Use Proxmox for a template before reaching for linuxcontainers.org

[MickLesk]

✍️ Description

Every ARM64 container took the custom-template path, so pveam was never consulted on that architecture.

-> Template lookup now runs the same way on both architectures: local templates first, then the catalog, both matched on OS, version and exact architecture. Only when Proxmox has nothing does linuxcontainers.org step in, which is still the only source for Ubuntu, Fedora and the rest on ARM64.

The interactive "pick another version" fallback matched by name only, so on a host whose catalog carries both architectures — now the normal case — it could offer an amd64 template to an ARM64 host.

🔗 Related Issue

Refs #5

✅ Prerequisites (X in brackets)

• Self-review completed – Code follows project standards.
• Tested thoroughly – routing unit-tested against a real pveam available catalog; not run on an ARM64 host.
• No security risks – No hardcoded secrets, unnecessary privilege escalations, or permission issues.
• API.txt regenerated – n/a, this repo has no API.txt.

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🤖 AI Assistance (X in brackets)

If you used an AI tool (GitHub Copilot, Claude, ChatGPT, etc.) to write or generate any code in this PR, you must confirm compliance below.
Select exactly one option.

• No AI used – Code was written without AI assistance.
• AI was used – The output has been reviewed and corrected, and I take responsibility for it matching this repo's conventions.

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🛠️ Type of Change (X in brackets)

• 🐞 Bug fix – Resolves an issue without breaking functionality.
• ✨ New feature – Adds new, non-breaking functionality.
• 💥 Breaking change – Alters existing behavior in a way that may require updates in every downstream script.
• 🔧 Refactoring / Code Cleanup – Improves readability or maintainability without changing functionality.
• 📝 Documentation update – Changes to README, docs/, CONTRIBUTING.md, or other docs.

[github-actions]

Try this branch

The engine and the scripts resolve independently, so a production script can
be run against the engine from this PR by setting one variable:

COMMUNITY_SCRIPTS_CORE_URL=https://raw.githubusercontent.com/community-scripts/core/feat/pveam-first-template-lookup \
bash -c "$(curl -fsSL https://raw.githubusercontent.com/community-scripts/ProxmoxVED/main/ct/debian.sh)"

Swap ct/debian.sh for whatever exercises the change.

This PR touches both backends. Worth running on a Proxmox VE and an Incus host.

Run a script from a fork as well

curl -fsSL https://raw.githubusercontent.com/community-scripts/core/feat/pveam-first-template-lookup/tools/run.sh |
  bash -s -- https://raw.githubusercontent.com/YOU/ProxmoxVED/your-branch ct/debian.sh \
             https://raw.githubusercontent.com/community-scripts/core/feat/pveam-first-template-lookup

Note that run.sh is reached through a pipe, so the script it starts inherits
an exhausted stdin. Whiptail is fine — it opens /dev/tty — but a plain read
would see EOF. The single-variable form above does not have that problem.

Useful flags while testing

dev_mode=net logs every engine fetch with status and duration, which is the
quickest way to confirm the branch is really being used. dev_mode=keep stops a
failed build from deleting the container along with the evidence.

[MickLesk]

@asylumexp fyi