Implement identity graph stitching and configurable profile storage

Issue persistent signed anonymous IDs and accept cookie/token-bound events.
Resolve verified email, phone, OAuth, and namespaced third-party IDs into
transactionally merged master identities with historical event aliases.
Protect shared-device account switching, tenant isolation, and event retries.

Store sparse canonical profiles as PostgreSQL JSONB or local SQLite JSON.
Support an optional versioned Cassandra wide-column projection through a
transactional outbox, retry worker, and immediate canonical read fallback.
Document deployment settings and provide opt-in database integration tests.

Validation: 43 local tests passed; 6 external database tests skipped.
Ruff checks, formatting, and offline uv lock verification passed.

tests/test_postgres.py

@@ -0,0 +1,105 @@
+"""Optional real PostgreSQL integration: set ADCLOUD_TEST_POSTGRES_URL."""
+
+import os
+from concurrent.futures import ThreadPoolExecutor
+from uuid import uuid4
+
+import pytest
+from sqlalchemy import text
+
+from adcloud_server.database import Database
+from adcloud_server.identity_models import EventRequest, ProfilePatch, StitchRequest
+from adcloud_server.identity_service import IdentityService
+from adcloud_server.settings import Settings
+
+pytestmark = pytest.mark.skipif(
+    not os.getenv("ADCLOUD_TEST_POSTGRES_URL"),
+    reason="No PostgreSQL integration URL configured",
+)
+
+
+@pytest.fixture
+def service():
+    settings = Settings(
+        database_url=os.environ["ADCLOUD_TEST_POSTGRES_URL"],
+        tenant_id="test-" + str(uuid4()),
+        identity_secret="postgres-test-" + "x" * 48,
+        profile_backend="cassandra",
+    )
+    db = Database(settings.database_url, settings.tenant_id)
+    db.initialize()
+    try:
+        yield IdentityService(settings, db)
+    finally:
+        db.close()
+
+
+def test_postgres_jsonb_stitch_and_immediate_history(service):
+    known = service.anonymous()
+    identity = StitchRequest(
+        identifiers=[{"kind": "email", "value": "alice@example.com"}]
+    )
+    service.stitch(known["anonymous_token"], identity)
+    visitor = service.anonymous(rotate=True)
+    service.patch_profile(
+        visitor["master_id"],
+        ProfilePatch(
+            attributes={"nested": {"interest": "running"}, "absent": None},
+            tags=["runner"],
+        ),
+    )
+    event = service.record_event(
+        visitor["anonymous_token"], EventRequest(name="product.view")
+    )
+    stitched = service.stitch(visitor["anonymous_token"], identity)
+    assert stitched["master_id"] == known["master_id"]
+    assert service.profile(known["master_id"])["attributes"] == {
+        "nested": {"interest": "running"}
+    }
+    assert service.history(visitor["master_id"])["items"][0]["id"] == event["event_id"]
+    with service.db.transaction() as conn:
+        result = conn.execute(
+            text(
+                "SELECT pg_typeof(document)::text FROM identity_profiles WHERE tenant_id=:tenant LIMIT 1"
+            ),
+            {"tenant": service.tenant},
+        ).scalar_one()
+        assert result == "jsonb"
+
+
+def test_postgres_multiple_process_connections_serialize_identity_merges(service):
+    second_db = Database(service.settings.database_url, service.tenant)
+    other = IdentityService(service.settings, second_db)
+    tokens = [
+        service.anonymous()["anonymous_token"],
+        other.anonymous()["anonymous_token"],
+    ]
+    instances = [service, other]
+    request = StitchRequest(identifiers=[{"kind": "phone", "value": "+14155552671"}])
+    try:
+        with ThreadPoolExecutor(max_workers=2) as pool:
+            results = list(
+                pool.map(lambda i: instances[i].stitch(tokens[i], request), [0, 1])
+            )
+        assert results[0]["master_id"] == results[1]["master_id"]
+        assert len(service.graph(results[0]["master_id"])["identifiers"]) == 1
+    finally:
+        second_db.close()
+
+
+def test_postgres_failed_transaction_rolls_back_graph_and_outbox(service, monkeypatch):
+    visitor = service.anonymous()
+
+    def fail(*args):
+        raise OSError("Simulated outbox failure")
+
+    monkeypatch.setattr(service, "_queue", fail)
+    with pytest.raises(OSError):
+        service.stitch(
+            visitor["anonymous_token"],
+            StitchRequest(
+                identifiers=[{"kind": "email", "value": "alice@example.com"}]
+            ),
+        )
+    assert service.graph(visitor["master_id"])["identifiers"] == []
+    assert service.profile(visitor["master_id"])["revision"] == 1