diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index f4200857..dab40bbe 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -31,4 +31,4 @@ jobs:
       contents: read
     # Caller выбирает revision, который чекаутит worker, включая код PR. Сам код
     # считается недоверенным и исполняется только внутри одноразовой ячейки.
-    uses: Labpics-Team/lab-colors/.github/workflows/ci-worker.yml@1461bc2ed60142aed3a8723e618b883be6418156
+    uses: Labpics-Team/lab-colors/.github/workflows/ci-worker.yml@beecd257371a7a6421079b0d8207a109969aa332
diff --git a/packages/colors/bench/private-program-wasm.json b/packages/colors/bench/private-program-wasm.json
new file mode 100644
index 00000000..8c647b94
--- /dev/null
+++ b/packages/colors/bench/private-program-wasm.json
@@ -0,0 +1,33 @@
+{
+  "schemaVersion": 1,
+  "role": "private-program-consumer",
+  "artifact": "packages/colors/private-program/labcolors_private_program.wasm",
+  "toolchain": {
+    "rust": "1.96.0",
+    "rustcCommit": "ac68faa20c58cbccd01ee7208bf3b6e93a7d7f96",
+    "cargo": "1.96.0",
+    "cargoCommit": "30a34c6821b57de0aaec83a901aca39f88f6778c",
+    "target": "wasm32-unknown-unknown",
+    "profile": "release",
+    "feature": "private-fixture",
+    "node": "24.14.0",
+    "binaryenRelease": "version_117",
+    "binaryenNodeArchiveSha256": "2d5a42f2d167a7cc2b4b6664c44c5ace1690d13db4f527324f052afbad461a07",
+    "binaryenComponentSha256": {
+      "wasm-opt.js": "c0b4bc26f1a588dc686ae36b32c4fea3d7b99f4fb8a1778d0ba4129f326f8449",
+      "wasm-opt.wasm": "d823328d8fcad3a59aa605c61d1620d30b9156f086d30ff3246b43c32526856b",
+      "wasm-opt.worker.js": "5b7952731f6ea1d5954db968e45b13f862853e6ef14a03b3f35d036f6136b624"
+    },
+    "wasmOptFlags": "-Oz --enable-bulk-memory --enable-nontrapping-float-to-int"
+  },
+  "measurement": {
+    "source": "github-actions-run-31473003387",
+    "platform": "linux-x64",
+    "rawBytes": 339336
+  },
+  "policy": {
+    "maxRawBytes": 339336,
+    "basis": "exact optimized private Program artifact from GitHub Actions Linux",
+    "gzip": "diagnostic-only"
+  }
+}
diff --git a/packages/colors/test/javascript-source-contract.mjs b/packages/colors/test/javascript-source-contract.mjs
new file mode 100644
index 00000000..684ebfd9
--- /dev/null
+++ b/packages/colors/test/javascript-source-contract.mjs
@@ -0,0 +1,89 @@
+function tokens(source) {
+  const result = [];
+  for (let index = 0; index < source.length; ) {
+    const character = source[index];
+    const next = source[index + 1];
+    if (/\s/u.test(character)) {
+      index += 1;
+    } else if (character === "/" && next === "/") {
+      index = source.indexOf("\n", index + 2);
+      if (index === -1) break;
+    } else if (character === "/" && next === "*") {
+      index = source.indexOf("*/", index + 2);
+      if (index === -1) throw new Error("unterminated JavaScript block comment");
+      index += 2;
+    } else if (character === '"' || character === "'") {
+      const quote = character;
+      const start = index;
+      index += 1;
+      while (index < source.length && source[index] !== quote) {
+        index += source[index] === "\\" ? 2 : 1;
+      }
+      if (index >= source.length) throw new Error("unterminated JavaScript string literal");
+      const raw = source.slice(start, index + 1);
+      result.push({ type: "string", value: quote === '"' ? JSON.parse(raw) : raw.slice(1, -1) });
+      index += 1;
+    } else if (character === "`") {
+      index += 1;
+      while (index < source.length && source[index] !== "`") {
+        index += source[index] === "\\" ? 2 : 1;
+      }
+      if (index >= source.length) throw new Error("unterminated JavaScript template literal");
+      index += 1;
