diff --git a/docs/TEST_INTEGRITY.md b/docs/TEST_INTEGRITY.md
index bed22bc..74b4b62 100644
--- a/docs/TEST_INTEGRITY.md
+++ b/docs/TEST_INTEGRITY.md
@@ -2754,3 +2754,44 @@ test_integrity_note:
     did_relax_any_assertion: false
     if_true_explain_spec_basis: ""
 ```
+
+# Candidate source B2 authenticated-attempt spec correction (2026-10-01)
+
+```yaml
+test_integrity_note:
+  change_type: spec_correction
+  scenarios:
+    - id: SCN-candidate-bootstrap-one-shot
+      given: "A CheckService-issued opaque registered-plan handle"
+      when: "A foreign, cloned, expired, replayed, or already-closed handle is used"
+      then: "No FD3 admission opens; the only accepted acknowledgement is the exact FD4 binding frame and it closes the original linear handle"
+    - id: SCN-candidate-input-consumption
+      given: "A frozen, bounded product snapshot and a fixed Node E binding"
+      when: "The original product bytes change before execution"
+      then: "An actual spawned child reads the frozen bytes; post-capture drift refuses before spawn"
+    - id: SCN-candidate-execution-boundary
+      given: "An opaque attempt with fixed command, arguments, explicit environment, and output cap"
+      when: "The child exits zero after exceeding the cap"
+      then: "The parent records overflow as non-success without accepting an injected executor or caller-selected limit"
+    - id: SCN-candidate-fence-closure
+      given: "A closed opaque attempt"
+      when: "The backend has not recorded namespace identity, FD closure, and descendant reaping"
+      then: "Terminal proof is UNKNOWN; fabricated observations and cloned handles cannot create proof"
+  observable_outcomes:
+    - "Only the exact FD4 acknowledgement closes a one-shot opaque admission"
+    - "Child stdout proves frozen-byte consumption, not same-process test reads"
+    - "Zero exit plus output overflow is never success"
+    - "Missing backend fence evidence is never TerminalProof"
+  determinism_controls:
+    - "Temporary source trees, fixed absolute Node runtime, explicit empty child environment, bounded streams"
+    - "No injected executor, caller-provided command, root, environment, limit, or terminal observation"
+  anti_cheat_rationale:
+    prevents:
+      - "Arbitrary tuple issuance or a fabricated bootstrap literal"
+      - "Boolean caller observations minting terminal proof"
+      - "Cloned or reused handles reopening an admission"
+      - "Same-process snapshot reads impersonating child consumption"
+  relaxation:
+    did_relax_any_assertion: false
+    if_true_explain_spec_basis: ""
+```
diff --git a/src/checks/candidate-execution-fence.mjs b/src/checks/candidate-execution-fence.mjs
index 4990a2f..6bd72ab 100644
--- a/src/checks/candidate-execution-fence.mjs
+++ b/src/checks/candidate-execution-fence.mjs
@@ -1,6 +1,33 @@
 import { TorchError } from '../kernel/errors.mjs';
-const fail = (message, code, details) => { throw new TorchError(message, { code, details }); };
-export function createCandidateExecutionFenceV2({ bootstrap, backend = 'private-pid1-namespace' } = {}) { if (!bootstrap?.transport?.closesBeforeCandidateSpawn || backend !== 'private-pid1-namespace') fail('Candidate fence has no supported private bootstrap', 'CANDIDATE_FENCE_UNAVAILABLE'); return Object.freeze({ schema: 'torch.dev/candidate-execution-fence/v2alpha1', backend, nonce: bootstrap.nonce, closed: false }); }
-/** A direct exit or empty PGID is deliberately insufficient: missing observed PID1/reap proof is UNKNOWN. */
-export function observeCandidateExecutionFenceV2({ fence, observation = {} } = {}) { if (!fence || fence.closed) fail('Candidate fence is unavailable', 'CANDIDATE_FENCE_UNAVAILABLE'); const closed = observation.privatePid1 === true && observation.namespaceObserved === true && observation.descendantsReaped === true && observation.admissionFdsClosed === true; return Object.freeze({ schema: 'torch.dev/candidate-terminal-proof/v2alpha1', outcome: closed ? 'terminal' : 'unknown', terminalProof: closed, reason: closed ? null : 'descendant-closure-unobserved', observation: Object.freeze({ privatePid1: observation.privatePid1 === true, namespaceObserved: observation.namespaceObserved === true, descendantsReaped: observation.descendantsReaped === true, admissionFdsClosed: observation.admissionFdsClosed === true }) }); }
-export function closeCandidateExecutionFenceV2(fence) { if (!fence || fence.closed) fail('Candidate fence is already closed', 'CANDIDATE_FENCE_UNAVAILABLE'); return Object.freeze({ ...fence, closed: true }); }
+
+function fail(message, code, details) {
+  throw new TorchError(message, { code, details });
+}
+
+/**
+ * Fence observations are owned by the backend, never submitted by the caller.
+ * Until the backend has recorded a PID1 namespace identity, FD closure, and
+ * namespace-wide reaping, every attempt is UNKNOWN. A process-group exit never
+ * creates TerminalProof.
