fix(config): fail closed on POW_REQUIRED without FEATURE_POW; harden premium key check

- Reject boot when POW_REQUIRED (or the per-pubkey PoW list) is set while
  FEATURE_POW is off: the gate would silently never apply and /capabilities
  would report pow_required:false — a signup endpoint the operator believes
  is protected but isn't.
- Validate the premium PAYMENT_API_KEY through the same require_secret path
  the pay-to-register flow uses, so a placeholder key cannot reach production.
- Advertise the premium-post write policy in MessagingCapability and
  regenerate openapi.json to match.
- Give the premium integration fixtures unique per-run ids so the suite is
  re-runnable against a persistent local test database.

src/api/capabilities.rs

@@ -60,7 +60,7 @@ pub struct FeatureCapabilities {
 pub struct MessagingCapability {
     /// The ws(s):// relay URL clients connect to.
     pub relay_url: String,
-    /// Write policy: `inbox-outbox` | `author-allowlist` | `open`.
+    /// Write policy: `inbox-outbox` | `author-allowlist` | `open` | `premium-post`.
     pub write_policy: String,
     /// NIP-13 PoW bits required on cross-ecosystem inbound (0 = off).
     pub inbound_pow_bits: u8,

src/config.rs

@@ -865,6 +865,16 @@ impl Config {
         if self.pow.enabled {
             require_secret("ALTCHA_HMAC_KEY", &self.pow.hmac_key, 32)?;
         }
+        // Fail closed on the silent-disarm footgun: asking for PoW (POW_REQUIRED or a
+        // per-pubkey list) while the feature master switch is off means the gate never
+        // applies and /capabilities reports pow_required:false — a signup endpoint the
+        // operator believes is protected but isn't.
+        if !self.pow.enabled && (self.pow.required || !self.pow.required_for_pubkeys.is_empty()) {
+            return Err(cfg_err(
+                "POW_REQUIRED (or TEST_POW_REQUIRED_FOR_PUBKEYS) is set but FEATURE_POW is off \
+                 — the PoW gate would never apply; set FEATURE_POW=true",
+            ));
+        }
 
         // Admin surface: dedicated secrets + a real public URL when enabled.
         if self.admin.enabled {
@@ -1116,11 +1126,7 @@ impl Config {
             if p.store_id.trim().is_empty() {
                 return Err(cfg_err("PREMIUM_ENABLED needs PAYMENT_STORE_ID"));
             }
-            if p.api_key.len() < 8 {
-                return Err(cfg_err(
-                    "PREMIUM_ENABLED needs PAYMENT_API_KEY (>= 8 bytes)",
-                ));
-            }
+            require_secret("PAYMENT_API_KEY", &p.api_key, 8)?;
             // The same processor-safety floors the pay-to-register path enforces —
             // premium's common case is require_payment=false, which skips that
             // block. A 0-conf invoice settles on first mempool sighting and can
@@ -1388,6 +1394,19 @@ mod tests {
         assert!(c.validate().is_err());
     }
 
+    #[test]
+    fn pow_required_without_feature_pow_rejected() {
+        // POW_REQUIRED=true while FEATURE_POW is off silently disarms the gate.
+        let mut c = valid();
+        c.pow.enabled = false;
+        c.pow.required = true;
+        assert!(c.validate().is_err());
+        // Enabling the master switch (with a key) makes it valid.
+        c.pow.enabled = true;
+        c.pow.hmac_key = "a".repeat(32);
+        assert!(c.validate().is_ok());
+    }
+
     #[test]
     fn enabled_chain_requires_secret_in_production() {
         let mut c = valid();