+    } else if (/[A-Za-z_$]/u.test(character)) {
+      const start = index;
+      index += 1;
+      while (/[A-Za-z0-9_$]/u.test(source[index] ?? "")) index += 1;
+      result.push({ type: "identifier", value: source.slice(start, index) });
+    } else {
+      result.push({ type: "punctuator", value: character });
+      index += 1;
+    }
+  }
+  return result;
+}
+
+export function chromeArguments(source) {
+  const sourceTokens = tokens(source);
+  for (let index = 0; index < sourceTokens.length - 4; index += 1) {
+    if (
+      sourceTokens[index].type !== "string" ||
+      sourceTokens[index].value !== "goog:chromeOptions" ||
+      sourceTokens[index + 1].value !== ":" ||
+      sourceTokens[index + 2].value !== "{"
+    ) {
+      continue;
+    }
+    let objectDepth = 1;
+    for (let cursor = index + 3; cursor < sourceTokens.length && objectDepth > 0; cursor += 1) {
+      const token = sourceTokens[cursor];
+      if (token.value === "{") objectDepth += 1;
+      if (token.value === "}") objectDepth -= 1;
+      if (
+        objectDepth === 1 &&
+        token.type === "identifier" &&
+        token.value === "args" &&
+        sourceTokens[cursor + 1]?.value === ":" &&
+        sourceTokens[cursor + 2]?.value === "["
+      ) {
+        const args = [];
+        let nestedDepth = 0;
+        let element = [];
+        for (let argument = cursor + 3; argument < sourceTokens.length; argument += 1) {
+          const argumentToken = sourceTokens[argument];
+          if (nestedDepth === 0 && (argumentToken.value === "," || argumentToken.value === "]")) {
+            if (element.length === 1 && element[0].type === "string") args.push(element[0].value);
+            element = [];
+            if (argumentToken.value === "]") return args;
+            continue;
+          }
+          if (["[", "{", "("].includes(argumentToken.value)) nestedDepth += 1;
+          if (["]", "}", ")"].includes(argumentToken.value)) nestedDepth -= 1;
+          element.push(argumentToken);
+        }
+        throw new Error("unterminated goog:chromeOptions args array");
+      }
+    }
+  }
+  throw new Error("goog:chromeOptions args array is absent");
+}
diff --git a/packages/colors/test/private-program-ci-contract.test.mjs b/packages/colors/test/private-program-ci-contract.test.mjs
index e8b33213..f0282737 100644
--- a/packages/colors/test/private-program-ci-contract.test.mjs
+++ b/packages/colors/test/private-program-ci-contract.test.mjs
@@ -12,12 +12,14 @@ import { dirname, join, resolve } from "node:path";
 import { test } from "node:test";
 import { fileURLToPath } from "node:url";
 
+import { chromeArguments } from "./javascript-source-contract.mjs";
+
 const here = dirname(fileURLToPath(import.meta.url));
 const root = resolve(here, "../../..");
 const read = (...parts) => readFileSync(join(root, ...parts), "utf8");
 const normalizeNewlines = (value) => value.replaceAll("\r\n", "\n");
 
-const CALLER_WORKER_SHA = "1461bc2ed60142aed3a8723e618b883be6418156";
+const CALLER_WORKER_SHA = "beecd257371a7a6421079b0d8207a109969aa332";
 const CALLER_WORKER_REFERENCE =
   `    uses: Labpics-Team/lab-colors/.github/workflows/ci-worker.yml@${CALLER_WORKER_SHA}`;
 const RUNTIME_BUDGET_COMMAND = "        run: node scripts/check-wasm-size-budget.mjs";
@@ -182,12 +184,15 @@ function assertPrivateMutationDeadline(workflow) {
   assert.ok(70 > 40 + 20 + 5, "outer timeout must exceed declared budgets and teardown headroom");
 }
 
-test("Stage A keeps the public caller pinned to the pre-Stage-B immutable worker", () => {
+test("Stage B activates the public caller at the merged Stage A worker commit", () => {
   const caller = read(".github", "workflows", "ci.yml");
