XAML injection dump latency (~7.7s per dump)

[asklar]

Summary

Each XAML dump that injects the TAP DLL takes ~7.7s consistently (measured on Calculator, 617 nodes, warm). This is slow enough to hurt usability and makes --watch\ impractical for XAML/WinUI targets.

Evidence

\
dump6: 617 elements (7642 ms)
dump7: 617 elements (7789 ms)
dump8: 617 elements (7921 ms)
\\

Investigate

• Pipe connect/read waits (\xaml_diag_common.cpp\ uses 15s overlapped waits), connection-name iteration, any settle delays, and TAP-side tree serialization.
• Determine whether a fixed sleep or a per-node cost dominates; optimize or make the wait adaptive (return as soon as the tree is delivered).
• Found during PR Durable element identity (stable keys) + --query #26 validation. Not a correctness bug.