ci(all-green): skip the json coverage merge for already-uploaded runs

Skipping a cached run's codecovcli upload still paid for merging its
istanbul JSON report, which only Codecov reads — istanbul-lib-coverage's
merge is far slower than the lcov merge on a run with many cells, so it
dominated rerun time even with the upload itself skipped. Pass skipJson
through to mergeRunCoverage so a cached run only redoes the cheap lcov
merge that the Datadog batch upload still needs.

Generated by Claude Code.

Author: rochdev

scripts/group-coverage.mjs

@@ -253,17 +253,22 @@ function mergeCoverageJson (reportPaths) {
  * @param {string|number} runId
  * @param {string} [inputDir]
  * @param {string} [outputDir]
+ * @param {boolean} [skipJson] Skip merging the istanbul JSON reports — only Codecov reads them
+ *   (see `upload-coverage.mjs`), and `istanbul-lib-coverage`'s merge is far slower than `mergeLcov`
+ *   on a run with many cells, so a run whose Codecov upload already succeeded in a previous job
+ *   attempt can skip this merge entirely instead of paying for it only to discard the result.
  * @returns {{ lcovDir: string|null, jsonDir: string|null }} Directories containing the merged
- *   `lcov.info` and `coverage-final.json`, each null if the run produced no report in that format.
+ *   `lcov.info` and `coverage-final.json`, each null if the run produced no report in that format
+ *   (or, for `jsonDir`, if `skipJson` was set).
  */
-function mergeRunCoverage (runId, inputDir = INPUT_DIR, outputDir = OUTPUT_DIR) {
+function mergeRunCoverage (runId, inputDir = INPUT_DIR, outputDir = OUTPUT_DIR, skipJson = false) {
   const files = collectCoverageFiles(join(inputDir, String(runId)), [], { runId: String(runId) })
   if (files.length === 0) return { lcovDir: null, jsonDir: null }
 
   const { reportsByArtifact, artifacts } = planCoverageGroups(files)
   const reports = artifacts.flatMap(artifact => reportsByArtifact.get(artifact))
   const lcovReportPaths = reports.filter(r => r.format === 'lcov').map(r => r.reportPath)
-  const jsonReportPaths = reports.filter(r => r.format === 'json').map(r => r.reportPath)
+  const jsonReportPaths = skipJson ? [] : reports.filter(r => r.format === 'json').map(r => r.reportPath)
 
   let lcovDir = null
   if (lcovReportPaths.length > 0) {

scripts/group-coverage.spec.mjs

@@ -218,6 +218,21 @@ describe('group-coverage', () => {
       )
     })
 
+    it('skips the json merge when skipJson is set, but still merges lcov', () => {
+      const input = join(dir, 'coverage-results')
+      const output = join(dir, 'coverage-upload')
+      const cellDir = join(input, '42', 'coverage-apm-integrations-axios__a-0', 'node-20-x')
+      mkdirSync(cellDir, { recursive: true })
+      writeFileSync(join(cellDir, 'lcov.info'), 'SF:a.js\nDA:1,1\nend_of_record\n')
+      writeFileSync(join(cellDir, 'coverage-final.json'), JSON.stringify({}))
+
+      const { lcovDir, jsonDir } = mergeRunCoverage('42', input, output, true)
+
+      assert.equal(lcovDir, join(output, '42', 'lcov'))
+      assert.equal(jsonDir, null)
+      assert.equal(existsSync(join(output, '42', 'json')), false)
+    })
+
     it('ignores other runs\' cells', () => {
       const input = join(dir, 'coverage-results')
       const otherCellDir = join(input, '7', 'coverage-appsec-express__job-0', 'node-20-x')

scripts/upload-coverage.mjs

@@ -93,18 +93,26 @@ export function hasCodecovCommit () {
  * lcov files that came from cells with the same content is safe, but merging Codecov uploads that
  * each need a different flag isn't.
  *
- * The merge always runs, even when `skipUpload` is set, since the lcov half it also produces feeds
- * the Datadog batch upload, which has no per-run cache of its own — see `all-green.mjs`.
+ * The lcov merge always runs, even when `skipUpload` is set, since it also feeds the Datadog batch
+ * upload, which has no per-run cache of its own — see `all-green.mjs`. The json merge is skipped
+ * along with the upload, since only Codecov reads it and it's the slow half of the merge on a run
+ * with many cells.
  *
  * @param {{ id: number, name: string }} run
  * @param {{ sha: string, branch: string, prNumber?: string, eventName: string, baseRef: string }} options
- * @param {boolean} [skipUpload] Skip the `codecovcli do-upload` call — set when a previous All
- *   Green job attempt already uploaded this run's coverage to Codecov successfully.
+ * @param {boolean} [skipUpload] Skip merging the json report and the `codecovcli do-upload` call —
+ *   set when a previous All Green job attempt already uploaded this run's coverage to Codecov
+ *   successfully.
  * @returns {Promise<import('./run-upload.mjs').UploadResult[]>}
  */
 export async function uploadCoverage (run, options, skipUpload = false) {
+  if (skipUpload) {
+    mergeRunCoverage(run.id, undefined, undefined, true)
+    return []
+  }
+
   const { jsonDir } = mergeRunCoverage(run.id)
-  if (!jsonDir || skipUpload) return []
+  if (!jsonDir) return []
 
   const commitReady = await ensureCodecovCommit(options)
   if (!commitReady) return []