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:
[15e1037a] url stuff

Side A — unified diff (full patch):
diff --git a/server/src/url_rules/graph.rs b/server/src/url_rules/graph.rs
new file mode 100644
index 0000000000000000000000000000000000000000..f7ac0f9a551a1727cb2f9294778c283b9885b147
--- /dev/null
+++ b/server/src/url_rules/graph.rs
@@ -0,0 +1,831 @@
+//! Semantic URL graph: DFA traversal on host + path, query in context, generic fallback.
+
+use std::collections::HashMap;
+use std::sync::OnceLock;
+
+use url::Url;
+
+use super::graph_builder::GraphBuilder;
+use super::parse::{normalize_match_host, strip_tracking_query, UrlParts};
+
+#[derive(Debug, Clone, Default)]
+pub struct Context {
+    pub vars: HashMap<String, String>,
+    pub query: HashMap<String, String>,
+}
+
+pub type CanonicalFn = fn(&Context) -> Option<String>;
+
+#[derive(Clone, Copy)]
+pub enum EdgePattern {
+    Literal(&'static str),
+    Variable(&'static str),
+    /// Absorb any trailing segment without leaving this node (e.g. post title slug).
+    AbsorbAny,
+    /// Absorb segment when `cond(seg)` (e.g. subreddit listing suffix).
+    AbsorbIf(fn(&str) -> bool),
+}
+
+pub struct Edge {
+    pub pattern: EdgePattern,
+    pub target: &'static str,
+}
+
+pub struct Node {
+    pub edges: Vec<Edge>,
+    pub canonical: CanonicalFn,
+    pub parent: Option<&'static str>,
+}
+
+impl Node {
+    pub(crate) fn empty() -> Self {
+        Self {
+            edges: Vec::new(),
+            canonical: |_| None,
+            parent: None,
+        }
+    }
+}
+
+pub struct Graph {
+    pub nodes: HashMap<&'static str, Node>,
+}
+
+static GRAPH: OnceLock<Graph> = OnceLock::new();
+
+pub fn graph() -> &'static Graph {
+    GRAPH.get_or_init(build_graph)
+}
+
+impl Graph {
+    pub fn resolve_canonical(&self, parts: &UrlParts) -> Option<String> {
+        let mut query = parts.query.clone();
+        strip_tracking_query(&mut query);
+        let mut ctx = Context {
+            vars: HashMap::new(),
+            query,
+        };
+
+        if let Some(node_id) = self.traverse(parts, &mut ctx) {
+            if let Some(canon) = (self.nodes.get(node_id)?.canonical)(&ctx) {
+                return Some(canon);
+            }
+        }
+        Some(generic_canonical(parts))
+    }
+
+    pub fn breadcrumbs(&self, parts: &UrlParts) -> Vec<String> {
+        let mut query = parts.query.clone();
+        strip_tracking_query(&mut query);
+        let mut ctx = Context {
+            vars: HashMap::new(),
+            query,
+        };
+
+        if let Some(mut node_id) = self.traverse(parts, &mut ctx) {
+            let mut paths = Vec::new();
+            loop {
+                let node = match self.nodes.get(node_id) {
+                    Some(n) => n,
+                    None => break,
+                };
+                if let Some(url) = (node.canonical)(&ctx) {
+                    if paths.last() != Some(&url) {
+                        paths.push(url);
+                    }
+                }
+                match node.parent {
+                    Some(p) => node_id = p,
+                    None => break,
+                }
+            }
+            paths.reverse();
+            if !paths.is_empty() {
+                return paths;
+            }
+        }
+        generic_breadcrumbs(parts)
+    }
+
+    fn traverse(&self, parts: &UrlParts, ctx: &mut Context) -> Option<&'static str> {
+        let host = parts.match_host();
+        let mut node_id = match host.as_str() {
+            "reddit.com" => "reddit_root",
+            "youtube.com" => "youtube_root",
+            "youtu.be" => "youtu_be_entry",
+            _ => return None,
+        };
+
+        let segs: Vec<&str> = parts.path_segments.iter().map(String::as_str).collect();
+        let mut i = 0;
+        while i < segs.len() {
+            let seg = segs[i];
+            match self.follow_edge(node_id, seg, ctx) {
+                Ok(next) => {
+                    node_id = next;
+                    i += 1;
+                }
+                Err(()) => {
+                    if self.try_absorb(node_id, seg) {
+                        i += 1;
+                        continue;
+                    }
+                    return None;
+                }
+            }
+        }
+        Some(node_id)
+    }
+
+    fn follow_edge(
+        &self,
+        node_id: &'static str,
+        seg: &str,
+        ctx: &mut Context,
+    ) -> Result<&'static str, ()> {
+        let node = self.nodes.get(node_id).ok_or(())?;
+        for edge in &node.edges {
+            match edge.pattern {
+                EdgePattern::Literal(lit) if lit == seg => return Ok(edge.target),
+                EdgePattern::Variable(name) => {
+                    ctx.vars.insert(name.to_string(), seg.to_string());
+                    return Ok(edge.target);
+                }
+                EdgePattern::AbsorbAny
+                | EdgePattern::AbsorbIf(_)
+                | EdgePattern::Literal(_)
+                | EdgePattern::Variable(_) => {}
+            }
+        }
+        Err(())
+    }
+
+    fn try_absorb(&self, node_id: &'static str, seg: &str) -> bool {
+        let node = match self.nodes.get(node_id) {
+            Some(n) => n,
+            None => return false,
+        };
+        for edge in &node.edges {
+            match edge.pattern {
+                EdgePattern::AbsorbAny => return true,
+                EdgePattern::AbsorbIf(cond) if cond(seg) => return true,
+                EdgePattern::AbsorbIf(_) | EdgePattern::Literal(_) | EdgePattern::Variable(_) => {}
+            }
+        }
+        false
+    }
+
+    /// Test hook: terminal graph node and captured context after traversal.
+    #[cfg(test)]
+    pub fn traverse_terminal(&self, parts: &UrlParts) -> Option<(&'static str, Context)> {
+        let mut query = parts.query.clone();
+        strip_tracking_query(&mut query);
+        let mut ctx = Context {
+            vars: HashMap::new(),
+            query,
+        };
+        let node = self.traverse(parts, &mut ctx)?;
+        Some((node, ctx))
+    }
+}
+
+fn is_reddit_listing_suffix(seg: &str) -> bool {
+    matches!(seg, "hot" | "top" | "new" | "rising" | "controversial")
+}
+
+/// Percent-encode a path or query fragment so `&`, `?`, etc. cannot break URL structure.
+fn enc(s: &str) -> String {
+    urlencoding::encode(s).into_owned()
+}
+
+// --- Canonical formatters ---
+
+fn canon_reddit_root(_: &Context) -> Option<String> {
+    Some("https://reddit.com".to_string())
+}
+
+fn canon_reddit_r_hub(_: &Context) -> Option<String> {
+    Some("https://reddit.com/r".to_string())
+}
+
+fn canon_reddit_subreddit(ctx: &Context) -> Option<String> {
+    let sub = ctx.vars.get("subreddit")?;
+    Some(format!(
+        "https://reddit.com/r/{}",
+        enc(&sub.to_ascii_lowercase())
+    ))
+}
+
+fn canon_reddit_post(ctx: &Context) -> Option<String> {
+    let sub = ctx.vars.get("subreddit")?.to_ascii_lowercase();
+    let id = ctx.vars.get("post_id")?;
+    Some(format!(
+        "https://reddit.com/r/{}/comments/{}",
+        enc(&sub),
+        enc(id)
+    ))
+}
+
+fn canon_youtube_root(_: &Context) -> Option<String> {
+    Some("https://youtube.com".to_string())
+}
+
+fn canon_youtube_watch(ctx: &Context) -> Option<String> {
+    let v = ctx
+        .query
+        .get("v")
+        .or_else(|| ctx.vars.get("video_id"))?;
+    Some(format!("https://youtube.com/watch?v={}", enc(v)))
+}
+
+fn canon_youtu_be(ctx: &Context) -> Option<String> {
