Add deterministic three-choice sessions

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Summary

• add deterministic finite three-choice sessions with source or seeded shuffled ordering
• construct distinct distractors and stable choice identities without exposing answer keys before evaluation
• support correct, incorrect, and host-reported expiry outcomes with stale-round protection
• expose typed validation errors and finite progress while keeping the session UI-, clock-, persistence-, and LexiconKit-agnostic
• add privacy-safe package-owned session observability and comprehensive Swift Testing coverage
• update README, DocC, changelog, and package logging specialization

Validation

• AgentGuidelines/Scripts/swift_format.sh format-and-lint Package.swift Sources Tests
• AgentGuidelines/Scripts/swift_format.sh lint-strict Package.swift Sources Tests
• swift test (21 tests passed)
• AgentGuidelines/Scripts/validate_consumer_setup.swift --consumer-root . --require-swift-format
• .agents/skills/agent-guidelines-audit/scripts/check_markdown_wrapping.swift README.md CHANGELOG.md Sources/FlashcardKit/FlashcardKit.docc
• git diff --check

Observability

Session creation, validation rejection, accepted response outcomes, and rejected submissions emit concise com.thatfactory.flashcardkit session events prefixed with 🃏. Logs contain only counts, stable reason tokens, and result classifications; they never include card identities, prompt or answer text, or asset references.

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Reasoning Relay exact-head review approved.

• Reviewed-Base: 764fac67200d274ac7858ae6b5348b95b3fb8ebb
• Reviewed-Head: 96e3434bbf979ca13401b0a9338a54afef8d0145
• Verdict: APPROVED
• Blocking findings: None
• Receipt hash: 00072d3a69be3680ba507b4408d6d139934cd6cc27b3345f2e1752f4cdb47d0f