fix(api): attach SessionsConfig so smart truncation stops dropping records

`SessionsConfig` was defined but never added to `AgentaConfig`, so reading
`env.agenta.sessions.records.smart_truncation` raised AttributeError. That read
sits inside the record-publish try/except, whose handler logs and returns False,
so with AGENTA_RECORDS_SMART_TRUNCATION on every record over the 64 KB cap was
discarded outright. The legacy path it replaces at least stored a marker, and
records are now the only copy of the conversation, so a dropped record is lost
context.

The existing tests call `_truncate_attributes` directly and never read the flag,
which is why they stayed green while the feature was unreachable. Added a guard
that pins the config path itself.

Claude-Session: https://claude.ai/code/session_01KM69J7uHafgciiN5zfG7qR

Author: mmabrouk

api/oss/src/utils/env.py

@@ -539,6 +539,7 @@ class AgentaConfig(BaseModel):
     otlp: OTLPConfig = OTLPConfig()
     redaction: RedactionConfig = RedactionConfig()
     services: ServicesConfig = ServicesConfig()
+    sessions: SessionsConfig = SessionsConfig()
     webhooks: WebhooksConfig = WebhooksConfig()
     workers: WorkersConfig = WorkersConfig()
 

api/oss/tests/pytest/unit/sessions/test_records_truncation.py

@@ -71,3 +71,14 @@ def test_non_dict_attributes_fall_back():
     huge = "z" * (MAX_ATTRIBUTES_BYTES * 2)
     out = _truncate_attributes(huge, MAX_ATTRIBUTES_BYTES, _size(huge))
     assert out == {"_truncated": True, "_original_bytes": _size(huge)}
+
+
+def test_smart_truncation_flag_is_reachable_from_the_env_object():
+    """The publish path reads `env.agenta.sessions.records.smart_truncation` inside a
+    try/except that swallows anything and drops the record. When `SessionsConfig` was not
+    attached to `AgentaConfig` this raised AttributeError, so every over-cap record was
+    discarded instead of truncated, and the tests above still passed because they call
+    `_truncate_attributes` directly and never touch the flag."""
+    from oss.src.utils.env import env
+
+    assert isinstance(env.agenta.sessions.records.smart_truncation, bool)