You are a constitutional council ranking individual git commits for ownership allocation.

Compare these two commits. Decide which contributed more lasting value to the project.

Judge substance, not spectacle:
- Prefer correct, lasting design and real bugfixes over churn, formatting, renames, or generated noise.
- Prefer clarity and necessity over sheer line count. A small precise change can beat a large diffuse one.
- Do not favor a side merely because its patch is longer or noisier.
- Weight what the change does for the project, not the contributor's name.

Return ONLY a JSON object: {"winner": "A" or "B", "ratio": "N:M", "explanation": "..."}
The explanation must cite concrete differences in the patches (1-3 sentences).

Side A — contributor: tommy-mor
Side A — commit message:
[2fe70b0e] themes

Side A — unified diff (full patch):
diff --git a/server/src/api/auth.rs b/server/src/api/auth.rs
index 559db65de14c6157690ffbf18eca0cf65b0a5202..b3631b06153d52f88348fef927e7a024b7b85ad6 100644
--- a/server/src/api/auth.rs
+++ b/server/src/api/auth.rs
@@ -1,7 +1,7 @@
 use axum::{
     body::Body,
     extract::{Path, Query, State},
-    http::{header, HeaderMap, HeaderValue, StatusCode},
+    http::{header, HeaderMap, HeaderValue, StatusCode, Uri},
     response::{IntoResponse, Redirect, Response},
     Form, Json,
 };
@@ -17,7 +17,7 @@ use crate::{
     events::{Event, GrantAdded, TokenIssued, UserRegistered},
     html::{
         auth_complete_page, auth_signed_in_fragment, choose_username_error_fragment,
-        choose_username_page, JsBuilder,
+        choose_username_page, theme_cookie_header_from_jar, theme_from_jar, theme_next_from_uri, JsBuilder,
     },
     identity::{parse_agent, parse_username},
     reducer::ReducerState,
@@ -48,15 +48,17 @@ fn js_form_error_fragment(session: &str, error: &str) -> Response {
         .into_response()
 }
 
-fn js_signed_in_fragment(bearer: &str) -> Response {
+fn js_signed_in_fragment(bearer: &str, jar: &CookieJar) -> Response {
     let mut response = JsBuilder::new()
         .id("choose-username-form")
         .morph_inner(auth_signed_in_fragment())
         .redirect("/auth/complete")
         .into_response();
-    response
-        .headers_mut()
-        .insert(header::SET_COOKIE, session_cookie_header_value(bearer));
+    let headers = response.headers_mut();
+    headers.append(header::SET_COOKIE, session_cookie_header_value(bearer));
+    if let Some(theme) = theme_cookie_header_from_jar(jar) {
+        headers.append(header::SET_COOKIE, theme);
+    }
     response
 }
 
@@ -69,13 +71,18 @@ pub fn optional_principal(headers: &HeaderMap, jar: &CookieJar, reduced: &Reduce
     verify_token(reduced, c.value()).ok()
 }
 
-fn redirect_with_session_cookie(public_url: &str, path_and_query: &str, bearer: &str) -> Response {
-    Response::builder()
+fn redirect_with_session_cookie(public_url: &str, path_and_query: &str, bearer: &str, jar: &CookieJar) -> Response {
+    let mut res = Response::builder()
         .status(StatusCode::TEMPORARY_REDIRECT)
         .header(header::LOCATION, format!("{public_url}{path_and_query}"))
-        .header(header::SET_COOKIE, session_cookie_header_value(bearer))
         .body(Body::empty())
-        .unwrap()
+        .unwrap();
+    let headers = res.headers_mut();
+    headers.append(header::SET_COOKIE, session_cookie_header_value(bearer));
+    if let Some(theme) = theme_cookie_header_from_jar(jar) {
+        headers.append(header::SET_COOKIE, theme);
+    }
+    res
 }
 
 async fn apply_invite_redemption(state: &AppState, invite_token: &str, grantee_username: &str) -> Result<(), String> {
@@ -286,7 +293,11 @@ pub struct AuthCallbackQuery {
     pub state: String,
 }
 
-pub async fn get_auth_callback(Query(q): Query<AuthCallbackQuery>, State(state): State<AppState>) -> impl IntoResponse {
+pub async fn get_auth_callback(
+    Query(q): Query<AuthCallbackQuery>,
+    State(state): State<AppState>,
+    jar: CookieJar,
+) -> impl IntoResponse {
     let sessions = pending_sessions(&state);
     {
         let sessions_read = sessions.read().await;
@@ -365,7 +376,7 @@ pub async fn get_auth_callback(Query(q): Query<AuthCallbackQuery>, State(state):
             }
             let cookie_bearer = bearer.clone();
             s.complete = Some((username, bearer));
-            return redirect_with_session_cookie(&public_url, "/", &cookie_bearer).into_response();
+            return redirect_with_session_cookie(&public_url, "/", &cookie_bearer, &jar).into_response();
         }
     }
 
@@ -378,14 +389,20 @@ pub struct ChooseUsernameQuery {
     pub error: Option<String>,
 }
 
-pub async fn get_choose_username(Query(q): Query<ChooseUsernameQuery>, State(state): State<AppState>) -> impl IntoResponse {
+pub async fn get_choose_username(
+    Query(q): Query<ChooseUsernameQuery>,
+    State(state): State<AppState>,
+    jar: CookieJar,
+    uri: Uri,
+) -> impl IntoResponse {
     let sessions = pending_sessions(&state);
     let sessions_read = sessions.read().await;
     if !sessions_read.contains_key(&q.session) {
         return api_error(StatusCode::NOT_FOUND, "unknown session", None).into_response();
     }
     drop(sessions_read);
-    choose_username_page(&q.session, q.error.as_deref()).into_response()
+    let next = theme_next_from_uri(&uri);
+    choose_username_page(&q.session, q.error.as_deref(), theme_from_jar(&jar), &next).into_response()
 }
 
 #[derive(Debug, Deserialize)]
@@ -396,6 +413,7 @@ pub struct ChooseUsernameForm {
 
 pub async fn post_choose_username(
     State(state): State<AppState>,
+    jar: CookieJar,
     Form(form): Form<ChooseUsernameForm>,
 ) -> impl IntoResponse {
     let canon_user = match parse_username(&form.username) {
@@ -477,7 +495,7 @@ pub async fn post_choose_username(
         s.complete = Some((canon_user.clone(), bearer.clone()));
     }
 
-    js_signed_in_fragment(&bearer).into_response()
+    js_signed_in_fragment(&bearer, &jar).into_response()
 }
 
 /// Start a browser-only OAuth flow (no CLI polling). Sets session cookie on success.
@@ -569,8 +587,9 @@ pub async fn get_pending_session(
     .into_response()
 }
 
-pub async fn get_auth_complete() -> impl IntoResponse {
-    auth_complete_page()
+pub async fn get_auth_complete(jar: CookieJar, uri: Uri) -> impl IntoResponse {
+    let next = theme_next_from_uri(&uri);
+    auth_complete_page(theme_from_jar(&jar), &next).into_response()
 }
 
 pub async fn get_whoami(State(state): State<AppState>, headers: HeaderMap) -> impl IntoResponse {
diff --git a/server/src/api/helpers.rs b/server/src/api/helpers.rs
index 81e2a55fa3abb8609b4099f91a989480336e11eb..9b71491e9f9efc44a2a4beba09be8f64bd2ff2ee 100644
--- a/server/src/api/helpers.rs
+++ b/server/src/api/helpers.rs
@@ -39,6 +39,55 @@ pub fn item_path_for_api(item: &str) -> String {
     }
 }
 
+/// Same as [`item_path_for_api`], but for private rooms ontology items are prefixed with
+/// `/r/{short}/{slug}` so the URL matches the web app (`/r/…/~/…` routes).
+pub fn item_path_for_api_in_room(item: &str, room_wire: &str) -> String {
+    let room = room_wire.trim();
+    if room.is_empty() || room == "public" {
+        return item_path_for_api(item);
+    }
+    let Some((short, slug)) = room.split_once('/') else {
+        return item_path_for_api(item);
+    };
+    if short.is_empty() || slug.is_empty() {
+        return item_path_for_api(item);
+    }
+    let Some(c) = CanonicalItemUrl::parse(item) else {
+        return item_path_for_api(item);
+    };
+    let root = CanonicalItemUrl::ontology_root();
+    let item_norm = c.as_str().trim_end_matches('/');
+    let root_norm = root.as_str().trim_end_matches('/');
+    if let Some(tail) = c.tilde_tail() {
+        return if tail.is_empty() {
+            format!("https://slug.social/r/{short}/{slug}/~")
+        } else {
+            format!("https://slug.social/r/{short}/{slug}/~/{}", tail)
+        };
+    }
+    if item_norm == root_norm {
+        return format!("https://slug.social/r/{short}/{slug}/~");
+    }
+    item_path_for_api(item)
+}
+
+/// Absolute thread URL for forum JSON (`/t/…` vs `/r/…/t/…`).
+pub fn forum_thread_web_url(room_wire: &str, thread_tag: &str) -> String {
+    let room = room_wire.trim();
+    let tag = thread_tag.trim().trim_start_matches('#');
+    if room.is_empty() || room == "public" {
+        format!("https://slug.social/t/{tag}")
+    } else if let Some((short, slug)) = room.split_once('/') {
+        if short.is_empty() || slug.is_empty() {
+            format!("https://slug.social/t/{tag}")
+        } else {
+            format!("https://slug.social/r/{short}/{slug}/t/{tag}")
+        }
+    } else {
+        format!("https://slug.social/t/{tag}")
+    }
+}
+
 /// Resolve an item path as a first-class canonical path.
 pub fn resolve_item(item: &str) -> Result<String, String> {
     let canonical = canonicalize_item(item);
@@ -188,3 +237,52 @@ pub fn vote_touches_path(a: &str, b: &str, parent_canon: &str) -> bool {
     let under = |item: &str| item == parent_canon || item.starts_with(&format!("{}/", parent_canon));
     under(a) || under(b)
 }
+
+#[cfg(test)]
+mod wire_url_tests {
+    use super::{forum_thread_web_url, item_path_for_api_in_room};
+
+    #[test]
+    fn public_room_unchanged() {
+        let u = "https://slug.social/~/a/b";
+        assert_eq!(item_path_for_api_in_room(u, "public"), u);
+    }
+
+    #[test]
+    fn private_room_prefixes_ontology() {
+        assert_eq!(
+            item_path_for_api_in_room("https://slug.social/~/topic/x", "9ab12cd/my-room"),
+            "https://slug.social/r/9ab12cd/my-room/~/topic/x"
+        );
+    }
+
+    #[test]
+    fn private_room_ontology_root() {
+        assert_eq!(
+            item_path_for_api_in_room("https://slug.social/~", "9ab12cd/my-room"),
+            "https://slug.social/r/9ab12cd/my-room/~"
+        );
+        assert_eq!(
+            item_path_for_api_in_room("https://slug.social/~/", "9ab12cd/my-room"),
+            "https://slug.social/r/9ab12cd/my-room/~"
+        );
+    }
+
+    #[test]
+    fn external_url_untouched_in_private_room() {
+        let u = "https://example.com/z";
+        assert_eq!(item_path_for_api_in_room(u, "9ab12cd/my-room"), u);
+    }
+
+    #[test]
+    fn forum_web_public_vs_room() {
+        assert_eq!(
+            forum_thread_web_url("public", "debate"),
+            "https://slug.social/t/debate"
+        );
+        assert_eq!(
+            forum_thread_web_url("9ab12cd/my-room", "#debate"),
+            "https://slug.social/r/9ab12cd/my-room/t/debate"
+        );
+    }
+}
diff --git a/server/src/api/rpc.rs b/server/src/api/rpc.rs
index 31f5fcfb4eaf4df0a9cbac532dd3dedfe3611810..5b91f5836625eedbb1cd9423168046e3fb576c17 100644
--- a/server/src/api/rpc.rs
+++ b/server/src/api/rpc.rs
@@ -27,8 +27,9 @@ use crate::{
 
