Task: Implement the AppImage Reader feature

TASK-DESCRIPTION

Create: sources/appimage/appimage_reader.h
Create: sources/appimage/appimage_reader.cpp
Create: sources/appimage/squashfs_reader.h
Create: sources/appimage/squashfs_reader.cpp
Create: tests/30-appimage-reader.sh
Create: tests/40-squashfs-payload-reader.sh The reader identifies the AppImage type, computes the payload offset, validates the SquashFS superblock, and reads payload entries, and implements the requirements in prompts/features/03-appimage-reader.md. The fixture is a real host ELF with the AppImage magic written at offset 8 and a SquashFS image appended at the computed payload offset.

TASK-OUTPUT

Produce these complete files in this order, then the VERIFICATION: line: 1. sources/appimage/appimage_reader.h 2. sources/appimage/appimage_reader.cpp 3. sources/appimage/squashfs_reader.h 4. sources/appimage/squashfs_reader.cpp 5. tests/30-appimage-reader.sh 6. tests/40-squashfs-payload-reader.sh

TASK-CONTEXT

Format facts and the payload offset algorithm are in documents/07-appimage-format.md. The SquashFS reader may use the host zlib, liblzma, and libzstd libraries, and the test skips cleanly when mksquashfs is absent.

TASK-FILES

Operation	Path
create	`sources/appimage/appimage_reader.h`
create	`sources/appimage/appimage_reader.cpp`
create	`sources/appimage/squashfs_reader.h`
create	`sources/appimage/squashfs_reader.cpp`
create	`tests/30-appimage-reader.sh`
create	`tests/40-squashfs-payload-reader.sh`

TASK-VERIFY

Run: make test from the repository root.
Expected: exit status 0, and the reader’s payload offset matches the offset the AppImage runtime reports for the same file.

TASK-FEATURES

prompts/features/03-appimage-reader.md

TASK-ACCEPTANCE

APPIMAGE-READER-R003
APPIMAGE-READER-R008
APPIMAGE-READER-R013
APPIMAGE-READER-R016
APPIMAGE-READER-R021
APPIMAGE-READER-R023
APPIMAGE-READER-R024
APPIMAGE-READER-R025

OUTPUT: the six complete files in the order listed, ending with the VERIFICATION: line.