diff --git a/.github/workflows/ci-required.yml b/.github/workflows/ci-required.yml
index 94e6f5b1c..f7c0d7a4d 100644
--- a/.github/workflows/ci-required.yml
+++ b/.github/workflows/ci-required.yml
@@ -89,9 +89,13 @@ permissions:
   # The required-lane gitleaks job runs in PR scan-mode, which reads the PR commit context. (#1132 review)
   pull-requests: read
 
+# A push run on refs/heads/main is landed-commit evidence, so an in-progress main run is not
+# cancelled by the next merge. GitHub keeps one in-progress plus one pending run per group, so
+# during a merge wave the run in flight completes and the newest tip runs next; intermediate
+# pending main runs are still superseded. PR refs keep cancelling (#2582).
 concurrency:
   group: ${{ github.workflow }}-${{ github.ref }}
-  cancel-in-progress: true
+  cancel-in-progress: ${{ github.ref != 'refs/heads/main' }}
 
 jobs:
   docs-governance:
diff --git a/scripts/ci/smart-ci/required-concurrency.test.mjs b/scripts/ci/smart-ci/required-concurrency.test.mjs
new file mode 100644
index 000000000..f98ca891d
--- /dev/null
+++ b/scripts/ci/smart-ci/required-concurrency.test.mjs
@@ -0,0 +1,89 @@
+import assert from 'node:assert/strict'
+import { readFile } from 'node:fs/promises'
+import { test } from 'node:test'
+
+const requiredWorkflowUrl = new URL('../../../.github/workflows/ci-required.yml', import.meta.url)
+
+// An in-progress push run on the default branch must not be cancelled by the next merge:
+// the run in flight completes and the newest tip runs next (GitHub keeps one in-progress
+// plus one pending run per group, so intermediate pending main runs are still superseded).
+// The tip's own required run is the landed-commit evidence (#2582).
+const EXPECTED_GROUP = '${{ github.workflow }}-${{ github.ref }}'
+const EXPECTED_CANCEL_IN_PROGRESS = "${{ github.ref != 'refs/heads/main' }}"
+
+function readLines(workflow) {
+  return workflow.replaceAll('\r\n', '\n').split('\n')
+}
+
+function indentOf(line) {
+  return line.search(/\S/)
+}
+
+// Line scan: every `concurrency:` mapping key, with its indentation and the
+// scalar entries nested directly beneath it.
+function collectConcurrencyBlocks(lines) {
+  const blocks = []
+  lines.forEach((line, index) => {
+    const header = line.match(/^(\s*)concurrency:\s*$/)
+    if (!header) return
+
+    const indent = header[1].length
+    const entries = new Map()
+    for (const next of lines.slice(index + 1)) {
+      if (next.trim() === '') continue
+      if (indentOf(next) <= indent) break
+      if (next.trimStart().startsWith('#')) continue
+      const entry = next.match(/^\s*([A-Za-z0-9_-]+):\s*(.*?)\s*$/)
+      if (entry) entries.set(entry[1], entry[2])
+    }
+    blocks.push({ lineNumber: index + 1, indent, entries })
+  })
+  return blocks
+}
+
+test('ci-required declares exactly one top-level concurrency block', async () => {
+  const lines = readLines(await readFile(requiredWorkflowUrl, 'utf8'))
+  const topLevel = collectConcurrencyBlocks(lines).filter((block) => block.indent === 0)
+
+  assert.equal(
+    topLevel.length,
+    1,
+    `expected one top-level concurrency block in ci-required.yml, found ${topLevel.length}`,
+  )
+})
+
+test('the top-level concurrency group stays per-workflow-and-ref', async () => {
+  const lines = readLines(await readFile(requiredWorkflowUrl, 'utf8'))
+  const [topLevel] = collectConcurrencyBlocks(lines).filter((block) => block.indent === 0)
+
+  assert.equal(
+    topLevel.entries.get('group'),
+    EXPECTED_GROUP,
+    'ci-required.yml must keep one concurrency group per ref so at most one main run is in flight at a time (#2582)',
+  )
+})
+
+test('in-progress cancellation is disabled on the default branch', async () => {
+  const lines = readLines(await readFile(requiredWorkflowUrl, 'utf8'))
+  const [topLevel] = collectConcurrencyBlocks(lines).filter((block) => block.indent === 0)
+
+  assert.equal(
+    topLevel.entries.get('cancel-in-progress'),
+    EXPECTED_CANCEL_IN_PROGRESS,
+    'ci-required.yml must not cancel an in-progress run on refs/heads/main (#2582)',
+  )
+})
+
+test('no job-level concurrency block re-enables cancellation on main', async () => {
+  const lines = readLines(await readFile(requiredWorkflowUrl, 'utf8'))
+  const nested = collectConcurrencyBlocks(lines).filter((block) => block.indent > 0)
+
+  for (const block of nested) {
+    const cancel = block.entries.get('cancel-in-progress')
+    if (cancel === undefined) continue
+    assert.ok(
+      cancel === 'false' || cancel === EXPECTED_CANCEL_IN_PROGRESS,
+      `job-level concurrency at ci-required.yml line ${block.lineNumber} sets cancel-in-progress: ${cancel}, which can cancel a main run (#2582)`,
+    )
+  }
+})