feat(ui): show member created dates when the system opts in

sheaf/app/src/main/java/systems/lupine/sheaf/data/model/Models.kt

@@ -251,6 +251,11 @@ data class SystemRead(
     // (each device renders in its own local clock). Synced across the account's
     // devices; a per-device override can shadow it locally. See [resolveDisplayZone].
     val timezone: String? = null,
+    // Display preference: show each member's created date on their profile.
+    // Opt-in per system (default false, matching the backend) - some systems
+    // want it, others find it noise. Purely a display gate; MemberRead.createdAt
+    // is always present regardless.
+    @Json(name = "show_member_created_date") val showMemberCreatedDate: Boolean = false,
     @Json(name = "created_at") val createdAt: String,
     @Json(name = "updated_at") val updatedAt: String,
 )
@@ -274,6 +279,7 @@ data class SystemUpdate(
     val color: String? = null,
     val privacy: String? = null,
     val note: String? = null,
+    @Json(name = "show_member_created_date") val showMemberCreatedDate: Boolean? = null,
 )
 
 // ── System Safety ─────────────────────────────────────────────────────────────

sheaf/app/src/main/java/systems/lupine/sheaf/ui/members/MembersScreen.kt

@@ -1085,6 +1085,27 @@ fun MemberProfileScreen(
                             leadingContent = { Icon(Icons.Default.Lock, contentDescription = null) },
                             colors = itemColors,
                         )
+
+                        // Created date, only when the system opted in (see
+                        // Settings > Profile). Web puts this as muted text under
+                        // the name; on Android the profile keeps facts like this
+                        // in the details card, next to birthday and privacy.
+                        if (state.showCreatedDate) {
+                            HorizontalDivider(modifier = Modifier.padding(horizontal = 16.dp))
+                            ListItem(
+                                headlineContent = { Text("Created") },
+                                trailingContent = {
+                                    Text(
+                                        formatCreatedDate(member.createdAt, LocalDisplayTimeZone.current),
+                                        style = MaterialTheme.typography.bodyMedium,
+                                    )
+                                },
+                                leadingContent = {
+                                    Icon(Icons.Default.CalendarToday, contentDescription = null)
+                                },
+                                colors = itemColors,
+                            )
+                        }
                     }
 
                     // Custom-field values. Only render when the viewer
@@ -1460,6 +1481,15 @@ private fun formatRevisionDate(iso: String, zone: ZoneId): String = runCatching
     OffsetDateTime.parse(iso).atZoneSameInstant(zone).toLocalDateTime().format(revisionDateFormatter)
 }.getOrDefault(iso)
 
+// Date only, no clock: "when was this member added" is a date-scale fact, and
+// the hour it happened is noise on a profile.
+private val createdDateFormatter: DateTimeFormatter =
+    DateTimeFormatter.ofPattern("MMM d, yyyy")
+
+private fun formatCreatedDate(iso: String, zone: ZoneId): String = runCatching {
+    OffsetDateTime.parse(iso).atZoneSameInstant(zone).toLocalDate().format(createdDateFormatter)
+}.getOrDefault(iso)
+
 private fun formatBirthday(value: String): String? {
     val full = Regex("(\\d{4})-(\\d{2})-(\\d{2})").matchEntire(value)
     val yearless = Regex("--(\\d{2})-(\\d{2})").matchEntire(value)

sheaf/app/src/main/java/systems/lupine/sheaf/ui/members/MembersViewModel.kt

@@ -697,6 +697,9 @@ data class MemberProfileUiState(
      *  the map are unset (display as em-dash). Fields the viewer isn't
      *  allowed to see are absent because the server omitted them. */
     val customFieldValues: Map<String, Any?> = emptyMap(),
+    /** System display preference: show this member's created date. Off unless
+     *  the system opted in, and off if we couldn't read the system at all. */
+    val showCreatedDate: Boolean = false,
 )
 
