fix: rewrite validation messages to guide learning instead of revealing answers (#4)

specs/004-validation-messages/spec.md

@@ -0,0 +1,57 @@
+# fix: validation error messages reveal the solution instead of guiding learning
+
+**Issue:** [#4](https://git.librete.ch/public/code-crispies/issues/4)
+**Repository:** public/code-crispies
+**Author:** libretech
+**State:** open
+**Labels:** none
+
+## Issue Body
+
+Pedagogy audit: 88% of exercises reveal the answer in error messages, creating a fail-then-copy loop. Change validation messages from 'Set padding: 1rem' to 'Which property adds space between content and the element edge?' This applies across all modules — start with flexbox, box-model, and colors (the 3 worst offenders).
+
+## Scope
+
+The three priority modules:
+
+1. **Flexbox** (`lessons/flexbox.json`) — already uses guiding messages (0 messages need changes)
+2. **Box Model** (`lessons/01-box-model.json`) — 11 validation messages reveal exact answers
+3. **Colors** (`lessons/03-colors.json`) — 4 validation messages reveal exact answers
+
+Localized versions that need corresponding updates:
+- `lessons/ar/01-box-model.json`
+- `lessons/de/01-box-model.json`
+- `lessons/es/01-box-model.json`
+- `lessons/pl/01-box-model.json`
+- `lessons/uk/01-box-model.json`
+
+No localized versions exist for colors.
+
+## Acceptance Criteria
+
+- [ ] All validation messages in box-model module guide the learner instead of revealing the answer
+- [ ] All validation messages in colors module guide the learner instead of revealing the answer
+- [ ] Messages use question or hint phrasing (e.g., "Which property..." or "Try the property that...")
+- [ ] Messages never include the exact property-value pair that solves the exercise
+- [ ] All 5 localized box-model files receive equivalent translated guiding messages
+- [ ] Existing tests continue to pass (message content is not tested, only validation logic)
+- [ ] Lesson JSON files remain valid against the module schema
+
+## Current vs Desired Pattern
+
+**Current (answer-revealing):**
+```
+"message": "Set <kbd>padding: 1rem</kbd>"
+```
+
+**Desired (guiding):**
+```
+"message": "Which property adds space between the content and the element's edge?"
+```
+
+## Prior Art
+
+The flexbox module already follows the desired pattern. Its messages serve as the style reference:
+- "Try changing the display mode to create a flex container"
+- "Use the property that adds spacing between flex items"
+- "Use the property that distributes items along the main axis"