{"messages":[{"content":"You are a constitutional council ranking individual git commits for ownership allocation.\n\nCompare these two commits. Decide which contributed more lasting value to the project.\n\nJudge substance, not spectacle:\n- Prefer correct, lasting design and real bugfixes over churn, formatting, renames, or generated noise.\n- Prefer clarity and necessity over sheer line count. A small precise change can beat a large diffuse one.\n- Do not favor a side merely because its patch is longer or noisier.\n- Weight what the change does for the project, not the contributor's name.\n\nReturn ONLY a JSON object: {\"winner\": \"A\" or \"B\", \"ratio\": \"N:M\", \"explanation\": \"...\"}\nThe explanation must cite concrete differences in the patches (1-3 sentences).\n\nSide A — contributor: tommy-mor\nSide A — commit message:\n[52f5c51c] Add Reddit OAuth linking and make UUID the only account identity.\n\nOAuth providers only attach to a session UUID (first link creates the\nprincipal); linked providers stay private on the account page.\n\nCo-authored-by: Cursor <cursoragent@cursor.com>\n\nSide A — unified diff (full patch):\ndiff --git a/AGENTS.md b/AGENTS.md\nindex 6e0fd8ebb65d665c9c1438e3275971d62b98fd95..e9cc3173dbeb21ad0fc090ca7b407b027c7820a9 100644\n--- a/AGENTS.md\n+++ b/AGENTS.md\n@@ -35,8 +35,11 @@ Environment variables (defaults in `server/src/state.rs`):\n - `SORTER2_DATA_DIR` — default `./data` (created on startup)\n - `SORTER2_EVENT_LOG` — default `{data_dir}/events.jsonl`\n - `SORTER2_BASE_URL` — public origin (also drives Secure cookies when `https://`)\n-- `GITHUB_CLIENT_ID` / `GITHUB_CLIENT_SECRET` — GitHub OAuth (optional; login disabled if unset)\n-- `SORTER2_ALLOW_MOCK_OAUTH=1` — allow `mock_user` on `/auth/github` (tests only)\n+- `GITHUB_CLIENT_ID` / `GITHUB_CLIENT_SECRET` — GitHub OAuth linking (optional)\n+- `REDDIT_CLIENT_ID` / `REDDIT_CLIENT_SECRET` (or `REDDIT_APP_*`) — Reddit API import + OAuth linking (optional)\n+- `SORTER2_ALLOW_MOCK_OAUTH=1` — allow `mock_user` on `/auth/github` and `/auth/reddit` (tests only)\n+\n+Identity: UUID is canonical. OAuth providers only *link* to a UUID (first link creates the principal). Linked providers are private to the account owner.\n \n Health check: `GET /healthz` → `ok`.\n \ndiff --git a/server/src/auth/mod.rs b/server/src/auth/mod.rs\nindex 5906f93b13853421e96a3c37bc9d8202a47842bf..c706ae8045a811e5941f5f6c72da88f42a403a82 100644\n--- a/server/src/auth/mod.rs\n+++ b/server/src/auth/mod.rs\n@@ -1,4 +1,8 @@\n-//! GitHub OAuth login, session cookies, and vote actor resolution.\n+//! OAuth linking, session cookies, and vote actor resolution.\n+//!\n+//! Canonical identity is a UUID. OAuth providers only *link* to that UUID\n+//! (first link creates the principal; later links attach while logged in).\n+//! Which providers are linked is private to the account owner.\n \n pub mod config;\n pub mod identity;\n@@ -22,7 +26,9 @@ use crate::{\n     form_template::template_json_compact,\n     html::layout,\n     state::AppState,\n-    storage_schema::{oauth_link_owner, pseudonym_owner, Store, StoreFields},\n+    storage_schema::{\n+        linked_providers_for_uuid, oauth_link_owner, pseudonym_owner, Store, StoreFields,\n+    },\n     ui_action::UI_RPC_FIELD,\n };\n \n@@ -53,10 +59,12 @@ fn new_actor_uuid() -> String {\n pub struct LoginQuery {\n     #[serde(default)]\n     pub return_to: Option<String>,\n+    #[serde(default)]\n+    pub error: Option<String>,\n }\n \n #[derive(Debug, Deserialize)]\n-pub struct GitHubStartQuery {\n+pub struct OAuthStartQuery {\n     #[serde(default)]\n     pub return_to: Option<String>,\n     #[serde(default)]\n@@ -72,15 +80,22 @@ fn return_from_query_or_jar(jar: &CookieJar, query: Option<&str>) -> String {\n         .unwrap_or_else(|| \"/\".to_string())\n }\n \n-fn oauth_providers(base_url: &str, return_to: &str) -> Vec<(&'static str, String)> {\n+/// Available OAuth link targets: `(provider_key, label, start_href)`.\n+fn oauth_providers(base_url: &str, return_to: &str) -> Vec<(&'static str, &'static str, String)> {\n     let mut out = Vec::new();\n+    let enc = urlencoding::encode(return_to);\n     if oauth::GitHubConfig::from_env(base_url).is_some() {\n         out.push((\n-            \"GitHub\",\n-            format!(\n-                \"/auth/github?return_to={}\",\n-                urlencoding::encode(return_to)\n-            ),\n+            \"github\",\n+            oauth::provider_label(\"github\"),\n+            format!(\"/auth/github?return_to={enc}\"),\n+        ));\n+    }\n+    if oauth::RedditConfig::from_env(base_url).is_some() {\n+        out.push((\n+            \"reddit\",\n+            oauth::provider_label(\"reddit\"),\n+            format!(\"/auth/reddit?return_to={enc}\"),\n         ));\n     }\n     out\n@@ -125,23 +140,41 @@ fn alias_claim_forms(return_to: &str, submit_label: &str) -> Result<Markup, Stat\n     })\n }\n \n-fn signed_out_body(providers: &[(&str, String)]) -> Markup {\n+fn login_error_message(code: Option<&str>) -> Option<&'static str> {\n+    match code {\n+        Some(\"oauth_taken\") => {\n+            Some(\"that OAuth account is already linked to a different sorter2 account\")\n+        }\n+        Some(\"oauth_failed\") => Some(\"OAuth failed — try again\"),\n+        _ => None,\n+    }\n+}\n+\n+fn signed_out_body(\n+    providers: &[(&str, &str, String)],\n+    error: Option<&str>,\n+) -> Markup {\n     html! {\n         main class=\"panel login-page\" {\n             section class=\"login-section\" {\n                 h1 { \"sign in\" }\n-                p class=\"muted\" { \"link an account to vote under a lasting alias\" }\n+                p class=\"muted\" {\n+                    \"link an OAuth account to create your identity, then claim an alias to vote\"\n+                }\n+                @if let Some(msg) = login_error_message(error) {\n+                    p class=\"alias-bad\" data-testid=\"login-error\" { (msg) }\n+                }\n                 @if providers.is_empty() {\n                     p class=\"muted\" {\n-                        \"OAuth is not configured. Set GITHUB_CLIENT_ID and GITHUB_CLIENT_SECRET.\"\n+                        \"OAuth is not configured. Set GitHub and/or Reddit client credentials.\"\n                     }\n                 } @else {\n                     ul class=\"oauth-provider-list\" {\n-                        @for (name, href) in providers {\n+                        @for (key, label, href) in providers {\n                             li {\n                                 a href=(href) class=\"btn-primary oauth-provider\"\n-                                    data-testid=(format!(\"oauth-{}\", name.to_lowercase())) {\n-                                    (format!(\"Continue with {name}\"))\n+                                    data-testid=(format!(\"oauth-{key}\")) {\n+                                    (format!