Add flyte.app.Subdomain for deploy-time subdomain resolution

[cosmicBboy]

Summary

Adds a new flyte.app.Subdomain class that lets app authors declare a subdomain whose final value is resolved at deploy time, when the deployment project/domain are known.

• Subdomain.from_app_name(app_name, project_domain_suffix="hash")
  • "hash" (default): subdomain is {app_name}-{hash}, where the hash is the first 8 hex chars of sha256 of "{project}-{domain}" — short, and stable per project/domain.
  • "default": subdomain is {app_name}-{project}-{domain}.
• Subdomain.from_function(fn): fn receives the AppEnvironment being deployed and the deployment SerializationContext (project, domain, org, version, ...) and returns the subdomain string, giving users full control. The return value is validated to be a non-empty string.
• Domain.subdomain now accepts str | Subdomain | None.
• Resolution happens in translate_app_env_to_idl: Subdomain instances are resolved via resolve(app_env, serialization_context) before being written into the IngressConfig; plain strings pass through unchanged.

Example

import flyte.app

# my-app-f7628a67 (hash of "{project}-{domain}")
flyte.app.Domain(subdomain=flyte.app.Subdomain.from_app_name("my-app"))

# my-app-my-project-development
flyte.app.Domain(subdomain=flyte.app.Subdomain.from_app_name("my-app", project_domain_suffix="default"))

# fully custom
flyte.app.Domain(subdomain=flyte.app.Subdomain.from_function(
    lambda app_env, ctx: f"{app_env.name}-{ctx.org}"
))

Test plan

• New unit tests in tests/flyte/app/test_types.py: both constructors, suffix/arg validation, hash stability per project/domain, missing project/domain errors.
• Parametrized end-to-end serde tests in tests/flyte/app/runtime/test_app_serde.py verifying the resolved subdomain lands in the ingress config.
• Full app serde suite passes (60 tests); pre-commit fmt/mypy/ty pass.

🤖 Generated with Claude Code

https://claude.ai/code/session_01KVnRzHRUANmCg7ZsLH6Fah