fix(schema): require hostnames of at least 2 characters

[GhostofGoes]

Description

Require topology node hostnames to be at least 2 characters long.

Background

The schema allowed 1-character hostnames, but two guest operating systems phenix configures reject them:

• VyOS and Vyatta validate system host-name against [A-Za-z0-9][-.A-Za-z0-9]*[A-Za-z0-9], which needs at least 2 characters (VyOS docs, vyos-1x constraint). The same rule applies in legacy Vyatta and in every VyOS release since 1.2.
• Windows DNS host names have a 2-character minimum (Microsoft Learn).

Linux (hostnamectl) accepts 1-character hostnames. Applying the minimum to every node keeps the rule in one place, and matches the limit the other supported guests already enforce.

Changes

• minLength: 2 and pattern ^[a-zA-Z0-9][a-zA-Z0-9-]*[a-zA-Z0-9]$ in the v1 and v2 topology schemas, with a comment linking the references above.
• The same change in the topology builder's client-side schemas, so the builder flags a 1-character hostname while editing.
• Schema regression tests for 1, 2, and 63 characters.
• CHANGELOG entry.

Related Issues/PRs

• Follows up fix(vrouter): preserve configured router hostnames #347, which stops rewriting router hostnames.
• Docs: docs(configuration): require hostnames of at least 2 characters sceptre-phenix-docs#70

Type of Change

• Bugfix (fix)
• Feature (feat)
• Documentation (docs)
• Refactor (refactor)
• Chore (CI, build, dependencies, etc.) (chore)
• Other (please describe):

Checklist

• This PR conforms to the process detailed in the Contributing Guide.
• I have included no proprietary/sensitive information in my code or the PR.
• I have commented my code, particularly in hard-to-understand areas.
• I have made corresponding changes to the documentation.
• I have tested my code (describe below).

Testing

Tested manually on a phenix deployment. Normal topologies work, but a node with a 1-character hostname like r will fail validation.

Additional Notes

This is a stricter validation rule. A stored config with a 1-character hostname fails validation the next time it is created or updated, until the node is renamed. The topologies in sceptre-phenix-topologies have no 1-character hostnames.

Not covered here: minimega parses an all-numeric VM name as a count (vm launch kvm 42 launches 42 VMs), and the schema still accepts all-numeric hostnames.

🤖 Generated with Claude Code

[cmulk]

looks good, just a changelog conflict

[GhostofGoes]

@cmulk resolved