[David-the-happy-piglet]

The client parses JSON responses and then calls .get() on the decoded value. A response such as [], null, or a string therefore raises AttributeError, bypassing the U2CliError handling in is_running().

Validate that the response envelope is a JSON object before accessing its fields. Invalid envelopes raise U2CliError, and is_running() returns false. Valid envelopes can still contain results of any JSON type; remote error handling is unchanged.

Validation on macOS with Python 3.12.15:

• Before the fix, 16 new regression cases failed and 9 controls passed; all 25 pass after the fix.
• Real loopback HTTP checks cover eight non-object responses and a valid status response.
• Independent review found no issues. The offline suite reports 96 passed and one existing no-argument CLI failure addressed separately by fix: show successful help for an empty u2cli invocation #1198.
• Import formatting, diff checks, and source/wheel builds passed.

Android device tests and the cross-platform CI matrix were not run locally.