diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 431860278..4a8c84d3b 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -47,6 +47,7 @@ jobs:
       dashboard: ${{ steps.filter.outputs.dashboard }}
       packaging: ${{ steps.filter.outputs.packaging }}
       workflows: ${{ steps.filter.outputs.workflows }}
+      env_docs: ${{ steps.filter.outputs.env_docs }}
     steps:
       - uses: actions/checkout@v7
       - uses: dorny/paths-filter@v4
@@ -99,6 +100,27 @@ jobs:
               - '.github/workflows/**'
             workflows:
               - '.github/workflows/**'
+            env_docs:
+              - 'headroom/**'
+              - 'crates/**'
+              - 'sdk/**'
+              - 'plugins/**'
+              - 'deploy/**'
+              - 'docker/**'
+              - 'scripts/**'
+
+  env-doc-consistency:
+    needs: changes
+    if: needs.changes.outputs.env_docs == 'true'
+    runs-on: ubuntu-latest
+    timeout-minutes: 5
+    steps:
+      - uses: actions/checkout@v7
+      - uses: actions/setup-python@v6
+        with:
+          python-version: ${{ env.PY_VERSION }}
+      - name: Verify documented environment variables
+        run: python scripts/ci/verify_documented_env_vars.py
 
   lint:
     needs: changes
diff --git a/.github/workflows/docs.yml b/.github/workflows/docs.yml
index c574cf636..bc6bd33c9 100644
--- a/.github/workflows/docs.yml
+++ b/.github/workflows/docs.yml
@@ -22,6 +22,9 @@ on:
     branches: [main]
     paths:
       - 'docs/**'
+      - 'README.md'
+      - 'SECURITY.md'
+      - 'scripts/ci/verify_documented_env_vars.py'
       - '.github/workflows/docs.yml'
   workflow_dispatch:
 
@@ -36,6 +39,13 @@ jobs:
     steps:
       - uses: actions/checkout@v6
 
+      - uses: actions/setup-python@v6
+        with:
+          python-version: '3.12'
+
+      - name: Verify documented environment variables
+        run: python scripts/ci/verify_documented_env_vars.py
+
       - name: Setup Node.js
         uses: actions/setup-node@v6
         with:
diff --git a/scripts/ci/verify_documented_env_vars.py b/scripts/ci/verify_documented_env_vars.py
new file mode 100644
index 000000000..4a5128a3f
--- /dev/null
+++ b/scripts/ci/verify_documented_env_vars.py
@@ -0,0 +1,341 @@
+#!/usr/bin/env python3
+"""Verify that documented environment variables exist in implementation source.
+
+The check is deliberately text-based and dependency-free so it can run before
+either the Python package or the documentation application is installed.  It
+guards against documentation for a misspelled or removed setting silently
+surviving after the implementation changes.
+"""
+
+from __future__ import annotations
+
+import argparse
+import re
+import sys
+from collections import defaultdict
+from dataclasses import dataclass
+from pathlib import Path
+
+# Match uppercase snake-case names without assuming who owns them.  Wildcard
+# families may be written as ``VENDOR_*`` or ``VENDOR_<FAMILY>``; both are
+# normalized to ``VENDOR_*`` before comparison with concrete source names.
+# Lowercase letters are part of the boundary so fragments such as ``DS_S`` in
+# ``.DS_Store`` are not mistaken for environment variables.
+ENV_VAR_PATTERN = re.compile(
+    r"(?<![A-Za-z0-9_])"
+    r"(?P<name>"
+    r"(?:[A-Z][A-Z0-9]*(?:_[A-Z0-9]+)*_(?:\*|<[A-Z][A-Z0-9_]*>))"
+    r"|(?:[A-Z][A-Z0-9]*(?:_[A-Z0-9]+)+)"
+    r")"
+    r"(?![A-Za-z0-9_])"
+)
+
+# Single-word names are too ambiguous to extract from prose, but shell syntax is
+# unambiguous.  This covers POSIX expansion (``$HOME`` / ``${HOME}``),
+# PowerShell (``$env:PATH``), and Windows expansion (``%USERPROFILE%``).
