Merge pull request #674: fix(mobile): give a sideways drag on the terminal to the session swipe alone

Second merge of #674: the author pushed the thumb-arc handback from the review themselves (e8fc08be), byte-identical in code to the merge-time fix already here, so this brings their round in and keeps the browser test and docs added at merge.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

# Conflicts:
#	docs/wiki/Mobile-Guide.md
#	src/web/public/terminal-ui.js
#	test/session-swipe-gesture.test.ts

src/web/public/terminal-ui.js

@@ -1233,7 +1233,8 @@ Object.assign(CodemanApp.prototype, {
       // slop, so a diagonal drag cannot pan and scroll at the same time. 'swipe'
       // is a sideways drag on a terminal that cannot pan: it is the session
       // swipe's (SwipeHandler, mobile-handlers.js), so it neither scrolls nor
-      // ends as a tap on the session being left. Published per gesture as
+      // ends as a tap on the session being left, until it drifts past the
+      // swipe's vertical limit and becomes a 'y' scroll. Published per gesture as
       // `this._terminalGestureAxis`, which SwipeHandler reads to stand aside
       // for a scroll or a pan.
       let panAxis = null;
@@ -1370,7 +1371,8 @@ Object.assign(CodemanApp.prototype, {
             ev.preventDefault();
             if (panAxis === 'swipe') {
               // Past the swipe's own vertical drift limit the session swipe has
-              // given up, so the drag is a scroll after all: hand it to 'y'.
+              // given up, so the drag is a scroll after all (a thumb arc whose
+              // first move leaned sideways): hand it to 'y'.
               const drift = typeof SwipeHandler !== 'undefined' ? SwipeHandler.maxVerticalDrift : 50;
               if (Math.abs(touchY - touchStartY) <= drift) return;
               panAxis = 'y';