feat: rebuild heap4 card around upstream FreeRTOS allocator

tests/check_task03_elf.sh

@@ -0,0 +1,15 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+elf="${1:?usage: check_task03_elf.sh ELF [tool-prefix]}"
+prefix="${2:-riscv64-unknown-elf-}"
+nm="${prefix}nm"
+objdump="${prefix}objdump"
+
+test -s "$elf"
+for symbol in pvPortMalloc vPortFree prvInsertBlockIntoFreeList ucHeap \
+              heap4_fragmented_checkpoint task03_debug_checkpoint g_task03_pass; do
+  "$nm" -a "$elf" | grep -E "[[:space:]]${symbol}$" >/dev/null
+done
+"$objdump" -d "$elf" | grep -E 'addi[[:space:]]+sp,sp,-' >/dev/null
+printf 'PASS Task 3 links upstream heap_4 and observable checkpoints: %s\n' "$elf"