fix(terminal): keep the terminal resize observer alive across SSE init

initTerminal() creates the ResizeObserver on #terminalContainer once per page,
and _resetAllAppState() (run by handleInit on EVERY SSE init, page load
included) disconnected and dropped it. From the first init on, only a window
resize refit the terminal, so anything that resized just the terminal box left
xterm at its old row count with the bottom rows clipped behind the toolbar.

Pre-existing since the March app.js module split, but this release makes it
constant: #538's state rows grow and shrink the header whenever a session
starts or stops working, and #544 reserves lineage room when the first child
appears. Measured on the beta: header 115 -> 170 px, container 743 -> 688 px,
xterm stayed at 35 rows (32 fit) until a tab switch. initTerminal() already
disconnects any previous observer before creating one, so the reset has
nothing to clean up.

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

src/web/public/app.js

@@ -4570,11 +4570,15 @@ class CodemanApp {
       }
       this.notificationManager.groupingMap.clear();
     }
-    // Disconnect terminal resize observer (prevents memory leak on reconnect)
-    if (this.terminalResizeObserver) {
-      this.terminalResizeObserver.disconnect();
-      this.terminalResizeObserver = null;
-    }
+    // ⚠️ The terminal resize observer is NOT reset here. initTerminal() owns its
+    // lifecycle (it runs once per page and disconnects any previous observer
+    // before creating one), and this reset runs on EVERY SSE init, page load
+    // included. It used to disconnect the observer "to prevent a leak", which
+    // left the terminal with no observer from the first init on: only a WINDOW
+    // resize ever refit it, so anything that resized just the terminal box
+    // (state rows and lineage room appearing in the header, the tab strip
+    // wrapping) clipped xterm's bottom rows behind the toolbar until a tab
+    // switch or a window resize.
     // Clear any other orphaned timers
     if (this.planLoadingTimer) {
       clearInterval(this.planLoadingTimer);

test/terminal-resize-observer-survives-init.test.ts

@@ -0,0 +1,46 @@
+// Port: none (static analysis of the shipped frontend source, no browser/server).
+//
+// The main terminal refits from a ResizeObserver on #terminalContainer, created
+// in initTerminal() (terminal-ui.js), which runs ONCE per page. handleInit() runs
+// _resetAllAppState() on EVERY SSE init, page load included, and that reset used
+// to disconnect the observer and null it "to prevent a leak on reconnect". So
+// from the first init on, the terminal had no observer at all: only a WINDOW
+// resize refit it, and anything that resized just the terminal box (the header's
+// state rows appearing when a session starts working, the lineage room, the tab
+// strip wrapping) left xterm at its old row count, its bottom rows clipped behind
+// the toolbar until a tab switch. Measured on the 1.36.0 beta: header 115 -> 170
+// px, container 743 -> 688 px, xterm stayed at 35 rows (32 fit) indefinitely.
+//
+// initTerminal() already disconnects a previous observer before creating one,
+// so the reset has nothing to clean up; it must leave the observer alone.
+import { readFileSync } from 'node:fs';
+import { resolve } from 'node:path';
+import { describe, expect, it } from 'vitest';
+
+const read = (f: string) => readFileSync(resolve(import.meta.dirname, '../src/web/public', f), 'utf8');
+
+function methodBody(source: string, signature: string): string {
+  const start = source.indexOf(signature);
+  expect(start, `${signature} not found`).toBeGreaterThan(-1);
+  // Methods in these files close with a two-space-indented brace at column 2.
+  const end = source.indexOf('\n  }\n', start);
+  return source.slice(start, end);
+}
+
+describe('the terminal resize observer survives SSE init', () => {
+  it('_resetAllAppState() does not disconnect or drop terminalResizeObserver', () => {
+    const body = methodBody(read('app.js'), '  _resetAllAppState(preserveTerminal = false) {');
+    expect(body).not.toMatch(/terminalResizeObserver\s*\.\s*disconnect\s*\(/);
+    expect(body).not.toMatch(/terminalResizeObserver\s*=\s*null/);
+  });
+
+  it('initTerminal() owns the lifecycle: disconnects any previous observer, then observes the container', () => {
+    const body = methodBody(read('terminal-ui.js'), '  initTerminal() {');
+    const disconnect = body.indexOf('this.terminalResizeObserver.disconnect()');
+    const create = body.indexOf('this.terminalResizeObserver = new ResizeObserver(');
+    const observe = body.indexOf('this.terminalResizeObserver.observe(container)');
+    expect(disconnect).toBeGreaterThan(-1);
+    expect(create).toBeGreaterThan(disconnect);
+    expect(observe).toBeGreaterThan(create);
+  });
+});