+    let v = ctx.vars.get("vid_id")?;
+    Some(format!("https://youtube.com/watch?v={}", enc(v)))
+}
+
+pub fn build_graph() -> Graph {
+    GraphBuilder::new()
+        .node("reddit_root")
+        .canonical(canon_reddit_root)
+        .edge(EdgePattern::Literal("r"), "reddit_r_hub")
+        .node("reddit_r_hub")
+        .parent("reddit_root")
+        .canonical(canon_reddit_r_hub)
+        .edge(EdgePattern::Variable("subreddit"), "reddit_subreddit")
+        .node("reddit_subreddit")
+        .parent("reddit_r_hub")
+        .canonical(canon_reddit_subreddit)
+        .edge(
+            EdgePattern::AbsorbIf(is_reddit_listing_suffix),
+            "reddit_subreddit",
+        )
+        .edge(EdgePattern::Literal("comments"), "reddit_comments_gate")
+        .node("reddit_comments_gate")
+        .parent("reddit_subreddit")
+        .canonical(canon_reddit_subreddit)
+        .edge(EdgePattern::Variable("post_id"), "reddit_post")
+        .node("reddit_post")
+        .parent("reddit_subreddit")
+        .canonical(canon_reddit_post)
+        .edge(EdgePattern::AbsorbAny, "reddit_post")
+        .node("youtube_root")
+        .canonical(canon_youtube_root)
+        .edge(EdgePattern::Literal("watch"), "youtube_watch")
+        .edge(EdgePattern::Literal("shorts"), "youtube_shorts_gate")
+        .node("youtube_watch")
+        .parent("youtube_root")
+        .canonical(canon_youtube_watch)
+        .node("youtube_shorts_gate")
+        .parent("youtube_root")
+        .canonical(canon_youtube_root)
+        .edge(EdgePattern::Variable("video_id"), "youtube_watch")
+        .node("youtu_be_entry")
+        .canonical(canon_youtube_root)
+        .edge(EdgePattern::Variable("vid_id"), "youtu_be_video")
+        .node("youtu_be_video")
+        .parent("youtube_root")
+        .canonical(canon_youtu_be)
+        .build()
+}
+
+// --- Generic internet fallback ---
+
+pub fn generic_canonical(parts: &UrlParts) -> String {
+    let host = normalize_match_host(&parts.host);
+    let path_segments: Vec<String> = parts.path_segments.clone();
+    let mut query = parts.query.clone();
+    strip_tracking_query(&mut query);
+
+    let mut url = if path_segments.is_empty() {
+        Url::parse(&format!("https://{host}"))
+            .unwrap_or_else(|_| Url::parse("https://invalid").unwrap())
+    } else {
+        let path = format!("/{}", path_segments.join("/"));
+        Url::parse(&format!("https://{host}{path}"))
+            .unwrap_or_else(|_| Url::parse("https://invalid").unwrap())
+    };
+
+    if !query.is_empty() {
+        let mut pairs: Vec<_> = query.iter().collect();
+        pairs.sort_by(|a, b| a.0.cmp(b.0));
+        url.query_pairs_mut().clear();
+        for (k, v) in pairs {
+            url.query_pairs_mut().append_pair(k, v);
+        }
+    }
+
+    let mut s = url.to_string();
+    if path_segments.is_empty() {
+        s = s.trim_end_matches('/').to_string();
+    }
+    s
+}
+
+pub fn generic_breadcrumbs(parts: &UrlParts) -> Vec<String> {
+    let host = normalize_match_host(&parts.host);
+    let n = parts.path_segments.len();
+    let mut out = Vec::new();
+
+    let base = generic_canonical(&UrlParts {
+        scheme: "https".to_string(),
+        host: host.clone(),
+        path_segments: vec![],
+        query: HashMap::new(),
+    });
+    out.push(base);
+
+    for i in 0..n {
+        let segs: Vec<String> = parts.path_segments[..=i].to_vec();
+        let url = generic_canonical(&UrlParts {
+            scheme: "https".to_string(),
+            host: host.clone(),
+            path_segments: segs,
+            query: HashMap::new(),
+        });
+        if out.last() != Some(&url) {
+            out.push(url);
+        }
+    }
+    out
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::url_rules::parse::test_parts;
+
+    fn g() -> &'static Graph {
+        graph()
+    }
+
+    fn canon(parts: &UrlParts) -> String {
+        g().resolve_canonical(parts).unwrap()
+    }
+
+    fn crumbs(parts: &UrlParts) -> Vec<String> {
+        g().breadcrumbs(parts)
+    }
+
+    fn terminal(parts: &UrlParts) -> Option<&'static str> {
+        g().traverse_terminal(parts).map(|(n, _)| n)
+    }
+
+    fn vars(parts: &UrlParts) -> HashMap<String, String> {
+        g().traverse_terminal(parts)
+            .map(|(_, c)| c.vars)
+            .unwrap_or_default()
+    }
+
+    #[test]
+    fn youtu_be_malicious_segment_encoded_not_injected() {
+        let p = test_parts("youtu.be", &["abc&t=1"], &[]);
+        assert_eq!(canon(&p), "https://youtube.com/watch?v=abc%26t%3D1");
+        assert!(!canon(&p).contains("abc&t=1"));
+    }
+
+    #[test]
+    fn youtube_query_v_encoded() {
+        let p = test_parts("youtube.com", &["watch"], &[("v", "a&b=c")]);
+        assert_eq!(canon(&p), "https://youtube.com/watch?v=a%26b%3Dc");
+    }
+
+    #[test]
+    fn absorb_patterns_live_on_edges_not_in_engine() {
+        let g = build_graph();
+        let sub = g.nodes.get("reddit_subreddit").unwrap();
+        assert!(sub
+            .edges
+            .iter()
+            .any(|e| matches!(e.pattern, EdgePattern::AbsorbIf(_))));
+        let post = g.nodes.get("reddit_post").unwrap();
+        assert!(post
+            .edges
+            .iter()
+            .any(|e| matches!(e.pattern, EdgePattern::AbsorbAny)));
+    }
+
+    #[test]
+    fn builder_rejects_missing_parent() {
+        let result = std::panic::catch_unwind(|| {
+            GraphBuilder::new()
+                .node("orphan")
+                .parent("nonexistent_parent")
+                .build();
+        });
+        assert!(result.is_err());
+    }
+
+    #[test]
+    fn generic_canonical_forces_https_and_strips_www() {
+        let p = test_parts("www.example.com", &["blog", "post"], &[]);
+        assert_eq!(canon(&p), "https://example.com/blog/post");
+    }
+
+    #[test]
+    fn generic_canonical_sorts_query_keys() {
+        let p = test_parts("example.com", &["search"], &[("q", "rust"), ("page", "2")]);
+        assert_eq!(canon(&p), "https://example.com/search?page=2&q=rust");
+    }
+
+    #[test]
+    fn generic_canonical_strips_tracking_from_query() {
+        let p = test_parts(
+            "news.ycombinator.com",
+            &["item"],
+            &[("id", "1"), ("utm_medium", "social")],
+        );
+        assert_eq!(canon(&p), "https://news.ycombinator.com/item?id=1");
+    }
+
+    #[test]
+    fn generic_breadcrumbs_cumulative_path() {
+        let p = test_parts("paulgraham.com", &["articles", "lisp.html"], &[]);
+        assert_eq!(
+            crumbs(&p),
+            vec![
+                "https://paulgraham.com",
+                "https://paulgraham.com/articles",
+                "https://paulgraham.com/articles/lisp.html"
+            ]
+        );
+    }
+
+    #[test]
+    fn generic_breadcrumbs_domain_only() {
+        let p = test_parts("example.com", &[], &[]);
+        assert_eq!(crumbs(&p), vec!["https://example.com"]);
+    }
+
+    #[test]
+    fn unknown_host_uses_generic_not_graph() {
+        let p = test_parts("hackernews.com", &["item", "123"], &[]);
+        assert_eq!(terminal(&p), None);
+        assert_eq!(canon(&p), "https://hackernews.com/item/123");
+    }
+
+    #[test]
+    fn traverse_captures_subreddit_variable() {
+        let p = test_parts("reddit.com", &["r", "Rust"], &[]);
+        assert_eq!(terminal(&p), Some("reddit_subreddit"));
+        assert_eq!(vars(&p).get("subreddit").map(String::as_str), Some("Rust"));
+    }
+
+    #[test]
+    fn traverse_captures_post_id() {