+CONTEXTUAL_SINGLE_ENV_VAR_PATTERN = re.compile(
+    r"(?:\$env:|\$\{?|%)"
+    r"(?P<name>[A-Z][A-Z0-9]*)"
+    r"(?:\}|%|(?![A-Za-z0-9_]))"
+)
+
+# Source can read a single-word variable through language APIs without shell
+# expansion.  Keep the accessors explicit so arbitrary quoted constants do not
+# become implementation evidence.
+SOURCE_SINGLE_ENV_ACCESS_PATTERN = re.compile(
+    r"(?:"
+    r"(?:os\.)?environ\.get|(?:os\.)?getenv|env\.get|getEnv|env_path|"
+    r"std::env::(?:var|var_os)"
+    r")\(\s*[\"'](?P<name>[A-Z][A-Z0-9]*)[\"']"
+    r"|(?:os\.)?environ\[\s*[\"'](?P<subscript_name>[A-Z][A-Z0-9]*)[\"']\s*\]"
+)
+
+# Uppercase snake-case is also used for enum members, error identifiers, and
+# explanatory path aliases.  These reviewed names occur in the scanned docs but
+# are not configuration.  Keep this list narrow: adding an entry opts that name
+# out of the documentation/source consistency guarantee.
+DOCUMENTED_NON_ENV_IDENTIFIERS = frozenset(
+    {
+        # Content types and pipeline stages.
+        "BUILD_OUTPUT",
+        "FIRST_LINE",
+        "INPUT_CACHED",
+        "INPUT_COMPRESSED",
+        "INPUT_RECEIVED",
+        "INPUT_REMEMBERED",
+        "INPUT_ROUTED",
+        "PLAIN_TEXT",
+        "POST_SEND",
+        "POST_START",
+        "PRE_SEND",
+        "PRE_START",
+        "RESPONSE_RECEIVED",
+        "SEARCH_RESULTS",
+        # Errors and library constants shown in troubleshooting guidance.
+        "CERTIFICATE_VERIFY_FAILED",
+        "MALFORMED_FUNCTION_CALL",
+        "UNSUPPORTED_METRIC_TYPE_MONOTONIC_CUMULATIVE_SUM",
+        "VERIFY_X509_STRICT",
+        # Symbolic bucket names used only in filesystem diagrams.
+        "CONFIG_DIR",
+        "WORKSPACE_DIR",
+    }
+)
+
+# Some documented variables are read by libraries or tools that Headroom invokes
+# rather than by a literal read site in this repository.  Listing them here keeps
+# typo detection strict while making that external ownership explicit and
+# reviewable.  The verifier itself is excluded from source scanning so this
+# policy cannot accidentally count as an implementation reference.
+EXTERNALLY_CONSUMED_VARIABLES = frozenset(
+    {
+        # Standard proxy and certificate variables read by HTTP clients.
+        "ALL_PROXY",
+        "CURL_CA_BUNDLE",
+        "HF_ENDPOINT",
+        "HTTPS_PROXY",
+        "HTTP_PROXY",
+        "NO_PROXY",
+        "REQUESTS_CA_BUNDLE",
+        "SSL_CERT_FILE",
+        # Standard shell / operating-system environment.
+        "HOME",
+        "PATH",
+        "PWD",
+        "TMPDIR",
+        "USERPROFILE",
+        # AWS SDK / Bedrock credential and endpoint discovery.
+        "AWS_ENDPOINT_URL_BEDROCK_RUNTIME",
+        # LiteLLM provider configuration.
+        "DEEPSEEK_API_KEY",
+        "GOOGLE_CLOUD_LOCATION",
+        "GOOGLE_CLOUD_PROJECT",
+        "GROK_CODE_XAI_API_KEY",
+        "VERTEXAI_LOCATION",
+        "VERTEXAI_PROJECT",
+        "XAI_API_KEY",
+        # ONNX Runtime build and dynamic-link controls.
