[codex-analytics] feature plumbing and emittance (#16640)

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[//]: # (BEGIN SAPLING FOOTER)
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with [ReviewStack](https://reviewstack.dev/openai/codex/pull/16640).
* #16870
* #16706
* #16641
* __->__ #16640

codex-rs/core/src/compact.rs

@@ -1,7 +1,5 @@
 use std::sync::Arc;
 use std::time::Instant;
-use std::time::SystemTime;
-use std::time::UNIX_EPOCH;
 
 use crate::Prompt;
 use crate::client::ModelClientSession;
@@ -19,6 +17,7 @@ use codex_analytics::CompactionReason;
 use codex_analytics::CompactionStatus;
 use codex_analytics::CompactionStrategy;
 use codex_analytics::CompactionTrigger;
+use codex_analytics::now_unix_seconds;
 use codex_features::Feature;
 use codex_model_provider_info::ModelProviderInfo;
 use codex_protocol::error::CodexErr;
@@ -372,13 +371,6 @@ pub(crate) fn compaction_status_from_result<T>(result: &CodexResult<T>) -> Compa
     }
 }
 
-fn now_unix_seconds() -> u64 {
-    SystemTime::now()
-        .duration_since(UNIX_EPOCH)
-        .map(|duration| duration.as_secs())
-        .unwrap_or_default()
-}
-
 pub fn content_items_to_text(content: &[ContentItem]) -> Option<String> {
     let mut pieces = Vec::new();
     for item in content {