fix: prevent accidental answer leaks during exercises

[ShengLin1001]

Summary

• remind Claude before drafting an exercise response
• detect trailing answer keys at Stop and void compromised items
• make reading and review prompts terminate cleanly

Why

Fixes #14. A leaked answer must not be graded or written as genuine mastery.

Validation

• python3 .claude/hooks/answer-leak-guard.py --selftest
• parsed .claude/hooks/hooks.json and .claude/settings.json as JSON
• git diff --check

The Stop hook cannot retract content already rendered to the learner. It blocks continuation, prevents grading/persistence of the compromised item, and requires a different replacement item.

[Copilot]

Pull request overview

This PR adds a hook-based “answer leak” guard to prevent compromised exercise items (where the learner can see an answer key) from being graded and persisted into the spaced-repetition/mastery databases, and updates skill instructions to reduce common leak patterns.

Changes:

• Added a Stop/UserPromptSubmit hook script to detect answer-key leaks and block continuation with remediation instructions.
• Wired the new guard into both .claude/settings.json (clone mode) and .claude/hooks/hooks.json (plugin mode).
• Tightened exercise prompt formatting guidance in review/reading skills and added a global “end at prompt line” rule.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
CLAUDE.md	Adds an explicit rule to end exercise messages exactly at the learner prompt line to avoid trailing leaks.
.claude/skills/fluent-review/SKILL.md	Clarifies that item_type must not include the tested item (to avoid leaking via metadata).
.claude/skills/fluent-reading/SKILL.md	Ensures MCQ-style prompts terminate with an explicit learner-input line.
.claude/settings.json	Registers the new guard for Stop + UserPromptSubmit in clone-mode settings.
.claude/hooks/hooks.json	Registers the new guard for Stop + UserPromptSubmit in plugin-mode hooks config.
.claude/hooks/answer-leak-guard.py	Implements leak detection and Stop-hook blocking behavior, plus a selftest mode.

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