diff --git a/commons/src/commonMain/kotlin/com/vitorpamplona/amethyst/commons/model/concord/ConcordMembership.kt b/commons/src/commonMain/kotlin/com/vitorpamplona/amethyst/commons/model/concord/ConcordMembership.kt
new file mode 100644
index 0000000000..ca9337671d
--- /dev/null
+++ b/commons/src/commonMain/kotlin/com/vitorpamplona/amethyst/commons/model/concord/ConcordMembership.kt
@@ -0,0 +1,87 @@
+/*
+ * Copyright (c) 2025 Vitor Pamplona
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to use,
+ * copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the
+ * Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
+ * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+package com.vitorpamplona.amethyst.commons.model.concord
+
+import com.vitorpamplona.quartz.concord.cord04Roles.AuthorityResolver
+import com.vitorpamplona.quartz.concord.cord04Roles.ConcordPermissions
+import com.vitorpamplona.quartz.nip01Core.core.HexKey
+
+/**
+ * A user's standing in a Concord community, derived from the locally-folded
+ * Control Plane (the owner-rooted [AuthorityResolver] + banlist).
+ *
+ * Unlike NIP-29 (where the relay's signed roster is the truth), Concord
+ * membership is **key possession**: anyone holding the community key is at least a
+ * [MEMBER]. Roles layer moderation power on top ([ADMIN]/[OWNER]); the banlist
+ * removes standing ([BANNED]). [NONE] is only for a user we can't place at all.
+ */
+enum class ConcordMembership {
+    /** The community founder — supreme, unremovable. */
+    OWNER,
+
+    /** Holds at least one moderation permission (manage roles/channels, kick, ban…). */
+    ADMIN,
+
+    /** Holds the community key, no elevated role. */
+    MEMBER,
+
+    /** On the community banlist — dropped everywhere. */
+    BANNED,
+
+    /** Not placeable in this community. */
+    NONE,
+    ;
+
+    /** True when the user is an active participant (holds the key and isn't banned). */
+    fun isMember(): Boolean = this == OWNER || this == ADMIN || this == MEMBER
+
+    /** True when the user may take moderation actions. */
+    fun canModerate(): Boolean = this == OWNER || this == ADMIN
+
+    companion object {
+        private val MOD_BITS =
+            intArrayOf(
+                ConcordPermissions.MANAGE_ROLES,
+                ConcordPermissions.MANAGE_CHANNELS,
+                ConcordPermissions.MANAGE_METADATA,
+                ConcordPermissions.KICK,
+                ConcordPermissions.BAN,
+                ConcordPermissions.MANAGE_MESSAGES,
+            )
+
+        /**
+         * Classifies [pubKey] against a folded [authority]. [holdsKey] tells us the
+         * user is a member of this community locally (we joined it / hold its key),
+         * which distinguishes a plain [MEMBER] from [NONE].
+         */
+        fun of(
+            authority: AuthorityResolver,
+            pubKey: HexKey,
+            holdsKey: Boolean = true,
+        ): ConcordMembership {
+            if (authority.isBanned(pubKey)) return BANNED
+            if (authority.isOwner(pubKey)) return OWNER
+            val perms = authority.effectivePermissions(pubKey)
+            if (MOD_BITS.any { perms.has(it) }) return ADMIN
+            return if (holdsKey) MEMBER else NONE
+        }
+    }
+}
diff --git a/commons/src/commonMain/kotlin/com/vitorpamplona/amethyst/commons/model/concord/ConcordViewMode.kt b/commons/src/commonMain/kotlin/com/vitorpamplona/amethyst/commons/model/concord/ConcordViewMode.kt
new file mode 100644
index 0000000000..2974e8361d
--- /dev/null
+++ b/commons/src/commonMain/kotlin/com/vitorpamplona/amethyst/commons/model/concord/ConcordViewMode.kt
@@ -0,0 +1,38 @@
+/*
+ * Copyright (c) 2025 Vitor Pamplona
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to use,
+ * copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the
+ * Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
+ * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+package com.vitorpamplona.amethyst.commons.model.concord
+
+/**
+ * How joined Concord Channels surface in the Messages inbox (mirrors
+ * `RelayGroupViewMode`).
