fix(meta): cover access-token env handling, JSON-encoded creative, and previews fail-fast contract

Address code review findings on the read-only Meta Graph client: add
monkeypatch-based tests for access_token_from_env/MetaNotConfiguredError,
assert generate_previews JSON-encodes the creative param, pin the
existing fail-fast-on-partial-error contract with a dedicated test, and
declare httpx as an explicit dependency since it was only resolving
transitively.

pyproject.toml

@@ -22,6 +22,7 @@ dependencies = [
     "google-genai>=1.0.0",
     "Pillow>=10.0.0",
     "psycopg[binary]>=3.2.0",
+    "httpx>=0.27",
 ]
 
 [tool.setuptools.dynamic]

tests/test_meta_client.py

@@ -1,8 +1,16 @@
 # -*- coding: utf-8 -*-
 """Read-only Meta Graph client behaviour."""
+import json
+
 import pytest
 
-from adclaw.meta.client import MetaClient, MetaError
+from adclaw.meta.client import (
+    ACCESS_TOKEN_ENV,
+    MetaClient,
+    MetaError,
+    MetaNotConfiguredError,
+    access_token_from_env,
+)
 
 
 class FakeTransport:
@@ -65,6 +73,12 @@ async def test_generate_previews_returns_body_per_format():
     assert previews["INSTAGRAM_STORY"] == "<iframe src='story'></iframe>"
     assert transport.calls[0]["params"]["ad_format"] == "DESKTOP_FEED_STANDARD"
 
+    # The creative must be sent as a JSON-encoded string in the query
+    # params, not as a raw dict, since Graph expects `creative` as JSON text.
+    sent = transport.calls[0]["params"]["creative"]
+    assert isinstance(sent, str)
+    assert json.loads(sent) == {"object_story_spec": {}}
+
 
 @pytest.mark.asyncio
 async def test_generate_previews_skips_formats_with_no_body():
@@ -78,3 +92,49 @@ async def test_generate_previews_skips_formats_with_no_body():
     )
 
     assert previews == {}
+
+
+@pytest.mark.asyncio
+async def test_generate_previews_fails_fast_on_partial_error():
+    # Deliberate contract (not accidental): if any requested ad format's
+    # Graph call errors out, generate_previews propagates that MetaError
+    # immediately instead of returning a partial dict. The creative is
+    # identical across formats, so a creative-level error would fail every
+    # format anyway, and surfacing Meta's real message beats a silently
+    # incomplete preview set.
+    transport = FakeTransport([
+        {"data": [{"body": "<iframe src='desktop'></iframe>"}]},
+        {"error": {"message": "Bad creative", "code": 100, "error_subcode": 33}},
+    ])
+    client = MetaClient(access_token="tok", transport=transport)
+
+    with pytest.raises(MetaError):
+        await client.generate_previews(
+            "act_1",
+            creative={"object_story_spec": {}},
+            ad_formats=["DESKTOP_FEED_STANDARD", "INSTAGRAM_STORY"],
+        )
+
+
+def test_access_token_from_env_returns_token(monkeypatch):
+    monkeypatch.setenv(ACCESS_TOKEN_ENV, "tok123")
+
+    assert access_token_from_env() == "tok123"
+
+
+def test_access_token_from_env_raises_when_whitespace_only(monkeypatch):
+    monkeypatch.setenv(ACCESS_TOKEN_ENV, "   ")
+
+    with pytest.raises(MetaNotConfiguredError):
+        access_token_from_env()
+
+
+def test_access_token_from_env_raises_when_unset(monkeypatch):
+    monkeypatch.delenv(ACCESS_TOKEN_ENV, raising=False)
+
+    with pytest.raises(MetaNotConfiguredError):
+        access_token_from_env()
+
+
+def test_meta_not_configured_error_is_a_meta_error():
+    assert issubclass(MetaNotConfiguredError, MetaError)