Apply suggestions from code review

Co-authored-by: Simon Gerber <[email protected]>

Author: HappyTetrahedron

docs/modules/SDDs/pages/0033-commodore-component-instance-versioning.adoc

@@ -1,8 +1,8 @@
 = SDD 0033 - Commodore Component Instance Versioning
 
 :sdd_author:    Aline Abler
-:sdd_owner:     Aline Abler
-:sdd_reviewers: SIG
+:sdd_owner:     Aldebaran
+:sdd_reviewers: Simon Gerber
 :sdd_date:      2025-01-08
 :sdd_status:    draft
 include::partial$meta-info-table.adoc[]
@@ -24,17 +24,13 @@ Commodore does not currently support specifying different component versions for
 
 * Define how different versions for each component instance can be specified and generated.
 
-=== Non-Goals
-
-
-
 == Design Proposal
 
 Commodore will leverage the existing configuration options in `.parameters.components` to retrieve version information for specific instances.
 Instance versions can be specified in `.parameters.components.<instance-name>` and override the value specified in `.parameters.components.<component-name>`.
 Even if all instances provide their own version, a version for the base component (`.parameters.components.<component-name>`) must still be specified.
 
-Component authors must explicitly declare that their component supports multi-versioning.
+Component authors must explicitly declare that their component supports multi-versioning by setting component parameter `_metadata.multi_versioning=true`.
 In a valid catalog, all used versions of the same component must advertise this support.
 
 Components with multi-versioning support must ensure they create no file conflicts when downloading dependencies.
@@ -51,24 +47,22 @@ Similarly, if the component includes a Jsonnet library that is made available to
 We can clone the repository of the base component and create a separate worktree for each instance to check out the correct version.
 
 If the instance version specifies a different URL from the base component, more work is needed: in this case, we clone the changed repository for the instance and create a worktree from that.
-
-This means that if two instances both override the URL to the same value, this repository is cloned twice, which can impact performance.
-However, since this only affects instances which override the repository URL, the impact is tolerable.
+We can leverage the existing MultiDependency architecture to avoid cloning the same repository multiple times.
 
 === Risks and Drawbacks
 
 * Since the Jsonnet dependencies and libraries are all provided from a single component version, there is a risk for some combinations of versions not compiling properly due to version compatibility issues.
 ** Even if a component's dependencies are sufficiently backwards-compatible at the moment, it's possible for future changes to break compatibility.
 This might force a component author to remove multi-version support in higher component versions, causing a catalog to stop compiling if either component instance is updated.
-* Overriding the repository URL in a component instance always causes a new repository to be cloned - even if the same URL is used in multiple instances.
 
 == Alternatives
 
 === Automatically detecting multi-version support
 
-It could be possible to automatically determine whether a component supports multi-versioning, by way of checking whether the `${_base_directory}` parameter is used in the component's compile configuration.
+We could try to automatically determine whether a component supports multi-versioning, by way of checking whether the `${_base_directory}` parameter is used in the component's compile configuration and for Jsonnet expressions that refer to downloaded data.
 However, automatically declaring components to be "safe for multi-versioning" carries some risk - even if a component is configured accordingly, it is not guaranteed that its provided Jsonnet libraries and/or its Jsonnet dependencies work if used across versions.
-Therefore, we deem it safer to let component authors decide if multi-versioning is safe to use for their component.
+Additionally, so far we've defined explicit flags for components to indicate that they support optional features, such as multiple instances.
+For all of those reasons, we've decided that component authors must explicitly declare whether multi-versioning is safe to use for their component.
 
 === Supporting different versions of Jsonnet dependencies per instance