(\"Link {label}\"))\n                                 }\n                             }\n                         }\n@@ -156,7 +189,10 @@ fn signed_out_body(providers: &[(&str, String)]) -> Markup {\n fn account_body(\n     actor: &session::SessionActor,\n     aliases: &[String],\n-    providers: &[(&str, String)],\n+    // Provider keys already linked to this UUID (private).\n+    linked: &[String],\n+    // Providers available to link: not yet attached.\n+    unlinkable: &[(&str, &str, String)],\n     claim_forms: Markup,\n ) -> Markup {\n     let current = actor.pseudonym.trim();\n@@ -212,16 +248,29 @@ fn account_body(\n                 (claim_forms)\n             }\n \n-            @if !providers.is_empty() {\n-                section class=\"login-section\" {\n-                    h2 { \"linked sign-in\" }\n-                    p class=\"muted small\" { \"sign in again with the same provider to return to this account\" }\n+            section class=\"login-section\" {\n+                h2 { \"linked sign-in\" }\n+                p class=\"muted small\" {\n+                    \"private to you — linking more providers raises trust weight without publishing which accounts you use\"\n+                }\n+                @if linked.is_empty() {\n+                    p class=\"muted\" data-testid=\"linked-providers-empty\" { \"none yet\" }\n+                } @else {\n+                    ul class=\"linked-provider-list\" data-testid=\"linked-providers\" {\n+                        @for key in linked {\n+                            li data-testid=(format!(\"linked-{key}\")) {\n+                                (oauth::provider_label(key))\n+                            }\n+                        }\n+                    }\n+                }\n+                @if !unlinkable.is_empty() {\n                     ul class=\"oauth-provider-list\" {\n-                        @for (name, href) in providers {\n+                        @for (key, label, href) in unlinkable {\n                             li {\n                                 a href=(href) class=\"btn-secondary oauth-provider\"\n-                                    data-testid=(format!(\"oauth-relink-{}\", name.to_lowercase())) {\n-                                    (format!(\"Re-link {name}\"))\n+                                    data-testid=(format!(\"oauth-link-{key}\")) {\n+                                    (format!(\"Link {label}\"))\n                                 }\n                             }\n                         }\n@@ -243,12 +292,21 @@ fn account_body(\n fn login_body(\n     session: Option<&session::SessionActor>,\n     aliases: &[String],\n-    providers: &[(&str, String)],\n+    linked: &[String],\n+    providers: &[(&str, &str, String)],\n     claim_forms: Option<Markup>,\n+    error: Option<&str>,\n ) -> Markup {\n     match (session, claim_forms) {\n-        (Some(actor), Some(forms)) => account_body(actor, aliases, providers, forms),\n-        _ => signed_out_body(providers),\n+        (Some(actor), Some(forms)) => {\n+            let unlinkable: Vec<_> = providers\n+                .iter()\n+                .filter(|(key, _, _)| !linked.iter().any(|p| p == key))\n+                .cloned()\n+                .collect();\n+            account_body(actor, aliases, linked, &unlinkable, forms)\n+        }\n+        _ => signed_out_body(providers, error),\n     }\n }\n \n@@ -268,6 +326,10 @@ pub async fn login_page(\n         .as_ref()\n         .map(|s| alias_list(db, &s.uuid))\n         .unwrap_or_default();\n+    let linked = session\n+        .as_ref()\n+        .map(|s| linked_providers_for_uuid(db, &s.uuid).unwrap_or_default())\n+        .unwrap_or_default();\n     let providers = oauth_providers(&base_url_from_env(state.cfg.port), &return_to);\n \n     let claim_forms = if session.is_some() {\n@@ -282,7 +344,14 @@ pub async fn login_page(\n         } else {\n             \"login · sorter2\"\n         },\n-        login_body(session.as_ref(), &aliases, &providers, claim_forms),\n+        login_body(\n+            session.as_ref(),\n+            &aliases,\n+            &linked,\n+            &providers,\n+            claim_forms,\n+            query.error.as_deref(),\n+        ),\n         state.views.get_views(\"/login\"),\n         session\n             .as_ref()\n@@ -302,7 +371,6 @@ pub async fn alias_page(\n     let db = state.projection_store.db();\n     let session = session::load_valid_session(db, &session_id).ok_or(StatusCode::UNAUTHORIZED)?;\n     if session::session_has_pseudonym(&session) {\n-        // Already onboarded — manage aliases on the account page.\n         return Ok(Redirect::to(\"/login\").into_response());\n     }\n \n@@ -331,7 +399,7 @@ pub async fn alias_page(\n pub async fn github_start(\n     State(state): State<AppState>,\n     jar: CookieJar,\n-    Query(query): Query<GitHubStartQuery>,\n+    Query(query): Query<OAuthStartQuery>,\n ) -> Result<Response, StatusCode> {\n     let cfg = oauth::GitHubConfig::from_env(&base_url_from_env(state.cfg.port))\n         .ok_or(StatusCode::SERVICE_UNAVAILABLE)?;\n@@ -342,7 +410,28 @@ pub async fn github_start(\n     } else {\n         None\n     };\n-    let url = oauth::authorize_url(&cfg, &state_token, mock_user);\n+    let url = oauth::github_authorize_url(&cfg, &state_token, mock_user);\n+    let jar = jar\n+        .add(session::oauth_state_cookie_value(&state_token))\n+        .add(session::auth_return_cookie_value(&return_to));\n+    Ok((jar, Redirect::temporary(&url)).into_response())\n+}\n+\n+pub async fn reddit_start(\n+    State(state): State<AppState>,\n+    jar: CookieJar,\n+    Query(query): Query<OAuthStartQuery>,\n+) -> Result<Response, StatusCode> {\n+    let cfg = oauth::RedditConfig::from_env(&base_url_from_env(state.cfg.port))\n+        .ok_or(StatusCode::SERVICE_UNAVAILABLE)?;\n+    let return_to = return_from_query_or_jar(&jar, query.return_to.as_deref());\n+    let state_token = session::new_oauth_state();\n+    let mock_user = if config::mock_oauth_allowed() {\n+        query.mock_user.as_deref()\n+    } else {\n+        None\n+    };\n+    let url = oauth::reddit_authorize_url(&cfg, &state_token, mock_user);\n     let jar = jar\n         .add(session::oauth_state_cookie_value(&state_token))\n         .add(session::auth_return_cookie_value(&return_to));\n@@ -355,6 +444,13 @@ pub struct OAuthCallbackQuery {\n     pub state: String,\n }\n \n+/// Link `provider:provider_id` to a UUID.\n+///\n+/// - Logged in + new provider → attach to session UUID\n+/// - Logged in + already ours → no-op\n+/// - Logged in + owned by someone else → conflict\n+/// - Logged out + known link → resume that UUID\n+/// - Logged out + unknown → create principal + first link\n async fn finish_oauth_login(\n     state: &AppState,\n     jar: CookieJar,\n@@ -364,11 +460,41 @@ async fn finish_oauth_login(\n     let db = state.projection_store.db();\n     let return_to = return_from_query_or_jar(&jar, None);\n \n-    let uuid = match oauth_link_owner(db, provider, &provider_id)\n-        .map_err(|_| StatusCode::INTERNAL_SERVER_ERROR)?