fix: run the provider sandbox and admit a release to a named environment

The provider sandbox never ran. bubblewrap 0.9.0 stops parsing an `--args`
file at the first non-option and never hands the remainder back, so the
command written into that file was silently dropped: bwrap printed its usage
text, exited 1, and the provider produced no evidence at all. The options
still travel in the args file — that is what keeps host paths and credentials
out of `/proc/<pid>/cmdline` — but the command now rides on real argv, and
`encodeProviderBwrapInput` refuses a `--` so the drop cannot come back.

The scope wrapper then could not exit. It read the supervisor's liveness pipe
through `fs`, which runs a blocking `read(2)` on a threadpool thread; the
supervisor holds that pipe open for the scope's whole life, so the read never
returned and closing the descriptor did not interrupt it. Once bubblewrap
finished the wrapper deadlocked in `process.exit`, the scope outlived the
provider, and a completed run was reported as a timeout kill. The channel is
now read through the event loop, so teardown is observable and terminal.

Creation modes were left to the ambient umask. `mkdir(mode)` and `open(mode)`
are requests the kernel subtracts the umask from, so a runner exporting a
restrictive umask produced directories it could not enter and handed `tar` a
file it could not re-open. Private modes are pinned instead of inherited.

Promotion cleanup deleted before it checked. Removals run through a pinned
descriptor, so a leaf substituted after validation had this promotion's exact
five destroyed first and the substitution reported afterwards, leaving a
half-emptied directory a retry could not tell from a completed one. The name
is re-bound to the inode before anything is removed, so the failure is total.

Separately, release coherence proved the artifacts agreed with each other but
never that they belonged where they were going: a build whose runtime document
said `APP_ENV: local`, `AUTH_MODE: demo` and a loopback API is coherent with
itself and passed every gate. `public/` is copied verbatim into `dist/`, so
that local document shipped with every build regardless of what the build was
for. Runtime configuration now comes from a declared profile, and FE-GATE-027
refuses to admit an artifact to an environment it does not match — including
refusing an undeclared destination, so nothing is admitted by omission.

`REQUEST_TIMEOUT_MS` and `VITE_ROUTER_BASE_PATH` were validated and then
dropped: the V3 executor ran every operation on its contract's own deadline,
and Vite emitted root-absolute assets for a sub-path deployment. The timeout is
now a ceiling that may tighten a contract but never loosen one, and one base
path feeds the router, the Service Worker scope and the asset base together.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

scripts/lib/ci-candidate-archive.ts

@@ -5,7 +5,6 @@ import type { FileHandle } from "node:fs/promises";
 import {
   lstat,
   mkdir,
-  mkdtemp,
   open,
   readFile,
   readdir,
@@ -28,6 +27,10 @@ import {
   assertSafePublishLeaf,
   ensureSafePublishDirectory,
 } from "./ci-gate-log.ts";
+import {
+  makePrivateTemporaryDirectory,
+  withPrivateUmask,
+} from "./private-filesystem.ts";
 
 const MAX_ARCHIVE_BYTES = 268_435_456;
 const MAX_CANDIDATE_FILES = 4_096;
@@ -147,11 +150,11 @@ export async function verifyCiCandidateArchive(
       path.dirname(extractionTarget),
     );
     await assertSafePublishLeaf(extractionTarget, input.extractTo);
-    extractionRoot = await mkdtemp(
+    extractionRoot = makePrivateTemporaryDirectory(
       path.join(path.dirname(extractionTarget), `.${path.basename(extractionTarget)}.verified-`),
     );
   } else {
-    extractionRoot = await mkdtemp(path.join(tmpdir(), "ci-candidate-archive-"));
+    extractionRoot = makePrivateTemporaryDirectory(path.join(tmpdir(), "ci-candidate-archive-"));
   }
   let published = false;
   try {
@@ -221,7 +224,7 @@ export async function verifyCapturedCiCandidateArchive(
     throw new Error("candidate archive SHA-256 mismatch");
   }
   const captured = await materializeCapturedArchive(archive);
-  const extractionRoot = await mkdtemp(path.join(tmpdir(), "ci-captured-candidate-"));
+  const extractionRoot = makePrivateTemporaryDirectory(path.join(tmpdir(), "ci-captured-candidate-"));
   try {
     const manifest = preflightArchiveHandle(captured.handle);
     extractArchiveHandle(captured.handle, extractionRoot);
@@ -318,25 +321,33 @@ function preflightArchiveHandle(archiveHandle: FileHandle): ReleaseCandidateMani
 }
 
 function extractArchiveHandle(archiveHandle: FileHandle, extractionRoot: string): void {
-  const extracted = spawnSync(
-    TAR_EXECUTABLE,
-    [
-      "--extract",
-      "--gzip",
-      "--file",
-      "/proc/self/fd/3",
-      "--directory",
-      extractionRoot,
-      "--no-same-owner",
-      "--no-same-permissions",
-    ],
-    {
-      encoding: "utf8",
-      maxBuffer: 1_048_576,
-      timeout: 30_000,
-      env: TAR_ENVIRONMENT,
-      stdio: ["ignore", "pipe", "pipe", archiveHandle.fd],
-    },
+  // `--no-same-permissions` is what keeps an untrusted archive from choosing
+  // its own modes, but it hands the decision to the inherited umask instead.
+  // Under a hardened `umask 077x` tar then creates directories it cannot
+  // descend into and extraction fails part-way. Pinning the umask for the
+  // duration makes the extracted tree exactly private, whatever the caller's
+  // ambient state is. `spawnSync` keeps this window free of interleaved work.
+  const extracted = withPrivateUmask(() =>
+    spawnSync(
+      TAR_EXECUTABLE,
+      [
+        "--extract",
+        "--gzip",
+        "--file",
+        "/proc/self/fd/3",
+        "--directory",
+        extractionRoot,
+        "--no-same-owner",
+        "--no-same-permissions",
+      ],
+      {
+        encoding: "utf8",
+        maxBuffer: 1_048_576,
+        timeout: 30_000,
+        env: TAR_ENVIRONMENT,
+        stdio: ["ignore", "pipe", "pipe", archiveHandle.fd],
+      },
+    ),
   );
   if (extracted.status !== 0 || extracted.signal || extracted.error) {
     throw new Error(
@@ -592,7 +603,7 @@ function readManifestFromArchive(archiveHandle: FileHandle): ReleaseCandidateMan
 async function materializeCapturedArchive(
   archive: Buffer,
 ): Promise<Readonly<{ root: string; handle: FileHandle }>> {
-  const root = await mkdtemp(path.join(tmpdir(), "ci-captured-archive-"));
+  const root = makePrivateTemporaryDirectory(path.join(tmpdir(), "ci-captured-archive-"));
   const file = path.join(root, "candidate.tar.gz");
   let handle: FileHandle | undefined;
   try {
@@ -601,6 +612,11 @@ async function materializeCapturedArchive(
       constants.O_RDWR | constants.O_CREAT | constants.O_EXCL | constants.O_NOFOLLOW,
       0o600,
     );
+    // `open` subtracts the umask too. The extractor re-opens this file by
+    // `/proc/self/fd/N` from a child process, and that re-open is a real
+    // permission check, so a umask-zeroed mode makes `tar` fail to read the
+    // candidate it was just handed.
+    await handle.chmod(0o600);
     await handle.writeFile(archive);
     await handle.sync();
     await unlink(file);