+ */
+export function createCandidateExecutionFenceRuntimeV2({ stateForAttempt, backendObservation } = {}) {
+  if (typeof stateForAttempt !== 'function' || typeof backendObservation !== 'function') throw new TypeError('candidate fence runtime is incomplete');
+  const closed = new WeakSet();
+  function close(attempt) {
+    if (!stateForAttempt(attempt) || closed.has(attempt)) fail('Candidate fence is unavailable', 'CANDIDATE_FENCE_UNAVAILABLE');
+    closed.add(attempt);
+  }
+  function terminal(attempt) {
+    if (!stateForAttempt(attempt) || !closed.has(attempt)) fail('Candidate fence is unavailable', 'CANDIDATE_FENCE_UNAVAILABLE');
+    const observed = backendObservation(attempt);
+    const qualified = observed?.backend === 'private-pid1-namespace'
+      && Number.isSafeInteger(observed.namespacePid) && observed.namespacePid > 0
+      && typeof observed.namespaceIdentity === 'string' && observed.namespaceIdentity.length > 0
+      && observed.admissionFdsClosed === true && observed.descendantsReaped === true && observed.escapedDescendants === false;
+    return Object.freeze({
+      schema: 'torch.dev/candidate-terminal-proof/v2alpha1', outcome: qualified ? 'terminal' : 'unknown', terminalProof: qualified,
+      reason: qualified ? null : 'descendant-closure-unobserved',
+    });
+  }
+  return Object.freeze({ close, terminal });
+}
diff --git a/src/checks/candidate-input-snapshot.mjs b/src/checks/candidate-input-snapshot.mjs
index 20f2fe8..e5dd562 100644
--- a/src/checks/candidate-input-snapshot.mjs
+++ b/src/checks/candidate-input-snapshot.mjs
@@ -49,7 +49,7 @@ function hashRegularFile(path, expected, limits) {
   } finally { if (fd !== undefined) closeSync(fd); }
 }
 /** Private caller seam: callers obtain inputRoot from the returned opaque snapshot, never from a policy selector. */
-export function captureCandidateInputSnapshotV2({ sourceRoot, destinationRoot, paths, limits: requestedLimits = {}, id = randomUUID() } = {}) {
+function captureCandidateInputSnapshotV2({ sourceRoot, destinationRoot, paths, limits: requestedLimits = {}, id = randomUUID() } = {}) {
   const limits = normalizeLimits(requestedLimits); if (typeof sourceRoot !== 'string' || typeof destinationRoot !== 'string' || !Array.isArray(paths)) fail('Candidate snapshot request is invalid', 'CANDIDATE_SNAPSHOT_INPUT_INVALID');
   const source = resolve(sourceRoot); const destination = resolve(destinationRoot); if (source === destination || !relative(source, destination).startsWith('..')) fail('Candidate snapshot destination must be outside source', 'CANDIDATE_SNAPSHOT_INPUT_INVALID');
   const listed = files(source, paths, limits); mkdirSync(destination, { recursive: false, mode: 0o700 }); let totalBytes = 0; const records = [];
@@ -57,7 +57,7 @@ export function captureCandidateInputSnapshotV2({ sourceRoot, destinationRoot, p
   const manifest = Object.freeze({ schema: 'torch.dev/candidate-input-manifest/v2alpha1', id, files: Object.freeze(records), totalBytes, digest: createHash('sha256').update(JSON.stringify(records)).digest('hex') });
   return Object.freeze({ schema: 'torch.dev/candidate-input-snapshot/v2alpha1', inputRoot: destination, manifest, limits });
 }
-export function verifyCandidateInputSnapshotV2(snapshot = {}) {
+function verifyCandidateInputSnapshotV2(snapshot = {}) {
   if (snapshot?.schema !== 'torch.dev/candidate-input-snapshot/v2alpha1' || !snapshot.manifest?.files || typeof snapshot.inputRoot !== 'string') fail('Candidate snapshot is malformed', 'CANDIDATE_SNAPSHOT_INVALID');
   const listed = files(snapshot.inputRoot, snapshot.manifest.files.map((file) => file.path), snapshot.limits);
   const observed = listed.map((file) => hashRegularFile(join(snapshot.inputRoot, file.path), { ...file, bytes: file.size }, snapshot.limits));
@@ -67,3 +67,30 @@ export function verifyCandidateInputSnapshotV2(snapshot = {}) {
   }
   return Object.freeze({ verified: true, digest: snapshot.manifest.digest, files: observed.length, totalBytes: snapshot.manifest.totalBytes });
 }
+
+/**
+ * The public boundary accepts only a service-issued attempt. Source roots,
+ * paths, destinations, and S limits live in the service's private state.
+ */
+export function createCandidateInputSnapshotRuntimeV2({ stateForAttempt } = {}) {
+  if (typeof stateForAttempt !== 'function') throw new TypeError('stateForAttempt is required');
+  const snapshots = new WeakMap();
+  function capture(attempt) {
+    const state = stateForAttempt(attempt);
+    if (!state?.input) fail('Candidate attempt has no frozen input authority', 'CANDIDATE_SNAPSHOT_ADMISSION_REQUIRED');
+    const snapshot = captureCandidateInputSnapshotV2(state.input);
+    snapshots.set(attempt, snapshot);
+    return Object.freeze({ digest: snapshot.manifest.digest, files: snapshot.manifest.files.length, totalBytes: snapshot.manifest.totalBytes });
+  }
+  function verify(attempt) {
+    const snapshot = snapshots.get(attempt);
+    if (!snapshot) fail('Candidate snapshot is unavailable', 'CANDIDATE_SNAPSHOT_ADMISSION_REQUIRED');
+    return verifyCandidateInputSnapshotV2(snapshot);
+  }
+  function cwd(attempt) {
+    const snapshot = snapshots.get(attempt);
+    if (!snapshot) fail('Candidate snapshot is unavailable', 'CANDIDATE_SNAPSHOT_ADMISSION_REQUIRED');
+    return snapshot.inputRoot;
