diff --git a/scripts/e2e-shard-reuse.ts b/scripts/e2e-shard-reuse.ts
new file mode 100644
index 000000000..692d89250
--- /dev/null
+++ b/scripts/e2e-shard-reuse.ts
@@ -0,0 +1,186 @@
+/**
+ * Verified first-attempt reuse for PR-lane E2E shards, on the same receipts as
+ * the workflow-judge reuse (scripts/eval-input-cache.ts).
+ *
+ * A PR-profile shard (a file, or one case of a case-sharded file) is reused
+ * only when every consumed input is byte-identical to a fresh pass recorded in
+ * this PR within the receipt age:
+ *   - files: the test file's literal import closure (helpers, fixtures loaded
+ *     as modules, installed packages), every tracked file matched by the
+ *     touchfile patterns of every case the file registers, the global
+ *     touchfiles, the paid runner and this module, the workflow and its setup
+ *     actions, bun.lock and the CI Dockerfile;
+ *   - prompts: the test source that builds each selected case's prompt;
+ *   - parameters: case ids, name pattern, expected count, retries, wall,
+ *     within-shard concurrency, tier/profile, the root package without its
+ *     release label, and every EVALS_/GSTACK_/CLAUDE_/ANTHROPIC_/... variable
+ *     the child receives (secrets contribute presence only);
+ *   - runtime: the immutable CI image manifest, Bun, Node, OS/arch and the
+ *     Claude CLI version.
+ * Anything unknown fails closed: a computed case registration, a touchfile
+ * pattern matching no tracked file, retries other than zero (a retried pass
+ * cannot prove its first attempt), custom preload/endpoints, missing scope,
+ * or a lane other than the PR gate. Failures are never stored; the weekly
+ * census, marathon and release lanes always execute fresh.
+ */
+import * as fs from 'node:fs';
+import * as path from 'node:path';
+import { spawnSync } from 'node:child_process';
+import { buildEvalInputIdentity, lookupEvalInputCache, sourceDependencyClosure, storeEvalInputCache,
+  type EvalCacheValue, type EvalInputIdentity, type EvalPassingProof } from './eval-input-cache';
+import { matchGlob } from '../test/helpers/test-selection';
+import { E2E_TOUCHFILES, GLOBAL_TOUCHFILES } from '../test/helpers/touchfiles-data';
+
+export interface E2EShardReuseRequest {
+  root: string;
+  /** Shard key: `<file>` or `<file>#<case id>`. */
+  key: string;
+  file: string;
+  /** Selected case ids this shard executes (the PR profile's exact expectation). */
+  caseIds: string[];
+  /** Every E2E id the file registers; all of their touchfiles are consumed inputs. */
+  registeredIds: string[];
+  registrationKnown: boolean;
+  casePattern: string;
+  expectedCases: number;
+  retries: number;
+  timeoutMs: number;
+  withinShardConcurrency: number;
+  tier: string;
+  profile: string;
+  /** The exact environment the child receives. */
+  env: NodeJS.ProcessEnv;
+}
+
+export interface E2EShardReuseHit { key: string; source: EvalPassingProof['source'] }
+
+const HARNESS_FILES = ['scripts/test-paid-shards.ts', 'scripts/e2e-shard-reuse.ts', 'scripts/eval-input-cache.ts',
+  'lib/eval-model.ts', 'bun.lock', '.github/docker/Dockerfile.ci', '.github/workflows/evals.yml',
+  '.github/actions/fix-bun-temp/action.yml', '.github/actions/restore-deps/action.yml',
+  '.github/actions/seed-claude-config/action.yml', '.github/actions/register-gstack-skills/action.yml'];
+const ENV_PREFIXES = ['EVALS_', 'GSTACK_', 'CLAUDE_', 'ANTHROPIC_', 'OPENAI_', 'GEMINI_', 'BUN_', 'NODE_', 'PLAYWRIGHT_'];
+/** Run-scoped values: provenance or transport, never behavior. Selection is bound as case ids. */
+const RUN_SCOPED_ENV = new Set(['EVALS_RUN_ID', 'GSTACK_EVAL_DIR', 'EVALS_CACHE_DIR', 'EVALS_CACHE_PR', 'EVALS_CACHE_REPOSITORY',
+  'EVALS_CACHE_RUNTIME_ID', 'EVALS_CACHE_PURPOSE', 'EVALS_SELECTION_JSON', 'EVALS_JUDGE_SELECTION_JSON']);
+const SECRET_ENV = /KEY|TOKEN|SECRET|PASSWORD|CREDENTIAL/;
+
+/** The reuse-relevant environment the child sees; secrets contribute presence only. */
+export function e2eReuseEnvironment(env: NodeJS.ProcessEnv): Record<string, string> {
+  return Object.fromEntries(Object.keys(env).sort()