   assertImmutableCaller(caller);
 
   for (const mutation of [
     caller.replace(CALLER_WORKER_SHA, "0".repeat(40)),
+    caller.replace(CALLER_WORKER_SHA, "main"),
+    caller.replace(CALLER_WORKER_SHA, CALLER_WORKER_SHA.slice(0, 12)),
+    caller.replace(CALLER_WORKER_REFERENCE, ""),
     caller.replace(CALLER_WORKER_REFERENCE, `${CALLER_WORKER_REFERENCE}\n${CALLER_WORKER_REFERENCE}`),
     caller.replace(
       CALLER_WORKER_REFERENCE,
@@ -261,6 +266,20 @@ test("worker binds the browser proof to the exact verified tarball bytes", () =>
   assert.throws(() => assertWorkerOrderAndRoles(reordered));
 });
 
+test("private Program browser proof owns the CI Chrome launch invariant", () => {
+  const browserProof = read("scripts", "test-private-program-browser.mjs");
+  assert.ok(
+    chromeArguments(browserProof).includes("--no-sandbox"),
+    "the userspace CfT proof must opt out of an unavailable host sandbox",
+  );
+  const flagInCommentOnly = browserProof.replace(
+    '                  "--no-sandbox",',
+    '                  // "--no-sandbox",',
+  );
+  assert.notEqual(flagInCommentOnly, browserProof);
+  assert.equal(chromeArguments(flagInCommentOnly).includes("--no-sandbox"), false);
+});
+
 test("private mutation keeps its own deadline reachable inside the wasm job", () => {
   const worker = read(".github", "workflows", "ci-worker.yml");
   assertPrivateMutationDeadline(worker);
diff --git a/packages/colors/test/private-program-mutation-contract.test.mjs b/packages/colors/test/private-program-mutation-contract.test.mjs
index bb4e2c74..28ca6f45 100644
--- a/packages/colors/test/private-program-mutation-contract.test.mjs
+++ b/packages/colors/test/private-program-mutation-contract.test.mjs
@@ -1,7 +1,7 @@
 import assert from "node:assert/strict";
 import { createHash } from "node:crypto";
 import { readFileSync } from "node:fs";
-import { mkdir, mkdtemp, rm, symlink, writeFile } from "node:fs/promises";
+import { lstat, mkdir, mkdtemp, readdir, rm, symlink, writeFile } from "node:fs/promises";
 import { tmpdir } from "node:os";
 import { join } from "node:path";
 import test from "node:test";
@@ -16,6 +16,7 @@ import {
   parseMutationTimeoutPolicy,
   validateMutationWasm,
 } from "../../../scripts/test-private-program-mutations.mjs";
+import { copyDeclaredCargoRegistryIndex } from "../../../scripts/build-private-program.mjs";
 
 const EXPECTED_MUTATIONS = Object.freeze([
   [
@@ -24,7 +25,7 @@ const EXPECTED_MUTATIONS = Object.freeze([
     "rust-wasm",
     "crates/labcolors-core/src/private_fixture.rs",
     "6d43e030e5d6f4df67b319276d3d9ea1ab33d5b91a2094019ce278476cecd412",
-    "PrivateProgramConsumerError: private Program run failed with status 6",
+    "PrivateProgramConsumerError: private Program consumer: run failed with status 6",
   ],
   [
     "hard-constraint-deletion",
@@ -32,7 +33,7 @@ const EXPECTED_MUTATIONS = Object.freeze([
     "rust-wasm",
     "crates/labcolors-core/src/private_fixture.rs",
     "0e43717331468ae6fb6c65bb6ba441cd5260b49b37ad3c6927a9bbf02494638b",
-    "PrivateProgramConsumerError: private Program run failed with status 6",
+    "PrivateProgramConsumerError: private Program consumer: run failed with status 6",
   ],
   [
     "final-recheck-call-edge-deletion",
@@ -40,7 +41,7 @@ const EXPECTED_MUTATIONS = Object.freeze([
     "rust-wasm",
     "crates/labcolors-core/src/program_session.rs",
     "8e218fddef0b8a13f044b91b7927faeb50e501a54ecb205c05696d6510fe615e",
-    "PrivateProgramConsumerError: private Program run failed with status 8",
+    "PrivateProgramConsumerError: private Program consumer: run failed with status 8",
   ],
   [
     "session-observed-update-bypass",
@@ -48,7 +49,7 @@ const EXPECTED_MUTATIONS = Object.freeze([