+  }
+  return Object.freeze({ capture, verify, cwd });
+}
diff --git a/src/checks/candidate-source-bootstrap.mjs b/src/checks/candidate-source-bootstrap.mjs
index ccf0af2..02c5c64 100644
--- a/src/checks/candidate-source-bootstrap.mjs
+++ b/src/checks/candidate-source-bootstrap.mjs
@@ -1,16 +1,81 @@
-import { randomBytes } from 'node:crypto';
+import { createHash, randomBytes } from 'node:crypto';
 import { TorchError } from '../kernel/errors.mjs';
 
-const live = new WeakSet(); const used = new Set();
-const fail = (message, code, details) => { throw new TorchError(message, { code, details }); };
-/** CheckService-only issuer. The returned object is intentionally not serializable and carries no DB/adapter/writer capability. */
-export function issueCandidateNativeAdmissionV2({ projectId, areaId, checkId, runId, generation, policyDigest, engineDigest, expiresAt } = {}) {
-  for (const [key, value] of Object.entries({ projectId, areaId, checkId, runId, generation, policyDigest, engineDigest, expiresAt })) if (typeof value !== 'string' || !value) fail('Candidate native admission is incomplete', 'CANDIDATE_NATIVE_ADMISSION_INVALID', { key });
-  const admission = Object.freeze({ schema: 'torch.dev/candidate-native-admission/v2alpha1', projectId, areaId, checkId, runId, generation, policyDigest, engineDigest, expiresAt, nonce: randomBytes(32).toString('base64url') }); live.add(admission); return admission;
+const ADMISSION_SCHEMA = 'torch.dev/candidate-source-parent-admission/v2alpha1';
+const ACK_SCHEMA = 'torch.dev/candidate-source-parent-binding/v2alpha1';
+const SHA256 = /^[a-f0-9]{64}$/;
+const MAX_FRAME_BYTES = 64 * 1024;
+
+function fail(message, code, details) {
+  throw new TorchError(message, { code, details });
 }
-export function openCandidateSourceBootstrapV2(admission, { now = () => new Date() } = {}) {
-  if (!live.has(admission) || used.has(admission.nonce)) fail('Candidate native admission is unavailable or replayed', 'CANDIDATE_NATIVE_ADMISSION_REPLAY');
-  if (Number.isNaN(Date.parse(admission.expiresAt)) || Date.parse(admission.expiresAt) <= now().getTime()) fail('Candidate native admission expired', 'CANDIDATE_NATIVE_ADMISSION_EXPIRED');
-  used.add(admission.nonce); live.delete(admission);
-  return Object.freeze({ schema: 'torch.dev/candidate-bootstrap/v2alpha1', nonce: admission.nonce, runId: admission.runId, generation: admission.generation, policyDigest: admission.policyDigest, engineDigest: admission.engineDigest, expiresAt: admission.expiresAt, transport: Object.freeze({ inputFd: 3, acknowledgementFd: 4, closesBeforeCandidateSpawn: true }) });
+
+function digest(bytes) {
+  return createHash('sha256').update(bytes).digest('hex');
+}
+
+function validString(value) {
+  return typeof value === 'string' && value.length > 0;
+}
+
+/**
+ * Service-only closure factory. It has no public issuer that accepts caller
+ * project/check/run tuples: CheckService supplies an opaque registered-plan
+ * handle to stateForPlan and this module serializes only that captured state.
+ */
+export function createCandidateSourceBootstrapRuntimeV2({ stateForPlan, now = () => new Date() } = {}) {
+  if (typeof stateForPlan !== 'function') throw new TypeError('stateForPlan is required');
+  const attempts = new WeakMap();
+
+  function create(plan) {
+    const state = stateForPlan(plan);
+    if (!state || typeof state !== 'object') fail('Registered candidate plan is unavailable', 'CANDIDATE_NATIVE_ADMISSION_REQUIRED');
+    const required = ['admissionId', 'leaseId', 'checkId', 'policyBytes', 'policyDigest', 'engine', 'subject', 'artifactManifest', 'expiresAt'];
+    for (const key of required) if (!Object.hasOwn(state, key)) fail('Registered candidate plan is incomplete', 'CANDIDATE_NATIVE_ADMISSION_INVALID', { key });
+    if (!Buffer.isBuffer(state.policyBytes) || state.policyBytes.length === 0 || state.policyBytes.length > 1024 * 1024
+      || !SHA256.test(state.policyDigest) || digest(state.policyBytes) !== state.policyDigest
+      || !validString(state.admissionId) || !validString(state.leaseId) || !validString(state.checkId)
+      || !Number.isSafeInteger(state.runGeneration) || !Number.isSafeInteger(state.guardGeneration)
+      || Number.isNaN(Date.parse(state.expiresAt))) fail('Registered candidate plan is invalid', 'CANDIDATE_NATIVE_ADMISSION_INVALID');
+    const handle = Object.freeze({});
+    attempts.set(handle, { state, used: false, closed: false, nonce: randomBytes(32).toString('base64url') });
+    return handle;
+  }
+
+  function open(handle) {
+    const attempt = attempts.get(handle);
+    if (!attempt || attempt.used || attempt.closed) fail('Candidate admission is unavailable or replayed', 'CANDIDATE_NATIVE_ADMISSION_REPLAY');
+    if (Date.parse(attempt.state.expiresAt) <= now().getTime()) {
+      attempt.closed = true;
+      fail('Candidate admission expired', 'CANDIDATE_NATIVE_ADMISSION_EXPIRED');
+    }
+    attempt.used = true;
+    const { state } = attempt;
+    const frame = Buffer.from(JSON.stringify({
+      schema: ADMISSION_SCHEMA, version: 2, admissionId: state.admissionId, leaseId: state.leaseId,
+      checkId: state.checkId, runGeneration: state.runGeneration, guardGeneration: state.guardGeneration,
+      policyBytesBase64: state.policyBytes.toString('base64'), policyDigest: state.policyDigest,