+    .filter(name => (ENV_PREFIXES.some(prefix => name.startsWith(prefix)) || ['PATH', 'HOME'].includes(name)) && !RUN_SCOPED_ENV.has(name))
+    .map(name => [name, SECRET_ENV.test(name) ? 'set' : env[name] ?? '']));
+}
+
+/** Why reuse cannot apply to this lane or environment, else null. */
+export function e2eReuseLaneProblem(env: NodeJS.ProcessEnv, profileMode: string | undefined): string | null {
+  const pr = Number(env.EVALS_CACHE_PR);
+  if (profileMode !== 'pr') return 'Only the fast PR profile reuses results';
+  if (!env.EVALS_CACHE_DIR || !env.EVALS_CACHE_REPOSITORY || !Number.isSafeInteger(pr) || pr <= 0) return 'No trusted same-PR cache scope';
+  if (!/^(?:sha256:)?[a-f0-9]{64}$/.test(env.EVALS_CACHE_RUNTIME_ID ?? '')) return 'No immutable runtime identity';
+  if (env.EVALS_TIER !== 'gate' || env.EVALS_FRESH === '1') return 'Fresh validation requested';
+  if (['release', 'periodic', 'marathon'].includes(env.EVALS_CACHE_PURPOSE ?? '')) return 'Scheduled and release lanes execute fresh';
+  if (env.NODE_OPTIONS || env.BUN_OPTIONS) return 'Preload options change execution outside the consumed source';
+  if (env.ANTHROPIC_BASE_URL && env.ANTHROPIC_BASE_URL !== 'https://api.anthropic.com') return 'Custom model endpoint';
+  return null;
+}
+
+function trackedFiles(root: string): string[] {
+  const listed = spawnSync('git', ['ls-files', '-z'], { cwd: root, encoding: 'utf8', timeout: 10_000, maxBuffer: 64 * 1024 * 1024 });
+  if (listed.status !== 0) throw new Error('Cannot list tracked files');
+  return listed.stdout.split('\0').filter(Boolean);
+}
+
+/**
+ * Every repository file one shard consumes: the test's import closure plus the
+ * harness closure, and every tracked file the registered cases' touchfiles and
+ * the global touchfiles match. Throws when a pattern matches nothing (unknown).
+ */
+export function e2eShardInputFiles(request: Pick<E2EShardReuseRequest, 'root' | 'file' | 'registeredIds'>): string[] {
+  const tracked = trackedFiles(request.root);
+  const declared = new Set<string>();
+  for (const pattern of new Set([...request.registeredIds.flatMap(id => E2E_TOUCHFILES[id] ?? []), ...GLOBAL_TOUCHFILES])) {
+    const matches = tracked.filter(file => matchGlob(file, pattern));
+    if (!matches.length) throw new Error(`Touchfile pattern matches no tracked file: ${pattern}`);
+    for (const file of matches) declared.add(file);
+  }
+  const closure = sourceDependencyClosure(request.root, [request.file, ...HARNESS_FILES]);
+  return [...new Set([...closure, ...declared])].filter(file => file !== 'package.json').sort();
+}
+
+/** The consumed input identity of one PR shard, or why it is ineligible. */
+export function e2eShardIdentity(request: E2EShardReuseRequest): { status: 'eligible'; identity: EvalInputIdentity } | { status: 'ineligible'; reason: string } {
+  try {
+    if (!/^test\/skill-e2e-.+\.test\.ts$/.test(request.file) || /overlay-harness/.test(request.file)) return { status: 'ineligible', reason: 'Not an audited E2E file' };
+    if (!request.registrationKnown || !request.registeredIds.length) return { status: 'ineligible', reason: 'Case registration is not statically complete' };
+    if (!request.caseIds.length || request.caseIds.length !== request.expectedCases || request.caseIds.some(id => !request.registeredIds.includes(id))) {
+      return { status: 'ineligible', reason: 'Selected cases are not exactly known' };
+    }
+    if (request.retries !== 0) return { status: 'ineligible', reason: 'A retried pass cannot prove its first attempt' };
+    const files = e2eShardInputFiles(request);
+    const { version: _releaseLabel, ...rootPackage } = JSON.parse(fs.readFileSync(path.join(request.root, 'package.json'), 'utf8'));
+    const source = fs.readFileSync(path.join(request.root, request.file), 'utf8');
+    const env = request.env;
+    const result = buildEvalInputIdentity({
+      root: request.root,
+      scope: { repository: env.EVALS_CACHE_REPOSITORY!, pullRequest: Number(env.EVALS_CACHE_PR) },
+      coverage: { dependencies: 'complete', prompts: 'complete', environment: 'complete' }, unknownDependencies: [],