     "rust-wasm",
     "crates/labcolors-core/src/private_fixture.rs",
     "8770e1a30407e9cd9ec3ee32feed44cd2b58a0d39be3c636cb428be8b1c472fe",
-    "PrivateProgramConsumerError: shipping trace permits exactly one SetAll callback",
+    "PrivateProgramConsumerError: private Program consumer: shipping trace permits exactly one SetAll callback",
   ],
   [
     "external-attachment-handoff-binding-bypass",
@@ -56,7 +57,7 @@ const EXPECTED_MUTATIONS = Object.freeze([
     "rust-wasm",
     "crates/labcolors-core/src/private_fixture.rs",
     "59f5bc640fbc270db4dbbda5572e339c90aa839d61cab0ac155ef8db5e1e5d59",
-    "PrivateProgramConsumerError: private Program run failed with status 7",
+    "PrivateProgramConsumerError: private Program consumer: run failed with status 7",
   ],
   [
     "javascript-publish-deletion",
@@ -64,7 +65,7 @@ const EXPECTED_MUTATIONS = Object.freeze([
     "javascript",
     "packages/colors/private-program/consumer.js",
     "354125be94020475d0e34beb0f4498474cf243adb89d3bb591589ff5d485af0b",
-    "Error: private Program browser fixture: computed background is the exact expected CSS literal",
+    "Error: private Program browser fixture: computed background is the exact expected CSS literal; expected \"rgba(64, 64, 64, 0.5)\", got \"rgba(0, 0, 0, 0)\"",
   ],
 ]);
 
@@ -73,6 +74,20 @@ const CI_WORKER = readFileSync(
   "utf8",
 );
 
+const directoryLinkType = process.platform === "win32" ? "junction" : "dir";
+
+async function assertTreeContainsNoLinks(root) {
+  const pending = [root];
+  while (pending.length > 0) {
+    const directory = pending.pop();
+    for (const entry of await readdir(directory, { withFileTypes: true })) {
+      const path = join(directory, entry.name);
+      assert.equal(entry.isSymbolicLink(), false, `copied registry index contains a link: ${path}`);
+      if (entry.isDirectory()) pending.push(path);
+    }
+  }
+}
+
 test("private Program mutation IDs bind six exact source transformations", () => {
   assert.deepEqual(
     PRIVATE_PROGRAM_MUTATION_CASES.map(
@@ -154,6 +169,147 @@ test("exact source mutation rejects missing, repeated, and no-op anchors", () =>
   );
 });
 
+test("isolated offline mutation builds copy the declared Cargo registry index", async () => {
+  const temporary = await mkdtemp(join(tmpdir(), "labcolors-mutation-cargo-index-"));
+  const declaredCargoHome = join(temporary, "declared-cargo");
+  const isolatedCargoHome = join(temporary, "isolated-cargo");
+  try {
+    await mkdir(join(declaredCargoHome, "registry", "index", "registry.example"), {
+      recursive: true,
+    });
+    await writeFile(
+      join(declaredCargoHome, "registry", "index", "registry.example", "config.json"),
+      "{}\n",
+    );
+    await copyDeclaredCargoRegistryIndex(isolatedCargoHome, { declaredCargoHome });
+    assert.equal(
+      readFileSync(
+        join(isolatedCargoHome, "registry", "index", "registry.example", "config.json"),
+        "utf8",
+      ),
+      "{}\n",
+    );
+  } finally {
+    await rm(temporary, { recursive: true, force: true });
+  }
+});
+
+test("isolated Cargo index materializes a symlinked index root", async () => {
+  const temporary = await mkdtemp(join(tmpdir(), "labcolors-mutation-cargo-index-root-link-"));
+  const declaredCargoHome = join(temporary, "declared-cargo");
+  const physicalIndex = join(temporary, "physical-index");
+  const isolatedCargoHome = join(temporary, "isolated-cargo");
+  try {
+    await mkdir(join(declaredCargoHome, "registry"), { recursive: true });
+    await mkdir(join(physicalIndex, "registry.example"), { recursive: true });
+    await writeFile(join(physicalIndex, "registry.example", "config.json"), "{}\n");
