Add Ubuntu 26.04 builds (#609)

[richardsimmonds]

Summary

Adds ubuntu26.04 (resolute) as a new OS target to the DEB packaging matrix, per documentdb#609.

Changes

• packaging/build_packages.sh — accept --os ubuntu26.04 in the whitelist and map it to the ubuntu:26.04 Docker base image; updated help text and error message
• packaging/gateway/build_gateway_packages.sh — same: whitelist, ubuntu:26.04 build + test images, reuses the existing Dockerfile_gateway_ubuntu (parameterized via BASE_IMAGE)
• .github/workflows/build_deb_packages.yml — added ubuntu26.04 to the full build matrix (the reduced PR matrix is unchanged to keep PR checks fast)
• packaging/README.md — documented the new distro in both supported-distro lists

Notes

• The deb Dockerfiles (packaging/deb/Dockerfile-deb, Dockerfile_gateway_ubuntu) take the base image as an ARG, so no Dockerfile changes were needed.
• No source changes; CI will validate that the extension and gateway build cleanly on the new base image.

Closes documentdb#609

[patty-chow]

Review Summary

Verdict: NEEDS CHANGES — 1 blocking issue, 1 process gap, 1 nit.

🔴 Blocking: gateway build will fail on ubuntu26.04 (resolute)

scripts/install_llvm.sh (run by Dockerfile_gateway_ubuntu) hard-pins LLVM_VERSION=20 and installs via apt.llvm.org's llvm.sh. Verified directly against apt.llvm.org:

• dists/llvm-toolchain-resolute-20/Release → 404 (no LLVM 20 repo for resolute)
• dists/llvm-toolchain-resolute-21/Release → 200

llvm.sh only check_urls the codename base path (which exists), so it adds the nonexistent llvm-toolchain-resolute-20 repo; the subsequent apt-get update fails and, with set -e, the Docker build dies. The gateway builds on the pg_version == '17' legs, so both ubuntu26.04 jobs (amd64 + arm64) in the full matrix will fail. scripts/install_llvm.sh needs distro awareness (LLVM 21 on resolute) before this matrix entry is safe.

⚠️ Process gap: nothing in this PR actually exercises the new leg

The PR description says CI will validate the new base image — but it won't. The workflow skips drafts, and the reduced PR matrix (deliberately unchanged) excludes ubuntu26.04. The new leg first runs post-merge on main, where it will hit the LLVM failure above. Please run a manual workflow_dispatch of build_deb_packages.yml on this branch (dispatch uses the full matrix) and link the run here before merge.

✅ Looks Good

• Extension (non-gateway) path checks out: Dockerfile-deb takes BASE_IMAGE as ARG and uses pgdg via $(lsb_release -cs)-pgdg. Verified resolute-pgdg exists on apt.postgresql.org with pg16/17/18 packages for amd64 and arm64, and ubuntu:26.04 exists on Docker Hub.
• Codename "resolute" correct; README updated in both supported-distro lists.
• Keeping the reduced PR matrix untouched is the right call for check speed.
• DCO: commit daaf317 carries a proper Signed-off-by. Scope is minimal — no unrelated changes.

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Reviewed by Hermes reviewer agent

[patty-chow]

🔴 Blocking: This case routes to Dockerfile_gateway_ubuntu, which runs scripts/install_llvm.sh — and that script hard-pins LLVM_VERSION=20. apt.llvm.org has no llvm-toolchain-resolute-20 repo (404; only -21 exists for resolute). The repo add succeeds but apt-get update then fails, killing the Docker build on both ubuntu26.04 pg17 legs (the only legs that build the gateway). install_llvm.sh needs distro awareness (LLVM 21 on resolute) before this entry works.

[patty-chow]

⚠️ Correct placement (full matrix only), but note: nothing in this PR's lifecycle exercises this new leg — drafts skip the workflow, and the reduced PR matrix excludes ubuntu26.04. Please run a manual workflow_dispatch of this workflow on the branch (dispatch uses the full matrix) and link the run here before merge. As-is, the first ubuntu26.04 build happens post-merge on main, where it will fail on the gateway LLVM issue.

[patty-chow]

💡 Nit: this help text (and the error message at line 50) omits deb13, which the case statement at line 41 accepts. Pre-existing inconsistency, but since this PR touches both lines anyway, add deb13 while you're here. The gateway script's equivalent text already lists it.