+        "ORT_LIB_LOCATION",
+        "ORT_PREFER_DYNAMIC_LINK",
+        "ORT_STRATEGY",
+        # OpenTelemetry SDK autoconfiguration.
+        "OTEL_EXPORTER_OTLP_ENDPOINT",
+        "OTEL_EXPORTER_OTLP_HEADERS",
+        "OTEL_EXPORTER_OTLP_METRICS_TEMPORALITY_PREFERENCE",
+        "OTEL_EXPORTER_OTLP_PROTOCOL",
+    }
+)
+
+DOCUMENTATION_FILES = (Path("README.md"), Path("SECURITY.md"))
+DOCUMENTATION_GLOB = "docs/content/docs/**/*.mdx"
+
+# These are implementation surfaces, not tests or examples.  Docker and install
+# sources are included because a few documented host-side variables are consumed
+# before the Python or Rust process starts.
+SOURCE_PATHS = (
+    Path(".github"),
+    Path("headroom"),
+    Path("crates"),
+    Path("sdk"),
+    Path("plugins"),
+    Path("deploy"),
+    Path("docker"),
+    Path("scripts"),
+)
+EXCLUDED_SOURCE_FILES = {Path("scripts/ci/verify_documented_env_vars.py")}
+SOURCE_SUFFIXES = {
+    ".cjs",
+    ".js",
+    ".json",
+    ".mjs",
+    ".ps1",
+    ".py",
+    ".rs",
+    ".sh",
+    ".toml",
+    ".ts",
+    ".tsx",
+    ".yaml",
+    ".yml",
+}
+EXCLUDED_SOURCE_PARTS = {
+    "__pycache__",
+    "examples",
+    "fixtures",
+    "node_modules",
+    "target",
+    "tests",
+}
+
+
+@dataclass(frozen=True)
+class Occurrence:
+    """One documented environment-variable reference."""
+
+    path: Path
+    line: int
+
+
+def _read_text(path: Path) -> str:
+    return path.read_text(encoding="utf-8", errors="ignore")
+
+
+def _documentation_paths(root: Path) -> list[Path]:
+    paths = [root / relative_path for relative_path in DOCUMENTATION_FILES]
+    paths.extend(root.glob(DOCUMENTATION_GLOB))
+    return sorted(path for path in paths if path.is_file())
+
+
+def _source_files(root: Path) -> list[Path]:
+    files: list[Path] = []
+    for relative_path in SOURCE_PATHS:
+        path = root / relative_path
+        if path.is_file():
+            candidates = [path]
+        elif path.is_dir():
+            candidates = path.rglob("*")
+        else:
+            continue
+
+        for candidate in candidates:
+            if not candidate.is_file() or candidate.suffix not in SOURCE_SUFFIXES:
+                continue
+            relative_path = candidate.relative_to(root)
+            if relative_path in EXCLUDED_SOURCE_FILES:
+                continue
+            relative_parts = relative_path.parts
+            if any(part in EXCLUDED_SOURCE_PARTS for part in relative_parts):
+                continue
+            files.append(candidate)
+    return sorted(files)
+
+
+def _normalized_name(match: re.Match[str]) -> str:
+    """Return a concrete name or a normalized ``PREFIX_*`` family."""
+
+    name = match.group("name")
+    if "_<" in name:
+        return f"{name.split('_<', maxsplit=1)[0]}_*"
+    return name
+
+
+def _is_dotted_member(line: str, start: int) -> bool:
+    """Return whether a candidate is a code member such as ``Stage.PRE_SEND``."""
+
+    return re.search(r"[A-Za-z_][A-Za-z0-9_]*\.$", line[:start]) is not None
+
+
+def _documented_names_in_line(line: str) -> set[str]:
+    """Extract environment-variable references from one documentation line."""
+
+    names: set[str] = set()
+    for match in ENV_VAR_PATTERN.finditer(line):
+        name = _normalized_name(match)
+        if name in DOCUMENTED_NON_ENV_IDENTIFIERS:
+            continue
+        # Dotted uppercase members are code constants, not process settings.
