diff --git a/emulators/fbneo.yml b/emulators/fbneo.yml
index 2a2a825e9..8534afb8c 100644
--- a/emulators/fbneo.yml
+++ b/emulators/fbneo.yml
@@ -51,10 +51,12 @@ data_directories:
   - ref: fbneo-cheats
     unread_on: [romm]
     destination: fbneo/cheats
+    required: false
     source_ref: "source src/burner/conc.cpp:167"
   - ref: fbneo-samples
     unread_on: [romm]
     destination: fbneo
+    required: false
     source_ref: "source src/burn/snd/samples.cpp:21-35"
 
 notes: |
diff --git a/install.ps1 b/install.ps1
index 28de54233..01c164290 100644
--- a/install.ps1
+++ b/install.ps1
@@ -16,7 +16,7 @@
     # and Invoke-WebRequest throws on a cut transfer before the hash is read:
     # the site's build rewrites this line there (scripts/sitebootstrap.py).
     $mismatchAdvice = "The download was most likely cut short: try again. Within minutes of an update of this project the two files can come from caches of different ages. Waiting five minutes settles that."
-    $defaultInstallSha256 = "57e3cb6739a701181908773e603f17d2b10e1b0e2a5cde5cc4d5c97426da5dd4"
+    $defaultInstallSha256 = "3a78bf2e5a910d0f5c21bc2dc490aa600fc3273c56ae01e9ce5061d9b3578f07"
     $maximumInstallerBytes = 2MB
     $installerExit = 0
     $installer = if ($PSScriptRoot) { Join-Path $PSScriptRoot "install.py" } else { $null }
diff --git a/install.py b/install.py
index 04a697af5..a5cf46c28 100644
--- a/install.py
+++ b/install.py
@@ -3724,6 +3724,8 @@ def _check_data_directory(entry: object, where: str) -> None:
         values = entry.get(field, [])
         if not isinstance(values, list) or not all(isinstance(v, str) for v in values):
             raise ValueError(f"{where}.{field} is invalid")
+    if entry.get("optional", True) is not True:
+        raise ValueError(f"{where}.optional is invalid")
     files = entry.get("files")
     if not isinstance(files, dict) or not files or len(files) > MAX_MANIFEST_FILES:
         raise ValueError(f"{where}.files is invalid")
@@ -7393,11 +7395,16 @@ def _install_data_member(
             scratch.unlink(missing_ok=True)
 
 
-def select_data_directories(manifest: dict, files: list[dict], narrowed: bool) -> list[dict]:
-    """The data trees this install keeps: all, or those of a kept system."""
-    entries = manifest.get("data_directories") or []
+def select_data_directories(manifest: dict, files: list[dict], narrowed: bool,
+                            required_only: bool = False) -> list[dict]:
+    """The data trees this install keeps: all, or those of a kept system.
+    --required-only leaves out a tree every core reading it runs without
+    (`optional`): a GBA and a SNES game took FBNeo's cheats and samples,
+    3,472 files no game opened."""
+    entries = [e for e in manifest.get("data_directories") or []
+               if not (required_only and e.get("optional"))]
     if not narrowed:
-        return list(entries)
+        return entries
     kept = {system for f in files for system in entry_systems(f)}
     return [e for e in entries if kept & set(e.get("systems") or [])]
 
