Failing test: exponent notation is split into a value plus a phantom E extrusion (#368)

[remcoder]

Adds a failing test for #368. CI will be red on this branch by design — do not merge as is.

The point is to pin the bug down as executable spec rather than prose, so whoever fixes the tokenizer has a target that goes green.

The failure

AssertionError: expected { x: 12, e: 5, y: 5 } to deeply equal { x: 1200000, y: 5 }

G1 X12e5 Y5 — the tokenizer splits a word at every letter, so the e of the exponent is read as a separate E parameter.

Why the fabricated e is the damaging part

This isn't just a lossy coordinate. Interpreter derives the path type from e:

const pathType = e ? PathType.Extrusion : PathType.Travel;

So the line is interpreted as a move to X12 that extrudes 5mm of filament:

• a travel move renders as extruded filament, drawing a solid line where the print has none
• extrusionDistance is inflated by 5
• the segment lands in an extrusion path, so it also stretches the bounding box

All silent — no parse error, no warning.

About the expectation

The test asserts option 3 from #368 (recognize exponent notation in the tokenizer), i.e. x: 1200000 and no e. If the team prefers option 2 (reject a word whose value is followed by a valueless letter), change the expectation to x being absent. Either resolution has to remove the fabricated e, which is what the test really guards.

Option 1 in #368 is "leave it, document it" — if that wins, close this PR and land a characterization test asserting the current {x: 12, e: 5, y: 5} instead.

Likelihood

Low: G-code has no exponent notation, and no slicer emits it. The realistic route is a generator doing naive float-to-string on an extreme coordinate, since String() reaches exponent form by itself — String(1e21) is '1e+21', String(1e-7) is '1e-7'.

Relationship to #367

Independent and pre-existing; this branch is off develop, not the #367 stack. #367 does not change this behavior. The characterization test for it was deliberately kept out of #367 so the current behavior isn't locked in before this is decided.

[github-actions]

Visit the preview URL for this PR (updated for commit 7ec2e7f):

https://gcode-preview--pr369-failing-test-exponen-57rcjimx.web.app

_{(expires Mon, 21 Sep 2026 16:40:03 GMT)}

_{🔥 via Firebase Hosting GitHub Action 🌎}

_{Sign: 59bd114ae4847b32c2bba0b68620b9069a3e3531}