal(report.results[0].individual.totalTokens, 200);
+  assert.equal(report.results[0].individual.qualityScore, 1);
+  assert.equal(report.results[0].sheet.modelCalls, 1);
+  assert.equal(report.results[0].sheet.totalTokens, 100);
+  assert.equal(report.results[0].sheet.qualityScore, 1);
+  assert.equal("response" in report.results[0].individual, false);
+  assert.equal("response" in report.results[0].sheet, false);
+  assert.match(report.manifestDigest, /^[a-f0-9]{64}$/);
+  assert.match(report.results[0].individual.responseDigest, /^[a-f0-9]{64}$/);
+  assert.match(report.results[0].sheet.responseDigest, /^[a-f0-9]{64}$/);
+});