diff --git a/Makefile b/Makefile
index fc1dded..df11c1d 100644
--- a/Makefile
+++ b/Makefile
@@ -70,7 +70,7 @@ db-reset: ## Recreate the local database volume
 	$(COMPOSE) up -d postgres
 
 api-import: ## Import an API snapshot
-	@echo "API import is scheduled for milestone B4" >&2; exit 2
+	$(BIN)/proxmox-api-contract import $(ARGS)
 
 api-diff: ## Compare API snapshots
 	@echo "API diff is scheduled for milestone B5" >&2; exit 2
@@ -82,4 +82,3 @@ clean: ## Remove generated local artifacts
 	rm -rf $(VENV) .coverage coverage.xml htmlcov .mypy_cache .pytest_cache .ruff_cache
 
 ci: format lint typecheck coverage ## Run the complete local quality gate
-
diff --git a/README.md b/README.md
index 4524a33..2582f9e 100644
--- a/README.md
+++ b/README.md
@@ -26,7 +26,20 @@ curl http://localhost:8006/health/live
 curl http://localhost:8006/health/ready
 ```
 
+Contract artifacts can be validated and imported into immutable local revisions:
+
+```bash
+.venv/bin/proxmox-api-contract validate tests/fixtures/api-viewer/pve-9.2.3-version.json
+.venv/bin/proxmox-api-contract --store contracts import \
+  --file tests/fixtures/api-viewer/pve-9.2.3-version.json --version 9.2.3
+.venv/bin/proxmox-api-contract --store contracts list
+```
+
+Remote imports accept HTTPS URLs on the explicit official-domain allowlist and
+reject private address resolution, unsafe redirects, oversized responses, and
+unbounded retries. Imported revisions are addressed by their normalized
+snapshot checksum and are never overwritten.
+
 See [the architecture](docs/architecture.md) for component boundaries and
 durability decisions. Commands for not-yet-implemented milestones intentionally
 return a non-zero status instead of pretending to succeed.
-
diff --git a/app/contracts/cli.py b/app/contracts/cli.py
new file mode 100644
index 0000000..375488f
--- /dev/null
+++ b/app/contracts/cli.py
@@ -0,0 +1,62 @@
+"""Command-line interface for contract imports and inspection."""
+
+from __future__ import annotations
+
+import argparse
+import asyncio
+import json
+from datetime import UTC, datetime
+from pathlib import Path
+
+from app.contracts.importer import RemoteSourceImporter
+from app.contracts.normalize import normalize_snapshot
+from app.contracts.source import ApiViewerParser, LocalFileImporter, SourceImporter
+from app.contracts.store import RevisionStore
+
+
+def parser() -> argparse.ArgumentParser:
+    root = argparse.ArgumentParser(prog="proxmox-api-contract")
+    root.add_argument("--store", type=Path, default=Path("contracts"))
+    commands = root.add_subparsers(dest="command", required=True)
+    import_command = commands.add_parser("import")
+    source = import_command.add_mutually_exclusive_group(required=True)
+    source.add_argument("--file", type=Path)
+    source.add_argument("--url")
+    import_command.add_argument("--version", required=True)
+    validate = commands.add_parser("validate")
+    validate.add_argument("file", type=Path)
+    commands.add_parser("list")
+    show = commands.add_parser("show")
+    show.add_argument("revision")
+    return root
+
+
+async def run(arguments: argparse.Namespace) -> int:
+    store = RevisionStore(arguments.store)
+    if arguments.command == "list":
+        for revision in store.list():
+            print(revision)
+        return 0
+    if arguments.command == "show":
+        print(json.dumps(store.manifest(arguments.revision).model_dump(mode="json"), indent=2))
+        return 0
+    if arguments.command == "validate":
+        parsed = ApiViewerParser().parse(arguments.file.read_bytes())
+        print(json.dumps({"nodes": len(parsed.nodes), "warnings": len(parsed.warnings)}))
+        return 0
+    importer: SourceImporter
+    if arguments.file is not None:
+        importer = LocalFileImporter(arguments.file)
+    else:
+        importer = RemoteSourceImporter(arguments.url)
+    raw = await importer.load()
+    parsed = ApiViewerParser().parse(raw)
+    snapshot, manifest = normalize_snapshot(
+        parsed, raw=raw, source_version=arguments.version, retrieved_at=datetime.now(UTC)
+    )
+    print(store.save(raw, snapshot, manifest))
+    return 0
+
+
+def main() -> None:
+    raise SystemExit(asyncio.run(run(parser().parse_args())))
diff --git a/app/contracts/importer.py b/app/contracts/importer.py
new file mode 100644
index 0000000..5622802
--- /dev/null
+++ b/app/contracts/importer.py
@@ -0,0 +1,95 @@
+"""Network-constrained remote contract retrieval."""
