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Description

This PR fixes issue #36994 where the cilium clustermesh disconnect command doesn't provide any feedback when run without a destination context.

Problem

When running cilium clustermesh disconnect without specifying a destination context via the --destination-context flag, the command silently executes but doesn't display any message or error to the user. This creates a confusing user experience as the user doesn't know what happened.

Current behavior:

cilium clustermesh disconnect -n cilium-system
ℹ️ Configuring Cilium in cluster kind-mgmt to disconnect from cluster

<no further output>

Solution

This PR adds a check at the beginning of the DisconnectWithHelm function to verify if a destination context was provided. If not, it returns a clear error message explaining that a destination context is required.

New behavior:

cilium clustermesh disconnect -n cilium-system

Error: Unable to disconnect clusters: no destination context specified, use --destination-context to specify which cluster to disconnect from

This makes the CLI behavior consistent with the case where an invalid destination context is provided, which already shows an error message.

Testing Information

This PR includes a unit test to verify the error behavior:

1. TestClusterMeshDisconnectWithoutDestination in cilium-cli/cli/clustermesh_test.go directly tests the DisconnectWithHelm function and verifies that it returns the correct error message when no destination context is provided.

This test ensures that the error message is displayed correctly to users when they attempt to use the clustermesh disconnect command without specifying a destination context.

To run the test

cd cilium-cli
go test -v ./cli -run TestClusterMeshDisconnectWithoutDestination

The test validates our fix by confirming the error message is exactly:
"no destination context specified, use --destination-context to specify which cluster to disconnect from"

Fixes: #36994

Fix cli disconnect error message