+ */
+enum class ConcordViewMode {
+    /** One inbox row per channel across all joined communities. */
+    INLINE,
+
+    /** One inbox row per community, collapsing its channels behind a drill-down. */
+    GROUPED,
+    ;
+
+    companion object {
+        val DEFAULT = INLINE
+    }
+}
diff --git a/commons/src/commonTest/kotlin/com/vitorpamplona/amethyst/commons/model/concord/ConcordMembershipTest.kt b/commons/src/commonTest/kotlin/com/vitorpamplona/amethyst/commons/model/concord/ConcordMembershipTest.kt
new file mode 100644
index 0000000000..770e7ed98e
--- /dev/null
+++ b/commons/src/commonTest/kotlin/com/vitorpamplona/amethyst/commons/model/concord/ConcordMembershipTest.kt
@@ -0,0 +1,73 @@
+/*
+ * Copyright (c) 2025 Vitor Pamplona
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to use,
+ * copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the
+ * Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
+ * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+package com.vitorpamplona.amethyst.commons.model.concord
+
+import com.vitorpamplona.quartz.concord.cord04Roles.AuthorityResolver
+import com.vitorpamplona.quartz.concord.cord04Roles.ControlEdition
+import com.vitorpamplona.quartz.concord.cord04Roles.ControlEntityKind
+import com.vitorpamplona.quartz.nip01Core.core.hexToByteArray
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+class ConcordMembershipTest {
+    private val owner = "0f".repeat(32)
+    private val admin = "a1".repeat(32)
+    private val member = "b2".repeat(32)
+    private val banned = "c3".repeat(32)
+    private val stranger = "d4".repeat(32)
+    private val adminRole = "11".repeat(32)
+
+    private fun ed(
+        kind: ControlEntityKind,
+        eid: String,
+        content: String,
+        author: String = owner,
+    ) = ControlEdition(kind, eid.hexToByteArray(), 0, null, null, content, author, "r-$eid", 0)
+
+    private val authority =
+        AuthorityResolver.resolve(
+            listOf(
+                ed(ControlEntityKind.ROLE, adminRole, """{"name":"Admin","position":1,"permissions":"25"}"""), // KICK|BAN|MANAGE_ROLES
+                ed(ControlEntityKind.GRANT, "ab".repeat(32), """{"member":"$admin","role_ids":["$adminRole"]}"""),
+                ed(ControlEntityKind.BANLIST, "44".repeat(32), """["$banned"]"""),
+            ),
+            owner,
+        )
+
+    @Test
+    fun classifiesStandingFromAuthority() {
+        assertEquals(ConcordMembership.OWNER, ConcordMembership.of(authority, owner))
+        assertEquals(ConcordMembership.ADMIN, ConcordMembership.of(authority, admin))
+        assertEquals(ConcordMembership.MEMBER, ConcordMembership.of(authority, member))
+        assertEquals(ConcordMembership.BANNED, ConcordMembership.of(authority, banned))
+        // A user we don't hold the key for reads as NONE.
+        assertEquals(ConcordMembership.NONE, ConcordMembership.of(authority, stranger, holdsKey = false))
+    }
+
+    @Test
+    fun capabilityHelpers() {
+        assertEquals(true, ConcordMembership.OWNER.canModerate())
+        assertEquals(true, ConcordMembership.ADMIN.canModerate())
+        assertEquals(false, ConcordMembership.MEMBER.canModerate())
+        assertEquals(true, ConcordMembership.MEMBER.isMember())
+        assertEquals(false, ConcordMembership.BANNED.isMember())
+    }
+}