test(sql): cover rollbackRestoresIndexStateEvenAcrossASavepoint

src/test/kotlin/kestrel/store/sql/DiskExecutorSavepointTest.kt

@@ -159,3 +159,174 @@ class DiskExecutorSavepointTest {
         db.run("COMMIT")
     }
 
+    @Test
+    fun rollbackRestoresIndexStateEvenAcrossASavepoint() {
+        val db = newDatabase()
+        db.seed()
+        db.run("CREATE INDEX idxBalance ON accounts (balance)")
+        db.run("BEGIN")
+        db.run("SAVEPOINT s1")
+        db.run("INSERT INTO accounts VALUES (3, 100)")
+        assertEquals(2, db.rowCount("SELECT * FROM accounts WHERE balance = 100"))
+        db.run("ROLLBACK TO SAVEPOINT s1")
+        assertEquals(1, db.rowCount("SELECT * FROM accounts WHERE balance = 100"))
+        db.run("ROLLBACK")
+    }
+
+    @Test
+    fun savepointOutsideATransactionIsRejected() {
+        val db = newDatabase()
+        db.seed()
+        assertFailsWith<KestrelException> { db.run("SAVEPOINT s1") }
+    }
+
+    @Test
+    fun releaseSavepointOutsideATransactionIsRejected() {
+        val db = newDatabase()
+        db.seed()
+        assertFailsWith<KestrelException> { db.run("RELEASE SAVEPOINT s1") }
+    }
+
+    @Test
+    fun rollbackToSavepointOutsideATransactionIsRejected() {
+        val db = newDatabase()
+        db.seed()
+        assertFailsWith<KestrelException> { db.run("ROLLBACK TO SAVEPOINT s1") }
+    }
+
+    @Test
+    fun rollbackToAnUnknownSavepointNameIsRejected() {
+        val db = newDatabase()
+        db.seed()
+        db.run("BEGIN")
+        db.run("SAVEPOINT s1")
+        assertFailsWith<KestrelException> { db.run("ROLLBACK TO SAVEPOINT nope") }
+        db.run("ROLLBACK")
+    }
+
+    @Test
+    fun releaseAnUnknownSavepointNameIsRejected() {
+        val db = newDatabase()
+        db.seed()
+        db.run("BEGIN")
+        db.run("SAVEPOINT s1")
+        assertFailsWith<KestrelException> { db.run("RELEASE SAVEPOINT nope") }
+        db.run("ROLLBACK")
+    }
+
+    @Test
+    fun fullRollbackClearsEveryOutstandingSavepoint() {
+        val db = newDatabase()
+        db.seed()
+        db.run("BEGIN")
+        db.run("SAVEPOINT s1")
+        db.run("INSERT INTO accounts VALUES (3, 300)")
+        db.run("ROLLBACK")
+        db.run("BEGIN")
+        assertFailsWith<KestrelException> { db.run("ROLLBACK TO SAVEPOINT s1") }
+        db.run("ROLLBACK")
+    }
+
+    @Test
+    fun commitClearsEveryOutstandingSavepoint() {
+        val db = newDatabase()
+        db.seed()
+        db.run("BEGIN")
+        db.run("SAVEPOINT s1")
+        db.run("INSERT INTO accounts VALUES (3, 300)")
+        db.run("COMMIT")
+        db.run("BEGIN")
+        assertFailsWith<KestrelException> { db.run("ROLLBACK TO SAVEPOINT s1") }
+        db.run("ROLLBACK")
+        assertEquals(3, db.rowCount("SELECT * FROM accounts"))
+    }
+
+    @Test
+    fun releaseKeywordAloneWithoutSavepointKeywordIsAccepted() {
+        val db = newDatabase()
+        db.seed()
+        db.run("BEGIN")
+        db.run("SAVEPOINT s1")
+        db.run("INSERT INTO accounts VALUES (3, 300)")
+        db.run("RELEASE s1")
+        assertEquals(3, db.rowCount("SELECT * FROM accounts"))
+        db.run("COMMIT")
+    }
+
+    @Test
+    fun beginResultTypeIsReturnedForTheEnclosingTransaction() {
+        val db = newDatabase()
+        db.seed()
+        assertEquals(BeginResult, db.run("BEGIN").single())