+      engine: state.engine, subject: state.subject, artifactManifest: state.artifactManifest,
+      receiptAdapterAdmission: null,
+    }), 'utf8');
+    if (frame.length > MAX_FRAME_BYTES) fail('Candidate parent admission frame exceeds its bound', 'CANDIDATE_NATIVE_ADMISSION_INVALID');
+    return Object.freeze({ frame, acknowledgement: Buffer.from(`${ACK_SCHEMA}\n${state.admissionId}\n${state.policyDigest}\n`, 'utf8'), nonce: attempt.nonce });
+  }
+
+  function acknowledgeAndClose(handle, acknowledgement) {
+    const attempt = attempts.get(handle);
+    if (!attempt || !attempt.used || attempt.closed || !Buffer.isBuffer(acknowledgement)) fail('Candidate acknowledgement is unavailable', 'CANDIDATE_NATIVE_ADMISSION_REPLAY');
+    const expected = Buffer.from(`${ACK_SCHEMA}\n${attempt.state.admissionId}\n${attempt.state.policyDigest}\n`, 'utf8');
+    if (!acknowledgement.equals(expected)) fail('Candidate parent acknowledgement mismatches admission', 'CANDIDATE_PARENT_ACK_MISMATCH');
+    attempt.closed = true;
+    return Object.freeze({ admissionFdsClosed: true, receiptEligible: false });
+  }
+
+  function cancel(handle) {
+    const attempt = attempts.get(handle);
+    if (!attempt || attempt.used || attempt.closed) fail('Candidate admission is unavailable', 'CANDIDATE_NATIVE_ADMISSION_REPLAY');
+    attempt.closed = true;
+  }
+
+  return Object.freeze({ create, open, acknowledgeAndClose, cancel });
 }
diff --git a/src/checks/candidate-source-execution.mjs b/src/checks/candidate-source-execution.mjs
index 30151d8..5f52511 100644
--- a/src/checks/candidate-source-execution.mjs
+++ b/src/checks/candidate-source-execution.mjs
@@ -1,15 +1,61 @@
 import { spawnSync } from 'node:child_process';
-import { isAbsolute } from 'node:path';
 import { TorchError } from '../kernel/errors.mjs';
-import { verifyCandidateInputSnapshotV2 } from './candidate-input-snapshot.mjs';
-const fail = (message, code, details) => { throw new TorchError(message, { code, details }); };
+
 export const CANDIDATE_EXECUTION_LIMITS_V2 = Object.freeze({ timeoutMs: 300000, maxOutputBytes: 1048576, maxArgs: 64, maxArgBytes: 4096 });
-function bound(value, limit, name) { if (typeof value !== 'string' || Buffer.byteLength(value, 'utf8') > limit) fail('Candidate execution value is invalid', 'CANDIDATE_EXECUTION_INVALID', { name }); return value; }
-export function runCandidateSourceExecutionV2({ command, args = [], inputSnapshot, environment = {}, executor = spawnSync, limits = CANDIDATE_EXECUTION_LIMITS_V2 } = {}) {
-  if (!isAbsolute(command) || inputSnapshot?.schema !== 'torch.dev/candidate-input-snapshot/v2alpha1' || typeof executor !== 'function' || !Array.isArray(args) || args.length > limits.maxArgs || Object.keys(environment).some((key) => ['PATH', 'HOME', 'NODE_PATH', 'npm_config_cache'].includes(key))) fail('Candidate execution request is invalid', 'CANDIDATE_EXECUTION_INVALID');
-  verifyCandidateInputSnapshotV2(inputSnapshot);
-  const safeArgs = args.map((arg) => bound(arg, limits.maxArgBytes, 'arg')); const env = Object.freeze(Object.fromEntries(Object.entries(environment).sort()));
-  let raw; try { raw = executor(command, safeArgs, { cwd: inputSnapshot.inputRoot, env, encoding: 'buffer', stdio: ['ignore', 'pipe', 'pipe'], timeout: limits.timeoutMs, maxBuffer: limits.maxOutputBytes, killSignal: 'SIGTERM' }); } catch (error) { raw = { status: null, error }; }
-  const stdout = Buffer.from(raw?.stdout ?? ''); const stderr = Buffer.from(raw?.stderr ?? ''); const overflow = stdout.length > limits.maxOutputBytes || stderr.length > limits.maxOutputBytes || raw?.error?.code === 'ENOBUFS'; const timeout = raw?.error?.code === 'ETIMEDOUT' || raw?.timedOut === true;
-  return Object.freeze({ schema: 'torch.dev/candidate-source-execution/v2alpha1', terminal: Object.freeze({ kind: timeout ? 'timeout' : overflow ? 'overflow' : raw?.signal ? 'signal' : raw?.error ? 'error' : 'exit', exitStatus: Number.isInteger(raw?.status) ? raw.status : null, signal: raw?.signal ?? null, overflow, timeout, success: !timeout && !overflow && !raw?.signal && !raw?.error && raw?.status === 0 }), output: Object.freeze({ stdout: stdout.subarray(0, limits.maxOutputBytes), stderr: stderr.subarray(0, limits.maxOutputBytes) }) });
+
+function fail(message, code, details) {
+  throw new TorchError(message, { code, details });
+}
+
+function validRuntime(state) {
+  const runtime = state?.runtime;
+  if (!runtime || typeof runtime.command !== 'string' || !runtime.command.startsWith('/') || !Array.isArray(runtime.args)
+    || !runtime.args.every((arg) => typeof arg === 'string' && Buffer.byteLength(arg, 'utf8') <= CANDIDATE_EXECUTION_LIMITS_V2.maxArgBytes)
+    || runtime.args.length > CANDIDATE_EXECUTION_LIMITS_V2.maxArgs
+    || !runtime.environment || Object.keys(runtime.environment).some((key) => ['PATH', 'HOME', 'NODE_PATH', 'npm_config_cache'].includes(key))) {
+    fail('Candidate fixed runtime is invalid', 'CANDIDATE_EXECUTION_RUNTIME_INVALID');
+  }
+  return runtime;
+}
+
+/**
+ * Runs a fixed, CheckService-derived E binding. `run` takes only an opaque
+ * attempt; command, arguments, environment, executor, cwd and limits cannot
+ * be selected by callers. It is raw terminal evidence, never a receipt PASS.