+        let p = test_parts("reddit.com", &["r", "aww", "comments", "abc123"], &[]);
+        assert_eq!(terminal(&p), Some("reddit_post"));
+        assert_eq!(vars(&p).get("post_id").map(String::as_str), Some("abc123"));
+    }
+
+    #[test]
+    fn traverse_absorbs_listing_suffix_stays_on_subreddit() {
+        let p = test_parts("reddit.com", &["r", "rust", "hot"], &[]);
+        assert_eq!(terminal(&p), Some("reddit_subreddit"));
+        assert_eq!(canon(&p), "https://reddit.com/r/rust");
+    }
+
+    #[test]
+    fn traverse_absorbs_all_listing_suffixes() {
+        for suffix in ["hot", "top", "new", "rising", "controversial"] {
+            let p = test_parts("reddit.com", &["r", "test", suffix], &[]);
+            assert_eq!(terminal(&p), Some("reddit_subreddit"), "suffix {suffix}");
+            assert_eq!(canon(&p), "https://reddit.com/r/test", "suffix {suffix}");
+        }
+    }
+
+    #[test]
+    fn traverse_absorbs_post_title_slug() {
+        let p = test_parts(
+            "reddit.com",
+            &["r", "rust", "comments", "aaa", "my_great_post_title"],
+            &[],
+        );
+        assert_eq!(terminal(&p), Some("reddit_post"));
+        assert_eq!(canon(&p), "https://reddit.com/r/rust/comments/aaa");
+    }
+
+    #[test]
+    fn traverse_unknown_segment_falls_back_to_generic() {
+        let p = test_parts("reddit.com", &["r", "rust", "wiki", "faq"], &[]);
+        assert_eq!(terminal(&p), None);
+        assert_eq!(canon(&p), "https://reddit.com/r/rust/wiki/faq");
+    }
+
+    #[test]
+    fn traverse_youtube_watch_requires_v_in_query() {
+        let p = test_parts("youtube.com", &["watch"], &[("v", "xyz")]);
+        assert_eq!(terminal(&p), Some("youtube_watch"));
+    }
+
+    #[test]
+    fn traverse_youtu_be_captures_vid_id() {
+        let p = test_parts("youtu.be", &["dQw4w9WgXcQ"], &[]);
+        assert_eq!(terminal(&p), Some("youtu_be_video"));
+        assert_eq!(vars(&p).get("vid_id").map(String::as_str), Some("dQw4w9WgXcQ"));
+    }
+
+    #[test]
+    fn traverse_shorts_sets_video_id_var() {
+        let p = test_parts("youtube.com", &["shorts", "abc99"], &[]);
+        assert_eq!(terminal(&p), Some("youtube_watch"));
+        assert_eq!(vars(&p).get("video_id").map(String::as_str), Some("abc99"));
+    }
+
+    #[test]
+    fn reddit_domain_canonical() {
+        let p = test_parts("reddit.com", &[], &[]);
+        assert_eq!(canon(&p), "https://reddit.com");
+    }
+
+    #[test]
+    fn reddit_r_hub_canonical() {
+        let p = test_parts("reddit.com", &["r"], &[]);
+        assert_eq!(terminal(&p), Some("reddit_r_hub"));
+        assert_eq!(canon(&p), "https://reddit.com/r");
+    }
+
+    #[test]
+    fn reddit_subreddit_lowercases_name() {
+        let p = test_parts("reddit.com", &["r", "AmITheAsshole"], &[]);
+        assert_eq!(canon(&p), "https://reddit.com/r/amitheasshole");
+    }
+
+    #[test]
+    fn reddit_host_aliases_old_new_www() {
+        for host in ["old.reddit.com", "new.reddit.com", "www.reddit.com"] {
+            let p = test_parts(host, &["r", "rust"], &[]);
+            assert_eq!(canon(&p), "https://reddit.com/r/rust", "host {host}");
+        }
+    }
+
+    #[test]
+    fn reddit_post_strips_slug_and_query() {
+        let p = test_parts(
+            "old.reddit.com",
+            &["r", "Rust", "comments", "1abc", "title_slug_here"],
+            &[("sort", "new")],
+        );
+        assert_eq!(canon(&p), "https://reddit.com/r/rust/comments/1abc");
+    }
+
+    #[test]
+    fn reddit_post_multiple_slugs_absorbed() {
+        let p = test_parts(
+            "reddit.com",
+            &["r", "x", "comments", "id1", "slug1", "extra"],
+            &[],
+        );
+        assert_eq!(canon(&p), "https://reddit.com/r/x/comments/id1");
+    }
+
+    #[test]
+    fn reddit_listing_with_query_only() {
+        let p = test_parts("www.reddit.com", &["r", "programming"], &[("sort", "top")]);
+        assert_eq!(canon(&p), "https://reddit.com/r/programming");
+    }
+
+    #[test]
+    fn reddit_subreddit_breadcrumbs_include_r_hub() {
+        let p = test_parts("reddit.com", &["r", "movies"], &[]);
+        assert_eq!(
+            crumbs(&p),
+            vec![
+                "https://reddit.com",
+                "https://reddit.com/r",
+                "https://reddit.com/r/movies"
+            ]
+        );
+    }
+
+    #[test]
+    fn reddit_post_breadcrumbs_skip_comments_node() {
+        let p = test_parts("reddit.com", &["r", "aww", "comments", "1trnvdl"], &[]);
+        let c = crumbs(&p);
+        assert!(!c.iter().any(|u| u.ends_with("/comments")));
+        assert_eq!(
+            c.last().map(String::as_str),
+            Some("https://reddit.com/r/aww/comments/1trnvdl")
+        );
+        assert!(c.contains(&"https://reddit.com/r/aww".to_string()));
+    }
+
+    #[test]
+    fn reddit_post_parent_is_subreddit_not_comments() {
+        let p = test_parts("reddit.com", &["r", "aww", "comments", "1trnvdl"], &[]);
+        let c = crumbs(&p);
+        let parent = c.get(c.len() - 2).unwrap();
+        assert_eq!(parent, "https://reddit.com/r/aww");
+    }
+
+    #[test]
+    fn reddit_domain_parent_is_none_in_breadcrumb_chain() {
+        let p = test_parts("reddit.com", &[], &[]);
+        assert_eq!(crumbs(&p), vec!["https://reddit.com"]);
+    }
+
+    #[test]
+    fn youtube_watch_canonical_uses_v_only() {
+        let p = test_parts("youtube.com", &["watch"], &[("v", "abc"), ("t", "99")]);
+        assert_eq!(canon(&p), "https://youtube.com/watch?v=abc");
+    }
+
+    #[test]
+    fn youtube_query_order_independent() {
+        let a = test_parts("youtube.com", &["watch"], &[("v", "abc"), ("t", "4")]);
+        let b = test_parts("youtube.com", &["watch"], &[("t", "4"), ("v", "abc")]);
+        assert_eq!(canon(&a), canon(&b));
+    }
+
+    #[test]
+    fn youtube_host_aliases() {
+        for host in ["www.youtube.com", "m.youtube.com"] {
+            let p = test_parts(host, &["watch"], &[("v", "x")]);
+            assert_eq!(canon(&p), "https://youtube.com/watch?v=x", "host {host}");
+        }
+    }
+
+    #[test]
+    fn youtube_shorts_canonical_matches_watch() {
+        let shorts = test_parts("youtube.com", &["shorts", "vid123"], &[]);
+        let watch = test_parts("youtube.com", &["watch"], &[("v", "vid123")]);
+        assert_eq!(canon(&shorts), canon(&watch));
+        assert_eq!(canon(&shorts), "https://youtube.com/watch?v=vid123");
+    }
+
+    #[test]
+    fn youtu_be_matches_youtube_watch() {
+        let be = test_parts("youtu.be", &["dQw4w9WgXcQ"], &[]);
+        let watch = test_parts("youtube.com", &["watch"], &[("v", "dQw4w9WgXcQ")]);
+        assert_eq!(canon(&be), canon(&watch));
+    }
+
+    #[test]
+    fn youtube_breadcrumbs_domain_then_watch() {
+        let p = test_parts("youtube.com", &["watch"], &[("v", "abc")]);
+        assert_eq!(
+            crumbs(&p),
+            vec!["https://youtube.com", "https://youtube.com/watch?v=abc"]
+        );
+    }
+
+    #[test]
+    fn youtu_be_breadcrumbs_include_youtube_domain() {
+        let p = test_parts("youtu.be", &["abc"], &[]);
+        let c = crumbs(&p);
+        assert_eq!(c.first().map(String::as_str), Some("https://youtube.com"));
+        assert_eq!(
+            c.last().map(String::as_str),
+            Some("https://youtube.com/watch?v=abc")
+        );
+    }
+
+    #[test]
+    fn parsed_urls_match_hand_built_parts() {
+        let raw = "https://www.reddit.com/r/rust/comments/aaa/title/?utm=x";
+        let parsed = UrlParts::parse(raw).unwrap();