 use super::auth::verify_bearer_principal;
 use super::helpers::{
-    compute_connectivity_stats, is_pair_voted, item_path_for_api, now_ms, paginate_rankings,
-    parse_parent_specs, pick_random_distinct, resolve_item, vote_touches_path,
+    compute_connectivity_stats, forum_thread_web_url, is_pair_voted, item_path_for_api,
+    item_path_for_api_in_room, now_ms, paginate_rankings, parse_parent_specs, pick_random_distinct,
+    resolve_item, vote_touches_path,
 };
 use super::validate::{normalize_room_and_thread, validate_ingest_document};
 
@@ -148,6 +149,7 @@ fn compute_scope_rank_changes(
     parent: &str,
     before: &crate::scope_rank::ChildrenRankings,
     after: &crate::scope_rank::ChildrenRankings,
+    room_wire: &str,
 ) -> Option<ScopeRankChanges> {
     fn build_positions(rankings: &crate::scope_rank::ChildrenRankings) -> HashMap<String, Option<RankPosition>> {
         let mut map = HashMap::new();
@@ -182,7 +184,7 @@ fn compute_scope_rank_changes(
         };
         if changed {
             changes.push(RankChange {
-                item: item_path_for_api(&item),
+                item: item_path_for_api_in_room(&item, room_wire),
                 before: b,
                 after: a,
             });
@@ -204,7 +206,7 @@ fn compute_scope_rank_changes(
         parent: if parent.is_empty() {
             "/".to_string()
         } else {
-            item_path_for_api(parent)
+            item_path_for_api_in_room(parent, room_wire)
         },
         changes,
     })
@@ -256,6 +258,7 @@ fn build_rank_response_for_content(
     offset: usize,
     limit: Option<usize>,
     want_percent: bool,
+    room_wire: &str,
 ) -> Result<RankResponse, RpcErr> {
     let parent_owned = parent.map(|s| s.to_string());
     let specs = parse_parent_specs(parent_owned.as_ref());
@@ -299,7 +302,7 @@ fn build_rank_response_for_content(
                     .ranked
                     .into_iter()
                     .map(|r| RankRow {
-                        item: item_path_for_api(r.item.as_str()),
+                        item: item_path_for_api_in_room(r.item.as_str(), room_wire),
                         percent: if want_percent {
                             Some((r.score / max_score) * 100.0)
                         } else {
@@ -315,7 +318,7 @@ fn build_rank_response_for_content(
     let prefixed_unranked: Vec<String> = rankings
         .unranked_items
         .into_iter()
-        .map(|s| item_path_for_api(s.as_str()))
+        .map(|s| item_path_for_api_in_room(s.as_str(), room_wire))
         .collect();
 
     let (components, unranked_items) = if offset > 0 || limit.is_some() {
@@ -522,7 +525,7 @@ async fn rpc_post(
             .filter_map(|p| {
                 let before = pre_rankings.get(p)?;
                 let after = crate::scope_rank::build_children_rankings(content, p);
-                compute_scope_rank_changes(p.as_str(), before, &after)
+                compute_scope_rank_changes(p.as_str(), before, &after, &room_key)
             })
             .collect();
         if v.is_empty() { None } else { Some(v) }
@@ -530,14 +533,28 @@ async fn rpc_post(
         None
     };
 
+    let (pair_hint, rank_hint, web_url) = if room_key == "public" {
+        (
+            "npx slugsocial public garden pair".to_string(),
+            "npx slugsocial public garden rank".to_string(),
+            forum_thread_web_url("public", &thread_id),
+        )
+    } else {
+        (
+            format!("npx slugsocial private {room_key} garden pair"),
+            format!("npx slugsocial private {room_key} garden rank"),
+            forum_thread_web_url(&room_key, &thread_id),
+        )
+    };
+
     Ok(RpcResult::PostOk {
         events_appended,
         ranking_changes,
         threads: vec![format!("#{}", thread_id)],
         next: NextMoves {
-            pair: "npx slugsocial public garden pair".to_string(),
-            rank: "npx slugsocial public garden rank".to_string(),
-            web: format!("https://slug.social/t/{}", thread_id),
+            pair: pair_hint,
+            rank: rank_hint,
+            web: web_url,
         },
     })
 }
@@ -609,7 +626,7 @@ async fn rpc_check(
         raw: v.raw_text.clone(),
         principal,
         delegate,
-        room_id: room_key,
+        room_id: room_key.clone(),
         thread_tag: thread_id.clone(),
     });
 
@@ -647,7 +664,7 @@ async fn rpc_check(
                         .ranked
                         .into_iter()
                         .map(|r| RankRow {
-                            item: item_path_for_api(r.item.as_str()),
+                            item: item_path_for_api_in_room(r.item.as_str(), &room_key),
                             score: r.score,
                             percent: None,
                         })
@@ -655,25 +672,35 @@ async fn rpc_check(
                 })
                 .collect();
             CheckScopeRanking {
-                parent: item_path_for_api(parent.as_str()),
+                parent: item_path_for_api_in_room(parent.as_str(), &room_key),
                 components,
                 unranked_items: scoped
                     .unranked_items
                     .into_iter()
-                    .map(|it| item_path_for_api(it.as_str()))
+                    .map(|it| item_path_for_api_in_room(it.as_str(), &room_key))
                     .collect(),
             }
         })
         .collect();
 
+    let check_next = if room_key == "public" {
+        vec![
+            "npx slugsocial public forum post <TAG> --delegate <uuid:rig:model>".to_string(),
+            "npx slugsocial public forum list".to_string(),
+            forum_thread_web_url("public", &thread_id),
+        ]
+    } else {
+        vec![
+            format!("npx slugsocial private {room_key} forum post <TAG> --delegate <uuid:rig:model>"),
+            format!("npx slugsocial private {room_key} forum list"),
+            forum_thread_web_url(&room_key, &thread_id),
+        ]
+    };
+
     Ok(RpcResult::CheckOk {
         rankings,
         threads: vec![format!("#{}", thread_id)],
-        next: vec![
-            "npx slugsocial public forum post <TAG> --delegate <uuid:rig:model>".to_string(),
-            "npx slugsocial public forum list".to_string(),
-            format!("https://slug.social/t/{}", thread_id),
-        ],
+        next: check_next,
     })
 }
 
@@ -690,7 +717,7 @@ fn rpc_list_forum_threads(reduced: &ReducerState, room: &str) -> ThreadsResponse
         .map(|((_, tag), ts)| ThreadSummary {
             thread: format!("#{tag}"),
             last_activity_ts: ts.last_activity_ts,
-            web: format!("https://slug.social/t/{}", tag),
+            web: forum_thread_web_url(room, tag),
         })
         .collect();
     out.sort_by(|a, b| b.last_activity_ts.cmp(&a.last_activity_ts));
@@ -1031,8 +1058,8 @@ async fn rpc_get_pair(state: &AppState, room: String, parent_path: String) -> Re
         .collect();
     let cs = compute_connectivity_stats(&content.ranking_group, &pool);
     Ok(RpcResult::Pair(PairResponse {
-        left: item_path_for_api(&left),
-        right: item_path_for_api(&right),
+        left: item_path_for_api_in_room(&left, &room),
+        right: item_path_for_api_in_room(&right, &room),
         left_body: lb,
         right_body: rb,
         threads: th,
@@ -1088,6 +1115,7 @@ pub async fn handle_rpc_batch(
                     offset.unwrap_or(0),
                     limit,
                     percent.unwrap_or(false),
+                    &room,
                 ) {
                     Ok(r) => line_ok(RpcResult::GardenRank(r)),
                     Err((e, h)) => line_err(e, h),
@@ -1109,7 +1137,7 @@ pub async fn handle_rpc_batch(
                 if !content.items.contains(&item) {
                     line_err(
                         "item not found",
-                        Some(format!("{} does not exist", item_path_for_api(&item_str))),
+                        Some(format!("{} does not exist", item_path_for_api_in_room(&item_str, &room))),
                     )
                 } else {
                     const MAX_ITEM_BODY: usize = 10_000;
@@ -1132,7 +1160,7 @@ pub async fn handle_rpc_batch(
                         .map(|s| s.iter().cloned().collect())
                         .unwrap_or_default();
                     line_ok(RpcResult::GardenItem(ItemResponse {
-                        item: item_str,
+                        item: item_path_for_api_in_room(&item_str, &room),
                         body,
                         truncated,
                         body_len,
@@ -1525,7 +1553,11 @@ pub async fn handle_rpc_batch(
                     let range = (top - bot).max(1e-12);
                     for r in items {
                         let pct = want_percent.then(|| ((r.score - bot) / range * 100.0).clamp(0.0, 100.0));
-                        ranked.push(RankRow { item: item_path_for_api(r.item.as_str()), score: r.score, percent: pct });
+                        ranked.push(RankRow {
+                            item: item_path_for_api_in_room(r.item.as_str(), &room),
+                            score: r.score,
+                            percent: pct,
+                        });
                     }
                 }
 