+    await symlink(physicalIndex, join(declaredCargoHome, "registry", "index"), directoryLinkType);
+
+    await copyDeclaredCargoRegistryIndex(isolatedCargoHome, { declaredCargoHome });
+
+    const copiedIndex = join(isolatedCargoHome, "registry", "index");
+    assert.equal((await lstat(copiedIndex)).isSymbolicLink(), false);
+    await assertTreeContainsNoLinks(copiedIndex);
+  } finally {
+    await rm(temporary, { recursive: true, force: true });
+  }
+});
+
+test("isolated Cargo index accepts a symlinked declared-home ancestor", async () => {
+  const temporary = await mkdtemp(join(tmpdir(), "labcolors-mutation-cargo-index-ancestor-link-"));
+  const physicalCargoHome = join(temporary, "physical-cargo");
+  const declaredCargoHome = join(temporary, "declared-cargo-link");
+  const sourceIndex = join(physicalCargoHome, "registry", "index");
+  const isolatedCargoHome = join(temporary, "isolated-cargo");
+  try {
+    await mkdir(join(sourceIndex, "registry.example", "snapshot"), { recursive: true });
+    await writeFile(join(sourceIndex, "registry.example", "snapshot", "config.json"), "{}\n");
+    await symlink(
+      join(sourceIndex, "registry.example", "snapshot"),
+      join(sourceIndex, "registry.example", "current"),
+      directoryLinkType,
+    );
+    await symlink(physicalCargoHome, declaredCargoHome, directoryLinkType);
+
+    await copyDeclaredCargoRegistryIndex(isolatedCargoHome, { declaredCargoHome });
+
+    assert.equal(
+      readFileSync(
+        join(isolatedCargoHome, "registry", "index", "registry.example", "current", "config.json"),
+        "utf8",
+      ),
+      "{}\n",
+    );
+  } finally {
+    await rm(temporary, { recursive: true, force: true });
+  }
+});
+
+test("isolated Cargo index materializes contained source links", async () => {
+  const temporary = await mkdtemp(join(tmpdir(), "labcolors-mutation-cargo-index-target-links-"));
+  const declaredCargoHome = join(temporary, "declared-cargo");
+  const sourceIndex = join(declaredCargoHome, "registry", "index");
+  const isolatedCargoHome = join(temporary, "isolated-cargo");
+  try {
+    await mkdir(join(sourceIndex, "registry.example", "snapshot"), { recursive: true });
+    await writeFile(join(sourceIndex, "registry.example", "snapshot", "config.json"), "{}\n");
+    await symlink(
+      join(sourceIndex, "registry.example", "snapshot"),
+      join(sourceIndex, "registry.example", "current"),
+      directoryLinkType,
+    );
+
+    await copyDeclaredCargoRegistryIndex(isolatedCargoHome, { declaredCargoHome });
+
+    await assertTreeContainsNoLinks(join(isolatedCargoHome, "registry", "index"));
+  } finally {
+    await rm(temporary, { recursive: true, force: true });
+  }
+});
+
+test("isolated Cargo index rejects a source link escaping the declared index", async () => {
+  const temporary = await mkdtemp(join(tmpdir(), "labcolors-mutation-cargo-index-escape-"));
+  const declaredCargoHome = join(temporary, "declared-cargo");
+  const sourceIndex = join(declaredCargoHome, "registry", "index");
+  const outside = join(temporary, "outside-index");
+  const isolatedCargoHome = join(temporary, "isolated-cargo");
+  try {
+    await mkdir(join(sourceIndex, "registry.example"), { recursive: true });
+    await mkdir(outside, { recursive: true });
+    await writeFile(join(outside, "config.json"), "{}\n");
+    await symlink(outside, join(sourceIndex, "registry.example", "escape"), directoryLinkType);
+
+    await assert.rejects(
+      copyDeclaredCargoRegistryIndex(isolatedCargoHome, { declaredCargoHome }),
+      /symlink resolves outside the declared Cargo index/u,
+    );
+  } finally {
+    await rm(temporary, { recursive: true, force: true });
+  }
+});
+