+        let hand = test_parts(
+            "www.reddit.com",
+            &["r", "rust", "comments", "aaa", "title"],
+            &[("utm", "x")],
+        );
+        assert_eq!(canon(&parsed), canon(&hand));
+    }
+
+    #[test]
+    fn equivalence_cluster_youtube_formats() {
+        let urls = [
+            "https://youtu.be/abc123",
+            "https://www.youtube.com/watch?v=abc123",
+            "https://youtube.com/watch?v=abc123&t=1",
+            "https://m.youtube.com/watch?t=1&v=abc123",
+        ];
+        let canonical: Vec<_> = urls
+            .iter()
+            .map(|u| canon(&UrlParts::parse(u).unwrap()))
+            .collect();
+        assert!(canonical.iter().all(|c| *c == "https://youtube.com/watch?v=abc123"));
+    }
+
+    #[test]
+    fn equivalence_cluster_reddit_post_formats() {
+        let urls = [
+            "https://old.reddit.com/r/Rust/comments/aaa/slug/",
+            "reddit.com/r/rust/comments/aaa/other_slug",
+            "https://reddit.com/r/RUST/comments/aaa",
+        ];
+        let canonical: Vec<_> = urls
+            .iter()
+            .map(|u| canon(&UrlParts::parse(u).unwrap()))
+            .collect();
+        assert!(
+            canonical
+                .iter()
+                .all(|c| *c == "https://reddit.com/r/rust/comments/aaa")
+        );
+    }
+
+    #[test]
+    fn graph_nodes_all_have_valid_parent_links() {
+        let g = build_graph();
+        for (id, node) in &g.nodes {
+            if let Some(parent) = node.parent {
+                assert!(g.nodes.contains_key(parent), "node {id} parent {parent}");
+            }
+        }
+    }
+
+    #[test]
+    fn graph_terminal_canonical_always_succeeds_for_reddit_paths() {
+        let cases: &[(&[&str], &str)] = &[
+            (&["r", "rust"], "https://reddit.com/r/rust"),
+            (
+                &["r", "rust", "comments", "x"],
+                "https://reddit.com/r/rust/comments/x",
+            ),
+        ];
+        for (segs, want) in cases {
+            let p = test_parts("reddit.com", segs, &[]);
+            assert_eq!(canon(&p), *want);
+        }
+    }
+
+    #[test]
+    fn breadcrumb_parent_walk_matches_parent_url_semantics() {
+        let p = test_parts("reddit.com", &["r", "aww", "comments", "id1"], &[]);
+        let c = crumbs(&p);
+        assert_eq!(c.len(), 4);
+        assert_eq!(
+            c.get(c.len() - 2).map(String::as_str),
+            Some("https://reddit.com/r/aww")
+        );
+    }
+
+    #[test]
+    fn youtube_watch_without_v_falls_back_to_generic() {
+        let p = test_parts("youtube.com", &["watch"], &[]);
+        assert_eq!(terminal(&p), Some("youtube_watch"));
+        assert_eq!(canon(&p), "https://youtube.com/watch");
+    }
+
+    #[test]
+    fn reddit_only_comments_path_stops_at_gate() {
+        let p = test_parts("reddit.com", &["r", "rust", "comments"], &[]);
+        assert_eq!(terminal(&p), Some("reddit_comments_gate"));
+        assert_eq!(canon(&p), "https://reddit.com/r/rust");
+    }
+
+    #[test]
+    fn generic_deep_path_many_segments() {
+        let segs: Vec<&str> = (0..10)
+            .map(|i| match i {
+                0 => "a",
+                1 => "b",
+                2 => "c",
+                3 => "d",
+                4 => "e",
+                5 => "f",
+                6 => "g",
+                7 => "h",
+                8 => "i",
+                _ => "j",
+            })
+            .collect();
+        let p = test_parts("site.com", &segs, &[]);
+        assert_eq!(crumbs(&p).len(), 11);
+    }
+
+    #[test]
+    fn traverse_literal_r_required_for_subreddit() {
+        let p = test_parts("reddit.com", &["rust"], &[]);
+        assert_eq!(terminal(&p), None);
+    }
+
+    #[test]
+    fn http_scheme_upgraded_via_generic_fallback_host() {
+        let parsed = UrlParts::parse("http://example.com/page").unwrap();
+        assert_eq!(canon(&parsed), "https://example.com/page");
+    }
+
+    #[test]
+    fn each_graph_node_canonical_is_invokable() {
+        let g = build_graph();
+        let empty = Context::default();
+        for (id, node) in &g.nodes {
+            let _ = (node.canonical)(&empty);
+            let _ = id;
+        }
+    }
+
+    #[test]
+    fn reddit_double_listing_suffix_both_absorbed() {
+        let p = test_parts("reddit.com", &["r", "rust", "hot", "new"], &[]);
+        assert_eq!(terminal(&p), Some("reddit_subreddit"));
+        assert_eq!(canon(&p), "https://reddit.com/r/rust");
+    }
+
+    #[test]
+    fn youtu_be_empty_path_stays_at_entry() {
+        let p = test_parts("youtu.be", &[], &[]);
+        assert_eq!(terminal(&p), Some("youtu_be_entry"));
+    }
+}
diff --git a/server/src/url_rules/graph_builder.rs b/server/src/url_rules/graph_builder.rs
new file mode 100644
index 0000000000000000000000000000000000000000..243204ad5ca514fff459057956080cacb5bf38e2
--- /dev/null
+++ b/server/src/url_rules/graph_builder.rs
@@ -0,0 +1,73 @@
+//! Declarative construction of the URL graph with build-time link validation.
+
+use std::collections::HashMap;
+
+use super::graph::{CanonicalFn, Edge, EdgePattern, Graph, Node};
+
+pub struct GraphBuilder {
+    nodes: HashMap<&'static str, Node>,
+    current: Option<&'static str>,
+}
+
+impl GraphBuilder {
+    pub fn new() -> Self {
+        Self {
+            nodes: HashMap::new(),
+            current: None,
+        }
+    }
+
+    pub fn node(mut self, id: &'static str) -> Self {
+        self.nodes.entry(id).or_insert_with(Node::empty);
+        self.current = Some(id);
+        self
+    }
+
+    pub fn canonical(mut self, f: CanonicalFn) -> Self {
+        let id = self.current.expect("canonical() without node()");
+        self.nodes.get_mut(id).expect("node missing").canonical = f;
+        self
+    }
+
+    pub fn parent(mut self, parent_id: &'static str) -> Self {
+        let id = self.current.expect("parent() without node()");
+        self.nodes.get_mut(id).expect("node missing").parent = Some(parent_id);
+        self
+    }
+
+    pub fn edge(mut self, pattern: EdgePattern, target: &'static str) -> Self {
+        let id = self.current.expect("edge() without node()");
+        self.nodes
+            .get_mut(id)
+            .expect("node missing")
+            .edges
+            .push(Edge { pattern, target });
+        self
+    }
+
+    pub fn build(self) -> Graph {
+        for (id, node) in &self.nodes {
+            if let Some(parent) = node.parent {
+                assert!(
+                    self.nodes.contains_key(parent),
+                    "node {id}: parent {parent} does not exist"
+                );
+            }
+            for edge in &node.edges {
+                if !matches!(
+                    edge.pattern,
+                    EdgePattern::AbsorbAny | EdgePattern::AbsorbIf(_)
+                ) {
+                    assert!(
+                        self.nodes.contains_key(edge.target),
+                        "node {id}: edge target {} does not exist",
+                        edge.target
+                    );
+                }
+            }
+        }
+        Graph {
+            nodes: self.nodes,
+        }
+    }
+}
diff --git a/server/src/url_rules/mod.rs b/server/src/url_rules/mod.rs
index 9e1445346ce77a49dd6a7e7713bf9c57aef353cc..ba4ac662acc7bd4d50ee34613eb7eb6fccbfb17b 100644
--- a/server/src/url_rules/mod.rs
+++ b/server/src/url_rules/mod.rs
@@ -1,6 +1,7 @@
 //! URL canonicalization and hierarchy via a semantic graph (DFA + generic fallback).
 
