feat(wal): add bounded durable client state with group commit

.github/workflows/rust-test.yml

@@ -76,6 +76,10 @@ jobs:
         run: |
           cargo clippy -p lance-context-wal --features raft-log --all-targets -- -D warnings
           cargo test -p lance-context-wal --features raft-log --lib --test raft_log --test raft_log_cache_identity
+      - name: Client journal durability and process recovery
+        run: |
+          cargo clippy -p lance-context-wal --features client-journal --all-targets -- -D warnings
+          cargo test -p lance-context-wal --features client-journal --lib client_journal
       - name: Replicated WAL quorum and process recovery
         run: |
           cargo clippy -p lance-context-wal --features replication --all-targets -- -D warnings

crates/lance-context-wal/Cargo.toml

@@ -7,6 +7,7 @@ publish = false
 description = "Independent Rust WAL experiments owned by lance-context"
 
 [features]
+client-journal = ["dep:anyhow", "dep:raft-engine", "dep:bytes", "dep:serde", "dep:serde_json", "dep:tokio", "tokio/sync"]
 replication = ["raft-log", "record", "dep:bincode", "dep:slog"]
 raft-log = ["placement", "dep:raft", "dep:raft-engine", "dep:raft-proto", "dep:protobuf"]
 vectored-io = ["dep:bytes", "dep:tokio"]

crates/lance-context-wal/README.md

@@ -7,6 +7,17 @@ Implementation and validation are tracked in
 [#378](https://github.com/lance-format/lance-context/issues/378). Related PRs should
 include `Refs #378`; individual steps should leave the tracking issue open.
 
+The optional `client-journal` feature stores recoverable client state in one
+local engine and shares durable barriers across writers. It returns latest
+values for a fixed set of keys, with immutable scope/settings binding, bounded
+admission, reclamation and a shared failure fence. Callers still own producer
+ordering, exact retry identity and recovery validation; a local completion does
+not establish a remote quorum ACK. See [the API and recovery contract](../../docs/design/client-journal.md).
+
+```bash
+cargo test -p lance-context-wal --features client-journal --lib client_journal
+```
+
 The independent `contract` feature defines ingestion routing keys, the schema
 fingerprint, immutable-ID policy and record byte/row limits. Validation checks
 the representation after decoding; callers must durably bind and compare the