diff --git a/.github/scripts/setup_android_sdk.py b/.github/scripts/setup_android_sdk.py
new file mode 100644
index 0000000..1ebbccf
--- /dev/null
+++ b/.github/scripts/setup_android_sdk.py
@@ -0,0 +1,306 @@
+#!/usr/bin/env python3
+# SPDX-License-Identifier: GPL-3.0-or-later
+"""Hardened Android SDK setup for CI (issue #389).
+
+The dominant merge-blocking flake was the **Set up Android SDK** step
+(`android-actions/setup-android`) dying *before* the emulator ever starts:
+
+    Wrong version in preinstalled sdkmanager
+    Warning: ... preparing SDK package Android Emulator: Error reading Zip
+    content from a SeekableByteChannel.
+    Error: The process '.../sdkmanager' failed with exit code 1
+
+Two root causes, both a corrupt/truncated download that a bare `sdkmanager`
+turns into an un-retried exit 1:
+
+  * the action's own **unverified** cmdline-tools re-download (its default
+    cmdline-tools version rarely matches the runner image's preinstalled one, so
+    it logs "Wrong version in preinstalled sdkmanager" and re-fetches with *no*
+    checksum), and
+  * the action's default ``packages: tools platform-tools`` install (the "SDK
+    Tools" corrupt zip seen on a #388 preview shard) plus the emulator/platform
+    package installs.
+
+This module hardens both with **verify -> reject -> retry**, never trusting
+sdkmanager's exit code alone:
+
+  ``bootstrap``  Download the *pinned* Android command-line tools zip, verify it
+                 against a pinned size + SHA-256, and install it to
+                 ``$ANDROID_SDK_ROOT/cmdline-tools/<rev>`` -- the exact path
+                 setup-android probes first, so the action reuses our verified
+                 tree and never does its own unverified "Wrong version"
+                 re-download. A size/hash mismatch (corrupt OR wrong version)
+                 => delete the bad zip + any half-extracted dir => re-download
+                 clean. Only a verified tree is ever left in place, so the
+                 success-gated cache can never bake in a corrupt SDK.
+
+  ``install``    Run ``sdkmanager --install <packages>`` with retry + backoff.
+                 "Error reading Zip content from a SeekableByteChannel" is a
+                 corrupt package zip, so on failure each requested package's dir
+                 (and sdkmanager's temp/intermediate dirs) is PURGED before the
+                 retry -- forcing a fresh re-download instead of a re-read of the
+                 corrupt file.
+
+stdlib only (urllib/hashlib/zipfile/...), cross-platform, per the repo's "prefer
+Python for dev/CI-helper scripts" rule. The pure helpers are unit-tested in
+``test_setup_android_sdk.py`` (run by the ``traffic-control-tests`` job); the
+full download/install path is validated by CI itself.
+"""
+
+from __future__ import annotations
+
+import argparse
+import hashlib
+import os
+import shutil
+import subprocess
+import sys
+import tempfile
+import time
+import urllib.request
+import zipfile
+
+# --- Pinned Android command-line tools (revision 20.0) --------------------
+# android-actions/setup-android v4.0.1 defaults to this same build (its
+# getVersionShort() maps "14742923" -> "20.0"). We provision it OURSELVES,
+# integrity-checked, into the path the action looks for first
+# ($ANDROID_SDK_ROOT/cmdline-tools/20.0), so the action finds it, skips its own
+# unverified download, and never prints "Wrong version in preinstalled
+# sdkmanager".
+#
+# CLT_SIZE + the SHA-1 are Google's published values for this immutable,
+# build-numbered zip (repository2-3.xml). CLT_SHA256 was computed locally from
+# bytes that matched BOTH of Google's published values, so it is an authoritative
+# integrity pin. A build-numbered URL is immutable, so these never drift; bumping
+# the tools means bumping all four constants together.
+CLT_VERSION_LONG = "14742923"
+CLT_VERSION_SHORT = "20.0"
+CLT_URL = (
+    "https://dl.google.com/android/repository/"
+    f"commandlinetools-linux-{CLT_VERSION_LONG}_latest.zip"
+)
+CLT_SIZE = 172789259
+CLT_SHA256 = "04453066b540409d975c676d781da1477479dde3761310f1a7eb92a1dfb15af7"
+
+# Total tries (1 initial + retries). Backoff is linear: 10s, 20s, 30s ...
+MAX_ATTEMPTS = 4
+
+
+def log(msg: str) -> None:
+    print(msg, flush=True)
+
+
+def warn(msg: str) -> None:
+    print(f"::warning::{msg}", flush=True)
+
+
+def error(msg: str) -> None:
+    print(f"::error::{msg}", flush=True)
+
+
+def backoff_seconds(attempt: int) -> int:
+    """Linear backoff before the next attempt: 10s after attempt 1, 20s after 2..."""
+    return 10 * attempt
+
+
+def sdk_root() -> str:
+    """The Android SDK root. GitHub-hosted runners preset ANDROID_SDK_ROOT /
+    ANDROID_HOME to /usr/local/lib/android/sdk; fall back to the SDK's default."""
+    root = os.environ.get("ANDROID_SDK_ROOT") or os.environ.get("ANDROID_HOME")
+    if not root:
+        root = os.path.join(os.path.expanduser("~"), ".android", "sdk")
+    return root
+
+
+def sha256_of(path: str) -> str:
+    h = hashlib.sha256()
+    with open(path, "rb") as fh:
+        for chunk in iter(lambda: fh.read(1024 * 1024), b""):
+            h.update(chunk)
+    return h.hexdigest()
+
+
+def verify_download(path, expected_size, expected_sha256):
+    """(ok, detail) for a downloaded file: size first (cheap), then SHA-256.
+    A mismatch means a corrupt/truncated download OR the wrong version -- both
+    must be rejected and re-fetched."""
+    if not os.path.exists(path):
+        return False, "download missing"
+    actual_size = os.path.getsize(path)
+    if actual_size != expected_size:
+        return False, f"size {actual_size} != expected {expected_size}"
+    actual_sha = sha256_of(path)
+    if actual_sha != expected_sha256:
+        return False, f"sha256 {actual_sha} != expected {expected_sha256}"
+    return True, "ok"
+
+
+def package_dir(root: str, package: str) -> str:
+    """On-disk dir for an sdkmanager package id. sdkmanager lays packages out by
+    turning the ';' separators into path separators, e.g.
+    'platforms;android-37.0' -> <root>/platforms/android-37.0, so this is exactly
+    the tree to purge to force a corrupt package to re-download."""
+    return os.path.join(root, *package.split(";"))
+
+
+def _rm(path: str) -> None:
+    """Best-effort recursive delete of a file or dir (reject a bad download)."""
+    if os.path.islink(path) or os.path.isfile(path):
+        try:
+            os.remove(path)
+        except FileNotFoundError:
+            pass
+    elif os.path.isdir(path):
+        shutil.rmtree(path, ignore_errors=True)
+
+
+def _extract_preserving_perms(zip_path: str, target_dir: str) -> None:
+    """Extract a zip, restoring the unix permission bits stored in each entry's
+    external attributes. ZipFile.extractall drops the executable bit, which would
+    leave bin/sdkmanager non-executable and break the action's `sdkmanager
+    --licenses`; Google's zip is unix-built, so external_attr carries the +x."""
+    with zipfile.ZipFile(zip_path) as zf:
+        for info in zf.infolist():
+            extracted = zf.extract(info, target_dir)
+            mode = (info.external_attr >> 16) & 0o7777
+            if mode:
+                os.chmod(extracted, mode)
+
+
+class _RejectAndRetry(Exception):
+    """Internal signal: discard this attempt's download and retry from scratch."""
+
+
+def bootstrap() -> int:
+    """Ensure $ANDROID_SDK_ROOT/cmdline-tools/<rev> is a verified install."""
+    root = sdk_root()
+    dest = os.path.join(root, "cmdline-tools", CLT_VERSION_SHORT)
+    sdkmanager = os.path.join(dest, "bin", "sdkmanager")
+    if os.path.exists(sdkmanager):
+        # Cache hit (or already provisioned): the cache is populated only after a
+        # passing integrity check, so a present tree is trusted -> no re-download.
+        log(f"cmdline-tools {CLT_VERSION_SHORT} already present at {dest} "
+            "(cache hit) -- skipping verified download")
+        return 0
+
+    tools_parent = os.path.join(root, "cmdline-tools")
+    os.makedirs(tools_parent, exist_ok=True)
+    for attempt in range(1, MAX_ATTEMPTS + 1):
+        log(f"::group::Download + verify cmdline-tools {CLT_VERSION_SHORT} "
+            f"(attempt {attempt}/{MAX_ATTEMPTS})")
+        tmp_zip = os.path.join(tempfile.gettempdir(), f"clt-{CLT_VERSION_LONG}.zip")
+        # Extract on the SAME filesystem as `dest` so the final move is an atomic
+        # rename that preserves the restored +x bit on bin/sdkmanager.
+        tmp_extract = tempfile.mkdtemp(prefix=".clt-extract-", dir=tools_parent)
+        _rm(tmp_zip)
+        try:
+            log(f"Downloading {CLT_URL}")
+            urllib.request.urlretrieve(CLT_URL, tmp_zip)  # noqa: S310 (pinned https)
+            ok, detail = verify_download(tmp_zip, CLT_SIZE, CLT_SHA256)
+            if not ok:
+                warn(f"cmdline-tools integrity check failed: {detail} -- "
+                     "rejecting the bad download and retrying clean")
+                raise _RejectAndRetry()
+            log(f"Integrity OK (size {CLT_SIZE}, sha256 {CLT_SHA256})")
+            _extract_preserving_perms(tmp_zip, tmp_extract)
+            unpacked = os.path.join(tmp_extract, "cmdline-tools")
+            if not os.path.isdir(unpacked):
+                warn("extracted zip has no top-level cmdline-tools/ dir -- retrying")
+                raise _RejectAndRetry()
+            _rm(dest)  # drop any half-extracted leftover before moving the good tree
+            shutil.move(unpacked, dest)
+            # Mirror the action: touch repositories.cfg so sdkmanager is happy.
+            open(os.path.join(root, "repositories.cfg"), "a", encoding="utf-8").close()
+            if os.path.exists(sdkmanager):
+                log(f"Installed verified cmdline-tools to {dest}")
+                return 0
+            warn("sdkmanager missing after extract -- retrying")
+        except _RejectAndRetry:
+            pass
+        except Exception as exc:  # noqa: BLE001 - any transient error is retryable
+            warn(f"cmdline-tools bootstrap attempt {attempt} failed: {exc}")
+        finally:
+            _rm(tmp_zip)
+            _rm(tmp_extract)
+            log("::endgroup::")
+        if attempt < MAX_ATTEMPTS:
+            time.sleep(backoff_seconds(attempt))
+    error(f"Failed to provision verified cmdline-tools after {MAX_ATTEMPTS} attempts")
+    return 1
+
+
+def find_sdkmanager(root: str):
+    """Locate sdkmanager: our pinned rev first, then the action's `latest`, then PATH."""
+    candidates = [
+        os.path.join(root, "cmdline-tools", CLT_VERSION_SHORT, "bin", "sdkmanager"),
+        os.path.join(root, "cmdline-tools", "latest", "bin", "sdkmanager"),
+    ]
+    for candidate in candidates:
+        if os.path.exists(candidate):
+            return candidate
+    return shutil.which("sdkmanager")
+
+
+def install(packages) -> int:
+    """`sdkmanager --install <packages>` with retry + purge-on-corrupt-zip."""
+    root = sdk_root()
+    sdkmanager = find_sdkmanager(root)
+    if not sdkmanager:
+        error("sdkmanager not found -- run the cmdline-tools bootstrap step first")
+        return 1
+    # Feed 'y' repeatedly in case any license needs accepting (setup-android's
+    # --licenses runs first, but this keeps the step self-contained).
+    accept = ("y\n" * 32).encode()
+    for attempt in range(1, MAX_ATTEMPTS + 1):
+        log(f"::group::sdkmanager --install {' '.join(packages)} "
+            f"(attempt {attempt}/{MAX_ATTEMPTS})")
+        result = subprocess.run([sdkmanager, "--install", *packages], input=accept)
+        log("::endgroup::")
+        if result.returncode == 0:
+            log(f"Installed SDK packages: {' '.join(packages)}")
+            return 0
+        warn(f"sdkmanager attempt {attempt} failed (exit {result.returncode}) -- "
+             "purging partial/corrupt packages before retry")
+        # REJECT: a corrupt package zip must be re-downloaded, not re-read. Purge
+        # each requested package's dir + sdkmanager's temp/intermediate dirs so
+        # the retry starts clean.
+        for pkg in packages:
+            _rm(package_dir(root, pkg))
+        _rm(os.path.join(root, ".temp"))
+        _rm(os.path.join(root, ".downloadIntermediates"))
+        if attempt < MAX_ATTEMPTS:
+            time.sleep(backoff_seconds(attempt))
+    error(f"sdkmanager failed to install {list(packages)} after {MAX_ATTEMPTS} attempts")
+    log("--- sdkmanager --list_installed ---")
+    subprocess.run([sdkmanager, "--list_installed"])
+    return 1
+
+
+def build_parser() -> argparse.ArgumentParser:
+    parser = argparse.ArgumentParser(
+        description="Hardened Android SDK setup for CI (issue #389)."
+    )
+    sub = parser.add_subparsers(dest="command", required=True)
+    sub.add_parser(
+        "bootstrap",
+        help="Download + SHA-256-verify the pinned Android command-line tools.",
+    )
+    installer = sub.add_parser(
+        "install",
+        help="sdkmanager --install with retry + purge-on-corrupt-zip.",
+    )
+    installer.add_argument("packages", nargs="+", help="sdkmanager package ids")
+    return parser
+
+
+def main(argv) -> int:
+    args = build_parser().parse_args(argv)
+    if args.command == "bootstrap":
+        return bootstrap()
+    if args.command == "install":
+        return install(args.packages)
+    return 2  # pragma: no cover - argparse requires a subcommand
+
+
+if __name__ == "__main__":
+    sys.exit(main(sys.argv[1:]))
diff --git a/.github/scripts/test_setup_android_sdk.py b/.github/scripts/test_setup_android_sdk.py
new file mode 100644
index 0000000..57c0cdb
--- /dev/null
+++ b/.github/scripts/test_setup_android_sdk.py
@@ -0,0 +1,178 @@
+#!/usr/bin/env python3
+# SPDX-License-Identifier: GPL-3.0-or-later
+"""Unit tests for the pure helpers of setup_android_sdk.py (no network, no SDK).
+
+Covers the bits whose correctness is load-bearing for the hardening in #389:
+the package-id -> purge-path mapping (a wrong mapping would purge the wrong dir),
+the size/SHA-256 integrity gate (verify -> reject), the pinned-constant
+self-consistency, the backoff schedule, sdkmanager discovery, and that extraction
+restores the executable bit that sdkmanager needs. The full download/install path
+is exercised by CI itself."""
+
+from __future__ import annotations
+
+import hashlib
+import os
+import stat
+import tempfile
+import unittest
+import zipfile
+
+import setup_android_sdk as sdk
+
+
+class PackageDirTests(unittest.TestCase):
+    def test_semicolon_ids_map_to_nested_dirs(self):
+        root = os.path.join("opt", "sdk")
+        self.assertEqual(
+            sdk.package_dir(root, "platforms;android-37.0"),
+            os.path.join(root, "platforms", "android-37.0"),
+        )
+        self.assertEqual(
+            sdk.package_dir(root, "build-tools;37.0.0"),
+            os.path.join(root, "build-tools", "37.0.0"),
+        )
+        self.assertEqual(
+            sdk.package_dir(root, "system-images;android-37.0;google_apis_ps16k;x86_64"),
+            os.path.join(root, "system-images", "android-37.0", "google_apis_ps16k", "x86_64"),
+        )
+
+    def test_flat_ids_map_to_single_dir(self):
+        root = os.path.join("opt", "sdk")
+        self.assertEqual(sdk.package_dir(root, "emulator"), os.path.join(root, "emulator"))
+        self.assertEqual(
+            sdk.package_dir(root, "platform-tools"), os.path.join(root, "platform-tools")
+        )
+
+    def test_purge_target_stays_under_root(self):
+        # The purge path must never escape the SDK root (no absolute/`..` package ids).
+        root = os.path.abspath(os.path.join("opt", "sdk"))
+        target = os.path.abspath(sdk.package_dir(root, "platforms;android-37.0"))
+        self.assertTrue(target.startswith(root + os.sep))
+
+
+class VerifyDownloadTests(unittest.TestCase):
+    def _write(self, data: bytes) -> str:
+        fd, path = tempfile.mkstemp()
+        with os.fdopen(fd, "wb") as fh:
+            fh.write(data)
+        self.addCleanup(lambda: os.path.exists(path) and os.remove(path))
+        return path
+
+    def test_accepts_matching_size_and_hash(self):
+        data = b"correct-cmdline-tools-bytes"
+        path = self._write(data)
+        ok, detail = sdk.verify_download(path, len(data), hashlib.sha256(data).hexdigest())
+        self.assertTrue(ok, detail)
+        self.assertEqual(detail, "ok")
+
+    def test_rejects_wrong_size_before_hashing(self):
+        data = b"truncated"
+        path = self._write(data)
+        ok, detail = sdk.verify_download(path, len(data) + 1, hashlib.sha256(data).hexdigest())
+        self.assertFalse(ok)
+        self.assertIn("size", detail)
+
+    def test_rejects_corrupt_bytes_with_right_size(self):
+        good = b"aaaaaaaa"
+        corrupt = b"aaaaaaab"  # same length, different content (silent corruption)
+        path = self._write(corrupt)
+        ok, detail = sdk.verify_download(path, len(good), hashlib.sha256(good).hexdigest())
+        self.assertFalse(ok)
+        self.assertIn("sha256", detail)
+
+    def test_rejects_missing_file(self):
+        ok, detail = sdk.verify_download(
+            os.path.join(tempfile.gettempdir(), "does-not-exist-clt.zip"), 1, "0" * 64
+        )
+        self.assertFalse(ok)
+
+
+class PinnedConstantsTests(unittest.TestCase):
+    def test_url_embeds_the_pinned_build_number(self):
+        self.assertIn(sdk.CLT_VERSION_LONG, sdk.CLT_URL)
+        self.assertTrue(sdk.CLT_URL.startswith("https://"))
+        self.assertTrue(sdk.CLT_URL.endswith("_latest.zip"))
+
+    def test_sha256_is_a_full_hex_digest(self):
+        self.assertEqual(len(sdk.CLT_SHA256), 64)
+        int(sdk.CLT_SHA256, 16)  # raises if not hex
+        self.assertEqual(sdk.CLT_SHA256, sdk.CLT_SHA256.lower())
+
+    def test_size_is_positive(self):
+        self.assertGreater(sdk.CLT_SIZE, 0)
+
+
+class BackoffTests(unittest.TestCase):
+    def test_backoff_is_linear_and_increasing(self):
+        seq = [sdk.backoff_seconds(a) for a in range(1, sdk.MAX_ATTEMPTS + 1)]
+        self.assertEqual(seq, [10, 20, 30, 40][: sdk.MAX_ATTEMPTS])
+        self.assertEqual(seq, sorted(seq))
+
+
+class SdkRootTests(unittest.TestCase):
+    def test_prefers_android_sdk_root_over_home(self):
+        with _env(ANDROID_SDK_ROOT="/a/sdk-root", ANDROID_HOME="/b/home"):
+            self.assertEqual(sdk.sdk_root(), "/a/sdk-root")
+
+    def test_falls_back_to_android_home(self):
+        with _env(ANDROID_SDK_ROOT=None, ANDROID_HOME="/b/home"):
+            self.assertEqual(sdk.sdk_root(), "/b/home")
+
+
+class FindSdkManagerTests(unittest.TestCase):
+    def test_prefers_pinned_revision_dir(self):
+        with tempfile.TemporaryDirectory() as root:
+            pinned = os.path.join(root, "cmdline-tools", sdk.CLT_VERSION_SHORT, "bin")
+            latest = os.path.join(root, "cmdline-tools", "latest", "bin")
+            for d in (pinned, latest):
+                os.makedirs(d)
+                open(os.path.join(d, "sdkmanager"), "w").close()
+            self.assertEqual(
+                sdk.find_sdkmanager(root),
+                os.path.join(pinned, "sdkmanager"),
+            )
+
+
+class ExtractPermsTests(unittest.TestCase):
+    @unittest.skipUnless(os.name == "posix", "unix exec bit only meaningful on POSIX")
+    def test_executable_bit_is_restored(self):
+        with tempfile.TemporaryDirectory() as work:
+            zip_path = os.path.join(work, "clt.zip")
+            with zipfile.ZipFile(zip_path, "w") as zf:
+                info = zipfile.ZipInfo("cmdline-tools/bin/sdkmanager")
+                info.external_attr = 0o755 << 16  # -rwxr-xr-x, as Google's zip stores it
+                zf.writestr(info, "#!/bin/sh\n")
+            out = os.path.join(work, "out")
+            sdk._extract_preserving_perms(zip_path, out)
+            mode = os.stat(os.path.join(out, "cmdline-tools", "bin", "sdkmanager")).st_mode
+            self.assertTrue(mode & stat.S_IXUSR, "sdkmanager must be executable after extract")
+
+
+class _env:
+    """Context manager to set/clear env vars for a test, restoring them after."""
+
+    def __init__(self, **values):
+        self._values = values
+        self._saved = {}
+
+    def __enter__(self):
+        for key, value in self._values.items():
+            self._saved[key] = os.environ.get(key)
+            if value is None:
+                os.environ.pop(key, None)
+            else:
+                os.environ[key] = value
+        return self
+
+    def __exit__(self, *exc):
+        for key, previous in self._saved.items():
+            if previous is None:
+                os.environ.pop(key, None)
+            else:
+                os.environ[key] = previous
+        return False
+
+
+if __name__ == "__main__":
+    unittest.main()
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 7c22280..1467be9 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -88,11 +88,57 @@ jobs:
           distribution: temurin
           java-version: "21"
 
