diff --git a/Dockerfile b/Dockerfile
index 723ce0d..e0002fa 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -10,15 +10,17 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
 
 WORKDIR /app
 
-# Install Python deps first (cache layer)
+# Install Python deps first (cache layer). requirements.txt is the core
+# package graph; the Spaces extra adds Gradio for app.py without pulling
+# the quantization extra.
 COPY requirements.txt .
 RUN pip install --no-cache-dir -r requirements.txt
 
 # Copy project
 COPY . .
 
-# Install the package itself (for obliteratus imports)
-RUN pip install --no-cache-dir .
+# Install the package itself (for obliteratus imports) plus the UI extra.
+RUN pip install --no-cache-dir ".[spaces]"
 
 # Run as non-root user for security
 RUN useradd -m appuser
diff --git a/README.md b/README.md
index 6bcd9b5..8516422 100644
--- a/README.md
+++ b/README.md
@@ -170,7 +170,9 @@ and rollback requirements.
 Install `.[spaces,quantization]` instead when the UI must load supported
 bitsandbytes 8-bit or 4-bit models. Jetson users must follow the dedicated
 [Jetson bootstrap](docs/platforms/jetson.md); its bitsandbytes path is not yet
-supported.
+supported. Android/Termux is not a supported runtime; if you install there
+anyway, follow the [Android install notes](docs/platforms/android.md) so pip
+does not isolate a second setuptools or replace host wheels.
 
 ### 3. Google Colab (free GPU)
 
diff --git a/ci/pr-test-policy.json b/ci/pr-test-policy.json
index 48184e6..edcff09 100644
--- a/ci/pr-test-policy.json
+++ b/ci/pr-test-policy.json
@@ -20,6 +20,9 @@
     "scripts/select_pr_tests.py",
     "scripts/setup_jetson.py",
     "pyproject.toml",
+    "requirements.txt",
+    "Dockerfile",
+    "docs/platforms/**",
     "uv.lock",
     "tests/fixtures/distributed_checkpoints/**"
   ],
diff --git a/docs/platforms/android.md b/docs/platforms/android.md
new file mode 100644
index 0000000..ef24604
--- /dev/null
+++ b/docs/platforms/android.md
@@ -0,0 +1,56 @@
+# Android / Termux install notes
+
+Android is not a supported OBLITERATUS runtime. These notes exist so a
+Termux (or other Android Python) install does not fight host wheels or
+download a second setuptools behind PEP 517 isolation.
+
+`sys.platform` on current Android CPython is `android`, not `linux`. The
+locked CPU PyTorch index in `pyproject.toml` is intentionally limited to
+`linux` and `win32` manylinux/Windows wheels. Do not point Android at that
+index.
+
+## Layout
+
+1. Install the platform's own `python`, `setuptools`, and scientific
+   wheels first (`torch`, `numpy`, and whatever Termux already packages).
+   Those builds carry the Android patches that PyPI wheels do not.
+   `safetensors` and `tokenizers` are Rust extensions; rustup does not
+   host `aarch64-linux-android`, so install Termux `rust` before pip
+   and export the API level Python was built against (24 on current
+   Termux):
+
+   ```bash
+   pkg install rust
+   export ANDROID_API_LEVEL=24
+   ```
+
+2. Isolated pip builds of meson packages (pandas, matplotlib) will try
+   to compile `cmake`/`ninja` from source and can hang under proot.
+   Install those binaries from Termux first (`pkg install ninja cmake
+   python-matplotlib python-scipy python-pillow python-psutil
+   python-pyarrow python-greenlet python-brotli python-cryptography
+   python-rpds-py python-msgpack libraqm harfbuzz`). PyPI `psutil`
+   sdists reject `sys.platform == "android"`; the Termux package is
+   patched. Termux matplotlib needs `libraqm`. PyPI `tokenizers` abi3
+   wheels fail on CPython 3.14 (`PyBaseObject_Type`); rebuild without
+   the `abi3` cargo feature so the extension is `cp314` instead of
+   `abi3`. Then install OBLITERATUS without build isolation:
+
+   ```bash
+   python -m pip install --no-build-isolation -e ".[spaces]"
+   ```
+
+3. If pip still tries to compile `torch` or `numpy` from source, install
+   the project over the host packages instead:
+
+   ```bash
+   python -m pip install --no-build-isolation --no-deps -e .
+   python -m pip install --no-build-isolation "gradio>=6.7,<7.0"
+   ```
+
+Do not use `uv sync --locked` on Android. The lock resolves Linux/Windows
+CPU PyTorch and does not contain `android_*` wheels for torch, numpy,
+pyarrow, tokenizers, or bitsandbytes.
+
+The `quantization` and `qwen-hybrid` extras are CUDA-oriented and are not
+an Android install path.
diff --git a/pyproject.toml b/pyproject.toml
index cb394da..02b1071 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -1,5 +1,7 @@
 [build-system]
-requires = ["setuptools==80.9.0", "wheel==0.45.1"]
+# Lower bound only. Exact backend pins block platform-specific setuptools patches.
+# A separate wheel package is not required for the PEP 517 backend.
+requires = ["setuptools>=80.9.0"]
 build-backend = "setuptools.build_meta"
 
