Inline response recording and remove process_items indirection (#7310)

- Inline response recording during streaming: `run_turn` now records
items as they arrive instead of building a `ProcessedResponseItem` list
and post‑processing via `process_items`.
- Simplify turn handling: `handle_output_item_done` returns the
follow‑up signal + optional tool future; `needs_follow_up` is set only
there, and in‑flight tool futures are drained once at the end (errors
logged, no extra state writes).
- Flattened stream loop: removed `process_items` indirection and the
extra output queue
- - Tests: relaxed `tool_parallelism::tool_results_grouped` to allow any
completion order while still requiring matching call/output IDs.

codex-rs/core/src/error.rs

@@ -1,4 +1,3 @@
-use crate::codex::ProcessedResponseItem;
 use crate::exec::ExecToolCallOutput;
 use crate::token_data::KnownPlan;
 use crate::token_data::PlanType;
@@ -61,9 +60,7 @@ pub enum SandboxErr {
 pub enum CodexErr {
     // todo(aibrahim): git rid of this error carrying the dangling artifacts
     #[error("turn aborted. Something went wrong? Hit `/feedback` to report the issue.")]
-    TurnAborted {
-        dangling_artifacts: Vec<ProcessedResponseItem>,
-    },
+    TurnAborted,
 
     /// Returned by ResponsesClient when the SSE stream disconnects or errors out **after** the HTTP
     /// handshake has succeeded but **before** it finished emitting `response.completed`.
@@ -181,9 +178,7 @@ pub enum CodexErr {
 
 impl From<CancelErr> for CodexErr {
     fn from(_: CancelErr) -> Self {
-        CodexErr::TurnAborted {
-            dangling_artifacts: Vec::new(),
-        }
+        CodexErr::TurnAborted
     }
 }