fix: let target installs match their target pack

install.ps1

@@ -8,7 +8,7 @@ param(
 
 $ErrorActionPreference = "Stop"
 $defaultInstallUrl = "https://raw.githubusercontent.com/Abdess/retrobios/main/install.py"
-$defaultInstallSha256 = "e0d8fad4e7e55afa57c412e98726992d82b92286b752c9a8cce0978f0a355127"
+$defaultInstallSha256 = "953240dab33c25e52005155ecc8cd694269234697ca2c3f55939994fc6b61951"
 $maximumInstallerBytes = 2MB
 $installer = if ($PSScriptRoot) { Join-Path $PSScriptRoot "install.py" } else { $null }
 $temporary = $null

install.py

@@ -1154,6 +1154,47 @@ def _check_download(entry: dict, where: str, dest: str) -> int:
     return size
 
 
+def _check_slot(entry: dict, where: str, dest: str) -> int:
+    """The copies a platform file takes as cores and systems drop; the largest size."""
+    choices = entry.get("slot_choices", [])
+    declared = entry.get("declared_choices")
+    if declared is None and not choices:
+        return 0
+    if (
+        entry.get("cores") is not None
+        or not isinstance(choices, list)
+        or not isinstance(declared, list)
+        or not declared
+        or len(choices) > MAX_SELECTION_TAGS
+        or len(declared) > MAX_SELECTION_TAGS
+    ):
+        raise ValueError(f"invalid slot choices for {dest}")
+    size = 0
+    for index, choice in enumerate(declared):
+        systems = choice.get("systems") if isinstance(choice, dict) else None
+        if (
+            not isinstance(systems, list)
+            or not systems
+            or not all(isinstance(s, str) for s in systems)
+            or not set(choice) <= (set(_COPY_FIELDS) - {"cores"}) | {"systems"}
+        ):
+            raise ValueError(f"invalid declared choice for {dest}")
+        size = max(size, _check_download(choice, f"{where}.declared_choices[{index}]", dest))
+    for index, choice in enumerate(choices):
+        if (
+            not isinstance(choice, dict)
+            or not choice.get("cores")
+            or not set(choice) <= set(_COPY_FIELDS)
+        ):
+            raise ValueError(f"invalid slot choice for {dest}")
+        # A choice naming only cores leaves the platform's own answer.
+        if set(choice) != {"cores"}:
+            size = max(size, _check_download(
+                choice, f"{where}.slot_choices[{index}]", dest
+            ))
+    return size
+
+
 def _validate_manifest(data: object, plat: str) -> dict:
     """Validate the untrusted install-manifest boundary using stdlib only."""
     if not isinstance(data, dict):
@@ -1192,6 +1233,7 @@ def _validate_manifest(data: object, plat: str) -> dict:
                 raise ValueError(f"invalid alternative for {dest}")
             # Narrowing can swap in any copy: the cap holds for the largest.
             size = max(size, _check_download(alternative, where, dest))
+        size = max(size, _check_slot(entry, f"files[{index}]", dest))
         largest_total += size
         if largest_total > MAX_TOTAL_DOWNLOAD_SIZE:
             raise ValueError("manifest total size exceeds safety limit")
@@ -1397,13 +1439,44 @@ def _for_cores(entry: dict, chosen: set[str]) -> dict | None:
         if chosen.intersection(alternative["cores"]):
             kept = {
                 k: v for k, v in entry.items()
-                if k not in _COPY_FIELDS and k != "alternatives"
+                if k not in _COPY_FIELDS
+                and k not in ("alternatives", "slot_choices", "declared_choices")
             }
             kept.update((k, alternative[k]) for k in _COPY_FIELDS if k in alternative)
             return kept
     return None
 
 
+def _settle_slot(entry: dict, chosen: set[str], kept_system=None) -> dict:
+    """A platform file as a pack built for the chosen cores carries it.
+
+    Where a core's own source contradicts the platform and the frontend only
+    checks the path, the pack serves the core's copy: the first of
+    `slot_choices` naming a chosen core decides. Otherwise the platform
+    answers, through the first of `declared_choices` whose systems remain.
+    """
+    declared = entry.get("declared_choices")
+    if declared is None:
+        return entry
+    copy = next(
+        (c for c in entry.get("slot_choices", []) if chosen.intersection(c["cores"])),
+        None,
+    )
+    if copy is None or "sha1" not in copy:
+        copy = next(
+            (c for c in declared
+             if kept_system is None or any(kept_system(s) for s in c["systems"])),
+            declared[0],
+        )
+    kept = {
+        k: v for k, v in entry.items()
+        if k not in _COPY_FIELDS and k not in ("slot_choices", "declared_choices")
+    }
+    kept.update((k, copy[k]) for k in _COPY_FIELDS if k in copy and k != "cores")
+    kept["cores"] = None
+    return kept
+
+
 def _filter_by_target(
     files: list[dict], target_cores: list[str]
 ) -> list[dict]:
@@ -1412,7 +1485,7 @@ def _filter_by_target(
     result: list[dict] = []
     for f in files:
         if f.get("cores") is None:
-            result.append(f)
+            result.append(_settle_slot(f, chosen))
             continue
         kept = _for_cores(f, chosen)
         if kept is not None:
@@ -1453,6 +1526,9 @@ def narrow_to_cores(
     cores = designated_cores(manifest, names)
     reach = manifest.get("system_cores") or {}
 
+    def kept_system(system: str) -> bool:
+        return system not in reach or bool(cores.intersection(reach[system]))
+
     def kept(entries: list[dict]) -> list[dict]:
         result: list[dict] = []
         for entry in entries:
@@ -1464,10 +1540,8 @@ def narrow_to_cores(
             # The systems declaring the file, where they are fewer than the
             # ones reading it.
             systems = entry.get("declared_in") or entry_systems(entry)
-            if not systems or any(
-                s not in reach or cores.intersection(reach[s]) for s in systems
-            ):
-                result.append(entry)
+            if not systems or any(kept_system(s) for s in systems):
+                result.append(_settle_slot(entry, cores, kept_system))
                 continue
             # The system is dropped, which frees its destination for the
             # first named core claiming it, as in a pack built for them.
@@ -1622,7 +1696,7 @@ def available_choices(files: list[dict], omitted: list[dict]) -> dict[str, list[
         ordered.append(OTHER_SYSTEMS)
     cores = {
         c for f in files
-        for copy in [f, *f.get("alternatives", [])]
+        for copy in [f, *f.get("alternatives", []), *f.get("slot_choices", [])]
         for c in (copy.get("cores") or [])
     }
     regions = {

install.sh

@@ -18,7 +18,7 @@ esac
 TEMP_INSTALLER=""
 TEMP_DIRECTORY=""
 DEFAULT_INSTALL_URL="https://raw.githubusercontent.com/Abdess/retrobios/main/install.py"
-DEFAULT_INSTALL_SHA256="e0d8fad4e7e55afa57c412e98726992d82b92286b752c9a8cce0978f0a355127"
+DEFAULT_INSTALL_SHA256="953240dab33c25e52005155ecc8cd694269234697ca2c3f55939994fc6b61951"
 MAX_INSTALLER_BYTES=2097152
 