 [project]
diff --git a/requirements.txt b/requirements.txt
index d985dd9..2ebfff7 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,4 +1,5 @@
-gradio>=6.7,<7.0
+# Mirrors [project].dependencies in pyproject.toml.
+# Optional extras (spaces, quantization, qwen-hybrid, dev) are not included.
 torch>=2.0
 transformers>=4.40
 datasets>=2.14
@@ -13,4 +14,3 @@ numpy>=1.24
 scikit-learn>=1.3
 tqdm>=4.64
 optuna>=4.9,<5
-bitsandbytes>=0.46.1
diff --git a/tests/test_ci_policy.py b/tests/test_ci_policy.py
index 1034eb4..1864846 100644
--- a/tests/test_ci_policy.py
+++ b/tests/test_ci_policy.py
@@ -225,6 +225,28 @@ def test_ci_evidence_names_the_pull_request_head_not_the_synthetic_merge_commit(
     assert '--head-sha "$GITHUB_SHA"' not in workflow
 
 
+def test_build_backend_requirements_use_lower_bounds_not_exact_pins():
+    pyproject = (ROOT / "pyproject.toml").read_text(encoding="utf-8")
+    match = re.search(
+        r"(?ms)^\[build-system\]\n(?:#[^\n]*\n)*requires = \[([^\]]+)\]",
+        pyproject,
+    )
+    assert match is not None
+    requires = re.findall(r'"([^"]+)"', match.group(1))
+    assert requires
+    for requirement in requires:
+        spec = requirement.split(";", 1)[0]
+        name = re.split(r"[<>=!~]", spec, maxsplit=1)[0].strip()
+        assert name != "wheel", requirement
+        assert "==" not in spec, requirement
+        assert ">=" in spec, requirement
+        lower = re.findall(r">=([^,]+)", spec)
+        upper = re.findall(r"<=([^,]+)", spec)
+        assert not (
+            lower and upper and lower[0] == upper[0]
+        ), f"collapsed exact pin written as a range: {requirement}"
+
+
 def test_ci_runs_checkpoint_portability_contracts_on_windows():
     workflow = WORKFLOW.read_text(encoding="utf-8")
     checkpoint_job = workflow.split("  checkpoint-windows:\n", maxsplit=1)[1].split(
diff --git a/tests/test_jetson_support_tooling.py b/tests/test_jetson_support_tooling.py
index 84e6f7e..3f89f84 100644
--- a/tests/test_jetson_support_tooling.py
+++ b/tests/test_jetson_support_tooling.py
@@ -217,6 +217,26 @@ def test_bitsandbytes_is_opt_in_for_quantization_only():
     assert extras["quantization"] == ["bitsandbytes>=0.46.1"]
 
 
+def test_requirements_txt_mirrors_core_pyproject_dependencies():
+    metadata = tomllib.loads((ROOT / "pyproject.toml").read_text())
+    requirements = [
+        line.strip()
+        for line in (ROOT / "requirements.txt").read_text().splitlines()
+        if line.strip() and not line.startswith("#")
+    ]
+
+    assert requirements == metadata["project"]["dependencies"]
+    assert not any(value.startswith("bitsandbytes") for value in requirements)
+    assert not any(value.startswith("gradio") for value in requirements)
+
+
+def test_dockerfile_installs_spaces_extra_not_quantization():
+    dockerfile = (ROOT / "Dockerfile").read_text()
+
+    assert 'pip install --no-cache-dir ".[spaces]"' in dockerfile
+    assert "bitsandbytes" not in dockerfile
+
+
 def test_jetson_issue_form_requires_reproducible_sanitized_hardware_evidence():
     form = yaml.safe_load(
         (ROOT / ".github" / "ISSUE_TEMPLATE" / "jetson-runtime.yml").read_text(),