aimgr list <pattern> --format=json returns plain text when no results instead of empty JSON array

[hk9890]

Bug

When running aimgr list <pattern> --format=json and no installed resources match the pattern, aimgr returns a plain text message instead of valid JSON.

Steps to Reproduce

aimgr list agent --format=json

Actual Output

No installed resources match pattern 'agent'.

Expected Output

[]

Impact

Any tooling that calls aimgr list --format=json and parses the output as JSON will crash with:

Unexpected token 'N', "No resourc"... is not valid JSON

This breaks setup wizards and scripts that use the JSON output to drive further logic (e.g. package installation flows).

Fix

When --format=json is specified, always return valid JSON — use [] for empty results instead of a human-readable text message.