+
+from __future__ import annotations
+
+import asyncio
+import ipaddress
+import socket
+from collections.abc import Awaitable, Callable
+from dataclasses import dataclass
+from urllib.parse import urljoin, urlsplit
+
+import httpx
+
+from app.contracts.source import SourceError
+
+Resolver = Callable[[str], Awaitable[tuple[str, ...]]]
+
+
+async def resolve_host(host: str) -> tuple[str, ...]:
+    loop = asyncio.get_running_loop()
+    results = await loop.getaddrinfo(host, 443, type=socket.SOCK_STREAM)
+    return tuple(sorted({str(result[4][0]) for result in results}))
+
+
+def validate_remote_url(url: str, allowed_hosts: frozenset[str]) -> str:
+    parsed = urlsplit(url)
+    if parsed.scheme != "https":
+        raise SourceError("remote imports require HTTPS")
+    if parsed.username or parsed.password or parsed.port not in (None, 443):
+        raise SourceError("remote URL contains forbidden authority components")
+    host = (parsed.hostname or "").rstrip(".").lower()
+    if host not in allowed_hosts:
+        raise SourceError("remote host is not in the official-domain allowlist")
+    if parsed.fragment:
+        raise SourceError("remote URL fragments are not allowed")
+    return host
+
+
+def validate_public_addresses(addresses: tuple[str, ...]) -> None:
+    if not addresses:
+        raise SourceError("remote host did not resolve")
+    for value in addresses:
+        address = ipaddress.ip_address(value)
+        if not address.is_global:
+            raise SourceError(f"remote host resolved to a non-public address: {value}")
+
+
+@dataclass(frozen=True, slots=True)
+class RemoteSourceImporter:
+    url: str
+    allowed_hosts: frozenset[str] = frozenset({"pve.proxmox.com"})
+    max_bytes: int = 16 * 1024 * 1024
+    max_redirects: int = 3
+    retries: int = 2
+    timeout_seconds: float = 20.0
+    resolver: Resolver = resolve_host
+    transport: httpx.AsyncBaseTransport | None = None
+
+    async def load(self) -> bytes:
+        current = self.url
+        timeout = httpx.Timeout(self.timeout_seconds)
+        async with httpx.AsyncClient(
+            follow_redirects=False, timeout=timeout, transport=self.transport
+        ) as client:
+            for redirect_count in range(self.max_redirects + 1):
+                host = validate_remote_url(current, self.allowed_hosts)
+                validate_public_addresses(await self.resolver(host))
+                response = await self._request(client, current)
+                if response.is_redirect:
+                    if redirect_count == self.max_redirects:
+                        raise SourceError("remote import exceeded redirect limit")
+                    location = response.headers.get("location")
+                    if not location:
+                        raise SourceError("remote redirect has no location")
+                    current = urljoin(current, location)
+                    continue
+                response.raise_for_status()
+                content_length = response.headers.get("content-length")
+                if content_length and int(content_length) > self.max_bytes:
+                    raise SourceError("remote artifact exceeds size limit")
+                content = response.content
+                if len(content) > self.max_bytes:
+                    raise SourceError("remote artifact exceeds size limit")
+                return content
+        raise SourceError("remote import failed")
+
+    async def _request(self, client: httpx.AsyncClient, url: str) -> httpx.Response:
+        for attempt in range(self.retries + 1):
+            try:
+                return await client.get(url)
+            except (httpx.TimeoutException, httpx.NetworkError):
+                if attempt == self.retries:
+                    raise
+                await asyncio.sleep(0.1 * (2**attempt))
+        raise SourceError("remote import retry loop exhausted")
diff --git a/app/contracts/store.py b/app/contracts/store.py
new file mode 100644
index 0000000..a1bd4d0
--- /dev/null
+++ b/app/contracts/store.py
@@ -0,0 +1,48 @@
+"""Immutable filesystem storage for imported contract revisions."""