+test("isolated Cargo index rejects a dangling source link", async () => {
+  const temporary = await mkdtemp(join(tmpdir(), "labcolors-mutation-cargo-index-dangling-"));
+  const declaredCargoHome = join(temporary, "declared-cargo");
+  const sourceIndex = join(declaredCargoHome, "registry", "index");
+  const isolatedCargoHome = join(temporary, "isolated-cargo");
+  try {
+    await mkdir(join(sourceIndex, "registry.example"), { recursive: true });
+    await symlink(
+      join(sourceIndex, "missing"),
+      join(sourceIndex, "registry.example", "dangling"),
+      directoryLinkType,
+    );
+
+    await assert.rejects(
+      copyDeclaredCargoRegistryIndex(isolatedCargoHome, { declaredCargoHome }),
+      /registry index symlink is dangling/u,
+    );
+  } finally {
+    await rm(temporary, { recursive: true, force: true });
+  }
+});
+
 test("a mutation kill requires its real-browser assertion and semantic marker", () => {
   const definition = PRIVATE_PROGRAM_MUTATION_CASES[0];
   const killed = Object.freeze({
@@ -162,7 +318,7 @@ test("a mutation kill requires its real-browser assertion and semantic marker",
     stdout: "",
     stderr:
       "Error: private Program browser proof: browser assertion failed: " +
-      "PrivateProgramConsumerError: private Program run failed with status 6",
+      "PrivateProgramConsumerError: private Program consumer: run failed with status 6",
   });
   assert.equal(assertMutationSpecificBrowserFailure(definition, killed), true);
   assert.throws(
@@ -189,7 +345,7 @@ test("a mutation kill requires its real-browser assertion and semantic marker",
         ...killed,
         stderr: "private Program browser proof: browser assertion failed: wrong failure",
       }),
-    /mutation-specific failure evidence/u,
+    /mutation-specific failure evidence: expected=.*actual=/u,
   );
   assert.throws(
     () =>
diff --git a/packages/colors/test/release-contract.test.mjs b/packages/colors/test/release-contract.test.mjs
index 52786006..42b1ab9a 100644
--- a/packages/colors/test/release-contract.test.mjs
+++ b/packages/colors/test/release-contract.test.mjs
@@ -52,6 +52,7 @@ import {
   POINT_SUPPORT_EVIDENCE_FILES,
   WCAG22_EVIDENCE_FILES,
 } from "../../../scripts/release-evidence.mjs";
+import { chromeArguments } from "./javascript-source-contract.mjs";
 
 const here = dirname(fileURLToPath(import.meta.url));
 const root = resolve(here, "../../..");
@@ -2174,6 +2175,16 @@ test("the atomic output sink has one bounded pinned-Chrome browser gate", () =>
     assert.match(source, /const chromeDriverPath = await executableFromEnv\("CHROMEDRIVER_PATH"\);/u);
     assert.match(source, /startChromeDriver\(\s*chromeDriverPath,/u);
     assert.match(source, /binary: chromePath,/u);
+    assert.ok(
+      chromeArguments(source).includes("--no-sandbox"),
+      "the userspace CfT proof must opt out of an unavailable host sandbox",
+    );
+    const flagOutsideChromeArguments = source.replace(
+      '                  "--no-sandbox",',
+      '                  "--window-size=800,600",\n                  // "--no-sandbox"',
+    );
+    assert.notEqual(flagOutsideChromeArguments, source);
+    assert.equal(chromeArguments(flagOutsideChromeArguments).includes("--no-sandbox"), false);
     assert.match(source, /spawn\(executable, \["--port=0"\]/u);
     assert.match(
       source,
diff --git a/scripts/build-private-program.mjs b/scripts/build-private-program.mjs
index 30c0c827..48f1c278 100644
--- a/scripts/build-private-program.mjs
+++ b/scripts/build-private-program.mjs
@@ -944,6 +944,22 @@ export async function assertCanonicalCargoConfigurationAbsent(options = {}) {
   return true;
 }
 
+export async function copyDeclaredCargoRegistryIndex(
