chore: add TODO doc about transient apply failures [skip ci]

lez/chain_state/DESIGN.md

@@ -6,10 +6,6 @@ backs decentralized sequencing. Status: **interface freeze** — the
 contract the produce-on-turn and follow-blocks tracks build against. Changing
 them after the tracks split forces rework in both.
 
-Branch: `erhant/lez-two-tip-chain-state` (off `erhant/indexer-recoverable-invalid-blocks`).
-
----
-
 ## 1. Motivation
 
 Decentralized sequencing requires every honest node — sequencer or indexer — to

lez/chain_state/src/apply.rs

@@ -30,6 +30,9 @@ pub enum AcceptOutcome {
     /// Chained but failed to apply, possibly transiently
     /// ([`BlockIngestError::is_retryable`]); nothing recorded, tip and state
     /// untouched. The caller retries and parks once it gives up.
+    ///
+    /// TODO: Only the indexer's `accept_block` emits this today; the sequencer's
+    /// `ChainState` parks on all failures without retrying (see `on_follow`).
     RetryableFailure(BlockIngestError),
 }
 

lez/sequencer/core/src/lib.rs

@@ -343,6 +343,12 @@ impl<BP: BlockPublisherTrait> SequencerCore<BP> {
     /// Feed one channel delta into the follow state and mirror it to the store:
     /// revert orphaned, then apply and persist adopted and finalized blocks.
     /// Production builds on this same head.
+    ///
+    /// TODO: unlike the indexer's ingest loop, this path does not retry
+    /// `is_retryable` (transient) apply failures — a failed block just parks and
+    /// relies on a valid successor or a restart. `ChainState` never emits
+    /// `AcceptOutcome::RetryableFailure` yet; adding retry parity here is a
+    /// follow-up.
     fn on_follow(
         dbio: Arc<RocksDBIO>,
         chain: Arc<Mutex<ChainState>>,