@@ -8824,7 +8831,8 @@ def _prompt_custom_selection(
     if bios_path is not None and not dry_run and current != INSTALLED_ONLY:
         kept = menu_choice(files, omitted, installed, current, False)[0]
         kept_trees = select_data_directories({"data_directories": trees}, kept,
-                                             narrowed or current is not None)
+                                             narrowed or current is not None,
+                                             isinstance(current, GamesChoice) and current.required)
         if kept and all_in_place(kept, kept_trees, bios_path):
             # Read before the menu, as the screen reads before it asks: a
             # rerun was offered an install that installs nothing, then told
@@ -8953,7 +8961,8 @@ def _print_menu_head(
     # The trees of the systems kept: 2636 data files of blueMSX, Dolphin
     # and PPSSPP were counted for every --system tried.
     kept_trees = select_data_directories({"data_directories": trees}, shown,
-                                         narrowed or current is not None)
+                                         narrowed or current is not None,
+                                         isinstance(current, GamesChoice) and current.required)
     data = sum(len(entry.get("files") or {}) for entry in kept_trees)
     data_size = sum(meta.get("size", 0) for entry in kept_trees
                     for meta in (entry.get("files") or {}).values())
@@ -9764,6 +9773,12 @@ def games_setups(index: dict, plat: str, bios_path: Path, os_type: str = "") ->
     if not named:
         above = card_root_above(bios_path)
         named = above[0] if above else ""
+    if not named:
+        # --dest on a handheld's games part from a computer (ArkOS's
+        # EASYROMS/bios): detection never ran there, and the card's own rom
+        # folders sit beside the BIOS folder.
+        part = games_part(bios_path.parent)
+        named = part.name if part else ""
     key = _setup_key(named) if named else ""
     found = [name for name in sorted(setups) if key and (name == key or name.startswith(key + "-"))]
     if not found and plat in setups:
@@ -15671,7 +15686,8 @@ def _install(args: argparse.Namespace, real_stdout: TextIO) -> None:
             != len(manifest.get("files", [])) + len(variants if case_kept else [])
             or games_applied
         )
-        data_dirs = select_data_directories(manifest, files, narrowed)
+        data_dirs = select_data_directories(manifest, files, narrowed,
+                                            bool(args.required_only))
         # The kinds as the plan and the menu head say them (parts_words),
         # the data files of the folders kept among them: this head said
         # BIOS files and game data beside a plan of three kinds, neither
@@ -21812,7 +21828,8 @@ def _plan_data(state: TuiState, check: dict) -> tuple[int, int | None]:
     if not _tui_estimating(state):
         data = check.get("data_missing", 0)
         return data, check.get("data_bytes") if data else None
-    trees = select_data_directories(state.manifest or {}, _choice_entries(state), True)
+    required = any(flag == "--required-only" for flag, _value in tui_flags(state))
+    trees = select_data_directories(state.manifest or {}, _choice_entries(state), True, required)
     sizes = [meta.get("size", 0) for entry in trees for meta in (entry.get("files") or {}).values()]
     return len(sizes), sum(sizes)
 
diff --git a/install.sh b/install.sh
index a03428f05..fce43f99f 100755
--- a/install.sh
+++ b/install.sh
@@ -23,7 +23,7 @@ DEFAULT_INSTALL_URL="https://raw.githubusercontent.com/Abdess/retrobios/main/ins
 # curl or wget stop on a cut transfer before the hash is read: the site's
 # build rewrites this line there (scripts/sitebootstrap.py).
 MISMATCH_ADVICE="The download was most likely cut short: try again. Within minutes of an update of this project the two files can come from caches of different ages. Waiting five minutes settles that."
-DEFAULT_INSTALL_SHA256="57e3cb6739a701181908773e603f17d2b10e1b0e2a5cde5cc4d5c97426da5dd4"
+DEFAULT_INSTALL_SHA256="3a78bf2e5a910d0f5c21bc2dc490aa600fc3273c56ae01e9ce5061d9b3578f07"
 MAX_INSTALLER_BYTES=2097152
 
