fix(traces): cap captured body size to keep admin Traces UI responsive (#9946)

The trace middleware buffered the full request and response bodies for every
JSON exchange. With a chatty agent-pool RAG workload, /embeddings responses
(large vector arrays) accumulated to tens of MB in the in-memory buffer; the
admin Traces page would then download and parse 40+ MB on every load and on
every 5s auto-refresh, locking the UI in a loading state.

Add LOCALAI_TRACING_MAX_BODY_BYTES (default 64 KiB) that caps each captured
body. The full payload still flows through to the real client; only the
trace copy is bounded. Exchanges record body_truncated and original
body_bytes so the dashboard can show that truncation happened. The cap is
configurable via env, CLI, and runtime_settings.json.

Also unblock recovery: the Traces page now keeps the Clear button enabled
while loading, since "buffer too large to render" is exactly when the user
needs to clear it.


Assisted-by: Claude:claude-opus-4-7

Signed-off-by: Ettore Di Giacinto <mudler@localai.io>
Co-authored-by: Ettore Di Giacinto <mudler@localai.io>

core/config/application_config.go

@@ -21,6 +21,7 @@ type ApplicationConfig struct {
 	Debug                               bool
 	EnableTracing                       bool
 	TracingMaxItems                     int
+	TracingMaxBodyBytes                 int // Per-body cap for captured request/response bodies; 0 disables the cap
 	EnableBackendLogging                bool
 	GeneratedContentDir                 string
 
@@ -187,6 +188,7 @@ func NewApplicationConfig(o ...AppOption) *ApplicationConfig {
 		LRUEvictionRetryInterval: 1 * time.Second,        // Default: 1 second
 		WatchDogInterval:         500 * time.Millisecond, // Default: 500ms
 		TracingMaxItems:          1024,
+		TracingMaxBodyBytes:      64 * 1024, // 64 KiB - caps each request/response body in the trace buffer
 		AgentPool: AgentPoolConfig{
 			Enabled:         true,
 			Timeout:         "5m",
@@ -578,6 +580,12 @@ func WithTracingMaxItems(items int) AppOption {
 	}
 }
 
+func WithTracingMaxBodyBytes(bytes int) AppOption {
+	return func(o *ApplicationConfig) {
+		o.TracingMaxBodyBytes = bytes
+	}
+}
+
 func WithGeneratedContentDir(generatedContentDir string) AppOption {
 	return func(o *ApplicationConfig) {
 		o.GeneratedContentDir = generatedContentDir
@@ -920,6 +928,7 @@ func (o *ApplicationConfig) ToRuntimeSettings() RuntimeSettings {
 	f16 := o.F16
 	debug := o.Debug
 	tracingMaxItems := o.TracingMaxItems
+	tracingMaxBodyBytes := o.TracingMaxBodyBytes
 	enableTracing := o.EnableTracing
 	enableBackendLogging := o.EnableBackendLogging
 	cors := o.CORS
@@ -1008,6 +1017,7 @@ func (o *ApplicationConfig) ToRuntimeSettings() RuntimeSettings {
 		F16:                       &f16,
 		Debug:                     &debug,
 		TracingMaxItems:           &tracingMaxItems,
+		TracingMaxBodyBytes:       &tracingMaxBodyBytes,
 		EnableTracing:             &enableTracing,
 		EnableBackendLogging:      &enableBackendLogging,
 		CORS:                      &cors,
@@ -1146,6 +1156,9 @@ func (o *ApplicationConfig) ApplyRuntimeSettings(settings *RuntimeSettings) (req
 	if settings.TracingMaxItems != nil {
 		o.TracingMaxItems = *settings.TracingMaxItems
 	}
+	if settings.TracingMaxBodyBytes != nil {
+		o.TracingMaxBodyBytes = *settings.TracingMaxBodyBytes
+	}
 	if settings.EnableBackendLogging != nil {
 		o.EnableBackendLogging = *settings.EnableBackendLogging
 	}

core/config/runtime_settings.go

@@ -38,6 +38,7 @@ type RuntimeSettings struct {
 	Debug                *bool `json:"debug,omitempty"`
 	EnableTracing        *bool `json:"enable_tracing,omitempty"`
 	TracingMaxItems      *int  `json:"tracing_max_items,omitempty"`
+	TracingMaxBodyBytes  *int  `json:"tracing_max_body_bytes,omitempty"` // Per-body cap in bytes; 0 disables the cap
 	EnableBackendLogging *bool `json:"enable_backend_logging,omitempty"`
 
 	// Security/CORS settings