telemetry: fix CRITICAL silent failures (Cardinal Rule #1)

Fixes #2, #3, #4

Issue #2 - Silent database errors in updateSpan():
- Add error handling for telemetry INSERT (ERR-TELEMETRY-004)
- Add error handling for all table/index creation (ERR-TELEMETRY-005 to -010)
- Return HTTP 500 to client on insert failure

Issue #3 - Silent failure in Kuma push:
- Return early on non-OK status from Kuma
- Proper error logging with body close handling

Issue #4 - Unchecked flush error in tarpit:
- Verify http.Flusher available before tarpit
- Log ERR-TELEMETRY-040 and abort if flusher unavailable
- Remove redundant flusher checks in loop

All changes: security failures are now LOUD (Cardinal Rule #1)

Author: Hans <hans-20250409-001>

clavis/clavis-telemetry/kuma.go

@@ -63,6 +63,10 @@ func sendKumaPush(kumaURL string) {
 	}
 	if resp.StatusCode != http.StatusOK {
 		log.Printf("ERR-TELEMETRY-031: Kuma returned non-OK status %d from %s", resp.StatusCode, kumaURL)
+		if err := resp.Body.Close(); err != nil {
+			log.Printf("ERR-TELEMETRY-032: Failed to close Kuma response body after non-OK status - %v", err)
+		}
+		return
 	}
 	if err := resp.Body.Close(); err != nil {
 		log.Printf("ERR-TELEMETRY-032: Failed to close Kuma response body - %v", err)

clavis/clavis-telemetry/main.go

@@ -130,9 +130,13 @@ func tarpit(w http.ResponseWriter, r *http.Request) {
 	w.Header().Set("Content-Type", "text/plain")
 	w.WriteHeader(200)
 	
-	if flusher, ok := w.(http.Flusher); ok {
+	// Verify flusher is available - otherwise tarpit is ineffective
-		flusher.Flush()
+	flusher, ok := w.(http.Flusher)
+	if !ok {
+		log.Printf("ERR-TELEMETRY-040: tarpit called with ResponseWriter that does not implement http.Flusher - aborting")
+		return
 	}
+	flusher.Flush()
 	
 	// Drip one byte per second for 30 seconds
 	for i := 0; i < 30; i++ {
@@ -140,18 +144,16 @@ func tarpit(w http.ResponseWriter, r *http.Request) {
 		if err != nil {
 			return // Client disconnected
 		}
-		if flusher, ok := w.(http.Flusher); ok {
+		// Flush has no return value per http.Flusher interface
-			// Flush has no return value per http.Flusher interface
+		// Write error above is the primary signal for client disconnect
-			// Write error above is the primary signal for client disconnect
+		flusher.Flush()
-			flusher.Flush()
-		}
 		time.Sleep(time.Second)
 	}
 }
 
 func ensureTables() {
 	// Telemetry table
-	db.Exec(`CREATE TABLE IF NOT EXISTS telemetry (
+	if _, err := db.Exec(`CREATE TABLE IF NOT EXISTS telemetry (
 		id INTEGER PRIMARY KEY AUTOINCREMENT,
 		node_id TEXT NOT NULL,
 		received_at INTEGER NOT NULL DEFAULT (strftime('%s','now')),
@@ -168,28 +170,40 @@ func ensureTables() {
 		vault_size_mb REAL NOT NULL DEFAULT 0,
 		vault_entries INTEGER NOT NULL DEFAULT 0,
 		mode TEXT NOT NULL DEFAULT ''
-	)`)
+	)`); err != nil {
-	db.Exec(`CREATE INDEX IF NOT EXISTS idx_telemetry_node_id ON telemetry(node_id)`)
+		log.Fatalf("ERR-TELEMETRY-005: Failed to create telemetry table - %v", err)
-	db.Exec(`CREATE INDEX IF NOT EXISTS idx_telemetry_node_latest ON telemetry(node_id, id DESC)`)
+	}
+	if _, err := db.Exec(`CREATE INDEX IF NOT EXISTS idx_telemetry_node_id ON telemetry(node_id)`); err != nil {
+		log.Fatalf("ERR-TELEMETRY-006: Failed to create telemetry node_id index - %v", err)
+	}
+	if _, err := db.Exec(`CREATE INDEX IF NOT EXISTS idx_telemetry_node_latest ON telemetry(node_id, id DESC)`); err != nil {
+		log.Fatalf("ERR-TELEMETRY-007: Failed to create telemetry node_latest index - %v", err)
+	}
 