 cleanup() {
diff --git a/install/amberelec.json b/install/amberelec.json
index 104db8e5e..c1390a71e 100644
--- a/install/amberelec.json
+++ b/install/amberelec.json
@@ -6,7 +6,7 @@
   "platform": "amberelec",
   "display_name": "AmberELEC",
   "version": "prerelease-20261019_1835",
-  "generated": "2026-11-05T23:59:37Z",
+  "generated": "2026-11-06T07:21:27Z",
   "base_destination": "",
   "detect": [
     {
@@ -77381,7 +77381,8 @@
         }
       },
       "strip_components": 1,
-      "archive_size": 5083767
+      "archive_size": 5083767,
+      "optional": true
     },
     {
       "ref": "fbneo-samples",
@@ -77615,7 +77616,8 @@
         }
       },
       "strip_components": 0,
-      "archive_size": 53006540
+      "archive_size": 53006540,
+      "optional": true
     },
     {
       "ref": "freeintv-overlays",
@@ -77988,7 +77990,8 @@
         }
       },
       "strip_components": 1,
-      "archive_size": 21311170
+      "archive_size": 21311170,
+      "optional": true
     }
   ]
 }
\ No newline at end of file
diff --git a/install/batocera.json b/install/batocera.json
index 583de52ee..c1f5c14e2 100644
--- a/install/batocera.json
+++ b/install/batocera.json
@@ -6,7 +6,7 @@
   "platform": "batocera",
   "display_name": "Batocera",
   "version": "43.1",
-  "generated": "2026-11-05T23:59:37Z",
+  "generated": "2026-11-06T07:21:27Z",
   "base_destination": "bios",
   "detect": [
     {
@@ -225291,7 +225291,8 @@
         }
       },
       "strip_components": 1,
-      "archive_size": 5083767
+      "archive_size": 5083767,
+      "optional": true
     },
     {
       "ref": "fbneo-samples",
@@ -225525,7 +225526,8 @@
         }
       },
       "strip_components": 0,
-      "archive_size": 53006540
+      "archive_size": 53006540,
+      "optional": true
     }
   ],
   "save_directory": {
diff --git a/install/emudeck.json b/install/emudeck.json
index 32f4ed6a2..3f01646ff 100644
--- a/install/emudeck.json
+++ b/install/emudeck.json
@@ -6,7 +6,7 @@
   "platform": "emudeck",
   "display_name": "EmuDeck",
   "version": "2.7EA",
-  "generated": "2026-11-05T23:59:37Z",
+  "generated": "2026-11-06T07:21:27Z",
   "base_destination": "bios",
   "detect": [
     {
@@ -123400,7 +123400,8 @@
         }
       },
       "strip_components": 1,
-      "archive_size": 5083767
+      "archive_size": 5083767,
+      "optional": true
     },
     {
       "ref": "fbneo-samples",
@@ -123634,7 +123635,8 @@
         }
       },
       "strip_components": 0,
-      "archive_size": 53006540
+      "archive_size": 53006540,
+      "optional": true
     },
     {
       "ref": "freeintv-overlays",
@@ -124007,7 +124009,8 @@
         }
       },
       "strip_components": 1,
-      "archive_size": 21311170
+      "archive_size": 21311170,
+      "optional": true
     },
     {
       "ref": "lrps2",
diff --git a/install/emuelec.json b/install/emuelec.json
index 32c8e5488..35ec58389 100644
--- a/install/emuelec.json
+++ b/install/emuelec.json
@@ -6,7 +6,7 @@
   "platform": "emuelec",
   "display_name": "EmuELEC",
   "version": "4.8",
-  "generated": "2026-11-05T23:59:37Z",
+  "generated": "2026-11-06T07:21:27Z",
   "base_destination": "",
   "detect": [
     {
@@ -83639,7 +83639,8 @@
         }
       },
       "strip_components": 1,
-      "archive_size": 5083767
+      "archive_size": 5083767,
+      "optional": true
     },
     {
       "ref": "fbneo-samples",
@@ -83873,7 +83874,8 @@
         }
       },
       "strip_components": 0,
-      "archive_size": 53006540
+      "archive_size": 53006540,
+      "optional": true
     },
     {
       "ref": "freeintv-overlays",
@@ -84246,7 +84248,8 @@
         }
       },
       "strip_components": 1,
-      "archive_size": 21311170
+      "archive_size": 21311170,
+      "optional": true
     }
   ]
 }
\ No newline at end of file
diff --git a/install/knulli.json b/install/knulli.json
index ccdbd73b9..fd6a9e45b 100644
--- a/install/knulli.json
+++ b/install/knulli.json
@@ -6,7 +6,7 @@
   "platform": "knulli",
   "display_name": "KNULLI",
   "version": "20260511",
-  "generated": "2026-11-05T23:59:37Z",
+  "generated": "2026-11-06T07:21:27Z",
   "base_destination": "bios",
   "detect": [
     {
@@ -157933,7 +157933,8 @@
         }
       },
       "strip_components": 1,
-      "archive_size": 5083767
+      "archive_size": 5083767,
+      "optional": true
     },
     {
       "ref": "fbneo-samples",
@@ -158167,7 +158168,8 @@
         }
       },
       "strip_components": 0,
-      "archive_size": 53006540
+      "archive_size": 53006540,
+      "optional": true
     },
     {
       "ref": "lrps2",
diff --git a/install/lakka.json b/install/lakka.json
index 5866fe5db..09f9de198 100644
--- a/install/lakka.json
+++ b/install/lakka.json
@@ -6,7 +6,7 @@
   "platform": "lakka",