@@ -1542,7 +1574,7 @@ pub async fn handle_rpc_batch(
                 let page: Vec<RankRow> = ranked
                     .into_iter()
                     .chain(unranked.into_iter().map(|it| RankRow {
-                        item: item_path_for_api(&it),
+                        item: item_path_for_api_in_room(&it, &room),
                         score: 0.0,
                         percent: want_percent.then_some(0.0),
                     }))
@@ -1586,7 +1618,7 @@ pub async fn handle_rpc_batch(
                 if !content.items.contains(&item) {
                     line_err(
                         "item not found",
-                        Some(format!("{} does not exist", item_path_for_api(&item_str))),
+                        Some(format!("{} does not exist", item_path_for_api_in_room(&item_str, &room))),
                     )
                 } else {
                     let votes: Vec<VoteRow> = content
@@ -1597,8 +1629,8 @@ pub async fn handle_rpc_batch(
                                 .take(limit)
                                 .map(|v| VoteRow {
                                     ts: v.ts,
-                                    a: v.a.as_str().to_string(),
-                                    b: v.b.as_str().to_string(),
+                                    a: item_path_for_api_in_room(v.a.as_str(), &room),
+                                    b: item_path_for_api_in_room(v.b.as_str(), &room),
                                     ratio: format!("{}:{}", v.ratio_left, v.ratio_right),
                                     actor: Some(v.principal.clone()),
                                     body: v.body.clone(),
@@ -1608,7 +1640,7 @@ pub async fn handle_rpc_batch(
                         })
                         .unwrap_or_default();
                     line_ok(RpcResult::Matchup(MatchupResponse {
-                        item: item_path_for_api(&item_str),
+                        item: item_path_for_api_in_room(&item_str, &room),
                         votes,
                     }))
                 }
@@ -1635,8 +1667,8 @@ pub async fn handle_rpc_batch(
                                     if a == item_str || b == item_str {
                                         Some(VoteRow {
                                             ts: e.ts,
-                                            a: item_path_for_api(&a),
-                                            b: item_path_for_api(&b),
+                                            a: item_path_for_api_in_room(&a, &room),
+                                            b: item_path_for_api_in_room(&b, &room),
                                             ratio: format!("{}:{}", ratio_left, ratio_right),
                                             actor: reduced.ingests_by_id.get(&e.post_id).map(|ing| ing.principal.clone()),
                                             body: explanation,
@@ -1672,7 +1704,7 @@ pub async fn handle_rpc_batch(
                     }
                 }).collect();
                 line_ok(RpcResult::RankHistory(RankHistoryResponse {
-                    item: item_path_for_api(&item_str),
+                    item: item_path_for_api_in_room(&item_str, &room),
                     history,
                 }))
                 }
@@ -1691,6 +1723,10 @@ pub async fn handle_rpc_batch(
                     .map(|p| p.as_str().to_string())
                     .collect();
                 paths.sort();
+                let paths: Vec<String> = paths
+                    .into_iter()
+                    .map(|p| item_path_for_api_in_room(&p, &room))
+                    .collect();
                 line_ok(RpcResult::Leaves(LeavesResponse { paths }))
                 }
             },
@@ -1707,10 +1743,21 @@ pub async fn handle_rpc_batch(
                         let mut v: Vec<PathSummary> = roots.iter()
                             .map(|path| {
                                 let children = content.item_children.get(path.as_str()).map(|s| s.len()).unwrap_or(0);
+                                let path_label = CanonicalItemUrl::parse(path.as_str())
+                                    .and_then(|c| {
+                                        c.tilde_tail().map(|t| {
+                                            if t.is_empty() {
+                                                "~/".to_string()
+                                            } else {
+                                                format!("~/{}", t)
+                                            }
+                                        })
+                                    })
+                                    .unwrap_or_else(|| path.to_string());
                                 PathSummary {
-                                    path: format!("~/{}", path),
+                                    path: path_label,
                                     children,
-                                    web: format!("https://slug.social/~/{}", path),
+                                    web: item_path_for_api_in_room(path.as_str(), &room),
                                 }
                             }).collect();
                         v.sort_by(|a, b| a.path.cmp(&b.path));
@@ -1743,8 +1790,8 @@ pub async fn handle_rpc_batch(
                     .take(limit)
                     .map(|v| VoteRow {
                         ts: v.ts,
-                        a: v.a.as_str().to_string(),
-                        b: v.b.as_str().to_string(),
+                        a: item_path_for_api_in_room(v.a.as_str(), &room),
+                        b: item_path_for_api_in_room(v.b.as_str(), &room),
                         ratio: format!("{}:{}", v.ratio_left, v.ratio_right),
                         actor: Some(v.principal.clone()),
                         body: v.body.clone(),
diff --git a/server/src/html/auth.rs b/server/src/html/auth.rs
index d57b1c725ce3e06b1d904882b9388c3da48d85cb..5df77c76b89ed2bb11d936e1dbb804d50a0e79a1 100644
--- a/server/src/html/auth.rs
+++ b/server/src/html/auth.rs
@@ -23,7 +23,7 @@ fn form_inner(session: &str, error: Option<&str>) -> Markup {
     }
 }
 
-pub fn choose_username_page(session: &str, error: Option<&str>) -> Markup {
+pub fn choose_username_page(session: &str, error: Option<&str>, theme: &str, theme_next: &str) -> Markup {
     let body = html! {
         nav.breadcrumb {
             a href="/" { "slug.social" }
@@ -36,7 +36,7 @@ pub fn choose_username_page(session: &str, error: Option<&str>) -> Markup {
             (form_inner(session, error))
         }
     };
-    super::layout("join — slug.social", "view-auth", body, None)
+    super::layout("join — slug.social", "view-auth", body, None, theme, theme_next)
 }
 
 /// Fragment returned to the poem JS on error — replaces the form's innerHTML.
@@ -52,7 +52,7 @@ pub fn auth_signed_in_fragment() -> Markup {
     }
 }
 
-pub fn auth_complete_page() -> Markup {
+pub fn auth_complete_page(theme: &str, theme_next: &str) -> Markup {
     let body = html! {
         nav.breadcrumb {
             a href="/" { "slug.social" }
@@ -63,5 +63,5 @@ pub fn auth_complete_page() -> Markup {
         p { "Return to your terminal — your agent is polling and will collect your token automatically." }
         p.auth-hint { "You can close this tab." }
     };
-    super::layout("signed in — slug.social", "view-auth", body, None)
+    super::layout("signed in — slug.social", "view-auth", body, None, theme, theme_next)
 }
diff --git a/server/src/html/editor.rs b/server/src/html/editor.rs
index 07f6ab3b778f07f60765fa3f39060ebc5f72bc1a..ecdd226b1b17d5f11d1b79f99add5759ef918281 100644
--- a/server/src/html/editor.rs
+++ b/server/src/html/editor.rs
@@ -1,8 +1,10 @@
 use axum::{
     extract::State,
+    http::Uri,
     response::{Html, IntoResponse},
     Form,
 };
+use axum_extra::extract::cookie::CookieJar;
 use maud::{html, Markup};
 use serde::Deserialize;
 
@@ -13,7 +15,7 @@ use crate::{
     state::AppState,
 };
 
-use super::{bc_segment, layout};
+use super::{bc_segment, layout, theme_from_jar, theme_next_from_uri};
 
 fn bc_try() -> Markup {
     html! {
@@ -23,7 +25,7 @@ fn bc_try() -> Markup {
 }
 
 /// The interactive editor page — `/try`.
-pub async fn editor_page() -> impl IntoResponse {
+pub async fn editor_page(jar: CookieJar, uri: Uri) -> impl IntoResponse {
     let page = layout(
         "try — slug.social",
         "view-thread",
@@ -68,6 +70,8 @@ pub async fn editor_page() -> impl IntoResponse {
 "#)) }
         },
         None,
+        theme_from_jar(&jar),
+        &theme_next_from_uri(&uri),
     );
     Html(page.into_string())
 }
diff --git a/server/src/html/forum.rs b/server/src/html/forum.rs
index 5c5f9e2ba0e5cb1d661c113117988ec80c01deca..368b1016eb43d83e9ff39464ff6164fa9a8b558a 100644
--- a/server/src/html/forum.rs
+++ b/server/src/html/forum.rs
@@ -1,6 +1,6 @@
 use axum::{
     extract::{Path, Query, State},
-    http::{HeaderMap, StatusCode},
+    http::{HeaderMap, StatusCode, Uri},
     response::{Html, IntoResponse},
 };
 use axum_extra::extract::cookie::CookieJar;
@@ -19,7 +19,7 @@ use crate::{
 
 use super::{
     bc_segment, bc_threads, cli_panel, layout, now_ms, profile_href, recency_class,
-    render_linkified_with_embeds_in_scope, JsBuilder,
+    render_linkified_with_embeds_in_scope, theme_from_jar, theme_next_from_uri, JsBuilder,
 };
 
