[codex-analytics] add compaction analytics event (#17155)

- event for compaction analytics
- introduces thread-connection and thread metadata caches for data
denormalization, expected to be useful for denormalization onto core
emitted events in general
- threads analytics event client into core (mirrors approved
implementation in #16640)
- denormalizes key thread metadata: thread_source, subagent_source,
parent_thread_id, as well as app-server client and runtime metadata)
- compaction strategy defaults to memento, forward compatible with
expected prefill_compaction strategy

1. Manual standalone compact, local
`INFO | 2026-04-09 17:35:50 | codex_backend.routers.analytics_events |
analytics_events.track_analytics_events:526 | Tracked
codex_compaction_event event params={'thread_id':
'019d74d0-5cfb-70c0-bef9-165c3bf9b2df', 'turn_id':
'019d74d0-d7f6-7c81-acc6-aae2030243d6', 'product_surface': 'codex',
'app_server_client': {'product_client_id': 'CODEX_CLI', 'client_name':
'codex-tui', 'client_version': '0.0.0', 'rpc_transport': 'in_process',
'experimental_api_enabled': True}, 'runtime': {'codex_rs_version':
'0.0.0', 'runtime_os': 'macos', 'runtime_os_version': '26.4.0',
'runtime_arch': 'aarch64'}, 'trigger': 'manual', 'reason':
'user_requested', 'implementation': 'responses', 'phase':
'standalone_turn', 'strategy': 'memento', 'status': 'completed',
'active_context_tokens_before': 20170, 'active_context_tokens_after':
4830, 'started_at': 1775781337, 'completed_at': 1775781350,
'thread_source': 'user', 'subagent_source': None, 'parent_thread_id':
None, 'error': None, 'duration_ms': 13524} | `

2. Auto pre-turn compact, local
`INFO | 2026-04-09 17:37:30 | codex_backend.routers.analytics_events |
analytics_events.track_analytics_events:526 | Tracked
codex_compaction_event event params={'thread_id':
'019d74d2-45ef-71d1-9c93-23cc0c13d988', 'turn_id':
'019d74d2-7b42-7372-9f0e-c0da3f352328', 'product_surface': 'codex',
'app_server_client': {'product_client_id': 'CODEX_CLI', 'client_name':
'codex-tui', 'client_version': '0.0.0', 'rpc_transport': 'in_process',
'experimental_api_enabled': True}, 'runtime': {'codex_rs_version':
'0.0.0', 'runtime_os': 'macos', 'runtime_os_version': '26.4.0',
'runtime_arch': 'aarch64'}, 'trigger': 'auto', 'reason':
'context_limit', 'implementation': 'responses', 'phase': 'pre_turn',
'strategy': 'memento', 'status': 'completed',
'active_context_tokens_before': 20063, 'active_context_tokens_after':
4822, 'started_at': 1775781444, 'completed_at': 1775781449,
'thread_source': 'user', 'subagent_source': None, 'parent_thread_id':
None, 'error': None, 'duration_ms': 5497} | `

3. Auto mid-turn compact, local
`INFO | 2026-04-09 17:38:28 | codex_backend.routers.analytics_events |
analytics_events.track_analytics_events:526 | Tracked
codex_compaction_event event params={'thread_id':
'019d74d3-212f-7a20-8c0a-4816a978675e', 'turn_id':
'019d74d3-3ee1-7462-89f6-2ffbeefcd5e3', 'product_surface': 'codex',
'app_server_client': {'product_client_id': 'CODEX_CLI', 'client_name':
'codex-tui', 'client_version': '0.0.0', 'rpc_transport': 'in_process',
'experimental_api_enabled': True}, 'runtime': {'codex_rs_version':
'0.0.0', 'runtime_os': 'macos', 'runtime_os_version': '26.4.0',
'runtime_arch': 'aarch64'}, 'trigger': 'auto', 'reason':
'context_limit', 'implementation': 'responses', 'phase': 'mid_turn',
'strategy': 'memento', 'status': 'completed',
'active_context_tokens_before': 20325, 'active_context_tokens_after':
14641, 'started_at': 1775781500, 'completed_at': 1775781508,
'thread_source': 'user', 'subagent_source': None, 'parent_thread_id':
None, 'error': None, 'duration_ms': 7507} | `

4. Remote /responses/compact, manual standalone
`INFO | 2026-04-09 17:40:20 | codex_backend.routers.analytics_events |
analytics_events.track_analytics_events:526 | Tracked
codex_compaction_event event params={'thread_id':
'019d74d4-7a11-78a1-89f7-0535a1149416', 'turn_id':
'019d74d4-e087-7183-9c20-b1e40b7578c0', 'product_surface': 'codex',
'app_server_client': {'product_client_id': 'CODEX_CLI', 'client_name':
'codex-tui', 'client_version': '0.0.0', 'rpc_transport': 'in_process',
'experimental_api_enabled': True}, 'runtime': {'codex_rs_version':
'0.0.0', 'runtime_os': 'macos', 'runtime_os_version': '26.4.0',
'runtime_arch': 'aarch64'}, 'trigger': 'manual', 'reason':
'user_requested', 'implementation': 'responses_compact', 'phase':
'standalone_turn', 'strategy': 'memento', 'status': 'completed',
'active_context_tokens_before': 23461, 'active_context_tokens_after':
6171, 'started_at': 1775781601, 'completed_at': 1775781620,
'thread_source': 'user', 'subagent_source': None, 'parent_thread_id':
None, 'error': None, 'duration_ms': 18971} | `

