Sideloaded titles: use ids Steam's create-shortcut accepts

On the Frame, Steam refused to register titles whose id had a hyphen
(fc-smoke-exe) with "missing/invalid arguments", and registered the same
program as FCSmokeProbe (headset smoke test, 2026-09-27, BUILD_ID
20260922.6101926). Valve's client only allows ^[A-Za-z_][A-Za-z0-9_.]+$.

title_id now makes ids of letters, digits and _, not starting with a
digit, 2 to 64 long; new installs are checked against that, while titles
already on the Frame are still listed, launched and removed. Steam's error
text is trimmed before it's quoted, and the "install it again with Steam
running" hint only follows a Steam-not-running error.

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

tests/test_frame_titles.py

@@ -347,14 +347,26 @@ class Zips(unittest.TestCase):
 class Names(unittest.TestCase):
     def test_title_id(self):
         self.assertEqual(frame_titles.title_id('Hollow Knight: Silksong!'), 'Hollow_Knight_Silksong')
-        self.assertEqual(frame_titles.title_id('steam'), 'steam-game')     # Valve's reserved sideload names
+        self.assertEqual(frame_titles.title_id('steam'), 'steam_game')     # Valve's reserved sideload names
         self.assertEqual(frame_titles.title_id('Devkit Steam'), 'Devkit_Steam')
-        self.assertEqual(frame_titles.title_id('devkit-steam'), 'devkit-steam-game')  # the trampoline file
-        self.assertEqual(frame_titles.title_id('--rm -rf /'), 'rm_-rf')
+        self.assertEqual(frame_titles.title_id('--rm -rf /'), 'rm_rf')
         self.assertEqual(len(frame_titles.title_id('x' * 200)), 64)
         with self.assertRaises(FrameError):
             frame_titles.title_id('!!!')
 
+    def test_title_id_is_one_steam_accepts(self):
+        # The Frame's Steam refused "fc-smoke-exe" ("missing/invalid arguments") and took
+        # "FCSmokeProbe" (2026-09-27): Valve's client allows ^[A-Za-z_][A-Za-z0-9_.]+$ only.
+        self.assertEqual(frame_titles.title_id('Half-Life 2'), 'Half_Life_2')
+        self.assertEqual(frame_titles.title_id('fc-smoke-exe'), 'fc_smoke_exe')
+        self.assertEqual(frame_titles.title_id('2048'), '_2048')
+        self.assertEqual(frame_titles.title_id('X'), 'X_game')
+        self.assertEqual(frame_titles.title_id('devkit-steam'), 'devkit_steam')
+        for name in ('Half-Life 2', '2048', 'X', 'steam', 'a' * 90, 'Ünïcödé game', '9' * 70):
+            gid = frame_titles.title_id(name)
+            self.assertRegex(gid, r'^[A-Za-z_][A-Za-z0-9_.]+$', name)
+            self.assertTrue(frame_titles.NEW_ID_RE.match(gid) and frame_titles.ID_RE.match(gid), gid)
+
     def test_display_name(self):
         self.assertEqual(frame_titles.display_name('MyGame-linux-arm64.zip'), 'MyGame')
         self.assertEqual(frame_titles.display_name('Portal 2.zip'), 'Portal 2')