SetPlanarLegacyAlignment does not restore environment state after child failure

[msg7086]

> Analysis attribution: This issue analysis was created by Codex GPT.
> The GitHub user who submits this issue does not claim authorship of the analysis.

Finding

• Finding ID: B11-planar-legacy-alignment-exception-safety
• Status: Reproduced defect
• Severity: High
• Affected component: SetPlanarLegacyAlignment
• Source location: avs_core/filters/debug.cpp:68-79

Summary

Environment alignment is changed before child GetFrame and restored only on normal return.

Affected Code

  PVideoFrame __stdcall GetFrame(int n, IScriptEnvironment* env)
  {
  const IScriptEnvironment::PlanarChromaAlignmentMode
    oldmode = env->PlanarChromaAlignment(mode)            // Set the PLANAR alignement mode
            ? IScriptEnvironment::PlanarChromaAlignmentOn
            : IScriptEnvironment::PlanarChromaAlignmentOff;

  PVideoFrame src = child->GetFrame(n, env);              // run the GetFrame chain

  env->PlanarChromaAlignment(oldmode);                    // reset the PLANAR alignement mode

  return src;
  }

Correct Behavior

Use RAII or a scope guard to restore the original alignment on every exit path.

Reproduction

Start with alignment On and use a child whose GetFrame throws.

Observed Result

observed: environment alignment remains Off after exception
expected: original On state is restored

Impact

One failed child request leaks mutable environment state into subsequent filters.

Validation Criteria

State is restored after success and every exception path.

Version and Environment

• AviSynthPlus revision: 815780226951f95dfc1fc74f1df90ef98824fcf5
• Platform and compiler: Linux x86_64 / Clang 22 debug
• CPU features used: host-default build.