Moving updated-at timestamps to unique millisecond times (#17489)

To allow the ability to have guaranteed-unique cursors, we make two
important updates:
* Add new updated_at_ms and created_at_ms columns that are in
millisecond precision
* Guarantee uniqueness -- if multiple items are inserted at the same
millisecond, bump the new one by one millisecond until it becomes unique

This lets us use single-number cursors for forwards and backwards paging
through resultsets and guarantee that the cursor is a fixed point to do
(timestamp > cursor) and get new items only.

This updated implementation is backwards-compatible since multiple
appservers can be running and won't handle the previous method well.

codex-rs/state/src/runtime.rs

@@ -22,7 +22,9 @@ use crate::migrations::runtime_state_migrator;
 use crate::model::AgentJobRow;
 use crate::model::ThreadRow;
 use crate::model::anchor_from_item;
+use crate::model::datetime_to_epoch_millis;
 use crate::model::datetime_to_epoch_seconds;
+use crate::model::epoch_millis_to_datetime;
 use crate::paths::file_modified_time_utc;
 use chrono::DateTime;
 use chrono::Utc;
@@ -47,6 +49,7 @@ use std::collections::BTreeSet;
 use std::path::Path;
 use std::path::PathBuf;
 use std::sync::Arc;
+use std::sync::atomic::AtomicI64;
 use std::time::Duration;
 use tracing::warn;
 
@@ -76,6 +79,7 @@ pub struct StateRuntime {
     default_provider: String,
     pool: Arc<sqlx::SqlitePool>,
     logs_pool: Arc<sqlx::SqlitePool>,
+    thread_updated_at_millis: Arc<AtomicI64>,
 }
 
 impl StateRuntime {
@@ -120,11 +124,17 @@ impl StateRuntime {
                 return Err(err);
             }
         };
+        let thread_updated_at_millis: Option<i64> =
+            sqlx::query_scalar("SELECT MAX(threads.updated_at_ms) FROM threads")
+                .fetch_one(pool.as_ref())
+                .await?;
+        let thread_updated_at_millis = thread_updated_at_millis.unwrap_or(0);
         let runtime = Arc::new(Self {
             pool,
             logs_pool,
             codex_home,
             default_provider,
+            thread_updated_at_millis: Arc::new(AtomicI64::new(thread_updated_at_millis)),
         });
         if let Err(err) = runtime.run_logs_startup_maintenance().await {
             warn!(