fix(raft): multi-stmt write gate, rich apply, delete kv convention

- Reject follower writes if any statement in the batch is DML/COMMIT
  (not only stmts[0]).
- COMMIT always emits empty-valued kvPairs for isDelete entries.
- applyCommand updates LSM plus secondary B-tree/FTS/HNSW indexes
  (applyReplicatedPut/Delete) so follower index scans see replicated rows.
- Tests: not-leader append, commit timeout, index apply unit, E2E
  index-backed SELECT on follower.

tests/bugfix_test.nim

@@ -396,3 +396,15 @@ suite "Raft write classification":
     check not isWrite(parse("CREATE TABLE t (id INT)").stmts[0])
     check not isWrite(parse("BEGIN").stmts[0])
     check not isWrite(parse("ROLLBACK").stmts[0])
+
+  test "multi-statement queries with a trailing write are still writes":
+    ## Server rejection must not look only at stmts[0] — a SELECT first
+    ## would otherwise let a follower execute the INSERT.
+    let ast = parse("SELECT 1; INSERT INTO t (id) VALUES (1)")
+    check ast.stmts.len == 2
+    check not isWrite(ast.stmts[0])
+    check isWrite(ast.stmts[1])
+    var anyWrite = false
+    for s in ast.stmts:
+      if isWrite(s): anyWrite = true
+    check anyWrite

tests/raft_writes_e2e_test.nim

@@ -211,14 +211,15 @@ proc runWritesScenario() =
       return
     echo "leader elected: ", nodes[leaderIdx].id, " (term ", leaderTerm, ")"
 
-    # Schema: CREATE TABLE is not a raft write (DML only is), and its _schema
-    # keys are not replicated — create the table locally on every node.
+    # Schema: CREATE TABLE / INDEX are not raft writes (no kvPairs), and
+    # _schema keys are not replicated — create them locally on every node.
     for i in 0 ..< nodes.len:
       let db = openClient(nodes[i].clientPort)
       try:
         db.exec(sql"CREATE TABLE rw_test (id INT PRIMARY KEY, name STRING)")
+        db.exec(sql"CREATE INDEX idx_rw_name ON rw_test (name)")
       except CatchableError as e:
-        echo "CREATE TABLE failed on ", nodes[i].id, ": ", e.msg
+        echo "CREATE TABLE/INDEX failed on ", nodes[i].id, ": ", e.msg
         dumpAll(nodes)
         fail()
         return
@@ -250,6 +251,31 @@ proc runWritesScenario() =
       return
     echo "row replicated to follower ", nodes[followerIdx].id
 
+    # Index path: rich apply must have updated the follower B-tree so a
+    # filtered SELECT (planner prefers secondary index) still finds the row.
+    block:
+      let db = openClient(nodes[followerIdx].clientPort)
+      var saw = false
+      try:
+        let rows = db.getAllRows(
+          sql"SELECT id, name FROM rw_test WHERE name = 'raft-row'")
+        for row in rows:
+          if row.len >= 2 and row[1] == "raft-row":
+            saw = true
+      except CatchableError as e:
+        echo "follower index SELECT failed: ", e.msg
+        dumpAll(nodes)
+        fail()
+        return
+      db.close()
+      if not saw:
+        echo "follower ", nodes[followerIdx].id,
+             " index-backed SELECT missed the replicated row"
+        dumpAll(nodes)
+        fail()
+        return
+    echo "follower index-backed SELECT saw the row"
+
     # Follower rejection: DML on a follower must fail with "not leader".
     block:
       let db = openClient(nodes[followerIdx].clientPort)

tests/test_all.nim

@@ -2706,6 +2706,44 @@ suite "Raft SQL Write Path":
     check res.keyValuePairs.len == 1
     check res.keyValuePairs[0][1].len == 0
 
+  test "appendWriteToRaft fails when node is not leader":
+    var n = newRaftNode("n1", @["n2"], raftPort = 29111)
+    # Still a follower — appendLog returns index 0.
+    let (ok, err) = waitFor appendWriteToRaft(n,
+      @[("k", cast[seq[byte]]("v"))], timeoutMs = 200)
+    check not ok
+    check "lost leadership" in err
+
+  test "appendWriteToRaft times out without majority replies":
+    # Leader with peers but no network — commitIndex never advances.
+    var n = newRaftNode("n1", @["n2", "n3"], raftPort = 29112)
+    n.becomeLeader()
+    let (ok, err) = waitFor appendWriteToRaft(n,
+      @[("k", cast[seq[byte]]("v"))], timeoutMs = 300)
+    check not ok
+    check "raft commit timeout" in err
+
+  test "applyReplicatedPut updates secondary B-tree indexes":
+    var testDir = getTempDir() / "baradb_raft_apply_idx_" & $getCurrentProcessId() & "_" & $getMonoTime().ticks
+    createDir(testDir)
+    var db = newLSMTree(testDir)
+    var ctx = qexec.newExecutionContext(db)
+    discard qexec.executeQuery(ctx, parse(
+      "CREATE TABLE t (id INT PRIMARY KEY, name STRING)"))
+    discard qexec.executeQuery(ctx, parse(
+      "CREATE INDEX idx_name ON t (name)"))
+    # Simulate follower apply of a leader-replicated INSERT (no execInsert).
+    applyReplicatedPut(ctx, "t.id=1", cast[seq[byte]]("name=alice"))
+    check "t.name" in ctx.btrees
+    let entries = ctx.btrees["t.name"].get("alice")
+    check entries.len >= 1
+    check entries[0].lsmKey == "t.id=1"
+    # Delete must drop the index entry too.
+    applyReplicatedDelete(ctx, "t.id=1")
+    check ctx.btrees["t.name"].get("alice").len == 0
+    let (found, _) = db.get("t.id=1")
+    check not found
+
 suite "CLI Autocomplete":
   test "Autocomplete commands":
     let res = autocomplete("he")