 @HiltViewModel
@@ -732,29 +735,53 @@ class MemberProfileViewModel @Inject constructor(
                     val vals = runCatching { api.getMemberFieldValues(memberId) }
                         .getOrDefault(emptyList())
                         .associate { it.fieldId to it.value }
+                    // Display preference comes from the cached system rather than
+                    // its own request: this screen's loads are sequential, so a
+                    // fifth call would add a round-trip to every profile open for
+                    // a setting that changes about never. Home refreshes the
+                    // cache on every resume and the system editor writes through
+                    // on save, so it doesn't go stale in practice.
+                    val showCreated = cache.getSystem()?.showMemberCreatedDate ?: false
                     _state.update {
                         it.copy(
                             member = member,
                             currentFronts = fronts,
                             customFields = defs,
                             customFieldValues = vals,
+                            showCreatedDate = showCreated,
                             isLoading = false,
                         )
                     }
                 }.onFailure { e ->
                     val cached = cache.getMember(memberId)
                     val fronts = cache.getFronts() ?: emptyList()
+                    val showCreated = cache.getSystem()?.showMemberCreatedDate ?: false
                     if (cached != null) {
-                        _state.update { it.copy(member = cached, currentFronts = fronts, isLoading = false) }
+                        _state.update {
+                            it.copy(
+                                member = cached,
+                                currentFronts = fronts,
+                                showCreatedDate = showCreated,
+                                isLoading = false,
+                            )
+                        }
                     } else {
                         _state.update { it.copy(isLoading = false, error = e.toUserMessage()) }
                     }
                 }
             } else {
                 val cached = cache.getMember(memberId)
                 val fronts = cache.getFronts() ?: emptyList()
+                val showCreated = cache.getSystem()?.showMemberCreatedDate ?: false
                 if (cached != null) {
-                    _state.update { it.copy(member = cached, currentFronts = fronts, isLoading = false) }
+                    _state.update {
+                        it.copy(
+                            member = cached,
+                            currentFronts = fronts,
+                            showCreatedDate = showCreated,
+                            isLoading = false,
+                        )
+                    }
                 } else {
                     _state.update { it.copy(isLoading = false) }
                 }

sheaf/app/src/main/java/systems/lupine/sheaf/ui/settings/SettingsScreen.kt

@@ -842,6 +842,34 @@ fun SystemEditScreen(
                 }
             }
 
+            SectionHeader("Display")
+            // Part of this form rather than an instant-apply toggle, so it
+            // saves with the Save Changes button like everything else here.
+            Row(
+                modifier = Modifier
+                    .fillMaxWidth()
+                    .clickable {
+                        viewModel.updateForm {
+                            copy(showMemberCreatedDate = !showMemberCreatedDate)
+                        }
+                    }
+                    .padding(vertical = 4.dp),
+                verticalAlignment = Alignment.CenterVertically,
+            ) {
+                Column(modifier = Modifier.weight(1f)) {
+                    Text("Show member created dates", style = MaterialTheme.typography.bodyLarge)
+                    Text(
+                        "Show when each member was added, on their profile.",
+                        style = MaterialTheme.typography.bodySmall,
+                        color = MaterialTheme.colorScheme.onSurfaceVariant,
+                    )
+                }
+                Switch(
+                    checked = form.showMemberCreatedDate,
+                    onCheckedChange = { viewModel.updateForm { copy(showMemberCreatedDate = it) } },
+                )
+            }
+
             Spacer(Modifier.height(8.dp))
 