+        # Explicit exclusions above still cover prose/table mentions of the same
+        # constants where the owning type is not present.
+        if _is_dotted_member(line, match.start()):
+            continue
+        names.add(name)
+    names.update(match.group("name") for match in CONTEXTUAL_SINGLE_ENV_VAR_PATTERN.finditer(line))
+    return names
+
+
+def documented_variables(root: Path) -> dict[str, list[Occurrence]]:
+    """Return documented variables and the locations that mention them."""
+
+    variables: dict[str, list[Occurrence]] = defaultdict(list)
+    for path in _documentation_paths(root):
+        for line_number, line in enumerate(_read_text(path).splitlines(), start=1):
+            for name in _documented_names_in_line(line):
+                variables[name].append(Occurrence(path=path.relative_to(root), line=line_number))
+    return dict(variables)
+
+
+def source_variables(root: Path) -> set[str]:
+    """Return environment-variable-shaped identifiers found in implementation source."""
+
+    variables: set[str] = set()
+    for path in _source_files(root):
+        text = _read_text(path)
+        variables.update(_normalized_name(match) for match in ENV_VAR_PATTERN.finditer(text))
+        variables.update(
+            match.group("name") for match in CONTEXTUAL_SINGLE_ENV_VAR_PATTERN.finditer(text)
+        )
+        variables.update(
+            match.group("name") or match.group("subscript_name")
+            for match in SOURCE_SINGLE_ENV_ACCESS_PATTERN.finditer(text)
+        )
+    return variables
+
+
+def _is_resolved(name: str, available: set[str] | frozenset[str]) -> bool:
+    """Return whether a concrete name or wildcard family is available."""
+
+    if name.endswith("*"):
+        prefix = name[:-1]
+        return any(
+            candidate.startswith(prefix) and not candidate.endswith("*") for candidate in available
+        )
+    return name in available
+
+
+def missing_variables(root: Path) -> dict[str, list[Occurrence]]:
+    """Return documented variables that have no implementation reference."""
+
+    documented = documented_variables(root)
+    implemented = source_variables(root)
+    available = implemented | EXTERNALLY_CONSUMED_VARIABLES
+    missing: dict[str, list[Occurrence]] = {}
+
+    for name, occurrences in documented.items():
+        if not _is_resolved(name, available):
+            missing[name] = occurrences
+
+    return missing
+
+
+def main(argv: list[str] | None = None) -> int:
+    parser = argparse.ArgumentParser(description=__doc__)
+    parser.add_argument(
+        "--root",
+        type=Path,
+        default=Path(__file__).resolve().parents[2],
+        help="Repository root (defaults to the checkout containing this script)",
+    )
+    args = parser.parse_args(argv)
+    root = args.root.resolve()
+
+    documented = documented_variables(root)
+    missing = missing_variables(root)
+    if missing:
+        for name, occurrences in sorted(missing.items()):
+            first = occurrences[0]
+            print(
+                f"::error file={first.path},line={first.line}::"
+                f"Documented environment variable {name} has no implementation reference",
+                file=sys.stderr,
+            )
+        print(
+            f"Found {len(missing)} documented environment variable(s) with no source reference.",
+            file=sys.stderr,
+        )
+        return 1
+
+    implemented = source_variables(root)
+    external_count = sum(
+        not _is_resolved(name, implemented) and _is_resolved(name, EXTERNALLY_CONSUMED_VARIABLES)
+        for name in documented
+    )
+    print(
+        f"Verified {len(documented)} documented environment variables "
+        f"({len(documented) - external_count} against repository source; "
+        f"{external_count} against the approved external-consumer policy)."
