[fix] Make ID the source of truth for vpc and subnet names

[cbbond]

What this PR does / why we need it:

We currently filter the Linode API's ListVPCs response by both VPC ID and label when deciding whether to create a new VPC or update an existing one. This PR removes the latter filter and only checks for existing VPCs that match the ID found on the LinodeVPC resource. VPC ID is immutable and should be a sufficient filter for finding VPCs. Without this fix, any change to the VPC's label outside of CAPL will result in CAPL trying to create a new VPC when the underlying resource still exists.

Similarly, we currently build a map of subnets by label based on a list of VPC subnets we get from the Linode API. This method is vulnerable to the same issue in which any change to a subnet label after creation will prevent CAPL from reconciling the subnet further. This PR fixes this issue by building two maps that are keyed by both label and subnet ID. The code defaults to ID where possible but falls back to the label when the subnet ID is not yet populated (i.e. the first time we are reconciling a new subnet).

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged): N/A

Special notes for your reviewer:

• Existing behavior is preserved for subnets, we either adopt an existing subnet or create a new one based on whether the subnet is in the API response map
• The Linode API is the new source of truth for subnet labels, i.e. if a subnet label is updated via CloudManager then CAPL will adopt that label and update the LinodeVPC spec
• Added a test case where both the VPC and subnet labels change

TODOs:

• squashed commits
• includes documentation
• adds unit tests
• adds or updates e2e tests

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 63.25%. Comparing base (eb218ad) to head (ceb865d).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #807      +/-   ##
==========================================
+ Coverage   63.16%   63.25%   +0.08%     
==========================================
  Files          71       71              
  Lines        7292     7304      +12     
==========================================
+ Hits         4606     4620      +14     
+ Misses       2415     2414       -1     
+ Partials      271      270       -1     

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[Copilot]

Pull Request Overview

This PR fixes an issue where CAPL (Cluster API Provider Linode) fails to properly reconcile VPCs and subnets when their labels are changed outside of CAPL. The fix makes resource IDs the primary source of truth instead of relying on label matching.

Key changes:

• Removes label-based filtering when looking up existing VPCs, using only VPC ID
• Implements dual mapping for subnets (by both ID and label) to handle label changes gracefully
• Updates subnet reconciliation logic to prefer ID-based lookups with label fallback

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
internal/controller/linodevpc_controller_helpers.go	Core logic changes to remove label filtering for VPCs and implement dual subnet mapping
internal/controller/linodevpc_controller_test.go	New test case covering VPC and subnet label changes

Comments suppressed due to low confidence (2)

internal/controller/linodevpc_controller_helpers.go:88

• [nitpick] The variable name 'subnetsByLabel' uses camelCase inconsistent with Go naming conventions. It should be 'subnetsByLabel' or consider 'subnetConfigByLabel' for clarity.

	subnetsByLabel := make(map[string]SubnetConfig, len(vpc.Subnets))

internal/controller/linodevpc_controller_helpers.go:89

• The variable name 'subnetsById' should be 'subnetsByID' to follow Go naming conventions where 'ID' should be capitalized.

	subnetsById := make(map[int]SubnetConfig, len(vpc.Subnets))

[komer3]

LGTM!