 cleanup() {

install/lakka.json

@@ -1536,6 +1536,28 @@
       "systems": [
         "arcade"
       ],
+      "slot_choices": [
+        {
+          "sha1": "9f84f563df14ea1a1bcaaf05b720c3f5545e5a83",
+          "sha256": "13d503ea6c7e7b9a2249837cf915bff6df862b7035f5c99b18240088ec10854a",
+          "size": 3556,
+          "repo_path": "bios/Arcade/Arcade/.variants/nmk004.zip.f70b6562",
+          "cores": [
+            "fbneo"
+          ]
+        }
+      ],
+      "declared_choices": [
+        {
+          "sha1": "489256f5e2001070d2ad94c90d255282c71ed274",
+          "sha256": "6ca3142ebe127f5d2cb755c53740a92d9bf1574bde8daa32642de2991af89aaa",
+          "size": 3556,
+          "repo_path": "bios/Arcade/Arcade/nmk004.zip",
+          "systems": [
+            "arcade"
+          ]
+        }
+      ],
       "alternatives": [
         {
           "sha1": "9f84f563df14ea1a1bcaaf05b720c3f5545e5a83",
@@ -1850,6 +1872,29 @@
         "arcade",
         "snk-neogeo-cd"
       ],
+      "slot_choices": [
+        {
+          "sha1": "985d935c06fe278ce39d7690aa6c53df88954cd6",
+          "sha256": "4919ba2a7650b24d1bf2c9107c89a80d93b50703a0a371fa5113c791bd03e114",
+          "size": 1184219,
+          "repo_path": "bios/Arcade/Arcade/.variants/neocdz.zip.ba20a7be",
+          "cores": [
+            "fbneo",
+            "fbneo_neogeo"
+          ]
+        }
+      ],
+      "declared_choices": [
+        {
+          "sha1": "4f28af31ca0defdd73d80edec2fa296908e624dc",
+          "sha256": "6aa507a5dc33c45d2592bf2bc77eb3e497762221ddd9225f18583a5c55d38667",
+          "size": 214681,
+          "repo_path": "bios/Arcade/Arcade/.variants/neocdz.zip.4f28af31",
+          "systems": [
+            "arcade"
+          ]
+        }
+      ],
       "declared_in": [
         "arcade"
       ],
@@ -2044,6 +2089,28 @@
         "atari-400-800",
         "atari-5200"
       ],
+      "slot_choices": [
+        {
+          "sha1": "db1031585968cfc6ec2ecda5c9a5a52f61444a3b",
+          "sha256": "63973d5e86b1ae5b6fca5b119a7f7589e817e19acc3ca54e54462c9dfb619e73",
+          "size": 10240,
+          "repo_path": "bios/Atari/400-800/ROM_OS_B_NTSC",
+          "cores": [
+            "atari800"
+          ]
+        }
+      ],
+      "declared_choices": [
+        {
+          "sha1": "f1f0741b1d34fb4350cf7cb8ab3b6ea11cdd8174",
+          "sha256": "bc6012f8ca2f7dde21ae895899b1d2af572ffaa28f819b84911ddb6a0bd8a5c7",
+          "size": 10240,
+          "repo_path": "bios/Atari/400-800/ATARIOSB.ROM",
+          "systems": [
+            "atari-400-800"
+          ]
+        }
+      ],
       "declared_in": [
         "atari-400-800"
       ],
@@ -5224,6 +5291,38 @@
         "nintendo-ds",
         "nintendo-dsi"
       ],
+      "slot_choices": [
+        {
+          "sha1": "c7c7570bfe51c3c7c5da3b01331b94e7e7cb4f53",
+          "sha256": "12a03016ba07cfd874fc002df49a2c6eb2414eb7cfa395c2043035ec5e9193e8",
+          "size": 65536,
+          "repo_path": "bios/Nintendo/DS/NDS_Bios7i.bin",
+          "cores": [
+            "melonds",
+            "melonds_ds"
+          ]
+        }
+      ],
+      "declared_choices": [
+        {
+          "sha1": "a3aa751eb6bdaaf8a827ba9e03576a6f1ab0f547",
+          "sha256": "2946281e730e71f7cafdb125f5cb60fed944ca5d610ee1e082c441b602b5f4e2",
+          "size": 65536,
+          "repo_path": "bios/Nintendo/Nintendo DS/biosdsi7.bin",
+          "systems": [
+            "nintendo-dsi"
+          ]
+        },
+        {
+          "sha1": "d2b17224e156ee5e55b5d8d9f323b1c9b86dd951",
+          "sha256": "28a13952901b4065ef3f08c3252b49a00b6525e301b7ddaa3a390b4c7cbef901",
+          "size": 65536,
+          "repo_path": "bios/Nintendo/DS/dsi_bios7.bin",
+          "systems": [
+            "nintendo-ds"
+          ]
+        }
+      ],
       "alternatives": [
         {
           "sha1": "c7c7570bfe51c3c7c5da3b01331b94e7e7cb4f53",
@@ -5248,6 +5347,38 @@
         "nintendo-ds",
         "nintendo-dsi"
       ],
+      "slot_choices": [
+        {
+          "sha1": "719b9eef33692406d7170ff526069615759c4dfc",
+          "sha256": "6e9f70b51dc4f26289b597f14e2513620c2af964374a95f4c5a62b5cad199afc",
+          "size": 65536,
+          "repo_path": "bios/Nintendo/DS/NDS_Bios9i.bin",
+          "cores": [
+            "melonds",
+            "melonds_ds"
+          ]
+        }
+      ],
+      "declared_choices": [
+        {
+          "sha1": "7bf549b8be9e48ab0cdc9b0fdadd49a5131f97eb",
+          "sha256": "47538922a8e8a8e79b922ff1203863ef5c40d9c54656a8d2c89c56ece52029ce",
+          "size": 65536,
+          "repo_path": "bios/Nintendo/Nintendo DS/biosdsi9.bin",
+          "systems": [
+            "nintendo-dsi"
+          ]
+        },
+        {
+          "sha1": "db61fa39ddbc5f5ed71fb19cda47609ef0201723",
+          "sha256": "664c608bd6ccfe583e87b3b924afa00f8697dc7ca92eeb6d206d68abb03d2e10",
+          "size": 65536,
+          "repo_path": "bios/Nintendo/DS/dsi_bios9.bin",
+          "systems": [
+            "nintendo-ds"
+          ]
+        }
+      ],
       "alternatives": [
         {
           "sha1": "719b9eef33692406d7170ff526069615759c4dfc",
@@ -9539,6 +9670,38 @@
       "systems": [
         "snk-neogeo-cd"
       ],
+      "slot_choices": [
+        {
+          "sha1": "712816a3c41baf4129e23d645305a536e03d69de",
+          "sha256": "f885f2cc79b5c0120ca316b0db360183c2b9a60bc727cbe211b7518e12bd5548",
+          "size": 955352,
+          "repo_path": "bios/SNK/Neo Geo CD/.variants/neocdz.zip.712816a3",
+          "cores": [
+            "geolith"
+          ]
+        },
+        {
+          "sha1": "985d935c06fe278ce39d7690aa6c53df88954cd6",
+          "sha256": "4919ba2a7650b24d1bf2c9107c89a80d93b50703a0a371fa5113c791bd03e114",
+          "size": 1184219,
+          "repo_path": "bios/Arcade/Arcade/.variants/neocdz.zip.ba20a7be",
+          "cores": [
+            "fbneo",
+            "fbneo_neogeo"
+          ]
+        }
+      ],
+      "declared_choices": [
+        {
+          "sha1": "9cab31cfe7eacb6871d36cee105d87b90fd85b64",
+          "sha256": "d828241905d390c5de4867646296f615c95bca2f5d8f7e81d50e08717373a821",
+          "size": 1181333,
+          "repo_path": "bios/Arcade/Arcade/neocdz.zip",
+          "systems": [
+            "snk-neogeo-cd"
+          ]
+        }
+      ],
       "alternatives": [
         {
           "sha1": "712816a3c41baf4129e23d645305a536e03d69de",
@@ -9831,6 +9994,29 @@
       "region_system_groups": [
         "sony-playstation"
       ],
+      "slot_choices": [
+        {
+          "sha1": "ffa7f9a7fb19d773a0c3985a541c8e5623d2c30d",
+          "sha256": "0c8359870cbac0ea091f1c87f188cd332dcc709753b91cafd9fd44a4a6188197",
+          "size": 524288,
+          "repo_path": "bios/Sony/PlayStation/scph5000.bin",
+          "cores": [
+            "duckstation",
+            "rustation"
+          ]
+        }
+      ],
+      "declared_choices": [
+        {
+          "sha1": "ffa7f9a7fb19d773a0c3985a541c8e5623d2c30d",
+          "sha256": "0c8359870cbac0ea091f1c87f188cd332dcc709753b91cafd9fd44a4a6188197",
+          "size": 524288,
+          "repo_path": "bios/Sony/PlayStation/scph5000.bin",
+          "systems": [
+            "sony-playstation"
+          ]
+        }
+      ],
       "alternatives": [
         {
           "sha1": "ffa7f9a7fb19d773a0c3985a541c8e5623d2c30d",
@@ -11675,6 +11861,46 @@
       "systems": [
         "sony-playstation-2"
       ],
+      "slot_choices": [
+        {
+          "sha1": "72bfdf91fa11a86e2810a7c167cdcf11e20418a8",
+          "sha256": "61c77b789ccde856096f024e4a3eef6891e15ca59c127e0dd13e762a7d338a7e",
+          "size": 2690355,
+          "repo_path": "bios/Other/armsx2/pcsx2/resources/GameIndex.yaml",
+          "cores": [
+            "armsx2"
+          ]
+        },
+        {
+          "sha1": "7efb2ed721cf0c0f0677324e09be311a8337e793",
+          "sha256": "3bf3c54d6f16d88d3669be698179bb8c2fb981ee5ce71bcb952719429a838cc1",
+          "size": 2693579,
+          "repo_path": "bios/Other/yaps2/GameIndex.yaml",
+          "cores": [
+            "yaps2"
+          ]
+        },
+        {
+          "sha1": "72bfdf91fa11a86e2810a7c167cdcf11e20418a8",
+          "sha256": "61c77b789ccde856096f024e4a3eef6891e15ca59c127e0dd13e762a7d338a7e",
+          "size": 2690355,
+          "repo_path": "bios/Other/armsx2/pcsx2/resources/GameIndex.yaml",
+          "cores": [
+            "lrps2"
+          ]
+        }
+      ],
+      "declared_choices": [
+        {
+          "sha1": "57369df9ca82a460e596cea7835c5a0797dee668",
+          "sha256": "efa94cb7b9208dc6812bb9407dc986560e523cce57f511eff30942f76b7288bf",
+          "size": 1737799,
+          "repo_path": "bios/Sony/PlayStation 2/.variants/GameIndex.yaml.57369df9",
+          "systems": [
+            "sony-playstation-2"
+          ]
+        }
+      ],
       "alternatives": [
         {
           "sha1": "72bfdf91fa11a86e2810a7c167cdcf11e20418a8",

