feat(backend): presence stats count time online from sessions in the browser time zone, capture uptime marks hours without data, presence reaches every stream of the account, message volume keeps empty days

backend/migrations/versions/d8f4a1c6e2b7_capture_uptime.py

@@ -0,0 +1,50 @@
+"""capture uptime
+
+Revision ID: d8f4a1c6e2b7
+Revises: d7a3c5e9f2b1
+Create Date: 2026-10-19 03:00:00.000000
+
+"""
+
+from collections.abc import Sequence
+
+from alembic import op
+
+revision: str = "d8f4a1c6e2b7"
+down_revision: str | None = "d7a3c5e9f2b1"
+branch_labels: str | Sequence[str] | None = None
+depends_on: str | Sequence[str] | None = None
+
+_UPTIME = """
+CREATE TABLE capture_uptime (
+    account_id integer NOT NULL,
+    started_at timestamptz NOT NULL,
+    seen_at timestamptz NOT NULL,
+    PRIMARY KEY (account_id, started_at)
+)
+"""
+
+_BACKFILL = """
+INSERT INTO capture_uptime (account_id, started_at, seen_at)
+SELECT account_id, min(ts), max(ts)
+FROM (
+    SELECT account_id, ts,
+           count(*) FILTER (WHERE gap > interval '30 minutes')
+               OVER (PARTITION BY account_id ORDER BY ts) AS stretch
+    FROM (
+        SELECT account_id, ts,
+               ts - lag(ts) OVER (PARTITION BY account_id ORDER BY ts) AS gap
+        FROM presence
+    ) gaps
+) stretches
+GROUP BY account_id, stretch
+"""
+
+
+def upgrade() -> None:
+    op.execute(_UPTIME)
+    op.execute(_BACKFILL)
+
+
+def downgrade() -> None:
+    op.execute("DROP TABLE IF EXISTS capture_uptime")