 mod graph;
+mod graph_builder;
 mod parse;
 mod registry;
 
diff --git a/server/src/url_rules/parse.rs b/server/src/url_rules/parse.rs
new file mode 100644
index 0000000000000000000000000000000000000000..19d0c82feb718817168b8b445fcbfa39cf6aa6ba
--- /dev/null
+++ b/server/src/url_rules/parse.rs
@@ -0,0 +1,169 @@
+//! Parse raw strings into host, path segments, and query (order-independent).
+
+use std::collections::HashMap;
+
+use url::Url;
+
+#[derive(Debug, Clone)]
+pub struct UrlParts {
+    pub scheme: String,
+    pub host: String,
+    pub path_segments: Vec<String>,
+    pub query: HashMap<String, String>,
+}
+
+impl UrlParts {
+    pub fn parse(raw: &str) -> Option<Self> {
+        let trimmed = raw.trim();
+        if trimmed.is_empty() {
+            return None;
+        }
+
+        let with_scheme = if trimmed.contains("://") {
+            trimmed.to_string()
+        } else if trimmed.starts_with("r/") || trimmed.starts_with("/r/") {
+            let rest = trimmed.trim_start_matches('/').trim_start_matches("r/");
+            format!("https://reddit.com/r/{rest}")
+        } else if trimmed.contains('.') && !trimmed.starts_with('/') {
+            format!("https://{trimmed}")
+        } else {
+            trimmed.to_string()
+        };
+
+        let url = Url::parse(&with_scheme).ok()?;
+        let host = url.host_str()?.to_string();
+        let path_segments: Vec<String> = url
+            .path_segments()
+            .map(|segs| segs.filter(|s| !s.is_empty()).map(str::to_string).collect())
+            .unwrap_or_default();
+
+        let mut query = HashMap::new();
+        for (k, v) in url.query_pairs() {
+            query.insert(k.into_owned(), v.into_owned());
+        }
+
+        Some(Self {
+            scheme: url.scheme().to_string(),
+            path_segments,
+            query,
+            host,
+        })
+    }
+
+    /// Host normalized for graph entry matching (lowercase, aliases).
+    pub fn match_host(&self) -> String {
+        normalize_match_host(&self.host)
+    }
+}
+
+pub fn normalize_match_host(host: &str) -> String {
+    let h = host
+        .strip_prefix("www.")
+        .unwrap_or(host)
+        .to_ascii_lowercase();
+    match h.as_str() {
+        "old.reddit.com" | "new.reddit.com" => "reddit.com".to_string(),
+        "m.youtube.com" => "youtube.com".to_string(),
+        _ => h,
+    }
+}
+
+pub fn strip_tracking_query(query: &mut HashMap<String, String>) {
+    query.retain(|k, _| {
+        let lower = k.to_ascii_lowercase();
+        !(lower.starts_with("utm_")
+            || matches!(
+                lower.as_str(),
+                "fbclid" | "gclid" | "ref" | "ref_src" | "ref_source" | "mc_cid" | "mc_eid"
+            ))
+    });
+}
+
+#[cfg(test)]
+pub(crate) fn test_parts(host: &str, segs: &[&str], query: &[(&str, &str)]) -> UrlParts {
+    UrlParts {
+        scheme: "https".to_string(),
+        host: host.to_string(),
+        path_segments: segs.iter().map(|s| (*s).to_string()).collect(),
+        query: query
+            .iter()
+            .map(|(k, v)| (k.to_string(), v.to_string()))
+            .collect(),
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn parse_full_url_splits_host_path_query() {
+        let p = UrlParts::parse("https://www.youtube.com/watch?v=abc&t=4").unwrap();
+        assert_eq!(p.host, "www.youtube.com");
+        assert_eq!(p.path_segments, vec!["watch"]);
+        assert_eq!(p.query.get("v").map(String::as_str), Some("abc"));
+        assert_eq!(p.query.get("t").map(String::as_str), Some("4"));
+    }
+
+    #[test]
+    fn parse_r_shortcut_expands_to_reddit() {
+        let p = UrlParts::parse("r/rust").unwrap();
+        assert_eq!(p.match_host(), "reddit.com");
+        assert_eq!(p.path_segments, vec!["r", "rust"]);
+    }
+
+    #[test]
+    fn parse_slash_r_shortcut() {
+        let p = UrlParts::parse("/r/aww").unwrap();
+        assert_eq!(p.path_segments, vec!["r", "aww"]);
+    }
+
+    #[test]
+    fn parse_schemeless_host_path() {
+        let p = UrlParts::parse("reddit.com/r/rust/comments/aaa/slug").unwrap();
+        assert_eq!(p.match_host(), "reddit.com");
+        assert_eq!(
+            p.path_segments,
+            vec!["r", "rust", "comments", "aaa", "slug"]
+        );
+    }
+
+    #[test]
+    fn parse_empty_returns_none() {
+        assert!(UrlParts::parse("").is_none());
+        assert!(UrlParts::parse("   ").is_none());
+    }
+
+    #[test]
+    fn normalize_match_host_reddit_aliases() {
+        assert_eq!(normalize_match_host("old.reddit.com"), "reddit.com");
+        assert_eq!(normalize_match_host("NEW.reddit.com"), "reddit.com");
+        assert_eq!(normalize_match_host("www.reddit.com"), "reddit.com");
+    }
+
+    #[test]
+    fn normalize_match_host_youtube_aliases() {
+        assert_eq!(normalize_match_host("m.youtube.com"), "youtube.com");
+        assert_eq!(normalize_match_host("www.youtube.com"), "youtube.com");
+    }
+
+    #[test]
+    fn strip_tracking_query_removes_known_params() {
+        let mut q = HashMap::from([
+            ("v".into(), "1".into()),
+            ("utm_source".into(), "x".into()),
+            ("fbclid".into(), "y".into()),
+            ("ref".into(), "z".into()),
+        ]);
+        strip_tracking_query(&mut q);
+        assert_eq!(q.len(), 1);
+        assert_eq!(q.get("v").map(String::as_str), Some("1"));
+    }
+
+    #[test]
+    fn strip_tracking_query_utm_prefix() {
+        let mut q = HashMap::from([("utm_campaign".into(), "email".into())]);
+        strip_tracking_query(&mut q);
+        assert!(q.is_empty());
+    }
+}
diff --git a/server/src/url_rules/registry_tests.rs b/server/src/url_rules/registry_tests.rs
new file mode 100644
index 0000000000000000000000000000000000000000..7b76b550f808f590e011469fdae02adf603b43d2
--- /dev/null
+++ b/server/src/url_rules/registry_tests.rs
@@ -0,0 +1,195 @@
+//! End-to-end tests for the public registry API (`canonicalize_raw`, breadcrumbs, parent).
+
+use super::registry::{
+    canonicalize_raw, looks_like_url, navigable_breadcrumbs, parent_url, resolve_id,
+};
+
+fn canon(raw: &str) -> String {
+    canonicalize_raw(raw).unwrap().canonical
+}
+
+#[test]
+fn looks_like_url_positive_cases() {
+    for raw in [
+        "https://reddit.com/r/rust",
+        "r/rust",
+        "/r/aww",
+        "reddit.com/r/x",
+        "www.example.com/path",
+        "youtu.be/abc",
+    ] {
+        assert!(looks_like_url(raw), "{raw}");
+    }
+}
+
+#[test]
+fn looks_like_url_negative_cases() {
+    for raw in ["alpha", "beta", "", "hello world", "no-dots"] {
+        assert!(!looks_like_url(raw), "{raw}");
+    }
+}
+
+#[test]
+fn resolve_id_matches_canonicalize_raw() {
+    let raw = "https://youtu.be/xyz";
+    assert_eq!(
+        resolve_id(raw).as_deref(),
+        Some(canon(raw).as_str())
+    );
+}
+
+#[test]
+fn canonicalize_empty_returns_none() {
+    assert!(canonicalize_raw("").is_none());
+}
+
+#[test]
+fn alias_when_slug_stripped() {
+    let r = canonicalize_raw(
+        "https://reddit.com/r/rust/comments/aaa/very_long_title_slug",
+    )
+    .unwrap();
+    assert_eq!(r.canonical, "https://reddit.com/r/rust/comments/aaa");
+    assert!(r.alias_of.is_some());
+}
+
+#[test]
+fn alias_none_when_already_canonical() {
+    let raw = "https://reddit.com/r/rust";
+    let r = canonicalize_raw(raw).unwrap();
+    assert_eq!(r.canonical, raw);
+    assert!(r.alias_of.is_none());
+}
+
+#[test]
+fn parent_url_subreddit_under_r_hub() {
+    assert_eq!(
+        parent_url("https://reddit.com/r/movies").as_deref(),
+        Some("https://reddit.com/r")
+    );
+}
+
+#[test]
+fn parent_url_domain_has_none() {
+    assert_eq!(parent_url("https://reddit.com").as_deref(), None);
+}
+
+#[test]
+fn parent_url_generic_site() {
+    assert_eq!(
+        parent_url("https://example.com/a/b").as_deref(),
+        Some("https://example.com/a")
+    );
+}
+
+#[test]
+fn breadcrumbs_from_canonical_string_roundtrip() {
+    let id = "https://reddit.com/r/golang/comments/abc123";
+    let crumbs = navigable_breadcrumbs(id);
+    assert_eq!(crumbs.last().map(String::as_str), Some(id));
+}
+
+// --- Table: Reddit raw URLs → canonical ---
+
+#[test]
+fn reddit_canonical_matrix() {
+    let cases: &[(&str, &str)] = &[
+        ("r/rust", "https://reddit.com/r/rust"),
+        ("/r/aww", "https://reddit.com/r/aww"),
+        ("https://reddit.com/r/rust", "https://reddit.com/r/rust"),
+        (
+            "https://www.reddit.com/r/programming/new",
+            "https://reddit.com/r/programming",
+        ),
+        (
+            "https://old.reddit.com/r/test/comments/xyz/slug/",
+            "https://reddit.com/r/test/comments/xyz",
+        ),
+        (
+            "reddit.com/r/Movies/comments/abc/Title_Case_Slug",
+            "https://reddit.com/r/movies/comments/abc",
+        ),
+    ];
+    for (raw, want) in cases {
+        assert_eq!(canon(raw), *want, "raw={raw}");
+    }
+}
+
+// --- Table: YouTube raw URLs → canonical ---
+
+#[test]
+fn youtube_canonical_matrix() {
+    let cases: &[(&str, &str)] = &[
+        (
+            "https://youtube.com/watch?v=abc",
+            "https://youtube.com/watch?v=abc",
+        ),
+        (
+            "https://www.youtube.com/watch?v=abc&t=1&feature=share",
+            "https://youtube.com/watch?v=abc",
+        ),
+        ("https://youtu.be/abc", "https://youtube.com/watch?v=abc"),
+        (
+            "https://youtube.com/shorts/abc",
+            "https://youtube.com/watch?v=abc",
+        ),
+    ];
+    for (raw, want) in cases {
+        assert_eq!(canon(raw), *want, "raw={raw}");
+    }
+}
+
+// --- Table: generic sites ---
+
+#[test]
+fn generic_canonical_matrix() {
+    let cases: &[(&str, &str)] = &[
+        (
+            "https://news.ycombinator.com/item?id=38472",
+            "https://news.ycombinator.com/item?id=38472",
+        ),
+        (
+            "https://www.github.com/rust-lang/rust/issues/1?utm_source=x",
+            "https://github.com/rust-lang/rust/issues/1",
+        ),
+        ("https://example.com", "https://example.com"),
+    ];
+    for (raw, want) in cases {
+        assert_eq!(canon(raw), *want, "raw={raw}");
+    }
+}
+
+// --- Phantom /comments/ regression (sorter2-specific) ---
+
+#[test]
+fn phantom_comments_not_in_breadcrumbs_for_post() {
+    let crumbs = navigable_breadcrumbs("https://reddit.com/r/rust/comments/aaa");
+    assert!(!crumbs.iter().any(|c| c.ends_with("/comments")));
+}
+
+#[test]
+fn phantom_comments_not_sibling_of_subreddit_in_breadcrumb_chain() {
+    let crumbs = navigable_breadcrumbs("https://reddit.com/r/rust/comments/aaa");
+    let subs: Vec<_> = crumbs
+        .iter()
+        .filter(|c| c.contains("/r/rust") && !c.contains("/comments/"))
+        .collect();
+    assert_eq!(subs, vec!["https://reddit.com/r/rust"]);
+}
+
+// --- Distinct items must stay distinct ---
+
+#[test]
+fn different_posts_different_canonical() {
+    let a = canon("https://reddit.com/r/rust/comments/aaa");
+    let b = canon("https://reddit.com/r/rust/comments/bbb");
+    assert_ne!(a, b);
+}
+
+#[test]
+fn different_subreddits_different_canonical() {
+    assert_ne!(
+        canon("https://reddit.com/r/rust"),
+        canon("https://reddit.com/r/golang")
+    );
+}


