Use exact container height for mobile viewport measurement

Instead of subtracting a hardcoded row count from window.innerHeight,
measure the terminal frame's pixel height via onLayout and pass it into
the WebView's measureFitDimensions. This gives pixel-accurate row
calculations regardless of accessory bar height or safe-area insets.

Co-authored-by: Orca <help@stably.ai>

mobile/app/h/[hostId]/session/[worktreeId].tsx

@@ -155,6 +155,10 @@ export default function SessionScreen() {
   const activeHandleRef = useRef<string | null>(null)
   const subscribeSeqRef = useRef<Map<string, number>>(new Map())
   const sendingRef = useRef(false)
+  // Why: tracks the pixel height of the terminal frame so measureFitDimensions
+  // can use the exact container height instead of relying on window.innerHeight,
+  // which can overstate the visible area due to layout timing.
+  const terminalFrameHeightRef = useRef<number>(0)
 
   const canSend = connState === 'connected' && activeHandle != null
 
@@ -189,7 +193,9 @@ export default function SessionScreen() {
   const measureViewportOnce = useCallback(
     async (handle: string) => {
       if (viewportMeasuredRef.current) return
-      const dims = await getTerminalRef(handle)?.measureFitDimensions()
+      const dims = await getTerminalRef(handle)?.measureFitDimensions(
+        terminalFrameHeightRef.current || undefined
+      )
       if (dims) {
         viewportRef.current = dims
         viewportMeasuredRef.current = true
@@ -255,7 +261,9 @@ export default function SessionScreen() {
             // resubscribe so the server gets the viewport and phone-fits.
             if (!viewportMeasuredRef.current) {
               void (async () => {
-                const dims = await getTerminalRef(handle)?.measureFitDimensions()
+                const dims = await getTerminalRef(handle)?.measureFitDimensions(
+                  terminalFrameHeightRef.current || undefined
+                )
                 if (dims && !viewportMeasuredRef.current) {
                   viewportRef.current = dims
                   viewportMeasuredRef.current = true
@@ -816,7 +824,12 @@ export default function SessionScreen() {
             </Pressable>
           </View>
         ) : (
-          <View style={styles.terminalFrame}>
+          <View
+            style={styles.terminalFrame}
+            onLayout={(e) => {
+              terminalFrameHeightRef.current = e.nativeEvent.layout.height
+            }}
+          >
             {terminals.map((terminal) => (
               <TerminalPaneView
                 key={terminal.handle}

mobile/src/terminal/TerminalWebView.tsx

@@ -8,7 +8,7 @@ export type TerminalWebViewHandle = {
   write: (data: string) => void
   init: (cols: number, rows: number, initialData?: string) => void
   clear: () => void
-  measureFitDimensions: () => Promise<{ cols: number; rows: number } | null>
+  measureFitDimensions: (containerHeight?: number) => Promise<{ cols: number; rows: number } | null>
   resetZoom: () => void
 }
 
@@ -21,7 +21,7 @@ type TerminalMessage =
   | { type: 'write'; id?: number; data: string }
   | { type: 'init'; id?: number; cols: number; rows: number; initialData?: string }
   | { type: 'clear'; id?: number }
-  | { type: 'measure'; id?: number }
+  | { type: 'measure'; id?: number; containerHeight?: number }
   | { type: 'reset-zoom'; id?: number }
 
 // Why: TUI apps (Claude Code / Ink) emit escape codes with absolute cursor
@@ -287,7 +287,7 @@ const XTERM_HTML = `<!DOCTYPE html>
     }
   }
 
-  function measureFitDimensions() {
+  function measureFitDimensions(containerHeightPx) {
     if (!term || !term.element) {
       notify({ type: 'measure-result', cols: null, rows: null });
       return;
@@ -307,13 +307,16 @@ const XTERM_HTML = `<!DOCTYPE html>
       return;
     }
     var vpWidth = window.innerWidth;
-    var vpHeight = window.innerHeight;
+    // Why: prefer the container height passed from React Native over
+    // window.innerHeight. The RN layout system knows the exact pixel
+    // height of the terminal frame after the accessory/input bars are
+    // subtracted, whereas innerHeight can overstate the visible area
+    // due to layout timing or safe-area insets.
+    var vpHeight = (typeof containerHeightPx === 'number' && containerHeightPx > 0)
+      ? containerHeightPx
+      : window.innerHeight;
     var cols = Math.floor(vpWidth / cellWidth);
-    // Why: subtract 2 rows so the bottom terminal line is never covered
-    // by the accessory bar. The WebView's innerHeight can slightly
-    // overstate the visible area due to layout timing or safe-area
-    // insets, causing the last rows to render behind the overlay.
-    var rows = Math.max(8, Math.floor(vpHeight / cellHeight) - 2);
+    var rows = Math.max(8, Math.floor(vpHeight / cellHeight));
     notify({ type: 'measure-result', cols: cols, rows: rows });
   }
 
@@ -334,7 +337,7 @@ const XTERM_HTML = `<!DOCTYPE html>
       writesDraining = false;
       if (term) { term.clear(); term.reset(); }
     } else if (msg.type === 'measure') {
-      measureFitDimensions();
+      measureFitDimensions(msg.containerHeight);
     } else if (msg.type === 'reset-zoom') {
       applyFitScale();
     }
@@ -576,12 +579,14 @@ export const TerminalWebView = forwardRef<TerminalWebViewHandle, Props>(function
       clear() {
         postMessage({ type: 'clear' })
       },
-      measureFitDimensions(): Promise<{ cols: number; rows: number } | null> {
+      measureFitDimensions(
+        containerHeight?: number
+      ): Promise<{ cols: number; rows: number } | null> {
         if (!isWebReadyRef.current) return Promise.resolve(null)
         return new Promise((resolve) => {
           measureResolveRef.current?.(null)
           measureResolveRef.current = resolve
-          sendToWebView({ type: 'measure' })
+          sendToWebView({ type: 'measure', containerHeight })
           // Why: if the WebView doesn't respond within 2s (e.g., xterm
           // failed to load), resolve null so the caller can disable
           // Fit to Phone rather than hanging indefinitely.