Add checkpoint shard merge command

ts/packages/benchmarks/README.AUTOGEN.md

@@ -3,7 +3,7 @@
 
 <!-- AUTOGEN:DOCS:START -->
 
-<!-- AUTOGEN:DOCS:HASH:sha256=8eabbae68e1f9fdf52bb037829f135283b7032402a9b0a9c857c6108c2f0fe9f -->
+<!-- AUTOGEN:DOCS:HASH:sha256=e263a2331f39cbba485c9bda960404c751bb06759e09ef1bd89683a6639f027c -->
 <!-- AUTOGEN:DOCS:SOURCE: ./README.md (hand-written documentation; this file is the AI-generated companion) -->
 
 # @typeagent/benchmarks — AI-generated documentation
@@ -52,10 +52,10 @@ _None._
 - [./src/core/prices.ts](./src/core/prices.ts)
 - [./src/core/rateLimiter.ts](./src/core/rateLimiter.ts)
 - [./src/core/tokenEstimate.ts](./src/core/tokenEstimate.ts)
-- _…and 53 more under `./src/`._
+- _…and 54 more under `./src/`._
 
 ---
 
-_Auto-generated against commit `493931d64a0633ed8909c52b3e84ff536fdab1ce` on `2026-08-27T00:20:31.457Z` by `docs-generate.yml`. Links validated at that commit; the working tree may have drifted by up to 24h. Re-run `pnpm --filter @typeagent/benchmarks docs:verify-links` to spot-check._
+_Auto-generated against commit `0acfc92bdba7c88a3026b17cc7048233458d67a4` on `2026-08-27T08:27:30.753Z` by `docs-generate.yml`. Links validated at that commit; the working tree may have drifted by up to 24h. Re-run `pnpm --filter @typeagent/benchmarks docs:verify-links` to spot-check._
 
 <!-- AUTOGEN:DOCS:END -->

ts/packages/benchmarks/package.json

@@ -27,6 +27,7 @@
     "gen-action-parameters-grader": "pnpm run build && node --max-old-space-size=4096 dist/translationBench/scripts/genActionParametersGrader.js",
     "gen-catalog": "pnpm run build && node --max-old-space-size=4096 dist/translationBench/scripts/genCatalog.js && node --max-old-space-size=4096 dist/translationBench/scripts/genActionParametersGrader.js",
     "jest-esm": "node --no-warnings --experimental-vm-modules ./node_modules/jest/bin/jest.js",
+    "merge-checkpoints": "pnpm run build && node dist/translationBench/scripts/mergeCheckpoints.js",
     "prettier": "prettier --check package.json tsconfig.json src scripts test --ignore-path ../../.prettierignore",
     "prettier:fix": "prettier --write package.json tsconfig.json src scripts test --ignore-path ../../.prettierignore",
     "test": "npm run test:local",

ts/packages/benchmarks/src/translationBench/scripts/mergeCheckpoints.ts

@@ -0,0 +1,14 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+
+import { Command } from "commander";
+import {
+    mergeTranslationBenchCheckpoints,
+    readTranslationBenchCheckpoint,
+} from "../synthesizer/generationSupport.js";
+
+const files = new Command().argument("<checkpoints...>").parse().args;
+const merged = mergeTranslationBenchCheckpoints(
+    files.map((filePath) => readTranslationBenchCheckpoint(filePath)),
+);
+process.stdout.write(`${JSON.stringify(merged.rows, null, 2)}\n`);

ts/packages/benchmarks/src/translationBench/synthesizer/generationSupport.ts

@@ -338,6 +338,60 @@ export function appendTranslationBenchCheckpointRows<T = unknown>(
     };
 }
 
+export function mergeTranslationBenchCheckpoints<T = unknown>(
+    checkpoints: readonly TranslationBenchCheckpoint<T>[],
+): TranslationBenchCheckpoint<T> {
+    if (checkpoints.length === 0) {
+        throw new Error("No translation bench checkpoints to merge");
+    }
+    const first = checkpoints[0]!.header;
+    const byShard = new Map<number, TranslationBenchCheckpoint<T>>();
+    for (const checkpoint of checkpoints) {
+        assertTranslationBenchCheckpointHeadersCompatible(checkpoint.header, {
+            ...first,
+            shardIndex: checkpoint.header.shardIndex,
+        });
+        if (byShard.has(checkpoint.header.shardIndex)) {
+            throw new Error(
+                `Duplicate translation bench checkpoint shard ${checkpoint.header.shardIndex}`,
+            );
+        }
+        byShard.set(checkpoint.header.shardIndex, checkpoint);
+    }
+
+    const rows: TranslationBenchCheckpointRow<T>[] = [];
+    const resumeKeys = new Set<string>();
+    for (let index = 0; index < first.shardCount; index++) {
+        const checkpoint = byShard.get(index);
+        if (checkpoint === undefined) {
+            throw new Error(`Missing checkpoint shard: ${index}`);
+        }
+        for (const row of checkpoint.rows) {
+            const normalized = parseTranslationBenchCheckpointRow<T>(row);
+            validateTranslationBenchCheckpointRowShard(
+                normalized,
+                checkpoint.header,
+            );
+            const key = translationBenchResumeKey(normalized);
+            if (resumeKeys.has(key)) {
+                throw new Error(
+                    `Duplicate translation bench resume key '${key}'`,
+                );
+            }
+            resumeKeys.add(key);
+            rows.push(normalized);
+        }
+    }
+    rows.sort((left, right) =>
+        compareText(
+            translationBenchResumeKey(left),
+            translationBenchResumeKey(right),
+        ),
+    );
+
+    return { header: byShard.get(0)!.header, rows, resumeKeys };
+}
+
 export function getTranslationBenchCatalogCensus(
     schemas: readonly TranslationBenchBenchmarkSchema[],
 ): TranslationBenchCatalogCensus {