\n-    {\n-        Some(existing) => existing,\n-        None => {\n+    let existing_owner = oauth_link_owner(db, provider, &provider_id)\n+        .map_err(|_| StatusCode::INTERNAL_SERVER_ERROR)?;\n+\n+    let session_uuid = session::session_id_from_jar(&jar)\n+        .as_deref()\n+        .and_then(|id| session::load_valid_session(db, id))\n+        .map(|s| s.uuid);\n+    let linking_while_logged_in = session_uuid.is_some();\n+\n+    let uuid = match (session_uuid, existing_owner) {\n+        (Some(session_uuid), Some(owner)) if owner == session_uuid => session_uuid,\n+        (Some(_), Some(_)) => {\n+            return Ok((\n+                jar.add(session::clear_oauth_state_cookie()),\n+                \"/login?error=oauth_taken\".into(),\n+            ));\n+        }\n+        (Some(session_uuid), None) => {\n+            let ts = now_ms();\n+            state\n+                .append_identity_events(vec![Event::OauthLinked {\n+                    uuid: session_uuid.clone(),\n+                    provider: provider.to_string(),\n+                    provider_id,\n+                    ts,\n+                }])\n+                .await\n+                .map_err(|e| {\n+                    tracing::warn!(err = %e, \"oauth link append failed\");\n+                    StatusCode::INTERNAL_SERVER_ERROR\n+                })?;\n+            session_uuid\n+        }\n+        (None, Some(owner)) => owner,\n+        (None, None) => {\n             let uuid = new_actor_uuid();\n             let ts = now_ms();\n             state\n@@ -409,6 +535,9 @@ async fn finish_oauth_login(\n             \"/login/alias?return_to={}\",\n             urlencoding::encode(&return_to)\n         )\n+    } else if linking_while_logged_in {\n+        // Additional link while already in an account → stay on account page.\n+        \"/login\".to_string()\n     } else {\n         return_to\n     };\n@@ -434,22 +563,57 @@ pub async fn github_callback(\n         .build()\n         .map_err(|_| StatusCode::INTERNAL_SERVER_ERROR)?;\n \n-    let token = oauth::exchange_code(&client, &cfg, &query.code)\n+    let token = oauth::github_exchange_code(&client, &cfg, &query.code)\n         .await\n         .map_err(|e| {\n             tracing::warn!(err = %e, \"github oauth token exchange failed\");\n             StatusCode::BAD_GATEWAY\n         })?;\n-    let user = oauth::fetch_user(&client, &cfg.api_base, &token)\n+    let user = oauth::github_fetch_user(&client, &cfg.api_base, &token)\n         .await\n         .map_err(|e| {\n             tracing::warn!(err = %e, \"github user fetch failed\");\n             StatusCode::BAD_GATEWAY\n         })?;\n \n-    let provider = \"github\";\n-    let provider_id = oauth::provider_id(&user);\n-    let (jar, dest) = finish_oauth_login(&state, jar, provider, provider_id).await?;\n+    let (jar, dest) =\n+        finish_oauth_login(&state, jar, \"github\", oauth::github_provider_id(&user)).await?;\n+    Ok((jar, Redirect::to(&dest)).into_response())\n+}\n+\n+pub async fn reddit_callback(\n+    State(state): State<AppState>,\n+    jar: CookieJar,\n+    Query(query): Query<OAuthCallbackQuery>,\n+) -> Result<Response, StatusCode> {\n+    let cfg = oauth::RedditConfig::from_env(&base_url_from_env(state.cfg.port))\n+        .ok_or(StatusCode::SERVICE_UNAVAILABLE)?;\n+\n+    let expected_state = session::oauth_state_from_jar(&jar).ok_or(StatusCode::BAD_REQUEST)?;\n+    if expected_state != query.state {\n+        return Err(StatusCode::BAD_REQUEST);\n+    }\n+\n+    let client = Client::builder()\n+        .timeout(std::time::Duration::from_secs(15))\n+        .build()\n+        .map_err(|_| StatusCode::INTERNAL_SERVER_ERROR)?;\n+\n+    let token = oauth::reddit_exchange_code(&client, &cfg, &query.code)\n+        .await\n+        .map_err(|e| {\n+            tracing::warn!(err = %e, \"reddit oauth token exchange failed\");\n+            StatusCode::BAD_GATEWAY\n+        })?;\n+    let user = oauth::reddit_fetch_user(&client, &cfg, &token)\n+        .await\n+        .map_err(|e| {\n+            tracing::warn!(err = %e, \"reddit user fetch failed\");\n+            StatusCode::BAD_GATEWAY\n+        })?;\n+\n+    let (jar, dest) =\n+        finish_oauth_login(&state, jar, \"reddit\", oauth::reddit_provider_id(&user)).await?;\n     Ok((jar, Redirect::to(&dest)).into_response())\n }\n \ndiff --git a/server/src/auth/oauth.rs b/server/src/auth/oauth.rs\nindex b80078fee0c5acd905b9125d29454e46c4e0d066..369b1527d9032cf312a07819279e0f988ef4a36e 100644\n--- a/server/src/auth/oauth.rs\n+++ b/server/src/auth/oauth.rs\n@@ -1,8 +1,15 @@\n-//! GitHub OAuth (raw reqwest, same style as reddit.rs).\n+//! OAuth providers (GitHub + Reddit). Provider accounts only *link* to a UUID;\n+//! the UUID is the canonical identity. Which providers are linked is private.\n \n use reqwest::Client;\n use serde::Deserialize;\n \n+use crate::reddit::{\n+    default_user_agent, reddit_oauth_api_base, reddit_oauth_token_base,\n+};\n+\n+// ── GitHub ──────────────────────────────────────────────────────────────────\n+\n #[derive(Debug, Clone)]\n pub struct GitHubConfig {\n     pub client_id: String,\n@@ -40,7 +47,7 @@ impl GitHubConfig {\n }\n \n #[derive(Debug, Deserialize)]\n-struct TokenResponse {\n+struct GitHubTokenResponse {\n     access_token: String,\n }\n \n@@ -50,7 +57,7 @@ pub struct GitHubUser {\n     pub login: String,\n }\n \n-pub fn authorize_url(cfg: &GitHubConfig, state: &str, mock_user: Option<&str>) -> String {\n+pub fn github_authorize_url(cfg: &GitHubConfig, state: &str, mock_user: Option<&str>) -> String {\n     let mut url = format!(\n         \"{}/login/oauth/authorize?client_id={}&redirect_uri={}&scope=read:user&state={}\",\n         cfg.oauth_base.trim_end_matches('/'),\n@@ -65,7 +72,7 @@ pub fn authorize_url(cfg: &GitHubConfig, state: &str, mock_user: Option<&str>) -\n     url\n }\n \n-pub async fn exchange_code(\n+pub async fn github_exchange_code(\n     client: &Client,\n     cfg: &GitHubConfig,\n     code: &str,\n@@ -90,14 +97,14 @@ pub async fn exchange_code(\n         return Err(format!(\"github token HTTP {}\", resp.status()));\n     }\n \n-    let body: TokenResponse = resp\n+    let body: GitHubTokenResponse = resp\n         .json()\n         .await\n         .map_err(|e| format!(\"github token parse failed: {e}\"))?;\n     Ok(body.access_token)\n }\n \n-pub async fn fetch_user(\n+pub async fn github_fetch_user(\n     client: &Client,\n     api_base: &str,\n     access_token: &str,\n@@ -120,10 +127,149 @@ pub async fn fetch_user(\n         .map_err(|e| format!(\"github user parse failed: {e}\"))\n }\n \n-pub fn provider_id(user: &GitHubUser) -> String {\n+pub fn github_provider_id(user: &GitHubUser) -> String {\n     user.id.to_string()\n }\n \n+// ── Reddit ──────────────────────────────────────────────────────────────────\n+\n+#[derive(Debug, Clone)]\n+pub struct RedditConfig {\n+    pub client_id: String,\n+    pub client_secret: String,\n+    pub redirect_uri: String,\n+    /// Host for `/api/v1/authorize` (www.reddit.com in production).