Side B — contributor: tommy-mor
Side B — commit message:
[52f5c51c] Add Reddit OAuth linking and make UUID the only account identity.

OAuth providers only attach to a session UUID (first link creates the
principal); linked providers stay private on the account page.

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

Side B — unified diff (full patch):
diff --git a/AGENTS.md b/AGENTS.md
index 6e0fd8ebb65d665c9c1438e3275971d62b98fd95..e9cc3173dbeb21ad0fc090ca7b407b027c7820a9 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -35,8 +35,11 @@ Environment variables (defaults in `server/src/state.rs`):
 - `SORTER2_DATA_DIR` — default `./data` (created on startup)
 - `SORTER2_EVENT_LOG` — default `{data_dir}/events.jsonl`
 - `SORTER2_BASE_URL` — public origin (also drives Secure cookies when `https://`)
-- `GITHUB_CLIENT_ID` / `GITHUB_CLIENT_SECRET` — GitHub OAuth (optional; login disabled if unset)
-- `SORTER2_ALLOW_MOCK_OAUTH=1` — allow `mock_user` on `/auth/github` (tests only)
+- `GITHUB_CLIENT_ID` / `GITHUB_CLIENT_SECRET` — GitHub OAuth linking (optional)
+- `REDDIT_CLIENT_ID` / `REDDIT_CLIENT_SECRET` (or `REDDIT_APP_*`) — Reddit API import + OAuth linking (optional)
+- `SORTER2_ALLOW_MOCK_OAUTH=1` — allow `mock_user` on `/auth/github` and `/auth/reddit` (tests only)
+
+Identity: UUID is canonical. OAuth providers only *link* to a UUID (first link creates the principal). Linked providers are private to the account owner.
 
 Health check: `GET /healthz` → `ok`.
 
diff --git a/server/src/auth/mod.rs b/server/src/auth/mod.rs
index 5906f93b13853421e96a3c37bc9d8202a47842bf..c706ae8045a811e5941f5f6c72da88f42a403a82 100644
--- a/server/src/auth/mod.rs
+++ b/server/src/auth/mod.rs
@@ -1,4 +1,8 @@
-//! GitHub OAuth login, session cookies, and vote actor resolution.
+//! OAuth linking, session cookies, and vote actor resolution.
+//!
+//! Canonical identity is a UUID. OAuth providers only *link* to that UUID
+//! (first link creates the principal; later links attach while logged in).
+//! Which providers are linked is private to the account owner.
 
 pub mod config;
 pub mod identity;
@@ -22,7 +26,9 @@ use crate::{
     form_template::template_json_compact,
     html::layout,
     state::AppState,
-    storage_schema::{oauth_link_owner, pseudonym_owner, Store, StoreFields},
+    storage_schema::{
+        linked_providers_for_uuid, oauth_link_owner, pseudonym_owner, Store, StoreFields,
+    },
     ui_action::UI_RPC_FIELD,
 };
 
@@ -53,10 +59,12 @@ fn new_actor_uuid() -> String {
 pub struct LoginQuery {
     #[serde(default)]
     pub return_to: Option<String>,
+    #[serde(default)]
+    pub error: Option<String>,
 }
 
 #[derive(Debug, Deserialize)]
-pub struct GitHubStartQuery {
+pub struct OAuthStartQuery {
     #[serde(default)]
     pub return_to: Option<String>,
     #[serde(default)]
@@ -72,15 +80,22 @@ fn return_from_query_or_jar(jar: &CookieJar, query: Option<&str>) -> String {
         .unwrap_or_else(|| "/".to_string())
 }
 
-fn oauth_providers(base_url: &str, return_to: &str) -> Vec<(&'static str, String)> {
+/// Available OAuth link targets: `(provider_key, label, start_href)`.
+fn oauth_providers(base_url: &str, return_to: &str) -> Vec<(&'static str, &'static str, String)> {
     let mut out = Vec::new();
+    let enc = urlencoding::encode(return_to);
     if oauth::GitHubConfig::from_env(base_url).is_some() {
         out.push((
-            "GitHub",
-            format!(
-                "/auth/github?return_to={}",
-                urlencoding::encode(return_to)
-            ),
+            "github",
+            oauth::provider_label("github"),
+            format!("/auth/github?return_to={enc}"),
+        ));
+    }
+    if oauth::RedditConfig::from_env(base_url).is_some() {
+        out.push((
+            "reddit",
+            oauth::provider_label("reddit"),
+            format!("/auth/reddit?return_to={enc}"),
         ));
     }
     out
@@ -125,23 +140,41 @@ fn alias_claim_forms(return_to: &str, submit_label: &str) -> Result<Markup, Stat
     })
 }
 
-fn signed_out_body(providers: &[(&str, String)]) -> Markup {
+fn login_error_message(code: Option<&str>) -> Option<&'static str> {
+    match code {
+        Some("oauth_taken") => {
+            Some("that OAuth account is already linked to a different sorter2 account")
+        }
+        Some("oauth_failed") => Some("OAuth failed — try again"),
+        _ => None,
+    }
+}
+
+fn signed_out_body(
+    providers: &[(&str, &str, String)],
+    error: Option<&str>,
+) -> Markup {
     html! {
         main class="panel login-page" {
             section class="login-section" {
                 h1 { "sign in" }
-                p class="muted" { "link an account to vote under a lasting alias" }
+                p class="muted" {
+                    "link an OAuth account to create your identity, then claim an alias to vote"
+                }
+                @if let Some(msg) = login_error_message(error) {
+                    p class="alias-bad" data-testid="login-error" { (msg) }
+                }
                 @if providers.is_empty() {
                     p class="muted" {
-                        "OAuth is not configured. Set GITHUB_CLIENT_ID and GITHUB_CLIENT_SECRET."
+                        "OAuth is not configured. Set GitHub and/or Reddit client credentials."
                     }
                 } @else {
                     ul class="oauth-provider-list" {
-                        @for (name, href) in providers {
+                        @for (key, label, href) in providers {
                             li {
                                 a href=(href) class="btn-primary oauth-provider"
-                                    data-testid=(format!("oauth-{}", name.to_lowercase())) {
-                                    (format!("Continue with {name}"))
+                                    data-testid=(format!("oauth-{key}")) {
+                                    (format!("Link {label}"))
                                 }
                             }
                         }
@@ -156,7 +189,10 @@ fn signed_out_body(providers: &[(&str, String)]) -> Markup {
 fn account_body(
     actor: &session::SessionActor,
     aliases: &[String],
-    providers: &[(&str, String)],
+    // Provider keys already linked to this UUID (private).
+    linked: &[String],
+    // Providers available to link: not yet attached.
+    unlinkable: &[(&str, &str, String)],
     claim_forms: Markup,
 ) -> Markup {
     let current = actor.pseudonym.trim();
@@ -212,16 +248,29 @@ fn account_body(
                 (claim_forms)
             }
 
