diff --git a/.github/workflows/pr.yml b/.github/workflows/pr.yml
index 19d243b..dbdf66b 100644
--- a/.github/workflows/pr.yml
+++ b/.github/workflows/pr.yml
@@ -33,6 +33,10 @@ jobs:
       - run: pnpm run format:check
       - run: pnpm run typecheck
       - run: pnpm --filter @tanstack/oracles run test
+      # Checks the partition of the end-to-end gap oracle into CI shards
+      # (packages/oracles/scripts/e2e-shards.mjs) ahead of the shard jobs,
+      # which CI does not run yet: every test is in exactly one shard.
+      - run: pnpm --filter @tanstack/oracles run test:oracle-gaps:shards
       - run: pnpm run test:publint
       - run: pnpm run test:sherif
   test-eslint-plugin:
diff --git a/packages/oracles/package.json b/packages/oracles/package.json
index b6e094e..bf7b48d 100644
--- a/packages/oracles/package.json
+++ b/packages/oracles/package.json
@@ -64,6 +64,7 @@
     "test:oracle-framework": "vitest --run --config vitest.oracle-framework.config.mjs",
     "test:oracle-gaps": "vitest --run --config oracle-gaps/vitest.config.mjs",
     "test:oracle-gaps:fast": "vitest --run --config oracle-gaps/vitest.config.mjs gap-report-static gap-report-classify gap-report-probe-form gap-report-mutant-validity",
+    "test:oracle-gaps:shards": "node scripts/e2e-shards.mjs check",
     "typecheck": "tsc --noEmit"
   },
   "dependencies": {
diff --git a/packages/oracles/scripts/e2e-shards.mjs b/packages/oracles/scripts/e2e-shards.mjs
new file mode 100644
index 0000000..197a982
--- /dev/null
+++ b/packages/oracles/scripts/e2e-shards.mjs
@@ -0,0 +1,135 @@
+// The CI shards of the end-to-end gap oracle
+// (oracle-gaps/gap-report-oracle.property.test.mjs).
+//
+// The oracle runs the real CLI on scratch packages. Its work is CPU-bound, so
+// shards run as separate CI jobs, never side by side on one runner. Each
+// shard names whole tests of the property. A shard's tests are chosen by
+// their measured cost, longest first, so that the slowest shard sets the
+// job's time. Every test of the file must be in exactly one shard: a test in
+// no shard would leave its law out of CI, and a test in two would run twice.
+//
+//   node scripts/e2e-shards.mjs check           checks the partition against
+//                                               `vitest list`
+//   node scripts/e2e-shards.mjs pattern <shard> prints the shard's `-t`
+//                                               pattern
+//
+// The pattern matches a test's full name, its suite's name and its own,
+// joined as Vitest 4 joins them (a space) or as Vitest 5 does (` > `).
+import { spawnSync } from 'node:child_process'
+import { dirname, join } from 'node:path'
+import { fileURLToPath } from 'node:url'
+
+const suite = `oracle-gaps.report`
+
+// The shards balance the costs measured in one full local run on main
+// (84cd34a, 2026-11-11, an idle 18-core Mac, one Vitest worker), in local
+// seconds: determinism about 345 (all 30 histories, twice each), the random
+// seed 160 to 600 by its seed, the fixed seed 157, the refused-run
+// calibration 102, the two daemon calibrations 56 and 53, and each other
+// calibration 38 to 46. CI took 2.31 times as long. The property registers
+// each campaign, each calibration, and the determinism test as one test, so
+// a shard cannot be smaller than its largest test, and the determinism test
+// alone sets the slowest shard. CI keeps its one fixed-seed job until the
+// property registers its parts as units that a shard can split.
+export const shards = {
+  'e2e-1': [`determinism`],
+  'e2e-2': [`random seed`],
+  'e2e-3': [
+    `fixed seed 20261105`,
+    `calibration: a refused run is reported as complete`,
+  ],
+  'e2e-4': [
+    `calibration: the daemon reports another outcome than the cold run`,
+    `calibration: a daemon is left after --stop-daemon`,
+    `calibration: a mutant is dropped from the enumeration`,
+    `calibration: an owned mutant is reported as unowned`,
+  ],
+  'e2e-5': [
+    `calibration: a crash is reported as a kill`,
+    `calibration: a key drops its statement text`,
+    `calibration: the summary omits a gap`,
+    `calibration: an edit moves a key`,
+    `calibration: production code is reported as probe code`,
+  ],
+}
+
+const escape = (text) => text.replace(/[.*+?^${}()|[\]\\]/g, `\\$&`)
+
+/** The `-t` pattern that selects exactly a shard's tests. */
+export function patternOf(shard) {
+  const tests = shards[shard]
+  if (tests === undefined)
+    throw new Error(
+      `no shard ${JSON.stringify(shard)}; the shards are ${Object.keys(shards).join(`, `)}`,
+    )
+  return `^${escape(suite)}(?: | > )(?:${tests.map(escape).join(`|`)})$`
+}
+
+/**
+ * The partition's errors against the tests that `vitest list` reports: a
+ * test in no shard or in several, and a shard entry that names no test.
+ */
+export function partitionErrors(listed) {
+  const errors = []
+  const patterns = Object.keys(shards).map((shard) => ({
+    shard,
+    pattern: new RegExp(patternOf(shard)),
+  }))
+  for (const name of listed) {
+    // `vitest list` joins the names with ` > `; Vitest 4's `-t` reads them
+    // joined with a space, so a pattern must select the test both ways.
+    const joined = [name, name.replace(/ > /, ` `)]
+    const owners = patterns.filter(({ pattern }) =>
+      joined.every((full) => pattern.test(full)),
+    )
+    if (owners.length !== 1)
+      errors.push(
+        `${JSON.stringify(name)} is in ${owners.length === 0 ? `no shard` : `shards ${owners.map(({ shard }) => shard).join(`, `)}`}`,
+      )
+  }
+  for (const [shard, tests] of Object.entries(shards))
+    for (const test of tests)
+      if (!listed.includes(`${suite} > ${test}`))
+        errors.push(`shard ${shard} names ${JSON.stringify(test)}, no test`)
+  return errors
+}
+
+function listed() {
+  const run = spawnSync(
+    `pnpm`,
+    [
+      `exec`,
+      `vitest`,
+      `list`,
+      `--json`,
+      `--config`,
+      `oracle-gaps/vitest.config.mjs`,
+      `gap-report-oracle`,
+    ],
+    {
+      cwd: join(dirname(fileURLToPath(import.meta.url)), `..`),
+      encoding: `utf8`,
+    },
+  )
+  if (run.status !== 0)
+    throw new Error(`vitest list failed:\n${run.stderr}${run.stdout}`)
+  return JSON.parse(run.stdout).map((test) => test.name)
+}
+
+const [command, shard] = process.argv.slice(2)
+if (command === `pattern`) process.stdout.write(`${patternOf(shard)}\n`)
+else if (command === `check`) {
+  const errors = partitionErrors(listed())
+  if (errors.length > 0) {
+    process.stderr.write(
+      `The e2e shards do not partition the tests:\n${errors.map((error) => `- ${error}`).join(`\n`)}\nEdit packages/oracles/scripts/e2e-shards.mjs so each test is in exactly one shard.\n`,
+    )
+    process.exit(1)
+  }
+  process.stdout.write(
+    `${Object.keys(shards).length} shards partition the e2e tests\n`,
+  )
+} else if (command !== undefined) {
+  process.stderr.write(`usage: e2e-shards.mjs check | pattern <shard>\n`)
+  process.exit(2)
+}