feat: add event metadata injector FFI and Go APIs

crates/core/src/api/runtime/state.rs

@@ -1788,8 +1788,7 @@ fn validate_event_metadata_attributes(attributes: &BTreeMap<String, Json>) -> Re
 #[derive(Clone, Copy, PartialEq, Eq)]
 enum OtelAttributePrimitiveKind {
     Boolean,
-    Integer,
-    Double,
+    Number,
     String,
 }
 
@@ -1799,12 +1798,12 @@ fn otel_compatible_attribute_number_kind(
     if let Some(value) = value.as_u64() {
         return i64::try_from(value)
             .is_ok()
-            .then_some(OtelAttributePrimitiveKind::Integer);
+            .then_some(OtelAttributePrimitiveKind::Number);
     }
     if value.as_i64().is_some() {
-        return Some(OtelAttributePrimitiveKind::Integer);
+        return Some(OtelAttributePrimitiveKind::Number);
     }
-    value.as_f64().map(|_| OtelAttributePrimitiveKind::Double)
+    value.as_f64().map(|_| OtelAttributePrimitiveKind::Number)
 }
 
 fn is_otel_compatible_attribute_number(value: &serde_json::Number) -> bool {

crates/core/tests/unit/runtime_state_tests.rs

@@ -41,6 +41,7 @@ async fn event_metadata_injection_accepts_flat_otel_values_and_empty_output() {
                 ("nv.test.booleans".into(), json!([true, false])),
                 ("nv.test.integers".into(), json!([1, 2])),
                 ("nv.test.doubles".into(), json!([1.0, 2.5])),
+                ("nv.test.numbers".into(), json!([1, 2.5])),
                 ("nv.test.empty".into(), json!([])),
             ]))
         })
@@ -71,6 +72,7 @@ async fn event_metadata_injection_accepts_flat_otel_values_and_empty_output() {
     assert_eq!(metadata["nv.test.booleans"], json!([true, false]));
     assert_eq!(metadata["nv.test.integers"], json!([1, 2]));
     assert_eq!(metadata["nv.test.doubles"], json!([1.0, 2.5]));
+    assert_eq!(metadata["nv.test.numbers"], json!([1, 2.5]));
     assert_eq!(metadata["nv.test.empty"], json!([]));
 }
 
@@ -94,7 +96,6 @@ async fn event_metadata_injection_rejects_invalid_output_atomically() {
         BTreeMap::from([("nv.test.object".into(), json!({"nested": true}))]),
         BTreeMap::from([("nv.test.nested_list".into(), json!([[1]]))]),
         BTreeMap::from([("nv.test.mixed_list".into(), json!([1, "two"]))]),
-        BTreeMap::from([("nv.test.mixed_numbers".into(), json!([1, 2.5]))]),
         BTreeMap::from([("nv.test.oversized_number".into(), json!(u64::MAX))]),
         BTreeMap::from([("nv.test.oversized_list".into(), json!([u64::MAX]))]),
     ];

crates/ffi/nemo_relay.h

@@ -252,12 +252,13 @@ typedef struct Option_NemoRelayFinalizerCb Option_NemoRelayFinalizerCb;
 typedef struct Option_NemoRelayPluginValidateCb Option_NemoRelayPluginValidateCb;
 
 /**
- * Callback for mark and scope event sanitizers.
- * The returned JSON string transfers to Relay and is freed exactly once.
+ * Callback for event metadata injection.
+ *
+ * The returned string must contain a JSON object whose properties are proposed
+ * metadata additions. It transfers to Relay and is freed exactly once. Return
+ * null after setting the last error message to report a callback failure.
  */
-typedef char *(*NemoRelayEventSanitizeCb)(void *user_data,
-                                          const struct FfiEvent *event,
-                                          const char *fields_json);
+typedef char *(*NemoRelayEventMetadataInjectorCb)(void *user_data, const struct FfiEvent *event);
 
 /**
  * Optional destructor for user data passed to callbacks.
@@ -269,6 +270,14 @@ typedef char *(*NemoRelayEventSanitizeCb)(void *user_data,
  */
 typedef void (*NemoRelayFreeFn)(void *user_data);
 