\n+    pub authorize_base: String,\n+    /// Host for `POST /api/v1/access_token`.\n+    pub token_base: String,\n+    /// Host for bearer `GET /api/v1/me` (oauth.reddit.com).\n+    pub api_base: String,\n+    pub user_agent: String,\n+}\n+\n+/// Authorize page base; defaults to the same host as token POSTs.\n+pub fn reddit_authorize_base() -> String {\n+    std::env::var(\"REDDIT_OAUTH_AUTHORIZE_BASE\")\n+        .or_else(|_| std::env::var(\"REDDIT_OAUTH_BASE\"))\n+        .unwrap_or_else(|_| \"https://www.reddit.com\".into())\n+}\n+\n+impl RedditConfig {\n+    pub fn from_env(base_url: &str) -> Option<Self> {\n+        let client_id = std::env::var(\"REDDIT_CLIENT_ID\")\n+            .or_else(|_| std::env::var(\"REDDIT_APP_ID\"))\n+            .ok()?;\n+        let client_secret = std::env::var(\"REDDIT_CLIENT_SECRET\")\n+            .or_else(|_| std::env::var(\"REDDIT_APP_SECRET\"))\n+            .ok()?;\n+        if client_id.is_empty() || client_secret.is_empty() {\n+            return None;\n+        }\n+        let base = base_url.trim_end_matches('/');\n+        Some(Self {\n+            client_id,\n+            client_secret,\n+            redirect_uri: format!(\"{base}/auth/reddit/callback\"),\n+            authorize_base: reddit_authorize_base(),\n+            token_base: reddit_oauth_token_base(),\n+            api_base: reddit_oauth_api_base(),\n+            user_agent: default_user_agent(),\n+        })\n+    }\n+}\n+\n+#[derive(Debug, Deserialize)]\n+struct RedditTokenResponse {\n+    access_token: String,\n+}\n+\n+#[derive(Debug, Deserialize)]\n+pub struct RedditUser {\n+    /// Stable id (`t2_…`); never use `name` as identity.\n+    pub id: String,\n+    pub name: String,\n+}\n+\n+pub fn reddit_authorize_url(cfg: &RedditConfig, state: &str, mock_user: Option<&str>) -> String {\n+    let mut url = format!(\n+        \"{}/api/v1/authorize?client_id={}&response_type=code&state={}&redirect_uri={}&duration=temporary&scope=identity\",\n+        cfg.authorize_base.trim_end_matches('/'),\n+        urlencoding::encode(&cfg.client_id),\n+        urlencoding::encode(state),\n+        urlencoding::encode(&cfg.redirect_uri),\n+    );\n+    if let Some(user) = mock_user {\n+        url.push_str(\"&mock_user=\");\n+        url.push_str(&urlencoding::encode(user));\n+    }\n+    url\n+}\n+\n+pub async fn reddit_exchange_code(\n+    client: &Client,\n+    cfg: &RedditConfig,\n+    code: &str,\n+) -> Result<String, String> {\n+    let resp = client\n+        .post(format!(\n+            \"{}/api/v1/access_token\",\n+            cfg.token_base.trim_end_matches('/')\n+        ))\n+        .header(\"User-Agent\", &cfg.user_agent)\n+        .basic_auth(&cfg.client_id, Some(&cfg.client_secret))\n+        .form(&[\n+            (\"grant_type\", \"authorization_code\"),\n+            (\"code\", code),\n+            (\"redirect_uri\", cfg.redirect_uri.as_str()),\n+        ])\n+        .send()\n+        .await\n+        .map_err(|e| format!(\"reddit token request failed: {e}\"))?;\n+\n+    if !resp.status().is_success() {\n+        let status = resp.status();\n+        let body = resp.text().await.unwrap_or_default();\n+        return Err(format!(\"reddit token HTTP {status}: {body}\"));\n+    }\n+\n+    let body: RedditTokenResponse = resp\n+        .json()\n+        .await\n+        .map_err(|e| format!(\"reddit token parse failed: {e}\"))?;\n+    Ok(body.access_token)\n+}\n+\n+pub async fn reddit_fetch_user(\n+    client: &Client,\n+    cfg: &RedditConfig,\n+    access_token: &str,\n+) -> Result<RedditUser, String> {\n+    let resp = client\n+        .get(format!(\n+            \"{}/api/v1/me\",\n+            cfg.api_base.trim_end_matches('/')\n+        ))\n+        .header(\"User-Agent\", &cfg.user_agent)\n+        .bearer_auth(access_token)\n+        .send()\n+        .await\n+        .map_err(|e| format!(\"reddit user request failed: {e}\"))?;\n+\n+    if !resp.status().is_success() {\n+        return Err(format!(\"reddit user HTTP {}\", resp.status()));\n+    }\n+\n+    resp.json()\n+        .await\n+        .map_err(|e| format!(\"reddit user parse failed: {e}\"))\n+}\n+\n+pub fn reddit_provider_id(user: &RedditUser) -> String {\n+    user.id.clone()\n+}\n+\n+// ── Shared helpers ──────────────────────────────────────────────────────────\n+\n pub fn validate_pseudonym(raw: &str) -> Result<String, &'static str> {\n     let trimmed = raw.trim();\n     if trimmed.is_empty() {\n@@ -144,3 +290,12 @@ pub fn validate_pseudonym(raw: &str) -> Result<String, &'static str> {\n pub fn sanitize_pseudonym(login: &str) -> String {\n     validate_pseudonym(login).unwrap_or_else(|_| \"user\".to_string())\n }\n+\n+/// Display name for a provider key (`github` → `GitHub`). Never show provider ids.\n+pub fn provider_label(provider: &str) -> &'static str {\n+    match provider {\n+        \"github\" => \"GitHub\",\n+        \"reddit\" => \"Reddit\",\n+        _ => \"OAuth\",\n+    }\n+}\ndiff --git a/server/src/lib.rs b/server/src/lib.rs\nindex 84f2565b105fb302241b949af64bd5e49916eab2..0d948af1457504fdbd34d0b14261f65ac58da0ec 100644\n--- a/server/src/lib.rs\n+++ b/server/src/lib.rs\n@@ -47,6 +47,8 @@ pub fn create_app(state: AppState) -> Router {\n         .route(\"/login/alias\", get(crate::auth::alias_page))\n         .route(\"/auth/github\", get(crate::auth::github_start))\n         .route(\"/auth/github/callback\", get(crate::auth::github_callback))\n+        .route(\"/auth/reddit\", get(crate::auth::reddit_start))\n+        .route(\"/auth/reddit/callback\", get(crate::auth::reddit_callback))\n         .route(\"/auth/logout\", post(crate::auth::logout))\n         .route(\"/auth/switch\", post(crate::auth::switch_pseudonym))\n         .route(\"/ui\", post(crate::api::ui_html::post_ui_html))\ndiff --git a/server/src/projection_apply.rs b/server/src/projection_apply.rs\nindex 4fb4b48ee0a53b7f673fae0c9731eed5acc33332..f50458c2ff3c447a3cfd28adb298e6883a2da4e9 100644\n--- a/server/src/projection_apply.rs\n+++ b/server/src/projection_apply.rs\n@@ -4,6 +4,8 @@\n //! child links, recent-vote appends) plus a cursor advance, all committed in\n //! one atomic `DisableWal` batch.\n \n+use std::collections::HashMap;\n+\n use crate::{\n     event_log::EventLogError,\n     events::{Event, EventRecord},\n@@ -44,6 +46,8 @@ pub fn apply_records(\n     let db = projection_store.db();\n     let mut batch = db.batch();\n     let mut last_seq = 0u64;\n+    // Weight reads must see earlier writes in this same batch.