-            @if !providers.is_empty() {
-                section class="login-section" {
-                    h2 { "linked sign-in" }
-                    p class="muted small" { "sign in again with the same provider to return to this account" }
+            section class="login-section" {
+                h2 { "linked sign-in" }
+                p class="muted small" {
+                    "private to you — linking more providers raises trust weight without publishing which accounts you use"
+                }
+                @if linked.is_empty() {
+                    p class="muted" data-testid="linked-providers-empty" { "none yet" }
+                } @else {
+                    ul class="linked-provider-list" data-testid="linked-providers" {
+                        @for key in linked {
+                            li data-testid=(format!("linked-{key}")) {
+                                (oauth::provider_label(key))
+                            }
+                        }
+                    }
+                }
+                @if !unlinkable.is_empty() {
                     ul class="oauth-provider-list" {
-                        @for (name, href) in providers {
+                        @for (key, label, href) in unlinkable {
                             li {
                                 a href=(href) class="btn-secondary oauth-provider"
-                                    data-testid=(format!("oauth-relink-{}", name.to_lowercase())) {
-                                    (format!("Re-link {name}"))
+                                    data-testid=(format!("oauth-link-{key}")) {
+                                    (format!("Link {label}"))
                                 }
                             }
                         }
@@ -243,12 +292,21 @@ fn account_body(
 fn login_body(
     session: Option<&session::SessionActor>,
     aliases: &[String],
-    providers: &[(&str, String)],
+    linked: &[String],
+    providers: &[(&str, &str, String)],
     claim_forms: Option<Markup>,
+    error: Option<&str>,
 ) -> Markup {
     match (session, claim_forms) {
-        (Some(actor), Some(forms)) => account_body(actor, aliases, providers, forms),
-        _ => signed_out_body(providers),
+        (Some(actor), Some(forms)) => {
+            let unlinkable: Vec<_> = providers
+                .iter()
+                .filter(|(key, _, _)| !linked.iter().any(|p| p == key))
+                .cloned()
+                .collect();
+            account_body(actor, aliases, linked, &unlinkable, forms)
+        }
+        _ => signed_out_body(providers, error),
     }
 }
 
@@ -268,6 +326,10 @@ pub async fn login_page(
         .as_ref()
         .map(|s| alias_list(db, &s.uuid))
         .unwrap_or_default();
+    let linked = session
+        .as_ref()
+        .map(|s| linked_providers_for_uuid(db, &s.uuid).unwrap_or_default())
+        .unwrap_or_default();
     let providers = oauth_providers(&base_url_from_env(state.cfg.port), &return_to);
 
     let claim_forms = if session.is_some() {
@@ -282,7 +344,14 @@ pub async fn login_page(
         } else {
             "login · sorter2"
         },
-        login_body(session.as_ref(), &aliases, &providers, claim_forms),
+        login_body(
+            session.as_ref(),
+            &aliases,
+            &linked,
+            &providers,
+            claim_forms,
+            query.error.as_deref(),
+        ),
         state.views.get_views("/login"),
         session
             .as_ref()
@@ -302,7 +371,6 @@ pub async fn alias_page(
     let db = state.projection_store.db();
     let session = session::load_valid_session(db, &session_id).ok_or(StatusCode::UNAUTHORIZED)?;
     if session::session_has_pseudonym(&session) {
-        // Already onboarded — manage aliases on the account page.
         return Ok(Redirect::to("/login").into_response());
     }
 
@@ -331,7 +399,7 @@ pub async fn alias_page(
 pub async fn github_start(
     State(state): State<AppState>,
     jar: CookieJar,
-    Query(query): Query<GitHubStartQuery>,
+    Query(query): Query<OAuthStartQuery>,
 ) -> Result<Response, StatusCode> {
     let cfg = oauth::GitHubConfig::from_env(&base_url_from_env(state.cfg.port))
         .ok_or(StatusCode::SERVICE_UNAVAILABLE)?;
@@ -342,7 +410,28 @@ pub async fn github_start(
     } else {
         None
     };
-    let url = oauth::authorize_url(&cfg, &state_token, mock_user);
+    let url = oauth::github_authorize_url(&cfg, &state_token, mock_user);
+    let jar = jar
+        .add(session::oauth_state_cookie_value(&state_token))
+        .add(session::auth_return_cookie_value(&return_to));
+    Ok((jar, Redirect::temporary(&url)).into_response())
+}
+
+pub async fn reddit_start(
+    State(state): State<AppState>,
+    jar: CookieJar,
+    Query(query): Query<OAuthStartQuery>,
+) -> Result<Response, StatusCode> {
+    let cfg = oauth::RedditConfig::from_env(&base_url_from_env(state.cfg.port))
+        .ok_or(StatusCode::SERVICE_UNAVAILABLE)?;
+    let return_to = return_from_query_or_jar(&jar, query.return_to.as_deref());
+    let state_token = session::new_oauth_state();
+    let mock_user = if config::mock_oauth_allowed() {
+        query.mock_user.as_deref()
+    } else {
+        None
+    };
+    let url = oauth::reddit_authorize_url(&cfg, &state_token, mock_user);
     let jar = jar
         .add(session::oauth_state_cookie_value(&state_token))
         .add(session::auth_return_cookie_value(&return_to));
@@ -355,6 +444,13 @@ pub struct OAuthCallbackQuery {
     pub state: String,
 }
 
+/// Link `provider:provider_id` to a UUID.
+///
+/// - Logged in + new provider → attach to session UUID
+/// - Logged in + already ours → no-op
+/// - Logged in + owned by someone else → conflict
+/// - Logged out + known link → resume that UUID
+/// - Logged out + unknown → create principal + first link
 async fn finish_oauth_login(
     state: &AppState,
     jar: CookieJar,
@@ -364,11 +460,41 @@ async fn finish_oauth_login(
     let db = state.projection_store.db();
     let return_to = return_from_query_or_jar(&jar, None);
 
-    let uuid = match oauth_link_owner(db, provider, &provider_id)
-        .map_err(|_| StatusCode::INTERNAL_SERVER_ERROR)?
-    {
-        Some(existing) => existing,
-        None => {
+    let existing_owner = oauth_link_owner(db, provider, &provider_id)
+        .map_err(|_| StatusCode::INTERNAL_SERVER_ERROR)?;
+
+    let session_uuid = session::session_id_from_jar(&jar)
+        .as_deref()
+        .and_then(|id| session::load_valid_session(db, id))
+        .map(|s| s.uuid);
+    let linking_while_logged_in = session_uuid.is_some();
+
+    let uuid = match (session_uuid, existing_owner) {
+        (Some(session_uuid), Some(owner)) if owner == session_uuid => session_uuid,
+        (Some(_), Some(_)) => {
+            return Ok((
+                jar.add(session::clear_oauth_state_cookie()),
+                "/login?error=oauth_taken".into(),
+            ));
+        }
+        (Some(session_uuid), None) => {
+            let ts = now_ms();
+            state
+                .append_identity_events(vec![Event::OauthLinked {
+                    uuid: session_uuid.clone(),
+                    provider: provider.to_string(),
+                    provider_id,
+                    ts,
+                }])
+                .await
+                .map_err(|e| {
+                    tracing::warn!(err = %e, "oauth link append failed");
+                    StatusCode::INTERNAL_SERVER_ERROR
+                })?;
+            session_uuid
+        }
+        (None, Some(owner)) => owner,
+        (None, None) => {
             let uuid = new_actor_uuid();
             let ts = now_ms();
             state
@@ -409,6 +535,9 @@ async fn finish_oauth_login(
             "/login/alias?return_to={}",
             urlencoding::encode(&return_to)
         )
+    } else if linking_while_logged_in {
+        // Additional link while already in an account → stay on account page.
+        "/login".to_string()
     } else {
         return_to
     };
@@ -434,22 +563,57 @@ pub async fn github_callback(
         .build()
         .map_err(|_| StatusCode::INTERNAL_SERVER_ERROR)?;
 
