capabilities: nip05_domain must keep the handle domain users already have

Deploying the previous version showed nip05_domain = api.smirk.cash, but handles
are name@smirk.cash: that is what v0.2 used, what the wallet derived by stripping
'api.' client-side, and what the kind-0 profiles already on relays carry. Since
the wallet now PREFERS this field, shipping it would have silently re-rendered
every handle as @api.smirk.cash and disagreed with the published profiles.

Caught by checking the deployed output rather than assuming the change was inert.

Default is now PUBLIC_API_URL's host with a leading 'api.' removed, preserving
the established behaviour, and NIP05_DOMAIN overrides it for operators whose
well-known lives elsewhere. Still explicit where it matters; the default just
stops being a regression.

src/api/capabilities.rs

@@ -249,16 +249,27 @@ pub fn effective_capabilities(config: &Config) -> CapabilitiesResponse {
         enabled: on,
         network: Some(net.to_string()),
     };
-    // The handle domain is the HOST of the operator's public API URL. No
-    // `api.` stripping here: if the operator wants handles at the bare domain,
-    // they say so by setting PUBLIC_API_URL to the host that actually serves
-    // /.well-known/nostr.json. Guessing is what produced unverifiable handles.
-    let nip05_domain = config
+    // The handle domain. `NIP05_DOMAIN` wins when set; otherwise derive it from
+    // PUBLIC_API_URL's host with a leading `api.` removed.
+    //
+    // The stripping is deliberate and load-bearing: handles have been
+    // `name@smirk.cash` (not `name@api.smirk.cash`) since v0.2, the wallet
+    // stripped `api.` client-side for exactly that reason, and published kind-0
+    // profiles already carry the bare form. Advertising the raw API host would
+    // silently re-render every existing handle and disagree with what is already
+    // on relays.
+    //
+    // It is still only a default. An operator whose well-known lives somewhere
+    // else sets NIP05_DOMAIN explicitly rather than being second-guessed.
+    let nip05_domain = config.identity.nip05_domain.clone().or_else(|| {
+        config
             .identity
             .public_api_url
             .as_deref()
             .and_then(|u| url::Url::parse(u).ok())
-        .and_then(|u| u.host_str().map(|h| h.to_ascii_lowercase()));
+            .and_then(|u| u.host_str().map(|h| h.to_ascii_lowercase()))
+            .map(|h| h.strip_prefix("api.").unwrap_or(&h).to_string())
+    });
     CapabilitiesResponse {
         version: env!("CARGO_PKG_VERSION").to_string(),
         contract_version: CAPABILITIES_CONTRACT_VERSION,

src/config.rs

@@ -215,6 +215,11 @@ pub struct IdentityConfig {
     /// Required when Nostr identity is enabled: it is the canonical value the
     /// NIP-98 `u` tag is verified against — never the request `Host` header.
     pub public_api_url: Option<String>,
+    /// The domain handles live at (`name@<domain>`), advertised in
+    /// `/capabilities`. Defaults to `public_api_url`'s host with a leading
+    /// `api.` removed, which is what the wallet used to derive client-side.
+    /// Set explicitly when your `/.well-known/nostr.json` lives elsewhere.
+    pub nip05_domain: Option<String>,
 }
 
 /// HMAC peppers and salts. Fail-closed: required and length-checked. These make
@@ -756,6 +761,7 @@ impl Config {
             },
             identity: IdentityConfig {
                 public_api_url: env_opt("PUBLIC_API_URL"),
+                nip05_domain: env_opt("NIP05_DOMAIN"),
             },
             secrets: SecretConfig {
                 seed_fingerprint_pepper: env_or("SEED_FINGERPRINT_PEPPER", ""),
@@ -1442,6 +1448,7 @@ mod tests {
             },
             identity: IdentityConfig {
                 public_api_url: Some("https://backend.example.org/api/v1".into()),
+                nip05_domain: None,
             },
             secrets: SecretConfig {
                 seed_fingerprint_pepper: "p".repeat(32),