+ */
+export function createCandidateSourceExecutionRuntimeV2({ stateForAttempt, snapshotRuntime } = {}) {
+  if (typeof stateForAttempt !== 'function' || !snapshotRuntime) throw new TypeError('candidate execution runtime is incomplete');
+  const results = new WeakMap();
+  function run(attempt) {
+    const state = stateForAttempt(attempt);
+    const runtime = validRuntime(state);
+    snapshotRuntime.verify(attempt);
+    const cwd = snapshotRuntime.cwd(attempt);
+    let raw;
+    try {
+      raw = spawnSync(runtime.command, runtime.args, {
+        cwd, env: Object.freeze({ ...runtime.environment }), encoding: 'buffer',
+        stdio: ['ignore', 'pipe', 'pipe'], timeout: CANDIDATE_EXECUTION_LIMITS_V2.timeoutMs,
+        maxBuffer: CANDIDATE_EXECUTION_LIMITS_V2.maxOutputBytes, killSignal: 'SIGTERM',
+      });
+    } catch (error) { raw = { status: null, error }; }
+    const stdout = Buffer.from(raw?.stdout ?? '');
+    const stderr = Buffer.from(raw?.stderr ?? '');
+    const overflow = stdout.length > CANDIDATE_EXECUTION_LIMITS_V2.maxOutputBytes || stderr.length > CANDIDATE_EXECUTION_LIMITS_V2.maxOutputBytes || raw?.error?.code === 'ENOBUFS';
+    const timeout = raw?.error?.code === 'ETIMEDOUT' || raw?.timedOut === true;
+    const observation = Object.freeze({
+      schema: 'torch.dev/candidate-source-execution/v2alpha1',
+      terminal: Object.freeze({ kind: timeout ? 'timeout' : overflow ? 'overflow' : raw?.signal ? 'signal' : raw?.error ? 'error' : 'exit', exitStatus: Number.isInteger(raw?.status) ? raw.status : null, signal: raw?.signal ?? null, overflow, timeout, success: !timeout && !overflow && !raw?.signal && !raw?.error && raw?.status === 0 }),
+      output: Object.freeze({ stdout: stdout.subarray(0, CANDIDATE_EXECUTION_LIMITS_V2.maxOutputBytes), stderr: stderr.subarray(0, CANDIDATE_EXECUTION_LIMITS_V2.maxOutputBytes) }),
+    });
+    snapshotRuntime.verify(attempt);
+    results.set(attempt, observation);
+    return observation;
+  }
+  function observation(attempt) {
+    const value = results.get(attempt);
+    if (!value) fail('Candidate execution has not run', 'CANDIDATE_EXECUTION_UNAVAILABLE');
+    return value;
+  }
+  return Object.freeze({ run, observation });
 }
diff --git a/test/fleet/candidate-execution-fence.test.mjs b/test/fleet/candidate-execution-fence.test.mjs
index 7b7590c..00d6ad1 100644
--- a/test/fleet/candidate-execution-fence.test.mjs
+++ b/test/fleet/candidate-execution-fence.test.mjs
@@ -1,5 +1,13 @@
 import assert from 'node:assert/strict';
 import test from 'node:test';
-import { createCandidateExecutionFenceV2, observeCandidateExecutionFenceV2 } from '../../src/checks/candidate-execution-fence.mjs';
-const bootstrap = { nonce: 'n', transport: { closesBeforeCandidateSpawn: true } };
-test('SCN-candidate-fence-closure: double-fork/escaped-descendant uncertainty is UNKNOWN, never terminal proof', () => { const fence = createCandidateExecutionFenceV2({ bootstrap }); const unknown = observeCandidateExecutionFenceV2({ fence, observation: { privatePid1: true, namespaceObserved: true, admissionFdsClosed: true, descendantsReaped: false } }); assert.equal(unknown.outcome, 'unknown'); assert.equal(unknown.terminalProof, false); const terminal = observeCandidateExecutionFenceV2({ fence, observation: { privatePid1: true, namespaceObserved: true, admissionFdsClosed: true, descendantsReaped: true } }); assert.equal(terminal.terminalProof, true); });
+import { createCandidateExecutionFenceRuntimeV2 } from '../../src/checks/candidate-execution-fence.mjs';
+
+test('SCN-candidate-fence-closure: a closed opaque attempt without backend namespace/reaping evidence is UNKNOWN and clones cannot be reused', () => {
+  const states = new WeakMap(); const attempt = Object.freeze({}); states.set(attempt, { authenticated: true });
+  const fence = createCandidateExecutionFenceRuntimeV2({ stateForAttempt: (value) => states.get(value), backendObservation: () => null });
+  assert.throws(() => fence.close({}), { code: 'CANDIDATE_FENCE_UNAVAILABLE' });
+  fence.close(attempt); const terminal = fence.terminal(attempt);
+  assert.equal(terminal.outcome, 'unknown'); assert.equal(terminal.terminalProof, false);
+  assert.throws(() => fence.terminal({ ...attempt }), { code: 'CANDIDATE_FENCE_UNAVAILABLE' });
+  assert.throws(() => fence.close(attempt), { code: 'CANDIDATE_FENCE_UNAVAILABLE' });
+});
diff --git a/test/fleet/candidate-input-consumption.test.mjs b/test/fleet/candidate-input-consumption.test.mjs
index 3aac9fb..6ab8ca0 100644
--- a/test/fleet/candidate-input-consumption.test.mjs
+++ b/test/fleet/candidate-input-consumption.test.mjs
@@ -1,10 +1,28 @@
 import assert from 'node:assert/strict';
-import { chmodSync, mkdirSync, mkdtempSync, readFileSync, writeFileSync } from 'node:fs';
+import { chmodSync, mkdirSync, mkdtempSync, realpathSync, writeFileSync } from 'node:fs';
 import { tmpdir } from 'node:os';
 import { join } from 'node:path';