+      - name: Restore Android SDK cache
+        id: android-sdk-cache
+        uses: actions/cache/restore@55cc8345863c7cc4c66a329aec7e433d2d1c52a9 # v6.1.0
+        with:
+          # Cache the SHA-256-verified command-line tools + platform/build-tools so a
+          # green run doesn't re-download (and risk re-corrupting) them. Restore-only
+          # here + the success-gated save below == "integrity gates the cache": a
+          # corrupt/failed SDK is never saved (#389). Shared key (identical contents).
+          path: |
+            /usr/local/lib/android/sdk/cmdline-tools/20.0
+            /usr/local/lib/android/sdk/platforms
+            /usr/local/lib/android/sdk/build-tools
+            /usr/local/lib/android/sdk/platform-tools
+          # Bump the prefix if ANDROID_PLATFORM/ANDROID_BUILD_TOOLS or the pinned
+          # cmdline-tools build (14742923) change.
+          key: android-sdk-v1-${{ runner.os }}-clt14742923-plat37.0-bt37.0.0
+
+      # Provision the SHA-256-verified command-line tools into the exact path
+      # setup-android probes first, so the action reuses it and never does its own
+      # unverified "Wrong version in preinstalled sdkmanager" re-download (#389).
+      - name: Bootstrap verified Android command-line tools
+        run: python3 .github/scripts/setup_android_sdk.py bootstrap
+
       - name: Set up Android SDK
         uses: android-actions/setup-android@40fd30fb8d7440372e1316f5d1809ec01dcd3699 # v4.0.1
+        with:
+          # Reuse the verified cmdline-tools bootstrapped above (matching version =>
+          # no unverified re-download) and pass '' packages so the action does NOT run
+          # the flaky `sdkmanager tools platform-tools` install — the corrupt-zip
+          # surface that failed the "Set up Android SDK" step (#389).
+          cmdline-tools-version: "14742923"
+          packages: ""
 
