feat: support composed CLI render registries

[alongubkin]

Background

The official Alien developer CLI is composed in the Platform repository so it can include Platform-owned cloud controllers. Terraform and CloudFormation have the same OSS/private split: OSS owns the generator and registry, while Platform owns additional emitters in alien-terraformx and alien-cloudformationx.

The registries are already intentionally extensible, but alien render always constructed built_in() internally. A composed binary therefore could register runtime controllers but could not make its Platform emitters visible to the shared render command.

Root cause

render_cloudformation and render_terraform created their registries inside private command functions with no composition hook. The only alternatives were duplicating the render command in Platform or moving Platform emitters into OSS; neither matches the existing ownership boundary.

Change

Add one process-startup registration hook per generator:

alien_cli::commands::render::register_terraform_registry_extension(...);
alien_cli::commands::render::register_cloudformation_registry_extension(...);

Each render invocation starts with the normal OSS built_in() registry and then applies the registered extension. The ordinary OSS alien binary registers nothing and behaves exactly as before. Duplicate registration fails immediately, matching the existing controller-extension contract.

End-to-end use

The Platform alien-clix composition root will register:

• alien_terraformx::register_platform_extensions
• alien_cloudformationx::register_platform_extensions

before delegating to the shared alien_cli::run_cli. Commands, parsing, output, and generators remain implemented in OSS Alien.

Verification

• cargo fmt -p alien-cli
• Platform integration compiles the real extension functions against these callback types and exercises generated Terraform/CloudFormation artifacts in the dependent composition PR.

[greptile-apps]

Confidence Score: 4/5

The PR appears safe to merge, with a non-blocking need for regression coverage around the new public registry-composition hooks.

Findings

1.  Registry composition lacks tests ▶

Fix with agent prompt

### Issue 1
crates/alien-cli/src/commands/render.rs:24-28
The new process-global hooks are not covered by a test that registers an extension and confirms a fresh registry contains both built-in and extension emitters. The only existing render unit test covers Azure preflight mutation, so incorrect callback wiring, skipped callbacks, or lost built-ins could reach downstream composed CLIs without being caught here. Please add isolated integration coverage for both generator hooks; using a separate test binary would avoid leaking the `OnceLock` state into other tests.

Note: If this suggestion doesn't match your team's coding style, reply to this and let me know. I'll remember it for next time!

---

For each issue above, determine whether it is valid and should be fixed. If so, fix it directly.

Summary

This PR adds process-startup hooks allowing composed Alien CLI binaries to extend the Terraform and CloudFormation emitter registries while preserving the normal built-in emitters.

• Stores one extension function per generator in a process-global OnceLock.
• Applies each registered extension to a fresh built-in registry for every render invocation.
• Leaves the ordinary OSS CLI behavior unchanged when no extension is registered.
• The implementation is straightforward, but the new public composition contract lacks repository-level regression coverage.

Diagram

%%{init: {'theme': 'neutral'}}%%
flowchart LR
    A[Composed CLI startup] --> B[Register Terraform extension]
    A --> C[Register CloudFormation extension]
    D[alien render] --> E{Requested format}
    E -->|Terraform| F[Create built-in TfRegistry]
    E -->|CloudFormation| G[Create built-in CfRegistry]
    B --> F
    C --> G
    F --> H[Apply extension]
    G --> I[Apply extension]
    H --> J[Generate Terraform module]
    I --> K[Generate CloudFormation template]

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[greptile-apps]

Registry composition lacks tests

The new process-global hooks are not covered by a test that registers an extension and confirms a fresh registry contains both built-in and extension emitters. The only existing render unit test covers Azure preflight mutation, so incorrect callback wiring, skipped callbacks, or lost built-ins could reach downstream composed CLIs without being caught here. Please add isolated integration coverage for both generator hooks; using a separate test binary would avoid leaking the OnceLock state into other tests.

Knowledge Base Used: Deployment and packaging

Prompt To Fix With AI

This is a comment left during a code review.
Path: crates/alien-cli/src/commands/render.rs
Line: 24-28

Comment:
**Registry composition lacks tests**

The new process-global hooks are not covered by a test that registers an extension and confirms a fresh registry contains both built-in and extension emitters. The only existing render unit test covers Azure preflight mutation, so incorrect callback wiring, skipped callbacks, or lost built-ins could reach downstream composed CLIs without being caught here. Please add isolated integration coverage for both generator hooks; using a separate test binary would avoid leaking the `OnceLock` state into other tests.

**Knowledge Base Used:** [Deployment and packaging](https://app.greptile.com/alien/-/custom-context/knowledge-base/alienplatform/alien/-/docs/deployment-and-packaging.md)

---

For each issue above, determine whether it is valid and should be fixed. If so, fix it directly.

Note: If this suggestion doesn't match your team's coding style, reply to this and let me know. I'll remember it for next time!