+/**
+ * Callback for mark and scope event sanitizers.
+ * The returned JSON string transfers to Relay and is freed exactly once.
+ */
+typedef char *(*NemoRelayEventSanitizeCb)(void *user_data,
+                                          const struct FfiEvent *event,
+                                          const char *fields_json);
+
 /**
  * Callback for LLM execution (default callable). Receives a native JSON C string,
  * returns the response as a JSON C string.
@@ -871,6 +880,50 @@ NemoRelayStatus nemo_relay_adaptive_build_cache_telemetry_event(const char *opti
  */
 NemoRelayStatus nemo_relay_adaptive_set_latency_sensitivity(uint32_t value);
 
+/**
+ * Register a global event metadata injector.
+ *
+ * # Safety
+ * Pointers must remain valid for the documented call lifetime. The callback
+ * and user data remain owned by Relay until deregistration.
+ */
+NemoRelayStatus nemo_relay_register_event_metadata_injector(const char *name,
+                                                            int32_t priority,
+                                                            NemoRelayEventMetadataInjectorCb cb,
+                                                            void *user_data,
+                                                            NemoRelayFreeFn free_fn);
+
+/**
+ * Deregister a global event metadata injector.
+ *
+ * # Safety
+ * `name` must be a valid C string.
+ */
+NemoRelayStatus nemo_relay_deregister_event_metadata_injector(const char *name);
+
+/**
+ * Register an event metadata injector owned by an active scope.
+ *
+ * # Safety
+ * Pointers must remain valid for the documented call lifetime. The callback
+ * and user data remain owned by Relay until deregistration or scope cleanup.
+ */
+NemoRelayStatus nemo_relay_scope_register_event_metadata_injector(const char *scope_uuid,
+                                                                  const char *name,
+                                                                  int32_t priority,
+                                                                  NemoRelayEventMetadataInjectorCb cb,
+                                                                  void *user_data,
+                                                                  NemoRelayFreeFn free_fn);
+
+/**
+ * Deregister an event metadata injector owned by an active scope.
+ *
+ * # Safety
+ * String pointers must be valid C strings.
+ */
+NemoRelayStatus nemo_relay_scope_deregister_event_metadata_injector(const char *scope_uuid,
+                                                                    const char *name);
+
 /**
  * Register a global mark event sanitizer.
  * # Safety
@@ -2057,6 +2110,20 @@ NemoRelayStatus nemo_relay_plugin_context_register_subscriber(struct FfiPluginCo
                                                               void *user_data,
                                                               NemoRelayFreeFn free_fn);
 
+/**
+ * Register an event metadata injector into a plugin context.
+ *
+ * # Safety
+ * Pointers must remain valid for the documented call lifetime. The callback
+ * and user data remain owned by the plugin registration until rollback.
+ */
+NemoRelayStatus nemo_relay_plugin_context_register_event_metadata_injector(struct FfiPluginContext *ctx,
+                                                                           const char *name,
+                                                                           int32_t priority,
+                                                                           NemoRelayEventMetadataInjectorCb cb,
+                                                                           void *user_data,
+                                                                           NemoRelayFreeFn free_fn);
+
 /**
  * Register a mark event sanitizer into a plugin context.
  * # Safety

crates/ffi/src/api/event_registry.rs

@@ -2,8 +2,9 @@
 // SPDX-License-Identifier: Apache-2.0
 
 use super::{
-    NemoRelayEventSanitizeCb, NemoRelayFreeFn, NemoRelayStatus, c_char, c_str_to_string,
-    clear_last_error, core_registry_api, set_last_error, status_from_error, wrap_event_sanitize_fn,
+    NemoRelayEventMetadataInjectorCb, NemoRelayEventSanitizeCb, NemoRelayFreeFn, NemoRelayStatus,
+    c_char, c_str_to_string, clear_last_error, core_registry_api, set_last_error,
+    status_from_error, wrap_event_metadata_injector_fn, wrap_event_sanitize_fn,
 };
 