install/retroarch.json

@@ -1775,6 +1775,28 @@
       "systems": [
         "arcade"
       ],
+      "slot_choices": [
+        {
+          "sha1": "9f84f563df14ea1a1bcaaf05b720c3f5545e5a83",
+          "sha256": "13d503ea6c7e7b9a2249837cf915bff6df862b7035f5c99b18240088ec10854a",
+          "size": 3556,
+          "repo_path": "bios/Arcade/Arcade/.variants/nmk004.zip.f70b6562",
+          "cores": [
+            "fbneo"
+          ]
+        }
+      ],
+      "declared_choices": [
+        {
+          "sha1": "489256f5e2001070d2ad94c90d255282c71ed274",
+          "sha256": "6ca3142ebe127f5d2cb755c53740a92d9bf1574bde8daa32642de2991af89aaa",
+          "size": 3556,
+          "repo_path": "bios/Arcade/Arcade/nmk004.zip",
+          "systems": [
+            "arcade"
+          ]
+        }
+      ],
       "alternatives": [
         {
           "sha1": "9f84f563df14ea1a1bcaaf05b720c3f5545e5a83",
@@ -2089,6 +2111,29 @@
         "arcade",
         "snk-neogeo-cd"
       ],
+      "slot_choices": [
+        {
+          "sha1": "985d935c06fe278ce39d7690aa6c53df88954cd6",
+          "sha256": "4919ba2a7650b24d1bf2c9107c89a80d93b50703a0a371fa5113c791bd03e114",
+          "size": 1184219,
+          "repo_path": "bios/Arcade/Arcade/.variants/neocdz.zip.ba20a7be",
+          "cores": [
+            "fbneo",
+            "fbneo_neogeo"
+          ]
+        }
+      ],
+      "declared_choices": [
+        {
+          "sha1": "4f28af31ca0defdd73d80edec2fa296908e624dc",
+          "sha256": "6aa507a5dc33c45d2592bf2bc77eb3e497762221ddd9225f18583a5c55d38667",
+          "size": 214681,
+          "repo_path": "bios/Arcade/Arcade/.variants/neocdz.zip.4f28af31",
+          "systems": [
+            "arcade"
+          ]
+        }
+      ],
       "declared_in": [
         "arcade"
       ],
@@ -2283,6 +2328,28 @@
         "atari-400-800",
         "atari-5200"
       ],
+      "slot_choices": [
+        {
+          "sha1": "db1031585968cfc6ec2ecda5c9a5a52f61444a3b",
+          "sha256": "63973d5e86b1ae5b6fca5b119a7f7589e817e19acc3ca54e54462c9dfb619e73",
+          "size": 10240,
+          "repo_path": "bios/Atari/400-800/ROM_OS_B_NTSC",
+          "cores": [
+            "atari800"
+          ]
+        }
+      ],
+      "declared_choices": [
+        {
+          "sha1": "f1f0741b1d34fb4350cf7cb8ab3b6ea11cdd8174",
+          "sha256": "bc6012f8ca2f7dde21ae895899b1d2af572ffaa28f819b84911ddb6a0bd8a5c7",
+          "size": 10240,
+          "repo_path": "bios/Atari/400-800/ATARIOSB.ROM",
+          "systems": [
+            "atari-400-800"
+          ]
+        }
+      ],
       "declared_in": [
         "atari-400-800"
       ],
@@ -5463,6 +5530,38 @@
         "nintendo-ds",
         "nintendo-dsi"
       ],
+      "slot_choices": [
+        {
+          "sha1": "c7c7570bfe51c3c7c5da3b01331b94e7e7cb4f53",
+          "sha256": "12a03016ba07cfd874fc002df49a2c6eb2414eb7cfa395c2043035ec5e9193e8",
+          "size": 65536,
+          "repo_path": "bios/Nintendo/DS/NDS_Bios7i.bin",
+          "cores": [
+            "melonds",
+            "melonds_ds"
+          ]
+        }
+      ],
+      "declared_choices": [
+        {
+          "sha1": "a3aa751eb6bdaaf8a827ba9e03576a6f1ab0f547",
+          "sha256": "2946281e730e71f7cafdb125f5cb60fed944ca5d610ee1e082c441b602b5f4e2",
+          "size": 65536,
+          "repo_path": "bios/Nintendo/Nintendo DS/biosdsi7.bin",
+          "systems": [
+            "nintendo-dsi"
+          ]
+        },
+        {
+          "sha1": "d2b17224e156ee5e55b5d8d9f323b1c9b86dd951",
+          "sha256": "28a13952901b4065ef3f08c3252b49a00b6525e301b7ddaa3a390b4c7cbef901",
+          "size": 65536,
+          "repo_path": "bios/Nintendo/DS/dsi_bios7.bin",
+          "systems": [
+            "nintendo-ds"
+          ]
+        }
+      ],
       "alternatives": [
         {
           "sha1": "c7c7570bfe51c3c7c5da3b01331b94e7e7cb4f53",
@@ -5487,6 +5586,38 @@
         "nintendo-ds",
         "nintendo-dsi"
       ],
+      "slot_choices": [
+        {
+          "sha1": "719b9eef33692406d7170ff526069615759c4dfc",
+          "sha256": "6e9f70b51dc4f26289b597f14e2513620c2af964374a95f4c5a62b5cad199afc",
+          "size": 65536,
+          "repo_path": "bios/Nintendo/DS/NDS_Bios9i.bin",
+          "cores": [
+            "melonds",
+            "melonds_ds"
+          ]
+        }
+      ],
+      "declared_choices": [
+        {
+          "sha1": "7bf549b8be9e48ab0cdc9b0fdadd49a5131f97eb",
+          "sha256": "47538922a8e8a8e79b922ff1203863ef5c40d9c54656a8d2c89c56ece52029ce",
+          "size": 65536,
+          "repo_path": "bios/Nintendo/Nintendo DS/biosdsi9.bin",
+          "systems": [
+            "nintendo-dsi"
+          ]
+        },
+        {
+          "sha1": "db61fa39ddbc5f5ed71fb19cda47609ef0201723",
+          "sha256": "664c608bd6ccfe583e87b3b924afa00f8697dc7ca92eeb6d206d68abb03d2e10",
+          "size": 65536,
+          "repo_path": "bios/Nintendo/DS/dsi_bios9.bin",
+          "systems": [
+            "nintendo-ds"
+          ]
+        }
+      ],
       "alternatives": [
         {
           "sha1": "719b9eef33692406d7170ff526069615759c4dfc",
@@ -9778,6 +9909,38 @@
       "systems": [
         "snk-neogeo-cd"
       ],
+      "slot_choices": [
+        {
+          "sha1": "712816a3c41baf4129e23d645305a536e03d69de",
+          "sha256": "f885f2cc79b5c0120ca316b0db360183c2b9a60bc727cbe211b7518e12bd5548",
+          "size": 955352,
+          "repo_path": "bios/SNK/Neo Geo CD/.variants/neocdz.zip.712816a3",
+          "cores": [
+            "geolith"
+          ]
+        },
+        {
+          "sha1": "985d935c06fe278ce39d7690aa6c53df88954cd6",
+          "sha256": "4919ba2a7650b24d1bf2c9107c89a80d93b50703a0a371fa5113c791bd03e114",
+          "size": 1184219,
+          "repo_path": "bios/Arcade/Arcade/.variants/neocdz.zip.ba20a7be",
+          "cores": [
+            "fbneo",
+            "fbneo_neogeo"
+          ]
+        }
+      ],
+      "declared_choices": [
+        {
+          "sha1": "9cab31cfe7eacb6871d36cee105d87b90fd85b64",
+          "sha256": "d828241905d390c5de4867646296f615c95bca2f5d8f7e81d50e08717373a821",
+          "size": 1181333,
+          "repo_path": "bios/Arcade/Arcade/neocdz.zip",
+          "systems": [
+            "snk-neogeo-cd"
+          ]
+        }
+      ],
       "alternatives": [
         {
           "sha1": "712816a3c41baf4129e23d645305a536e03d69de",
@@ -10070,6 +10233,29 @@
       "region_system_groups": [
         "sony-playstation"
       ],
+      "slot_choices": [
+        {
+          "sha1": "ffa7f9a7fb19d773a0c3985a541c8e5623d2c30d",
+          "sha256": "0c8359870cbac0ea091f1c87f188cd332dcc709753b91cafd9fd44a4a6188197",
+          "size": 524288,
+          "repo_path": "bios/Sony/PlayStation/scph5000.bin",
+          "cores": [
+            "duckstation",
+            "rustation"
+          ]
+        }
+      ],
+      "declared_choices": [
+        {
+          "sha1": "ffa7f9a7fb19d773a0c3985a541c8e5623d2c30d",
+          "sha256": "0c8359870cbac0ea091f1c87f188cd332dcc709753b91cafd9fd44a4a6188197",
+          "size": 524288,
+          "repo_path": "bios/Sony/PlayStation/scph5000.bin",
+          "systems": [
+            "sony-playstation"
+          ]
+        }
+      ],
       "alternatives": [
         {
           "sha1": "ffa7f9a7fb19d773a0c3985a541c8e5623d2c30d",
@@ -11914,6 +12100,46 @@
       "systems": [
         "sony-playstation-2"
       ],
+      "slot_choices": [
+        {
+          "sha1": "72bfdf91fa11a86e2810a7c167cdcf11e20418a8",
+          "sha256": "61c77b789ccde856096f024e4a3eef6891e15ca59c127e0dd13e762a7d338a7e",
+          "size": 2690355,
+          "repo_path": "bios/Other/armsx2/pcsx2/resources/GameIndex.yaml",
+          "cores": [
+            "armsx2"
+          ]
+        },
+        {
+          "sha1": "7efb2ed721cf0c0f0677324e09be311a8337e793",
+          "sha256": "3bf3c54d6f16d88d3669be698179bb8c2fb981ee5ce71bcb952719429a838cc1",
+          "size": 2693579,
+          "repo_path": "bios/Other/yaps2/GameIndex.yaml",
+          "cores": [
+            "yaps2"
+          ]
+        },
+        {
+          "sha1": "72bfdf91fa11a86e2810a7c167cdcf11e20418a8",
+          "sha256": "61c77b789ccde856096f024e4a3eef6891e15ca59c127e0dd13e762a7d338a7e",
+          "size": 2690355,
+          "repo_path": "bios/Other/armsx2/pcsx2/resources/GameIndex.yaml",
+          "cores": [
+            "lrps2"
+          ]
+        }
+      ],
+      "declared_choices": [
+        {
+          "sha1": "57369df9ca82a460e596cea7835c5a0797dee668",
+          "sha256": "efa94cb7b9208dc6812bb9407dc986560e523cce57f511eff30942f76b7288bf",
+          "size": 1737799,
+          "repo_path": "bios/Sony/PlayStation 2/.variants/GameIndex.yaml.57369df9",
+          "systems": [
+            "sony-playstation-2"
+          ]
+        }
+      ],
       "alternatives": [
         {
           "sha1": "72bfdf91fa11a86e2810a7c167cdcf11e20418a8",

