v0.5.7: allocator corruption guard + full register dump for real-hardware repro

The OptiPlex #GP (vec=13 in __rust_dealloc) frees a garbage pointer: the
back-pointer at [ptr-8] is clobbered by the time the shell drops its
Parsed struct.  A blind store to the bogus block header was an opaque
#GP — now it is a readable report:

- dealloc validates the back-pointer (in-heap block, sane size, in-use)
  before trusting it; on failure it prints ptr/block/heap range, the
  memory around the block header, and the live stack chain, writes the
  crash band + crash.log, and halts (memory.rs: heap_guard_report).
- fault dumps now carry the full register set (rax..rdi, rbx, r8..r15)
  so the next repro shows the exact freed ptr and clobbered value.
- new 'corrupt' shell hook deliberately clobbers a live block's
  back-pointer to prove the guard fires (test-fault-style halt).

Verified: test-msg/test-disk/test-fault pass; corrupt hook reports
ptr=.. block=0xdeedbeef... with mem dump instead of #GP. rs-dos.img
rebuilt with the release kernel.

1 files changed, 3 insertions, 3 deletions

diff --git a/Cargo.lock b/Cargo.lock
index 431db32..4cef15c 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -4,7 +4,7 @@ version = 4
 
 [[package]]
 name = "rsdos"
-version = "0.5.5"
+version = "0.5.7"
 dependencies = [
  "rsnix",
  "shell",
@@ -19,11 +19,11 @@ dependencies = [
 
 [[package]]
 name = "rsnix"
-version = "0.5.5"
+version = "0.5.7"
 
 [[package]]
 name = "shell"
-version = "0.5.5"
+version = "0.5.7"
 dependencies = [
  "rsdosedit",
  "rsnix",