diff --git a/backend/app/platform/config.py b/backend/app/platform/config.py
index 70251e7..c44b98c 100644
--- a/backend/app/platform/config.py
+++ b/backend/app/platform/config.py
@@ -68,3 +68,31 @@ def smtp_from() -> str:
 def smtp_starttls() -> bool:
     """STARTTLS on the relay connection (default on; disable only for odd relays)."""
     return os.environ.get("ECOMM_SMTP_STARTTLS", "1").strip().lower() not in {"0", "false", "no", "off"}
+
+
+def objectstore_kind() -> str:
+    """Which objectstore adapter to build: 'local' (dev/tests) or 'gcs' (deployed)."""
+    return os.environ.get("ECOMM_OBJECTSTORE_KIND") or "local"
+
+
+def objectstore_bucket() -> str:
+    """The GCS bucket name for the media objects (gcs adapter; deployment overlay)."""
+    return os.environ.get("ECOMM_OBJECTSTORE_BUCKET", "")
+
+
+def objectstore_local_dir() -> str:
+    """Base directory for the local-disk objectstore adapter (dev/tests)."""
+    return os.environ.get("ECOMM_OBJECTSTORE_DIR") or "/tmp/ecomm-objectstore"
+
+
+def public_base_url() -> str:
+    """Absolute origin for hosted image URLs in export (e.g. APP_URL); '' → relative."""
+    return (os.environ.get("APP_URL") or "").rstrip("/")
+
+
+def image_fetch_allow_private() -> bool:
+    """Allow image fetch from private/loopback hosts (dev/E2E fixture host only).
+    Default off — the SSRF guard rejects private ranges in deployed envs."""
+    return os.environ.get("ECOMM_IMAGE_FETCH_ALLOW_PRIVATE", "").strip().lower() in {
+        "1", "true", "yes", "on",
+    }
diff --git a/backend/app/platform/objectstore.py b/backend/app/platform/objectstore.py
new file mode 100644
index 0000000..2a7ef6f
--- /dev/null
+++ b/backend/app/platform/objectstore.py
@@ -0,0 +1,103 @@
+"""platform/objectstore — the media-blob port (SD-0002 §6.2, §6.3.1).
+
+A tiny put/get/delete port with two adapters, mirroring the SD-0001 mailer
+pattern: local-disk (dev/tests) and GCS (deployed). Owns no semantics — keys
+and content types come from the caller (the image-fetch phase). Objects are
+written once, never mutated (immutable, image-id-addressed).
+"""
+from __future__ import annotations
+
+import os
+from pathlib import Path
+from typing import Protocol
+
+from app.platform import config
+
+
+class ObjectNotFound(Exception):
+    """Raised by get() when the key has no object."""
+
+
+class ObjectStore(Protocol):
+    def put(self, key: str, data: bytes, content_type: str) -> None: ...
+    def get(self, key: str) -> bytes: ...
+    def delete(self, key: str) -> None: ...
+
+
+def build_objectstore(kind: str) -> ObjectStore:
+    """Select the objectstore adapter by configured kind (config.objectstore_kind, INV-8)."""
+    if kind == "local":
+        return LocalObjectStore(config.objectstore_local_dir())
+    if kind == "gcs":
+        return GcsObjectStore(config.objectstore_bucket())
+    raise ValueError(f"unknown objectstore kind: {kind!r}")
+
+
+def _safe_segments(key: str) -> tuple[str, ...]:
+    parts = tuple(p for p in key.split("/") if p)
+    if not parts or any(p in {".", ".."} for p in parts):
+        raise ValueError(f"unsafe objectstore key: {key!r}")
+    return parts
+
+
+class LocalObjectStore:
+    """Disk-backed adapter under a base dir; key path-segments become subdirs."""