+
+from __future__ import annotations
+
+import os
+import tempfile
+from dataclasses import dataclass
+from pathlib import Path
+
+from app.contracts.model import Manifest, Snapshot, canonical_json
+
+
+@dataclass(frozen=True, slots=True)
+class RevisionStore:
+    root: Path
+
+    def save(self, raw: bytes, snapshot: Snapshot, manifest: Manifest) -> Path:
+        revision = self.root / manifest.snapshot_sha256
+        if revision.exists():
+            return revision
+        self.root.mkdir(parents=True, exist_ok=True)
+        temporary = Path(tempfile.mkdtemp(prefix=".import-", dir=self.root))
+        try:
+            self._write(temporary / "raw.js", raw)
+            self._write(temporary / "snapshot.json", snapshot.canonical_bytes())
+            self._write(temporary / "manifest.json", canonical_json(manifest))
+            os.replace(temporary, revision)
+        except BaseException:
+            for child in temporary.iterdir():
+                child.unlink()
+            temporary.rmdir()
+            raise
+        return revision
+
+    def list(self) -> tuple[str, ...]:
+        if not self.root.exists():
+            return ()
+        return tuple(sorted(path.name for path in self.root.iterdir() if path.is_dir()))
+
+    def manifest(self, revision: str) -> Manifest:
+        return Manifest.model_validate_json((self.root / revision / "manifest.json").read_bytes())
+
+    @staticmethod
+    def _write(path: Path, content: bytes) -> None:
+        with path.open("xb") as stream:
+            stream.write(content)
+            stream.flush()
+            os.fsync(stream.fileno())
diff --git a/pyproject.toml b/pyproject.toml
index b8b5887..3953099 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -13,6 +13,7 @@ authors = [{ name = "proxmox-api-simulator contributors" }]
 dependencies = [
   "asyncpg>=0.30,<0.31",
   "fastapi>=0.116,<0.117",
+  "httpx>=0.28,<0.29",
   "pydantic>=2.11,<3",
   "pydantic-settings>=2.10,<3",
   "uvicorn[standard]>=0.35,<0.36",
@@ -21,7 +22,6 @@ dependencies = [
 [project.optional-dependencies]
 dev = [
   "hypothesis>=6.135,<7",
-  "httpx>=0.28,<0.29",
   "mypy>=1.17,<1.18",
   "pytest>=8.4,<9",
   "pytest-asyncio>=1.1,<2",
@@ -29,6 +29,9 @@ dev = [
   "ruff>=0.12,<0.13",
 ]
 
+[project.scripts]
+proxmox-api-contract = "app.contracts.cli:main"
+
 [tool.hatch.build.targets.wheel]
 packages = ["app"]
 
diff --git a/tests/unit/test_contract_cli.py b/tests/unit/test_contract_cli.py
new file mode 100644
index 0000000..9d57fee
--- /dev/null
+++ b/tests/unit/test_contract_cli.py
@@ -0,0 +1,52 @@
+"""Offline command workflows for contract management."""
