feat(install): say why ARM64 Linux has no local runtime

[benceruleanlu]

Part of a stack of review fixes for #1486. Based on #1508. Top of the stack.

Summary

#1486 correctly stops a Linux ARM64 app from selecting x64 bundles, but the resulting state is returned as a bare empty list. It reaches the user as "No options available" and telemetry as express.fallback with reason precondition_failed, which is also what an empty or mis-published catalog produces. The one state we know exactly was indistinguishable from the one we do not, so a user cannot tell "wait for an ARM64 bundle" from "retry later", and metrics cannot separate this deliberate gap from a real catalog regression.

Feature behavior

The reason now lives next to the filter that creates it, as unsupportedHostReason in envPaths.ts, and validateHardware reports it. Linux ARM64 therefore takes the explain-and-block path the wizard already gives an Intel Mac: a message naming the platform, and express install falling back with unsupported_hardware.

Cloud and remote workspaces are unaffected. The wizard blocks only the standalone source card, and the message says so. No new i18n key or renderer plumbing is introduced; this reuses the existing hardware-validation mechanism end to end.

Removing the carve-out when linux-*-arm64 bundles ship is a one-function deletion. The architecture filter already accepts suffixed ids with no further change.

Test coverage and validation

• unsupportedHostReason is tested against the filter it must agree with: on linux/arm64 no catalog id survives variantMatchesHost and a reason is returned; on win32/x64, win32/arm64, darwin/arm64 and linux/x64 at least one id survives and the reason is null. That pairing is what keeps the two from drifting apart.
• validateHardware blocks on linux/arm64 with a message naming the platform and the cloud alternative, and does not gate linux/x64 on architecture.
• Full unit suite: 274 files, 4736 passed, 2 skipped. Repeated with the whole suite stubbed as linux/arm64: identical result.
• Typecheck, lint and format pass.

Change breakdown

Total changed lines: 92 (90 added, 2 deleted).

Product code

• 2 files; +30 / -2; 32 changed lines; 34.8% of total.
• src/main/lib/gpu.ts
• src/main/sources/standalone/envPaths.ts

Test code

• 2 files; +60 / -0; 60 changed lines; 65.2% of total.
• src/main/lib/gpu.test.ts
• src/main/sources/standalone/envPaths.test.ts

Documentation

• 0 files; +0 / -0; 0 changed lines; 0%.

Configuration and CI

• 0 files; +0 / -0; 0 changed lines; 0%.

Generated files

• 0 files; +0 / -0; 0 changed lines; 0%.

Lockfiles

• 0 files; +0 / -0; 0 changed lines; 0%.

Vendored code

• 0 files; +0 / -0; 0 changed lines; 0%.

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: ASSERTIVE

Plan: Advanced

Run ID: 8271e339-0c54-4608-a1dc-ab5bb917be36

📥 Commits

Reviewing files that changed from the base of the PR and between 7f104b0 and 25cad3e.

📒 Files selected for processing (4)

• src/main/lib/gpu.test.ts
• src/main/lib/gpu.ts
• src/main/sources/standalone/envPaths.test.ts
• src/main/sources/standalone/envPaths.ts

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📝 Walkthrough

Walkthrough

Changes

Host architecture validation

Layer / File(s)	Summary
Unsupported host explanation src/main/sources/standalone/envPaths.ts, src/main/sources/standalone/envPaths.test.ts	unsupportedHostReason() reports that ARM64 Linux has no local runtime bundle. Tests cover unsupported ARM64 Linux and supported Windows, macOS, and Linux combinations.
Hardware validation gate src/main/lib/gpu.ts, src/main/lib/gpu.test.ts	validateHardware returns the unsupported-host error before GPU probing. Tests verify ARM64 Linux is rejected and x64 Linux is not architecture-gated.

Suggested reviewers: kosinkadink

Priority: ⬇️ Low

Merge Risk: ⚪ Minimal · up to 25cad

Linux ARM64 hosts without a local runtime now receive a clear blocking message and cloud or remote alternative, while supported hosts continue through hardware validation. The change is covered by focused architecture-gate tests and has no remaining concrete merge-blocking risk.

🚥 Pre-merge checks | ✅ 2

✅ Passed checks (2 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch bl/arm64-unsupported-arch-state

✨ Simplify code

• Create PR with simplified code
• Commit simplified code in branch bl/arm64-unsupported-arch-state

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