[codex-analytics] Emit structured compaction codex errors (#27082)

## Summary
- replace raw compaction `error` analytics with `codex_error_kind` and
`codex_error_http_status_code`
- derive compaction error telemetry from `CodexErr` using the same
`CodexErrKind` mapping and HTTP status helper used by turn events
- remove the pre-compact hook stop reason from the internal compaction
outcome now that it is no longer emitted as raw analytics text

## Why
Compaction `error` was a raw `CodexErr::to_string()` value, which can
carry free-form provider or user-derived text. Structured Codex error
fields preserve useful low-cardinality telemetry without sending the raw
string.

## Validation
- `just fmt`
- `just test -p codex-analytics`
- `just test -p codex-core
compact::tests::build_token_limited_compacted_history_appends_summary_message`

Attempted `just test -p codex-core`; the changed crate compiled, but the
full target failed in unrelated environment-dependent tests such as
missing helper binaries and shell snapshot timeouts.

codex-rs/analytics/src/analytics_client_tests.rs

@@ -43,6 +43,7 @@ use crate::facts::AppInvocation;
 use crate::facts::AppMentionedInput;
 use crate::facts::AppUsedInput;
 use crate::facts::CodexCompactionEvent;
+use crate::facts::CodexErrKind;
 use crate::facts::CompactionImplementation;
 use crate::facts::CompactionPhase;
 use crate::facts::CompactionReason;
@@ -1278,7 +1279,8 @@ fn compaction_event_serializes_expected_shape() {
                 phase: CompactionPhase::MidTurn,
                 strategy: CompactionStrategy::Memento,
                 status: CompactionStatus::Completed,
-                error: None,
+                codex_error_kind: None,
+                codex_error_http_status_code: None,
                 active_context_tokens_before: 120_000,
                 active_context_tokens_after: 18_000,
                 retained_image_count: None,
@@ -1329,7 +1331,8 @@ fn compaction_event_serializes_expected_shape() {
                 "phase": "mid_turn",
                 "strategy": "memento",
                 "status": "completed",
-                "error": null,
+                "codex_error_kind": null,
+                "codex_error_http_status_code": null,
                 "active_context_tokens_before": 120000,
                 "active_context_tokens_after": 18000,
                 "retained_image_count": null,
@@ -1852,7 +1855,8 @@ async fn compaction_event_ingests_custom_fact() {
                     phase: CompactionPhase::StandaloneTurn,
                     strategy: CompactionStrategy::Memento,
                     status: CompactionStatus::Failed,
-                    error: Some("context limit exceeded".to_string()),
+                    codex_error_kind: Some(CodexErrKind::ContextWindowExceeded),
+                    codex_error_http_status_code: None,
                     active_context_tokens_before: 131_000,
                     active_context_tokens_after: 131_000,
                     retained_image_count: None,
@@ -1873,6 +1877,14 @@ async fn compaction_event_ingests_custom_fact() {
     assert_eq!(payload[0]["event_params"]["session_id"], "session-thread-1");
     assert_eq!(payload[0]["event_params"]["thread_id"], "thread-1");
     assert_eq!(payload[0]["event_params"]["turn_id"], "turn-compact");
+    assert_eq!(
+        payload[0]["event_params"]["codex_error_kind"],
+        json!("context_window_exceeded")
+    );
+    assert_eq!(
+        payload[0]["event_params"]["codex_error_http_status_code"],
+        json!(null)
+    );
     assert_eq!(
         payload[0]["event_params"]["app_server_client"]["product_client_id"],
         DEFAULT_ORIGINATOR
@@ -2779,7 +2791,8 @@ async fn subagent_events_use_inherited_connection_unless_turn_connection_is_expl
                     phase: CompactionPhase::StandaloneTurn,
                     strategy: CompactionStrategy::Memento,
                     status: CompactionStatus::Completed,
-                    error: None,
+                    codex_error_kind: None,
+                    codex_error_http_status_code: None,
                     active_context_tokens_before: 131_000,
                     active_context_tokens_after: 64_000,
                     retained_image_count: None,