 #[derive(Clone)]
@@ -577,6 +577,7 @@ pub async fn home(
     State(state): State<AppState>,
     headers: HeaderMap,
     jar: CookieJar,
+    uri: Uri,
 ) -> impl IntoResponse {
     let now = now_ms();
     let reduced = state.reduced.read().await;
@@ -624,6 +625,8 @@ pub async fn home(
             (cli_panel("npx slugsocial public forum list"))
         },
         None,
+        theme_from_jar(&jar),
+        &theme_next_from_uri(&uri),
     );
     Html(page.into_string())
 }
@@ -679,6 +682,7 @@ async fn thread_view_inner(
     nav: ThreadNav,
     headers: HeaderMap,
     jar: CookieJar,
+    uri: Uri,
 ) -> impl IntoResponse {
     let tag = canonicalize_tag(&tag);
     let scope = nav.scope();
@@ -778,6 +782,8 @@ async fn thread_view_inner(
             (cli_panel(&cli))
         },
         None,
+        theme_from_jar(&jar),
+        &theme_next_from_uri(&uri),
     );
     Html(page.into_string()).into_response()
 }
@@ -789,8 +795,9 @@ pub async fn thread_view(
     Query(q): Query<ThreadViewQuery>,
     headers: HeaderMap,
     jar: CookieJar,
+    uri: Uri,
 ) -> impl IntoResponse {
-    thread_view_inner(state, tag, q, ThreadNav::public(), headers, jar).await
+    thread_view_inner(state, tag, q, ThreadNav::public(), headers, jar, uri).await
 }
 
 /// Room thread — `/r/:short/:slug/t/:tag`
@@ -800,31 +807,39 @@ pub async fn room_thread_view(
     Query(q): Query<ThreadViewQuery>,
     headers: HeaderMap,
     jar: CookieJar,
+    uri: Uri,
 ) -> impl IntoResponse {
     let room_id = format!("{room_short}/{room_slug}");
     let reduced = state.reduced.read().await;
     let user = optional_principal(&headers, &jar, &reduced);
     if !user_can_view_room(&reduced, &room_id, user.as_deref()) {
         drop(reduced);
-        return room_not_found_page().into_response();
+        return room_not_found_page(&jar, &uri).into_response();
     }
     drop(reduced);
     let Some(nav) = ThreadNav::from_room_id(&room_id) else {
         return (StatusCode::NOT_FOUND, "bad room path").into_response();
     };
-    thread_view_inner(state, tag, q, nav, headers, jar)
+    thread_view_inner(state, tag, q, nav, headers, jar, uri)
         .await
         .into_response()
 }
 
-fn room_not_found_page() -> impl IntoResponse {
+fn room_not_found_page(jar: &CookieJar, uri: &Uri) -> impl IntoResponse {
     let body = html! {
         nav class="breadcrumb" { a href="/" { "slug.social" } }
         h1 { "not found" }
         p { "The requested page could not be found." }
         p { a href="/" { "home" } }
     };
-    let page = layout("not found — slug.social", "view-thread", body, None);
+    let page = layout(
+        "not found — slug.social",
+        "view-thread",
+        body,
+        None,
+        theme_from_jar(jar),
+        &theme_next_from_uri(uri),
+    );
     (StatusCode::NOT_FOUND, Html(page.into_string()))
 }
 
@@ -834,6 +849,7 @@ pub async fn room_page(
     Path((room_short, room_slug)): Path<(String, String)>,
     headers: HeaderMap,
     jar: CookieJar,
+    uri: Uri,
 ) -> impl IntoResponse {
     let room_id = format!("{room_short}/{room_slug}");
     let now = now_ms();
@@ -845,7 +861,7 @@ pub async fn room_page(
     let user = optional_principal(&headers, &jar, &reduced);
     if !user_can_view_room(&reduced, &room_id, user.as_deref()) {
         drop(reduced);
-        return room_not_found_page().into_response();
+        return room_not_found_page(&jar, &uri).into_response();
     }
     let scope = ScopeId::Room(room_id.clone());
     let mut rows = collect_thread_rows_for_scope(&reduced, &scope, now);
@@ -902,6 +918,8 @@ pub async fn room_page(
             (cli_panel(&audit_cli))
         },
         None,
+        theme_from_jar(&jar),
+        &theme_next_from_uri(&uri),
     );
     Html(page.into_string()).into_response()
 }
@@ -943,6 +961,8 @@ async fn thread_post_view_inner(
     index_str: String,
     nav: ThreadNav,
     viewer: Option<String>,
+    jar: CookieJar,
+    uri: Uri,
 ) -> impl IntoResponse {
     let tag = canonicalize_tag(&tag);
     let index: usize = index_str.parse().unwrap_or(0);
@@ -987,6 +1007,8 @@ async fn thread_post_view_inner(
             }
         },
         None,
+        theme_from_jar(&jar),
+        &theme_next_from_uri(&uri),
     );
     Html(page.into_string()).into_response()
 }
@@ -996,11 +1018,12 @@ pub async fn thread_post_view(
     Path((tag, index_str)): Path<(String, String)>,
     headers: HeaderMap,
     jar: CookieJar,
+    uri: Uri,
 ) -> impl IntoResponse {
     let reduced = state.reduced.read().await;
     let viewer = optional_principal(&headers, &jar, &reduced);
     drop(reduced);
-    thread_post_view_inner(state, tag, index_str, ThreadNav::public(), viewer)
+    thread_post_view_inner(state, tag, index_str, ThreadNav::public(), viewer, jar, uri)
         .await
 }
 
@@ -1009,19 +1032,20 @@ pub async fn room_thread_post_view(
     Path((room_short, room_slug, tag, index_str)): Path<(String, String, String, String)>,
     headers: HeaderMap,
     jar: CookieJar,
+    uri: Uri,
 ) -> impl IntoResponse {
     let room_id = format!("{room_short}/{room_slug}");
     let reduced = state.reduced.read().await;
     let user = optional_principal(&headers, &jar, &reduced);
     if !user_can_view_room(&reduced, &room_id, user.as_deref()) {
         drop(reduced);
-        return room_not_found_page().into_response();
+        return room_not_found_page(&jar, &uri).into_response();
     }
     drop(reduced);
     let Some(nav) = ThreadNav::from_room_id(&room_id) else {
         return (StatusCode::NOT_FOUND, "bad room path").into_response();
     };
-    thread_post_view_inner(state, tag, index_str, nav, user)
+    thread_post_view_inner(state, tag, index_str, nav, user, jar, uri)
         .await
         .into_response()
 }
@@ -1193,6 +1217,7 @@ pub async fn user_profile_page(
     Path(username): Path<String>,
     headers: HeaderMap,
     jar: CookieJar,
+    uri: Uri,
 ) -> impl IntoResponse {
     let canon = match parse_username(&username) {
         Ok(u) => u,
@@ -1270,6 +1295,8 @@ pub async fn user_profile_page(
             (cli_panel(&format!("npx slugsocial public forum list")))
         },
         None,
+        theme_from_jar(&jar),
+        &theme_next_from_uri(&uri),
     );
     Html(page.into_string()).into_response()
 }
@@ -1292,13 +1319,14 @@ pub async fn room_thread_post_expand(
     Path((room_short, room_slug, tag, index_str)): Path<(String, String, String, String)>,
     headers: HeaderMap,
     jar: CookieJar,
+    uri: Uri,
 ) -> impl IntoResponse {
     let room_id = format!("{room_short}/{room_slug}");
     let reduced = state.reduced.read().await;
     let user = optional_principal(&headers, &jar, &reduced);
     if !user_can_view_room(&reduced, &room_id, user.as_deref()) {
         drop(reduced);
-        return room_not_found_page().into_response();
+        return room_not_found_page(&jar, &uri).into_response();
     }
     let Some(nav) = ThreadNav::from_room_id(&room_id) else {
         drop(reduced);
@@ -1328,13 +1356,14 @@ pub async fn room_thread_post_expand_deleted(
     Path((room_short, room_slug, tag, index_str)): Path<(String, String, String, String)>,
     headers: HeaderMap,
     jar: CookieJar,
+    uri: Uri,
 ) -> impl IntoResponse {
     let room_id = format!("{room_short}/{room_slug}");
     let reduced = state.reduced.read().await;
     let user = optional_principal(&headers, &jar, &reduced);
     if !user_can_view_room(&reduced, &room_id, user.as_deref()) {
         drop(reduced);
-        return room_not_found_page().into_response();
+        return room_not_found_page(&jar, &uri).into_response();
     }
     let Some(nav) = ThreadNav::from_room_id(&room_id) else {
         drop(reduced);
@@ -1364,13 +1393,14 @@ pub async fn room_thread_post_collapse_deleted(
     Path((room_short, room_slug, tag, index_str)): Path<(String, String, String, String)>,
     headers: HeaderMap,
     jar: CookieJar,
+    uri: Uri,
 ) -> impl IntoResponse {
     let room_id = format!("{room_short}/{room_slug}");
     let reduced = state.reduced.read().await;
     let user = optional_principal(&headers, &jar, &reduced);
     if !user_can_view_room(&reduced, &room_id, user.as_deref()) {
         drop(reduced);
-        return room_not_found_page().into_response();
+        return room_not_found_page(&jar, &uri).into_response();
     }
     let Some(nav) = ThreadNav::from_room_id(&room_id) else {
         drop(reduced);
diff --git a/server/src/html/garden.rs b/server/src/html/garden.rs
index e08f068ae04f5a2542ec2c43c240f931f87146bf..9b4789a79c3e293cbfc5f033a0eac8650320d94d 100644
--- a/server/src/html/garden.rs
+++ b/server/src/html/garden.rs
@@ -1,6 +1,6 @@
 use axum::{
     extract::{Path, State},
-    http::{HeaderMap, StatusCode},
+    http::{HeaderMap, StatusCode, Uri},
     response::{Html, IntoResponse},
 };
 use axum_extra::extract::cookie::CookieJar;
@@ -20,7 +20,8 @@ use crate::{
 
 use super::{
     bc_path, bc_segment, cli_panel, layout, now_ms, ratio_pct,
-    render_linkified_with_embeds_in_scope, breadcrumb_path::OntologyPath,
+    render_linkified_with_embeds_in_scope, theme_from_jar, theme_next_from_uri,
+    breadcrumb_path::OntologyPath,
     forum::ThreadNav,
 };
 
@@ -59,14 +60,21 @@ fn scoped_bc_path(path: &OntologyPath, nav: &ThreadNav) -> maud::Markup {
     }
 }
 
