fix: use HEX() for short UUID prefix lookup in SQLite

CAST(blob AS VARCHAR) produces raw bytes in SQLite, not a formatted UUID
string, causing prefix lookups to always return empty results. Switch to
LOWER(HEX(id)) for SQLite and LOWER(RAWTOHEX(id)) for H2, which both
produce dashless lowercase hex strings suitable for LIKE prefix matching.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: jpicklyk

current/src/main/kotlin/io/github/jpicklyk/mcptask/current/infrastructure/repository/SQLiteWorkItemRepository.kt

@@ -8,6 +8,8 @@ import io.github.jpicklyk.mcptask.current.domain.repository.Result
 import io.github.jpicklyk.mcptask.current.domain.repository.WorkItemRepository
 import io.github.jpicklyk.mcptask.current.infrastructure.database.DatabaseManager
 import io.github.jpicklyk.mcptask.current.infrastructure.database.schema.WorkItemsTable
+import org.jetbrains.exposed.v1.core.CustomFunction
+import org.jetbrains.exposed.v1.core.LowerCase
 import org.jetbrains.exposed.v1.core.Op
 import org.jetbrains.exposed.v1.core.ResultRow
 import org.jetbrains.exposed.v1.core.SortOrder
@@ -18,9 +20,10 @@ import org.jetbrains.exposed.v1.core.SqlExpressionBuilder.lessEq
 import org.jetbrains.exposed.v1.core.SqlExpressionBuilder.like
 import org.jetbrains.exposed.v1.core.VarCharColumnType
 import org.jetbrains.exposed.v1.core.and
-import org.jetbrains.exposed.v1.core.castTo
 import org.jetbrains.exposed.v1.core.dao.id.EntityID
 import org.jetbrains.exposed.v1.core.or
+import org.jetbrains.exposed.v1.core.vendors.H2Dialect
+import org.jetbrains.exposed.v1.core.vendors.currentDialect
 import org.jetbrains.exposed.v1.jdbc.Query
 import org.jetbrains.exposed.v1.jdbc.deleteWhere
 import org.jetbrains.exposed.v1.jdbc.insert
@@ -364,40 +367,25 @@ class SQLiteWorkItemRepository(
         prefix: String,
         limit: Int
     ): Result<List<WorkItem>> {
-        // Convert a hex-only prefix into a UUID-formatted prefix for LIKE matching.
-        // UUID format: xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx (8-4-4-4-12)
-        // Dash positions in the hex string: after 8, 12, 16, 20
-        val formattedPrefix = formatHexAsUuidPrefix(prefix.lowercase())
+        val normalizedPrefix = prefix.lowercase()
         return databaseManager.suspendedTransaction("Failed to find WorkItems by ID prefix") {
+            // Convert UUID id column to lowercase hex string (no dashes) for prefix matching.
+            // H2 uses RAWTOHEX() for native UUID columns; SQLite uses HEX() for BLOB columns.
+            // Both produce uppercase hex without dashes — wrap in LOWER for case-insensitive match.
+            val hexFunctionName = if (currentDialect is H2Dialect) "RAWTOHEX" else "HEX"
+            val hexId = LowerCase(
+                CustomFunction(hexFunctionName, VarCharColumnType(32), WorkItemsTable.id)
+            )
             val items =
                 WorkItemsTable
                     .selectAll()
-                    .where {
-                        WorkItemsTable.id.castTo<String>(VarCharColumnType(36)).like("$formattedPrefix%")
-                    }.limit(limit)
+                    .where { hexId like "$normalizedPrefix%" }
+                    .limit(limit)
                     .mapNotNull { toWorkItemOrNull(it) }
             Result.Success(items)
         }
     }
 
-    /**
-     * Converts a hex-only prefix string into UUID-formatted prefix with dashes
-     * inserted at the correct positions (after hex positions 8, 12, 16, 20).
-     */
-    private fun formatHexAsUuidPrefix(hexPrefix: String): String {
-        val dashPositions = listOf(8, 12, 16, 20)
-        val sb = StringBuilder()
-        var hexIndex = 0
-        for (ch in hexPrefix) {
-            if (hexIndex in dashPositions) {
-                sb.append('-')
-            }
-            sb.append(ch)
-            hexIndex++
-        }
-        return sb.toString()
-    }
-
     override suspend fun findAncestorChains(itemIds: Set<UUID>): Result<Map<UUID, List<WorkItem>>> {
         if (itemIds.isEmpty()) return Result.Success(emptyMap())
         return databaseManager.suspendedTransaction("Failed to find ancestor chains") {