+      # verify -> reject -> retry: a corrupt package zip ("Error reading Zip
+      # content ...") is purged and re-downloaded instead of failing on sdkmanager's
+      # bare exit 1 (#389; supersedes the inline retry loop from #387/#388).
       - name: Install SDK platform and build-tools
-        run: sdkmanager "$ANDROID_PLATFORM" "$ANDROID_BUILD_TOOLS"
+        run: python3 .github/scripts/setup_android_sdk.py install "platform-tools" "$ANDROID_PLATFORM" "$ANDROID_BUILD_TOOLS"
+
+      # Save the verified SDK only on success (never cache a corrupt SDK) and only on
+      # a miss (avoid redundant re-saves).
+      - name: Save Android SDK cache
+        if: success() && steps.android-sdk-cache.outputs.cache-hit != 'true'
+        uses: actions/cache/save@55cc8345863c7cc4c66a329aec7e433d2d1c52a9 # v6.1.0
+        with:
+          path: |
+            /usr/local/lib/android/sdk/cmdline-tools/20.0
+            /usr/local/lib/android/sdk/platforms
+            /usr/local/lib/android/sdk/build-tools
+            /usr/local/lib/android/sdk/platform-tools
+          key: android-sdk-v1-${{ runner.os }}-clt14742923-plat37.0-bt37.0.0
 
