--family is ignored for font.familyname; FontForge/potrace failures exit 0

I found a few correctness issues in the font-generation pipeline. They look distinct from #92 (alpha threshold) and #83/#82 (FontForge missing).

1. --family does not set the font’s internal family name

In handwrite/svgtottf.py set_properties() (around lines 47–55):

family = self.metadata.get("family", None) or fontname
self.font.familyname = fontname   # uses --filename, not --family

--family is written into SFNT names when sfnt_names exists (lines 64–67), but self.font.familyname always uses fontname (--filename / config). Installed fonts then show the wrong family in font pickers.

Fix: self.font.familyname = family, and keep fontname / fullname consistent with the SFNT names.

2. FontForge and potrace failures are ignored

• svgtottf.py lines 28–41: subprocess.run(...) with no check=True and no return-code check. If ffpython/fontforge fails, the CLI can still exit 0 with no .ttf.
• pngtosvg.py line 48: same for potrace.

Fix: subprocess.run(..., check=True, capture_output=True) and surface stderr. You already raise PotraceNotFound when the binary is missing; a failed conversion should be just as visible.

3. Missing sfnt_names in a custom config → KeyError

Lines 64–68 guard updates to sfnt_names, but line 70 always does:

self.config["sfnt_names"]["UniqueID"] = ...

A minimal config without sfnt_names crashes.

Fix: self.config.setdefault("sfnt_names", {}) before writing UniqueID.

4. Temp directory leaked on failure

handwrite/cli.py converters() (lines 17–37) creates tempfile.mkdtemp() when --directory is omitted, and only rmtrees it if run() succeeds. Any exception in SHEETtoPNG / PNGtoSVG / SVGtoTTF leaves the temp dir behind.

Fix: try/finally around run().

Also, output_directory is never makedirs’d; a missing output path fails late inside FontForge.

Happy to open a PR if you want.

Start with handwrite/svgtottf.py, especially set_properties() and its subprocess calls, then inspect handwrite/pngtosvg.py and handwrite/cli.py converters(). Verify the family and sfnt_names cases, conversion failures, cleanup on exceptions, and creation of a missing output directory. Done means each reported failure is surfaced and temporary resources are cleaned up.