Harden timing-sensitive tests: replace Process.sleep with proper synchronization

[ppsplus-bradh]

Problem

Several tests use Process.sleep for synchronization instead of message-based waiting (assert_receive, MockCLI.poll_until, etc.). These are brittle and can fail on slow or fast CI runners.

Additionally, some assertions are effectively meaningless due to overly loose conditions.

Affected Tests

Process.sleep used for synchronization

test/claude_code/session_test.exs (lines 110, 118, 311, 324, 453, 461, 811, 851)

• Process.sleep(50) between action and state inspection
• Should use assert_receive or poll-based waiting

test/claude_code_test.exs (lines 197, 213)

• Process.sleep(100) after stop() before checking Process.alive?
• Should poll or use monitor-based waiting

test/claude_code/supervisor_test.exs (lines 65, 115, 211, 237, 264)

• Process.sleep(100) for supervisor restart/shutdown timing
• Should use assert_receive on supervisor events or poll child counts

Meaningless assertions

test/claude_code/supervisor_test.exs (line 117)

• assert ClaudeSupervisor.count_sessions(supervisor) >= 0 — always true, provides no test value
• Should assert a specific expected count or use polling to wait for a known state

Recommended Approach

The codebase already has a good pattern in port_test.exs using MockCLI.poll_until:

MockCLI.poll_until(fn ->
  state = :sys.get_state(adapter)
  if condition_met?(state), do: {:ok, state}, else: :retry
end, timeout: 5000)

Replace Process.sleep + assertion pairs with this pattern or assert_receive where applicable.