Session-level usage summary (Enterprise)

Enterprise — session-level usage reporting (#2759). The Community build mounts the same route but returns 501 Not Implemented.

Buckets audit logs into per-session aggregates for the date window: a bucket is per-session when session_id is present on its rows, otherwise rows without a session id fall back to a per-user-day bucket (the day field is set instead of session_id). Buckets are capped at bucket_limit (most-recent activity first); truncated is true when the window held more buckets than the cap — narrow the window or raise limit. Drill into a bucket's raw events via POST /api/v1/audit/search with its session_id (#2857).

The window start is clamped to the tenant's tier retention floor, like /api/v1/audit/search and /api/v1/audit/export.

avg_latency_ms is nullable on the bucket and on every entry of its tools array (#3433), paired with a latency_sample_count. null means no row in that bucket carried a measurement, which is a different fact from a measured zero and used to be coalesced onto it. A strict deserializer binding it to a non-optional float will raise; see the SessionSummaryBucket schema.