Update web-ui handoff with PDF, strip specs, YAML-in-PNG features

Document four new capabilities ported from upstream PRs since the
initial handoff: PDF output (#367), connector strip lengths (#446),
YAML-in-PNG round-trip (#234), and code quality improvements.
Updated dependencies and next-steps checklist.

docs/agent-threads/web-ui-handoff.md

@@ -4,7 +4,7 @@
 |-------|-------|
 | From | wireviz-integration-agent |
 | To | web-ui-agent |
-| Date | 2026-02-13 |
+| Date | 2026-02-13 (Update 2) |
 | Re | Community features merged for web UI consumption |
 
 ---
@@ -96,15 +96,84 @@ jumpers:
       - [1, 2]  # jumper between pins 1 and 2
 ```
 
+## Update 2 — Additional Ports & Hardening (2026-02-13)
+
+The following features were ported from upstream PRs and landed on `testing/web-ui-features` after the initial handoff.
+
+### 3. PDF Output (port of upstream PR #367)
+
+PDF is now a supported output format via GraphViz native rendering.
+
+**What changed:**
+- New CLI flag: `-f P` generates PDF alongside other outputs
+- `P` added to the allowed format list in `wv_harness.py` and `wv_cli.py`
+- GraphViz renders the PDF natively (no intermediate conversion step)
+
+**Web UI implications:**
+- Offer a "Download PDF" option alongside SVG/PNG
+- PDF output is vector-based, so it scales well for printing wiring diagrams
+
+### 4. Strip Length Specs (port of upstream PR #446)
+
+Connectors now support a `strip` property specifying sleeve and insulation removal lengths. Useful for documenting wire prep instructions alongside the harness diagram.
+
+**What changed:**
+- New dataclasses: `StripSpec` and `Strip` in `wv_dataclasses.py`
+- Strip info rendered in connector diagram nodes via `wv_graphviz.py`
+- New `strip:` key under connector definitions in YAML
+
+**Example:**
+```yaml
+connectors:
+  X1:
+    type: Molex KK
+    pincount: 4
+    strip:
+      sleeve: "25 mm"
+      insulation: "5 mm"
+```
+
+**Web UI implications:**
+- Connector detail views / forms should expose strip length fields
+- Values are strings (include units), so a simple text input works
+- Strip info appears in the rendered diagram, no special rendering needed in the UI
+
+### 5. YAML-in-PNG Round-Trip (port of upstream PR #234, hardened)
+
+PNGs now embed the original YAML source as compressed iTXT metadata. This allows round-tripping: export a PNG, then later extract the full harness definition back out.
+
+**What changed:**
+- New module: `wv_png_metadata.py` with key functions:
+  - `save_yaml_to_png(yaml_str, png_path)` — embed YAML into an existing PNG
+  - `read_yaml_from_png(png_path)` — extract YAML from a PNG
+  - `has_yaml_metadata(png_path)` — check if a PNG contains embedded YAML
+- Uses atomic writes (temp file + rename) to avoid corrupting PNGs on failure
+- Preserves existing PNG metadata (doesn't clobber other iTXT chunks)
+- 10 MB size guard when reading untrusted PNGs
+- Version tag: `wireviz_meta_version: "1"` for future compatibility
+- 19-test suite in `tests/test_png_metadata.py`
+
+**Web UI implications:**
+- Users can drag-and-drop a WireViz PNG to import a harness definition
+- Use `has_yaml_metadata()` to detect whether a PNG is a WireViz export
+- Sharing harness designs becomes trivial — the PNG *is* the source file
+- The 10 MB guard protects the server from oversized uploads
+
+### 6. Code Quality Improvements
+
+- `ParsedInput` NamedTuple in `wireviz.py` for clean data flow between parsing stages
+- `output_formats` normalized to a tuple internally, preventing substring matching bugs (e.g., `"P" in "PNG"` no longer incorrectly matches)
+
 ## Dependencies
 
 The merged branch requires these Python packages beyond upstream:
 - `jinja2` (for template preprocessor)
-- `pillow` (for image handling, from jumpers PR)
+- `pillow` (for image handling, PNG metadata, from jumpers PR)
 - `pyyaml` (explicit dep, from jumpers PR)
 - `tabulate` (for BOM formatting, from jumpers PR)
+- `pytest` (for running the test suite)
 
-Install: `pip install jinja2 pillow pyyaml tabulate`
+Install: `pip install jinja2 pillow pyyaml tabulate pytest`
 
 Or from the repo: `pip install -e .` (setup.py includes all deps)
 
@@ -124,3 +193,7 @@ Or from the repo: `pip install -e .` (setup.py includes all deps)
 - [ ] Add Jinja2 template support in the UI (include path, template variables)
 - [ ] Test BOM output parsing against the new format
 - [ ] Create a combined test case using both Jinja2 templates and jumper definitions
+- [ ] Expose PDF output option in web UI
+- [ ] Display strip length info in connector detail views
+- [ ] Leverage YAML-in-PNG for sharing/importing harness diagrams from PNGs
+- [ ] Run test suite: `.venv/bin/pytest tests/`