-fn room_not_found_page() -> impl IntoResponse {
+fn room_not_found_page(jar: &CookieJar, uri: &Uri) -> impl IntoResponse {
     let body = html! {
         nav class="breadcrumb" { a href="/" { "slug.social" } }
         h1 { "not found" }
         p { "The requested page could not be found." }
         p { a href="/" { "home" } }
     };
-    let page = layout("not found — slug.social", "view-thread", body, None);
+    let page = layout(
+        "not found — slug.social",
+        "view-thread",
+        body,
+        None,
+        theme_from_jar(jar),
+        &theme_next_from_uri(uri),
+    );
     (StatusCode::NOT_FOUND, Html(page.into_string()))
 }
 
@@ -81,7 +89,11 @@ fn user_can_view_room(reduced: &ReducerState, room_id: &str, username: Option<&s
 }
 
 /// Ontology index — root-level paths. Private (UUID) roots are excluded.
-pub async fn garden_index(State(state): State<AppState>) -> impl IntoResponse {
+pub async fn garden_index(
+    State(state): State<AppState>,
+    jar: CookieJar,
+    uri: Uri,
+) -> impl IntoResponse {
     let nav = ThreadNav::public();
     let child_rankings = {
         let reduced = state.reduced.read().await;
@@ -130,6 +142,8 @@ pub async fn garden_index(State(state): State<AppState>) -> impl IntoResponse {
             (cli_panel("npx slugsocial garden tree"))
         },
         None,
+        theme_from_jar(&jar),
+        &theme_next_from_uri(&uri),
     );
     Html(page.into_string())
 }
@@ -138,9 +152,11 @@ pub async fn garden_index(State(state): State<AppState>) -> impl IntoResponse {
 pub async fn ontology_path(
     State(state): State<AppState>,
     Path(path): Path<String>,
+    jar: CookieJar,
+    uri: Uri,
 ) -> impl IntoResponse {
     let path = OntologyPath::from_input(&path);
-    render_scope_view(state, path, ThreadNav::public()).await
+    render_scope_view(state, path, ThreadNav::public(), jar, uri).await
 }
 
 pub async fn room_garden_index(
@@ -148,19 +164,20 @@ pub async fn room_garden_index(
     Path((room_short, room_slug)): Path<(String, String)>,
     headers: HeaderMap,
     jar: CookieJar,
+    uri: Uri,
 ) -> impl IntoResponse {
     let room_id = format!("{room_short}/{room_slug}");
     let reduced = state.reduced.read().await;
     let user = optional_principal(&headers, &jar, &reduced);
     if !user_can_view_room(&reduced, &room_id, user.as_deref()) {
         drop(reduced);
-        return room_not_found_page().into_response();
+        return room_not_found_page(&jar, &uri).into_response();
     }
     drop(reduced);
     let Some(nav) = ThreadNav::from_room_id(&room_id) else {
         return (StatusCode::NOT_FOUND, "bad room path").into_response();
     };
-    render_scope_view(state, OntologyPath::root(), nav).await
+    render_scope_view(state, OntologyPath::root(), nav, jar, uri).await
 }
 
 pub async fn room_ontology_path(
@@ -168,20 +185,21 @@ pub async fn room_ontology_path(
     Path((room_short, room_slug, path)): Path<(String, String, String)>,
     headers: HeaderMap,
     jar: CookieJar,
+    uri: Uri,
 ) -> impl IntoResponse {
     let room_id = format!("{room_short}/{room_slug}");
     let reduced = state.reduced.read().await;
     let user = optional_principal(&headers, &jar, &reduced);
     if !user_can_view_room(&reduced, &room_id, user.as_deref()) {
         drop(reduced);
-        return room_not_found_page().into_response();
+        return room_not_found_page(&jar, &uri).into_response();
     }
     drop(reduced);
     let Some(nav) = ThreadNav::from_room_id(&room_id) else {
         return (StatusCode::NOT_FOUND, "bad room path").into_response();
     };
     let path = OntologyPath::from_input(&path);
-    render_scope_view(state, path, nav).await
+    render_scope_view(state, path, nav, jar, uri).await
 }
 
 #[derive(Debug, Clone)]
@@ -375,6 +393,8 @@ async fn render_scope_view(
     state: AppState,
     path: OntologyPath,
     nav: ThreadNav,
+    jar: CookieJar,
+    uri: Uri,
 ) -> axum::response::Response {
     let scope = nav.scope();
     let model = {
@@ -525,6 +545,8 @@ async fn render_scope_view(
             (cli_panel(&cli))
         },
         None,
+        theme_from_jar(&jar),
+        &theme_next_from_uri(&uri),
     );
 
     Html(page.into_string()).into_response()
diff --git a/server/src/html/mod.rs b/server/src/html/mod.rs
index a8fd73433d120b07351dd027faf0b25f8f101321..53041a0cf0b30e6f20749c92ecc15a4e9ac56e09 100644
--- a/server/src/html/mod.rs
+++ b/server/src/html/mod.rs
@@ -1,10 +1,13 @@
 use axum::{
     body::Body,
     extract::Path,
-    http::{header, StatusCode},
+    http::{header, HeaderValue, StatusCode, Uri},
     response::{IntoResponse, Response},
+    Form,
 };
+use axum_extra::extract::cookie::CookieJar;
 use maud::{html, Markup, DOCTYPE};
+use serde::Deserialize;
 use std::collections::HashSet;
 
 mod auth;
@@ -33,6 +36,75 @@ pub(crate) fn profile_href(username: &str) -> String {
     format!("/u/{username}")
 }
 
+/// Cookie name for UI theme (must match document.cookie migration in [`layout`]).
+pub const SLUG_THEME_COOKIE: &str = "slug-theme";
+
+/// Normalize a requested theme id to a known stylesheet key.
+pub fn normalize_theme(raw: &str) -> &'static str {
+    match raw {
+        "retro" => "retro",
+        "retro_craft" => "retro_craft",
+        _ => "default",
+    }
+}
+
+/// Resolved theme for rendering and cookie re-issue.
+pub fn theme_from_jar(jar: &CookieJar) -> &'static str {
+    jar.get(SLUG_THEME_COOKIE)
+        .map(|c| normalize_theme(c.value()))
+        .unwrap_or("default")
+}
+
+/// `Path` + optional `?query` for round-tripping after `POST /theme`.
+pub fn theme_next_from_uri(uri: &Uri) -> String {
+    uri.path_and_query()
+        .map(|pq| pq.as_str().to_string())
+        .filter(|s| !s.is_empty())
+        .unwrap_or_else(|| "/".to_string())
+}
+
+/// `Set-Cookie` for a validated theme (ASCII cookie value).
+pub fn theme_cookie_header_value(theme: &str) -> HeaderValue {
+    let t = normalize_theme(theme);
+    let s = format!("{SLUG_THEME_COOKIE}={t}; Path=/; SameSite=Lax; Max-Age=31536000");
+    HeaderValue::from_str(&s).expect("theme cookie must be ASCII")
+}
+
+/// Re-issue theme cookie on responses that also set `slug_session`, so login does not drop theme.
+pub fn theme_cookie_header_from_jar(jar: &CookieJar) -> Option<HeaderValue> {
+    let c = jar.get(SLUG_THEME_COOKIE)?;
+    Some(theme_cookie_header_value(c.value()))
+}
+
+fn sanitize_theme_next(next: Option<&str>) -> String {
+    let s = next.unwrap_or("/").trim();
+    if s.starts_with('/') && !s.starts_with("//") && s.len() < 8192 {
+        s.to_string()
+    } else {
+        "/".to_string()
+    }
+}
+
+#[derive(Debug, Deserialize)]
+pub struct ThemeForm {
+    theme: String,
+    next: Option<String>,
+}
+
+/// `POST /theme` — set theme cookie and redirect back (full navigation, no fetch).
+pub async fn post_theme(Form(form): Form<ThemeForm>) -> impl IntoResponse {
+    let theme = normalize_theme(&form.theme);
+    let next = sanitize_theme_next(form.next.as_deref());
+    let loc = HeaderValue::try_from(next.as_str())
+        .unwrap_or_else(|_| HeaderValue::from_static("/"));
+    Response::builder()
+        .status(StatusCode::SEE_OTHER)
+        .header(header::LOCATION, loc)
+        .header(header::SET_COOKIE, theme_cookie_header_value(theme))
+        .body(Body::empty())
+        .expect("theme redirect response")
+}
+
 // Embed CSS files at compile time
 const THEME_DEFAULT_CSS: &str = include_str!("../../static/theme_default.css");
 const THEME_RETRO_CSS: &str = include_str!("../../static/theme_retro.css");
@@ -173,7 +245,9 @@ impl JsQueryBuilder {
     }
 }
 