 #[derive(Clone, Copy)]
@@ -67,6 +68,108 @@ fn parse_scope_uuid(value: *const c_char) -> Result<uuid::Uuid, NemoRelayStatus>
     })
 }
 
+/// Register a global event metadata injector.
+///
+/// # Safety
+/// Pointers must remain valid for the documented call lifetime. The callback
+/// and user data remain owned by Relay until deregistration.
+#[unsafe(no_mangle)]
+pub unsafe extern "C" fn nemo_relay_register_event_metadata_injector(
+    name: *const c_char,
+    priority: i32,
+    cb: NemoRelayEventMetadataInjectorCb,
+    user_data: *mut libc::c_void,
+    free_fn: NemoRelayFreeFn,
+) -> NemoRelayStatus {
+    clear_last_error();
+    let Some(cb) = cb else {
+        set_last_error("event metadata injector callback is null");
+        return NemoRelayStatus::NullPointer;
+    };
+    let callback = wrap_event_metadata_injector_fn(cb, user_data, free_fn);
+    let name = match c_str_to_string(name) {
+        Ok(value) => value,
+        Err(status) => return status,
+    };
+    core_registry_api::register_event_metadata_injector(&name, priority, callback)
+        .map(|()| NemoRelayStatus::Ok)
+        .unwrap_or_else(|error| status_from_error(&error))
+}
+
+/// Deregister a global event metadata injector.
+///
+/// # Safety
+/// `name` must be a valid C string.
+#[unsafe(no_mangle)]
+pub unsafe extern "C" fn nemo_relay_deregister_event_metadata_injector(
+    name: *const c_char,
+) -> NemoRelayStatus {
+    clear_last_error();
+    let name = match c_str_to_string(name) {
+        Ok(value) => value,
+        Err(status) => return status,
+    };
+    core_registry_api::deregister_event_metadata_injector(&name)
+        .map(|_| NemoRelayStatus::Ok)
+        .unwrap_or_else(|error| status_from_error(&error))
+}
+
+/// Register an event metadata injector owned by an active scope.
+///
+/// # Safety
+/// Pointers must remain valid for the documented call lifetime. The callback
+/// and user data remain owned by Relay until deregistration or scope cleanup.
+#[unsafe(no_mangle)]
+pub unsafe extern "C" fn nemo_relay_scope_register_event_metadata_injector(
+    scope_uuid: *const c_char,
+    name: *const c_char,
+    priority: i32,
+    cb: NemoRelayEventMetadataInjectorCb,
+    user_data: *mut libc::c_void,
+    free_fn: NemoRelayFreeFn,
+) -> NemoRelayStatus {
+    clear_last_error();
+    let Some(cb) = cb else {
+        set_last_error("event metadata injector callback is null");
+        return NemoRelayStatus::NullPointer;
+    };
+    let callback = wrap_event_metadata_injector_fn(cb, user_data, free_fn);
+    let uuid = match parse_scope_uuid(scope_uuid) {
+        Ok(value) => value,
+        Err(status) => return status,
+    };
+    let name = match c_str_to_string(name) {
+        Ok(value) => value,
+        Err(status) => return status,
+    };
+    core_registry_api::scope_register_event_metadata_injector(&uuid, &name, priority, callback)
+        .map(|()| NemoRelayStatus::Ok)
+        .unwrap_or_else(|error| status_from_error(&error))
+}
+
+/// Deregister an event metadata injector owned by an active scope.
+///
+/// # Safety
+/// String pointers must be valid C strings.
+#[unsafe(no_mangle)]
+pub unsafe extern "C" fn nemo_relay_scope_deregister_event_metadata_injector(
+    scope_uuid: *const c_char,
+    name: *const c_char,
+) -> NemoRelayStatus {
+    clear_last_error();
+    let uuid = match parse_scope_uuid(scope_uuid) {
+        Ok(value) => value,
+        Err(status) => return status,
+    };
+    let name = match c_str_to_string(name) {
+        Ok(value) => value,
+        Err(status) => return status,
+    };
+    core_registry_api::scope_deregister_event_metadata_injector(&uuid, &name)
+        .map(|_| NemoRelayStatus::Ok)
+        .unwrap_or_else(|error| status_from_error(&error))
+}
+
 unsafe fn register_scope(
     scope_uuid: *const c_char,
     name: *const c_char,

