# pdftract-2vd1y — JavaScript Presence Detection

## Summary

The JavaScript detection module (`crates/pdftract-core/src/javascript.rs`) already implements complete JavaScript presence detection. All acceptance criteria pass.

## Implementation Verified

### Public API
- `contains_javascript(catalog, pages, acroform, resolver) -> bool` — lines 140-200
- `detect_javascript(catalog, pages, resolver) -> (Vec<JavascriptAction>, Vec<Diagnostic>)` — lines 42-96

### Detection Sites (all covered)
1. **Catalog /OpenAction** — lines 148-153
2. **Catalog /AA** — lines 155-160
3. **Page /AA** — lines 164-169
4. **AcroForm field /AA** — lines 192-197 (recursive walk via `walk_field_for_js`)
5. **Annotation /A or /AA** — lines 171-189

### Key Features Verified
- **/JavaScript and /JS spellings** — line 237: `s_name == "JavaScript" || s_name == "JS"`
- **/Next chaining** — `action_contains_js` recurses through /Next (line 244-247)
- **Cycle protection** — `visited: HashSet<ObjRef>` prevents infinite loops (line 146, 215-218)
- **Field tree recursion** — `walk_field_for_js` tracks `field_visited` separately (lines 336-386)

### Test Results
```
16 tests run: 16 passed
- test_contains_javascript_catalog_openaction: PASS
- test_contains_javascript_catalog_aa: PASS
- test_contains_javascript_page_aa: PASS
- test_contains_javascript_acroform_field_aa: PASS
- test_contains_javascript_annotation_with_action: PASS
- test_contains_javascript_empty: PASS
- test_contains_javascript_next_chain: PASS
- test_contains_javascript_cycle_protection: PASS
- test_contains_javascript_recognizes_js_short_form: PASS
- test_contains_javascript_non_javascript_action: PASS
- test_detect_javascript_empty: PASS
- TH-04 integration tests (4): PASS
```

## Acceptance Criteria Status

| Criterion | Status | Test |
|-----------|--------|------|
| /OpenAction /S /JavaScript → true | PASS | test_contains_javascript_catalog_openaction |
| Page /AA /O /S /JS → true | PASS | test_contains_javascript_page_aa |
| Form field /AA /K /S /JavaScript → true | PASS | test_contains_javascript_acroform_field_aa |
| Annotation /A /S /JavaScript → true | PASS | test_contains_javascript_annotation_with_action |
| No JS → false | PASS | test_contains_javascript_empty |
| /Next-chained action → true | PASS | test_contains_javascript_next_chain |
| Cyclic /Next → no infinite loop | PASS | test_contains_javascript_cycle_protection |

## Code Quality

- **Documentation**: Clear module-level docs stating "pdftract NEVER executes embedded JavaScript"
- **Error handling**: Resolves indirect objects safely, returns false on resolution failure
- **Performance**: Early exit on first JS detection in `contains_javascript`
- **Safety**: Separate visited sets for action chains vs field tree traversal

## Retrospective

### What worked
- The implementation was already complete with comprehensive test coverage
- Code follows the pattern described in the bead (recursive walker, cycle protection)
- Both `/JavaScript` and `/JS` spellings are recognized

### What didn't
- No issues encountered; implementation is complete

### Surprise
- The module already had two functions: `contains_javascript` (bool) and `detect_javascript` (detailed actions). The bead asked for the boolean return which already exists.

### Reusable pattern
- The cycle protection pattern (`visited: HashSet<ObjRef>`) is reusable for any recursive PDF structure walk
- The separate `action_visited` and `field_visited` sets in `walk_field_for_js` shows how to handle nested recursive structures with different cycle domains