diff --git a/tests/runner-e2e/CHAT-FEATURES.md b/tests/runner-e2e/CHAT-FEATURES.md
index 5cf2ac9f0cf..9a04d43973c 100644
--- a/tests/runner-e2e/CHAT-FEATURES.md
+++ b/tests/runner-e2e/CHAT-FEATURES.md
@@ -225,6 +225,9 @@ Initial setup uses the existing workflow operations:
    binding. Only the observed single `Branch/defaultValue` definition for
    `refs/heads/master` is accepted. Bootstrap enables the job and assigns cases
    while preserving that definition; the plan uses its default branch.
+   Assignment inspection records unassigned and existing-job counts before
+   binding. A single unassigned bucket must cover the exact selected cases;
+   foreign jobs and unknown or incomplete buckets stop before writes.
 2. Read the closed registration receipt. Store its observed `binding` JSON as
    `CHAT_COMPLETION_TESTOPS_BINDING` in `runner-e2e-testops-reporting`.
 3. Use TestOps **Run**. For the initial operator launch, set an exact next
diff --git a/tests/runner-e2e/chat-completion-testops-api.mjs b/tests/runner-e2e/chat-completion-testops-api.mjs
index feaae741e62..e6eba6bc284 100644
--- a/tests/runner-e2e/chat-completion-testops-api.mjs
+++ b/tests/runner-e2e/chat-completion-testops-api.mjs
@@ -72,6 +72,11 @@ function assertBranchDefinition(job) {
     || job.parameters[0].name !== 'Branch' || job.parameters[0].defaultValue !== 'refs/heads/master'
     || Object.hasOwn(job.parameters[0], 'value')) reject('job_parameters');
 }
+function isUnassignedBucket(row, expectedCount) {
+  return row !== null && typeof row === 'object' && !Array.isArray(row)
+    && Object.keys(row).every(key => ['job', 'testCasesCount'].includes(key))
+    && (row.job === null || !Object.hasOwn(row, 'job')) && row.testCasesCount === expectedCount;
+}
 
 export async function validatePilotSelection(api, env, context, workflowId) {
   const { cases, targetSha, planName } = catalogDefinition(context);
@@ -168,6 +173,7 @@ export async function completePilotRegistration(api, prepared, official, context
   const binding = { ...prepared, jobId: run.job.id };
   assertPlan(await api(`/api/testplan/${binding.planId}`), binding, context);
   const job = await api(`/api/job/${binding.jobId}`); assertJob(job, binding, workflowId, context);
+  const assignments = await api(`/api/testplan/${binding.planId}/job`);
   await observe({ schema: 'paperclip.chat-completion-testops-registration-observed/v1', ...context,
     projectId: 1, jobId: job.id, launchId: official.launchId, allureJobRunId: official.jobRunId,
     parameterCount: Array.isArray(job.parameters) ? job.parameters.length : null,
@@ -175,17 +181,22 @@ export async function completePilotRegistration(api, prepared, official, context
       id: positive(row?.id) ? row.id : null, name: row?.name === 'Branch' ? 'Branch' : 'UNRESOLVED',
       defaultValue: row?.defaultValue === 'refs/heads/master' ? 'refs/heads/master' : 'NOT_PROJECTED',
       runtimeValuePresent: Object.hasOwn(row ?? {}, 'value') })) : null,
+    assignmentCount: Array.isArray(assignments) ? assignments.length : null,
+    assignments: Array.isArray(assignments) ? assignments.slice(0, 4).map(row => ({
+      kind: isUnassignedBucket(row, cases.length) ? 'unassigned' : row?.job?.id === binding.jobId ? 'owned' : 'foreign_or_unrecognized',
+      jobId: positive(row?.job?.id) ? row.job.id : null,
+      testCasesCount: Number.isSafeInteger(row?.testCasesCount) && row.testCasesCount >= 0 ? row.testCasesCount : null })) : null,
     qualification: 'inspection_only', actualResult: null });
   assertBranchDefinition(job);
-  const assignments = await api(`/api/testplan/${binding.planId}/job`);
-  if (!Array.isArray(assignments) || assignments.length > 1 || assignments.some(row => row.job?.id !== binding.jobId || row.testCasesCount !== cases.length)) reject('plan_job_mismatch');
+  if (!Array.isArray(assignments) || assignments.length > 1 || assignments.some(row => !isUnassignedBucket(row, cases.length)
+    && (row?.job?.id !== binding.jobId || row?.testCasesCount !== cases.length))) reject('plan_job_mismatch');
   await markOnce('bind_owned_job');
   // PATCH only the documented enable/integration fields. Preserve the opaque
   // definition exactly; no guessed parameter-definition write codec is used.
   await api(`/api/job/${binding.jobId}`, 'PATCH', { integrationId: binding.integrationId, canRun: true });
   const patched = await api(`/api/job/${binding.jobId}`); assertJob(patched, binding, workflowId, context); assertBranchDefinition(patched);
   if (!same(patched.parameters, job.parameters) || (Object.hasOwn(patched, 'canRun') && patched.canRun !== true)) reject('job_parameters');
-  if (!assignments.length) {
+  if (!assignments.length || isUnassignedBucket(assignments[0], cases.length)) {
     await markOnce('assign_plan');
     await api(`/api/testplan/${binding.planId}/assign`, 'POST', { jobId: binding.jobId,
       selection: { inverted: false, manual: false, leafsInclude: binding.cases.map(row => row.caseId) } });
diff --git a/tests/runner-e2e/chat-completion-testops-api.test.mjs b/tests/runner-e2e/chat-completion-testops-api.test.mjs
index ac52c469549..40a1da85cc2 100644
--- a/tests/runner-e2e/chat-completion-testops-api.test.mjs
+++ b/tests/runner-e2e/chat-completion-testops-api.test.mjs
@@ -92,6 +92,24 @@ test('registration keeps an existing exact assignment without assigning it twice
   assert.equal(f.calls.filter(row => row.route.endsWith('/assign')).length, 0);
 });
 
+for (const bucket of [{ job: null, testCasesCount: 3 }, { testCasesCount: 3 }]) {
+  test(`registration binds an explicit unassigned bucket (${Object.hasOwn(bucket, 'job') ? 'null' : 'omitted'} job)`, async () => {
+    const f = mutationApi({ assignments: [bucket] }), markers = []; let observed;
+    await completePilotRegistration(f.api, prepared, official, context, 999, async stage => markers.push(stage), async value => { observed = value; });
+    assert.deepEqual(markers, ['bind_owned_job', 'assign_plan']);
+    assert.equal(f.calls.filter(row => row.route.endsWith('/assign')).length, 1);
+    assert.deepEqual(observed.assignments, [{ kind: 'unassigned', jobId: null, testCasesCount: 3 }]);
+  });
+}
+
+for (const bucket of [{ job: null, testCasesCount: 2 }, { job: null, testCasesCount: 3, otherJobId: 99 }]) {
+  test('registration rejects incomplete or unknown unassigned bucket data without writes', async () => {
+    const f = mutationApi({ assignments: [bucket] });
+    await assert.rejects(completePilotRegistration(f.api, prepared, official, context, 999, async () => assert.fail('no mutation marker')));
+    assert.equal(f.calls.filter(row => row.method !== 'GET').length, 0);
+  });
+}
+
 test('bootstrap retains a closed observation before rejecting an unknown parameter shape', async () => {
   const f = mutationApi({ parameters: [{ id: 34, name: 'PRIVATE_NAME', defaultValue: 'PRIVATE_DEFAULT', value: 'PRIVATE_VALUE' }] });
   let observed;