install/retrodeck.json

@@ -6570,6 +6570,26 @@
         "arcade",
         "philips-cdi"
       ],
+      "declared_choices": [
+        {
+          "sha1": "e7d2a0dad62d6f75bc10f48a376da0a99b764571",
+          "sha256": "aa8a33813531795de9739b06b65960e0f86cdec504c8452a956d184eac3cdcd4",
+          "size": 468660,
+          "repo_path": "bios/Arcade/Arcade/.variants/cdibios.zip.e7d2a0da",
+          "systems": [
+            "arcade"
+          ]
+        },
+        {
+          "sha1": "16072afaa65d1b059346616ac5b5a600c63ff1d1",
+          "sha256": "b53d206ae81607bf6866411b720ad82ce75122423058ce08c6df84cdc1ca3496",
+          "size": 472798,
+          "repo_path": "bios/Philips/CD-i/cdibios.zip",
+          "systems": [
+            "philips-cdi"
+          ]
+        }
+      ],
       "alternatives": [
         {
           "sha1": "16072afaa65d1b059346616ac5b5a600c63ff1d1",
@@ -17884,6 +17904,26 @@
         "arcade",
         "sega-saturn"
       ],
+      "declared_choices": [
+        {
+          "sha1": "330a2ab5ce2e2c29987b2086e021de7aa04aa102",
+          "sha256": "bbdf6a9ef4bad6bd9ad16f9f7669071dd4ee3bb2387d49124f024ea8dd750f88",
+          "size": 2699375,
+          "repo_path": "bios/Arcade/MAME/.variants/stvbios.zip.330a2ab5",
+          "systems": [
+            "arcade"
+          ]
+        },
+        {
+          "sha1": "7783ab663bb1a8d62ff60d583674355c2af556b1",
+          "sha256": "38ceb2792c72770f56aadb1865cf66dc33a3017db1ee05e11c2b2dff397ad39e",
+          "size": 2955630,
+          "repo_path": "bios/Arcade/MAME/stvbios.zip",
+          "systems": [
+            "sega-saturn"
+          ]
+        }
+      ],
       "alternatives": [
         {
           "sha1": "b14bbed4bf459439cf7e96d2f79d7adea5d31448",
@@ -20260,6 +20300,26 @@
         "atari-400-800",
         "atari-5200"
       ],
+      "declared_choices": [
+        {
+          "sha1": "f1f0741b1d34fb4350cf7cb8ab3b6ea11cdd8174",
+          "sha256": "bc6012f8ca2f7dde21ae895899b1d2af572ffaa28f819b84911ddb6a0bd8a5c7",
+          "size": 10240,
+          "repo_path": "bios/Atari/400-800/ATARIOSB.ROM",
+          "systems": [
+            "atari-400-800"
+          ]
+        },
+        {
+          "sha1": "db1031585968cfc6ec2ecda5c9a5a52f61444a3b",
+          "sha256": "63973d5e86b1ae5b6fca5b119a7f7589e817e19acc3ca54e54462c9dfb619e73",
+          "size": 10240,
+          "repo_path": "bios/Atari/400-800/ROM_OS_B_NTSC",
+          "systems": [
+            "atari-5200"
+          ]
+        }
+      ],
       "alternatives": [
         {
           "sha1": "db1031585968cfc6ec2ecda5c9a5a52f61444a3b",
@@ -23088,6 +23148,26 @@
       "systems": [
         "nec-pc-88",
         "tandy-coco"
+      ],
+      "declared_choices": [
+        {
+          "sha1": "bb7103a0818850a039c67ff666a31ce49a8d516f",
+          "sha256": "9dc63118728a171ce2ed437ad38ef280b8b7bcf4a5a95fedf18946501b010456",
+          "size": 2048,
+          "repo_path": "bios/NEC/PC-88/N88SUB.ROM",
+          "systems": [
+            "nec-pc-88"
+          ]
+        },
+        {
+          "sha1": "892b85cc96f0ff31cae8ad8d409b9f6c04b32e5e",
+          "sha256": "b9b4bfe42b4957d4c6b532ceb5a1946c9e4d9d4f55a6e3eb600cc7f236e09ca9",
+          "size": 8194,
+          "repo_path": "bios/Tandy/CoCo/disk.rom",
+          "systems": [
+            "tandy-coco"
+          ]
+        }
       ]
     },
     {