-pub(super) fn layout(title: &str, view: &str, body: Markup, views: Option<u64>) -> Markup {
+pub(super) fn layout(title: &str, view: &str, body: Markup, views: Option<u64>, theme: &str, theme_next: &str) -> Markup {
+    let theme = normalize_theme(theme);
+    let css_href = format!("/static/theme_{theme}.css");
     html! {
         (DOCTYPE)
         html {
@@ -181,7 +255,20 @@ pub(super) fn layout(title: &str, view: &str, body: Markup, views: Option<u64>)
                 meta charset="utf-8";
                 meta name="viewport" content="width=device-width, initial-scale=1";
                 title { (title) }
-                link rel="stylesheet" href="/static/theme_default.css" id="theme-stylesheet";
+                script { (maud::PreEscaped(r#"
+(function() {
+  try {
+    var ls = localStorage.getItem('slug-theme');
+    if (!ls) return;
+    var m = document.cookie.match(/(?:^|;\s*)slug-theme=([^;]+)/);
+    var c = m ? decodeURIComponent(m[1].replace(/\+/g, ' ')) : '';
+    if (ls === c) { localStorage.removeItem('slug-theme'); return; }
+    document.cookie = 'slug-theme=' + encodeURIComponent(ls) + '; Path=/; SameSite=Lax; Max-Age=31536000';
+    location.reload();
+  } catch (e) {}
+})();
+"#)) }
+                link rel="stylesheet" href=(css_href) id="theme-stylesheet";
                 script src="https://unpkg.com/idiomorph@0.3.0/dist/idiomorph.min.js" {}
             }
             body class=(view) {
@@ -196,32 +283,21 @@ pub(super) fn layout(title: &str, view: &str, body: Markup, views: Option<u64>)
                         input type="range" id="spread-slider" min="0" max="1" step="0.05" value="1";
                     }
                     a id="search-btn" href="/search" { "search" }
-                    div id="theme-switcher" { "theme" }
+                    form id="slug-theme-form" method="post" action="/theme" {
+                        input type="hidden" name="next" value=(theme_next);
+                        select id="theme-select" name="theme" onchange="this.form.submit()" aria-label="Theme" {
+                            @for (val, label) in [("default", "default"), ("retro", "retro"), ("retro_craft", "craft")] {
+                                @if theme == val {
+                                    option value=(val) selected { (label) }
+                                } @else {
+                                    option value=(val) { (label) }
+                                }
+                            }
+                        }
+                    }
                 }
 script { (maud::PreEscaped(r#"
                     (function() {
-                        // Theme switching
-                        const themes = ['default', 'retro', 'retro_craft'];
-                        const themeLabel = { default: 'default', retro: 'retro', retro_craft: 'craft' };
-                        const storedTheme = localStorage.getItem('slug-theme') || 'default';
-                        const switcher = document.getElementById('theme-switcher');
-                        const stylesheet = document.getElementById('theme-stylesheet');
-
-                        function setTheme(name) {
-                            stylesheet.href = `/static/theme_${name}.css`;
-                            localStorage.setItem('slug-theme', name);
-                            switcher.textContent = themeLabel[name] || name;
-                            setTimeout(() => setSpread(parseFloat(slider.value)), 50);
-                        }
-
-                        setTheme(storedTheme);
-
-                        switcher.addEventListener('click', function() {
-                            const current = themes.indexOf(localStorage.getItem('slug-theme') || 'default');
-                            const next = (current + 1) % themes.length;
-                            setTheme(themes[next]);
-                        });
-
                         // Spread control
                         const slider = document.getElementById('spread-slider');
                         const storedSpread = localStorage.getItem('slug-spread');
@@ -245,6 +321,7 @@ script { (maud::PreEscaped(r#"
                             const f = e.target;
                             if (!f || f.tagName !== 'FORM') return;
                             if ((f.method || 'get').toLowerCase() !== 'post') return;
+                            if (f.id === 'slug-theme-form') return;
                             e.preventDefault();
                             const resp = await fetch(f.action, {
                                 method: 'POST',
diff --git a/server/src/html/search.rs b/server/src/html/search.rs
index 0871ddb7a87e3153e2cb6c1f827b46de2c9f0f3b..28ceaa53c3fcac6777311535e95fb771b19438f5 100644
--- a/server/src/html/search.rs
+++ b/server/src/html/search.rs
@@ -1,6 +1,6 @@
 use axum::{
     extract::{Query, State},
-    http::HeaderMap,
+    http::{HeaderMap, Uri},
     response::{Html, IntoResponse},
 };
 use axum_extra::extract::cookie::CookieJar;
@@ -15,7 +15,7 @@ use crate::{
     timeago,
 };
 
-use super::{authorship_address, bc_segment, cli_panel, layout, now_ms};
+use super::{authorship_address, bc_segment, cli_panel, layout, now_ms, theme_from_jar, theme_next_from_uri};
 
 /// Escape HTML special chars for safe injection.
 fn escape_html(s: &str) -> String {
@@ -396,6 +396,7 @@ pub async fn search_page(
     Query(params): Query<SearchQuery>,
     headers: HeaderMap,
     jar: CookieJar,
+    uri: Uri,
 ) -> impl IntoResponse {
     let query = params.q.clone().unwrap_or_default();
     let results = if query.len() >= 2 {
@@ -420,6 +421,8 @@ pub async fn search_page(
             (cli_panel("npx slugsocial search <query>"))
         },
         None,
+        theme_from_jar(&jar),
+        &theme_next_from_uri(&uri),
     );
     Html(page.into_string())
 }
diff --git a/server/src/lib.rs b/server/src/lib.rs
index 43b63293c2a62b9700948767c618cb0614ddf6d9..b9d4b79791ba8dd3a3c26ff777943a2548092de5 100644
--- a/server/src/lib.rs
+++ b/server/src/lib.rs
@@ -33,6 +33,7 @@ pub fn create_app(state: AppState) -> Router {
         .route("/post", post(api::post_web_ingest))
         .route("/post/redact", post(api::post_web_redact))
         .route("/post/check", post(api::check_web_ingest))
+        .route("/theme", post(crate::html::post_theme))
         .route("/sse", get(api::get_html_stream))
         .route("/stream", get(api::get_stream))
         .route("/search", get(crate::html::search_page))
diff --git a/server/src/path_types.rs b/server/src/path_types.rs
index 997597f6659c1ba2092bc5348e393bf7a8fa7ae0..cad58cac7da948f92d6ea2a5587d917ab21d57ea 100644
--- a/server/src/path_types.rs
+++ b/server/src/path_types.rs
@@ -8,6 +8,12 @@
 //!
 //! This module adds lightweight newtypes so code can be explicit about what it
 //! expects without changing core storage formats.
+//!
+//! **Storage vs wire:** [`CanonicalItemUrl`] values are shared across scopes
+//! (`https://slug.social/~/…`); which [`crate::reducer::ContentState`] they live in
+//! is determined by scope, not by embedding the room id in the string. For JSON/RPC
+//! and browser links in a private room, use [`crate::api::helpers::item_path_for_api_in_room`]
+//! so ontology items become `https://slug.social/r/{short}/{slug}/~/…`.
 
 use std::borrow::Borrow;
 use std::fmt;
diff --git a/server/static/theme_default.css b/server/static/theme_default.css
index 2b06b12f3e77c9ed305272fe3ab47a8ad08504df..5e6304bcc36caed8aeda913fd241fc8fb9cf6d25 100644
--- a/server/static/theme_default.css
+++ b/server/static/theme_default.css
@@ -678,7 +678,10 @@ details > summary::-webkit-details-marker { display: none; }
   gap: 6px;
 }
 #spread-slider { accent-color: var(--ui); width: 80px; }
-#theme-switcher {
+#slug-theme-form {
+  display: contents;
+}
+#theme-select {
   background: var(--g4);
   border: var(--bv) solid;
   border-color: var(--hi) var(--lo) var(--lo) var(--hi);
@@ -688,8 +691,8 @@ details > summary::-webkit-details-marker { display: none; }
   padding: 2px 10px;
   user-select: none;
 }
-#theme-switcher:hover  { color: var(--signal); }
-#theme-switcher:active {
+#theme-select:hover  { color: var(--signal); }
+#theme-select:active {
   border-color: var(--lo) var(--hi) var(--hi) var(--lo);
   transform: translate(1px, 1px);
 }
diff --git a/server/static/theme_retro_craft.css b/server/static/theme_retro_craft.css
index 508222443a3bb2f16d3034a07af53a7df37a0314..3fde7e2b77fa4e4f46418927eb0fb0e5cd195c75 100644
--- a/server/static/theme_retro_craft.css
+++ b/server/static/theme_retro_craft.css
@@ -35,7 +35,6 @@ h1, h2, h3 {
   font-weight: 600;
   letter-spacing: 0.14em;
   margin: 1.5rem 0 0.5rem;
-  text-transform: uppercase;
 }
 
 a {
@@ -354,7 +353,10 @@ div.cli-panel {
   accent-color: var(--accent);
   width: 72px;
 }
-#theme-switcher,
+#slug-theme-form {
+  display: contents;
+}
+#theme-select,
 #search-btn,
 a#src-link {
   border: 1px solid var(--line);
@@ -365,7 +367,7 @@ a#src-link {
   padding: 0.25rem 0.6rem;
   text-decoration: none;
 }
-#theme-switcher:hover,
+#theme-select:hover,
 #search-btn:hover,
 a#src-link:hover {
   border-color: var(--accent);


Side B — contributor: tommy-mor
Side B — commit message:
[9e20d06c] Add sorterc dev tool for offline DSL compile and JSONL lint.

Introduce a workspace-only binary that validates .sorter files into ranking JSON and scans events.jsonl for corrupt or unreplayable ingests.

Co-authored-by: Cursor <cursoragent@cursor.com>

Side B — unified diff (full patch):
diff --git a/Cargo.lock b/Cargo.lock
index bf8153d9c723af97122c9ffdd4a7cfe82e853bb6..a07734f089b466440c3ae6fc1087ce85fc24ce62 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1826,6 +1826,17 @@ dependencies = [
  "windows-sys 0.60.2",
 ]
 
+[[package]]
+name = "sorterc"
+version = "0.0.1"
+dependencies = [
+ "anyhow",
+ "clap",
+ "serde",
+ "serde_json",
+ "slugsocial-server",
+]
+
 [[package]]
 name = "spin"
 version = "0.9.8"
diff --git a/Cargo.toml b/Cargo.toml
index 149cbf07901eab57c593184ff8719a75d530f1da..25337acdd61e44b20f354c78fed4a88caf896280 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -1,5 +1,5 @@
 [workspace]
-members = ["server", "cli"]
+members = ["server", "cli", "sorterc"]
 resolver = "2"
 
 
diff --git a/agents.md b/agents.md
index d8b801e454fdf37e7ac6038b91a69f83b0746d59..ce646ed3cd7123be4732dccec4a6800467e651e7 100644
--- a/agents.md
+++ b/agents.md
@@ -93,6 +93,17 @@ SLUG_GOOGLE_CLIENT_SECRET=mock
 
 After OAuth completes, the pending-session poll returns a `slug_…` bearer token for API calls.
 