+
+    def __init__(self, base_dir: str) -> None:
+        self._base = Path(base_dir)
+
+    def _path(self, key: str) -> Path:
+        return self._base.joinpath(*_safe_segments(key))
+
+    def put(self, key: str, data: bytes, content_type: str) -> None:
+        path = self._path(key)
+        path.parent.mkdir(parents=True, exist_ok=True)
+        path.write_bytes(data)
+
+    def get(self, key: str) -> bytes:
+        path = self._path(key)
+        try:
+            return path.read_bytes()
+        except FileNotFoundError as exc:
+            raise ObjectNotFound(key) from exc
+
+    def delete(self, key: str) -> None:
+        try:
+            os.remove(self._path(key))
+        except FileNotFoundError:
+            pass
+
+
+class GcsObjectStore:
+    """GCS adapter; auth via the VM service account ADC (no secret bytes).
+
+    google-cloud-storage is imported lazily so dev/test runs (local adapter)
+    don't require the package at import time.
+    """
+
+    def __init__(self, bucket_name: str) -> None:
+        if not bucket_name:
+            raise ValueError("gcs objectstore requires ECOMM_OBJECTSTORE_BUCKET")
+        from google.cloud import storage  # lazy
+
+        self._bucket = storage.Client().bucket(bucket_name)
+
+    def put(self, key: str, data: bytes, content_type: str) -> None:
+        _safe_segments(key)
+        self._bucket.blob(key).upload_from_string(data, content_type=content_type)
+
+    def get(self, key: str) -> bytes:
+        from google.cloud.exceptions import NotFound  # lazy
+
+        try:
+            return self._bucket.blob(key).download_as_bytes()
+        except NotFound as exc:
+            raise ObjectNotFound(key) from exc
+
+    def delete(self, key: str) -> None:
+        from google.cloud.exceptions import NotFound  # lazy
+
+        try:
+            self._bucket.blob(key).delete()
+        except NotFound:
+            pass
diff --git a/backend/requirements.txt b/backend/requirements.txt
index e0cc306..8aaa1da 100644
--- a/backend/requirements.txt
+++ b/backend/requirements.txt
@@ -8,3 +8,4 @@ import-linter>=2.0
 nh3>=0.2
 python-multipart>=0.0.9
 Pillow>=11.0
+google-cloud-storage>=2.18
diff --git a/backend/tests/test_platform_objectstore.py b/backend/tests/test_platform_objectstore.py
new file mode 100644
index 0000000..0968570
--- /dev/null
+++ b/backend/tests/test_platform_objectstore.py
@@ -0,0 +1,44 @@
+"""platform/objectstore — local-disk adapter round-trip (SD-0002 §6.2/§6.3.1)."""
+import pytest
+
+from app.platform import objectstore
+
+
+def test_local_put_get_round_trip(tmp_path):
+    store = objectstore.LocalObjectStore(str(tmp_path))
+    key = "storefronts/1/product-images/9/original"
+    store.put(key, b"\x89PNG-bytes", "image/png")
+    assert store.get(key) == b"\x89PNG-bytes"
+
+
+def test_local_get_missing_raises_not_found(tmp_path):
+    store = objectstore.LocalObjectStore(str(tmp_path))
+    with pytest.raises(objectstore.ObjectNotFound):
+        store.get("nope/missing")
+
+
+def test_local_delete_is_idempotent(tmp_path):
+    store = objectstore.LocalObjectStore(str(tmp_path))
+    store.put("a/b", b"x", "text/plain")
+    store.delete("a/b")
+    store.delete("a/b")  # no error second time
+    with pytest.raises(objectstore.ObjectNotFound):
+        store.get("a/b")
+
+
+def test_local_keys_cannot_escape_base_dir(tmp_path):
+    store = objectstore.LocalObjectStore(str(tmp_path))
+    with pytest.raises(ValueError):
+        store.put("../escape", b"x", "text/plain")
+
+
+def test_build_objectstore_local(tmp_path, monkeypatch):
+    monkeypatch.setenv("ECOMM_OBJECTSTORE_KIND", "local")
+    monkeypatch.setenv("ECOMM_OBJECTSTORE_DIR", str(tmp_path))
+    store = objectstore.build_objectstore("local")
+    assert isinstance(store, objectstore.LocalObjectStore)
+
+
+def test_build_objectstore_unknown_kind_raises():
+    with pytest.raises(ValueError):
+        objectstore.build_objectstore("s3")