[codex-analytics] add compaction analytics event

[rhan-oai]

• 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 [codex-analytics] feature plumbing and emittance #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} |

[owenlin0]

maybe we should log some warns if we don't find these, since that would be unexpected right?

[owenlin0]

hmm this logic is weird, why do we set it to 0 if the feature is disabled? i think we can always just grab the token count