       - name: Set up Gradle
         uses: gradle/actions/setup-gradle@3f131e8634966bd73d06cc69884922b02e6faf92 # v6.2.0
@@ -120,11 +166,57 @@ jobs:
           distribution: temurin
           java-version: "21"
 
+      - name: Restore Android SDK cache
+        id: android-sdk-cache
+        uses: actions/cache/restore@55cc8345863c7cc4c66a329aec7e433d2d1c52a9 # v6.1.0
+        with:
+          # Cache the SHA-256-verified command-line tools + platform/build-tools so a
+          # green run doesn't re-download (and risk re-corrupting) them. Restore-only
+          # here + the success-gated save below == "integrity gates the cache": a
+          # corrupt/failed SDK is never saved (#389). Shared key (identical contents).
+          path: |
+            /usr/local/lib/android/sdk/cmdline-tools/20.0
+            /usr/local/lib/android/sdk/platforms
+            /usr/local/lib/android/sdk/build-tools
+            /usr/local/lib/android/sdk/platform-tools
+          # Bump the prefix if ANDROID_PLATFORM/ANDROID_BUILD_TOOLS or the pinned
+          # cmdline-tools build (14742923) change.
+          key: android-sdk-v1-${{ runner.os }}-clt14742923-plat37.0-bt37.0.0
+
+      # Provision the SHA-256-verified command-line tools into the exact path
+      # setup-android probes first, so the action reuses it and never does its own
+      # unverified "Wrong version in preinstalled sdkmanager" re-download (#389).
+      - name: Bootstrap verified Android command-line tools
+        run: python3 .github/scripts/setup_android_sdk.py bootstrap
+
       - name: Set up Android SDK
         uses: android-actions/setup-android@40fd30fb8d7440372e1316f5d1809ec01dcd3699 # v4.0.1
+        with:
+          # Reuse the verified cmdline-tools bootstrapped above (matching version =>
+          # no unverified re-download) and pass '' packages so the action does NOT run
+          # the flaky `sdkmanager tools platform-tools` install — the corrupt-zip
+          # surface that failed the "Set up Android SDK" step (#389).
+          cmdline-tools-version: "14742923"
+          packages: ""
 