 import test from 'node:test';
-import { captureCandidateInputSnapshotV2, verifyCandidateInputSnapshotV2 } from '../../src/checks/candidate-input-snapshot.mjs';
-import { runCandidateSourceExecutionV2 } from '../../src/checks/candidate-source-execution.mjs';
-function roots() { const root = mkdtempSync(join(tmpdir(), 'torch-b2-source-')); mkdirSync(join(root, 'src')); writeFileSync(join(root, 'src', 'input.txt'), 'captured'); return { root, snapshot: `${root}-snapshot` }; }
-test('SCN-candidate-input-consumption: child execution seam receives frozen cwd bytes after original source mutation', () => { const { root, snapshot: destination } = roots(); const input = captureCandidateInputSnapshotV2({ sourceRoot: root, destinationRoot: destination, paths: ['src'] }); writeFileSync(join(root, 'src', 'input.txt'), 'mutated'); const result = runCandidateSourceExecutionV2({ command: process.execPath, args: [], inputSnapshot: input, executor: (_command, _args, execution) => ({ status: 0, stdout: readFileSync(join(execution.cwd, 'src', 'input.txt')) }) }); assert.equal(result.terminal.success, true); assert.equal(result.output.stdout.toString(), 'captured'); assert.equal(verifyCandidateInputSnapshotV2(input).verified, true); });
-test('SCN-candidate-input-drift: frozen-input mutation refuses rather than relabeling evidence', () => { const { root, snapshot: destination } = roots(); const input = captureCandidateInputSnapshotV2({ sourceRoot: root, destinationRoot: destination, paths: ['src'] }); const file = join(input.inputRoot, 'src', 'input.txt'); chmodSync(file, 0o600); writeFileSync(file, 'drift'); assert.throws(() => verifyCandidateInputSnapshotV2(input), { code: 'CANDIDATE_SNAPSHOT_DRIFT' }); });
+import { createCandidateInputSnapshotRuntimeV2 } from '../../src/checks/candidate-input-snapshot.mjs';
+import { createCandidateSourceExecutionRuntimeV2 } from '../../src/checks/candidate-source-execution.mjs';
+
+function attemptWithInput() {
+  const root = mkdtempSync(join(tmpdir(), 'torch-b2-source-')); mkdirSync(join(root, 'src')); writeFileSync(join(root, 'src', 'input.txt'), 'captured');
+  const states = new WeakMap(); const attempt = Object.freeze({});
+  states.set(attempt, { input: { sourceRoot: root, destinationRoot: `${root}-snapshot`, paths: ['src'] }, runtime: { command: realpathSync(process.execPath), args: ['-e', 'process.stdout.write(require("node:fs").readFileSync("src/input.txt"))'], environment: {} } });
+  return { root, attempt, states };
+}
+
+test('SCN-candidate-input-consumption: an actual fixed Node child reads frozen bytes after the original source mutates', () => {
+  const { root, attempt, states } = attemptWithInput();
+  const snapshots = createCandidateInputSnapshotRuntimeV2({ stateForAttempt: (value) => states.get(value) });
+  snapshots.capture(attempt); writeFileSync(join(root, 'src', 'input.txt'), 'mutated');
+  const execution = createCandidateSourceExecutionRuntimeV2({ stateForAttempt: (value) => states.get(value), snapshotRuntime: snapshots }).run(attempt);
+  assert.equal(execution.terminal.success, true); assert.equal(execution.output.stdout.toString(), 'captured');
+});
+
+test('SCN-candidate-input-drift: a post-capture mutation refuses before a real child can be launched', () => {
+  const { attempt, states } = attemptWithInput(); const snapshots = createCandidateInputSnapshotRuntimeV2({ stateForAttempt: (value) => states.get(value) });
+  snapshots.capture(attempt); const file = join(snapshots.cwd(attempt), 'src', 'input.txt'); chmodSync(file, 0o600); writeFileSync(file, 'drift');
+  assert.throws(() => createCandidateSourceExecutionRuntimeV2({ stateForAttempt: (value) => states.get(value), snapshotRuntime: snapshots }).run(attempt), { code: 'CANDIDATE_SNAPSHOT_DRIFT' });
+});
diff --git a/test/fleet/candidate-snapshot-policy.test.mjs b/test/fleet/candidate-snapshot-policy.test.mjs
index 61c2352..19a8887 100644
--- a/test/fleet/candidate-snapshot-policy.test.mjs
+++ b/test/fleet/candidate-snapshot-policy.test.mjs
@@ -3,5 +3,12 @@ import { mkdtempSync, symlinkSync, writeFileSync } from 'node:fs';
 import { tmpdir } from 'node:os';
 import { join } from 'node:path';
 import test from 'node:test';
-import { captureCandidateInputSnapshotV2 } from '../../src/checks/candidate-input-snapshot.mjs';
-test('SCN-candidate-snapshot-policy: product links and S caps refuse before a snapshot is admitted', () => { const root = mkdtempSync(join(tmpdir(), 'torch-b2-policy-')); writeFileSync(join(root, 'file'), 'x'); symlinkSync('file', join(root, 'link')); assert.throws(() => captureCandidateInputSnapshotV2({ sourceRoot: root, destinationRoot: `${root}-snapshot`, paths: ['link'] }), { code: 'CANDIDATE_SNAPSHOT_LINK_REJECTED' }); });
+import { createCandidateInputSnapshotRuntimeV2 } from '../../src/checks/candidate-input-snapshot.mjs';
+
+test('SCN-candidate-snapshot-policy: an opaque service attempt still refuses product links before capture', () => {
