docs(pdftract-2vd1y): verify JavaScript detection implementation

The JavaScript presence detection module was already complete in
crates/pdftract-core/src/javascript.rs. Verified all acceptance criteria:

- Catalog /OpenAction /S /JavaScript → detected
- Page /AA /O /S /JS → detected
- AcroForm field /AA /K /S /JavaScript → detected
- Annotation /A /S /JavaScript → detected
- /Next-chained actions → detected
- Cyclic /Next → bounded by visited set
- No JS present → returns false

All 16 JavaScript tests pass. Created verification note documenting
the implementation.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

notes/pdftract-2vd1y.md

@@ -0,0 +1,77 @@
+# 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