\n+    let mut pending_weights: HashMap<String, f64> = HashMap::new();\n \n     for record in records {\n         match &record.event {\n@@ -85,6 +89,7 @@ pub fn apply_records(\n                 ensure_path_writes(&mut batch, &parsed);\n             }\n             Event::PrincipalCreated { uuid, .. } => {\n+                pending_weights.insert(uuid.clone(), BASE_TRUST_WEIGHT);\n                 batch.write(\n                     Store::root()\n                         .user_weights()\n@@ -112,17 +117,25 @@ pub fn apply_records(\n                     }\n                 } else {\n                     batch.write(Store::root().oauth_links().key(&link_key).set(uuid));\n-                    let current = Store::root()\n-                        .user_weights()\n-                        .key(&uuid.clone())\n-                        .get(db)\n-                        .map_err(|e| EventLogError::Apply(e.to_string()))?\n+                    let current = pending_weights\n+                        .get(uuid)\n+                        .copied()\n+                        .or_else(|| {\n+                            Store::root()\n+                                .user_weights()\n+                                .key(&uuid.clone())\n+                                .get(db)\n+                                .ok()\n+                                .flatten()\n+                        })\n                         .unwrap_or(BASE_TRUST_WEIGHT);\n+                    let next = trust_weight_after_link(current);\n+                    pending_weights.insert(uuid.clone(), next);\n                     batch.write(\n                         Store::root()\n                             .user_weights()\n                             .key(&uuid.clone())\n-                            .set(&trust_weight_after_link(current)),\n+                            .set(&next),\n                     );\n                 }\n             }\n@@ -205,6 +218,15 @@ mod tests {\n                 ),\n                 record(\n                     3,\n+                    Event::OauthLinked {\n+                        uuid: uuid.into(),\n+                        provider: \"reddit\".into(),\n+                        provider_id: \"t2_abc\".into(),\n+                        ts,\n+                    },\n+                ),\n+                record(\n+                    4,\n                     Event::PseudonymClaimed {\n                         uuid: uuid.into(),\n                         pseudonym: \"octocat\".into(),\n@@ -219,8 +241,12 @@ mod tests {\n             oauth_link_owner(store.db(), \"github\", \"42\").unwrap(),\n             Some(uuid.to_string())\n         );\n+        assert_eq!(\n+            crate::storage_schema::linked_providers_for_uuid(store.db(), uuid).unwrap(),\n+            vec![\"github\".to_string(), \"reddit\".to_string()]\n+        );\n         assert_eq!(resolve_actor_uuid(store.db(), \"octocat\").unwrap(), uuid);\n-        assert_eq!(user_trust_weight(store.db(), uuid).unwrap(), 1.5);\n+        assert_eq!(user_trust_weight(store.db(), uuid).unwrap(), 2.0);\n         let aliases = Store::root()\n             .user_pseudonyms()\n             .key(&uuid.to_string())\ndiff --git a/server/src/storage_schema.rs b/server/src/storage_schema.rs\nindex b942810afd96d3bf01b7765718303a39be4ef8d2..dac6f8e6080e3f5683c24dbb8861f5a981d456c4 100644\n--- a/server/src/storage_schema.rs\n+++ b/server/src/storage_schema.rs\n@@ -103,6 +103,25 @@ pub fn oauth_link_owner(db: &Db, provider: &str, provider_id: &str) -> durable::\n         .get(db)\n }\n \n+/// Provider names linked to a UUID (`github`, `reddit`, …). Private — for the\n+/// account owner's page only; never expose which providers are linked publicly.\n+pub fn linked_providers_for_uuid(db: &Db, uuid: &str) -> durable::Result<Vec<String>> {\n+    let mut providers = Vec::new();\n+    for (key, owner) in Store::root().oauth_links().iter(db)? {\n+        if owner != uuid {\n+            continue;\n+        }\n+        let Some((provider, _)) = key.split_once(':') else {\n+            continue;\n+        };\n+        if !providers.iter().any(|p| p == provider) {\n+            providers.push(provider.to_string());\n+        }\n+    }\n+    providers.sort();\n+    Ok(providers)\n+}\n+\n pub const RECENT_VOTES_CAP: u64 = 200;\n \n fn id_key(id: &ItemId) -> String {\ndiff --git a/test/support/harness.clj b/test/support/harness.clj\nindex 4505ece5aa193e826ca61c52f1467d252080d66b..741024aab1d14269e225791189633287980ae2e4 100644\n--- a/test/support/harness.clj\n+++ b/test/support/harness.clj\n@@ -48,12 +48,15 @@\n          \"GITHUB_CLIENT_SECRET\" \"test-secret\"\n          \"GITHUB_OAUTH_BASE\" (str \"http://127.0.0.1:\" oauth-port)\n          \"GITHUB_API_BASE\" (str \"http://127.0.0.1:\" oauth-port)\n+         ;; Reddit import fixtures + Reddit OAuth on reddit-port.\n          \"REDDIT_API_BASE\" (str \"http://127.0.0.1:\" reddit-port)\n+         \"REDDIT_CLIENT_ID\" \"test-reddit\"\n+         \"REDDIT_CLIENT_SECRET\" \"test-reddit-secret\"\n          \"REDDIT_OAUTH_BASE\" (str \"http://127.0.0.1:\" reddit-port)\n-         \"REDDIT_CLIENT_ID\" \"\"\n-         \"REDDIT_CLIENT_SECRET\" \"\"\n-         \"REDDIT_APP_ID\" \"\"\n-         \"REDDIT_APP_SECRET\" \"\"}))\n+         \"REDDIT_OAUTH_AUTHORIZE_BASE\" (str \"http://127.0.0.1:\" reddit-port)\n+         \"REDDIT_OAUTH_TOKEN_BASE\" (str \"http://127.0.0.1:\" reddit-port)\n+         \"REDDIT_OAUTH_API_BASE\" (str \"http://127.0.0.1:\" reddit-port)\n+         \"REDDIT_USER_AGENT\" \"web:sorter2-test:v0 (by /u/test)\"}))\n \n (defn with-auth-servers\n   \"Start mock Reddit + mock OAuth + release sorter2-server.\ndiff --git a/test/support/mock_oauth.clj b/test/support/mock_oauth.clj\nindex 909d7a7be8b159ea54a122d69c46af3db3318118..5ba7e9be3cf6d2226648e9609a09ed45f306930f 100644\n--- a/test/support/mock_oauth.clj\n+++ b/test/support/mock_oauth.clj\n@@ -1,5 +1,5 @@\n (ns test.support.mock-oauth\n-  \"In-process HTTP stub for GitHub OAuth (authorize, token, /user).\"\n+  \"In-process HTTP stub for GitHub + Reddit OAuth (authorize, token, user).\"\n   (:require [clojure.string :as str])\n   (:import [com.sun.net.httpserver HttpServer HttpHandler HttpExchange]\n            [java.net InetSocketAddress URLDecoder]))\n@@ -12,11 +12,14 @@\n                 (URLDecoder/decode (or v \"\") \"UTF-8\"))))\n           (str/split query #\"&\"))))\n \n-(defn- parse-mock-user [raw]\n+(defn- parse-mock-user\n+  \"GitHub-style `id:login` (numeric id). Reddit-style `t2_xxx:name`.\"\n+  [raw]\n   (let [s (or raw \"1002:newbie\")\n         [id login] (str/split s #\":\" 2)]\n-    {:id (Long/parseLong id)\n-     :login (or login \"newbie\")}))\n+    {:id id\n+     :login (or login \"newbie\")\n+     :numeric? (re-matches #\"\\d+\" id)}))\n \n (defn- send-json [^HttpExchange ex status body]\n   (let [bytes (.getBytes body \"UTF-8\")]\n@@ -31,9 +34,10 @@\n   (.sendResponseHeaders ex 302 -1)\n   (.close (.getResponseBody ex)))\n \n-(defn- read-form-code [^HttpExchange ex]\n+(defn- read-form [^HttpExchange ex]\n   (let [body (slurp (.getInputStream ex))]\n-    (query-param body \"code\")))\n+    {:code (query-param body \"code\")\n+     :grant (query-param body \"grant_type\")}))\n \n (defn- bearer-token [^HttpExchange ex]\n   (some-> (.getRequestHeaders ex)\n@@ -44,8 +48,18 @@\n   (when (str/starts-with? token \"mock:\")\n     (parse-mock-user (subs token 5))))\n \n+(defn- authorize-redirect [exchange query]\n+  (let [redirect-uri (query-param query \"redirect_uri\")\n+        state (query-param query \"state\")\n+        mock-user (query-param query \"mock_user\")\n+        user (parse-mock-user mock-user)\n+        code (str \"mock:\" (:id user) \":\" (:login user))\n+        loc (str redirect-uri \"?code=\" (java.net.URLEncoder/encode code \"UTF-8\")\n+                 \"&state=\" (java.net.URLEncoder/encode state \"UTF-8\"))]\n+    (send-redirect exchange loc)))\n+\n (defn start-mock-oauth\n-  \"Start mock GitHub OAuth on `port`. Returns a zero-arg `stop` function.