fix: truncate labels for deletion hook resources

[choejwoo]

Closes #27527

While reproducing the issue locally I found that the missing label truncation is not specific to PreDelete, PostDelete hooks and applications that declare both hook types together hit the exact same failure as soon as the Application name exceeds 63 characters. In every one of those cases the Application gets stuck in Terminating because Kubernetes rejects the hook resource with error like below.

The fix routes hook resources through ResourceTracking.SetAppInstance, so they follow the same path as regularly synced resources. The truncation logic was extracted into TruncateLabel helper. The label value is clamped to 63 characters and the full Application name is preserved in the argocd.argoproj.io/tracking-id annotation.

2026-04-26.2.53.27.mov

The legacy label-only mode is left unchanged on purpose #18237.
Applications with names of 63 characters or fewer, and applications without deletion hooks, are unaffected.

Checklist:

• Either (a) I've created an enhancement proposal and discussed it with the community, (b) this is a bug fix, or (c) this does not need to be in the release notes.
• The title of the PR states what changed and the related issues number (used for the release note).
• The title of the PR conforms to the Title of the PR
• I've included "Closes [ISSUE #]" or "Fixes [ISSUE #]" in the description to automatically close the associated issue.
• I've updated both the CLI and UI to expose my feature, or I plan to submit a second PR with them.
• Does this PR require documentation updates?
• I've updated documentation as required by this PR.
• I have signed off all my commits as required by DCO
• I have written unit and/or e2e tests for my change. PRs without these are unlikely to be merged.
• My build is green (troubleshooting builds).
• My new feature complies with the feature status guidelines.
• I have added a brief description of why this PR is necessary and/or what this PR solves.
• Optional. My organization is added to USERS.md.
• Optional. For bug fixes, I've indicated what older releases this fix should be cherry-picked into (this may or may not happen depending on risk/complexity).

[bunnyshell]

❌ Preview Environment deleted from Bunnyshell

Available commands (reply to this comment):

• 🚀 /bns:deploy to deploy the environment

[Copilot]

Pull request overview

Fixes Application deletion hooks getting rejected by Kubernetes when app instance labels exceed the 63-character label-value limit by ensuring hook resources use the same resource-tracking path (and truncation behavior) as normal synced resources.

Changes:

• Extracted label truncation logic into a reusable TruncateLabel helper and added unit tests for it.
• Updated deletion hook creation to apply tracking metadata via ResourceTracking.SetAppInstance, honoring the configured tracking method.
• Added a controller regression test for long application names during PreDelete hook creation.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

File	Description
util/argo/resource_tracking.go	Introduces TruncateLabel and refactors SetAppInstance to reuse it for annotation+label tracking.
util/argo/resource_tracking_test.go	Adds direct unit tests for TruncateLabel.
controller/hook.go	Routes hook resources through ResourceTracking.SetAppInstance using configured tracking method + installation ID.
controller/appcontroller_test.go	Adds a regression test for long app names when creating PreDelete hooks.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[codecov]

Codecov Report

❌ Patch coverage is 65.51724% with 10 lines in your changes missing coverage. Please review.
✅ Project coverage is 63.52%. Comparing base (d654515) to head (c840fe8).
⚠️ Report is 31 commits behind head on master.

Files with missing lines	Patch %	Lines
controller/hook.go	40.00%	3 Missing and 3 partials ⚠️
util/argo/resource_tracking.go	78.94%	1 Missing and 3 partials ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master   #27542   +/-   ##
=======================================
  Coverage   63.51%   63.52%           
=======================================
  Files         417      417           
  Lines       57102    57112   +10     
=======================================
+ Hits        36269    36280   +11     
+ Misses      17431    17426    -5     
- Partials     3402     3406    +4     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[ppapapetrou76]

The code looks good to me and I like the way the Truncate function sets the caller expectations ( it doesn't trim short values for instance )

Do you think we can add the following unit test?

PostDelete for a long name just like PreDelete_HookIsCreatedForLongAppName

[choejwoo]

@ppapapetrou76

Thanks for the review! I've added a unit test for PostDelete_HookIsCreatedForLongAppName as well.

[ppapapetrou76]

LGTM 🏅 - thanks for addressing my comments

[dmarquez-splunk]

Anything blocking this from getting merged?

[snakethatlovesstaticlibs]

Hello, would it be possible to cherry pick this for 3.3 and 3.4?

[argo-cd-cherry-pick-bot]

🍒 Cherry-pick PR created for 3.4: #27714

[argo-cd-cherry-pick-bot]

❌ Cherry-pick failed for 3.3. Please check the workflow logs for details.