crates/ffi/src/api/mod.rs

@@ -14,12 +14,13 @@ use std::sync::{Arc, OnceLock};
 use std::time::Duration;
 
 use crate::callable::{
-    NemoRelayCodecDecodeFn, NemoRelayCodecEncodeFn, NemoRelayCollectorCb, NemoRelayEventSanitizeCb,
-    NemoRelayEventSubscriberCb, NemoRelayFinalizerCb, NemoRelayFreeFn, NemoRelayLlmConditionalCb,
-    NemoRelayLlmExecCb, NemoRelayLlmExecInterceptCb, NemoRelayLlmRequestInterceptCb,
-    NemoRelayLlmSanitizeRequestCb, NemoRelayLlmSanitizeResponseCb, NemoRelayPluginRegisterCb,
-    NemoRelayPluginValidateCb, NemoRelayToolConditionalCb, NemoRelayToolExecCb,
-    NemoRelayToolExecInterceptCb, NemoRelayToolSanitizeCb, wrap_codec_fn, wrap_collector_fn,
+    NemoRelayCodecDecodeFn, NemoRelayCodecEncodeFn, NemoRelayCollectorCb,
+    NemoRelayEventMetadataInjectorCb, NemoRelayEventSanitizeCb, NemoRelayEventSubscriberCb,
+    NemoRelayFinalizerCb, NemoRelayFreeFn, NemoRelayLlmConditionalCb, NemoRelayLlmExecCb,
+    NemoRelayLlmExecInterceptCb, NemoRelayLlmRequestInterceptCb, NemoRelayLlmSanitizeRequestCb,
+    NemoRelayLlmSanitizeResponseCb, NemoRelayPluginRegisterCb, NemoRelayPluginValidateCb,
+    NemoRelayToolConditionalCb, NemoRelayToolExecCb, NemoRelayToolExecInterceptCb,
+    NemoRelayToolSanitizeCb, wrap_codec_fn, wrap_collector_fn, wrap_event_metadata_injector_fn,
     wrap_event_sanitize_fn, wrap_event_subscriber, wrap_finalizer_fn, wrap_llm_conditional_fn,
     wrap_llm_exec_fn, wrap_llm_exec_intercept_fn, wrap_llm_request_intercept_fn,
     wrap_llm_sanitize_request_fn, wrap_llm_sanitize_response_fn, wrap_llm_stream_exec_fn,