+      # verify -> reject -> retry: a corrupt package zip ("Error reading Zip
+      # content ...") is purged and re-downloaded instead of failing on sdkmanager's
+      # bare exit 1 (#389; supersedes the inline retry loop from #387/#388).
       - name: Install SDK platform and build-tools
-        run: sdkmanager "$ANDROID_PLATFORM" "$ANDROID_BUILD_TOOLS"
+        run: python3 .github/scripts/setup_android_sdk.py install "platform-tools" "$ANDROID_PLATFORM" "$ANDROID_BUILD_TOOLS"
+
+      # Save the verified SDK only on success (never cache a corrupt SDK) and only on
+      # a miss (avoid redundant re-saves).
+      - name: Save Android SDK cache
+        if: success() && steps.android-sdk-cache.outputs.cache-hit != 'true'
+        uses: actions/cache/save@55cc8345863c7cc4c66a329aec7e433d2d1c52a9 # v6.1.0
+        with:
+          path: |
+            /usr/local/lib/android/sdk/cmdline-tools/20.0
+            /usr/local/lib/android/sdk/platforms
+            /usr/local/lib/android/sdk/build-tools
+            /usr/local/lib/android/sdk/platform-tools
+          key: android-sdk-v1-${{ runner.os }}-clt14742923-plat37.0-bt37.0.0
 
       - name: Set up Gradle
         uses: gradle/actions/setup-gradle@3f131e8634966bd73d06cc69884922b02e6faf92 # v6.2.0
@@ -177,11 +269,57 @@ jobs:
           java-version: "21"
 
       # AGP configuration needs the SDK even for ktlint/detekt (they run on the :app module).
+      - name: Restore Android SDK cache
+        id: android-sdk-cache
+        uses: actions/cache/restore@55cc8345863c7cc4c66a329aec7e433d2d1c52a9 # v6.1.0
+        with:
+          # Cache the SHA-256-verified command-line tools + platform/build-tools so a
+          # green run doesn't re-download (and risk re-corrupting) them. Restore-only
+          # here + the success-gated save below == "integrity gates the cache": a
+          # corrupt/failed SDK is never saved (#389). Shared key (identical contents).
+          path: |
+            /usr/local/lib/android/sdk/cmdline-tools/20.0
+            /usr/local/lib/android/sdk/platforms
+            /usr/local/lib/android/sdk/build-tools
+            /usr/local/lib/android/sdk/platform-tools
+          # Bump the prefix if ANDROID_PLATFORM/ANDROID_BUILD_TOOLS or the pinned
+          # cmdline-tools build (14742923) change.
+          key: android-sdk-v1-${{ runner.os }}-clt14742923-plat37.0-bt37.0.0
+
+      # Provision the SHA-256-verified command-line tools into the exact path
+      # setup-android probes first, so the action reuses it and never does its own
+      # unverified "Wrong version in preinstalled sdkmanager" re-download (#389).
+      - name: Bootstrap verified Android command-line tools
+        run: python3 .github/scripts/setup_android_sdk.py bootstrap
+
       - name: Set up Android SDK
         uses: android-actions/setup-android@40fd30fb8d7440372e1316f5d1809ec01dcd3699 # v4.0.1
+        with:
+          # Reuse the verified cmdline-tools bootstrapped above (matching version =>
+          # no unverified re-download) and pass '' packages so the action does NOT run
+          # the flaky `sdkmanager tools platform-tools` install — the corrupt-zip
+          # surface that failed the "Set up Android SDK" step (#389).
+          cmdline-tools-version: "14742923"
+          packages: ""
 
+      # verify -> reject -> retry: a corrupt package zip ("Error reading Zip
+      # content ...") is purged and re-downloaded instead of failing on sdkmanager's
+      # bare exit 1 (#389; supersedes the inline retry loop from #387/#388).
       - name: Install SDK platform and build-tools
-        run: sdkmanager "$ANDROID_PLATFORM" "$ANDROID_BUILD_TOOLS"
+        run: python3 .github/scripts/setup_android_sdk.py install "platform-tools" "$ANDROID_PLATFORM" "$ANDROID_BUILD_TOOLS"
+
+      # Save the verified SDK only on success (never cache a corrupt SDK) and only on
+      # a miss (avoid redundant re-saves).
+      - name: Save Android SDK cache
+        if: success() && steps.android-sdk-cache.outputs.cache-hit != 'true'
+        uses: actions/cache/save@55cc8345863c7cc4c66a329aec7e433d2d1c52a9 # v6.1.0
+        with:
+          path: |
+            /usr/local/lib/android/sdk/cmdline-tools/20.0
+            /usr/local/lib/android/sdk/platforms
+            /usr/local/lib/android/sdk/build-tools
+            /usr/local/lib/android/sdk/platform-tools
+          key: android-sdk-v1-${{ runner.os }}-clt14742923-plat37.0-bt37.0.0
 
       - name: Set up Gradle
         uses: gradle/actions/setup-gradle@3f131e8634966bd73d06cc69884922b02e6faf92 # v6.2.0
@@ -225,28 +363,61 @@ jobs:
           distribution: temurin
           java-version: "21"
 
+      - name: Restore Android SDK cache
+        id: android-sdk-cache
+        uses: actions/cache/restore@55cc8345863c7cc4c66a329aec7e433d2d1c52a9 # v6.1.0
+        with:
+          # Cache the SHA-256-verified command-line tools + platform/build-tools so a
+          # green run doesn't re-download (and risk re-corrupting) them. Restore-only
+          # here + the success-gated save below == "integrity gates the cache": a
+          # corrupt/failed SDK is never saved (#389). Shared key (identical contents).
+          # The emulator + system image stay with android-emulator-runner (boot logic
+          # is out of scope for #389).
+          path: |
+            /usr/local/lib/android/sdk/cmdline-tools/20.0
+            /usr/local/lib/android/sdk/platforms
+            /usr/local/lib/android/sdk/build-tools
+            /usr/local/lib/android/sdk/platform-tools
+          # Bump the prefix if ANDROID_PLATFORM/ANDROID_BUILD_TOOLS or the pinned
+          # cmdline-tools build (14742923) change.
+          key: android-sdk-v1-${{ runner.os }}-clt14742923-plat37.0-bt37.0.0
+
+      # Provision the SHA-256-verified command-line tools into the exact path
+      # setup-android probes first, so the action reuses it and never does its own
+      # unverified "Wrong version in preinstalled sdkmanager" re-download (#389).
+      - name: Bootstrap verified Android command-line tools
+        run: python3 .github/scripts/setup_android_sdk.py bootstrap
+
       - name: Set up Android SDK
         uses: android-actions/setup-android@40fd30fb8d7440372e1316f5d1809ec01dcd3699 # v4.0.1
+        with:
+          # Reuse the verified cmdline-tools bootstrapped above (matching version =>
+          # no unverified re-download) and pass '' packages so the action does NOT run
+          # the flaky `sdkmanager tools platform-tools` install — the corrupt-zip
+          # surface that failed the "Set up Android SDK" step (#389).
+          cmdline-tools-version: "14742923"
+          packages: ""
 
