fix: terminal flicker regression — move viewport clear inside dimension guard

Three fixes from the WIP flicker branch that were lost during master merges:

1. Move viewport clear (\x1b[3J\x1b[H\x1b[2J) inside the dimension-change
   guard so it only fires when cols/rows actually change. Previously every
   resize event cleared the screen even at identical dimensions, causing
   visible flicker with no subsequent Ink redraw to repaint.

2. Sync _lastResizeDims in sendResize() so restoreTerminalSize() doesn't
   trigger a redundant viewport clear on the next throttledResize tick.

3. Add didScroll tracking to touch events — tap (no scroll) now refocuses
   xterm's hidden textarea, fixing mobile keyboard input routing after
   tapping the terminal area.

src/web/public/terminal-ui.js

@@ -179,6 +179,7 @@ Object.assign(CodemanApp.prototype, {
       // Accumulate sub-line pixel deltas so slow swipes still scroll
       let pixelAccum = 0;
 
+      let didScroll = false; // track whether touchmove fired (tap vs scroll)
       container.addEventListener(
         'touchstart',
         (ev) => {
@@ -187,6 +188,7 @@ Object.assign(CodemanApp.prototype, {
             velocity = 0;
             pixelAccum = 0;
             isTouching = true;
+            didScroll = false;
             lastTime = 0;
             if (scrollFrame) {
               cancelAnimationFrame(scrollFrame);
@@ -201,6 +203,7 @@ Object.assign(CodemanApp.prototype, {
         'touchmove',
         (ev) => {
           if (ev.touches.length === 1 && isTouching) {
+            didScroll = true;
             const touchY = ev.touches[0].clientY;
             const delta = touchLastY - touchY; // positive = scroll down
             pixelAccum += delta;
@@ -225,6 +228,12 @@ Object.assign(CodemanApp.prototype, {
           if (!scrollFrame && Math.abs(velocity) > 0.3) {
             scrollFrame = requestAnimationFrame(scrollLoop);
           }
+          // Tap (no scroll): refocus xterm's hidden textarea so keyboard input
+          // routes back to the terminal. Without this, a tap on the terminal area
+          // consumes the touch event but xterm's textarea never regains focus.
+          if (!didScroll && this.terminal) {
+            this.terminal.focus();
+          }
         },
         { passive: true }
       );
@@ -284,22 +293,6 @@ Object.assign(CodemanApp.prototype, {
           }
           this.flushFlickerBuffer();
         }
-        // Clear viewport + scrollback for Ink-based sessions before sending SIGWINCH.
-        // fitAddon.fit() reflows content: lines at old width may wrap to more rows,
-        // pushing overflow into scrollback. Ink's cursor-up count is based on the
-        // pre-reflow line count, so ghost renders accumulate in scrollback.
-        // Fix: \x1b[3J (Erase Saved Lines) clears scrollback reflow debris,
-        // then \x1b[H\x1b[2J clears the viewport for a clean Ink redraw.
-        const activeResizeSession = this.activeSessionId ? this.sessions.get(this.activeSessionId) : null;
-        if (
-          activeResizeSession &&
-          activeResizeSession.mode !== 'shell' &&
-          !activeResizeSession._ended &&
-          this.terminal &&
-          this.isTerminalAtBottom()
-        ) {
-          this.terminal.write('\x1b[3J\x1b[H\x1b[2J');
-        }
         // Skip server resize while mobile keyboard is visible — sending SIGWINCH
         // causes Ink to re-render at the new row count, garbling terminal output.
         // Local fit() still runs so xterm knows the viewport size for scrolling.
@@ -311,6 +304,24 @@ Object.assign(CodemanApp.prototype, {
           const rows = dims ? Math.max(dims.rows, MIN_ROWS) : MIN_ROWS;
           // Only send resize if dimensions actually changed
           if (!this._lastResizeDims || cols !== this._lastResizeDims.cols || rows !== this._lastResizeDims.rows) {
+            // Clear viewport + scrollback ONLY when dimensions actually change.
+            // fitAddon.fit() reflows content: lines at old width may wrap to more rows,
+            // pushing overflow into scrollback. Ink's cursor-up count is based on the
+            // pre-reflow line count, so ghost renders accumulate in scrollback.
+            // Fix: \x1b[3J (Erase Saved Lines) clears scrollback reflow debris,
+            // then \x1b[H\x1b[2J clears the viewport for a clean Ink redraw.
+            // IMPORTANT: Only clear when we're actually sending SIGWINCH (dims changed).
+            // Clearing without a subsequent Ink redraw leaves the terminal blank.
+            const activeResizeSession = this.activeSessionId ? this.sessions.get(this.activeSessionId) : null;
+            if (
+              activeResizeSession &&
+              activeResizeSession.mode !== 'shell' &&
+              !activeResizeSession._ended &&
+              this.terminal &&
+              this.isTerminalAtBottom()
+            ) {
+              this.terminal.write('\x1b[3J\x1b[H\x1b[2J');
+            }
             this._lastResizeDims = { cols, rows };
             fetch(`/api/sessions/${this.activeSessionId}/resize`, {
               method: 'POST',
@@ -1348,6 +1359,10 @@ Object.assign(CodemanApp.prototype, {
     if (this.fitAddon) this.fitAddon.fit();
     const dims = this.getTerminalDimensions();
     if (!dims) return;
+    // Update _lastResizeDims so the throttledResize handler won't redundantly
+    // clear the terminal for the same dimensions (which would blank the screen
+    // without a subsequent Ink redraw to repaint it).
+    this._lastResizeDims = { cols: dims.cols, rows: dims.rows };
     // Fast path: WebSocket resize
     if (this._wsReady && this._wsSessionId === sessionId) {
       try {