+        db.run("ROLLBACK")
+    }
+
+    /**
+     * The SQL-level twin of `RecoveryManagerTest.fullRollbackAfterAPartialRollbackDoesNotMisapplyAnAlreadyUndoneBeforeImage` -
+     * proves the whole stack (DiskExecutor -> DiskCatalog -> StorageEngine -> TransactionManager ->
+     * RecoveryManager) wires the compensation-record undo-of-undo correctly end to end, not just at the
+     * page level.
+     */
+    @Test
+    fun fullRollbackAfterASavepointRollbackUndoesEverythingIncludingThePreSavepointWrite() {
+        val db = newDatabase()
+        db.seed()
+        db.run("BEGIN")
+        db.run("INSERT INTO accounts VALUES (3, 300)")
+        db.run("SAVEPOINT s1")
+        db.run("INSERT INTO accounts VALUES (4, 400)")
+        db.run("ROLLBACK TO SAVEPOINT s1")
+        assertEquals(3, db.rowCount("SELECT * FROM accounts"), "the pre-savepoint insert must still be visible in-session")
+        assertEquals(RollbackResult, db.run("ROLLBACK").single())
+        assertEquals(2, db.rowCount("SELECT * FROM accounts"), "a full rollback must also undo the pre-savepoint insert")
+    }
+
+    /**
+     * A crash that lands right after `ROLLBACK TO SAVEPOINT` but before the enclosing transaction ever
+     * commits or rolls back must still leave the database as if the whole transaction never happened:
+     * recovery resolves any still-open transaction with a full rollback regardless of what savepoints
+     * it touched along the way. This is the reopen-based proof that
+     * [kestrel.store.wal.RecoveryManager.rollbackTo]'s compensation records are genuinely durable, not
+     * just correct in the live process's buffer pool.
+     */
+    @Test
+    fun rollbackToSavepointSurvivesACrashBeforeTheTransactionResolves() {
+        val db = newDatabase()
+        db.seed()
+        db.run("BEGIN")
+        db.run("INSERT INTO accounts VALUES (3, 300)")
+        db.run("SAVEPOINT s1")
+        db.run("INSERT INTO accounts VALUES (4, 400)")
+        db.run("ROLLBACK TO SAVEPOINT s1")
+        // No COMMIT, no ROLLBACK: crash right here, mid-transaction.
+        db.reopen()
+
+        assertEquals(2, db.rowCount("SELECT * FROM accounts"), "the entire unresolved transaction must be undone by crash recovery")
+    }
+
+    /**
+     * The durable-happy-path counterpart to [rollbackToSavepointSurvivesACrashBeforeTheTransactionResolves]:
+     * a transaction that rolls back to a savepoint and then commits must persist exactly the rows that
+     * survived the rollback, including a write made *after* the savepoint rollback - proving the
+     * transaction's WAL chain still threads correctly (new writes point back at the compensation
+     * record, not at the undone update it replaced) once it resumes.
+     */
+    @Test
+    fun dataWrittenAfterASavepointRollbackSurvivesAReopenAfterCommit() {
+        val db = newDatabase()
+        db.seed()
+        db.run("BEGIN")
+        db.run("INSERT INTO accounts VALUES (3, 300)")
+        db.run("SAVEPOINT s1")
+        db.run("INSERT INTO accounts VALUES (4, 400)")
+        db.run("ROLLBACK TO SAVEPOINT s1")
+        db.run("INSERT INTO accounts VALUES (5, 500)")
+        db.run("COMMIT")
+        db.reopen()
+
+        assertEquals(
+            listOf(int(1), int(2), int(3), int(5)),
+            db.select("SELECT id FROM accounts ORDER BY id").rows.map { it[0] }
+        )
+    }
+}