install/retropie.json

@@ -1553,6 +1553,28 @@
       "systems": [
         "arcade"
       ],
+      "slot_choices": [
+        {
+          "sha1": "9f84f563df14ea1a1bcaaf05b720c3f5545e5a83",
+          "sha256": "13d503ea6c7e7b9a2249837cf915bff6df862b7035f5c99b18240088ec10854a",
+          "size": 3556,
+          "repo_path": "bios/Arcade/Arcade/.variants/nmk004.zip.f70b6562",
+          "cores": [
+            "fbneo"
+          ]
+        }
+      ],
+      "declared_choices": [
+        {
+          "sha1": "489256f5e2001070d2ad94c90d255282c71ed274",
+          "sha256": "6ca3142ebe127f5d2cb755c53740a92d9bf1574bde8daa32642de2991af89aaa",
+          "size": 3556,
+          "repo_path": "bios/Arcade/Arcade/nmk004.zip",
+          "systems": [
+            "arcade"
+          ]
+        }
+      ],
       "alternatives": [
         {
           "sha1": "9f84f563df14ea1a1bcaaf05b720c3f5545e5a83",
@@ -1867,6 +1889,29 @@
         "arcade",
         "snk-neogeo-cd"
       ],
+      "slot_choices": [
+        {
+          "sha1": "985d935c06fe278ce39d7690aa6c53df88954cd6",
+          "sha256": "4919ba2a7650b24d1bf2c9107c89a80d93b50703a0a371fa5113c791bd03e114",
+          "size": 1184219,
+          "repo_path": "bios/Arcade/Arcade/.variants/neocdz.zip.ba20a7be",
+          "cores": [
+            "fbneo",
+            "fbneo_neogeo"
+          ]
+        }
+      ],
+      "declared_choices": [
+        {
+          "sha1": "4f28af31ca0defdd73d80edec2fa296908e624dc",
+          "sha256": "6aa507a5dc33c45d2592bf2bc77eb3e497762221ddd9225f18583a5c55d38667",
+          "size": 214681,
+          "repo_path": "bios/Arcade/Arcade/.variants/neocdz.zip.4f28af31",
+          "systems": [
+            "arcade"
+          ]
+        }
+      ],
       "declared_in": [
         "arcade"
       ],
@@ -2061,6 +2106,28 @@
         "atari-400-800",
         "atari-5200"
       ],
+      "slot_choices": [
+        {
+          "sha1": "db1031585968cfc6ec2ecda5c9a5a52f61444a3b",
+          "sha256": "63973d5e86b1ae5b6fca5b119a7f7589e817e19acc3ca54e54462c9dfb619e73",
+          "size": 10240,
+          "repo_path": "bios/Atari/400-800/ROM_OS_B_NTSC",
+          "cores": [
+            "atari800"
+          ]
+        }
+      ],
+      "declared_choices": [
+        {
+          "sha1": "f1f0741b1d34fb4350cf7cb8ab3b6ea11cdd8174",
+          "sha256": "bc6012f8ca2f7dde21ae895899b1d2af572ffaa28f819b84911ddb6a0bd8a5c7",
+          "size": 10240,
+          "repo_path": "bios/Atari/400-800/ATARIOSB.ROM",
+          "systems": [
+            "atari-400-800"
+          ]
+        }
+      ],
       "declared_in": [
         "atari-400-800"
       ],
@@ -2346,6 +2413,34 @@
       "systems": [
         "coleco-colecovision"
       ],
+      "slot_choices": [
+        {
+          "cores": [
+            "jollycv",
+            "openmsx"
+          ]
+        },
+        {
+          "sha1": "99ba9be24ada3e86e5c17aeecb7a2d68c5edfe59",
+          "sha256": "25cdb7ff4ad675ac25e11663e9e9472afc1c7cf59ba40c330081abda9881a968",
+          "size": 8192,
+          "repo_path": "bios/Coleco/ColecoVision/colecoa.rom",
+          "cores": [
+            "zesarux"
+          ]
+        }
+      ],
+      "declared_choices": [
+        {
+          "sha1": "45bedc4cbdeac66c7df59e9e599195c778d86a92",
+          "sha256": "990bf1956f10207d8781b619eb74f89b00d921c8d45c95c334c16c8cceca09ad",
+          "size": 8192,
+          "repo_path": "bios/Coleco/ColecoVision/BIOS.col",
+          "systems": [
+            "coleco-colecovision"
+          ]
+        }
+      ],
       "alternatives": [
         {
           "sha1": "45bedc4cbdeac66c7df59e9e599195c778d86a92",
@@ -4113,6 +4208,33 @@
       "systems": [
         "microsoft-msx"
       ],
+      "slot_choices": [
+        {
+          "cores": [
+            "fmsx"
+          ]
+        },
+        {
+          "sha1": "fec451b9256570a0e4869355a40329c57f40705f",
+          "sha256": "a3a6a325935d031cee662b56e2c810c73d35a8375a2c5ffa03f6d27405bc569e",
+          "size": 65536,
+          "repo_path": "bios/Microsoft/MSX/openmsx/fmpac.rom",
+          "cores": [
+            "openmsx"
+          ]
+        }
+      ],
+      "declared_choices": [
+        {
+          "sha1": "9d789166e3caf28e4742fe933d962e99618c633d",
+          "sha256": "3cfe44646b69a622656b96305f1b975f48ca018839f7946895f7a1352d9720aa",
+          "size": 65536,
+          "repo_path": "bios/Microsoft/MSX/FMPAC.ROM",
+          "systems": [
+            "microsoft-msx"
+          ]
+        }
+      ],
       "alternatives": [
         {
           "sha1": "9d789166e3caf28e4742fe933d962e99618c633d",
@@ -4190,6 +4312,33 @@
       "systems": [
         "microsoft-msx"
       ],
+      "slot_choices": [
+        {
+          "cores": [
+            "fmsx"
+          ]
+        },
+        {
+          "sha1": "e998f0c441f4f1800ef44e42cd1659150206cf79",
+          "sha256": "1c85dac5536fa3ba6f2cb70deba02ff680b34ac6cc787d2977258bd663a99555",
+          "size": 32768,
+          "repo_path": "bios/Microsoft/MSX/MSX_8020-20bios.rom",
+          "cores": [
+            "zesarux"
+          ]
+        }
+      ],
+      "declared_choices": [
+        {
+          "sha1": "409e82adac40f6bdd18eb6c84e8b2fbdc7fb5498",
+          "sha256": "999564a371dd2fdf7fbe8d853e82a68d557c27b7d87417639b2fa17704b83f78",
+          "size": 32768,
+          "repo_path": "bios/Microsoft/MSX/MSX.ROM",
+          "systems": [
+            "microsoft-msx"
+          ]
+        }
+      ],
       "alternatives": [
         {
           "sha1": "409e82adac40f6bdd18eb6c84e8b2fbdc7fb5498",
@@ -5250,6 +5399,38 @@
         "nintendo-ds",
         "nintendo-dsi"
       ],
+      "slot_choices": [
+        {
+          "sha1": "c7c7570bfe51c3c7c5da3b01331b94e7e7cb4f53",
+          "sha256": "12a03016ba07cfd874fc002df49a2c6eb2414eb7cfa395c2043035ec5e9193e8",
+          "size": 65536,
+          "repo_path": "bios/Nintendo/DS/NDS_Bios7i.bin",
+          "cores": [
+            "melonds",
+            "melonds_ds"
+          ]
+        }
+      ],
+      "declared_choices": [
+        {
+          "sha1": "a3aa751eb6bdaaf8a827ba9e03576a6f1ab0f547",
+          "sha256": "2946281e730e71f7cafdb125f5cb60fed944ca5d610ee1e082c441b602b5f4e2",
+          "size": 65536,
+          "repo_path": "bios/Nintendo/Nintendo DS/biosdsi7.bin",
+          "systems": [
+            "nintendo-dsi"
+          ]
+        },
+        {
+          "sha1": "d2b17224e156ee5e55b5d8d9f323b1c9b86dd951",
+          "sha256": "28a13952901b4065ef3f08c3252b49a00b6525e301b7ddaa3a390b4c7cbef901",
+          "size": 65536,
+          "repo_path": "bios/Nintendo/DS/dsi_bios7.bin",
+          "systems": [
+            "nintendo-ds"
+          ]
+        }
+      ],
       "alternatives": [
         {
           "sha1": "c7c7570bfe51c3c7c5da3b01331b94e7e7cb4f53",
@@ -5274,6 +5455,38 @@
         "nintendo-ds",
         "nintendo-dsi"
       ],
+      "slot_choices": [
+        {
+          "sha1": "719b9eef33692406d7170ff526069615759c4dfc",
+          "sha256": "6e9f70b51dc4f26289b597f14e2513620c2af964374a95f4c5a62b5cad199afc",
+          "size": 65536,
+          "repo_path": "bios/Nintendo/DS/NDS_Bios9i.bin",
+          "cores": [
+            "melonds",
+            "melonds_ds"
+          ]
+        }
+      ],
+      "declared_choices": [
+        {
+          "sha1": "7bf549b8be9e48ab0cdc9b0fdadd49a5131f97eb",
+          "sha256": "47538922a8e8a8e79b922ff1203863ef5c40d9c54656a8d2c89c56ece52029ce",
+          "size": 65536,
+          "repo_path": "bios/Nintendo/Nintendo DS/biosdsi9.bin",
+          "systems": [
+            "nintendo-dsi"
+          ]
+        },
+        {
+          "sha1": "db61fa39ddbc5f5ed71fb19cda47609ef0201723",
+          "sha256": "664c608bd6ccfe583e87b3b924afa00f8697dc7ca92eeb6d206d68abb03d2e10",
+          "size": 65536,
+          "repo_path": "bios/Nintendo/DS/dsi_bios9.bin",
+          "systems": [
+            "nintendo-ds"
+          ]
+        }
+      ],
       "alternatives": [
         {
           "sha1": "719b9eef33692406d7170ff526069615759c4dfc",
@@ -9587,6 +9800,38 @@
       "systems": [
         "snk-neogeo-cd"
       ],
+      "slot_choices": [
+        {
+          "sha1": "712816a3c41baf4129e23d645305a536e03d69de",
+          "sha256": "f885f2cc79b5c0120ca316b0db360183c2b9a60bc727cbe211b7518e12bd5548",
+          "size": 955352,
+          "repo_path": "bios/SNK/Neo Geo CD/.variants/neocdz.zip.712816a3",
+          "cores": [
+            "geolith"
+          ]
+        },
+        {
+          "sha1": "985d935c06fe278ce39d7690aa6c53df88954cd6",
+          "sha256": "4919ba2a7650b24d1bf2c9107c89a80d93b50703a0a371fa5113c791bd03e114",
+          "size": 1184219,
+          "repo_path": "bios/Arcade/Arcade/.variants/neocdz.zip.ba20a7be",
+          "cores": [
+            "fbneo",
+            "fbneo_neogeo"
+          ]
+        }
+      ],
+      "declared_choices": [
+        {
+          "sha1": "9cab31cfe7eacb6871d36cee105d87b90fd85b64",
+          "sha256": "d828241905d390c5de4867646296f615c95bca2f5d8f7e81d50e08717373a821",
+          "size": 1181333,
+          "repo_path": "bios/Arcade/Arcade/neocdz.zip",
+          "systems": [
+            "snk-neogeo-cd"
+          ]
+        }
+      ],
       "alternatives": [
         {
           "sha1": "712816a3c41baf4129e23d645305a536e03d69de",
@@ -9879,6 +10124,29 @@
       "region_system_groups": [
         "sony-playstation"
       ],
+      "slot_choices": [
+        {
+          "sha1": "ffa7f9a7fb19d773a0c3985a541c8e5623d2c30d",
+          "sha256": "0c8359870cbac0ea091f1c87f188cd332dcc709753b91cafd9fd44a4a6188197",
+          "size": 524288,
+          "repo_path": "bios/Sony/PlayStation/scph5000.bin",
+          "cores": [
+            "duckstation",
+            "rustation"
+          ]
+        }
+      ],
+      "declared_choices": [
+        {
+          "sha1": "ffa7f9a7fb19d773a0c3985a541c8e5623d2c30d",
+          "sha256": "0c8359870cbac0ea091f1c87f188cd332dcc709753b91cafd9fd44a4a6188197",
+          "size": 524288,
+          "repo_path": "bios/Sony/PlayStation/scph5000.bin",
+          "systems": [
+            "sony-playstation"
+          ]
+        }
+      ],
       "alternatives": [
         {
           "sha1": "ffa7f9a7fb19d773a0c3985a541c8e5623d2c30d",
@@ -11723,6 +11991,46 @@
       "systems": [
         "sony-playstation-2"
       ],
+      "slot_choices": [
+        {
+          "sha1": "72bfdf91fa11a86e2810a7c167cdcf11e20418a8",
+          "sha256": "61c77b789ccde856096f024e4a3eef6891e15ca59c127e0dd13e762a7d338a7e",
+          "size": 2690355,
+          "repo_path": "bios/Other/armsx2/pcsx2/resources/GameIndex.yaml",
+          "cores": [
+            "armsx2"
+          ]
+        },
+        {
+          "sha1": "7efb2ed721cf0c0f0677324e09be311a8337e793",
+          "sha256": "3bf3c54d6f16d88d3669be698179bb8c2fb981ee5ce71bcb952719429a838cc1",
+          "size": 2693579,
+          "repo_path": "bios/Other/yaps2/GameIndex.yaml",
+          "cores": [
+            "yaps2"
+          ]
+        },
+        {
+          "sha1": "72bfdf91fa11a86e2810a7c167cdcf11e20418a8",
+          "sha256": "61c77b789ccde856096f024e4a3eef6891e15ca59c127e0dd13e762a7d338a7e",
+          "size": 2690355,
+          "repo_path": "bios/Other/armsx2/pcsx2/resources/GameIndex.yaml",
+          "cores": [
+            "lrps2"
+          ]
+        }
+      ],
+      "declared_choices": [
+        {
+          "sha1": "57369df9ca82a460e596cea7835c5a0797dee668",
+          "sha256": "efa94cb7b9208dc6812bb9407dc986560e523cce57f511eff30942f76b7288bf",
+          "size": 1737799,
+          "repo_path": "bios/Sony/PlayStation 2/.variants/GameIndex.yaml.57369df9",
+          "systems": [
+            "sony-playstation-2"
+          ]
+        }
+      ],
       "alternatives": [
         {
           "sha1": "72bfdf91fa11a86e2810a7c167cdcf11e20418a8",