   "display_name": "Lakka",
   "version": "v6.1",
-  "generated": "2026-11-05T23:59:37Z",
+  "generated": "2026-11-06T07:21:27Z",
   "base_destination": "system",
   "detect": [
     {
@@ -130677,7 +130677,8 @@
         }
       },
       "strip_components": 1,
-      "archive_size": 5083767
+      "archive_size": 5083767,
+      "optional": true
     },
     {
       "ref": "fbneo-samples",
@@ -130911,7 +130912,8 @@
         }
       },
       "strip_components": 0,
-      "archive_size": 53006540
+      "archive_size": 53006540,
+      "optional": true
     },
     {
       "ref": "freeintv-overlays",
@@ -131284,7 +131286,8 @@
         }
       },
       "strip_components": 1,
-      "archive_size": 21311170
+      "archive_size": 21311170,
+      "optional": true
     },
     {
       "ref": "yaps2-resources",
diff --git a/install/myminui.json b/install/myminui.json
index 85de7b9bc..7cb542e4e 100644
--- a/install/myminui.json
+++ b/install/myminui.json
@@ -6,7 +6,7 @@
   "platform": "myminui",
   "display_name": "MyMinUI",
   "version": "2026-08-09",
-  "generated": "2026-11-05T23:59:37Z",
+  "generated": "2026-11-06T07:21:27Z",
   "base_destination": "",
   "detect": [
     {
@@ -18958,7 +18958,8 @@
         }
       },
       "strip_components": 1,
-      "archive_size": 5083767
+      "archive_size": 5083767,
+      "optional": true
     },
     {
       "ref": "fbneo-cheats",
@@ -32688,7 +32689,8 @@
         }
       },
       "strip_components": 1,
-      "archive_size": 5083767
+      "archive_size": 5083767,
+      "optional": true
     },
     {
       "ref": "fbneo-samples",
@@ -32922,7 +32924,8 @@
         }
       },
       "strip_components": 0,
-      "archive_size": 53006540
+      "archive_size": 53006540,
+      "optional": true
     },
     {
       "ref": "fbneo-samples",
@@ -33156,7 +33159,8 @@
         }
       },
       "strip_components": 0,
-      "archive_size": 53006540
+      "archive_size": 53006540,
+      "optional": true
     }
   ]
 }
\ No newline at end of file
diff --git a/install/nextui.json b/install/nextui.json
index 4518d3d5c..933ec3af5 100644
--- a/install/nextui.json
+++ b/install/nextui.json
@@ -6,7 +6,7 @@
   "platform": "nextui",
   "display_name": "NextUI",
   "version": "2026-10-20",
-  "generated": "2026-11-05T23:59:37Z",
+  "generated": "2026-11-06T07:21:27Z",
   "base_destination": "",
   "detect": [
     {
@@ -19366,7 +19366,8 @@
         }
       },
       "strip_components": 1,
-      "archive_size": 5083767
+      "archive_size": 5083767,
+      "optional": true
     },
     {
       "ref": "fbneo-samples",
@@ -19600,7 +19601,8 @@
         }
       },
       "strip_components": 0,
-      "archive_size": 53006540
+      "archive_size": 53006540,
+      "optional": true
     }
   ]
 }
\ No newline at end of file
diff --git a/install/recalbox.json b/install/recalbox.json
index 9b97c9d50..6db9f7daa 100644
--- a/install/recalbox.json
+++ b/install/recalbox.json
@@ -6,7 +6,7 @@
   "platform": "recalbox",
   "display_name": "Recalbox",
   "version": "10.1.1",
-  "generated": "2026-11-05T23:59:37Z",
+  "generated": "2026-11-06T07:21:27Z",
   "base_destination": "bios",
   "detect": [
     {
@@ -62834,7 +62834,8 @@
         }
       },
       "strip_components": 1,
-      "archive_size": 5083767
+      "archive_size": 5083767,
+      "optional": true
     },
     {
       "ref": "fbneo-samples",
@@ -63068,7 +63069,8 @@
         }
       },
       "strip_components": 0,
-      "archive_size": 53006540
+      "archive_size": 53006540,
+      "optional": true
     }
   ],
   "save_directory": {
diff --git a/install/retroarch.json b/install/retroarch.json
index 11b60b965..5e89fef85 100644
--- a/install/retroarch.json
+++ b/install/retroarch.json
@@ -6,7 +6,7 @@
   "platform": "retroarch",
   "display_name": "RetroArch",
   "version": "v1.22.2",
-  "generated": "2026-11-05T23:59:37Z",
+  "generated": "2026-11-06T07:21:27Z",
   "base_destination": "system",
   "detect": [
     {
@@ -140789,7 +140789,8 @@
         }
       },
       "strip_components": 1,
-      "archive_size": 5083767
+      "archive_size": 5083767,
+      "optional": true
     },
     {
       "ref": "fbneo-samples",
@@ -141023,7 +141024,8 @@
         }
       },
       "strip_components": 0,
-      "archive_size": 53006540
+      "archive_size": 53006540,
+      "optional": true
     },
     {
       "ref": "freeintv-overlays",
@@ -141396,7 +141398,8 @@
         }
       },
       "strip_components": 1,
-      "archive_size": 21311170
+      "archive_size": 21311170,
+      "optional": true
     },
     {
       "ref": "ppsspp-assets",
diff --git a/install/retrobat.json b/install/retrobat.json
index ca7459771..aec7d58a0 100644
--- a/install/retrobat.json
+++ b/install/retrobat.json
@@ -6,7 +6,7 @@