+    )
+    return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())
diff --git a/scripts/tests/test_ci_workflow.py b/scripts/tests/test_ci_workflow.py
index c38c399b9..56bbc01f0 100644
--- a/scripts/tests/test_ci_workflow.py
+++ b/scripts/tests/test_ci_workflow.py
@@ -21,3 +21,19 @@ def test_sharded_ci_uploads_only_explicit_coverage_reports() -> None:
 
     assert "files: coverage-${{ matrix.shard }}.xml" in upload_step
     assert "disable_search: true" in upload_step
+
+
+def test_ci_checks_documented_environment_variables_for_source_changes() -> None:
+    workflow = Path(".github/workflows/ci.yml").read_text(encoding="utf-8")
+
+    assert "env_docs: ${{ steps.filter.outputs.env_docs }}" in workflow
+    assert "env-doc-consistency:" in workflow
+    assert "python scripts/ci/verify_documented_env_vars.py" in workflow
+
+
+def test_docs_workflow_checks_environment_variables_for_documentation_changes() -> None:
+    workflow = Path(".github/workflows/docs.yml").read_text(encoding="utf-8")
+
+    assert "- 'README.md'" in workflow
+    assert "- 'SECURITY.md'" in workflow
+    assert "python scripts/ci/verify_documented_env_vars.py" in workflow
diff --git a/scripts/tests/test_verify_documented_env_vars.py b/scripts/tests/test_verify_documented_env_vars.py
new file mode 100644
index 000000000..d599f28e4
--- /dev/null
+++ b/scripts/tests/test_verify_documented_env_vars.py
@@ -0,0 +1,255 @@
+"""Tests for the documented environment-variable consistency check."""
+
+from __future__ import annotations
+
+import importlib.util
+import sys
+from pathlib import Path
+
+
+def _load_module():
+    script = Path(__file__).parent.parent / "ci" / "verify_documented_env_vars.py"
+    spec = importlib.util.spec_from_file_location("verify_documented_env_vars", script)
+    assert spec is not None
+    assert spec.loader is not None
+    module = importlib.util.module_from_spec(spec)
+    sys.modules[spec.name] = module
+    spec.loader.exec_module(module)
+    return module
+
+
+def _write_minimal_project(root: Path, *, docs: str, source: str) -> None:
+    docs_path = root / "docs" / "content" / "docs" / "configuration.mdx"
+    docs_path.parent.mkdir(parents=True)
+    docs_path.write_text(docs, encoding="utf-8")
+    source_path = root / "headroom" / "config.py"
+    source_path.parent.mkdir(parents=True)
+    source_path.write_text(source, encoding="utf-8")
+
+
+def test_exact_documented_variable_must_exist_in_source(tmp_path: Path) -> None:
+    module = _load_module()
+    _write_minimal_project(
+        tmp_path,
+        docs="Use `HEADROOM_REAL_SETTING` and `HEADROOM_MISSPELLED_SETTING`.\n",
+        source='REAL_SETTING = "HEADROOM_REAL_SETTING"\n',
+    )
+
+    missing = module.missing_variables(tmp_path)
+
+    assert list(missing) == ["HEADROOM_MISSPELLED_SETTING"]
+    assert missing["HEADROOM_MISSPELLED_SETTING"][0].line == 1
+
+
+def test_documented_wildcard_matches_a_concrete_source_variable(tmp_path: Path) -> None:
+    module = _load_module()
+    _write_minimal_project(
+        tmp_path,
+        docs="Leave `HEADROOM_OTEL_*` unset to use the ambient provider.\n",
+        source='ENABLED = "HEADROOM_OTEL_METRICS_ENABLED"\n',
+    )
+
+    assert module.missing_variables(tmp_path) == {}
+
+
+def test_placeholder_wildcard_is_normalized_and_matches_source(tmp_path: Path) -> None:
+    module = _load_module()
+    _write_minimal_project(
+        tmp_path,
+        docs="Set `DISABLE_PROMPT_CACHING_<FAMILY>` for one model family.\n",
+        source='SETTING = "DISABLE_PROMPT_CACHING_OPUS"\n',
+    )
+
+    documented = module.documented_variables(tmp_path)
