Validate m_frag_offset_count and offset during cache unmarshal

[traeak]

Adds an overflow check in case of cache device corruption.

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Adds bounds validation when unmarshaling HTTP cache alternates to guard against corrupted on-disk data triggering out-of-buffer reads via m_frag_offset_count or the embedded fragment-offset pointer.

Changes:

• Validate m_frag_offset_count and the encoded fragment-offset position against both remaining length and original buffer length in HTTPInfo::unmarshal.
• Apply analogous validation in HTTPInfo::unmarshal_v24_1 using the "extra beyond integral slots" size.
• Return -1 (with assertion) on validation failure instead of proceeding with invalid sizes.

[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.