+      files,
+      prompts: Object.fromEntries(request.caseIds.map(id => [id, source])),
+      parameters: { rootPackage, key: request.key, caseIds: [...request.caseIds].sort(), casePattern: request.casePattern,
+        expectedCases: request.expectedCases, retries: request.retries, timeoutMs: request.timeoutMs,
+        withinShardConcurrency: request.withinShardConcurrency, tier: request.tier, profile: request.profile,
+        environment: e2eReuseEnvironment(env) },
+      runtime: { image: env.EVALS_CACHE_RUNTIME_ID!, bun: Bun.version, node: process.versions.node,
+        platform: process.platform, arch: process.arch, claudeCli: claudeCliVersion(env) },
+    });
+    return result;
+  } catch (error) {
+    return { status: 'ineligible', reason: error instanceof Error ? error.message : 'Cannot identify consumed inputs' };
+  }
+}
+
+function claudeCliVersion(env: NodeJS.ProcessEnv): string {
+  const version = spawnSync('claude', ['--version'], { encoding: 'utf8', timeout: 5_000, env });
+  const line = version.status === 0 ? version.stdout.split('\n')[0]!.trim() : '';
+  if (!line) throw new Error('Claude CLI version is unknown');
+  return line;
+}
+
+const validResult = (identity: EvalInputIdentity, key: string) => (value: EvalCacheValue) =>
+  !!value && typeof value === 'object' && !Array.isArray(value)
+  && value.key === key && JSON.stringify(value.cases) === JSON.stringify(identity.caseIds);
+
+/**
+ * Prepare reuse for one shard: `lookup` returns a verified receipt for these
+ * exact inputs; `publish` stores a receipt after a fresh first-attempt pass
+ * whose inputs did not change during execution.
+ */
+export function prepareE2EShardReuse(request: E2EShardReuseRequest): {
+  lookup(): E2EShardReuseHit | null;
+  publish(): void;
+} | null {
+  if (e2eReuseLaneProblem(request.env, 'pr') !== null) return null;
+  const before = e2eShardIdentity(request);
+  if (before.status !== 'eligible') return null;
+  const common = { cacheDir: request.env.EVALS_CACHE_DIR!, purpose: 'gate' as const };
+  return {
+    lookup() {
+      const found = lookupEvalInputCache({ ...common, identity: before.identity, validateResult: validResult(before.identity, request.key) });
+      return found.status === 'reused' ? { key: found.key, source: found.source } : null;
+    },
+    publish() {
+      const after = e2eShardIdentity(request);
+      const env = request.env;
+      const runId = env.GITHUB_RUN_ID ? `${env.GITHUB_RUN_ID}/${env.GITHUB_RUN_ATTEMPT ?? '1'}` : env.EVALS_RUN_ID;
+      const revision = spawnSync('git', ['rev-parse', 'HEAD'], { cwd: request.root, encoding: 'utf8', timeout: 3_000 });
+      if (after.status !== 'eligible' || !runId || revision.status !== 0) return;
+      storeEvalInputCache({ ...common, before: before.identity, after: after.identity, proof: {
+        execution: 'new', finalized: true, completeAttemptHistory: true, exitCode: 0, timedOut: false,
+        cancelled: false, skipped: 0, failed: 0, passed: before.identity.caseIds.length,
+        cases: before.identity.caseIds.map(id => ({ id, outcome: 'passed' as const, attempt: 1 as const })),
+        source: { runId, revision: revision.stdout.trim(), completedAt: Date.now() },
+        result: { key: request.key, cases: before.identity.caseIds },
+      } });
+    },
+  };
+}
diff --git a/scripts/eval-input-cache.ts b/scripts/eval-input-cache.ts
index e4ecdbb7b..9b489d2bb 100644
--- a/scripts/eval-input-cache.ts
+++ b/scripts/eval-input-cache.ts
@@ -16,9 +16,50 @@
  */
 import * as fs from 'node:fs';
 import * as path from 'node:path';
+import { isBuiltin } from 'node:module';
 import { createHash } from 'node:crypto';
 import { atomicWriteSync } from '../lib/fs-atomic';
 
+/**
+ * Follow literal module imports from `entries` (repo-relative) without
+ * executing them, including installed package bytes and the package.json that
+ * governs each resolved module; root bunfig/tsconfig/jsconfig are included
+ * when present. The root package.json is left to the caller, which hashes its
+ * semantic fields without the release version label.
