bugfix: truncate header sync percentage

[arejula27]

During IBD, if LoadingBlocks() is true (e.g. during a chainstate rebuild after a crash), the node rejects incoming headers from peers. The GUI has headers loaded from the block index on disk, but bestHeaderDate becomes stale over time.

After ~4 hours (HEADER_HEIGHT_DELTA_SYNC * nPowTargetSpacing), the time-based heuristic in modaloverlay.cpp considers headers as "not synced" and falls into the else branch, displaying "Unknown" for both blocks remaining and estimated time. Meanwhile, UpdateHeaderSyncLabel() computes a percentage that rounds up to 100.0%, creating a contradictory display: "Unknown. Syncing Headers (942188, 100.0%)". Please read issue #65 for more context.

This patch truncates the percentage to one decimal place instead of rounding, so it only shows 100.0% when headers are truly up to date. The same fix is applied to
UpdateHeaderPresyncLabel() for consistency.

Fixes #65 .

[DrahtBot]

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Possible places where named args for integral literals may be used (e.g. func(x, /*named_arg=*/0) in C++, and func(x, named_arg=0) in Python):

• QString::number(pct, 'f', 1) in src/qt/modaloverlay.cpp (ModalOverlay::UpdateHeaderSyncLabel)
• QString::number(pct, 'f', 1) in src/qt/modaloverlay.cpp (ModalOverlay::UpdateHeaderPresyncLabel)

^{2026-03-28 12:54:29}