Harden DEX obfuscation against malformed module input

[Shallow-dusty]

## Summary

Harden the daemon DEX obfuscation path against malformed module-controlled DEX input before it reaches slicer.

Root Cause

ObfuscationManager.obfuscateDex only checked whether the mapped DEX bytes contained a target signature before passing the whole buffer to dex::Reader::CreateFullIr(). Slicer's structural guards are implemented with SLICER_CHECK / SLICER_WEAK_CHECK, but those checks compile out under NDEBUG, so malformed table offsets and indexes can still be dereferenced in release-compatible builds.

Changes

• Add a Vector-side DEX preflight before calling slicer.
• Validate the standard DEX header, core indexed-section ranges, map/data bounds, alignment, and the type/proto/field/method/class references that CreateFullIr() touches first.
• Keep the JNI/Kotlin interface unchanged.
• Skip obfuscation and return the original SharedMemory wrapper for malformed inputs, no-signature inputs, and writer-output failures so the daemon does not crash.

Validation

• git diff --check
• ./gradlew.bat --no-daemon :daemon:assembleDebug
• ./gradlew.bat --no-daemon :daemon:assembleRelease

The release daemon build covers the NDEBUG-style path where slicer's own checks are compiled out.

Fixes #766

Device-side harness validation (PJD110, Android 16, KernelSU root, arm64 release -DNDEBUG):

• Used issue Malformed module DEX can crash release daemon during JNI DEX obfuscation #766 PoC bad_vector_obfuscation.dex with SHA-256 ca6598344db1eb878a3bf13cd99d0a0890acc9106e76c3b2050905911ee6a738.
• Baseline slicer release harness on device reproduced the crash: HARNESS_RC:139, logcat Fatal signal 11 (SIGSEGV).
• Fixed Vector preflight harness on the same PoC returned HARNESS_RC:0 with preflight rejected malformed input; slicer skipped, and no crash log.
• Smoke-tested a valid DEX containing Lorg/matrix/vector/core/: preflight accepted it, CreateFullIr() parsed IR classes: 1, HARNESS_RC:0.

[Copilot]

Pull request overview

This PR hardens the daemon’s JNI DEX obfuscation pipeline by adding a Vector-side preflight validator for module-controlled DEX buffers before handing them to slicer, preventing release (-DNDEBUG) crashes on malformed inputs (Fixes #766).

Changes:

• Added isDexSafeForSlicer() plus supporting helpers to validate DEX header/section bounds and key indexed references.
• Updated ObfuscationManager.obfuscateDex() to (a) handle invalid sizes, (b) skip slicer for malformed/no-signature inputs, and (c) return the original SharedMemory wrapper on failures.
• Refactored SharedMemory wrapping into a helper (wrapSharedMemoryFd).

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.