\"\n+  \"Start mock GitHub + Reddit OAuth on `port`. Returns a zero-arg `stop` function.\"\n   [port]\n   (let [server (HttpServer/create (InetSocketAddress. \"127.0.0.1\" port) 0)\n         handler\n@@ -53,28 +67,45 @@\n           (handle [^HttpExchange exchange]\n             (let [uri (.getRequestURI exchange)\n                   path (.getPath uri)\n-                  query (.getQuery uri)]\n+                  query (.getQuery uri)\n+                  method (.getRequestMethod exchange)]\n               (cond\n+                ;; GitHub authorize\n                 (str/ends-with? path \"/login/oauth/authorize\")\n-                (let [redirect-uri (query-param query \"redirect_uri\")\n-                      state (query-param query \"state\")\n-                      mock-user (query-param query \"mock_user\")\n-                      user (parse-mock-user mock-user)\n-                      code (str \"mock:\" (:id user) \":\" (:login user))\n-                      loc (str redirect-uri \"?code=\" (java.net.URLEncoder/encode code \"UTF-8\")\n-                               \"&state=\" (java.net.URLEncoder/encode state \"UTF-8\"))]\n-                  (send-redirect exchange loc))\n+                (authorize-redirect exchange query)\n+\n+                ;; Reddit authorize\n+                (str/ends-with? path \"/api/v1/authorize\")\n+                (authorize-redirect exchange query)\n \n-                (str/ends-with? path \"/login/oauth/access_token\")\n-                (let [code (or (read-form-code exchange) \"mock:1002:newbie\")]\n+                ;; GitHub token\n+                (and (= method \"POST\") (str/ends-with? path \"/login/oauth/access_token\"))\n+                (let [code (or (:code (read-form exchange)) \"mock:1002:newbie\")]\n                   (send-json exchange 200 (str \"{\\\"access_token\\\":\\\"\" code \"\\\",\\\"token_type\\\":\\\"bearer\\\"}\")))\n \n+                ;; Reddit token (client_credentials for import + authorization_code for login)\n+                (and (= method \"POST\") (str/ends-with? path \"/api/v1/access_token\"))\n+                (let [form (read-form exchange)\n+                      grant (or (:grant form) \"\")\n+                      code (or (:code form) \"mock:t2_test:redditor\")]\n+                  (if (= grant \"client_credentials\")\n+                    (send-json exchange 200 \"{\\\"access_token\\\":\\\"app-token\\\",\\\"token_type\\\":\\\"bearer\\\",\\\"expires_in\\\":3600}\")\n+                    (send-json exchange 200 (str \"{\\\"access_token\\\":\\\"\" code \"\\\",\\\"token_type\\\":\\\"bearer\\\",\\\"expires_in\\\":3600}\"))))\n+\n+                ;; GitHub user\n                 (= path \"/user\")\n                 (let [token (bearer-token exchange)\n-                      user (or (parse-token-user token) {:id 1002 :login \"newbie\"})]\n+                      user (or (parse-token-user token) {:id \"1002\" :login \"newbie\" :numeric? true})]\n                   (send-json exchange 200\n                              (str \"{\\\"id\\\":\" (:id user) \",\\\"login\\\":\\\"\" (:login user) \"\\\"}\")))\n \n+                ;; Reddit /api/v1/me\n+                (str/ends-with? path \"/api/v1/me\")\n+                (let [token (bearer-token exchange)\n+                      user (or (parse-token-user token) {:id \"t2_test\" :login \"redditor\"})]\n+                  (send-json exchange 200\n+                             (str \"{\\\"id\\\":\\\"\" (:id user) \"\\\",\\\"name\\\":\\\"\" (:login user) \"\\\"}\")))\n+\n                 :else\n                 (send-json exchange 404 \"{\\\"error\\\":\\\"not found\\\"}\")))))]\n     (.createContext server \"/\" handler)\ndiff --git a/test/support/mock_reddit.clj b/test/support/mock_reddit.clj\nindex 5efa92db3e1f79b8f423a2f1adcbda959123c1ad..a630cf0938722193e9af88382d60e777ff371be4 100644\n--- a/test/support/mock_reddit.clj\n+++ b/test/support/mock_reddit.clj\n@@ -1,14 +1,56 @@\n (ns test.support.mock-reddit\n-  \"In-process HTTP stub for Reddit API fixtures (`test/fixtures/reddit/`).\"\n+  \"In-process HTTP stub for Reddit API fixtures + OAuth login endpoints.\"\n   (:require [clojure.java.io :as io]\n             [clojure.string :as str])\n   (:import [com.sun.net.httpserver HttpServer HttpHandler HttpExchange]\n-           [java.net InetSocketAddress]))\n+           [java.net InetSocketAddress URLDecoder]))\n \n (defn fixtures-dir\n   ([] (fixtures-dir (System/getProperty \"user.dir\")))\n   ([root] (str root \"/test/fixtures/reddit\")))\n \n+(defn- query-param [query key]\n+  (when query\n+    (some (fn [pair]\n+            (let [[k v] (str/split pair \"=\" 2)]\n+              (when (= k key)\n+                (URLDecoder/decode (or v \"\") \"UTF-8\"))))\n+          (str/split query #\"&\"))))\n+\n+(defn- parse-mock-user [raw]\n+  (let [s (or raw \"t2_test:redditor\")\n+        [id login] (str/split s #\":\" 2)]\n+    {:id id :login (or login \"redditor\")}))\n+\n+(defn- send-bytes [^HttpExchange ex status ^bytes body content-type]\n+  (.set (.getResponseHeaders ex) \"Content-Type\" content-type)\n+  (.sendResponseHeaders ex status (alength body))\n+  (doto (.getResponseBody ex)\n+    (.write body)\n+    (.close)))\n+\n+(defn- send-json [^HttpExchange ex status body]\n+  (send-bytes ex status (.getBytes body \"UTF-8\") \"application/json\"))\n+\n+(defn- send-redirect [^HttpExchange ex location]\n+  (.set (.getResponseHeaders ex) \"Location\" location)\n+  (.sendResponseHeaders ex 302 -1)\n+  (.close (.getResponseBody ex)))\n+\n+(defn- read-form [^HttpExchange ex]\n+  (let [body (slurp (.getInputStream ex))]\n+    {:code (query-param body \"code\")\n+     :grant (query-param body \"grant_type\")}))\n+\n+(defn- bearer-token [^HttpExchange ex]\n+  (some-> (.getRequestHeaders ex)\n+          (.getFirst \"Authorization\")\n+          (str/replace #\"^[Bb]earer \" \"\")))\n+\n+(defn- parse-token-user [token]\n+  (when (str/starts-with? token \"mock:\")\n+    (parse-mock-user (subs token 5))))\n+\n (defn start-mock-reddit\n   \"Start a mock Reddit API on `port`. Returns a zero-arg `stop` function.\"\n   ([port] (start-mock-reddit port (fixtures-dir)))\n@@ -19,15 +61,38 @@\n          handler\n          (proxy [HttpHandler] []\n            (handle [^HttpExchange exchange]\n-             ;; `/r/<sub>/about.json` → subreddit entity; `/r/<sub>.json` → listing.