-      # sdkmanager can exit 1 on a transient package-mirror/network hiccup with no useful trail —
-      # an `E2E (31)` leg died exactly this way (#387). Retry up to 3x with backoff so a transient
-      # failure self-heals, and on a hard failure print the installed-package list so the cause is
-      # visible in the step log instead of a bare exit 1.
+      # verify -> reject -> retry (#389, supersedes the #387/#388 inline loop): sdkmanager
+      # can exit 1 on a corrupt/truncated package zip ("Error reading Zip content ...") — an
+      # `E2E (31)` leg died this way. The helper purges each partial/corrupt package and
+      # re-downloads it clean, and on a hard failure prints the installed-package list so the
+      # cause is visible in the step log instead of a bare exit 1.
       - name: Install SDK platform and build-tools
-        run: |
-          for attempt in 1 2 3; do
-            echo "::group::sdkmanager install (attempt $attempt)"
-            if sdkmanager "$ANDROID_PLATFORM" "$ANDROID_BUILD_TOOLS"; then
-              echo "::endgroup::"
-              exit 0
-            fi
-            echo "::endgroup::"
-            echo "::warning::sdkmanager attempt $attempt failed to install $ANDROID_PLATFORM / $ANDROID_BUILD_TOOLS"
-            if [ "$attempt" -lt 3 ]; then sleep "$((attempt * 15))"; fi
-          done
-          echo "::error::sdkmanager failed to install the SDK packages after 3 attempts"
-          echo "--- sdkmanager --list_installed ---"; sdkmanager --list_installed 2>&1 || true
-          exit 1
+        run: python3 .github/scripts/setup_android_sdk.py install "platform-tools" "$ANDROID_PLATFORM" "$ANDROID_BUILD_TOOLS"
+
+      # Save the verified SDK only on success (never cache a corrupt SDK) and only on
+      # a miss (avoid redundant re-saves).
+      - name: Save Android SDK cache
+        if: success() && steps.android-sdk-cache.outputs.cache-hit != 'true'
+        uses: actions/cache/save@55cc8345863c7cc4c66a329aec7e433d2d1c52a9 # v6.1.0
+        with:
+          path: |
+            /usr/local/lib/android/sdk/cmdline-tools/20.0
+            /usr/local/lib/android/sdk/platforms
+            /usr/local/lib/android/sdk/build-tools
+            /usr/local/lib/android/sdk/platform-tools
+          key: android-sdk-v1-${{ runner.os }}-clt14742923-plat37.0-bt37.0.0
 
       - name: Set up Gradle
         uses: gradle/actions/setup-gradle@3f131e8634966bd73d06cc69884922b02e6faf92 # v6.2.0
@@ -402,8 +573,39 @@ jobs:
           distribution: temurin
           java-version: "21"
 
+      - name: Restore Android SDK cache
+        id: android-sdk-cache
+        uses: actions/cache/restore@55cc8345863c7cc4c66a329aec7e433d2d1c52a9 # v6.1.0
+        with:
+          # Cache the SHA-256-verified command-line tools + platform/build-tools so a
+          # green run doesn't re-download (and risk re-corrupting) them. Restore-only
+          # here + the success-gated save below == "integrity gates the cache": a
+          # corrupt/failed SDK is never saved (#389). The ~1 GB preview system image
+          # keeps its own cache below.
+          path: |
+            /usr/local/lib/android/sdk/cmdline-tools/20.0
+            /usr/local/lib/android/sdk/platforms
+            /usr/local/lib/android/sdk/build-tools
+            /usr/local/lib/android/sdk/platform-tools
+          # Bump the prefix if ANDROID_PLATFORM/ANDROID_BUILD_TOOLS or the pinned
+          # cmdline-tools build (14742923) change.
+          key: android-sdk-v1-${{ runner.os }}-clt14742923-plat37.0-bt37.0.0
+
+      # Provision the SHA-256-verified command-line tools into the exact path
+      # setup-android probes first, so the action reuses it and never does its own
+      # unverified "Wrong version in preinstalled sdkmanager" re-download (#389).
+      - name: Bootstrap verified Android command-line tools
+        run: python3 .github/scripts/setup_android_sdk.py bootstrap
+
       - name: Set up Android SDK
         uses: android-actions/setup-android@40fd30fb8d7440372e1316f5d1809ec01dcd3699 # v4.0.1
+        with:
+          # Reuse the verified cmdline-tools bootstrapped above (matching version =>
+          # no unverified re-download) and pass '' packages so the action does NOT run
+          # the flaky `sdkmanager tools platform-tools` install — the corrupt-zip
+          # surface that failed the "Set up Android SDK" step (#389).
+          cmdline-tools-version: "14742923"
+          packages: ""
 
       - name: Set up Gradle
         uses: gradle/actions/setup-gradle@3f131e8634966bd73d06cc69884922b02e6faf92 # v6.2.0
@@ -425,8 +627,25 @@ jobs:
           path: /usr/local/lib/android/sdk/system-images/android-37.0
           key: sysimg-android-37.0-google_apis_ps16k-x86_64
 
+      # verify -> reject -> retry (#389): the preview emulator + 16 KB-page system image
+      # download here; a corrupt/truncated package zip ("Error reading Zip content ...") is
+      # purged and re-downloaded clean instead of failing on sdkmanager's bare exit 1.
       - name: Install SDK packages + preview system image
-        run: sdkmanager "$ANDROID_PLATFORM" "$ANDROID_BUILD_TOOLS" "platform-tools" "emulator" "$API37_IMAGE"
+        run: python3 .github/scripts/setup_android_sdk.py install "platform-tools" "emulator" "$ANDROID_PLATFORM" "$ANDROID_BUILD_TOOLS" "$API37_IMAGE"
+
+      # Save the verified command-line tools + platform/build-tools only on success and only
+      # on a miss. The ~1 GB system image keeps its own cache above; the emulator re-downloads
+      # (self-healing via the retry) to keep this shared key small.
+      - name: Save Android SDK cache
+        if: success() && steps.android-sdk-cache.outputs.cache-hit != 'true'
+        uses: actions/cache/save@55cc8345863c7cc4c66a329aec7e433d2d1c52a9 # v6.1.0
+        with:
+          path: |
+            /usr/local/lib/android/sdk/cmdline-tools/20.0
+            /usr/local/lib/android/sdk/platforms
+            /usr/local/lib/android/sdk/build-tools
+            /usr/local/lib/android/sdk/platform-tools
+          key: android-sdk-v1-${{ runner.os }}-clt14742923-plat37.0-bt37.0.0
 
       - name: Create API 37 AVD
         run: |
diff --git a/app/build.gradle.kts b/app/build.gradle.kts
index 946b482..829b32c 100644
--- a/app/build.gradle.kts
+++ b/app/build.gradle.kts
@@ -147,6 +147,12 @@ android {
     }
 