+ */
+export function sourceDependencyClosure(root: string, entries: string[]): string[] {
+  const seen = new Set<string>();
+  const scan = new Bun.Transpiler({ loader: 'tsx' });
+  const visit = (file: string) => {
+    file = path.resolve(file);
+    const relative = path.relative(root, file).split(path.sep).join('/');
+    if (relative.startsWith('../') || path.isAbsolute(relative)) throw new Error('Dependency outside checkout');
+    if (relative === 'package.json') return;
+    if (seen.has(relative)) return;
+    seen.add(relative);
+    const source = fs.readFileSync(file, 'utf8');
+    if (!/\.[cm]?[jt]sx?$/.test(file)) return;
+    // Entrypoint scripts carry hashbangs, which scanImports does not accept.
+    // Strip only for parsing; buildEvalInputIdentity still hashes the full file.
+    for (const entry of scan.scanImports(source.replace(/^#![^\n]*(?:\n|$)/, '\n'))) {
+      if (isBuiltin(entry.path) || entry.path.startsWith('bun:')) continue;
+      const resolved = Bun.resolveSync(entry.path, path.dirname(file));
+      visit(resolved);
+      // Package export maps/defaults affect resolution independently of code.
+      let directory = path.dirname(resolved);
+      while (directory !== root && directory.startsWith(root + path.sep)) {
+        const manifest = path.join(directory, 'package.json');
+        if (fs.existsSync(manifest)) { visit(manifest); break; }
+        directory = path.dirname(directory);
+      }
+    }
+  };
+  for (const file of entries) visit(path.join(root, file));
+  for (const file of ['bunfig.toml', 'tsconfig.json', 'jsconfig.json'])
+    if (fs.existsSync(path.join(root, file))) visit(path.join(root, file));
+  return [...seen].sort();
+}
+
 export const EVAL_CACHE_MAX_AGE_MS = 24 * 60 * 60 * 1000;
 export const EVAL_CACHE_RESULT_MAX_BYTES = 16 * 1024;
 const SCHEMA = 1;
@@ -49,7 +90,7 @@ export type EvalInputIdentityResult =
   | { status: 'eligible'; identity: EvalInputIdentity }
   | { status: 'ineligible'; reason: string };
 export interface EvalCachePolicy {
-  purpose: 'gate' | 'periodic' | 'release';
+  purpose: 'gate' | 'periodic' | 'release' | 'marathon';
   fresh?: boolean;
   now?: number;
   maxAgeMs?: number;
@@ -146,7 +187,7 @@ function validIdentity(value: unknown): value is EvalInputIdentity {
     && canonical(value.caseIds) === canonical(sorted(value.caseIds));
 }
 function bypass(policy: EvalCachePolicy): string | null {
-  if (policy.purpose !== 'gate') return 'Periodic and release validation must execute fresh';
+  if (policy.purpose !== 'gate') return 'Periodic, marathon and release validation must execute fresh';
   if (policy.fresh) return 'Fresh validation requested';
   if (!positive(policy.now ?? Date.now()) || !positive(policy.maxAgeMs ?? EVAL_CACHE_MAX_AGE_MS)) return 'Invalid cache age policy';
   return null;
diff --git a/test/helpers/workflow-judge-cache.ts b/test/helpers/workflow-judge-cache.ts
index db9733e15..0b421567a 100644
--- a/test/helpers/workflow-judge-cache.ts
+++ b/test/helpers/workflow-judge-cache.ts
@@ -1,13 +1,12 @@
 /** Audited cache adapter for runWorkflowJudge only. Native/PTY evals stay fresh. */
 import * as fs from 'node:fs';
 import * as path from 'node:path';
-import { isBuiltin } from 'node:module';
 import { spawnSync } from 'node:child_process';
 import { DEFAULT_JUDGE_MAX_TOKENS, resolveEvalModel } from '../../lib/eval-model';
 import { JUDGE_MS } from './eval-budgets';
 import type { JudgeScore } from './llm-judge';
