Support pinch-to-zoom for reader text size in the article view

Pinching in ReaderScreen's article WebView now adjusts the same
persisted reader font size the Settings slider controls, instead of
doing nothing (WebView's own page zoom was never enabled, so a pinch
previously had no effect at all).

A ScaleGestureDetector is fed through setOnTouchListener, which always
returns false so it never consumes the touch -- WebView's existing
one-finger scrolling, link taps and long-press-link handling are
unaffected, since ScaleGestureDetector only fires once a second pointer
is down. During the gesture the WebView is scaled live via View.scaleX/
scaleY for immediate visual feedback; at gesture end the scale resets
to 1x and the computed, clamped font size is persisted, which drives
ReaderScreen's existing content-reload-on-fontSizePx-change path to
re-render the actual HTML at the new size.

TDD: pinchZoomFontSizePx (the pure scale-factor -> clamped-px
calculation) was written test-first, red on a TODO() stub, green on the
real implementation -- covered by SettingsTest.

newReaderWebView grew from 6 to 8 parameters to carry the new gesture
hooks, which pushed it over detekt's LongParameterList threshold;
bundled all of its callbacks into a ReaderWebViewCallbacks data class
rather than baselining past it, updating both call sites (ReaderScreen,
LinkReaderScreen). ReaderContent gained no new parameter -- it now
independently remembers its own Settings instance to persist the
pinch-committed size, matching how it already remembers its own db and
scope rather than threading them from ReaderScreen.

LinkReaderScreen's WebView is untouched: it doesn't read the reader
font size setting at all today, so wiring pinch-zoom there would be a
separate, unrelated fix.

1 files changed, 7 insertions, 0 deletions

diff --git a/app/src/main/java/org/terst/feedreader/data/Settings.kt b/app/src/main/java/org/terst/feedreader/data/Settings.kt
index be3e809..ebeba6c 100644
--- a/app/src/main/java/org/terst/feedreader/data/Settings.kt
+++ b/app/src/main/java/org/terst/feedreader/data/Settings.kt
@@ -13,6 +13,7 @@ import kotlinx.coroutines.flow.Flow
 import kotlinx.coroutines.flow.first
 import kotlinx.coroutines.flow.map
 import kotlinx.coroutines.withContext
+import kotlin.math.roundToInt
 
 val Context.settingsDataStore by preferencesDataStore(name = "settings")
 
@@ -38,6 +39,12 @@ private const val READER_FONT_SIZE_MIN_PX = 14
 private const val READER_FONT_SIZE_MAX_PX = 28
 val READER_FONT_SIZE_RANGE_PX = READER_FONT_SIZE_MIN_PX..READER_FONT_SIZE_MAX_PX
 
+// Pure so the pinch-to-zoom math is testable without a WebView/gesture detector in the loop --
+// ReaderWebView.kt calls this once per gesture (at pinch-end, with the cumulative scale factor
+// accumulated across the whole gesture), not per touch-move frame.
+fun pinchZoomFontSizePx(basePx: Int, scaleFactor: Float): Int =
+    (basePx * scaleFactor).roundToInt().coerceIn(READER_FONT_SIZE_RANGE_PX.first, READER_FONT_SIZE_RANGE_PX.last)
+
 /** Stash connection settings, configured on the Settings screen. Both blank until set. */
 class Settings(private val context: Context) {
     val stashBaseUrl: Flow<String> =