+
+    assert set(documented) == {"DISABLE_PROMPT_CACHING_*"}
+    assert module.missing_variables(tmp_path) == {}
+
+
+def test_single_word_variable_is_discovered_from_shell_context(tmp_path: Path) -> None:
+    module = _load_module()
+    _write_minimal_project(
+        tmp_path,
+        docs="The wrapper reads `$ACME` and a typo such as `$ACMEE` must fail.\n",
+        source='value = os.environ.get("ACME")\n',
+    )
+
+    assert set(module.documented_variables(tmp_path)) == {"ACME", "ACMEE"}
+    assert set(module.missing_variables(tmp_path)) == {"ACMEE"}
+
+
+def test_host_side_variable_can_be_implemented_by_install_source(tmp_path: Path) -> None:
+    module = _load_module()
+    _write_minimal_project(
+        tmp_path,
+        docs="Set `HEADROOM_DOCKER_IMAGE` before installation.\n",
+        source="",
+    )
+    install_script = tmp_path / "scripts" / "install.sh"
+    install_script.parent.mkdir(parents=True)
+    install_script.write_text('IMAGE="${HEADROOM_DOCKER_IMAGE:-latest}"\n', encoding="utf-8")
+
+    assert module.missing_variables(tmp_path) == {}
+
+
+def test_root_docs_and_generic_environment_variable_names_are_scanned(
+    tmp_path: Path,
+) -> None:
+    module = _load_module()
+    (tmp_path / "README.md").write_text(
+        "Use `ANTHROPIC_BASE_URL`, `OPENAI_BASE_URL`, or `ACME_SERVICE_TOKEN`.\n",
+        encoding="utf-8",
+    )
+    (tmp_path / "SECURITY.md").write_text("Set `DO_NOT_TRACK=1`.\n", encoding="utf-8")
+    source_path = tmp_path / "headroom" / "proxy.py"
+    source_path.parent.mkdir(parents=True)
+    source_path.write_text(
+        'VARIABLES = ("ANTHROPIC_BASE_URL", "OPENAI_BASE_URL", '
+        '"ACME_SERVICE_TOKEN", "DO_NOT_TRACK")\n',
+        encoding="utf-8",
+    )
+
+    documented = module.documented_variables(tmp_path)
+
+    assert set(documented) == {
+        "ACME_SERVICE_TOKEN",
+        "ANTHROPIC_BASE_URL",
+        "DO_NOT_TRACK",
+        "OPENAI_BASE_URL",
+    }
+    assert module.missing_variables(tmp_path) == {}
+
+
+def test_code_constants_and_lowercase_name_fragments_are_not_variables(
+    tmp_path: Path,
+) -> None:
+    module = _load_module()
+    _write_minimal_project(
+        tmp_path,
+        docs=(
+            "Use `HEADROOM_REAL_SETTING`.\n"
+            "Compare PipelineStage.PRE_SEND with `FIRST_LINE`.\n"
+            "An install may contain .DS_Store or report CERTIFICATE_VERIFY_FAILED.\n"
+        ),
+        source='SETTING = "HEADROOM_REAL_SETTING"\n',
+    )
+
+    assert set(module.documented_variables(tmp_path)) == {"HEADROOM_REAL_SETTING"}
+
+
+def test_external_consumer_policy_is_explicit_and_does_not_hide_typos(
+    tmp_path: Path,
+) -> None:
+    module = _load_module()
+    _write_minimal_project(
+        tmp_path,
+        docs="Set `OTEL_EXPORTER_OTLP_ENDPOINT` and `OTEL_EXPORTER_OTLP_ENDPONT`.\n",
+        source="",
+    )
+
+    missing = module.missing_variables(tmp_path)
+
+    assert set(missing) == {"OTEL_EXPORTER_OTLP_ENDPONT"}
+
+
+def test_cli_success_reports_source_and_external_policy_scope(tmp_path: Path, capsys) -> None:
+    module = _load_module()
+    _write_minimal_project(
+        tmp_path,
+        docs="Set `HEADROOM_REAL_SETTING` and `OTEL_EXPORTER_OTLP_ENDPOINT`.\n",
+        source='SETTING = "HEADROOM_REAL_SETTING"\n',
+    )
+
+    exit_code = module.main(["--root", str(tmp_path)])
+
+    captured = capsys.readouterr()
+    assert exit_code == 0
+    assert (
+        "Verified 2 documented environment variables "
+        "(1 against repository source; 1 against the approved external-consumer policy)."
