[vishnujayvel]

What

Enabling Powerline mode with manual separator widgets in a line permanently
deleted those widgets (buildEnabledPowerlineSettings(settings, true)
filtered every type === 'separator' item out of settings.lines).
Disabling Powerline only flips powerline.enabled back to false — it never
restores anything, because by then the separators are already gone. This
closes #531: a manual separator now survives an enable → disable round trip.

Why

renderer.ts already keeps flex-separator widgets in the configuration
through Powerline rendering and treats them as merge-run boundaries
(isSeparatorBoundary), filtering them only out of the final rendered
glyphs. That's not the same as "inert": a flex-separator still drives
active layout underneath — it sizes flex slots, advances segment offsets,
and produces the start/end caps used by the flex-width distribution pass.
A separator widget, once it stops being deleted, gets the same
config-preservation and merge-boundary treatment flex-separator already
has, and likewise disappears from the rendered glyphs — but it doesn't pick
up that flex-layout role; it's only ever a boundary, never a spacing
control.

Being a merge-run boundary is also not a no-op. If a retained separator
sits between two widgets that would otherwise merge (e.g. one of them has
merge: 'no-padding'), hasNextRenderedWidgetBeforeSeparator now stops that
merge once Powerline is enabled, so the padding that merge was suppressing
comes back, and the two widgets no longer share a position in the
merge-aware theme color sequence (the color index only advances between
widgets that aren't merged with each other). So enabling Powerline on a line
with a retained separator inside a merged, themed group can change that
group's grouping, padding and color assignment — an expected consequence of
keeping the separator instead of deleting it, not a defect, but a real
rendering effect rather than a no-op.

How

• buildEnabledPowerlineSettings no longer takes a removeManualSeparators
  flag and never filters settings.lines. The parameter had no remaining
  use once nothing is filtered.
• Both call sites in PowerlineSetup.tsx (the no-existing-separators path
  and the confirm-dialog path) call the function with just settings.
• The enable confirmation dialog (shown when a line already has manual
  separators) warned that enabling would remove them. That's no longer true,
  so the copy now says what actually happens: separators stay in the
  configuration but aren't shown while Powerline is enabled.

Tests

• src/utils/__tests__/powerline-settings.test.ts: the test that encoded
  the destructive behavior as a requirement now asserts the separator is
  kept alongside a flex separator when enabling. Added a round-trip test
  that enables then disables and asserts the separator is still in
  settings.lines.
• src/tui/components/__tests__/PowerlineSetup.test.ts: existing suite,
  unchanged, still passes — it doesn't exercise the t-toggle/confirm-dialog
  callback (checked by inspection), so no new UI-level test was added for the
  reworded warning text; the coverage above is at the settings-helper level
  where the actual logic change lives.
• bun test src/utils/__tests__/powerline-settings.test.ts: 4 pass, 0 fail.
• bun test src/tui/components/__tests__/PowerlineSetup.test.ts: 8 pass, 0 fail.
• bun run lint (tsc --noEmit && eslint . --max-warnings=0): clean.
• Full suite was not run for this change.