Cryptext x64 0.5a on-disk verification test
===========================================

0.5a keeps the deliberately safe writer behavior from 0.5: the selected source
is opened READ ONLY and is always retained. The generated artifact is still:

  original-name.$#!.temp

What is new
-----------
After the writer has completed and FlushFileBuffers succeeds, Cryptext closes
the write handle, reopens the .temp READ ONLY, validates the header and exact
file size, derives the key again from the salt/iteration count stored on disk,
and verifies every AES-256-GCM record. Decrypted bytes exist only in RAM and are
compared directly with the original source. No plaintext output file is created.

Suggested boundary tests
------------------------
Use the same four disposable files already proven with 0.5:

  0 bytes          -> expected encrypted size       136 bytes
  1 byte           -> expected encrypted size       153 bytes
  4,194,304 bytes  -> expected encrypted size 4,194,456 bytes
  4,194,305 bytes  -> expected encrypted size 4,194,473 bytes

Test procedure
--------------
1. Delete/rename any old .$#!.temp from the 0.5 run, because CREATE_NEW still
   deliberately refuses to overwrite it.
2. Build and start bin\Cryptext64.exe.
3. Enter any non-empty password.
4. Click OK and select one test file.
5. Expect: "Dateitest 0.5a: OK".
6. Confirm the .temp size remains exactly as listed above.
7. Confirm the original file remains unchanged.
8. Repeat for all four boundary sizes.

A success now means more than the 0.5 size check: the flushed bytes were read
back from the .temp, each GCM tag was accepted, all records were decrypted, and
the recovered data matched the source byte-for-byte.

Still intentionally disabled
----------------------------
- no rename from .$#!.temp to final .$#!
- no source deletion
- no functional keep-original checkbox
- no user-facing decryption path yet
- no free-space preflight yet

On a normal write or verification error a partial/failed .temp is removed. A
hard process/OS crash may still leave a hidden .temp, as intended by the later
transactional design.