             Button(

sheaf/app/src/main/java/systems/lupine/sheaf/ui/settings/SystemEditViewModel.kt

@@ -24,6 +24,7 @@ data class SystemEditForm(
     val avatarUrl: String = "",
     val color: String = "",
     val privacy: String = "private",
+    val showMemberCreatedDate: Boolean = false,
 )
 
 data class SystemEditUiState(
@@ -37,6 +38,7 @@ data class SystemEditUiState(
 @HiltViewModel
 class SystemEditViewModel @Inject constructor(
     private val api: SheafApiService,
+    private val cache: systems.lupine.sheaf.data.db.LocalCache,
     @ApplicationContext private val context: Context,
     val markdownImages: systems.lupine.sheaf.ui.components.MarkdownImageDelegate,
 ) : ViewModel() {
@@ -65,6 +67,7 @@ class SystemEditViewModel @Inject constructor(
                         avatarUrl = system.avatarUrl ?: "",
                         color = system.color ?: "",
                         privacy = system.privacy,
+                        showMemberCreatedDate = system.showMemberCreatedDate,
                     )
                     _state.update { it.copy(isLoading = false) }
                 }
@@ -91,9 +94,16 @@ class SystemEditViewModel @Inject constructor(
                     avatarUrl = f.avatarUrl.takeIf { it.isNotBlank() },
                     color = f.color.takeIf { it.isNotBlank() },
                     privacy = f.privacy,
+                    showMemberCreatedDate = f.showMemberCreatedDate,
                 ))
             }
-                .onSuccess { _state.update { it.copy(isSaving = false, saved = true) } }
+                .onSuccess { updated ->
+                    // Write through so display preferences read from the cached
+                    // system (the member profile's created-date row) reflect the
+                    // change straight away, without waiting for a Home refresh.
+                    runCatching { cache.saveSystem(updated) }
+                    _state.update { it.copy(isSaving = false, saved = true) }
+                }
                 .onFailure { e -> _state.update { it.copy(isSaving = false, error = e.toUserMessage()) } }
         }
     }

sheaf/app/src/test/java/systems/lupine/sheaf/data/model/ModelContractsTest.kt

@@ -90,4 +90,46 @@ class ModelContractsTest {
         assertEquals(false, active.isArchived)
         assertEquals(true, active.copy(archivedAt = "2026-01-02T00:00:00Z").isArchived)
     }
+
+    @Test fun `show_member_created_date round-trips under its wire name`() {
+        // A camelCase slip here wouldn't fail anything loudly: the toggle would
+        // just never stick, because the server ignores unknown keys on PATCH and
+        // reports its unchanged value back.
+        val adapter = moshi.adapter(SystemUpdate::class.java)
+        assertEquals(
+            """{"show_member_created_date":true}""",
+            adapter.toJson(SystemUpdate(showMemberCreatedDate = true)),
+        )
+        val read = moshi.adapter(SystemRead::class.java).fromJson(
+            """
+            {"id":"s1","name":"Sys","description":null,"tag":null,"avatar_url":null,
+             "color":null,"privacy":"private","delete_confirmation":null,
+             "show_member_created_date":true,
+             "created_at":"2026-01-01T00:00:00Z","updated_at":"2026-01-01T00:00:00Z"}
+            """.trimIndent(),
+        )
+        assertEquals(true, read?.showMemberCreatedDate)
+    }
+
+    @Test fun `an omitted show_member_created_date reads as off`() {
+        // Older cached payloads and older servers won't carry the field; the
+        // display has to default to off rather than blow up or leak the date.
+        val read = moshi.adapter(SystemRead::class.java).fromJson(
+            """
+            {"id":"s1","name":"Sys","description":null,"tag":null,"avatar_url":null,
+             "color":null,"privacy":"private","delete_confirmation":null,
+             "created_at":"2026-01-01T00:00:00Z","updated_at":"2026-01-01T00:00:00Z"}
+            """.trimIndent(),
+        )
+        assertEquals(false, read?.showMemberCreatedDate)
+    }
+
+    @Test fun `a false toggle is still sent rather than omitted`() {
+        // Turning the setting back off has to reach the wire. Moshi drops nulls,
+        // so the form's Boolean must be non-null false, not null.
+        assertEquals(
+            """{"show_member_created_date":false}""",
+            moshi.adapter(SystemUpdate::class.java).toJson(SystemUpdate(showMemberCreatedDate = false)),
+        )
+    }
 }