   "platform": "retrobat",
   "display_name": "RetroBat",
   "version": "8.3.1",
-  "generated": "2026-11-05T23:59:37Z",
+  "generated": "2026-11-06T07:21:27Z",
   "base_destination": "bios",
   "detect": [
     {
@@ -89076,7 +89076,8 @@
         }
       },
       "strip_components": 1,
-      "archive_size": 5083767
+      "archive_size": 5083767,
+      "optional": true
     },
     {
       "ref": "fbneo-samples",
@@ -89310,7 +89311,8 @@
         }
       },
       "strip_components": 0,
-      "archive_size": 53006540
+      "archive_size": 53006540,
+      "optional": true
     },
     {
       "ref": "freeintv-overlays",
@@ -89683,7 +89685,8 @@
         }
       },
       "strip_components": 1,
-      "archive_size": 21311170
+      "archive_size": 21311170,
+      "optional": true
     }
   ],
   "save_directory": {
diff --git a/install/retrodeck.json b/install/retrodeck.json
index b9b4b4a10..2938c951d 100644
--- a/install/retrodeck.json
+++ b/install/retrodeck.json
@@ -6,7 +6,7 @@
   "platform": "retrodeck",
   "display_name": "RetroDECK",
   "version": "0.10.10b",
-  "generated": "2026-11-05T23:59:37Z",
+  "generated": "2026-11-06T07:21:27Z",
   "base_destination": "",
   "detect": [
     {
@@ -153141,7 +153141,8 @@
         }
       },
       "strip_components": 1,
-      "archive_size": 5083767
+      "archive_size": 5083767,
+      "optional": true
     },
     {
       "ref": "fbneo-samples",
@@ -153375,7 +153376,8 @@
         }
       },
       "strip_components": 0,
-      "archive_size": 53006540
+      "archive_size": 53006540,
+      "optional": true
     },
     {
       "ref": "freeintv-overlays",
@@ -153748,7 +153750,8 @@
         }
       },
       "strip_components": 1,
-      "archive_size": 21311170
+      "archive_size": 21311170,
+      "optional": true
     },
     {
       "ref": "yaps2-resources",
diff --git a/install/retropie.json b/install/retropie.json
index 3db3da56e..b6ab50768 100644
--- a/install/retropie.json
+++ b/install/retropie.json
@@ -6,7 +6,7 @@
   "platform": "retropie",
   "display_name": "RetroPie",
   "version": "4.8.12",
-  "generated": "2026-11-05T23:59:37Z",
+  "generated": "2026-11-06T07:21:27Z",
   "base_destination": "BIOS",
   "detect": [
     {
@@ -146474,7 +146474,8 @@
         }
       },
       "strip_components": 1,
-      "archive_size": 5083767
+      "archive_size": 5083767,
+      "optional": true
     },
     {
       "ref": "fbneo-samples",
@@ -146708,7 +146709,8 @@
         }
       },
       "strip_components": 0,
-      "archive_size": 53006540
+      "archive_size": 53006540,
+      "optional": true
     },
     {
       "ref": "freeintv-overlays",
@@ -147081,7 +147083,8 @@
         }
       },
       "strip_components": 1,
-      "archive_size": 21311170
+      "archive_size": 21311170,
+      "optional": true
     },
     {
       "ref": "yaps2-resources",
diff --git a/install/rocknix.json b/install/rocknix.json
index f06bd3144..e15cda7e5 100644
--- a/install/rocknix.json
+++ b/install/rocknix.json
@@ -6,7 +6,7 @@
   "platform": "rocknix",
   "display_name": "ROCKNIX",
   "version": "20261001",
-  "generated": "2026-11-05T23:59:37Z",
+  "generated": "2026-11-06T07:21:27Z",
   "base_destination": "bios",
   "detect": [
     {
@@ -109453,7 +109453,8 @@
         }
       },
       "strip_components": 1,
-      "archive_size": 5083767
+      "archive_size": 5083767,
+      "optional": true
     },
     {
       "ref": "fbneo-samples",
@@ -109687,7 +109688,8 @@
         }
       },
       "strip_components": 0,
-      "archive_size": 53006540
+      "archive_size": 53006540,
+      "optional": true
     },
     {
       "ref": "freeintv-overlays",
@@ -110060,7 +110062,8 @@
         }
       },
       "strip_components": 1,
-      "archive_size": 21311170
+      "archive_size": 21311170,
+      "optional": true
     },
     {
       "ref": "lrps2",
diff --git a/schemas/install-manifest.schema.json b/schemas/install-manifest.schema.json
index 264c08558..a72245722 100644
--- a/schemas/install-manifest.schema.json
+++ b/schemas/install-manifest.schema.json
@@ -452,6 +452,11 @@
             },
             "description": "Platform systems whose cores read the tree."
           },
+          "optional": {
+            "type": "boolean",
+            "const": true,
+            "description": "Every core reading the tree runs without it (required: false in its profile): --required-only leaves it out."
+          },
           "files": {
             "type": "object",
             "additionalProperties": {
diff --git a/scripts/generate_pack.py b/scripts/generate_pack.py
index 3934830a9..c0a20376b 100644
--- a/scripts/generate_pack.py
+++ b/scripts/generate_pack.py
@@ -518,7 +518,8 @@ def _data_directory_members(
     gets it from the tree's archive.
 