+  const root = mkdtempSync(join(tmpdir(), 'torch-b2-policy-')); writeFileSync(join(root, 'file'), 'x'); symlinkSync('file', join(root, 'link'));
+  const states = new WeakMap(); const attempt = Object.freeze({}); states.set(attempt, { input: { sourceRoot: root, destinationRoot: `${root}-snapshot`, paths: ['link'] } });
+  const snapshots = createCandidateInputSnapshotRuntimeV2({ stateForAttempt: (value) => states.get(value) });
+  assert.throws(() => snapshots.capture(attempt), { code: 'CANDIDATE_SNAPSHOT_LINK_REJECTED' });
+  assert.throws(() => snapshots.capture(Object.freeze({})), { code: 'CANDIDATE_SNAPSHOT_ADMISSION_REQUIRED' });
+});
diff --git a/test/fleet/candidate-source-bootstrap.test.mjs b/test/fleet/candidate-source-bootstrap.test.mjs
index 95116dc..f496762 100644
--- a/test/fleet/candidate-source-bootstrap.test.mjs
+++ b/test/fleet/candidate-source-bootstrap.test.mjs
@@ -1,12 +1,28 @@
 import assert from 'node:assert/strict';
+import { createHash } from 'node:crypto';
 import test from 'node:test';
-import { issueCandidateNativeAdmissionV2, openCandidateSourceBootstrapV2 } from '../../src/checks/candidate-source-bootstrap.mjs';
+import { createCandidateSourceBootstrapRuntimeV2 } from '../../src/checks/candidate-source-bootstrap.mjs';
 
-const issued = (expiresAt = '2030-01-01T00:00:00.000Z') => issueCandidateNativeAdmissionV2({ projectId: 'project', areaId: 'work-integration', checkId: 'test', runId: 'run', generation: 'g1', policyDigest: 'a'.repeat(64), engineDigest: 'b'.repeat(64), expiresAt });
-test('SCN-candidate-bootstrap-one-shot: only issued native admission opens once and supplies no authority handles', () => {
-  assert.throws(() => openCandidateSourceBootstrapV2({}), { code: 'CANDIDATE_NATIVE_ADMISSION_REPLAY' });
-  const admission = issued(); const bootstrap = openCandidateSourceBootstrapV2(admission, { now: () => new Date('2029-01-01T00:00:00.000Z') });
-  assert.equal(bootstrap.transport.closesBeforeCandidateSpawn, true); assert.deepEqual(Object.keys(bootstrap).sort(), ['engineDigest', 'expiresAt', 'generation', 'nonce', 'policyDigest', 'runId', 'schema', 'transport']);
-  assert.equal(Object.hasOwn(bootstrap, 'controlPlane'), false); assert.throws(() => openCandidateSourceBootstrapV2(admission, { now: () => new Date('2029-01-01T00:00:00.000Z') }), { code: 'CANDIDATE_NATIVE_ADMISSION_REPLAY' });
+function planState(expiresAt = '2030-01-01T00:00:00.000Z') {
+  const policyBytes = Buffer.from('policy\n');
+  return { admissionId: 'admission-1', leaseId: 'lease-1', checkId: 'test', runGeneration: 1, guardGeneration: 1, policyBytes, policyDigest: createHash('sha256').update(policyBytes).digest('hex'), engine: { pre: {}, post: {} }, subject: {}, artifactManifest: { schema: 'torch.dev/artifact-manifest/v1alpha1', manifestSha256: 'a'.repeat(64) }, expiresAt };
+}
+
+test('SCN-candidate-bootstrap-one-shot: only a service-issued opaque plan opens once and its observed FD acknowledgement closes it', () => {
+  const states = new WeakMap(); const plan = Object.freeze({}); states.set(plan, planState());
+  const runtime = createCandidateSourceBootstrapRuntimeV2({ stateForPlan: (value) => states.get(value), now: () => new Date('2029-01-01T00:00:00.000Z') });
+  assert.throws(() => runtime.create(Object.freeze({})), { code: 'CANDIDATE_NATIVE_ADMISSION_REQUIRED' });
+  const handle = runtime.create(plan); const clone = { ...handle };
+  assert.throws(() => runtime.open(clone), { code: 'CANDIDATE_NATIVE_ADMISSION_REPLAY' });
+  const channel = runtime.open(handle);
+  assert.equal(JSON.parse(channel.frame).receiptAdapterAdmission, null);
+  runtime.acknowledgeAndClose(handle, channel.acknowledgement);
+  assert.throws(() => runtime.open(handle), { code: 'CANDIDATE_NATIVE_ADMISSION_REPLAY' });
+  assert.throws(() => runtime.acknowledgeAndClose(handle, channel.acknowledgement), { code: 'CANDIDATE_NATIVE_ADMISSION_REPLAY' });
+});
+
+test('SCN-candidate-bootstrap-expiry: an expired service plan refuses before a parent frame is made', () => {
+  const states = new WeakMap(); const plan = Object.freeze({}); states.set(plan, planState('2020-01-01T00:00:00.000Z'));
+  const runtime = createCandidateSourceBootstrapRuntimeV2({ stateForPlan: (value) => states.get(value) });
+  assert.throws(() => runtime.open(runtime.create(plan)), { code: 'CANDIDATE_NATIVE_ADMISSION_EXPIRED' });
 });
-test('SCN-candidate-bootstrap-expiry: expired admission refuses before any child protocol exists', () => assert.throws(() => openCandidateSourceBootstrapV2(issued('2020-01-01T00:00:00.000Z')), { code: 'CANDIDATE_NATIVE_ADMISSION_EXPIRED' }));
diff --git a/test/fleet/candidate-source-execution.test.mjs b/test/fleet/candidate-source-execution.test.mjs
index 11b5f0e..c3b0025 100644
--- a/test/fleet/candidate-source-execution.test.mjs
+++ b/test/fleet/candidate-source-execution.test.mjs
@@ -1,9 +1,16 @@
 import assert from 'node:assert/strict';
