diff --git a/crates/lance-context-master/src/config.rs b/crates/lance-context-master/src/config.rs
index 753c684..bba4dcd 100644
--- a/crates/lance-context-master/src/config.rs
+++ b/crates/lance-context-master/src/config.rs
@@ -99,6 +99,13 @@ pub struct MasterConfig {
     #[arg(long, env = "COMPACTION_MAX_SOURCE_FRAGMENTS", default_value_t = 32)]
     pub compaction_max_source_fragments: usize,
 
+    /// Rebuild the `id` ZoneMap index after every compaction that rewrote
+    /// fragments, as a dependent `IndexId` task. Compaction replaces the
+    /// fragments the index describes, so without this the index only ever
+    /// covers whatever was on disk when it was last built by hand.
+    #[arg(long, env = "INDEX_AFTER_COMPACTION", default_value_t = true, action = clap::ArgAction::Set)]
+    pub index_after_compaction: bool,
+
     /// Maximum bytes per compacted output file. `0` uses Lance's default.
     #[arg(
         long,
diff --git a/crates/lance-context-master/src/routes.rs b/crates/lance-context-master/src/routes.rs
index d5a0a25..cf648ab 100644
--- a/crates/lance-context-master/src/routes.rs
+++ b/crates/lance-context-master/src/routes.rs
@@ -679,6 +679,7 @@ mod tests {
             compaction_threads: 1,
             compaction_batch_size: 8,
             compaction_max_source_fragments: 32,
+            index_after_compaction: false,
             compaction_max_bytes_per_file: 1024 * 1024 * 1024,
             merge_wal_interval_secs: 0,
             merge_wal_min_generations: 8,
diff --git a/crates/lance-context-master/src/scheduler.rs b/crates/lance-context-master/src/scheduler.rs
index 1d5b197..0ae6cb0 100644
--- a/crates/lance-context-master/src/scheduler.rs
+++ b/crates/lance-context-master/src/scheduler.rs
@@ -143,7 +143,7 @@ async fn run_task(state: &Arc<MasterState>, claim: TaskClaim, timing: TaskClaimT
 
     let started = std::time::Instant::now();
     let outcome = match task.kind {
-        TaskKind::Compact => run_compaction(state, &task.target).await,
+        TaskKind::Compact => run_compaction(state, &task).await,
         TaskKind::MergeWal => run_merge_wal(state, &task.target).await,
         TaskKind::IndexId => run_index_id(state, &task.target).await,
     };
@@ -174,15 +174,39 @@ async fn run_task(state: &Arc<MasterState>, claim: TaskClaim, timing: TaskClaimT
 
 /// Compact one experiment. The task-store claim owns the per-experiment write
 /// lock for the full execution.
-async fn run_compaction(state: &Arc<MasterState>, target: &str) -> Result<String, String> {
-    let (kind, name) = parse_target(target);
+///
+/// A compaction that rewrote fragments invalidates the `id` ZoneMap index
+/// (per-fragment min/max), so it enqueues an [`TaskKind::IndexId`] that
+/// depends on this task. The dependency keeps the two from contending for the
+/// per-target lock and lets the index wait its turn behind the queue. Skipped
+/// when nothing was rewritten and when `index_after_compaction` is off.
+async fn run_compaction(state: &Arc<MasterState>, task: &TaskRecord) -> Result<String, String> {
+    let (kind, name) = parse_target(&task.target);
     if kind != StoreKind::Rollout {
         // Base-table compaction of generic stores is not scheduled by the
         // master yet; only WAL merges are. Refuse rather than open the store
         // through the rollout code path with the wrong URI and schema.
         return Err(format!("compaction is not scheduled for {kind:?} stores"));
     }
-    compact_inner(state, name).await
+    let metrics = compact_inner(state, name).await?;
+    if state.config.index_after_compaction && metrics.fragments_added > 0 {
+        // Best-effort: the compaction itself is done; the next compaction of
+        // this target re-enqueues the index anyway.
+        if let Err(error) = enqueue_with_deps(
+            state,
+            TaskKind::IndexId,
+            &task.target,
+            vec![task.id.clone()],
+        )
+        .await
+        {
+            tracing::warn!(target = %task.target, %error, "failed to enqueue post-compaction id index");
+        }
+    }
+    Ok(format!(
+        "removed {} / added {} fragments",
+        metrics.fragments_removed, metrics.fragments_added
+    ))
 }
 
 /// Build a ZoneMap scalar index on one experiment's `id` column. Shares the
@@ -209,7 +233,10 @@ async fn index_id_inner(state: &Arc<MasterState>, name: &str) -> Result<String,
     Ok("built zonemap index on id".to_string())
 }
 