     ``refs_out``, when given, maps each yielded destination to
-    (registry key, system ids, directory destination), for the manifest.
+    (registry key, system ids, directory destination, whether the core
+    needs the tree), for the manifest.
 
     These are not BIOS and carry no hash of their own: they are whole
     trees an emulator reads, refreshed from upstream, so what ships is
@@ -532,7 +533,8 @@ def _data_directory_members(
         ref_key = dd.get("ref", "")
         if not ref_key or not data_registry or ref_key not in data_registry:
             continue
-        if required_only and dd.get("required") is False:
+        needed = dd.get("required") is not False
+        if required_only and not needed:
             continue
         if ref_key in installed_data_refs(platform_name):
             continue
@@ -567,7 +569,7 @@ def _data_directory_members(
                     ):
                         del reclaim[full]
                         if refs_out is not None:
-                            refs_out[full] = (ref_key, systems, dd_prefix)
+                            refs_out[full] = (ref_key, systems, dd_prefix, needed)
                         yield src, full
                         continue
                     if full in seen_destinations or (
@@ -581,7 +583,7 @@ def _data_directory_members(
                     if case_insensitive:
                         seen_lower.add(full.lower())
                     if refs_out is not None:
-                        refs_out[full] = (ref_key, systems, dd_prefix)
+                        refs_out[full] = (ref_key, systems, dd_prefix, needed)
                     yield src, full
 
