chore: Apply dashboard audit remediations, sync engine counts, update APIs

internal/infrastructure/auth/usage.go

@@ -65,12 +65,24 @@ func currentPeriod() (time.Time, time.Time) {
 }
 
 // RecordScan atomically increments the scan counter and checks quota.
-// Returns remaining scans. Returns error if quota exceeded.
+// Uses the free tier default limit (1000). For plan-aware quotas, use RecordScanWithLimit.
 func (t *UsageTracker) RecordScan(userID, ip string) (int, error) {
+	return t.RecordScanWithLimit(userID, ip, 1000)
+}
+
+// RecordScanWithLimit atomically increments the scan counter and checks against planLimit.
+// planLimit: -1=unlimited, 0=no scans allowed, >0=monthly cap.
+// Returns remaining scans. Returns error if quota exceeded.
+func (t *UsageTracker) RecordScanWithLimit(userID, ip string, planLimit int) (int, error) {
 	if t.db == nil {
 		return 999, nil // no DB = no limits
 	}
 
+	// Plan explicitly forbids scanning
+	if planLimit == 0 {
+		return 0, fmt.Errorf("scanning not available on current plan")
+	}
+
 	t.mu.Lock()
 	defer t.mu.Unlock()
 
@@ -84,6 +96,12 @@ func (t *UsageTracker) RecordScan(userID, ip string) (int, error) {
 		lookupVal = userID
 	}
 
+	// Resolve effective limit for DB storage (unlimited = 0 sentinel in DB)
+	dbLimit := planLimit
+	if planLimit < 0 {
+		dbLimit = 0 // 0 in DB = unlimited
+	}
+
 	// Try to get existing quota record for current period
 	var scansUsed, scansLimit int
 	var quotaID string
@@ -94,10 +112,14 @@ func (t *UsageTracker) RecordScan(userID, ip string) (int, error) {
 	err := t.db.QueryRow(query, lookupVal, periodStart).Scan(&quotaID, &scansUsed, &scansLimit)
 
 	if err == sql.ErrNoRows {
-		// Create new quota record
+		// Create new quota record with plan-based limit
 		quotaID = generateID("usg")
 		plan := "free"
-		limit := 1000
+		if planLimit > 1000 {
+			plan = "paid"
+		} else if planLimit < 0 {
+			plan = "unlimited"
+		}
 		var insertQuery string
 		if userID != "" {
 			insertQuery = `INSERT INTO usage_quotas (id, user_id, plan, scans_used, scans_limit, period_start, period_end)
@@ -106,12 +128,15 @@ func (t *UsageTracker) RecordScan(userID, ip string) (int, error) {
 			insertQuery = `INSERT INTO usage_quotas (id, ip_addr, plan, scans_used, scans_limit, period_start, period_end)
 				VALUES ($1, $2, $3, 1, $4, $5, $6)`
 		}
-		_, err = t.db.Exec(insertQuery, quotaID, lookupVal, plan, limit, periodStart, periodEnd)
+		_, err = t.db.Exec(insertQuery, quotaID, lookupVal, plan, dbLimit, periodStart, periodEnd)
 		if err != nil {
 			slog.Error("usage: create quota", "error", err)
 			return 999, nil // fail open — don't block on DB errors
 		}
-		return limit - 1, nil
+		if planLimit < 0 {
+			return -1, nil // unlimited
+		}
+		return planLimit - 1, nil
 	}
 
 	if err != nil {
@@ -119,7 +144,13 @@ func (t *UsageTracker) RecordScan(userID, ip string) (int, error) {
 		return 999, nil // fail open
 	}
 
-	// Unlimited plan (scans_limit = 0)
+	// Update stored limit if plan changed (e.g. upgrade mid-month)
+	if scansLimit != dbLimit {
+		t.db.Exec(`UPDATE usage_quotas SET scans_limit = $1 WHERE id = $2`, dbLimit, quotaID)
+		scansLimit = dbLimit
+	}
+
+	// Unlimited plan (scans_limit = 0 in DB)
 	if scansLimit == 0 {
 		t.db.Exec(`UPDATE usage_quotas SET scans_used = scans_used + 1 WHERE id = $1`, quotaID)
 		return -1, nil // unlimited
@@ -127,7 +158,7 @@ func (t *UsageTracker) RecordScan(userID, ip string) (int, error) {
 
 	// Check quota
 	if scansUsed >= scansLimit {
-		return 0, fmt.Errorf("quota exceeded: %d/%d scans used this month", scansUsed, scansLimit)
+		return 0, fmt.Errorf("quota exceeded: %d/%d scans used this month — upgrade at syntrex.pro/pricing", scansUsed, scansLimit)
 	}
 
 	// Increment