-async fn compact_inner(state: &Arc<MasterState>, name: &str) -> Result<String, String> {
+async fn compact_inner(
+    state: &Arc<MasterState>,
+    name: &str,
+) -> Result<lance::dataset::optimize::CompactionMetrics, String> {
     let uri = state.rollout_uri(name);
     let config = state.compaction_config();
     let _permit = state
@@ -227,10 +254,7 @@ async fn compact_inner(state: &Arc<MasterState>, name: &str) -> Result<String, S
         .await
         .map_err(|e| e.to_string())?;
     update_stats_after_compaction(state, name, &store).await;
-    Ok(format!(
-        "removed {} / added {} fragments",
-        metrics.fragments_removed, metrics.fragments_added
-    ))
+    Ok(metrics)
 }
 
 /// Shape of the worker's merge-wal response (`{ "reclaimed": n }`).
@@ -737,6 +761,7 @@ mod tests {
             compaction_threads: 1,
             compaction_batch_size: 8,
             compaction_max_source_fragments: 32,
+            index_after_compaction: false,
             compaction_max_bytes_per_file: 1024 * 1024 * 1024,
             merge_wal_interval_secs: 0,
             merge_wal_min_generations: 2,
@@ -828,6 +853,74 @@ mod tests {
         worker.abort();
     }
 
+    /// A compaction that rewrote fragments enqueues an `IndexId` that depends
+    /// on it, and that index runs to Done after the compaction.
+    #[tokio::test]
+    #[ignore = "requires ETCD_TEST_ENDPOINTS"]
+    async fn compaction_that_rewrites_fragments_enqueues_id_index() {
+        let dir = TempDir::new().unwrap();
+        let mut cfg = config(&dir);
+        cfg.index_after_compaction = true;
+        let state = MasterState::new(cfg).await.unwrap();
+        let worker = spawn_scheduler(&state);
+
+        let name = "exp";
+        let uri = state.rollout_uri(name);
+        {
+            let mut store = RolloutStore::open(&uri).await.unwrap();
+            for i in 0..4 {
+                let rec = rollout_record(&format!("r{i}"));
+                store.add(&[rec]).await.unwrap();
+                store.cleanup_own_shard().await.unwrap();
+            }
+        }
+        state
+            .registry
+            .write()
+            .await
+            .upsert(name, &uri)
+            .await
+            .unwrap();
+        crate::scanner::scan_once(&state).await.unwrap();
+
+        let compact = enqueue(&state, TaskKind::Compact, name).await.unwrap();
+        assert_eq!(
+            await_terminal(&state, &compact.id).await.state,
+            TaskState::Done
+        );
+
+        let index = state
+            .task_store
+            .list()
+            .await
+            .unwrap()
+            .into_iter()
+            .find(|task| task.kind == TaskKind::IndexId && task.target == name)
+            .expect("compaction enqueued an IndexId task");
+        assert_eq!(index.depends_on, vec![compact.id.clone()]);
+        let status = await_terminal(&state, &index.id).await;
+        assert_eq!(status.state, TaskState::Done, "got {status:?}");
+        assert_eq!(status.detail.as_deref(), Some("built zonemap index on id"));
+
+        // A second compaction with nothing to rewrite does not enqueue another.
+        let again = enqueue(&state, TaskKind::Compact, name).await.unwrap();
+        assert_eq!(
+            await_terminal(&state, &again.id).await.state,
+            TaskState::Done
+        );
+        let indexes = state
+            .task_store
+            .list()
+            .await
+            .unwrap()
+            .into_iter()
+            .filter(|task| task.kind == TaskKind::IndexId)
+            .count();
+        assert_eq!(indexes, 1);
+
+        worker.abort();
+    }
+
     /// Manual enqueue of an `IndexId` task -> dispatcher builds the ZoneMap
     /// index -> task reaches Done with the expected detail summary.
     #[tokio::test]
diff --git a/crates/lance-context-master/src/state.rs b/crates/lance-context-master/src/state.rs
index dba767d..b3dadbf 100644
--- a/crates/lance-context-master/src/state.rs
+++ b/crates/lance-context-master/src/state.rs
@@ -252,6 +252,7 @@ mod tests {
             compaction_threads: 1,
             compaction_batch_size: 8,
             compaction_max_source_fragments: 32,
+            index_after_compaction: false,
             compaction_max_bytes_per_file: 1024 * 1024 * 1024,
             merge_wal_interval_secs: 0,
             merge_wal_min_generations: 8,
diff --git a/crates/lance-context-master/src/task_store.rs b/crates/lance-context-master/src/task_store.rs
index b522c90..d3e5b43 100644
--- a/crates/lance-context-master/src/task_store.rs
+++ b/crates/lance-context-master/src/task_store.rs
@@ -1251,6 +1251,7 @@ mod tests {
             compaction_threads: 1,
             compaction_batch_size: 8,
             compaction_max_source_fragments: 32,
+            index_after_compaction: false,
             compaction_max_bytes_per_file: 1024 * 1024 * 1024,
             merge_wal_interval_secs: 0,
             merge_wal_min_generations: 8,