Spec: Fix History Element Validation Bug

Status: done Priority: P0 Created: 2026-02-08 Completed: 2026-02-08 Owner: AI

Context

The invalid-history-elements function in chart.cljc:398-415 has multiple inverted conditions in a cond-> chain. It reports errors for VALID history configurations and silently accepts INVALID ones.

NOTE: I can swear there are charts using history in circulation. Perhaps they are not running validation, but be very very sure we're right here.

Requirements

1. Fix the inverted condition on line 409: (= 1 (count transitions)) should be (not= 1 (count transitions))
2. Fix the inverted condition on line 410: (and (nil? event) (nil? cond)) should be (or (some? event) (some? cond))
3. Review line 413 condition: (or deep? (= 1 (count immediate-children))) — appears to flag deep history as always problematic
4. Complete the TODO on line 412: "Validate deep history"
5. Add regression tests for all validation conditions
6. Verify no existing charts in the codebase rely on the broken behavior

Affected Modules

• src/main/com/fulcrologic/statecharts/chart.cljc:398-415 - Fix validation logic
• src/test/ - Add validation tests

Approach

1. Write failing tests first that demonstrate the incorrect validation
2. Fix the conditions
3. Run full test suite to check for regressions
4. Review any callers of invalid-history-elements

Verification

1. [ ] Test: valid history node (1 transition, no event/cond) passes validation
2. [ ] Test: history node with 0 transitions fails validation
3. [ ] Test: history node with 2+ transitions fails validation
4. [ ] Test: history node with event attribute fails validation
5. [ ] Test: history node with cond attribute fails validation
6. [ ] Test: shallow history with multiple targets fails validation
7. [ ] Test: deep history validation implemented
8. [ ] Full test suite passes