feat: add phase 1 mem db (#10634)

- Schema: thread_id (PK, FK to threads.id with cascade delete),
trace_summary, memory_summary, updated_at.
- Migration: creates the table and an index on (updated_at DESC,
thread_id DESC) for efficient recent-first reads.
  - Runtime API (DB-only):
      - `get_thread_memory(thread_id)`: fetch one memory row.
- `upsert_thread_memory(thread_id, trace_summary, memory_summary)`:
insert/update by thread id and always advance updated_at.
- `get_last_n_thread_memories_for_cwd(cwd, n)`: join thread_memory with
threads and return newest n rows for an exact cwd match.
- Model layer: introduced ThreadMemory and row conversion types to keep
query decoding typed and consistent with existing state models.

codex-rs/core/src/state_db.rs

@@ -280,6 +280,60 @@ pub async fn persist_dynamic_tools(
     }
 }
 
+/// Get memory summaries for a thread id using SQLite.
+pub async fn get_thread_memory(
+    context: Option<&codex_state::StateRuntime>,
+    thread_id: ThreadId,
+    stage: &str,
+) -> Option<codex_state::ThreadMemory> {
+    let ctx = context?;
+    match ctx.get_thread_memory(thread_id).await {
+        Ok(memory) => memory,
+        Err(err) => {
+            warn!("state db get_thread_memory failed during {stage}: {err}");
+            None
+        }
+    }
+}
+
+/// Upsert memory summaries for a thread id using SQLite.
+pub async fn upsert_thread_memory(
+    context: Option<&codex_state::StateRuntime>,
+    thread_id: ThreadId,
+    trace_summary: &str,
+    memory_summary: &str,
+    stage: &str,
+) -> Option<codex_state::ThreadMemory> {
+    let ctx = context?;
+    match ctx
+        .upsert_thread_memory(thread_id, trace_summary, memory_summary)
+        .await
+    {
+        Ok(memory) => Some(memory),
+        Err(err) => {
+            warn!("state db upsert_thread_memory failed during {stage}: {err}");
+            None
+        }
+    }
+}
+
+/// Get the last N memories corresponding to a cwd using an exact path match.
+pub async fn get_last_n_thread_memories_for_cwd(
+    context: Option<&codex_state::StateRuntime>,
+    cwd: &Path,
+    n: usize,
+    stage: &str,
+) -> Option<Vec<codex_state::ThreadMemory>> {
+    let ctx = context?;
+    match ctx.get_last_n_thread_memories_for_cwd(cwd, n).await {
+        Ok(memories) => Some(memories),
+        Err(err) => {
+            warn!("state db get_last_n_thread_memories_for_cwd failed during {stage}: {err}");
+            None
+        }
+    }
+}
+
 /// Reconcile rollout items into SQLite, falling back to scanning the rollout file.
 pub async fn reconcile_rollout(
     context: Option<&codex_state::StateRuntime>,