feat: reuse compressed rollout search snippets (#25814)

## Summary
- teach rollout search to return precomputed snippets for compressed
rollouts
- reuse those snippets in local thread search instead of reopening
matching compressed files
- keep the no-`rg` fallback single-pass and add regression coverage for
the compressed path

## Why
`thread/search` currently decodes matching compressed rollouts twice:
once to discover the matching path and again to extract the snippet
shown in results. That defeats a meaningful part of the compressed-read
optimization work.

## Impact
Compressed rollout hits now pay one decode pass on the search path while
plain `.jsonl` hits keep the existing ripgrep-driven flow.

## Validation
- `just test -p codex-rollout`
- `just test -p codex-thread-store`
- `just fix -p codex-rollout`
- `just fix -p codex-thread-store`
- `just fmt`

codex-rs/rollout/src/compression_tests.rs

@@ -23,6 +23,7 @@ use crate::RolloutConfig;
 use crate::RolloutRecorder;
 use crate::RolloutRecorderParams;
 use crate::append_rollout_item_to_path;
+use crate::search_rollout_matches;
 
 #[tokio::test]
 async fn load_rollout_items_reads_compressed_rollout() -> anyhow::Result<()> {
@@ -104,6 +105,31 @@ async fn append_rollout_item_materializes_compressed_rollout() -> anyhow::Result
     Ok(())
 }
 
+#[tokio::test]
+async fn search_rollout_matches_returns_compressed_snippet() -> anyhow::Result<()> {
+    let home = TempDir::new()?;
+    let uuid = Uuid::from_u128(15);
+    let thread_id = ThreadId::from_string(&uuid.to_string())?;
+    let rollout_path = rollout_path(home.path(), "2025-01-03T12-00-00", uuid);
+    write_rollout(&rollout_path, thread_id, "targeted search term")?;
+    compress_now(&rollout_path)?;
+    let compressed_path = compressed_rollout_path(&rollout_path);
+
+    let matches = search_rollout_matches(
+        std::path::Path::new("missing-rg-for-test"),
+        home.path(),
+        /*archived*/ false,
+        "search term",
+    )
+    .await?;
+
+    assert_eq!(
+        matches.get(compressed_path.as_path()),
+        Some(&Some("targeted search term".to_string()))
+    );
+    Ok(())
+}
+
 #[tokio::test]
 async fn worker_compresses_old_archived_rollouts_only() -> anyhow::Result<()> {
     let home = TempDir::new()?;