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Trim first-turn rollback context scaffolding

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Co-authored-by: Codex <noreply@openai.com>
This commit is contained in:
Charles Cunningham
2026-03-25 10:47:32 -07:00
parent 303d0190c5
commit 120251eb5a
2 changed files with 32 additions and 10 deletions
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13
codex-rs/core/src/context_manager/history.rs
View File

@@ -244,8 +244,7 @@ impl ContextManager {
user_positions[user_positions.len() - n_from_end]
};
cut_idx =
self.trim_pre_turn_context_updates(&snapshot, first_instruction_turn_idx, cut_idx);
cut_idx = self.trim_pre_turn_context_updates(&snapshot, cut_idx);
self.replace(snapshot[..cut_idx].to_vec());
}
@@ -401,13 +400,10 @@ impl ContextManager {
/// Returns the adjusted cut index after removing contextual developer/user items immediately
/// above the rolled-back turn boundary.
///
/// `first_instruction_turn_idx` is the earliest rollback-eligible instruction-turn boundary
/// in `snapshot`; the trim walk never crosses it so any session-prefix items that predate the
/// first real turn survive rollback.
///
/// `cut_idx` is the tentative slice boundary after dropping the requested number of
/// instruction turns, before stripping contextual pre-turn items that sit immediately above
/// that boundary.
/// that boundary. The trim walk may continue all the way to index `0`, but it stops as soon
/// as it encounters a non-contextual item, so only actual per-turn scaffolding is removed.
///
/// If any trimmed developer message was a mixed `build_initial_context` bundle containing both
/// rollback-trimmable contextual fragments and persistent developer text, this also clears the
@@ -416,10 +412,9 @@ impl ContextManager {
fn trim_pre_turn_context_updates(
&mut self,
snapshot: &[ResponseItem],
first_instruction_turn_idx: usize,
mut cut_idx: usize,
) -> usize {
while cut_idx > first_instruction_turn_idx {
while cut_idx > 0 {
match &snapshot[cut_idx - 1] {
ResponseItem::Message { role, content, .. }
if role == "developer" && is_contextual_dev_message_content(content) =>

29
codex-rs/core/src/context_manager/history_tests.rs
View File

@@ -954,7 +954,34 @@ fn drop_last_n_user_turns_trims_context_updates_above_rolled_back_turn() {
);
}
#[test]
fn drop_last_n_user_turns_trims_context_updates_above_first_rolled_back_turn() {
let items = vec![
assistant_msg("session prefix item"),
developer_msg("<collaboration_mode>ROLLED_BACK_DEV_INSTRUCTIONS</collaboration_mode>"),
user_input_text_msg(
"<environment_context><cwd>PRETURN_CONTEXT_DIFF_CWD</cwd></environment_context>",
),
user_input_text_msg("turn 1 user"),
assistant_msg("turn 1 assistant"),
];
let modalities = default_input_modalities();
let mut history = create_history_with_items(items);
let reference_context_item = reference_context_item();
history.set_reference_context_item(Some(reference_context_item.clone()));
history.drop_last_n_user_turns(1);
assert_eq!(
history.clone().for_prompt(&modalities),
vec![assistant_msg("session prefix item")]
);
assert_eq!(
serde_json::to_value(history.reference_context_item())
.expect("serialize retained reference context item"),
serde_json::to_value(Some(reference_context_item))
.expect("serialize expected reference context item")
);
}
fn drop_last_n_user_turns_clears_reference_context_for_mixed_developer_context_bundles() {
let items = vec![
user_input_text_msg("turn 1 user"),