fix(sqlite): don't hard fail migrator if DB is newer (#16924)

## Description

This PR makes the SQLite state runtime tolerate databases that have
already been migrated by a newer Codex binary.

Today, if an older CLI sees migration versions in `_sqlx_migrations`
that it doesn't know about, startup fails. This change relaxes that
check for the runtime migrators we use in `codex-state` so older
binaries can keep opening the DB in that case.

## Why

We can end up with mixed-version CLIs running against the same local
state DB. In that setup, treating "the database is ahead of me" as a
hard error is unnecessarily strict and breaks the older client even when
the migration history is otherwise fine.

## Follow-up

We still clean up versioned `state_*.sqlite` and `logs_*.sqlite` files
during init, so older binaries can treat newer DB files as legacy. That
should probably be tightened separately if we want mixed-version local
usage to be fully safe.

codex-rs/state/src/migrations.rs

@@ -1,4 +1,29 @@
+use std::borrow::Cow;
+
 use sqlx::migrate::Migrator;
 
 pub(crate) static STATE_MIGRATOR: Migrator = sqlx::migrate!("./migrations");
 pub(crate) static LOGS_MIGRATOR: Migrator = sqlx::migrate!("./logs_migrations");
+
+/// Allow an older Codex binary to open a database that has already been
+/// migrated by a newer binary running in parallel.
+///
+/// We intentionally ignore applied migration versions that are newer than the
+/// embedded migration set. Known migration versions are still validated by
+/// checksum, so this only relaxes the "database is ahead of me" case.
+fn runtime_migrator(base: &'static Migrator) -> Migrator {
+    Migrator {
+        migrations: Cow::Borrowed(base.migrations.as_ref()),
+        ignore_missing: true,
+        locking: base.locking,
+        no_tx: base.no_tx,
+    }
+}
+
+pub(crate) fn runtime_state_migrator() -> Migrator {
+    runtime_migrator(&STATE_MIGRATOR)
+}
+
+pub(crate) fn runtime_logs_migrator() -> Migrator {
+    runtime_migrator(&LOGS_MIGRATOR)
+}