feat: annotate conversations with model_provider for filtering (#5658)

Because conversations that use the Responses API can have encrypted
reasoning messages, trying to resume a conversation with a different
provider could lead to confusing "failed to decrypt" errors. (This is
reproducible by starting a conversation using ChatGPT login and resuming
it as a conversation that uses OpenAI models via Azure.)

This changes `ListConversationsParams` to take a `model_providers:
Option<Vec<String>>` and adds `model_provider` on each
`ConversationSummary` it returns so these cases can be disambiguated.

Note this ended up making changes to
`codex-rs/core/src/rollout/tests.rs` because it had a number of cases
where it expected `Some` for the value of `next_cursor`, but the list of
rollouts was complete, so according to this docstring:


bcd64c7e72/codex-rs/app-server-protocol/src/protocol.rs (L334-L337)

If there are no more items to return, then `next_cursor` should be
`None`. This PR updates that logic.






---
[//]: # (BEGIN SAPLING FOOTER)
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with [ReviewStack](https://reviewstack.dev/openai/codex/pull/5658).
* #5803
* #5793
* __->__ #5658

codex-rs/core/src/rollout/recorder.rs

@@ -97,8 +97,18 @@ impl RolloutRecorder {
         page_size: usize,
         cursor: Option<&Cursor>,
         allowed_sources: &[SessionSource],
+        model_providers: Option<&[String]>,
+        default_provider: &str,
     ) -> std::io::Result<ConversationsPage> {
-        get_conversations(codex_home, page_size, cursor, allowed_sources).await
+        get_conversations(
+            codex_home,
+            page_size,
+            cursor,
+            allowed_sources,
+            model_providers,
+            default_provider,
+        )
+        .await
     }
 
     /// Attempt to create a new [`RolloutRecorder`]. If the sessions directory
@@ -137,6 +147,7 @@ impl RolloutRecorder {
                         cli_version: env!("CARGO_PKG_VERSION").to_string(),
                         instructions,
                         source,
+                        model_provider: Some(config.model_provider_id.clone()),
                     }),
                 )
             }