fix(observability-proxy): reject negative limits at startup

Zero is the documented way to disable a limit; a negative value
disabled it too, silently. Refuse it so a typo in the chart cannot turn
off a per-user or total cap unnoticed.

Assisted-by: LLM
Signed-off-by: ZverGuy <maximbel2003@gmail.com>

cmd/observability-proxy/main.go

@@ -104,6 +104,9 @@ func parseFlags(args []string) (options, error) {
 		return o, errors.New("--logs-max-tail-resume must not be negative")
 	case o.requestTimeout < 0 || o.tailIdleTimeout < 0 || o.authCacheTTL < 0 || o.shutdownTimeout < 0:
 		return o, errors.New("timeouts and the auth cache TTL must not be negative")
+	case o.limiter.RatePerUser < 0 || o.limiter.RateBurst < 0 || o.limiter.MaxConcurrentPerUser < 0 ||
+		o.limiter.MaxTailsPerUser < 0 || o.limiter.MaxTails < 0:
+		return o, errors.New("limits must not be negative; 0 disables a limit")
 	}
 	return o, nil
 }

cmd/observability-proxy/main_test.go

@@ -56,6 +56,11 @@ func TestParseFlagsInvalid(t *testing.T) {
 		{"--request-timeout=-1s"},
 		{"--tail-idle-timeout=-1s"},
 		{"--auth-cache-ttl=-1s"},
+		{"--rate-limit-per-user=-1"},
+		{"--rate-limit-burst=-1"},
+		{"--max-concurrent-per-user=-1"},
+		{"--max-tails-per-user=-1"},
+		{"--max-tails=-1"},
 		{"--unknown"},
 	} {
 		if _, err := parseFlags(args); err == nil {