\n-             (let [path (.getPath (.getRequestURI exchange))\n-                   body (if (str/includes? path \"/about\")\n-                          about\n-                          listing)]\n-               (.sendResponseHeaders exchange 200 (alength body))\n-               (let [out (.getResponseBody exchange)]\n-                 (.write out body)\n-                 (.close out)))))]\n+             (let [uri (.getRequestURI exchange)\n+                   path (.getPath uri)\n+                   query (.getQuery uri)\n+                   method (.getRequestMethod exchange)]\n+               (cond\n+                 (str/ends-with? path \"/api/v1/authorize\")\n+                 (let [redirect-uri (query-param query \"redirect_uri\")\n+                       state (query-param query \"state\")\n+                       user (parse-mock-user (query-param query \"mock_user\"))\n+                       code (str \"mock:\" (:id user) \":\" (:login user))\n+                       loc (str redirect-uri \"?code=\" (java.net.URLEncoder/encode code \"UTF-8\")\n+                                \"&state=\" (java.net.URLEncoder/encode state \"UTF-8\"))]\n+                   (send-redirect exchange loc))\n+\n+                 (and (= method \"POST\") (str/ends-with? path \"/api/v1/access_token\"))\n+                 (let [form (read-form exchange)\n+                       grant (or (:grant form) \"\")\n+                       code (or (:code form) \"mock:t2_test:redditor\")]\n+                   (if (= grant \"client_credentials\")\n+                     (send-json exchange 200 \"{\\\"access_token\\\":\\\"app-token\\\",\\\"token_type\\\":\\\"bearer\\\",\\\"expires_in\\\":3600}\")\n+                     (send-json exchange 200 (str \"{\\\"access_token\\\":\\\"\" code \"\\\",\\\"token_type\\\":\\\"bearer\\\",\\\"expires_in\\\":3600}\"))))\n+\n+                 (str/ends-with? path \"/api/v1/me\")\n+                 (let [user (or (parse-token-user (bearer-token exchange))\n+                                {:id \"t2_test\" :login \"redditor\"})]\n+                   (send-json exchange 200\n+                              (str \"{\\\"id\\\":\\\"\" (:id user) \"\\\",\\\"name\\\":\\\"\" (:login user) \"\\\"}\")))\n+\n+                 ;; `/r/<sub>/about.json` → subreddit entity; `/r/<sub>.json` → listing.\n+                 :else\n+                 (let [body (if (str/includes? path \"/about\") about listing)]\n+                   (send-bytes exchange 200 body \"application/json\"))))))]\n      (.createContext server \"/\" handler)\n      (.setExecutor server nil)\n      (.start server)\n\n\nSide B — contributor: tommy-mor\nSide B — commit message:\n[595b3850] Fix star-topology ranking by using degree-based d_max (#146).\n\nA pure forward star at the default `>` ratio (2:1) produced uniform 1/3\nscores, and the alphabetical-fallback sort placed the unambiguous winner\nlast. Root cause: `compute_scores_from_edges` divided by the max sum of\npairwise-normalized weights, so every node ended up with P_ii = 0 — a\nbipartite Markov chain whose power iteration oscillated and, after the\nconfigured even iteration count, returned to the uniform initial state.\n\nSwitch the divisor to the unweighted max neighbor degree, matching the\ncanonical Rank Centrality definition in Negahban–Oh–Shah 2012 §3.1\n(arXiv:1209.1688, eq. defP and the d_max definition in §6). This gives\nevery non-saturated node a positive self-loop, makes the chain aperiodic,\nand converges the star to π_zebra = 1/2, π_alpha = π_beta = 1/4.\n\nAdd Rust regression test and a Clojure test that drives the sorterc\nbinary against four .sorter fixtures (star, inverse star, chain, cycle).\n\nCo-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>\n\nSide B — unified diff (full patch):\ndiff --git a/server/src/ranking.rs b/server/src/ranking.rs\nindex 3710c9f64437f5bef3b2121905b6f3bcb7611047..38e6d09b4370e5f8cbae09c0e5760b4e7f1ef7db 100644\n--- a/server/src/ranking.rs\n+++ b/server/src/ranking.rs\n@@ -1,4 +1,4 @@\n-use std::collections::HashMap;\n+use std::collections::{HashMap, HashSet};\n \n use crate::path_types::ItemId;\n use crate::reducer::GroupState;\n@@ -143,23 +143,35 @@ fn compute_scores_from_edges(n: usize, edges: impl Iterator<Item = ((usize, usiz\n         }\n     }\n \n+    // Rank Centrality (Negahban, Oh, Shah 2012, §3.1):\n+    //   P_ij = (1/d_max) * A_ij           for i ≠ j compared\n+    //   P_ii = 1 - (1/d_max) * Σ_k A_ik\n+    // where d_i is the *degree* (number of distinct neighbors compared) and\n+    // d_max = max_i d_i. Using the unweighted degree — not the sum of\n+    // pairwise-normalized weights — is what guarantees aperiodicity: it\n+    // forces P_ii > 0 for every non-maximum-degree node, and for max-degree\n+    // nodes whenever any neighbor weight is below 1 (i.e. not a unanimous\n+    // loss). Without this, regular comparison graphs (e.g. a pure star at\n+    // ratio 2:1) produce a bipartite chain that oscillates instead of\n+    // converging — see issue #146.\n     let mut out_edges: Vec<Vec<(usize, f64)>> = vec![Vec::new(); n];\n-    let mut out_deg: Vec<f64> = vec![0.0; n];\n+    let mut neighbors: Vec<HashSet<usize>> = vec![HashSet::new(); n];\n \n     for ((src, dst), w) in &normalized {\n         out_edges[*src].push((*dst, *w));\n-        out_deg[*src] += w;\n+        neighbors[*src].insert(*dst);\n+        neighbors[*dst].insert(*src);\n     }\n \n-    let mut max_out = 0.0f64;\n-    for &d in &out_deg {\n-        if d > max_out {\n-            max_out = d;\n-        }\n-    }\n-    if max_out <= 1e-12 {\n+    let weight_sum: Vec<f64> = out_edges\n+        .iter()\n+        .map(|es| es.iter().map(|(_, w)| *w).sum())\n+        .collect();\n+    let d_max = neighbors.iter().map(|s| s.len()).max().unwrap_or(0);\n+    if d_max == 0 {\n         return vec![1.0 / n as f64; n];\n     }\n+    let d_max_f = d_max as f64;\n \n     let mut scores = vec![1.0 / n as f64; n];\n     let mut next = vec![0.0f64; n];\n@@ -167,14 +179,14 @@ fn compute_scores_from_edges(n: usize, edges: impl Iterator<Item = ((usize, usiz\n     for _ in 0..max_iters {\n         next.fill(0.0);\n         for i in 0..n {\n-            let stay_prob = (max_out - out_deg[i]) / max_out;\n+            let stay_prob = (d_max_f - weight_sum[i]) / d_max_f;\n             next[i] += scores[i] * stay_prob;\n \n             if out_edges[i].is_empty() {\n                 continue;\n             }\n             for &(dst, w) in &out_edges[i] {\n-                next[dst] += scores[i] * (w / max_out);\n+                next[dst] += scores[i] * (w / d_max_f);\n             }\n         }\n \n@@ -270,6 +282,38 @@ mod tests {\n         }\n     }\n \n+    /// Regression for issue #146: pure forward star at default `>` ratio (2:1).\n+    /// Under the old (sum-of-weights) divisor every node had P_ii = 0 and the\n+    /// chain was bipartite; power iteration oscillated and returned the\n+    /// uniform initial distribution after an even number of steps. Using the\n+    /// paper's degree-based d_max gives every node a positive self-loop and\n+    /// the chain converges to the correct stationary distribution.