feat(server): configurable bind address with loopback default and non-loopback warning

- Add optional `bind` field to ServerRegistry (TOML + ARCHIVR_BIND env var)
- Default bind address remains 127.0.0.1:8080; non-loopback prints a warning
- Add route security classification comment block (READ/ADMIN/WRITE/STATIC)
- Add Security and Deployment section to docs/README.md
- Replace vague auth note in ARCHIVR-MENTAL-MODEL.md with concrete model description
- Add three registry tests covering bind field round-trip and defaults

crates/archivr-server/src/main.rs

@@ -1,9 +1,11 @@
 mod registry;
 mod routes;
 
-use anyhow::Result;
+use anyhow::{Context, Result};
 use std::{net::SocketAddr, path::PathBuf};
 
+const DEFAULT_BIND: &str = "127.0.0.1:8080";
+
 #[tokio::main]
 async fn main() -> Result<()> {
     let config_path = std::env::args()
@@ -11,8 +13,27 @@ async fn main() -> Result<()> {
         .map(PathBuf::from)
         .unwrap_or_else(|| PathBuf::from("archivr-server.toml"));
     let registry = registry::load_registry(&config_path)?;
-    let app = routes::app(registry);
-    let addr = SocketAddr::from(([127, 0, 0, 1], 8080));
+    let app = routes::app(registry.clone());
+
+    // Bind address priority: ARCHIVR_BIND env var > TOML bind field > default loopback.
+    let bind_str = std::env::var("ARCHIVR_BIND")
+        .ok()
+        .or_else(|| registry.bind.clone())
+        .unwrap_or_else(|| DEFAULT_BIND.to_string());
+
+    let addr: SocketAddr = bind_str
+        .parse()
+        .with_context(|| format!("invalid bind address: {bind_str}"))?;
+
+    // Warn when the server is reachable beyond localhost — it has no authentication.
+    if !addr.ip().is_loopback() {
+        eprintln!(
+            "warn: archivr-server is bound to {addr} — \
+             this server has no authentication. \
+             Only expose it on a trusted network."
+        );
+    }
+
     let listener = tokio::net::TcpListener::bind(addr).await?;
     println!("archivr-server listening on http://{addr}");
     axum::serve(listener, app).await?;

crates/archivr-server/src/registry.rs

@@ -14,7 +14,12 @@ pub struct MountedArchive {
 
 #[derive(Debug, Clone, Serialize, Deserialize, Default, PartialEq, Eq)]
 pub struct ServerRegistry {
+    #[serde(default)]
     pub archives: Vec<MountedArchive>,
+    /// Optional bind address for the server. Defaults to `127.0.0.1:8080`.
+    /// Set this to `0.0.0.0:8080` only on trusted networks — the server has no authentication.
+    #[serde(default)]
+    pub bind: Option<String>,
 }
 
 pub fn load_registry(path: &Path) -> Result<ServerRegistry> {
@@ -78,6 +83,7 @@ mod tests {
                 label: "Personal".to_string(),
                 archive_path: archive_path.clone(),
             }],
+            bind: None,
         };
         let path = temp.path().join("server.toml");
         save_registry(&path, &registry).unwrap();
@@ -102,10 +108,36 @@ mod tests {
                     archive_path: PathBuf::from("/tmp/b/.archivr"),
                 },
             ],
+            bind: None,
         };
 
         let err = validate_registry(&registry).unwrap_err().to_string();
 
         assert!(err.contains("duplicate archive id"));
     }
+
+    #[test]
+    fn registry_bind_field_round_trips() {
+        let toml = r#"bind = "127.0.0.1:9090""#;
+        let registry: ServerRegistry = toml::from_str(toml).unwrap();
+        assert_eq!(registry.bind.as_deref(), Some("127.0.0.1:9090"));
+        assert!(registry.archives.is_empty());
+    }
+
+    #[test]
+    fn registry_bind_field_defaults_to_none_when_absent() {
+        let toml = r#""#;
+        let registry: ServerRegistry = toml::from_str(toml).unwrap();
+        assert!(registry.bind.is_none());
+    }
+
+    #[test]
+    fn registry_bind_field_does_not_affect_archive_validation() {
+        let registry = ServerRegistry {
+            archives: vec![],
+            bind: Some("0.0.0.0:8080".to_string()),
+        };
+        // validate_registry does not reject non-loopback bind — that's main's concern.
+        assert!(validate_registry(&registry).is_ok());
+    }
 }

crates/archivr-server/src/routes.rs

@@ -1,3 +1,27 @@
+// ── Security Boundary ────────────────────────────────────────────────────────
+// All routes are currently trusted-local: no authentication or authorization
+// middleware is applied. The server is designed to bind on 127.0.0.1 only.
+//
+// Route classification (for when middleware is added later):
+//
+//   STATIC  — safe to expose publicly: GET / and static /assets/*
+//   READ    — safe to expose read-only: GET /health
+//                                       GET /api/archives
+//                                       GET /api/archives/:id/entries
+//                                       GET /api/archives/:id/entries/search
+//                                       GET /api/archives/:id/entries/:uid
+//                                       GET /api/archives/:id/entries/:uid/artifacts/:idx
+//                                       GET /api/archives/:id/runs
+//                                       GET /api/archives/:id/tags
+//   ADMIN   — requires auth if ever public: GET /api/admin/archives
+//   WRITE   — requires auth if ever public: POST /api/archives/:id/captures
+//                                           POST /api/archives/:id/tags
+//                                           PUT  /api/archives/:id/tags/:tag_id
+//                                           DELETE /api/archives/:id/tags/:tag_id
+//
+// Do not add middleware here until the auth model is chosen. See docs/README.md.
+// ─────────────────────────────────────────────────────────────────────────────
+
 use std::{path::PathBuf, sync::Arc};
 
 use archivr_core::{archive, capture, database};
@@ -301,6 +325,7 @@ mod tests {
                 label: "Personal".to_string(),
                 archive_path: std::path::PathBuf::from("/tmp/personal/.archivr"),
             }],
+            bind: None,
         };
         let response = app(registry)
             .oneshot(
@@ -361,6 +386,7 @@ mod tests {
                 label: "Test".to_string(),
                 archive_path,
             }],
+            bind: None,
         };
         let response = app(registry)
             .oneshot(
@@ -391,6 +417,7 @@ mod tests {
                 label: "Test".to_string(),
                 archive_path,
             }],
+            bind: None,
         };
         let response = app(registry)
             .oneshot(
@@ -483,6 +510,7 @@ mod tests {
                 label: "Test".to_string(),
                 archive_path: paths.archive_path.clone(),
             }],
+            bind: None,
         };
         let uri = format!(
             "/api/archives/test/entries/{}/artifacts/0",
@@ -526,6 +554,7 @@ mod tests {
                 label: "Test".to_string(),
                 archive_path,
             }],
+            bind: None,
         };
         let response = app(registry)
             .oneshot(
@@ -556,6 +585,7 @@ mod tests {
                 label: "Test".to_string(),
                 archive_path,
             }],
+            bind: None,
         };
         let response = app(registry)
             .oneshot(
@@ -585,6 +615,7 @@ mod tests {
                 label: "Test".to_string(),
                 archive_path: paths.archive_path.clone(),
             }],
+            bind: None,
         };
         (registry, paths.archive_path)
     }