crates/ffi/src/api/plugin.rs

@@ -3,20 +3,21 @@
 
 use super::{
     Arc, CStr, ConfigDiagnostic, DiagnosticLevel, DynamicPluginActivationSpec, FfiPluginActivation,
-    FfiPluginContext, Future, NemoRelayEventSanitizeCb, NemoRelayEventSubscriberCb,
-    NemoRelayFreeFn, NemoRelayLlmConditionalCb, NemoRelayLlmExecInterceptCb,
-    NemoRelayLlmRequestInterceptCb, NemoRelayLlmSanitizeRequestCb, NemoRelayLlmSanitizeResponseCb,
-    NemoRelayPluginRegisterCb, NemoRelayPluginValidateCb, NemoRelayStatus,
-    NemoRelayToolConditionalCb, NemoRelayToolExecInterceptCb, NemoRelayToolSanitizeCb, Pin, Plugin,
-    PluginConfig, PluginError, PluginHostActivation, PluginRegistrationContext,
-    active_plugin_report, c_char, c_str_to_json, c_str_to_string, clear_last_error,
-    clear_plugin_configuration, deregister_plugin, initialize_plugins, json_to_c_string,
-    last_error_message, list_plugin_kinds, nemo_relay_string_free, register_adaptive_component,
-    register_plugin, set_last_error, status_from_plugin_error, tokio_runtime,
-    validate_plugin_config, wrap_event_sanitize_fn, wrap_event_subscriber, wrap_llm_conditional_fn,
-    wrap_llm_exec_intercept_fn, wrap_llm_request_intercept_fn, wrap_llm_sanitize_request_fn,
-    wrap_llm_sanitize_response_fn, wrap_llm_stream_exec_intercept_fn, wrap_tool_conditional_fn,
-    wrap_tool_exec_intercept_fn, wrap_tool_request_intercept_fn, wrap_tool_sanitize_fn,
+    FfiPluginContext, Future, NemoRelayEventMetadataInjectorCb, NemoRelayEventSanitizeCb,
+    NemoRelayEventSubscriberCb, NemoRelayFreeFn, NemoRelayLlmConditionalCb,
+    NemoRelayLlmExecInterceptCb, NemoRelayLlmRequestInterceptCb, NemoRelayLlmSanitizeRequestCb,
+    NemoRelayLlmSanitizeResponseCb, NemoRelayPluginRegisterCb, NemoRelayPluginValidateCb,
+    NemoRelayStatus, NemoRelayToolConditionalCb, NemoRelayToolExecInterceptCb,
+    NemoRelayToolSanitizeCb, Pin, Plugin, PluginConfig, PluginError, PluginHostActivation,
+    PluginRegistrationContext, active_plugin_report, c_char, c_str_to_json, c_str_to_string,
+    clear_last_error, clear_plugin_configuration, deregister_plugin, initialize_plugins,
+    json_to_c_string, last_error_message, list_plugin_kinds, nemo_relay_string_free,
+    register_adaptive_component, register_plugin, set_last_error, status_from_plugin_error,
+    tokio_runtime, validate_plugin_config, wrap_event_metadata_injector_fn, wrap_event_sanitize_fn,
+    wrap_event_subscriber, wrap_llm_conditional_fn, wrap_llm_exec_intercept_fn,
+    wrap_llm_request_intercept_fn, wrap_llm_sanitize_request_fn, wrap_llm_sanitize_response_fn,
+    wrap_llm_stream_exec_intercept_fn, wrap_tool_conditional_fn, wrap_tool_exec_intercept_fn,
+    wrap_tool_request_intercept_fn, wrap_tool_sanitize_fn,
 };
 use crate::api::event_registry::Surface;
 use nemo_relay_pii_redaction::component::register_pii_redaction_component;
@@ -542,6 +543,40 @@ pub unsafe extern "C" fn nemo_relay_plugin_context_register_subscriber(
     }
 }
 
+/// Register an event metadata injector into a plugin context.
+///
+/// # Safety
+/// Pointers must remain valid for the documented call lifetime. The callback
+/// and user data remain owned by the plugin registration until rollback.
+#[unsafe(no_mangle)]
+pub unsafe extern "C" fn nemo_relay_plugin_context_register_event_metadata_injector(
+    ctx: *mut FfiPluginContext,
+    name: *const c_char,
+    priority: i32,
+    cb: NemoRelayEventMetadataInjectorCb,
+    user_data: *mut libc::c_void,
+    free_fn: NemoRelayFreeFn,
+) -> NemoRelayStatus {
+    clear_last_error();
+    if ctx.is_null() {
+        set_last_error("plugin context is null");
+        return NemoRelayStatus::NullPointer;
+    }
+    let Some(cb) = cb else {
+        set_last_error("event metadata injector callback is null");
+        return NemoRelayStatus::NullPointer;
+    };
+    let callback = wrap_event_metadata_injector_fn(cb, user_data, free_fn);
+    let name = match c_str_to_string(name) {
+        Ok(value) => value,
+        Err(status) => return status,
+    };
+    match unsafe { &mut *((*ctx).0) }.register_event_metadata_injector(&name, priority, callback) {
+        Ok(()) => NemoRelayStatus::Ok,
+        Err(error) => status_from_plugin_error(&error),
+    }
+}
+
 unsafe fn plugin_register_event_sanitizer(
     ctx: *mut FfiPluginContext,
     name: *const c_char,