+  cargoHome,
+  { declaredCargoHome = resolve(environmentValue(process.env, "CARGO_HOME")?.trim() || join(homedir(), ".cargo")) } = {},
+) {
+  const sourceIndex = resolve(declaredCargoHome, "registry", "index");
+  const targetIndex = resolve(cargoHome, "registry", "index");
+  let canonicalSourceIndex;
+  try {
+    canonicalSourceIndex = await realpath(sourceIndex);
+  } catch (error) {
+    fail(`cannot resolve declared Cargo registry index ${sourceIndex}: ${error.message}`);
+  }
+  await assertRegistryIndexLinksContained(canonicalSourceIndex);
+  await cp(canonicalSourceIndex, targetIndex, { recursive: true, dereference: true });
+}
+
 async function assertRegistryIndexLinksContained(root) {
   const pending = [root];
   while (pending.length > 0) {
@@ -984,14 +1000,8 @@ async function createBuildSandbox({ canonical }) {
   await mkdir(temporaryDirectory, { recursive: true, mode: 0o700 });
   if (canonical) {
     await mkdir(cargoHome, { recursive: true, mode: 0o700 });
-    const declaredCargoHome = resolve(
-      environmentValue(process.env, "CARGO_HOME")?.trim() || join(homedir(), ".cargo"),
-    );
-    const sourceIndex = resolve(declaredCargoHome, "registry", "index");
-    const targetIndex = resolve(cargoHome, "registry", "index");
     try {
-      await assertRegistryIndexLinksContained(sourceIndex);
-      await cp(sourceIndex, targetIndex, { recursive: true });
+      await copyDeclaredCargoRegistryIndex(cargoHome);
     } catch (error) {
       fail(`canonical build requires the declared Cargo registry index: ${error.message}`);
     }
diff --git a/scripts/test-browser-output-sink.mjs b/scripts/test-browser-output-sink.mjs
index ff5750a1..e7d5536a 100644
--- a/scripts/test-browser-output-sink.mjs
+++ b/scripts/test-browser-output-sink.mjs
@@ -1335,6 +1335,7 @@ async function main() {
                   "--disable-sync",
                   "--metrics-recording-only",
                   "--no-first-run",
+                  "--no-sandbox",
                   "--window-size=800,600",
                 ],
               },
diff --git a/scripts/test-private-program-browser.mjs b/scripts/test-private-program-browser.mjs
index e8039f8a..63abf4a7 100644
--- a/scripts/test-private-program-browser.mjs
+++ b/scripts/test-private-program-browser.mjs
@@ -614,6 +614,7 @@ async function main() {
                   "--disable-sync",
                   "--metrics-recording-only",
                   "--no-first-run",
+                  "--no-sandbox",
                   "--no-proxy-server",
                   "--password-store=basic",
                   "--safebrowsing-disable-auto-update",
diff --git a/scripts/test-private-program-mutations.mjs b/scripts/test-private-program-mutations.mjs
index 5de672e6..acfaee68 100644
--- a/scripts/test-private-program-mutations.mjs
+++ b/scripts/test-private-program-mutations.mjs
@@ -35,6 +35,7 @@ import {
   PRIVATE_PROGRAM_CONSUMER_PATH,
   PRIVATE_PROGRAM_WASM_PATH,
   PRIVATE_PROGRAM_WASM_SURFACE,
+  copyDeclaredCargoRegistryIndex,
   validatePrivateProgramWasmSurface,
 } from "./build-private-program.mjs";
 import { PRIVATE_PROGRAM_BROWSER_PASS_RECEIPT } from "./test-private-program-browser.mjs";
@@ -91,7 +92,7 @@ export const PRIVATE_PROGRAM_MUTATION_CASES = Object.freeze([
     ),
     replacement: "",
     expectedBrowserAssertion:
-      "PrivateProgramConsumerError: private Program run failed with status 6",
+      "PrivateProgramConsumerError: private Program consumer: run failed with status 6",
   }),
   mutation({
     id: "hard-constraint-deletion",
@@ -107,7 +108,7 @@ export const PRIVATE_PROGRAM_MUTATION_CASES = Object.freeze([
     ),
     replacement: "",
     expectedBrowserAssertion:
