milestone 26: upstream health answers for the selected period

PLAN.md

@@ -325,7 +325,7 @@ Per-group boolean. Rewrites known engine domains to their safe-search CNAME targ
 
 - Schemes: `https://…` → DoH, `tls://host:853` → DoT.
 - Ordered by priority; sequential attempt; per-upstream failure counters; exponential backoff with jitter; success resets.
-- `UpstreamHealth` per upstream: last_success_at, last_error_at, last_error_message, rolling success rate, consecutive failures, backoff-until. Exposed via `GET /api/upstream/health`, dashboard, `/metrics`, and `nxdns check`.
+- `UpstreamHealth` per upstream: last_success_at, last_error_at, last_error_message, rolling success rate, consecutive failures, backoff-until. This is routing state: it drives failover and backoff, and is exposed through `/metrics` and `nxdns check`. `GET /api/upstream/health?period=…` exposes none of it except the live `enabled`/`available` pair; its counts, success rate and last failure are ranged aggregates read from the per-minute upstream history in `querylog.db`, so the dashboard's period scopes them like every other number on the page.
 - DoH client: `std.http.Client` with `content-type/accept: application/dns-message`; strict status + payload checks.
 - `platform/tls_client.zig` enforces per-connection read/write deadlines, classifies TLS errors explicitly, retries with backoff. Integration tests cover timeout/hang scenarios so compiler upgrades can't silently regress them.
 - Connect, read, and total-budget timeouts each configurable.
@@ -460,6 +460,24 @@ CREATE TABLE query_log (
 CREATE INDEX idx_query_log_ts ON query_log(timestamp);
 CREATE INDEX idx_query_log_client ON query_log(client_ip);
 CREATE INDEX idx_query_log_domain ON query_log(domain_id);
+
+CREATE TABLE upstream_targets (
+    id INTEGER PRIMARY KEY,
+    url TEXT NOT NULL UNIQUE   -- the historical identity: config.db ids cannot cross database files
+);
+
+CREATE TABLE upstream_minute (
+    upstream_id INTEGER NOT NULL REFERENCES upstream_targets(id),
+    minute_ts INTEGER NOT NULL,
+    successes INTEGER NOT NULL,
+    failures INTEGER NOT NULL,
+    last_failure_ts INTEGER,
+    last_error TEXT,
+    PRIMARY KEY (upstream_id, minute_ts),
+    CHECK (successes >= 0),
+    CHECK (failures >= 0)
+) WITHOUT ROWID;
+CREATE INDEX idx_upstream_minute_ts ON upstream_minute(minute_ts);
 ```
 
 ### 11.4 Query Logger
@@ -522,7 +540,7 @@ Scalars in `settings(key, value)`; ordered/structured items in dedicated tables.
 - `GET /api/lookup?domain=…&group_id=…`
 - `GET/POST /api/pause`
 - `GET/PUT /api/settings`
-- `GET /api/upstream/health`
+- `GET /api/upstream/health?period=…`
 - `POST /api/certs/reload`
 - `GET /api/health` — overall + disk + upstream + queries_dropped rollup
 - `GET /metrics` — Prometheus text exposition: query counters (total/blocked/cached), per-upstream health, cache stats, queries_dropped, disk gauges