 	// Uptime spans table
-	db.Exec(`CREATE TABLE IF NOT EXISTS uptime_spans (
+	if _, err := db.Exec(`CREATE TABLE IF NOT EXISTS uptime_spans (
 		id INTEGER PRIMARY KEY AUTOINCREMENT,
 		node_id TEXT NOT NULL,
 		start_at INTEGER NOT NULL,
 		end_at INTEGER NOT NULL
-	)`)
+	)`); err != nil {
-	db.Exec(`CREATE INDEX IF NOT EXISTS idx_spans_node_end ON uptime_spans(node_id, end_at DESC)`)
+		log.Fatalf("ERR-TELEMETRY-008: Failed to create uptime_spans table - %v", err)
+	}
+	if _, err := db.Exec(`CREATE INDEX IF NOT EXISTS idx_spans_node_end ON uptime_spans(node_id, end_at DESC)`); err != nil {
+		log.Fatalf("ERR-TELEMETRY-009: Failed to create uptime_spans index - %v", err)
+	}
 
 	// Maintenance table
-	db.Exec(`CREATE TABLE IF NOT EXISTS maintenance (
+	if _, err := db.Exec(`CREATE TABLE IF NOT EXISTS maintenance (
 		id INTEGER PRIMARY KEY AUTOINCREMENT,
 		start_at INTEGER NOT NULL DEFAULT (strftime('%s','now')),
 		end_at INTEGER,
 		reason TEXT NOT NULL DEFAULT '',
 		started_by TEXT NOT NULL DEFAULT '',
 		ended_by TEXT NOT NULL DEFAULT ''
-	)`)
+	)`); err != nil {
+		log.Fatalf("ERR-TELEMETRY-010: Failed to create maintenance table - %v", err)
+	}
 }
 
 func handleHealth(w http.ResponseWriter, r *http.Request) {
@@ -313,8 +327,12 @@ func handleTelemetry(w http.ResponseWriter, r *http.Request) {
 	}
 
 	// Insert telemetry
-	db.Exec(`INSERT INTO telemetry (node_id, version, hostname, uptime_seconds, cpu_percent, memory_total_mb, memory_used_mb, disk_total_mb, disk_used_mb, load_1m, vault_count, vault_size_mb, vault_entries, mode) VALUES (?,?,?,?,?,?,?,?,?,?,?,?,?,?)`,
+	if _, err := db.Exec(`INSERT INTO telemetry (node_id, version, hostname, uptime_seconds, cpu_percent, memory_total_mb, memory_used_mb, disk_total_mb, disk_used_mb, load_1m, vault_count, vault_size_mb, vault_entries, mode) VALUES (?,?,?,?,?,?,?,?,?,?,?,?,?,?)`,
-		t.NodeID, t.Version, t.Hostname, t.UptimeSeconds, t.CPUPercent, t.MemTotalMB, t.MemUsedMB, t.DiskTotalMB, t.DiskUsedMB, t.Load1m, t.VaultCount, t.VaultSizeMB, t.VaultEntries, t.Mode)
+		t.NodeID, t.Version, t.Hostname, t.UptimeSeconds, t.CPUPercent, t.MemTotalMB, t.MemUsedMB, t.DiskTotalMB, t.DiskUsedMB, t.Load1m, t.VaultCount, t.VaultSizeMB, t.VaultEntries, t.Mode); err != nil {
+		log.Printf("ERR-TELEMETRY-004: Failed to insert telemetry for node=%s - %v", t.NodeID, err)
+		http.Error(w, `{"error":"database error"}`, 500)
+		return
+	}
 
 	// Uptime span tracking
 	updateSpan(t.NodeID, t.Hostname, t.Version, t.CPUPercent, t.MemUsedMB, t.MemTotalMB, t.DiskUsedMB, t.DiskTotalMB, t.Load1m, t.UptimeSeconds)