spike(historian): QuestDB behaviours confirmed against pinned image; spec §2–§4 amended

questdb/questdb:10.0.1 (pushed 2026-08-24). Q1–Q13 answered with harness output in
docs/plans/2026-10-10-questdb-spike.md; confirmed DDL, visibility wait, bucket/neighbour
SQL and connection keywords folded into the design spec, marked T0-confirmed.

Claude-Session: https://claude.ai/code/session_01Ef2ozxS7QPanGT8uoATbTe

docker-dev/docker-compose.questdb.yml

@@ -0,0 +1,28 @@
+# docker-dev/docker-compose.questdb.yml — optional QuestDB fixture for the QuestDB historian backend (#666).
+#
+# Up (touches ONLY the questdb service; it has no depends_on, and --no-deps makes that explicit):
+#   docker compose -f docker-dev/docker-compose.yml -f docker-dev/docker-compose.questdb.yml up -d --no-deps questdb
+#
+# Image pinned by the T0 spike (docs/plans/2026-10-10-questdb-spike.md): questdb/questdb:10.0.1,
+# pushed to Docker Hub 2026-08-24 (≥ 2 weeks before 2026-10-10; ≥ 8.2.3, the first release with table TTL).
+# The image ships /usr/bin/curl, so the healthcheck uses it against the min-HTTP health endpoint on :9003.
+#
+#   PG wire  -> localhost:18812  (Host=localhost;Port=18812;Username=admin;Password=quest;Database=qdb;...)
+#   Console  -> http://localhost:19000
+services:
+  questdb:
+    image: questdb/questdb:10.0.1
+    container_name: otopcua-dev-questdb-1
+    ports:
+      - "18812:8812"   # PG wire
+      - "19000:9000"   # web console / REST
+    volumes:
+      - otopcua-questdb-data:/var/lib/questdb
+    healthcheck:
+      test: ["CMD-SHELL", "curl -fs http://localhost:9003/status || exit 1"]
+      interval: 10s
+      timeout: 5s
+      retries: 12
+volumes:
+  otopcua-questdb-data:
+    name: otopcua-questdb-data