schemas/install-manifest.schema.json

@@ -482,6 +482,104 @@
               }
             }
           },
+          "slot_choices": {
+            "description": "On a platform file a core's own source contradicts while the frontend only checks the path: the copy each core's presence puts there, in the order the pack builder settles the slot. A narrowing serves the first whose cores remain; one naming only cores, or none remaining, leaves `declared_choices`.",
+            "type": "array",
+            "items": {
+              "type": "object",
+              "additionalProperties": false,
+              "required": [
+                "cores"
+              ],
+              "properties": {
+                "sha1": {
+                  "type": "string",
+                  "pattern": "^[a-f0-9]{40}$"
+                },
+                "sha256": {
+                  "type": "string",
+                  "pattern": "^[a-f0-9]{64}$"
+                },
+                "size": {
+                  "type": "integer",
+                  "minimum": 0
+                },
+                "repo_path": {
+                  "type": "string"
+                },
+                "storage": {
+                  "const": "release"
+                },
+                "release_asset": {
+                  "type": "string",
+                  "pattern": "^[^/\\\\]+$"
+                },
+                "cores": {
+                  "type": "array",
+                  "items": {
+                    "type": "string"
+                  },
+                  "minItems": 1,
+                  "uniqueItems": true
+                },
+                "executable": {
+                  "type": "boolean"
+                }
+              }
+            }
+          },
+          "declared_choices": {
+            "description": "The platform's own answer at the destination by the declaring systems that remain, in the order the pack builder takes the declarations; a narrowing serves the first whose systems remain.",
+            "type": "array",
+            "minItems": 1,
+            "items": {
+              "type": "object",
+              "additionalProperties": false,
+              "required": [
+                "sha1",
+                "sha256",
+                "size",
+                "repo_path",
+                "systems"
+              ],
+              "properties": {
+                "sha1": {
+                  "type": "string",
+                  "pattern": "^[a-f0-9]{40}$"
+                },
+                "sha256": {
+                  "type": "string",
+                  "pattern": "^[a-f0-9]{64}$"
+                },
+                "size": {
+                  "type": "integer",
+                  "minimum": 0
+                },
+                "repo_path": {
+                  "type": "string"
+                },
+                "storage": {
+                  "const": "release"
+                },
+                "release_asset": {
+                  "type": "string",
+                  "pattern": "^[^/\\\\]+$"
+                },
+                "executable": {
+                  "type": "boolean"
+                },
+                "systems": {
+                  "type": "array",
+                  "items": {
+                    "type": "string",
+                    "minLength": 1
+                  },
+                  "minItems": 1,
+                  "uniqueItems": true
+                }
+              }
+            }
+          },
           "executable": {
             "description": "The repository keeps the file executable; the installer gives it the execute bits the umask allows.",
             "type": "boolean"

scripts/generate_pack.py

@@ -3160,6 +3160,66 @@ def _attach_claims(
         entry.pop("alternatives", None)
 
 
+def _record_slot_choices(
+    entry: dict,
+    choices: list[tuple[str, str | None]],
+    declarations: list[tuple[list[str], dict, str]],
+    settle,
+    dest: str,
+    db: dict,
+    repo_root: str,
+) -> None:
+    """Record what a pack built for fewer cores serves at a platform destination.
+
+    `slot_choices` lists, in the order slots decides, the cores whose claim
+    settles the slot and the copy it serves, a choice without a copy leaving
+    the platform's answer. `declared_choices` is the platform's answer by the
+    declaring systems that remain, in the order the builder takes them.
+    Nothing is recorded where every narrowing gets the entry's own copy.
+    """
+
+    def download(file_entry: dict, sys_id: str, override: str | None) -> dict | None:
+        local_path, _status = settle(file_entry, sys_id, dest, override)
+        if local_path is None:
+            return None
+        copy, _size = _manifest_entry(local_path, dest, None, db, repo_root, {})
+        if copy is None:
+            return None
+        return {k: v for k, v in copy.items() if k not in ("dest", "cores")}
+
+    declared: list[dict] = []
+    for systems, file_entry, sys_id in declarations:
+        copy = download(file_entry, sys_id, None)
+        if copy is None:
+            # An omission is not a copy the installer can switch to.
+            return
+        if declared and declared[-1]["sha1"] == copy["sha1"]:
+            declared[-1]["systems"].extend(systems)
+        else:
+            declared.append({**copy, "systems": list(systems)})
+    _systems, first, first_sys = declarations[0]
+    recorded: list[dict] = []
+    seen: set[str] = set()
+    for emulator, path in choices:
+        if emulator in seen:
+            continue
+        seen.add(emulator)
+        copy = {} if path is None else download(first, first_sys, path)
+        if copy is None:
+            return
+        if recorded and recorded[-1].get("sha1") == copy.get("sha1"):
+            recorded[-1]["cores"].append(emulator)
+        else:
+            recorded.append({**copy, "cores": [emulator]})
+    while recorded and "sha1" not in recorded[-1]:
+        recorded.pop()
+    if not recorded and len(declared) == 1:
+        return
+    if recorded:
+        entry["slot_choices"] = recorded
+    entry["declared_choices"] = declared
+
+
 def _manifest_core_entries(
     core_files: list,
     config: dict,
@@ -3441,6 +3501,13 @@ def generate_manifest(
         config, emu_profiles, db, zip_contents, data_registry,
         target_cores=target_cores, source=source,
     )
+    # The full manifest records every core's answer at a contested slot, so a
+    # target narrowed from it gets what that target's own pack serves.
+    slot_choices = (
+        slots.slot_choices(config, emu_profiles, db, zip_contents, data_registry)
+        if target_cores is None and source != "platform" and emu_profiles
+        else {}
+    )
 
