fix: harden terronnd wasm gauge

[Saschl]

Fixes #[issue_no]

Summary of Changes

As we encounter some wasm crashes in the terrain module recently (hard to reproduce) I checked the code to find some possible trigger points (Claude assisted).

• Adds some sanity checks before reserving memory (will definitely crash if expectedBytes is a bogus number that comes from Simbridge via simconnect)
• Discard potential garbage data (e.g. if more is sent than expected)
• Fix potential UB in vector handling

Sorry for the formatting change. I adapted the formatting file to use the same rules as the FBW gauges now.

Cockpit API Changes

Screenshots (if necessary)

References

Additional context

Discord username (if different from GitHub):

Testing instructions

• Launch Plane and Simbridge and ensure the terrain display still works and updates
• Verify the gauge does not crash (ND turns orange in this case)

How to download the PR for QA

Every new commit to this PR will cause new A32NX and A380X artifacts to be created, built, and uploaded.

1. Make sure you are signed in to GitHub
2. Click on the Checks tab on the PR
3. On the left side, find and click on the PR Build tab
4. Click on either flybywire-aircraft-a320-neo or flybywire-aircraft-a380-842 download link at the bottom of the page

[Saschl]

Not entirely sure if this was an issue, but as size never gets initialized with reserve, the later usage with memcpy and the underlying pointer is not really defined when size = 0.

[BravoMike99]

Dev team QA report

Discord Username : bruno_pt99
Object of testing : #10908
Aircraft : A32NX
Simulator : 2024
Tier of Testing : 1
Date : 05/09/2026

Testing Process:
Turned on TERR on ND, switched ranges and modes on the ND and terrain kept working normally.

Testing Results:
Passed