     testOptions {
+        // Robolectric-backed Compose UI unit tests (issue #373) need the merged Android resources
+        // (drawables, strings, the compiled resource table) on the JVM unit-test classpath so
+        // `stringResource(...)` and Material3 theming resolve without an emulator. Off by default in
+        // AGP; JVM tests that don't touch resources are unaffected.
+        unitTests.isIncludeAndroidResources = true
+
         // Gradle Managed Devices define the per-API E2E matrix as config-as-code: one virtual
         // device per supported Android version (a rolling ~7-year window, API 29 → latest stable).
         // Run the whole matrix with `./gradlew e2eGroupDebugAndroidTest`, or one level with e.g.
@@ -251,7 +257,14 @@ val jacocoGeneratedExcludes = listOf(
 // audit): unlike `jacocoGeneratedExcludes` above, none of this is generated code — it is hand-written
 // but structurally unreachable from a JVM unit test, so counting it against the metric just measures
 // how much Compose/framework glue exists rather than how well the logic is tested. Four buckets:
-//  1. Compose screen/component render code — only exercisable via a Compose UI test or an emulator.
+//  1. Compose screen/component render code. Historically only exercisable via an emulator, so it was
+//     excluded here. Issue #373 changes that: Robolectric runs the Android framework on the JVM, so a
+//     `createComposeRule()` test in the `test` source set now gives these files real JVM coverage
+//     without an emulator. This bucket therefore SHRINKS one screen at a time — each glob is deleted
+//     in the same PR that adds that screen's Robolectric JVM Compose test. AddAnotherAccountScreen was
+//     the first (see AddAnotherAccountScreenJvmTest) and has been removed below; the rest are tracked
+//     as per-area conversion tickets under #373. The coverage-floor re-ratchet is deferred until the
+//     whole conversion is done and stable (#373) — do NOT raise it in a conversion PR.
 //  2. Android framework entry points the OS instantiates directly (Activity/Service/Application/
 //     BackupAgent) rather than the app's own code constructing them.
 //  3. Hilt DI modules — `@Provides`/`@Binds` one-liners with no branching logic.
@@ -298,7 +311,7 @@ val jacocoNonJvmTestableSurface = listOf(
     "**/AppLockGateHost*",
     "**/FolderDrawer*",
     "**/MailboxScreen*",
-    "**/AddAnotherAccountScreen*",
+    // AddAnotherAccountScreen converted to a Robolectric JVM Compose test (#373) — now JVM-covered.
     "**/BatteryOptimizationScreen*",
     "**/ContactsAccessScreen*",
     "**/LicenseScreen*",
@@ -408,6 +421,45 @@ tasks.named("check") {
     dependsOn("jacocoTestCoverageVerification")
 }
 
+// --- Robolectric android-all offline resolution (issue #373) ------------------------------------
+// Robolectric runs the real Android framework on the JVM from a large `android-all-instrumented`
+// jar. By default it resolves that jar LAZILY AT TEST TIME by downloading it from Maven Central
+// (org.robolectric.internal.dependency.MavenDependencyResolver -> MavenArtifactFetcher). That
+// runtime download is unreliable on CI runners and failed the JVM Compose PoC in CI with
+// `java.lang.AssertionError at MavenArtifactFetcher ... Caused by: java.io.IOException` ("Failed to
+// fetch maven artifact"). Fix: resolve the jar through Gradle instead — reliable, cached, and
+// persisted by the CI Gradle cache, using the same repositories as every other dependency — then
+// hand it to Robolectric in OFFLINE mode so it never touches the network at test time.
+//
+// A DEDICATED resolvable configuration (deliberately NOT testImplementation/testRuntimeOnly) keeps
+// the ~200 MB instrumented framework jar OFF the JVM unit-test classpath: it must be loaded only by
+// Robolectric's sandbox classloader, never flattened onto the app's test classpath where it would
+// collide with the stub `android.jar`. `syncRobolectricAndroidAll` stages the resolved jar under
+// its Maven filename (android-all-instrumented-<version>.jar) — exactly what Robolectric's
+// LocalDependencyResolver looks up as <artifactId>-<version>.jar — and the two system properties
+// below switch Robolectric onto that offline directory (see LegacyDependencyResolver). Every
+// Robolectric test pins @Config(sdk = 36) (app/src/test/resources/robolectric.properties), so the
+// single sdk=36 jar covers them all; a test on a different SDK must add that android-all version to
+// this configuration too. The offline properties are inert for non-Robolectric JVM tests.
+val robolectricAndroidAll: Configuration = configurations.create("robolectricAndroidAll") {
+    isCanBeConsumed = false
+    isCanBeResolved = true
+}
+
+val robolectricDepsDir = layout.buildDirectory.dir("robolectric-android-all")
+
+val syncRobolectricAndroidAll = tasks.register<Sync>("syncRobolectricAndroidAll") {
+    description = "Stages Robolectric's android-all-instrumented jar for offline resolution (issue #373)."
+    from(robolectricAndroidAll)
+    into(robolectricDepsDir)
+}
+
+tasks.withType<Test>().configureEach {
+    dependsOn(syncRobolectricAndroidAll)
+    systemProperty("robolectric.offline", "true")
+    systemProperty("robolectric.dependency.dir", robolectricDepsDir.get().asFile.absolutePath)
+}
+
 dependencies {
     implementation(libs.androidx.core.ktx)
     implementation(libs.androidx.lifecycle.runtime.ktx)
@@ -468,6 +520,24 @@ dependencies {
     // The real org.json for unit tests (android.jar ships a stubbed, no-op version).
     testImplementation("org.json:json:20231013")
 
