Three ways `engineering/pid/lines.py` could emit a silent wrong result or
an opaque crash instead of an honest refusal:
- `format_line_number` only recognised a token that was exactly `{field}`;
`P-{seq:04d}`, `{size}"-{service}` or `{bogus}x` were copied verbatim,
braces and all, into the line number. Tokens are now parsed with
`string.Formatter`: one named known field per token, a format spec is
honoured (`{seq:04d}` -> `0007`), literal decoration around the field
survives with it and drops out with it, and conversions, positional
fields, multi-field tokens, unbalanced braces and specs the value cannot
take are all refused by token name.
- `route` never checked finiteness: a NaN `end` collapsed the U candidate
to a valid two-point "straight" path ending at the stub point. Every
coordinate of start/end/waypoints and the stub are now checked and the
refusal names the offending `end.x` / `waypoints[1].y` / stub.
- A non-axis port direction (45.0, 90.5, nan) raised `KeyError` from the
AXIS lookup. `axis_direction()` now normalises with a 1e-6 deg tolerance
for engine drift and otherwise raises ValueError naming `start_dir` /
`end_dir` and how to resolve it (rotate to a multiple of 90 or pass
waypoints).
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FKFStjEFzpGyLq5bMpWxTd
