Fix lineSliceAlong() dropping altitude of the line's vertices

[natiginfo]

Fixes MAPSAND-2853 / #1636.

Problem

TurfMisc.lineSliceAlong() returns 2D points for a 3D input LineString since v7.10.0; v7.9.0 preserved altitude on the vertices.

Root cause

The flat-coordinate rewrite (#1630) changed lineSliceAlong() to read FlattenListOfPoints#getFlattenLngLatArray() and rebuild every point with the 2-arg Point.fromLngLat(lng, lat). The altitudes live in a parallel array (FlattenListOfPoints#getAltitudes()) that the rewrite never read. The previous implementation used line.coordinates() and passed the Points straight through, so altitude survived.

Fix

Read the altitudes alongside the flat array and rebuild the emitted vertices through a small private helper that mirrors the null/NaN handling in FlattenListOfPoints#points().

The interpolated start and stop points stay 2D: they come from TurfMeasurement#destination(), which has always been 2D, and bearing()/distance() ignore altitude. With the vertices restored the output matches v7.9.0 exactly, which is the behaviour the report asks for.

getFlattenLngLatArray() has exactly one call site outside services-geojson, so no other Turf method is affected. TurfMeasurement.along()/length() never use the flatten path.

Verification

New TurfMiscTest#testLineSliceAlongPreservesAltitude slices a 3D line from 0 to its full length, so every returned point is an original vertex, and asserts altitude on each. Confirmed failing before the fix and passing after; :services-turf:test and :services-geojson:test are green.

Note: checkstyleMain could not be run locally — it fails the same way on unmodified main (SuppressionFilter - Unable to find: config/checkstyle/suppressions.xml), so CI gates it here.

🤖 Generated with Claude Code

[ox-security]

Successfully scanned changes introduced in a pull request into main from nb/fix-lineSliceAlong.

Internal scan identifier: 1cd85dfb-346b-4010-b575-1b036c868192.

Total issues	Blocking issues	Scan status
1	0	✔️

Category	Issues
Secret/PII Scan	1

See all issues found during this scan in the OX Security Application.

Detailed information

Issue #	1
Name	Generic Key • Public Repo
Status	Old
Enforcement	Monitor
Severity	High
Category	Secret/PII Scan
Source tools	OX Secret/PII Scan
Recommendation	Please verify if the Generic Key in the code is in use. Then do the following: 1. If the secret is in use, please revoke it. 2. Moving forward, store secrets in an environment variable or secret manager. 3. Change the code to access secrets using the method chosen above. WARNING: The found Generic Key will still be visible in the Git History. Ensure it is revoked/disabled.

1 aggregation

File	Match
scripts/coverage.sh	d56942c32a1bb70af75bf972302b6114********************************

[codecov]

Codecov Report

❌ Patch coverage is 90.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 79.36%. Comparing base (53a24f5) to head (3c245c9).

Files with missing lines	Patch %	Lines
...s-turf/src/main/java/com/mapbox/turf/TurfMisc.java	90.00%	0 Missing and 1 partial ⚠️

@@            Coverage Diff            @@
##               main    #1637   +/-   ##
=========================================
  Coverage     79.35%   79.36%           
- Complexity     1129     1131    +2     
=========================================
  Files           162      162           
  Lines          4698     4705    +7     
  Branches        659      660    +1     
=========================================
+ Hits           3728     3734    +6     
  Misses          702      702           
- Partials        268      269    +1     

Files with missing lines	Coverage Δ
...s-turf/src/main/java/com/mapbox/turf/TurfMisc.java	88.57% <90.00%> (-0.12%)	⬇️

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