-import { mkdtempSync, writeFileSync } from 'node:fs';
+import { mkdtempSync, realpathSync, writeFileSync } from 'node:fs';
 import { tmpdir } from 'node:os';
 import { join } from 'node:path';
 import test from 'node:test';
-import { captureCandidateInputSnapshotV2 } from '../../src/checks/candidate-input-snapshot.mjs';
-import { runCandidateSourceExecutionV2 } from '../../src/checks/candidate-source-execution.mjs';
-function snapshot() { const source = mkdtempSync(join(tmpdir(), 'torch-b2-execution-')); writeFileSync(join(source, 'input'), 'x'); return captureCandidateInputSnapshotV2({ sourceRoot: source, destinationRoot: `${source}-snapshot`, paths: ['input'] }); }
-test('SCN-candidate-execution-boundary: ambient PATH/HOME fallback and output overflow cannot become success', () => { const frozen = snapshot(); assert.throws(() => runCandidateSourceExecutionV2({ command: process.execPath, inputSnapshot: frozen, environment: { PATH: '/bin' } }), { code: 'CANDIDATE_EXECUTION_INVALID' }); const observed = runCandidateSourceExecutionV2({ command: process.execPath, inputSnapshot: frozen, limits: { timeoutMs: 1000, maxOutputBytes: 4, maxArgs: 64, maxArgBytes: 4096 }, executor: () => ({ status: 0, stdout: Buffer.from('xxxxxxxx') }) }); assert.equal(observed.terminal.overflow, true); assert.equal(observed.terminal.success, false); });
+import { createCandidateInputSnapshotRuntimeV2 } from '../../src/checks/candidate-input-snapshot.mjs';
+import { createCandidateSourceExecutionRuntimeV2 } from '../../src/checks/candidate-source-execution.mjs';
+
+test('SCN-candidate-execution-boundary: only fixed E is run and actual zero-exit output overflow is not success', () => {
+  const root = mkdtempSync(join(tmpdir(), 'torch-b2-execution-')); writeFileSync(join(root, 'input'), 'x');
+  const states = new WeakMap(); const attempt = Object.freeze({});
+  states.set(attempt, { input: { sourceRoot: root, destinationRoot: `${root}-snapshot`, paths: ['input'] }, runtime: { command: realpathSync(process.execPath), args: ['-e', 'process.stdout.write("x".repeat(1048577))'], environment: {} } });
+  const snapshots = createCandidateInputSnapshotRuntimeV2({ stateForAttempt: (value) => states.get(value) }); snapshots.capture(attempt);
+  const result = createCandidateSourceExecutionRuntimeV2({ stateForAttempt: (value) => states.get(value), snapshotRuntime: snapshots }).run(attempt);
+  assert.equal(result.terminal.overflow, true); assert.equal(result.terminal.success, false);
+});
diff --git a/test/fleet/candidate-source-parent.test.mjs b/test/fleet/candidate-source-parent.test.mjs
index b1c426b..bf3c7d4 100644
--- a/test/fleet/candidate-source-parent.test.mjs
+++ b/test/fleet/candidate-source-parent.test.mjs
@@ -1,8 +1,14 @@
 import assert from 'node:assert/strict';
+import { createHash } from 'node:crypto';
 import test from 'node:test';
-import { issueCandidateNativeAdmissionV2, openCandidateSourceBootstrapV2 } from '../../src/checks/candidate-source-bootstrap.mjs';
-test('SCN-candidate-parent-capability: bootstrap frame carries only a bound tuple, never roots, env, writers, adapters, or receipt authority', () => {
-  const ticket = issueCandidateNativeAdmissionV2({ projectId: 'p', areaId: 'a', checkId: 'c', runId: 'r', generation: 'g', policyDigest: 'a'.repeat(64), engineDigest: 'b'.repeat(64), expiresAt: '2030-01-01T00:00:00.000Z' });
-  const frame = openCandidateSourceBootstrapV2(ticket, { now: () => new Date('2029-01-01T00:00:00.000Z') });
-  for (const forbidden of ['projectId', 'areaId', 'checkId', 'inputRoot', 'cwd', 'environment', 'writer', 'adapter', 'receipt']) assert.equal(Object.hasOwn(frame, forbidden), false);
+import { createCandidateSourceBootstrapRuntimeV2 } from '../../src/checks/candidate-source-bootstrap.mjs';
+
+test('SCN-candidate-parent-capability: the private FD3 record carries M only and reserves A as null', () => {
+  const policyBytes = Buffer.from('policy\n'); const states = new WeakMap(); const plan = Object.freeze({});
+  states.set(plan, { admissionId: 'admission-2', leaseId: 'lease-2', checkId: 'test', runGeneration: 1, guardGeneration: 2, policyBytes, policyDigest: createHash('sha256').update(policyBytes).digest('hex'), engine: { pre: {}, post: {} }, subject: {}, artifactManifest: { schema: 'torch.dev/artifact-manifest/v1alpha1', manifestSha256: 'a'.repeat(64) }, expiresAt: '2030-01-01T00:00:00.000Z' });
+  const runtime = createCandidateSourceBootstrapRuntimeV2({ stateForPlan: (value) => states.get(value), now: () => new Date('2029-01-01T00:00:00.000Z') });
+  const frame = JSON.parse(runtime.open(runtime.create(plan)).frame);
+  for (const forbidden of ['root', 'cwd', 'environment', 'writer', 'adapter', 'receipt', 'command', 'executor']) assert.equal(Object.hasOwn(frame, forbidden), false);
+  assert.equal(frame.receiptAdapterAdmission, null);
+  assert.deepEqual(Object.keys(frame.artifactManifest).sort(), ['manifestSha256', 'schema']);
 });