fix(display): don't emit stray newline on repaint of empty buffer

[dbactual]

Problem

Repainting an empty input line with a zero-width primary prompt emitted a spurious newline — one blank line at startup and one more per repaint of an empty buffer (e.g. backspace on an empty line), causing the display to scroll and drift.

Root cause

In internal/display/refresh.go, displayLine() computed:

wrappedAtRightEdge := e.lineCol == 0 && len(line) > 0

line is the rendered string and always contains ANSI escape codes (selection/background resets, autosuggest styling) even when the input buffer is empty, so len(line) > 0 is always true. When the primary prompt is zero-width, e.lineCol == 0 too, so the forced-wrap newline fired on every repaint of an empty buffer.

Fix

Test the actual buffer length instead of the rendered string's:

wrappedAtRightEdge := e.lineCol == 0 && e.line.Len() > 0

Testing

• go build ./... passes
• go test ./internal/display/ passes
• Manual: with rl.Prompt.Primary(func() string { return "" }), no newline is emitted at startup or on backspace of an empty line; wrapped long lines still print correctly

Verified via a pty harness while integrating v1.3.0.

[maxlandon]

Thanks for the fix !

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 39.82%. Comparing base (8c6cfe7) to head (5b14153).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #123   +/-   ##
=======================================
  Coverage   39.82%   39.82%           
=======================================
  Files          60       60           
  Lines        9594     9594           
=======================================
  Hits         3821     3821           
  Misses       5679     5679           
  Partials       94       94           

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.