-      "PrivateProgramConsumerError: private Program run failed with status 6",
+      "PrivateProgramConsumerError: private Program consumer: run failed with status 6",
   }),
   mutation({
     id: "final-recheck-call-edge-deletion",
@@ -141,7 +142,7 @@ export const PRIVATE_PROGRAM_MUTATION_CASES = Object.freeze([
     ),
     replacement: lines("    let has_hard_violation = false;"),
     expectedBrowserAssertion:
-      "PrivateProgramConsumerError: private Program run failed with status 8",
+      "PrivateProgramConsumerError: private Program consumer: run failed with status 8",
   }),
   mutation({
     id: "session-observed-update-bypass",
@@ -161,7 +162,7 @@ export const PRIVATE_PROGRAM_MUTATION_CASES = Object.freeze([
       "    })",
     ).slice(0, -1),
     expectedBrowserAssertion:
-      "PrivateProgramConsumerError: shipping trace permits exactly one SetAll callback",
+      "PrivateProgramConsumerError: private Program consumer: shipping trace permits exactly one SetAll callback",
   }),
   mutation({
     id: "external-attachment-handoff-binding-bypass",
@@ -178,7 +179,7 @@ export const PRIVATE_PROGRAM_MUTATION_CASES = Object.freeze([
       "            ),",
     ),
     expectedBrowserAssertion:
-      "PrivateProgramConsumerError: private Program run failed with status 7",
+      "PrivateProgramConsumerError: private Program consumer: run failed with status 7",
   }),
   mutation({
     id: "javascript-publish-deletion",
@@ -193,7 +194,7 @@ export const PRIVATE_PROGRAM_MUTATION_CASES = Object.freeze([
     ),
     replacement: lines("    frozenPublication(outputBinding, css);"),
     expectedBrowserAssertion:
-      "Error: private Program browser fixture: computed background is the exact expected CSS literal",
+      "Error: private Program browser fixture: computed background is the exact expected CSS literal; expected \"rgba(64, 64, 64, 0.5)\", got \"rgba(0, 0, 0, 0)\"",
   }),
 ]);
 
@@ -316,7 +317,11 @@ export function assertMutationSpecificBrowserFailure(definition, result) {
     .slice(assertionLine.indexOf(BROWSER_ASSERTION_PREFIX) + BROWSER_ASSERTION_PREFIX.length)
     .trim();
   if (actualAssertion !== definition.expectedBrowserAssertion) {
-    fail(`${definition.id} did not emit its mutation-specific failure evidence`);
+    fail(
+      `${definition.id} did not emit its mutation-specific failure evidence: ` +
+        `expected=${JSON.stringify(definition.expectedBrowserAssertion)} ` +
+        `actual=${JSON.stringify(actualAssertion)}`,
+    );
   }
   return true;
 }
@@ -1090,6 +1095,7 @@ async function executeMutationProof({ tarball, expectedSha256 }, policy) {
       mkdir(resolve(root, "cargo-home"), { recursive: true }),
       mkdir(resolve(root, "cargo-temp"), { recursive: true }),
     ]);
+    await copyDeclaredCargoRegistryIndex(resolve(root, "cargo-home"));
     const executors = await resolveCanonicalRustExecutors(runner);
     const optimizer = await resolveCanonicalOptimizer(root, runner);
     const cargo = cargoEnvironment({ workspace, root, target, executors });
diff --git a/scripts/test_mutation.py b/scripts/test_mutation.py
index bf50c3f1..0fb067d6 100644
--- a/scripts/test_mutation.py
+++ b/scripts/test_mutation.py
@@ -1849,7 +1849,7 @@ def test_reusable_workers_bound_jobs_and_binaryen_transport(self) -> None:
         ci_caller = (workflows / "ci.yml").read_text(encoding="utf-8")
         admitted_ci_worker = (
             "uses: Labpics-Team/lab-colors/.github/workflows/ci-worker.yml@"
-            "1461bc2ed60142aed3a8723e618b883be6418156"
+            "beecd257371a7a6421079b0d8207a109969aa332"
         )
         self.assertEqual(ci_caller.count("ci-worker.yml@"), 1)
         self.assertIn(admitted_ci_worker, ci_caller)