codex-rs/analytics/src/events.rs

@@ -1,4 +1,5 @@
 use crate::facts::AppInvocation;
+use crate::facts::CodexCompactionEvent;
 use crate::facts::InvocationType;
 use crate::facts::PluginState;
 use crate::facts::SubAgentThreadStartedInput;
@@ -37,6 +38,7 @@ pub(crate) enum TrackEventRequest {
     ThreadInitialized(ThreadInitializedEvent),
     AppMentioned(CodexAppMentionedEventRequest),
     AppUsed(CodexAppUsedEventRequest),
+    Compaction(Box<CodexCompactionEventRequest>),
     PluginUsed(CodexPluginUsedEventRequest),
     PluginInstalled(CodexPluginEventRequest),
     PluginUninstalled(CodexPluginEventRequest),
@@ -122,6 +124,35 @@ pub(crate) struct CodexAppUsedEventRequest {
     pub(crate) event_params: CodexAppMetadata,
 }
 
+#[derive(Serialize)]
+pub(crate) struct CodexCompactionEventParams {
+    pub(crate) thread_id: String,
+    pub(crate) turn_id: String,
+    pub(crate) app_server_client: CodexAppServerClientMetadata,
+    pub(crate) runtime: CodexRuntimeMetadata,
+    pub(crate) thread_source: Option<&'static str>,
+    pub(crate) subagent_source: Option<String>,
+    pub(crate) parent_thread_id: Option<String>,
+    pub(crate) trigger: crate::facts::CompactionTrigger,
+    pub(crate) reason: crate::facts::CompactionReason,
+    pub(crate) implementation: crate::facts::CompactionImplementation,
+    pub(crate) phase: crate::facts::CompactionPhase,
+    pub(crate) strategy: crate::facts::CompactionStrategy,
+    pub(crate) status: crate::facts::CompactionStatus,
+    pub(crate) error: Option<String>,
+    pub(crate) active_context_tokens_before: i64,
+    pub(crate) active_context_tokens_after: i64,
+    pub(crate) started_at: u64,
+    pub(crate) completed_at: u64,
+    pub(crate) duration_ms: Option<u64>,
+}
+
+#[derive(Serialize)]
+pub(crate) struct CodexCompactionEventRequest {
+    pub(crate) event_type: &'static str,
+    pub(crate) event_params: CodexCompactionEventParams,
+}
+
 #[derive(Serialize)]
 pub(crate) struct CodexPluginMetadata {
     pub(crate) plugin_id: Option<String>,
@@ -201,6 +232,37 @@ pub(crate) fn codex_plugin_metadata(plugin: PluginTelemetryMetadata) -> CodexPlu
     }
 }
 
+pub(crate) fn codex_compaction_event_params(
+    input: CodexCompactionEvent,
+    app_server_client: CodexAppServerClientMetadata,
+    runtime: CodexRuntimeMetadata,
+    thread_source: Option<&'static str>,
+    subagent_source: Option<String>,
+    parent_thread_id: Option<String>,
+) -> CodexCompactionEventParams {
+    CodexCompactionEventParams {
+        thread_id: input.thread_id,
+        turn_id: input.turn_id,
+        app_server_client,
+        runtime,
+        thread_source,
+        subagent_source,
+        parent_thread_id,
+        trigger: input.trigger,
+        reason: input.reason,
+        implementation: input.implementation,
+        phase: input.phase,
+        strategy: input.strategy,
+        status: input.status,
+        error: input.error,
+        active_context_tokens_before: input.active_context_tokens_before,
+        active_context_tokens_after: input.active_context_tokens_after,
+        started_at: input.started_at,
+        completed_at: input.completed_at,
+        duration_ms: input.duration_ms,
+    }
+}
+
 pub(crate) fn codex_plugin_used_metadata(
     tracking: &TrackEventsContext,
     plugin: PluginTelemetryMetadata,
@@ -260,7 +322,7 @@ pub(crate) fn subagent_thread_started_event_request(
     }
 }
 
-fn subagent_source_name(subagent_source: &SubAgentSource) -> String {
+pub(crate) fn subagent_source_name(subagent_source: &SubAgentSource) -> String {
     match subagent_source {
         SubAgentSource::Review => "review".to_string(),
         SubAgentSource::Compact => "compact".to_string(),
@@ -270,7 +332,7 @@ fn subagent_source_name(subagent_source: &SubAgentSource) -> String {
     }
 }
 
-fn subagent_parent_thread_id(subagent_source: &SubAgentSource) -> Option<String> {
+pub(crate) fn subagent_parent_thread_id(subagent_source: &SubAgentSource) -> Option<String> {
     match subagent_source {
         SubAgentSource::ThreadSpawn {
             parent_thread_id, ..