Function heap_dump_json 

pub fn heap_dump_json(
    include_blocks: bool,
    hash_addresses: bool,
) -> Option<String>

Live per-heap -> per-page -> (optional) per-block JSON snapshot of the current subprocess (issue #269, Bun parity P4). Backs Bun’s shipped bun:jsc heapStats({dump:true|"blocks"}).mimallocDump; see src/heap-dump.c for the JSON shape ({"heaps":[{"seq":N,"pages":[{"id","block_size","used","reserved","thread_id"}], "blocks":[[id,size],...]}]}, blocks present only when include_blocks).

Set hash_addresses to mix every reported address through a per-process key so a dump can be shared or diffed without exposing raw ASLR-derived pointers.

Safe, best-effort capture under concurrent frees (#374), using HEAP_DUMP_JSON_DEFAULT_WAIT_MS as the owner-acquisition deadline. See heap_dump_json_ex for the complete waiting and coverage contract.

Requires the diagnostics feature (#414): without it the dump is compiled out of the C library and this returns None.

Otherwise returns None only on allocation failure (out of memory building the JSON buffer), not for an empty subprocess.