fix underflow and crash on malformed stream

[patchzyy]

Hardened the decompressor against malformed data
as talked about here #17

Summary by CodeRabbit

• Bug Fixes
  • Improved handling of malformed compressed data during Yaz0 decompression.
  • Prevented invalid memory reads when back-references point outside already decoded data.
  • Added clear error reporting and a fatal prompt when decompression exceeds the output buffer, instead of continuing with invalid results.

[coderabbitai]

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: de1f836c-3c1d-4b9d-b247-ba7824a7716a

📥 Commits

Reviewing files that changed from the base of the PR and between 8d5d93f and 9c4f4b7.

📒 Files selected for processing (1)

• runtime/src/hle/egg_decomp.cpp

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📝 Walkthrough

Walkthrough

The Yaz0 back-reference decoder now validates copy distances against written output. It also aborts on malformed references and output overruns after logging errors and showing fatal popups.

Changes

Yaz0 decompression validation

Layer / File(s)	Summary
Decompression error handling runtime/src/hle/egg_decomp.cpp	The decoder rejects back-references beyond the current output position. It reports malformed streams and output overruns, shows fatal corruption messages, and aborts instead of returning expandSize on overrun.

Estimated code review effort: 2 (Simple) | ~10 minutes

Merge Risk: ⚪ Minimal · up to 9c4f4

This localized decompressor hardening change has no actionable merge-blocking risk remaining based on the available review evidence and is merge-ready after normal checks.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	Docstring check was indeterminate for this PR — some files could not be analyzed in time. Not blocking.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: preventing underflow and crashes when processing malformed streams.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch Premature-success-fix

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