\n+    #[test]\n+    fn star_topology_winner_at_top_via_subset() {\n+        let mut g = mk_group();\n+        g.apply_vote(vote(1, \"zebra\", \"alpha\", 2, 1));\n+        g.apply_vote(vote(2, \"zebra\", \"beta\", 2, 1));\n+\n+        let mut items: Vec<(usize, String)> = g\n+            .idx_to_item\n+            .iter()\n+            .enumerate()\n+            .map(|(i, it)| (i, it.as_str().to_string()))\n+            .collect();\n+        items.sort_by(|a, b| a.1.cmp(&b.1));\n+        let idxs: Vec<usize> = items.iter().map(|(i, _)| *i).collect();\n+\n+        let ranked = ranked_items_subset(&g, &idxs, 10000, 1e-8);\n+        for r in &ranked {\n+            eprintln!(\"{}: {}\", r.item.as_str(), r.score);\n+        }\n+        assert_eq!(\n+            ranked[0].item.as_str(),\n+            \"https://slug.social/zebra\",\n+            \"zebra won both votes and should rank #1\"\n+        );\n+    }\n+\n     #[test]\n     fn group_ranking_cache_dirty_flow() {\n         let mut g = mk_group();\ndiff --git a/test/fixtures/ranking/chain.sorter b/test/fixtures/ranking/chain.sorter\nnew file mode 100644\nindex 0000000000000000000000000000000000000000..912a96bdc08f631be27f3c9afc7e05004a2457c0\n--- /dev/null\n+++ b/test/fixtures/ranking/chain.sorter\n@@ -0,0 +1,10 @@\n+#t3\n+\n+~/t3/a { head of chain }\n+~/t3/b { middle }\n+~/t3/c { tail }\n+\n+{ a > b }\n+~/t3/a > ~/t3/b\n+{ b > c }\n+~/t3/b > ~/t3/c\ndiff --git a/test/fixtures/ranking/cycle.sorter b/test/fixtures/ranking/cycle.sorter\nnew file mode 100644\nindex 0000000000000000000000000000000000000000..771731ae176e5d77e00ab89767ff2d7465bb7c6b\n--- /dev/null\n+++ b/test/fixtures/ranking/cycle.sorter\n@@ -0,0 +1,12 @@\n+#t4\n+\n+~/t4/a { node a }\n+~/t4/b { node b }\n+~/t4/c { node c }\n+\n+{ a > b }\n+~/t4/a > ~/t4/b\n+{ b > c }\n+~/t4/b > ~/t4/c\n+{ c > a }\n+~/t4/c > ~/t4/a\ndiff --git a/test/fixtures/ranking/star.sorter b/test/fixtures/ranking/star.sorter\nnew file mode 100644\nindex 0000000000000000000000000000000000000000..135c9f9097d57b73c7ab18fac737ed3598d76fbe\n--- /dev/null\n+++ b/test/fixtures/ranking/star.sorter\n@@ -0,0 +1,11 @@\n+#repro\n+\n+~/repro/zebra { winner — beats both others }\n+~/repro/alpha { loser — alphabetically first }\n+~/repro/beta { loser — alphabetically middle }\n+\n+{ zebra beats alpha }\n+~/repro/zebra > ~/repro/alpha\n+\n+{ zebra beats beta }\n+~/repro/zebra > ~/repro/beta\ndiff --git a/test/fixtures/ranking/star_inverse.sorter b/test/fixtures/ranking/star_inverse.sorter\nnew file mode 100644\nindex 0000000000000000000000000000000000000000..dab842fa924e5124865ee216b9565f6c7471c812\n--- /dev/null\n+++ b/test/fixtures/ranking/star_inverse.sorter\n@@ -0,0 +1,11 @@\n+#t2\n+\n+~/t2/win { source of incoming edges (loses both) }\n+~/t2/loss-a { winner }\n+~/t2/loss-b { winner }\n+\n+{ loss-a beats win }\n+~/t2/loss-a > ~/t2/win\n+\n+{ loss-b beats win }\n+~/t2/loss-b > ~/t2/win\ndiff --git a/test/ranking.clj b/test/ranking.clj\nnew file mode 100644\nindex 0000000000000000000000000000000000000000..e1358783a84a264ee633bd79151ba29750b717cf\n--- /dev/null\n+++ b/test/ranking.clj\n@@ -0,0 +1,74 @@\n+(ns test.ranking\n+  \"Drives sorterc on .sorter fixtures and asserts ranking properties.\n+\n+   Regression coverage for issue #146 — pure forward star at default ratio\n+   (2:1 for `>`) used to produce tied uniform scores because the random walk\n+   on the normalized edge weights was bipartite. Fixed by switching to the\n+   degree-based d_max from Negahban–Oh–Shah rank centrality (§3.1).\"\n+  (:require [clojure.test :refer [deftest is testing]]\n+            [babashka.process :as p]\n+            [cheshire.core :as json]\n+            [clojure.java.io :as io]))\n+\n+(def sorterc-bin\n+  \"Path to the locally-built sorterc binary. Builds on demand if missing.\"\n+  (let [dbg     \"target/debug/sorterc\"\n+        release \"target/release/sorterc\"]\n+    (cond\n+      (.exists (io/file release)) release\n+      (.exists (io/file dbg))     dbg\n+      :else\n+      (do (println \"building sorterc…\")\n+          (let [r (p/shell {:out :string :err :string :continue true}\n+                           \"cargo build -p sorterc\")]\n+            (when-not (zero? (:exit r))\n+              (throw (ex-info \"cargo build -p sorterc failed\"\n+                              {:stderr (:err r)}))))\n+          dbg))))\n+\n+(defn compile-sorter [fixture-path]\n+  (let [{:keys [out exit]} (p/shell {:out :string :err :string :continue true}\n+                                    sorterc-bin \"compile\" fixture-path)]\n+    (when-not (zero? exit)\n+      (throw (ex-info \"sorterc exit nonzero\" {:fixture fixture-path :out out})))\n+    (json/parse-string out true)))\n+\n+(defn first-component-ranking [result]\n+  (-> result :rankings first :components first :ranking))\n+\n+(defn item-leaf [item]\n+  (last (clojure.string/split item #\"/\")))\n+\n+(deftest chain-ranks-head-first\n+  (let [ranking (first-component-ranking (compile-sorter \"test/fixtures/ranking/chain.sorter\"))\n+        names   (mapv (comp item-leaf :item) ranking)]\n+    (is (= [\"a\" \"b\" \"c\"] names)\n+        \"chain a>b>c should rank a, b, c in order\")\n+    (is (apply > (map :score ranking))\n+        \"scores should attenuate strictly down the chain\")))\n+\n+(deftest inverse-star-puts-winners-on-top\n+  (let [ranking (first-component-ranking (compile-sorter \"test/fixtures/ranking/star_inverse.sorter\"))\n+        names   (mapv (comp item-leaf :item) ranking)]\n+    (is (= \"win\" (last names))\n+        \"the item that lost to both others should be ranked last\")))\n+\n+(deftest cycle-produces-uniform-scores\n+  (let [ranking (first-component-ranking (compile-sorter \"test/fixtures/ranking/cycle.sorter\"))\n+        scores  (map :score ranking)]\n+    (is (every? #(< (Math/abs (- % 1/3)) 1e-3) scores)\n+        \"a perfectly symmetric 3-cycle should give every node ~1/3\")))\n+\n+(deftest star-topology-winner-at-top\n+  ;; Issue #146 regression: source-only star at default `>` ratio (2:1).\n+  ;; Pre-fix produced uniform 1/3 scores; alphabetical fallback put the\n+  ;; unambiguous winner at the bottom. Post-fix the chain is aperiodic and\n+  ;; converges to π_zebra = 1/2, π_alpha = π_beta = 1/4.\n+  (let [ranking (first-component-ranking (compile-sorter \"test/fixtures/ranking/star.sorter\"))\n+        names   (mapv (comp item-leaf :item) ranking)\n+        by-name (into {} (map (juxt (comp item-leaf :item) :score) ranking))]\n+    (is (= \"zebra\" (first names))\n+        \"zebra won both votes and should rank #1\")\n+    (is (< (Math/abs (- (by-name \"zebra\") 0.5)) 1e-3))\n+    (is (< (Math/abs (- (by-name \"alpha\") 0.25)) 1e-3))\n+    (is (< (Math/abs (- (by-name \"beta\") 0.25)) 1e-3))))\n","role":"user"}],"model":"~anthropic/claude-sonnet-latest"}