 
@@ -4910,7 +4912,7 @@ def generate_manifest(
     # Phase 3: data directories. They are not files of the collection: the
     # installer fetches each from its source archive and keeps the members
     # whose hash the list below records, the same tree the pack carries.
-    data_refs: dict[str, tuple[str, tuple[str, ...], str]] = {}
+    data_refs: dict[str, tuple[str, tuple[str, ...], str, bool]] = {}
     reclaim = {full: path for full, (path, _size) in cache_held.items()}
     data_members = list(_data_directory_members(
         pack_systems, data_registry, platform_name, base_dest,
@@ -5021,7 +5023,7 @@ def generate_manifest(
 
 def _manifest_data_directories(
     members: list[tuple[str, str]],
-    refs: dict[str, tuple[str, tuple[str, ...], str]],
+    refs: dict[str, tuple[str, tuple[str, ...], str, bool]],
     registry: dict,
     base_dest: str,
 ) -> list[dict]:
@@ -5034,11 +5036,14 @@ def _manifest_data_directories(
     changed since is refused rather than installed. archive_size is the
     size of the archive refresh_data_dirs last downloaded, what fetching
     the tree costs: a tarball whose tree is 10 KB is a download of 21 MB.
+    ``optional`` marks a tree every core reading it runs without
+    (``required: false``): install.py --required-only leaves it out, as the
+    pack built with --required-only does.
     """
     grouped: dict[tuple[str, str], dict] = {}
     versions: dict[str, dict[str, dict]] = {}
     for src, full in members:
-        ref, systems, prefix = refs[full]
+        ref, systems, prefix, needed = refs[full]
         entry = registry.get(ref, {})
         key = (ref, prefix)
         group = grouped.get(key)
@@ -5072,11 +5077,19 @@ def _manifest_data_directories(
                 size = versions[str(recorded)].get(ref, {}).get("archive_size")
                 if isinstance(size, int) and size > 0:
                     group["archive_size"] = size
+        if needed:
+            group["needed"] = True
         group["systems"].extend(s for s in systems if s not in group["systems"])
         rel = full[len(prefix):].lstrip("/") if prefix else full
         hashes = compute_hashes(src, frozenset({"sha1"}))
         group["files"][rel] = {"sha1": hashes["sha1"], "size": os.path.getsize(src)}
-    return [grouped[key] for key in sorted(grouped)]
+    trees = []
+    for key in sorted(grouped):
+        group = grouped[key]
+        if not group.pop("needed", False):
+            group["optional"] = True
+        trees.append(group)
+    return trees
 
 
 def _manifest_core_index(
diff --git a/tests/test_audit_regressions.py b/tests/test_audit_regressions.py
index c5e4a8ecc..685e4082a 100644
--- a/tests/test_audit_regressions.py
+++ b/tests/test_audit_regressions.py
@@ -6923,9 +6923,11 @@ class RequiredOnlyReachesDataDirectories(unittest.TestCase):
 
     def test_every_tree_walk_reads_the_flag(self):
         source = (ROOT / "scripts" / "generate_pack.py").read_text(encoding="utf-8")
-        self.assertEqual(
-            source.count('if required_only and dd.get("required") is False:'), 2
-        )
+        # The pack's walk and the manifest's, which records the flag for
+        # install.py --required-only.
+        self.assertEqual(source.count('if required_only and dd.get("required") is False:'), 1)
+        self.assertIn('needed = dd.get("required") is not False\n        if required_only and not needed:',
+                      source)
         self.assertIn("seen_parents, required_only=required_only,", source)
         self.assertIn("data_refs, required_only=required_only,", source)
 
diff --git a/tests/test_install.py b/tests/test_install.py
index 9effcdd49..7e6689029 100644
--- a/tests/test_install.py
+++ b/tests/test_install.py
@@ -3880,6 +3880,20 @@ class DataDirectoriesAreInstalled(unittest.TestCase):
             },
         }
 
