core: refresh developer instructions after compaction replacement history (#10574)

## Summary

When replaying compacted history (especially `replacement_history` from
remote compaction), we should not keep stale developer messages from
older session state. This PR trims developer-
role messages from compacted replacement history and reinjects fresh
developer instructions derived from current turn/session state.

This aligns compaction replay behavior with the intended "fresh
instructions after summary" model.

## Problem

Compaction replay had two paths:

- `Compacted { replacement_history: None }`: rebuilt with fresh initial
context
- `Compacted { replacement_history: Some(...) }`: previously used raw
replacement history as-is

The second path could carry stale developer instructions
(permissions/personality/collab-mode guidance) across session changes.

## What Changed

### 1) Added helper to refresh compacted developer instructions

- **File:** `codex-rs/core/src/compact.rs`
- **Function:** `refresh_compacted_developer_instructions(...)`

Behavior:
- remove all `ResponseItem::Message { role: "developer", .. }` from
compacted history
- append fresh developer messages from current
`build_initial_context(...)`

### 2) Applied helper in remote compaction flow

- **File:** `codex-rs/core/src/compact_remote.rs`
- After receiving compact endpoint output, refresh developer
instructions before replacing history and persisting
`replacement_history`.

### 3) Applied helper while reconstructing history from rollout

- **File:** `codex-rs/core/src/codex.rs`
- In `reconstruct_history_from_rollout(...)`, when processing
`Compacted` entries with `replacement_history`, refresh developer
instructions instead of directly replacing with raw history.

## Non-Goals / Follow-up

This PR does **not** address the existing first-turn-after-resume
double-injection behavior.
A follow-up PR will handle resume-time dedup/idempotence separately.

If you want, I can also give you a shorter “squash-merge friendly”
version of the description.

## Codex author
`codex fork 019c25e6-706e-75d1-9198-688ec00a8256`

codex-rs/core/src/compact_remote.rs

@@ -90,6 +90,9 @@ async fn run_remote_compact_task_inner_impl(
             &turn_context.otel_manager,
         )
         .await?;
+    new_history = sess
+        .process_compacted_history(turn_context, new_history)
+        .await;
 
     if !ghost_snapshots.is_empty() {
         new_history.extend(ghost_snapshots);