+
+import argparse
+import json
+from pathlib import Path
+
+import pytest
+
+from app.contracts.cli import parser, run
+
+FIXTURE = Path(__file__).parents[1] / "fixtures" / "api-viewer" / "pve-9.2.3-version.json"
+
+
+async def test_validate_command_reports_source_counts(
+    tmp_path: Path, capsys: pytest.CaptureFixture[str]
+) -> None:
+    arguments = argparse.Namespace(command="validate", store=tmp_path, file=FIXTURE)
+
+    assert await run(arguments) == 0
+    output = capsys.readouterr().out
+    assert json.loads(output) == {"nodes": 1, "warnings": 0}
+
+
+async def test_local_import_list_and_show(
+    tmp_path: Path, capsys: pytest.CaptureFixture[str]
+) -> None:
+    import_arguments = argparse.Namespace(
+        command="import",
+        store=tmp_path,
+        file=FIXTURE,
+        url=None,
+        version="9.2.3",
+    )
+    assert await run(import_arguments) == 0
+    revision = Path(capsys.readouterr().out.strip()).name
+
+    assert await run(argparse.Namespace(command="list", store=tmp_path)) == 0
+    assert capsys.readouterr().out.strip() == revision
+
+    assert await run(argparse.Namespace(command="show", store=tmp_path, revision=revision)) == 0
+    manifest = json.loads(capsys.readouterr().out)
+    assert manifest["source_version"] == "9.2.3"
+    assert manifest["snapshot_sha256"] == revision
+
+
+def test_cli_parser_accepts_local_import() -> None:
+    arguments = parser().parse_args(
+        ["--store", "saved", "import", "--file", str(FIXTURE), "--version", "9.2.3"]
+    )
+
+    assert arguments.command == "import"
+    assert arguments.store == Path("saved")
diff --git a/tests/unit/test_contract_importer.py b/tests/unit/test_contract_importer.py
new file mode 100644
index 0000000..715a98b
--- /dev/null
+++ b/tests/unit/test_contract_importer.py
@@ -0,0 +1,90 @@
+"""Security and idempotency tests for contract imports."""
+
+from datetime import UTC, datetime
+from pathlib import Path
+
+import httpx
+import pytest
+
+from app.contracts.importer import RemoteSourceImporter, validate_remote_url
+from app.contracts.normalize import normalize_snapshot
+from app.contracts.source import ApiViewerParser, SourceError
+from app.contracts.store import RevisionStore
+
+
+async def public_resolver(_host: str) -> tuple[str, ...]:
+    return ("93.184.216.34",)
+
+
+@pytest.mark.parametrize(
+    "url",
+    [
+        "http://pve.proxmox.com/apidoc.js",
+        "https://evil.example/apidoc.js",
+        "https://pve.proxmox.com.evil.example/apidoc.js",
+        "https://user@pve.proxmox.com/apidoc.js",
+        "https://pve.proxmox.com:444/apidoc.js",
+    ],
+)
+def test_remote_url_policy_rejects_unsafe_urls(url: str) -> None:
+    with pytest.raises(SourceError):
+        validate_remote_url(url, frozenset({"pve.proxmox.com"}))
+
+
+async def test_remote_import_rejects_private_resolution() -> None:
+    async def private_resolver(_host: str) -> tuple[str, ...]:
+        return ("127.0.0.1",)
+
+    importer = RemoteSourceImporter(
+        "https://pve.proxmox.com/apidoc.js",
+        resolver=private_resolver,
+        transport=httpx.MockTransport(lambda request: httpx.Response(200, content=b"[]")),
+    )
+
+    with pytest.raises(SourceError, match="non-public"):
+        await importer.load()
+
+
+async def test_redirect_is_revalidated() -> None:
+    def handler(request: httpx.Request) -> httpx.Response:
+        return httpx.Response(302, headers={"location": "https://evil.example/private"})
+
+    importer = RemoteSourceImporter(
+        "https://pve.proxmox.com/apidoc.js",
+        resolver=public_resolver,
+        transport=httpx.MockTransport(handler),
+    )
+
+    with pytest.raises(SourceError, match="allowlist"):
+        await importer.load()
+
+
+async def test_remote_import_enforces_size_limit() -> None:
+    importer = RemoteSourceImporter(
+        "https://pve.proxmox.com/apidoc.js",
+        max_bytes=2,
+        resolver=public_resolver,
+        transport=httpx.MockTransport(lambda request: httpx.Response(200, content=b"[]\n")),
+    )
+
+    with pytest.raises(SourceError, match="size"):
+        await importer.load()
+
+
+def test_revision_store_is_idempotent(tmp_path: Path) -> None:
+    raw = b'[{"path":"/version","info":{}}]'
+    parsed = ApiViewerParser().parse(raw)
+    snapshot, manifest = normalize_snapshot(
+        parsed,
+        raw=raw,
+        source_version="test",
+        retrieved_at=datetime(2026, 1, 1, tzinfo=UTC),
+    )
+    store = RevisionStore(tmp_path)
+
+    first = store.save(raw, snapshot, manifest)
+    second = store.save(raw, snapshot, manifest)
+
+    assert first == second
+    assert store.list() == (manifest.snapshot_sha256,)
+    assert store.manifest(manifest.snapshot_sha256) == manifest