+### Dev-only offline tooling
+
+**`sorterc`** — workspace binary, not published via npm. Compiles `.sorter` files and lints `events.jsonl` without a server:
+
+```
+cargo run -p sorterc -- compile path/to/doc.sorter [--base events.jsonl] [--room public] [--pretty]
+cargo run -p sorterc -- scan path/to/events.jsonl [--pretty]
+```
+
+`compile` validates DSL, simulates ingest against empty (or `--base`) reducer state, and prints JSON rankings. `scan` reports corrupt JSONL lines and ingests that fail DSL replay.
+
 ### Testing
 
 - **Rust tests:** `cargo nextest run --workspace` (163 tests; requires `cargo-nextest`)
diff --git a/server/src/lib.rs b/server/src/lib.rs
index c1d477d21aea03aff00e6f0689b0b4379d0d68d2..ad8e31099c807fb5844acb16cd5086a2f19327a7 100644
--- a/server/src/lib.rs
+++ b/server/src/lib.rs
@@ -10,6 +10,7 @@ pub mod form_template;
 pub mod html;
 pub mod identity;
 pub mod middleware;
+pub mod offline;
 pub mod path_types;
 pub mod ranking;
 pub mod reducer;
diff --git a/server/src/offline.rs b/server/src/offline.rs
new file mode 100644
index 0000000000000000000000000000000000000000..54ad0ded096a305ef8454ab2cdd1c3af71b14f5d
--- /dev/null
+++ b/server/src/offline.rs
@@ -0,0 +1,333 @@
+//! Offline `.sorter` compilation and JSONL diagnostics (no network, no auth).
+
+use std::collections::HashSet;
+use std::path::Path;
+
+use serde::Serialize;
+use slug_types::{CheckScopeRanking, RankComponent, RankRow, paths::GardenItemUrl};
+
+use crate::{
+    api::{resolve_item, validate_ingest_document},
+    dsl,
+    events::{Event, Ingest},
+    path_types::ItemId,
+    reducer::{ReducerState, ScopeId, scope_from_room_wire},
+    scope_rank::build_children_rankings,
+};
+
+#[derive(Debug, Clone, Serialize)]
+pub struct CompileStats {
+    pub items: usize,
+    pub votes: usize,
+    pub prose_blocks: usize,
+}
+
+#[derive(Debug, Serialize)]
+pub struct CompileResult {
+    pub ok: bool,
+    pub threads: Vec<String>,
+    pub rankings: Vec<CheckScopeRanking>,
+    pub stats: CompileStats,
+}
+
+#[derive(Debug, Clone, Serialize)]
+pub struct CompileError {
+    pub ok: bool,
+    pub error: String,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub hint: Option<String>,
+}
+
+#[derive(Debug, Clone, Serialize)]
+pub struct BadJsonLine {
+    pub line: usize,
+    pub message: String,
+}
+
+#[derive(Debug, Clone, Serialize)]
+pub struct MalformedIngest {
+    pub line: usize,
+    pub id: String,
+    pub room_id: String,
+    pub thread_tag: String,
+    pub reason: String,
+}
+
+#[derive(Debug, Clone, Serialize)]
+pub struct ScanResult {
+    pub ok: bool,
+    pub path: String,
+    pub total_lines: usize,
+    pub parsed_events: usize,
+    pub bad_json_lines: Vec<BadJsonLine>,
+    pub malformed_ingests: Vec<MalformedIngest>,
+    pub skipped_ingests: usize,
+}
+
+fn document_stats(doc: &dsl::Document) -> CompileStats {
+    let mut items = 0usize;
+    let mut votes = 0usize;
+    let mut prose_blocks = 0usize;
+    for stmt in &doc.statements {
+        match stmt {
+            dsl::Stmt::Item { .. } => items += 1,
+            dsl::Stmt::Vote { .. } => votes += 1,
+            dsl::Stmt::Prose { .. } => prose_blocks += 1,
+        }
+    }
+    CompileStats {
+        items,
+        votes,
+        prose_blocks,
+    }
+}
+
+fn threads_in_document(text: &str) -> Vec<String> {
+    let mut out = HashSet::new();
+    for line in text.lines() {
+        let trimmed = line.trim();
+        if !trimmed.starts_with('#') {
+            continue;
+        }
+        let rest = trimmed.trim_start_matches('#').trim();
+        if rest.is_empty() {
+            continue;
+        }
+        let tag = rest.split_whitespace().next().unwrap_or(rest);
+        let tag = tag.split(':').next().unwrap_or(tag).trim();
+        if tag.is_empty() {
+            continue;
+        }
+        out.insert(format!("#{}", crate::canonical_path::canonicalize_tag(tag)));
+    }
+    let mut tags: Vec<String> = out.into_iter().collect();
+    tags.sort();
+    tags
+}
+
+fn voted_parent_scopes(doc: &dsl::Document) -> Vec<ItemId> {
+    let mut parents = HashSet::new();
+    for stmt in &doc.statements {
+        if let dsl::Stmt::Vote { item1, item2, .. } = stmt {
+            if let (Ok(a), Ok(b)) = (resolve_item(item1), resolve_item(item2)) {
+                if let Some(p) = a.parent() {
+                    parents.insert(p);
+                }
+                if let Some(p) = b.parent() {
+                    parents.insert(p);
+                }
+            }
+        }
+    }
+    let mut out: Vec<ItemId> = parents.into_iter().collect();
+    out.sort();
+    out
+}
+
+fn rankings_for_simulated(
+    simulated: &ReducerState,
+    scope: &ScopeId,
+    room_wire: &str,
+    doc: &dsl::Document,
+) -> Vec<CheckScopeRanking> {
+    voted_parent_scopes(doc)
+        .iter()
+        .map(|parent| {
+            let scoped_content = simulated
+                .content_for_scope(&scope)
+                .unwrap_or_else(|| simulated.public());
+            let scoped = build_children_rankings(scoped_content, parent);
+            let components: Vec<RankComponent> = scoped
+                .component_rankings
+                .into_iter()
+                .map(|comp| RankComponent {
+                    pairs: comp.pairs,
+                    ranking: comp
+                        .ranked
+                        .into_iter()
+                        .map(|r| RankRow {
+                            item: GardenItemUrl::from_stored(&r.item, room_wire),
+                            score: r.score,
+                            percent: None,
+                        })
+                        .collect(),
+                })
+                .collect();
+            CheckScopeRanking {
+                parent: GardenItemUrl::from_stored(parent, room_wire).into_inner(),
+                components,
+                unranked_items: scoped
+                    .unranked_items
+                    .into_iter()
+                    .map(|it| GardenItemUrl::from_stored(&it, room_wire))
+                    .collect(),
+            }
+        })
+        .collect()
+}
+
+/// Validate and simulate one `.sorter` document against optional base reducer state.
+pub fn compile_document(
+    base: &ReducerState,
+    room: &str,
+    text: &str,
+) -> Result<CompileResult, CompileError> {
+    let room_key = room.trim();
+    let scope = scope_from_room_wire(room_key);
+    let validated = validate_ingest_document(base, text, &scope).map_err(|(_, message, hint)| {
+        CompileError {
+            ok: false,
+            error: message,
+            hint,
+        }
+    })?;
+
+    let event = Event::Ingest(Ingest {
+        ts: validated.ts,
+        id: uuid::Uuid::new_v4().to_string(),
+        raw: validated.raw_text.clone(),
+        principal: "offline".to_string(),
+        delegate: None,
+        room_id: room_key.to_string(),
+        thread_tag: "offline".to_string(),
+    });
+
+    let mut simulated = base.clone();
+    simulated.apply_event(event);
+
+    Ok(CompileResult {
+        ok: true,
+        threads: threads_in_document(text),
+        rankings: rankings_for_simulated(&simulated, &scope, room_key, &validated.doc),
+        stats: document_stats(&validated.doc),
+    })
+}
+
+fn ingest_parse_error(raw: &str) -> Option<String> {
+    dsl::parse_full(raw).err().map(|e| e.to_string())
+}
+
+fn load_events_from_jsonl(path: &Path) -> Result<(Vec<(usize, Event)>, Vec<BadJsonLine>), std::io::Error> {
+    let text = std::fs::read_to_string(path)?;
+    let mut events = Vec::new();
+    let mut bad_json_lines = Vec::new();
+    for (idx, line) in text.lines().enumerate() {
+        let line_no = idx + 1;
+        let trimmed = line.trim();
+        if trimmed.is_empty() {
+            continue;
+        }
+        match serde_json::from_str::<Event>(trimmed) {
+            Ok(ev) => events.push((line_no, ev)),
+            Err(e) => bad_json_lines.push(BadJsonLine {
+                line: line_no,
+                message: e.to_string(),
+            }),
+        }
+    }
+    Ok((events, bad_json_lines))
+}
+
+/// Replay a JSONL event log into reducer state (same rules as server boot).
+pub fn load_reducer_from_jsonl(path: &Path) -> Result<(ReducerState, Vec<BadJsonLine>), std::io::Error> {
+    let (events, bad_json_lines) = load_events_from_jsonl(path)?;
+    let mut state = ReducerState::default();
+    for (_line_no, ev) in events {
+        state.apply_event(ev);
+    }
+    Ok((state, bad_json_lines))
+}
+
+/// Scan an events.jsonl for corrupt JSON lines and ingests that fail DSL replay.
+pub fn scan_jsonl(path: &Path) -> Result<ScanResult, std::io::Error> {
+    let text = std::fs::read_to_string(path)?;
+    let total_lines = text.lines().count();
+    let (events, bad_json_lines) = load_events_from_jsonl(path)?;
+
+    let mut malformed_ingests = Vec::new();
+    let mut skipped_ingests = 0usize;
+    let mut state = ReducerState::default();
+    let parsed_events = events.len();
+
+    for (line_no, ev) in events {
+        if let Event::Ingest(ref ing) = ev {
+            if let Some(reason) = ingest_parse_error(&ing.raw) {
+                malformed_ingests.push(MalformedIngest {
+                    line: line_no,
+                    id: ing.id.clone(),
+                    room_id: ing.room_id.clone(),
+                    thread_tag: ing.thread_tag.clone(),