+    def test_required_only_leaves_out_an_optional_tree(self):
+        """A GBA and a SNES game with --for-games --required-only took
+        FBNeo's cheats and samples, 3,472 files no game opened."""
+        cheats = {**self._entry(), "ref": "fbneo-cheats", "systems": ["snes"], "optional": True}
+        sys_tree = {**self._entry(), "systems": ["snes"]}
+        manifest = {"data_directories": [cheats, sys_tree]}
+        files = [{"dest": "a.rom", "systems": ["snes"]}]
+        self.assertEqual(install.select_data_directories(manifest, files, True), [cheats, sys_tree])
+        self.assertEqual(install.select_data_directories(manifest, files, True, True), [sys_tree])
+        self.assertEqual(install.select_data_directories(manifest, files, False, True), [sys_tree])
+        install._check_data_directory(cheats, "data_directories[0]")
+        with self.assertRaises(ValueError):
+            install._check_data_directory({**cheats, "optional": False}, "data_directories[0]")
+
     def test_the_archive_is_drawn_and_counted(self):
         """82 MB of archives came with no progress line, and the run ended
         on "310.5 KB downloaded", the BIOS files alone."""
diff --git a/tests/test_install_tui.py b/tests/test_install_tui.py
index a7584e71b..f8a7eea48 100644
--- a/tests/test_install_tui.py
+++ b/tests/test_install_tui.py
@@ -12912,6 +12912,18 @@ class DriveIsACardByItsFiles(unittest.TestCase):
                 self.assertEqual([install.card_system(mount) for mount in mounts],
                                  [None, None, None])
 
+    def test_a_dest_on_a_games_part_reads_its_rom_folders(self):
+        """--dest EASYROMS/bios --for-games from a computer: detection never
+        ran on the card, the generic RetroArch folders were tried, and the
+        run kept every file of the list."""
+        arkos = games_part(self.root / "media" / "EASYROMS")
+        index = {"setups": {"arkos": {}, "retroarch": {}}}
+        with mock.patch.object(install, "_mount_points", return_value=frozenset()), \
+                mock.patch.object(install, "_drive_not_removable", return_value=False):
+            self.assertEqual(install.games_setups(index, "retroarch", arkos / "bios"), ["arkos"])
+            self.assertEqual(install.games_setups(index, "retroarch", self.root / "bios"),
+                             ["retroarch"])
+
     def test_a_card_beside_a_data_drive_comes_first(self):
         """The ArkOS card and the data drive mounted,
         the data drive sorted first and took Enter. The card comes first in
diff --git a/wiki/installer.md b/wiki/installer.md
index 6378b191a..1f109d861 100644
--- a/wiki/installer.md
+++ b/wiki/installer.md
@@ -405,7 +405,7 @@ lists record these files as omitted.
 
 <!-- generated: dry-run -->
 
-A RetroArch dry run into an empty folder, with the list of 2026-11-05, printed this:
+A RetroArch dry run into an empty folder, with the list of 2026-11-06, printed this:
 
 ```
 Fetching file index for retroarch...
@@ -435,7 +435,7 @@ the installer can fetch them.
 <!-- generated: run-date -->
 
 Each line a first install prints, and what it means. The run below is a
-Batocera install into an empty folder, from the list of 2026-11-05.
+Batocera install into an empty folder, from the list of 2026-11-06.
 The figures change with each release.
 <!-- /generated: run-date -->
 
@@ -531,7 +531,7 @@ would save, once that saving is over half.
 
 <!-- generated: bulk-hint -->
 
-RetroArch with `--system sony-playstation`, from the list of 2026-11-05:
+RetroArch with `--system sony-playstation`, from the list of 2026-11-06:
 
 ```
   duckstation pulls 316.5 MB of this 329.0 MB download for sony-playstation. --core pcsx1 keeps 11.0 MB of it and saves 318.0 MB (96%).
@@ -876,7 +876,9 @@ BIOS sets of its parent chain (`neogeo.zip` for `mslug.zip`).
 
 A game that is not recognised gets every BIOS of its system, and the run names
 it. So does an arcade set the core does not know. **Only what starts**
-(`--required-only`) leaves out the files the cores mark optional.
+(`--required-only`) leaves out the files the cores mark optional, and the data
+folders every core reading them runs without (FinalBurn Neo's cheats and
+samples).
 
 The games are read without hashing whole discs, and a cache keeps what was
 read, so a second run over the same card reads only new files. It is a