     def manifest_destination(full_destination: str) -> str:
         if base_dest and full_destination.startswith(f"{base_dest}/"):
@@ -3489,6 +3556,80 @@ def generate_manifest(
             pack_systems, db, bios_dir, base_dest, required_only,
             zip_contents, offline,
         )
+        declarations: dict[str, dict[str, list[dict]]] = {}
+        for sys_id, system in sorted(pack_systems.items()):
+            for file_entry in system.get("files", []):
+                if required_only and file_entry.get("required") is False:
+                    continue
+                dest = sanitize_pack_path(file_entry.get("destination", file_entry["name"]))
+                if dest and not (region_drops and dest in region_drops):
+                    full_dest = f"{base_dest}/{dest}" if base_dest else dest
+                    declarations.setdefault(full_dest, {}).setdefault(sys_id, []).append(
+                        file_entry
+                    )
+
+        def declaration_order(full_dest: str) -> list[tuple[list[str], dict, str]]:
+            """The declarations answering a destination as its systems drop.
+
+            A pack built for a target loses the systems no available core
+            reads, and the next declaration takes the destination by the
+            same rule: RetroArch's bare nintendo-ds dsi_bios9.bin once the
+            pinned nintendo-dsi one is gone.
+            """
+            remaining = dict(declarations.get(full_dest, {}))
+            order: list[tuple[list[str], dict, str]] = []
+            while remaining:
+                winner = _preferred_entries(
+                    {sid: {"files": fes} for sid, fes in remaining.items()},
+                    db, bios_dir, base_dest, required_only, zip_contents, offline,
+                ).get(full_dest)
+                first_sys, first = next(
+                    (sid, fe) for sid, fes in sorted(remaining.items()) for fe in fes
+                    if winner is None or id(fe) == winner
+                )
+                systems = sorted(
+                    sid for sid, fes in remaining.items()
+                    if any(fe is first for fe in fes)
+                )
+                order.append((systems, first, first_sys))
+                for sid in systems:
+                    del remaining[sid]
+            return order
+
+        def settle(file_entry: dict, sys_id: str, dest: str, override: str | None):
+            """The file served once the slot is settled, or None and why not."""
+            local_path, status = slots.apply_override(override, *resolve_file(
+                file_entry,
+                db,
+                bios_dir,
+                zip_contents,
+                data_dir_registry=data_registry,
+                offline=offline,
+            ))
+            if status == "not_found" and not reads_file_contents(verification_mode):
+                found = agnostic_substitute(file_entry, sys_id, db, manifest_profiles)
+                if found:
+                    local_path, status = found[0], "agnostic_fallback"
+                    if os.path.basename(local_path) != file_entry.get("name", ""):
+                        # The pack explains the rename in a note of its own.
+                        rename_notes.add(file_entry.get("name", ""))
+            # The builder's verdict: a hash platform omits what its frontend
+            # would reject, a zipped_file archive included when the member is
+            # missing whatever the outer resolution said. An existence
+            # platform never reads the bytes.
+            status, refusal = baseline_verdict(
+                file_entry, local_path, status, verification_mode
+            )
+            if refusal or status in ("not_found", "external"):
+                return None, "hash_mismatch" if refusal else status
+            # The variant the pack ships when an emulator rejects the
+            # resolved file: the installer must place the same bytes.
+            local_path, _disagreement = validated_choice(
+                file_entry, local_path, db, manifest_validation, bios_dir,
+                digest_algorithm(verification_mode), dest, manifest_owners,
+            )
+            return local_path, status
+
         for sys_id, system in sorted(pack_systems.items()):
             for file_entry in system.get("files", []):
                 if required_only and file_entry.get("required") is False:
@@ -3524,48 +3665,24 @@ def generate_manifest(
                     )
                     continue
 
-                local_path, status = resolve_file(
-                    file_entry,
-                    db,
-                    bios_dir,
-                    zip_contents,
-                    data_dir_registry=data_registry,
-                    offline=offline,
+                local_path, status = settle(
+                    file_entry, sys_id, dest, slot_overrides.get(full_dest)
                 )
-                local_path, status = slots.apply_override(
-                    slot_overrides.get(full_dest), local_path, status
-                )
-                if status == "not_found" and not reads_file_contents(verification_mode):
-                    found = agnostic_substitute(file_entry, sys_id, db, manifest_profiles)
-                    if found:
-                        local_path, status = found[0], "agnostic_fallback"
-                        if os.path.basename(local_path) != file_entry.get("name", ""):
-                            # The pack explains the rename in a note of its own.
-                            rename_notes.add(file_entry.get("name", ""))
-                # The builder's verdict: a hash platform omits what its
-                # frontend would reject, a zipped_file archive included when
-                # the member is missing whatever the outer resolution said.
-                # An existence platform never reads the bytes.
-                status, refusal = baseline_verdict(
-                    file_entry, local_path, status, verification_mode
-                )
-                if refusal or status in ("not_found", "external"):
-                    record_omission(
-                        full_dest, file_entry, sys_id,
-                        "hash_mismatch" if refusal else status, None,
-                    )
+                if local_path is None:
+                    record_omission(full_dest, file_entry, sys_id, status, None)
                     continue
-                # The variant the pack ships when an emulator rejects the
-                # resolved file: the installer must place the same bytes.
-                local_path, _disagreement = validated_choice(
-                    file_entry, local_path, db, manifest_validation, bios_dir,
-                    digest_algorithm(verification_mode), dest, manifest_owners,
-                )
 
                 entry, file_size = _manifest_entry(
                     local_path, dest, None, db, repo_root,
                     selection.fields(dest, file_entry["name"]),
                 )
+                if entry is not None and target_cores is None:
+                    order = declaration_order(full_dest)
+                    if full_dest in slot_choices or len(order) > 1:
+                        _record_slot_choices(
+                            entry, slot_choices.get(full_dest, []), order,
+                            settle, dest, db, repo_root,
+                        )
                 if entry is None:
                     record_omission(full_dest, file_entry, sys_id, "not_found", None)
                     if file_size and full_dest not in seen_destinations:
@@ -3706,7 +3823,7 @@ def _manifest_core_index(
     }
     named = {
         c for entry in [*files, *omitted]
-        for copy in [entry, *entry.get("alternatives", [])]
+        for copy in [entry, *entry.get("alternatives", []), *entry.get("slot_choices", [])]
         for c in copy.get("cores") or []
     }
     named |= {c for cores in system_cores.values() for c in cores}

scripts/slots.py

@@ -28,6 +28,7 @@ from common import (
     parse_md5_list,
     resolution_is_hash_exact,
     resolve_local_file,
+    resolve_platform_cores,
     runs_standalone,
 )
 from packresolve import preferred_entries
@@ -302,20 +303,16 @@ def _claim_rank(claim: Claim) -> int:
     return 1 if claim.is_proven else 0
 
 
-def find_conflicts(
+def _slot_claims(
     config: dict,
     profiles: dict,
     db: dict,
-    base_dest: str = "",
-    standalone_cores: set[str] | None = None,
-    zip_contents: dict | None = None,
-    data_dir_registry: dict | None = None,
-) -> list[Conflict]:
-    """Destinations where a proven profile claim contradicts what ships.
-
-    Only proven claims are compared. A claim resolved by filename alone
-    asserts nothing about content and cannot contradict anything.
-    """
+    base_dest: str,
+    standalone_cores: set[str] | None,
+    zip_contents: dict | None,
+    data_dir_registry: dict | None,
+) -> tuple[dict[str, Claim], dict[str, list[Claim]]]:
+    """The platform claim and the proven profile claims at each destination."""
     fold = bool(config.get("case_insensitive_fs", False))
     # The builder's own choice among declarations sharing a destination,
     # read from the same function: the most accepting archive for zipped_file
@@ -369,6 +366,27 @@ def find_conflicts(
             continue
         by_slot.setdefault(key, []).append(claim)
 