+                    reason,
+                });
+            }
+            let before = state.ingests_by_id.len();
+            state.apply_event(ev);
+            if state.ingests_by_id.len() == before {
+                skipped_ingests += 1;
+            }
+        } else {
+            state.apply_event(ev);
+        }
+    }
+
+    let ok = bad_json_lines.is_empty() && malformed_ingests.is_empty() && skipped_ingests == 0;
+
+    Ok(ScanResult {
+        ok,
+        path: path.display().to_string(),
+        total_lines,
+        parsed_events,
+        bad_json_lines,
+        malformed_ingests,
+        skipped_ingests,
+    })
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const TUTORIAL: &str = include_str!("../tests/fixtures/tutorial.sorter");
+
+    #[test]
+    fn compile_tutorial_fixture_emits_rankings() {
+        let result = compile_document(&ReducerState::default(), "public", TUTORIAL).unwrap();
+        assert!(result.ok);
+        assert!(!result.threads.is_empty());
+        assert!(result.stats.items >= 6);
+        assert!(result.stats.votes >= 6);
+        assert!(!result.rankings.is_empty());
+    }
+
+    #[test]
+    fn compile_rejects_vote_on_missing_item() {
+        let err = compile_document(
+            &ReducerState::default(),
+            "public",
+            "{ reason }\n~/missing/a 2:1 ~/missing/b",
+        )
+        .unwrap_err();
+        assert!(!err.ok);
+        assert!(err.error.contains("undefined"));
+    }
+
+    #[test]
+    fn scan_empty_jsonl_is_ok() {
+        let dir = tempfile::tempdir().unwrap();
+        let path = dir.path().join("events.jsonl");
+        std::fs::write(&path, "").unwrap();
+        let report = scan_jsonl(&path).unwrap();
+        assert!(report.ok);
+        assert!(report.bad_json_lines.is_empty());
+    }
+
+    #[test]
+    fn scan_reports_bad_json_line() {
+        let dir = tempfile::tempdir().unwrap();
+        let path = dir.path().join("events.jsonl");
+        std::fs::write(&path, "{not json}\n").unwrap();
+        let report = scan_jsonl(&path).unwrap();
+        assert!(!report.ok);
+        assert_eq!(report.bad_json_lines.len(), 1);
+    }
+}
diff --git a/sorterc/Cargo.toml b/sorterc/Cargo.toml
new file mode 100644
index 0000000000000000000000000000000000000000..92d477aff9b53291fb1a266db83065c1c800791d
--- /dev/null
+++ b/sorterc/Cargo.toml
@@ -0,0 +1,18 @@
+[package]
+name = "sorterc"
+version = "0.0.1"
+edition = "2021"
+license = "MIT"
+publish = false
+description = "Offline .sorter compiler and events.jsonl linter (dev only)"
+
+[[bin]]
+name = "sorterc"
+path = "src/main.rs"
+
+[dependencies]
+anyhow = "1"
+clap = { version = "4", features = ["derive"] }
+serde = { version = "1", features = ["derive"] }
+serde_json = "1"
+slugsocial-server = { path = "../server" }
diff --git a/sorterc/readme.md b/sorterc/readme.md
new file mode 100644
index 0000000000000000000000000000000000000000..1ebcc3fc935541ea9e47e0458ec67a750fe19fff
--- /dev/null
+++ b/sorterc/readme.md
@@ -0,0 +1,92 @@
+# sorterc
+
+Dev-only offline tooling for the slug `.sorter` DSL and `events.jsonl` event log.
+
+`sorterc` is **not** published via npm and does not talk to slug.social. It reuses the same parser, validator, and ranking code as the server, but runs entirely on local files.
+
+## Build
+
+From the repo root:
+
+```bash
+cargo build -p sorterc
+cargo run -p sorterc -- --help
+```
+
+## Commands
+
+### `compile` — evaluate a `.sorter` document
+
+Reads a `.sorter` file (or `-` for stdin), validates the DSL, simulates one ingest against reducer state, and prints JSON rankings to stdout.
+
+```bash
+cargo run -p sorterc -- compile path/to/doc.sorter
+cargo run -p sorterc -- compile path/to/doc.sorter --pretty
+cargo run -p sorterc -- compile - --pretty                    # stdin
+cargo run -p sorterc -- compile doc.sorter --base events.jsonl  # seed garden from log
+cargo run -p sorterc -- compile doc.sorter --room public         # default room
+```
+
+**Flags**
+
+| Flag | Description |
+|------|-------------|
+| `--base PATH` | Replay an `events.jsonl` first, then compile against that garden state |
+| `--room ID` | Room wire id (`public` or private room id). Default: `public` |
+| `--pretty` | Pretty-print JSON |
+
+**Success output** (shape):
+
+```json
+{
+  "ok": true,
+  "threads": ["#my-thread"],
+  "rankings": [ … ],
+  "stats": { "items": 3, "votes": 2, "prose_blocks": 5 }
+}
+```
+
+Rankings use the same structure as the server's dry-run check: parent scope, connected components, scores, unranked items.
+
+**Error output** exits with code 1:
+
+```json
+{
+  "ok": false,
+  "error": "parse error",
+  "hint": "…"
+}
+```
+
+### `scan` — lint an `events.jsonl`
+
+Reads a JSONL event log and reports problems without starting a server.
+
+```bash
+cargo run -p sorterc -- scan events.jsonl
+cargo run -p sorterc -- scan events.jsonl --pretty
+```
+
+Reports:
+
+- **bad JSON lines** — lines that are not valid JSON
+- **malformed ingests** — ingest events whose `raw` DSL fails to parse
+- **skipped ingests** — ingests dropped during replay (same behavior as server boot)
+
+Exits 0 when clean, 1 when any issue is found.
+
+## Typical uses
+
+- Iterate on `.sorter` files in an editor and pipe through `compile` to see rankings instantly
+- Verify a downloaded or edited `events.jsonl` before uploading to Fly
+- Debug "malformed ingest" warnings from production boot logs
+- CI or pre-commit checks on fixture docs (no OAuth, no network)
+
+## What it does not do
+
+- Post to slug.social or append to a live log
+- Authenticate users or bind agents
+- Run browser/UI tests
+- Replace `slugsocial public check` for operators who want the full RPC path against a running server
+
+For live server dry-run against current garden state, use `npx slugsocial public check` or `POST /try/check` in the browser.
diff --git a/sorterc/src/main.rs b/sorterc/src/main.rs
new file mode 100644
index 0000000000000000000000000000000000000000..71382c180085cb0ad71043c852f8db5d3a48a284
--- /dev/null
+++ b/sorterc/src/main.rs
@@ -0,0 +1,117 @@
+use std::path::{Path, PathBuf};
+
+use anyhow::{bail, Context, Result};
+use clap::{Parser, Subcommand};
+use slugsocial_server::{
+    offline::{self, CompileError, CompileResult, ScanResult},
+    reducer::ReducerState,
+};
+
+#[derive(Parser)]
+#[command(
+    name = "sorterc",
+    about = "Offline .sorter compiler and events.jsonl linter (dev only)",
+    version
+)]
+struct Cli {
+    #[command(subcommand)]
+    cmd: Command,
+}
+
+#[derive(Subcommand)]
+enum Command {
+    /// Parse and simulate a .sorter document; emit ranking JSON to stdout.
+    Compile {
+        /// `.sorter` file, or `-` for stdin.
+        file: PathBuf,
+        /// Room wire id (`public` or private room id).
+        #[arg(long, default_value = "public")]
+        room: String,
+        /// Optional events.jsonl to replay before compiling (seed garden state).
+        #[arg(long)]
+        base: Option<PathBuf>,
+        /// Pretty-print JSON.
+        #[arg(long)]
+        pretty: bool,
+    },
+    /// Scan an events.jsonl for corrupt JSON lines and malformed ingests.
+    Scan {
+        file: PathBuf,
+        #[arg(long)]
+        pretty: bool,
+    },
+}
+
+fn read_input(path: &Path) -> Result<String> {
+    if path.as_os_str() == "-" {
+        use std::io::Read;
+        let mut buf = String::new();
+        std::io::stdin().read_to_string(&mut buf)?;
+        Ok(buf)
+    } else {
+        std::fs::read_to_string(path)
+            .with_context(|| format!("read {}", path.display()))
+    }
+}
+
+fn load_base_state(base: Option<&Path>) -> Result<ReducerState> {
+    let Some(path) = base else {
+        return Ok(ReducerState::default());
+    };
+    let (state, bad_lines) = offline::load_reducer_from_jsonl(path)
+        .with_context(|| format!("load base jsonl {}", path.display()))?;
+    if !bad_lines.is_empty() {
+        bail!(
+            "base jsonl has {} corrupt line(s); fix or omit --base",
+            bad_lines.len()
+        );
+    }
+    Ok(state)
+}
+
+fn print_json<T: serde::Serialize>(value: &T, pretty: bool) -> Result<()> {
+    if pretty {
+        println!("{}", serde_json::to_string_pretty(value)?);
+    } else {
+        println!("{}", serde_json::to_string(value)?);
+    }
+    Ok(())
+}
+
+fn run_compile(file: PathBuf, room: String, base: Option<PathBuf>, pretty: bool) -> Result<()> {
+    let text = read_input(&file)?;
+    let base_state = load_base_state(base.as_deref())?;
+    match offline::compile_document(&base_state, &room, &text) {
+        Ok(result) => {
+            print_json::<CompileResult>(&result, pretty)?;
+            Ok(())
+        }
+        Err(err) => {
+            print_json::<CompileError>(&err, pretty)?;
+            std::process::exit(1);
+        }
+    }
+}
+
+fn run_scan(file: PathBuf, pretty: bool) -> Result<()> {
+    let report = offline::scan_jsonl(&file)
+        .with_context(|| format!("scan {}", file.display()))?;
+    print_json::<ScanResult>(&report, pretty)?;
+    if !report.ok {
+        std::process::exit(1);
+    }
+    Ok(())
+}
+
+fn main() -> Result<()> {
+    let cli = Cli::parse();
+    match cli.cmd {
+        Command::Compile {
+            file,
+            room,
+            base,
+            pretty,
+        } => run_compile(file, room, base, pretty),
+        Command::Scan { file, pretty } => run_scan(file, pretty),
+    }
+}