 import { readWorkflowJudgeInput, buildWorkflowJudgePrompt, WORKFLOW_JUDGE_RESPONSE_SCHEMA, WORKFLOW_JUDGE_REASONING_WORD_LIMIT } from './workflow-judge-input';
-import { buildEvalInputIdentity, lookupEvalInputCache, storeEvalInputCache,
+import { buildEvalInputIdentity, lookupEvalInputCache, sourceDependencyClosure, storeEvalInputCache,
   type EvalCacheValue, type EvalInputIdentity, type EvalPassingProof } from '../../scripts/eval-input-cache';
 
 type Thresholds = { clarity: number; completeness: number; actionability: number };
@@ -25,44 +24,13 @@ export interface WorkflowJudgeReuse {
   key: string; source: EvalPassingProof['source'];
 }
 
-/** Follow literal module imports, including installed SDK bytes, without executing them. */
+/** The judge's audited closure: its runner, rubric and documents, installed SDK bytes included. */
 export function workflowJudgeDependencies(root: string, documents: string[]): string[] {
-  const seen = new Set<string>();
-  const scan = new Bun.Transpiler({ loader: 'tsx' });
-  const visit = (file: string) => {
-    file = path.resolve(file);
-    const relative = path.relative(root, file).split(path.sep).join('/');
-    if (relative.startsWith('../') || path.isAbsolute(relative)) throw new Error('Dependency outside checkout');
-    // Root version labels collector output only; its remaining semantic fields
-    // are hashed separately. Installed package manifests remain byte-exact.
-    if (relative === 'package.json') return;
-    if (seen.has(relative)) return;
-    seen.add(relative);
-    const source = fs.readFileSync(file, 'utf8');
-    if (!/\.[cm]?[jt]sx?$/.test(file)) return;
-    // Entrypoint scripts carry hashbangs, which scanImports does not accept.
-    // Strip only for parsing; buildEvalInputIdentity still hashes the full file.
-    for (const entry of scan.scanImports(source.replace(/^#![^\n]*(?:\n|$)/, '\n'))) {
-      if (isBuiltin(entry.path) || entry.path.startsWith('bun:')) continue;
-      const resolved = Bun.resolveSync(entry.path, path.dirname(file));
-      visit(resolved);
-      // Package export maps/defaults affect resolution independently of code.
-      let directory = path.dirname(resolved);
-      while (directory !== root && directory.startsWith(root + path.sep)) {
-        const manifest = path.join(directory, 'package.json');
-        if (fs.existsSync(manifest)) { visit(manifest); break; }
-        directory = path.dirname(directory);
-      }
-    }
-  };
-  for (const file of ['test/skill-llm-eval.test.ts', 'test/helpers/workflow-judge-cache.ts',
+  return sourceDependencyClosure(root, ['test/skill-llm-eval.test.ts', 'test/helpers/workflow-judge-cache.ts',
     'test/helpers/llm-judge.ts', 'lib/eval-model.ts', 'test/helpers/eval-budgets.ts',
     'scripts/test-paid-shards.ts', 'scripts/test-strict-output.ts', 'scripts/eval-select.ts',
     'scripts/test-pr-profile.ts', '.github/workflows/evals.yml',
-    'package.json', 'bun.lock', '.github/docker/Dockerfile.ci', ...documents]) visit(path.join(root, file));
-  for (const file of ['bunfig.toml', 'tsconfig.json', 'jsconfig.json'])
-    if (fs.existsSync(path.join(root, file))) visit(path.join(root, file));
-  return [...seen].sort();
+    'package.json', 'bun.lock', '.github/docker/Dockerfile.ci', ...documents]);
 }
 
 export function validWorkflowJudgeScore(value: EvalCacheValue, thresholds: Thresholds, structuredResponse = false): value is JudgeScore & EvalCacheValue {