fix(gateway): re-apply tool rate limiter after system_configs overlay (#1111)

setupToolRegistry creates the rate limiter from cfg.Tools.RateLimitPerHour
during early bootstrap (gateway.go line 137). System_configs DB overlay
runs ~50 lines later via cfg.ApplySystemConfigs (line 191), so any DB
override of tools.rate_limit_per_hour was silently lost - the limiter
object was already initialised from the JSON5 default.

Symptom in production: editing tools.rate_limit_per_hour via system_configs
table or the config HTTP API had no effect on running gateways. Operators
had to inject a config.json file to change the value, defeating the
DB-as-source-of-truth pattern that other tunables rely on.

Re-apply the limiter after ApplySystemConfigs runs. Safe ordering: server
has not started yet, no in-flight tool calls, and SetRateLimiter is a
plain field assignment with no shutdown cost on the discarded limiter.
nil case (rate_limit_per_hour <= 0) also handled so DB writes can disable
the limiter without restart.

Tests: new TestRegistry_SetRateLimiter_ReplacesPriorLimiter covers both
the replace-with-higher-limit path and the nil-disables path. All
existing rate limiter tests still pass.

Note: the same ordering pattern likely affects other config consumed
inside setupToolRegistry (tools.scrub_credentials, MCP server wiring).
Out of scope for this hotfix - they need a deeper restructure.

Author: nguyennguyenit

cmd/gateway.go

@@ -226,6 +226,18 @@ func runGateway() {
 			slog.Info("system_configs applied to in-memory config", "keys", len(sysConfigs))
 		}
 	}
+
+	// Re-apply tool rate limiter using DB-overlaid config. setupToolRegistry
+	// initialised the limiter from the JSON5 default before ApplySystemConfigs
+	// ran, so DB-driven changes to tools.rate_limit_per_hour were lost. Replace
+	// the limiter object now that cfg reflects the DB value. Safe: server has
+	// not started, no in-flight tool calls.
+	if cfg.Tools.RateLimitPerHour > 0 {
+		toolsReg.SetRateLimiter(tools.NewToolRateLimiter(cfg.Tools.RateLimitPerHour))
+		slog.Info("tool rate limiting reapplied from system_configs", "per_hour", cfg.Tools.RateLimitPerHour)
+	} else {
+		toolsReg.SetRateLimiter(nil)
+	}
 	setupMemoryEmbeddings(pgStores, providerRegistry)
 	usageCapSvc := usagecaps.NewService(pgStores.UsageCaps, pgStores.Providers)
 

internal/tools/registry_test.go

@@ -168,6 +168,42 @@ func TestRegistry_ExecuteWithContext_RateLimiting(t *testing.T) {
 	}
 }
 
+// SetRateLimiter must be re-callable so that startup code can swap the limiter
+// after DB-overlaid config is applied (cmd/gateway.go re-applies once
+// system_configs has overlaid the JSON5 default).
+func TestRegistry_SetRateLimiter_ReplacesPriorLimiter(t *testing.T) {
+	reg := NewRegistry()
+	reg.SetRateLimiter(NewToolRateLimiter(1)) // simulate JSON5 default
+	reg.Register(&mockTool{name: "tool"})
+
+	// Replace with higher limit (simulates DB overlay = 5)
+	reg.SetRateLimiter(NewToolRateLimiter(5))
+
+	for i := range 5 {
+		result := reg.ExecuteWithContext(context.Background(), "tool", nil,
+			"", "", "", "session-replace", nil)
+		if result.IsError {
+			t.Errorf("call %d should succeed under new 5/h limit: %s", i, result.ForLLM)
+		}
+	}
+	result := reg.ExecuteWithContext(context.Background(), "tool", nil,
+		"", "", "", "session-replace", nil)
+	if !result.IsError {
+		t.Error("6th call should hit the 5/h limit")
+	}
+
+	// Disable rate limiting via nil — verifies the gateway path that disables
+	// the limiter when cfg.Tools.RateLimitPerHour <= 0.
+	reg.SetRateLimiter(nil)
+	for i := range 10 {
+		result := reg.ExecuteWithContext(context.Background(), "tool", nil,
+			"", "", "", "session-replace", nil)
+		if result.IsError {
+			t.Errorf("call %d after nil limiter should be unbounded", i)
+		}
+	}
+}
+
 func TestRegistry_ExecuteWithContext_NoRateLimitWithoutSessionKey(t *testing.T) {
 	reg := NewRegistry()
 	reg.SetRateLimiter(NewToolRateLimiter(1))