feat(feed): operator-configurable public feed advertised via /capabilities

A read-only web feed (feed.<domain>) is a backend-operator knob: FEED_ENABLED
plus curation switches (show owner / show premium members / a featured npub
allowlist / extra relays) surface in /capabilities.feed so the feed page adapts
per instance. Reads from the relay, so validate() fail-closes FEED_ENABLED
without RELAY_ENABLED. Off by default; all public display config, no secrets.

src/api/capabilities.rs

@@ -49,6 +49,8 @@ pub struct FeatureCapabilities {
     pub nostr_relay: bool,
     /// Paid premium tier for general Nostr posting to the relay. See `premium`.
     pub premium_relay: bool,
+    /// Public curated Nostr feed for this instance. See `feed`.
+    pub feed: bool,
     /// Tipping (parked).
     pub tips: bool,
 }
@@ -88,6 +90,25 @@ pub struct PremiumCapability {
     pub relay_url: String,
 }
 
+/// Public curated feed details (present only when `features.feed`). A read-only
+/// web feed (e.g. `feed.<domain>`) reads from the relay and shows posts per the
+/// operator's curation knobs.
+#[derive(Debug, Serialize, utoipa::ToSchema)]
+pub struct FeedCapability {
+    /// The relay the feed reads from (mirrors `messaging.relay_url`).
+    pub relay_url: String,
+    /// Include the operator's own posts.
+    pub show_owner: bool,
+    /// Include premium members' posts (all general notes on the gated relay).
+    pub show_premium: bool,
+    /// The operator's npub for owner filtering + display; `null` when unset.
+    pub owner_npub: Option<String>,
+    /// Specific featured npubs to surface.
+    pub allowlist_npubs: Vec<String>,
+    /// Extra relays to also pull the allowlisted authors from.
+    pub extra_relays: Vec<String>,
+}
+
 /// This instance's wallet-restore (import) policy. The wallet uses it to adapt
 /// its import UX — hide/grey the restore-height field under `create-only`, warn
 /// when a chosen date exceeds the bound. `max_depth_days` is present only for
@@ -142,6 +163,9 @@ pub struct CapabilitiesResponse {
     /// Premium tier details; present only when `features.premium_relay`.
     #[serde(skip_serializing_if = "Option::is_none")]
     pub premium: Option<PremiumCapability>,
+    /// Public curated feed details; present only when `features.feed`.
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub feed: Option<FeedCapability>,
 }
 
 /// Whether an enabled chain can actually be served (its infra secret/URL is
@@ -202,6 +226,7 @@ pub fn effective_capabilities(config: &Config) -> CapabilitiesResponse {
             // presence downgrade — never advertise a relay clients can't reach).
             nostr_relay: relay_advertised(config),
             premium_relay: premium_advertised(config),
+            feed: feed_advertised(config),
             tips: config.features.tips,
         },
         restore: RestoreCapability {
@@ -252,6 +277,17 @@ pub fn effective_capabilities(config: &Config) -> CapabilitiesResponse {
                 .collect(),
             relay_url: config.messaging.relay.advertised_url.clone(),
         }),
+        feed: feed_advertised(config).then(|| {
+            let f = &config.feed;
+            FeedCapability {
+                relay_url: config.messaging.relay.advertised_url.clone(),
+                show_owner: f.show_owner,
+                show_premium: f.show_premium,
+                owner_npub: (!f.owner_npub.is_empty()).then(|| f.owner_npub.clone()),
+                allowlist_npubs: f.allowlist_npubs.clone(),
+                extra_relays: f.extra_relays.clone(),
+            }
+        }),
     }
 }
 
@@ -268,6 +304,11 @@ fn premium_advertised(config: &Config) -> bool {
     config.premium.enabled && relay_advertised(config)
 }
 
+/// Whether the public feed is enabled AND the relay it reads is advertised.
+fn feed_advertised(config: &Config) -> bool {
+    config.feed.enabled && relay_advertised(config)
+}
+
 /// Describe this instance's enabled chains and features.
 #[utoipa::path(
     get,

src/api/openapi.rs

@@ -77,6 +77,7 @@ use utoipa::OpenApi;
         crate::api::capabilities::MessagingCapability,
         crate::api::capabilities::PremiumCapability,
         crate::api::capabilities::PremiumPlanInfo,
+        crate::api::capabilities::FeedCapability,
         crate::api::prices::PricesResponse,
         crate::api::auth::AuthResponse,
         crate::api::auth::UserInfo,