+        in captured.out
+    )
+
+
+def test_verifier_policy_does_not_count_as_an_implementation_reference(
+    tmp_path: Path,
+) -> None:
+    module = _load_module()
+    _write_minimal_project(
+        tmp_path,
+        docs="Set `ACME_EXTERNAL_SETTING`.\n",
+        source="",
+    )
+    verifier = tmp_path / "scripts" / "ci" / "verify_documented_env_vars.py"
+    verifier.parent.mkdir(parents=True)
+    verifier.write_text('POLICY = {"ACME_EXTERNAL_SETTING"}\n', encoding="utf-8")
+
+    assert set(module.missing_variables(tmp_path)) == {"ACME_EXTERNAL_SETTING"}
+
+
+def test_verifier_tests_do_not_count_as_implementation_references(tmp_path: Path) -> None:
+    module = _load_module()
+    _write_minimal_project(
+        tmp_path,
+        docs="Set `ACME_TEST_ONLY_SETTING`.\n",
+        source="",
+    )
+    verifier_test = tmp_path / "scripts" / "tests" / "test_verify_documented_env_vars.py"
+    verifier_test.parent.mkdir(parents=True)
+    verifier_test.write_text(
+        'REPRESENTATIVE_VARIABLE = "ACME_TEST_ONLY_SETTING"\n',
+        encoding="utf-8",
+    )
+
+    assert "ACME_TEST_ONLY_SETTING" not in module.source_variables(tmp_path)
+    assert set(module.missing_variables(tmp_path)) == {"ACME_TEST_ONLY_SETTING"}
+
+
+def test_repository_docs_discover_representative_environment_variable_families() -> None:
+    module = _load_module()
+    repository_root = Path(__file__).resolve().parents[2]
+
+    documented = set(module.documented_variables(repository_root))
+
+    assert {
+        # AWS and Bedrock.
+        "AWS_ACCESS_KEY_ID",
+        "AWS_ENDPOINT_URL_BEDROCK_RUNTIME",
+        "BEDROCK_TARGET_API_URL",
+        # Claude's alternate cloud runtimes.
+        "CLAUDE_CODE_USE_BEDROCK",
+        "CLAUDE_CODE_USE_FOUNDRY",
+        "CLAUDE_CODE_USE_VERTEX",
+        # Google and Vertex.
+        "GOOGLE_APPLICATION_CREDENTIALS",
+        "VERTEXAI_PROJECT",
+        # GitHub Copilot.
+        "GITHUB_COPILOT_ENTERPRISE_URL",
+        # Process-wide proxy and TLS controls.
+        "HTTP_PROXY",
+        "HTTPS_PROXY",
+        "NO_PROXY",
+        "REQUESTS_CA_BUNDLE",
+        "SSL_CERT_FILE",
+        # OpenTelemetry.
+        "OTEL_EXPORTER_OTLP_ENDPOINT",
+        # Provider keys outside the original prefix policy.
+        "OPENROUTER_API_KEY",
+        "XAI_API_KEY",
+    } <= documented
+
+
+def test_cli_fails_with_a_github_annotation_for_missing_variable(tmp_path: Path, capsys) -> None:
+    module = _load_module()
+    _write_minimal_project(
+        tmp_path,
+        docs="Configuration: `HEADROOM_REMOVED_SETTING`\n",
+        source="",
+    )
+
+    exit_code = module.main(["--root", str(tmp_path)])
+
+    captured = capsys.readouterr()
+    assert exit_code == 1
+    assert "::error file=docs/content/docs/configuration.mdx,line=1::" in captured.err
+    assert "HEADROOM_REMOVED_SETTING" in captured.err