source_window was defined around line 880 but referenced in the
before.event_stopped listener inside ensure_dapui (around line 730).
Lua closures only capture upvalues that existed as locals BEFORE
the closure was created — source_window fell back to a global
lookup which resolved to nil, breaking every attempt to start a
debug session.
Forward-declare `local source_window` at the top of the file and
assign (rather than declare) the implementation later. Both
ensure_dapui's listener and the later call sites now refer to the
same upvalue.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
swaitsandClaude Opus 4.6
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