+    return by_dest, by_slot
+
+
+def find_conflicts(
+    config: dict,
+    profiles: dict,
+    db: dict,
+    base_dest: str = "",
+    standalone_cores: set[str] | None = None,
+    zip_contents: dict | None = None,
+    data_dir_registry: dict | None = None,
+) -> list[Conflict]:
+    """Destinations where a proven profile claim contradicts what ships.
+
+    Only proven claims are compared. A claim resolved by filename alone
+    asserts nothing about content and cannot contradict anything.
+    """
+    by_dest, by_slot = _slot_claims(
+        config, profiles, db, base_dest, standalone_cores, zip_contents,
+        data_dir_registry,
+    )
     # A declaration that lists several accepted hashes is satisfied by any of
     # them: Recalbox names both scph1001.bin revisions, and mesence names
     # four BS-X dumps among which System.dat pins one. The resolver stops on
@@ -428,20 +446,45 @@ def pack_overrides(
     verify all read this: two of them deciding alone gave the one-line
     installer different bytes than the ZIP.
     """
-    from common import resolve_platform_cores
-
     # A baseline-only pack serves what the platform declares, and a target's
     # pack answers to the cores that hardware builds: DuckStation does not
     # exist on any RetroArch target and still replaced its scph5000.bin.
     if not profiles or source == "platform":
         return {}
-    platform_profiles = {
-        name: profiles[name]
-        for name in resolve_platform_cores(config, profiles, target_cores=target_cores)
-    }
-    mode = config.get("verification_mode", "existence")
+    cores = set(resolve_platform_cores(config, profiles, target_cores=target_cores))
     overrides: dict[str, str] = {}
-    for conflict in find_conflicts(
+    for destination, choices in slot_choices(
+        config, profiles, db, zip_contents, data_dir_registry
+    ).items():
+        path = next((path for emulator, path in choices if emulator in cores), None)
+        if path:
+            overrides[destination] = path
+    return overrides
+
+
+def slot_choices(
+    config: dict,
+    profiles: dict,
+    db: dict,
+    zip_contents: dict | None = None,
+    data_dir_registry: dict | None = None,
+) -> dict[str, list[tuple[str, str | None]]]:
+    """Destination -> (core, the file it has served there) in decision order.
+
+    A pack built for a set of cores serves the first choice whose core is in
+    it, None standing for the platform's own answer; no core in it leaves
+    the platform's answer too. The order is arbitrate's: a core agreeing with
+    the platform settles the slot whatever else is present, then the
+    strongest proof decides. Read for one core set by pack_overrides and
+    recorded whole in the install manifest, so a target narrowed from the
+    full manifest gets the bytes the target's own pack carries.
+    """
+    if nativemode.reads_file_contents(config.get("verification_mode", "existence")):
+        return {}
+    platform_profiles = {
+        name: profiles[name] for name in resolve_platform_cores(config, profiles)
+    }
+    by_dest, by_slot = _slot_claims(
         config,
         platform_profiles,
         db,
@@ -449,11 +492,23 @@ def pack_overrides(
         {str(c) for c in config.get("standalone_cores", [])},
         zip_contents,
         data_dir_registry,
-    ):
-        decision = arbitrate(conflict, mode)
-        if decision.serves_both and decision.winner.local_path:
-            overrides[conflict.destination] = decision.winner.local_path
-    return overrides
+    )
+    choices: dict[str, list[tuple[str, str | None]]] = {}
+    for key, claims in sorted(by_slot.items()):
+        platform = by_dest[key]
+        agree = [_satisfies(c, platform, db) for c in claims]
+        agreeing = [c for c, ok in zip(claims, agree) if ok]
+        others = sorted(
+            (c for c, ok in zip(claims, agree) if not ok),
+            key=lambda claim: (-_claim_rank(claim), claims.index(claim)),
+        )
+        if not others:
+            continue
+        choices[platform.destination] = [
+            *((c.emulator, None) for c in agreeing),
+            *((c.emulator, c.local_path) for c in others),
+        ]
+    return choices
 
 
 def apply_override(

tests/test_install_cores.py

@@ -244,6 +244,74 @@ class APlatformOmissionKeepsItsClaim(unittest.TestCase):
                 )
 
 
+class APlatformFileSettledByCoresAndSystems(unittest.TestCase):
+    """RetroArch's dsi_bios9.bin ships melonds' copy where melonds runs; on
+    a target without it the pack serves the platform's answer, and the
+    pinned nintendo-dsi declaration gives way to the bare nintendo-ds one
+    once its system drops. The installer kept melonds' copy on rpi4."""
+
+    def copy(self, letter: str) -> dict:
+        return {"sha1": letter * 40, "size": 1, "repo_path": f"bios/{letter}.bin"}
+
+    def manifest(self) -> dict:
+        entry = {
+            "dest": "dsi_bios9.bin", **self.copy("a"), "cores": None,
+            "systems": ["nintendo-ds", "nintendo-dsi"],
+            "slot_choices": [{"cores": ["desmume"]}, {**self.copy("a"), "cores": ["melonds"]}],
+            "declared_choices": [
+                {**self.copy("c"), "systems": ["nintendo-dsi"]},
+                {**self.copy("b"), "systems": ["nintendo-ds"]},
+            ],
+        }
+        return {
+            "manifest_version": 2, "platform": "retroarch",
+            "files": [entry], "omitted_files": [],
+            "core_names": {},
+            "system_cores": {"nintendo-ds": ["desmume", "melonds", "nds"],
+                             "nintendo-dsi": ["melonds", "dsi"]},
+        }
+
+    def served(self, names: list[str]) -> str:
+        files, _ = install.narrow_to_cores(self.manifest(), names)
+        self.assertEqual(len(files), 1)
+        self.assertNotIn("declared_choices", files[0])
+        return files[0]["sha1"][0]
+
+    def test_the_first_chosen_core_decides(self):
+        self.assertEqual(self.served(["melonds"]), "a")
+
+    def test_a_core_agreeing_with_the_platform_leaves_its_answer(self):
+        self.assertEqual(self.served(["desmume", "melonds"]), "c")
+        self.assertEqual(self.served(["desmume"]), "b")
+
+    def test_the_remaining_system_answers_without_the_cores(self):
+        self.assertEqual(self.served(["dsi"]), "c")
+        self.assertEqual(self.served(["nds"]), "b")
+
+    def test_the_boundary_checks_every_copy(self):
+        install._validate_manifest(self.manifest(), "retroarch")
+        bad_choices = (
+            [{"cores": []}],
+            [{"cores": ["x"], "repo_path": "../x", "sha1": "a" * 40, "size": 1}],
+            [{"cores": ["x"], "dest": "../evil"}],
+        )
+        for choices in bad_choices:
+            manifest = self.manifest()
+            manifest["files"][0]["slot_choices"] = choices
+            with self.subTest(choices=choices), self.assertRaises(ValueError):
+                install._validate_manifest(manifest, "retroarch")
+        for declared in ([], [self.copy("c")], [{**self.copy("c"), "systems": []}],
+                         [{**self.copy("c"), "systems": ["s"], "cores": ["x"]}]):
+            manifest = self.manifest()
+            manifest["files"][0]["declared_choices"] = declared
+            with self.subTest(declared=declared), self.assertRaises(ValueError):
+                install._validate_manifest(manifest, "retroarch")
+        manifest = self.manifest()
+        del manifest["files"][0]["declared_choices"]
+        with self.assertRaises(ValueError):
+            install._validate_manifest(manifest, "retroarch")
+
+
 class RefusedBeforeAnyInstall(unittest.TestCase):
     def test_a_platform_shipping_its_cores_stops_the_run_first(self):
         tmp = Path(tempfile.mkdtemp(dir=REPO_ROOT / "tmp"))

wiki/installer.md

@@ -173,7 +173,11 @@ What stays is what a pack built for exactly those cores carries, the rule
 emulates it or reads its files, or when no core of the platform does; a
 file a core loads stays when that core is installed. Where two cores read
 one path and want different bytes, the copy of the first installed core in
-the builder's order is the one installed.
+the builder's order is the one installed. The same holds for a file of the
+platform's own list: where a core's source contradicts the platform and the
+frontend only checks the path, the core's copy is installed while that core
+is, and otherwise the platform's answer, read from the first declaring
+system that stays.
 
 Batocera, Recalbox and the other distributions ship their cores with the
 system, so the option is refused there, as it is when no core is found or