[codex-analytics] ingest server requests and responses (#17088)

## Why

Codex analytics needs a typed seam for app-server-originated
request/response traffic so future tool-approval analytics can consume
those facts without adding bespoke callsite tracking each time. Server
responses arrive as JSON-RPC `id + result` payloads, so analytics has to
reconstruct the matching typed response from the original typed request
while that request context still exists in app-server.

This also puts analytics on the app-server outbound path, which needs to
avoid keeping the runtime alive during shutdown. The final ownership fix
keeps the normal strong auth-manager retention in analytics and makes
the external-auth refresh bridge hold a weak back-reference to
`OutgoingMessageSender`, breaking the runtime cycle at the bridge
boundary instead of exposing retention policy through the analytics
client API.

## What changed

- Adds typed `ServerRequest` and `ServerResponse` analytics facts, plus
`AnalyticsEventsClient::track_server_request` and
`track_server_response`.
- Renames the existing client-side facts to `ClientRequest` and
`ClientResponse` so reducers can distinguish client-to-server traffic
from server-to-client traffic.
- Adds `ServerRequest::response_from_result`, allowing a stored typed
request to decode the matching typed server response from a raw JSON-RPC
result payload.
- Threads `AnalyticsEventsClient` through `OutgoingMessageSender` and
records targeted server requests, replayed targeted requests, and
matching targeted responses with the responding connection id needed for
correlation.
- Intentionally leaves broadcast server requests/responses out of
analytics for now because the current model is per connection, while
broadcasts fan one logical request out across multiple connections.
- Breaks the app-server shutdown cycle by storing
`Weak<OutgoingMessageSender>` in `ExternalAuthRefreshBridge` and
upgrading it only when an external-auth refresh is actually requested.
- Keeps reducer ingestion of the new server-side facts as no-ops for
now; this PR is plumbing for later tool-approval analytics work.

## Verification

- `cargo test -p codex-analytics`
- `cargo test -p codex-app-server outgoing_message::tests::`
- Covers typed-response reconstruction plus the targeted, replayed,
broadcast-exclusion, and response-attribution analytics paths.

## Follow-up

This PR intentionally stops at ingestion plumbing, so `ServerRequest`
and `ServerResponse` facts are still reducer no-ops. Once a follow-up PR
adds real downstream analytics output for those facts:

- replace the temporary pre-reducer observation seam with reducer tests
for the emitted event shape;
- add end-to-end coverage in `app-server/tests/suite/v2/analytics.rs`
for the real app-server workflow and captured analytics payload;
- remove the temporary sender-level observer tests added here in favor
of the real-output coverage above.

---

[//]: # (BEGIN SAPLING FOOTER)
Stack created with [Sapling](https://sapling-scm.com). Best reviewed
with [ReviewStack](https://reviewstack.dev/openai/codex/pull/17088).
* #18748
* #18747
* #17090
* #17089
* #20241
* #20239
* __->__ #17088

codex-rs/app-server/src/message_processor.rs

@@ -247,6 +247,7 @@ impl ConnectionSessionState {
 
 pub(crate) struct MessageProcessorArgs {
     pub(crate) outgoing: Arc<OutgoingMessageSender>,
+    pub(crate) analytics_events_client: AnalyticsEventsClient,
     pub(crate) arg0_paths: Arg0DispatchPaths,
     pub(crate) config: Arc<Config>,
     pub(crate) config_manager: ConfigManager,
@@ -267,6 +268,7 @@ impl MessageProcessor {
     pub(crate) fn new(args: MessageProcessorArgs) -> Self {
         let MessageProcessorArgs {
             outgoing,
+            analytics_events_client,
             arg0_paths,
             config,
             config_manager,
@@ -283,11 +285,6 @@ impl MessageProcessor {
         auth_manager.set_external_auth(Arc::new(ExternalAuthRefreshBridge {
             outgoing: outgoing.clone(),
         }));
-        let analytics_events_client = AnalyticsEventsClient::new(
-            Arc::clone(&auth_manager),
-            config.chatgpt_base_url.trim_end_matches('/').to_string(),
-            config.analytics_enabled,
-        );
         let thread_manager = Arc::new(ThreadManager::new(
             config.as_ref(),
             auth_manager.clone(),