+    // Robolectric-backed JVM Compose UI tests (issue #373): Robolectric runs the Android framework
+    // on the JVM so `createComposeRule()` can drive composables without an emulator, bringing screen
+    // render code into the JaCoCo JVM-testable surface. The Compose test artifacts come from the same
+    // BOM as the app (aligned versions) and reuse the ui-test-junit4 / ui-test-manifest aliases the
+    // androidTest source set already declares — here in `test` (JVM), not `androidTest`. Robolectric
+    // sources Android's real org.json from its sandbox, so it does not clash with the stub-replacing
+    // org.json above (that is for the plain, non-Robolectric JVM tests).
+    testImplementation(libs.robolectric)
+    // The android-all-instrumented framework jar Robolectric loads into its sandbox — resolved via
+    // Gradle and staged for offline use by syncRobolectricAndroidAll above so no flaky test-time
+    // download happens in CI (issue #373). On its own dedicated configuration, NOT the test
+    // classpath — see that block for why. The artifact has no transitive dependencies (verified from
+    // its POM), so it resolves to exactly the one staged jar.
+    "robolectricAndroidAll"(libs.robolectric.android.all.instrumented)
+    testImplementation(platform(libs.androidx.compose.bom))
+    testImplementation(libs.androidx.compose.ui.test.junit4)
+    testImplementation(libs.androidx.compose.ui.test.manifest)
+
     androidTestImplementation(libs.androidx.junit)
     androidTestImplementation(libs.androidx.espresso.core)
     androidTestImplementation(libs.androidx.espresso.intents)
diff --git a/app/src/test/kotlin/org/libremail/ui/onboarding/AddAnotherAccountScreenJvmTest.kt b/app/src/test/kotlin/org/libremail/ui/onboarding/AddAnotherAccountScreenJvmTest.kt
new file mode 100644
index 0000000..84237bd
--- /dev/null
+++ b/app/src/test/kotlin/org/libremail/ui/onboarding/AddAnotherAccountScreenJvmTest.kt
@@ -0,0 +1,78 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+package org.libremail.ui.onboarding
+
+import android.content.Context
+import androidx.compose.ui.test.assertIsDisplayed
+import androidx.compose.ui.test.junit4.v2.createComposeRule
+import androidx.compose.ui.test.onNodeWithText
+import androidx.compose.ui.test.performClick
+import org.junit.Assert.assertTrue
+import org.junit.Rule
+import org.junit.Test
+import org.junit.runner.RunWith
+import org.libremail.R
+import org.libremail.ui.theme.LibreMailTheme
+import org.robolectric.RobolectricTestRunner
+import org.robolectric.RuntimeEnvironment
+import org.robolectric.annotation.Config
+import org.robolectric.annotation.GraphicsMode
+
+/**
+ * Robolectric feasibility PoC (issue #373): proves Jetpack Compose UI can be unit-tested on the JVM
+ * without an emulator. `createComposeRule()` drives [AddAnotherAccountScreen] under
+ * [RobolectricTestRunner]; `stringResource(...)` and Material3 theming resolve because
+ * `testOptions.unitTests.isIncludeAndroidResources` is enabled in `app/build.gradle.kts`. Runs under
+ * `:app:testDebugUnitTest`, NOT `androidTest` — the instrumented `AddAnotherAccountScreenTest` stays.
+ *
+ * `@Config(sdk = [36])` because compileSdk/targetSdk 37 (preview) has no Robolectric 4.16 sandbox
+ * (also the default in `src/test/resources/robolectric.properties`); `@GraphicsMode(NATIVE)` is
+ * required for Compose to render under Robolectric.
+ */
+@RunWith(RobolectricTestRunner::class)
+@GraphicsMode(GraphicsMode.Mode.NATIVE)
+@Config(sdk = [36])
+class AddAnotherAccountScreenJvmTest {
+
+    @get:Rule
+    val composeTestRule = createComposeRule()
+
+    private val context: Context get() = RuntimeEnvironment.getApplication()
+
+    private fun string(resId: Int): String = context.getString(resId)
+
+    private fun setContent(onAddAnother: () -> Unit = {}, onFinish: () -> Unit = {}) {
+        composeTestRule.setContent {
+            LibreMailTheme(darkTheme = false, dynamicColor = false) {
+                AddAnotherAccountScreen(onAddAnother = onAddAnother, onFinish = onFinish)
+            }
+        }
+    }
+
+    @Test
+    fun rendersAccountAddedTitleFromResources() {
+        setContent()
+
+        // Proves the merged Android resource table loaded on the JVM (isIncludeAndroidResources).
+        composeTestRule.onNodeWithText(string(R.string.onboarding_account_added_title)).assertIsDisplayed()
+    }
+
+    @Test
+    fun tappingYes_invokesOnAddAnother() {
+        var addAnother = false
+        setContent(onAddAnother = { addAnother = true })
+
+        composeTestRule.onNodeWithText(string(R.string.onboarding_add_another_yes)).performClick()
+
+        assertTrue(addAnother)
+    }
+
+    @Test
+    fun tappingNo_invokesOnFinish() {
+        var finished = false
+        setContent(onFinish = { finished = true })
+
+        composeTestRule.onNodeWithText(string(R.string.onboarding_add_another_no)).performClick()
+
+        assertTrue(finished)
+    }
+}
diff --git a/app/src/test/resources/robolectric.properties b/app/src/test/resources/robolectric.properties
new file mode 100644
index 0000000..eb85a88
--- /dev/null
+++ b/app/src/test/resources/robolectric.properties
@@ -0,0 +1,7 @@
+# SPDX-License-Identifier: GPL-3.0-or-later
+# Default SDK for every Robolectric (JVM) test (issue #373). compileSdk/targetSdk are 37, a
+# preview level Robolectric 4.16.x does not ship a sandbox for; 36 (Baklava) is its newest
+# supported level and needs JDK 21 (the project's Gradle JDK). Individual tests may still override
+# with @Config(sdk = [..]). Only affects tests run with RobolectricTestRunner; plain JUnit unit
+# tests are unaffected.
+sdk=36
diff --git a/gradle/libs.versions.toml b/gradle/libs.versions.toml
index f61fb86..baf07e0 100644
--- a/gradle/libs.versions.toml
+++ b/gradle/libs.versions.toml
@@ -30,6 +30,22 @@ androidxTestRules = "1.7.0"
 turbine = "1.2.1"
 mockk = "1.14.11"
 greenmail = "2.1.9"
+# Robolectric — runs the Android framework on the JVM so Compose UI (createComposeRule) can be
+# unit-tested without an emulator (issue #373). 4.16.x is the first line to support compileSdk 36
+# (Baklava) and requires JDK 21 for it; API 37 (preview) is unsupported, so Robolectric tests pin
+# @Config(sdk = 36) — also set in app/src/test/resources/robolectric.properties.
+robolectric = "4.16.1"
+# The instrumented android-all runtime jar Robolectric loads into its sandbox to run the Android
+# framework on the JVM. By DEFAULT Robolectric downloads this ~200 MB artifact from Maven Central
+# lazily at TEST time (MavenDependencyResolver -> MavenArtifactFetcher); that runtime fetch is
+# unreliable on CI runners and failed the JVM Compose PoC with "Failed to fetch maven artifact"
+# (issue #373). Pinning it lets Gradle resolve+cache it and hand it to Robolectric in offline mode
+# (see the robolectricAndroidAll wiring in app/build.gradle.kts) so no network fetch happens at
+# test time. The value is BOTH Robolectric-version- and SDK-specific: it is exactly what
+# Robolectric 4.16.1's DefaultSdkProvider maps @Config(sdk = 36) to — androidVersion "16", build
+# "13921718", preinstrumented suffix "-i7". Bump it together with `robolectric` above, and update
+# it if the pinned @Config(sdk = ..) / robolectric.properties SDK ever changes.
+robolectricAndroidAll = "16-robolectric-13921718-i7"
 errorprone = "2.50.0"
 # Lint/format. ktlint owns formatting; detekt owns static analysis (formatting ruleset off).
 # detekt 2.0 is the only line with Gradle 9 support (stable 1.23.x tops out at Gradle 8.12).
@@ -115,6 +131,11 @@ mockk = { group = "io.mockk", name = "mockk", version.ref = "mockk" }
 # mockk's Android artifact for instrumented tests (dexmaker/byte-buddy-android backed).
 mockk-android = { group = "io.mockk", name = "mockk-android", version.ref = "mockk" }
 greenmail = { group = "com.icegreen", name = "greenmail", version.ref = "greenmail" }
+# Robolectric — JVM Android framework for unit-testing Compose UI without an emulator (issue #373).
+robolectric = { group = "org.robolectric", name = "robolectric", version.ref = "robolectric" }
+# Resolved via Gradle (not Robolectric's runtime Maven fetch) and staged for offline use so the JVM
+# Compose tests run in CI without a flaky test-time download — see app/build.gradle.kts (issue #373).
+robolectric-android-all-instrumented = { group = "org.robolectric", name = "android-all-instrumented", version.ref = "robolectricAndroidAll" }
 androidx-junit = { group = "androidx.test.ext", name = "junit", version.ref = "androidxJunit" }
 androidx-espresso-core = { group = "androidx.test.espresso", name = "espresso-core", version.ref = "espresso" }
 androidx-espresso-intents = { group = "androidx.test.espresso", name = "espresso-intents", version.ref = "espresso" }