Fix corrupt session cache fail-closed parity

[salasebas]

Summary

• distinguish a secondary-session-cache miss from a present corrupt value before database fallback
• preserve pinned Better Auth v1.6.23 JavaScript truthiness and one-pass safeJSONParse control flow
• add real dual-storage regressions for missing, corrupt, raw/decoded falsy, and doubly encoded cache values

Upstream parity

Compared against Better Auth v1.6.23 at 9dfceee14021fc15a2fb93023f39635f25b0b5ba.

Verification

• bundle exec ruby -Ipackages/better_auth/lib -Ipackages/better_auth/test packages/better_auth/test/better_auth/adapters/internal_adapter_test.rb — 40 runs, 164 assertions
• BUNDLE_GEMFILE=Gemfile bundle exec rake test in packages/better_auth — 1,546 runs, 9,435 assertions
• bundle exec standardrb
• git diff --check
• fresh blind scoped review — Approve

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1 Skipped Deployment

Project	Deployment	Actions	Updated (UTC)
better-auth	Ignored		Aug 20, 2026 9:53pm