fix(tests): replace racy literal text with echo command in waiter test

why: Test was flaky - literal=True sends raw keystrokes that can be
captured mid-render, resulting in corrupted text (e.g., "NIQUE_TEST_STRING_123c")
what:
- Replace send_keys with literal=True with echo command
- Use wait_for_pane_content to wait for output instead of time.sleep()
- Increase timeout to 5.0s for CI reliability

Author: tony

tests/_internal/test_waiter.py

@@ -1842,34 +1842,21 @@ def test_wait_for_pane_content_exact_match_detailed(wait_pane: Pane) -> None:
     match type is handled, including the code path where a match
     is found and validated.
     """
-    # Clear the pane first to have more predictable content
+    # Clear and execute a command that produces predictable output
     wait_pane.clear()
+    wait_pane.send_keys("echo 'UNIQUE_TEST_STRING_123'")
 
-    # Send a unique string that we can test with an exact match
-    wait_pane.send_keys("UNIQUE_TEST_STRING_123", literal=True)
-
-    # Small delay to allow tmux to flush content (needed for older versions like 3.1b)
-    time.sleep(0.1)
-
-    # Get the current content to work with
-    content = wait_pane.capture_pane()
-    content_str = "\n".join(content if isinstance(content, list) else [content])
-
-    # Verify our test string is in the content
-    assert "UNIQUE_TEST_STRING_123" in content_str
-
-    # Test with CONTAINS match type first (more reliable)
+    # Use the waiter itself to wait for the string (dogfooding!)
     result = wait_for_pane_content(
         wait_pane,
         "UNIQUE_TEST_STRING_123",
         ContentMatchType.CONTAINS,
-        timeout=1.0,
-        interval=0.1,
+        timeout=5.0,
     )
-    assert result.success
+    assert result.success, f"String not found: {result.error}"
 
-    # Now test with EXACT match but with a simpler approach
-    # Find the exact line that contains our test string
+    # Now get the content and find the exact line for EXACT match testing
+    content = wait_pane.capture_pane()
     exact_line = next(
         (line for line in content if "UNIQUE_TEST_STRING_123" in line),
         "UNIQUE_TEST_STRING_123",