Qualify invokelatest in the variables request handler

[davidanthoff]

This PR was opened by Claude (Claude Code) on David's behalf.

Problem

Base.run(::DebugSession) registers the variables handler as

msg_dispatcher[variables_request_type] = params -> invokelatest(variables_request, debug_session, params)

Base only exports invokelatest from Julia 1.9 on, and this package supports Julia 1.0+. On 1.0–1.8, every variables request therefore threw UndefVarError: invokelatest not defined in the dispatcher before variables_request ran. The client got an error response and the variables pane never filled in. CI stayed green because the existing variables tests call variables_request directly and never go through this line. (PR #139 hit the same problem in a test and fixed it there.)

Change

• src/packagedef.jl: call Base.invokelatest, like every other use in the package. I grepped src/ and test/ and this was the only unqualified invokelatest.
• test/test_debugsession.jl: new test item, "a variables request sent to the session is answered". It uses the existing DapClient snippet (with_debug_session(requests_after=...)) to send a real variables request over the wire after the debuggee has finished. It checks that the request gets a successful, empty response and that nothing reaches the session's error handler. This needed no new harness code.

The test only covers the request after the debuggee has finished, with a stale reference, not while paused on a real frame. That is enough to exercise the dispatcher line, and the existing harness has no hook for sending requests while the debuggee is paused.

Verification (run locally on Windows)

• Julia 1.8.5 without the fix: the new test fails, and the error handler receives UndefVarError(:invokelatest).
• With the fix: the full suite passes on Julia 1.0.5, 1.6.7, 1.8.5 and 1.13.1.

🤖 Generated with Claude Code