Remediate remaining Ubuntu <24.04 references on main

[richlander]

Note

This issue was AI/Copilot-generated (Copilot CLI v1.0.11).

Audit of main found remaining references to Ubuntu versions older than 24.04 (excluding oldest-supported 22.04 helix containers, Android queues, and external/vendored code).

Tracking

WASM host VMs — switch to Azure Linux 3 (can do now)

• eng/pipelines/libraries/helix-queues-setup.yml:164 — Ubuntu.2204.Amd64.Open host VM for WASM container
• eng/pipelines/libraries/helix-queues-setup.yml:168 — same
• eng/pipelines/libraries/helix-queues-setup.yml:172 — same

helix-platforms.yml:271 already uses AzureLinux.3.Amd64.Open as the WASM host, so these should align.

WASM container images — needs updated prereqs image

• eng/pipelines/helix-platforms.yml:271 — ubuntu-22.04-helix-webassembly-amd64 container
• eng/pipelines/libraries/helix-queues-setup.yml:164,168,172 — ubuntu-22.04-helix-webassembly container

Requires a ubuntu-26.04-helix-webassembly (or AzureLinux-based) image in dotnet-buildtools-prereqs-docker.

Tizen cross-build container — needs updated prereqs image

• eng/pipelines/common/templates/pipeline-with-resources.yml:127 — ubuntu-22.04-cross-armel-tizen

Requires an updated Tizen cross-build image in dotnet-buildtools-prereqs-docker.

Docker-compose comments — cosmetic cleanup

• src/libraries/System.Net.Http/tests/StressTests/HttpStress/docker-compose.yml:1 — comment references Build.Ubuntu.2204.Amd64.Open
• src/libraries/System.Net.Security/tests/StressTests/SslStress/docker-compose.yml:1 — same

Documentation — stale examples

• docs/workflow/using-docker.md:51 — references ubuntu-22.04-cross-armel-tizen
• docs/workflow/building/libraries/webassembly-instructions.md:136,153 — references ubuntu-18.04-webassembly
• docs/workflow/building/coreclr/cross-building.md:171 — references ubuntu-18.04-cross-freebsd-12

Out of scope

• Oldest-supported Ubuntu 22.04 helix containers — 22.04 supported through April 2027
• Android queues (Ubuntu.2204.Amd64.Android.*) — separate infrastructure
• ARM host VMs — addressed in Move helix-platforms.yml ARM host VMs from Ubuntu 22.04 to Azure Linux 3 #126121
• External code (src/native/external/libunwind/) — vendored, not ours to change

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