Add thread/unarchive to restore archived rollouts (#9843)

## Summary
- Adds a new `thread/unarchive` RPC to move archived thread rollouts
back into the active `sessions/` tree.

## What changed
- **Protocol**
  - Adds `thread/unarchive` request/response types and wiring.
- **Server**
  - Implements `thread_unarchive` in the app server.
  - Validates the archived rollout path and thread ID.
- Restores the rollout to `sessions/YYYY/MM/DD/...` based on the rollout
filename timestamp.
- **Core**
- Adds `find_archived_thread_path_by_id_str` helper for archived
rollouts.
- **Docs**
  - Documents the new RPC and usage example.
- **Tests**
  - Adds an end-to-end server test that:
    1) starts a thread,
    2) archives it,
    3) unarchives it,
    4) asserts the file is restored to `sessions/`.

## How to use
```json
{ "method": "thread/unarchive", "id": 24, "params": { "threadId": "<thread-id>" } }
```

## Author Codex Session

`codex resume 019bf158-54b6-7960-a696-9d85df7e1bc1` (soon I'll make this
kind of session UUID forkable by anyone with the right
`session_object_storage_url` line in their config, but for now just
pasting it here for my reference)

codex-rs/core/src/lib.rs

@@ -98,6 +98,7 @@ pub use rollout::INTERACTIVE_SESSION_SOURCES;
 pub use rollout::RolloutRecorder;
 pub use rollout::SESSIONS_SUBDIR;
 pub use rollout::SessionMeta;
+pub use rollout::find_archived_thread_path_by_id_str;
 #[deprecated(note = "use find_thread_path_by_id_str")]
 pub use rollout::find_conversation_path_by_id_str;
 pub use rollout::find_thread_path_by_id_str;
@@ -108,6 +109,7 @@ pub use rollout::list::ThreadsPage;
 pub use rollout::list::parse_cursor;
 pub use rollout::list::read_head_for_summary;
 pub use rollout::list::read_session_meta_line;
+pub use rollout::rollout_date_parts;
 mod function_tool;
 mod state;
 mod tasks;

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

@@ -1,4 +1,5 @@
 use std::cmp::Reverse;
+use std::ffi::OsStr;
 use std::io::{self};
 use std::num::NonZero;
 use std::ops::ControlFlow;
@@ -15,6 +16,7 @@ use time::format_description::well_known::Rfc3339;
 use time::macros::format_description;
 use uuid::Uuid;
 
+use super::ARCHIVED_SESSIONS_SUBDIR;
 use super::SESSIONS_SUBDIR;
 use crate::protocol::EventMsg;
 use codex_file_search as file_search;
@@ -1054,11 +1056,9 @@ fn truncate_to_seconds(dt: OffsetDateTime) -> Option<OffsetDateTime> {
     dt.replace_nanosecond(0).ok()
 }
 
-/// Locate a recorded thread rollout file by its UUID string using the existing
-/// paginated listing implementation. Returns `Ok(Some(path))` if found, `Ok(None)` if not present
-/// or the id is invalid.
-pub async fn find_thread_path_by_id_str(
+async fn find_thread_path_by_id_str_in_subdir(
     codex_home: &Path,
+    subdir: &str,
     id_str: &str,
 ) -> io::Result<Option<PathBuf>> {
     // Validate UUID format early.
@@ -1067,7 +1067,7 @@ pub async fn find_thread_path_by_id_str(
     }
 
     let mut root = codex_home.to_path_buf();
-    root.push(SESSIONS_SUBDIR);
+    root.push(subdir);
     if !root.exists() {
         return Ok(None);
     }
@@ -1099,3 +1099,31 @@ pub async fn find_thread_path_by_id_str(
         .next()
         .map(|m| root.join(m.path)))
 }
+
+/// Locate a recorded thread rollout file by its UUID string using the existing
+/// paginated listing implementation. Returns `Ok(Some(path))` if found, `Ok(None)` if not present
+/// or the id is invalid.
+pub async fn find_thread_path_by_id_str(
+    codex_home: &Path,
+    id_str: &str,
+) -> io::Result<Option<PathBuf>> {
+    find_thread_path_by_id_str_in_subdir(codex_home, SESSIONS_SUBDIR, id_str).await
+}
+
+/// Locate an archived thread rollout file by its UUID string.
+pub async fn find_archived_thread_path_by_id_str(
+    codex_home: &Path,
+    id_str: &str,
+) -> io::Result<Option<PathBuf>> {
+    find_thread_path_by_id_str_in_subdir(codex_home, ARCHIVED_SESSIONS_SUBDIR, id_str).await
+}
+
+/// Extract the `YYYY/MM/DD` directory components from a rollout filename.
+pub fn rollout_date_parts(file_name: &OsStr) -> Option<(String, String, String)> {
+    let name = file_name.to_string_lossy();
+    let date = name.strip_prefix("rollout-")?.get(..10)?;
+    let year = date.get(..4)?.to_string();
+    let month = date.get(5..7)?.to_string();
+    let day = date.get(8..10)?.to_string();
+    Some((year, month, day))
+}

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

@@ -15,9 +15,11 @@ pub(crate) mod truncation;
 
 pub use codex_protocol::protocol::SessionMeta;
 pub(crate) use error::map_session_init_error;
+pub use list::find_archived_thread_path_by_id_str;
 pub use list::find_thread_path_by_id_str;
 #[deprecated(note = "use find_thread_path_by_id_str")]
 pub use list::find_thread_path_by_id_str as find_conversation_path_by_id_str;
+pub use list::rollout_date_parts;
 pub use recorder::RolloutRecorder;
 pub use recorder::RolloutRecorderParams;
 

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

@@ -1,5 +1,6 @@
 #![allow(clippy::unwrap_used, clippy::expect_used)]
 
+use std::ffi::OsStr;
 use std::fs::File;
 use std::fs::FileTimes;
 use std::fs::{self};
@@ -21,6 +22,7 @@ use crate::rollout::list::ThreadItem;
 use crate::rollout::list::ThreadSortKey;
 use crate::rollout::list::ThreadsPage;
 use crate::rollout::list::get_threads;
+use crate::rollout::rollout_date_parts;
 use anyhow::Result;
 use codex_protocol::ThreadId;
 use codex_protocol::models::ContentItem;
@@ -43,6 +45,16 @@ fn provider_vec(providers: &[&str]) -> Vec<String> {
         .collect()
 }
 
+#[test]
+fn rollout_date_parts_extracts_directory_components() {
+    let file_name = OsStr::new("rollout-2025-03-01T09-00-00-123.jsonl");
+    let parts = rollout_date_parts(file_name);
+    assert_eq!(
+        parts,
+        Some(("2025".to_string(), "03".to_string(), "01".to_string()))
+    );
+}
+
 fn write_session_file(
     root: &Path,
     ts_str: &str,