-    let token = oauth::exchange_code(&client, &cfg, &query.code)
+    let token = oauth::github_exchange_code(&client, &cfg, &query.code)
         .await
         .map_err(|e| {
             tracing::warn!(err = %e, "github oauth token exchange failed");
             StatusCode::BAD_GATEWAY
         })?;
-    let user = oauth::fetch_user(&client, &cfg.api_base, &token)
+    let user = oauth::github_fetch_user(&client, &cfg.api_base, &token)
         .await
         .map_err(|e| {
             tracing::warn!(err = %e, "github user fetch failed");
             StatusCode::BAD_GATEWAY
         })?;
 
-    let provider = "github";
-    let provider_id = oauth::provider_id(&user);
-    let (jar, dest) = finish_oauth_login(&state, jar, provider, provider_id).await?;
+    let (jar, dest) =
+        finish_oauth_login(&state, jar, "github", oauth::github_provider_id(&user)).await?;
+    Ok((jar, Redirect::to(&dest)).into_response())
+}
+
+pub async fn reddit_callback(
+    State(state): State<AppState>,
+    jar: CookieJar,
+    Query(query): Query<OAuthCallbackQuery>,
+) -> Result<Response, StatusCode> {
+    let cfg = oauth::RedditConfig::from_env(&base_url_from_env(state.cfg.port))
+        .ok_or(StatusCode::SERVICE_UNAVAILABLE)?;
+
+    let expected_state = session::oauth_state_from_jar(&jar).ok_or(StatusCode::BAD_REQUEST)?;
+    if expected_state != query.state {
+        return Err(StatusCode::BAD_REQUEST);
+    }
+
+    let client = Client::builder()
+        .timeout(std::time::Duration::from_secs(15))
+        .build()
+        .map_err(|_| StatusCode::INTERNAL_SERVER_ERROR)?;
+
+    let token = oauth::reddit_exchange_code(&client, &cfg, &query.code)
+        .await
+        .map_err(|e| {
+            tracing::warn!(err = %e, "reddit oauth token exchange failed");
+            StatusCode::BAD_GATEWAY
+        })?;
+    let user = oauth::reddit_fetch_user(&client, &cfg, &token)
+        .await
+        .map_err(|e| {
+            tracing::warn!(err = %e, "reddit user fetch failed");
+            StatusCode::BAD_GATEWAY
+        })?;
+
+    let (jar, dest) =
+        finish_oauth_login(&state, jar, "reddit", oauth::reddit_provider_id(&user)).await?;
     Ok((jar, Redirect::to(&dest)).into_response())
 }
 
diff --git a/server/src/auth/oauth.rs b/server/src/auth/oauth.rs
index b80078fee0c5acd905b9125d29454e46c4e0d066..369b1527d9032cf312a07819279e0f988ef4a36e 100644
--- a/server/src/auth/oauth.rs
+++ b/server/src/auth/oauth.rs
@@ -1,8 +1,15 @@
-//! GitHub OAuth (raw reqwest, same style as reddit.rs).
+//! OAuth providers (GitHub + Reddit). Provider accounts only *link* to a UUID;
+//! the UUID is the canonical identity. Which providers are linked is private.
 
 use reqwest::Client;
 use serde::Deserialize;
 
+use crate::reddit::{
+    default_user_agent, reddit_oauth_api_base, reddit_oauth_token_base,
+};
+
+// ── GitHub ──────────────────────────────────────────────────────────────────
+
 #[derive(Debug, Clone)]
 pub struct GitHubConfig {
     pub client_id: String,
@@ -40,7 +47,7 @@ impl GitHubConfig {
 }
 
 #[derive(Debug, Deserialize)]
-struct TokenResponse {
+struct GitHubTokenResponse {
     access_token: String,
 }
 
@@ -50,7 +57,7 @@ pub struct GitHubUser {
     pub login: String,
 }
 
-pub fn authorize_url(cfg: &GitHubConfig, state: &str, mock_user: Option<&str>) -> String {
+pub fn github_authorize_url(cfg: &GitHubConfig, state: &str, mock_user: Option<&str>) -> String {
     let mut url = format!(
         "{}/login/oauth/authorize?client_id={}&redirect_uri={}&scope=read:user&state={}",
         cfg.oauth_base.trim_end_matches('/'),
@@ -65,7 +72,7 @@ pub fn authorize_url(cfg: &GitHubConfig, state: &str, mock_user: Option<&str>) -
     url
 }
 
-pub async fn exchange_code(
+pub async fn github_exchange_code(
     client: &Client,
     cfg: &GitHubConfig,
     code: &str,
@@ -90,14 +97,14 @@ pub async fn exchange_code(
         return Err(format!("github token HTTP {}", resp.status()));
     }
 
-    let body: TokenResponse = resp
+    let body: GitHubTokenResponse = resp
         .json()
         .await
         .map_err(|e| format!("github token parse failed: {e}"))?;
     Ok(body.access_token)
 }
 
-pub async fn fetch_user(
+pub async fn github_fetch_user(
     client: &Client,
     api_base: &str,
     access_token: &str,
@@ -120,10 +127,149 @@ pub async fn fetch_user(
         .map_err(|e| format!("github user parse failed: {e}"))
 }
 
-pub fn provider_id(user: &GitHubUser) -> String {
+pub fn github_provider_id(user: &GitHubUser) -> String {
     user.id.to_string()
 }
 
+// ── Reddit ──────────────────────────────────────────────────────────────────
+
+#[derive(Debug, Clone)]
+pub struct RedditConfig {
+    pub client_id: String,
+    pub client_secret: String,
+    pub redirect_uri: String,
+    /// Host for `/api/v1/authorize` (www.reddit.com in production).
+    pub authorize_base: String,
+    /// Host for `POST /api/v1/access_token`.
+    pub token_base: String,
+    /// Host for bearer `GET /api/v1/me` (oauth.reddit.com).
+    pub api_base: String,
+    pub user_agent: String,
+}
+
+/// Authorize page base; defaults to the same host as token POSTs.
+pub fn reddit_authorize_base() -> String {
+    std::env::var("REDDIT_OAUTH_AUTHORIZE_BASE")
+        .or_else(|_| std::env::var("REDDIT_OAUTH_BASE"))
+        .unwrap_or_else(|_| "https://www.reddit.com".into())
+}
+
+impl RedditConfig {
+    pub fn from_env(base_url: &str) -> Option<Self> {
+        let client_id = std::env::var("REDDIT_CLIENT_ID")
+            .or_else(|_| std::env::var("REDDIT_APP_ID"))
+            .ok()?;
+        let client_secret = std::env::var("REDDIT_CLIENT_SECRET")
+            .or_else(|_| std::env::var("REDDIT_APP_SECRET"))
+            .ok()?;
+        if client_id.is_empty() || client_secret.is_empty() {
+            return None;
+        }
+        let base = base_url.trim_end_matches('/');
+        Some(Self {
+            client_id,
+            client_secret,
+            redirect_uri: format!("{base}/auth/reddit/callback"),
+            authorize_base: reddit_authorize_base(),
+            token_base: reddit_oauth_token_base(),
+            api_base: reddit_oauth_api_base(),
+            user_agent: default_user_agent(),
+        })
+    }
+}
+
+#[derive(Debug, Deserialize)]
+struct RedditTokenResponse {
+    access_token: String,
+}
+
+#[derive(Debug, Deserialize)]
+pub struct RedditUser {
+    /// Stable id (`t2_…`); never use `name` as identity.
+    pub id: String,
+    pub name: String,
+}
+
+pub fn reddit_authorize_url(cfg: &RedditConfig, state: &str, mock_user: Option<&str>) -> String {
+    let mut url = format!(
+        "{}/api/v1/authorize?client_id={}&response_type=code&state={}&redirect_uri={}&duration=temporary&scope=identity",
+        cfg.authorize_base.trim_end_matches('/'),
+        urlencoding::encode(&cfg.client_id),
+        urlencoding::encode(state),
+        urlencoding::encode(&cfg.redirect_uri),
+    );
+    if let Some(user) = mock_user {
+        url.push_str("&mock_user=");
+        url.push_str(&urlencoding::encode(user));
+    }
+    url
+}
+
+pub async fn reddit_exchange_code(
+    client: &Client,
+    cfg: &RedditConfig,
+    code: &str,
+) -> Result<String, String> {
+    let resp = client
+        .post(format!(
+            "{}/api/v1/access_token",
+            cfg.token_base.trim_end_matches('/')
+        ))
+        .header("User-Agent", &cfg.user_agent)
+        .basic_auth(&cfg.client_id, Some(&cfg.client_secret))
+        .form(&[
+            ("grant_type", "authorization_code"),
+            ("code", code),
+            ("redirect_uri", cfg.redirect_uri.as_str()),
+        ])
+        .send()
+        .await
+        .map_err(|e| format!("reddit token request failed: {e}"))?;
+
+    if !resp.status().is_success() {
+        let status = resp.status();
+        let body = resp.text().await.unwrap_or_default();
+        return Err(format!("reddit token HTTP {status}: {body}"));
+    }
+
+    let body: RedditTokenResponse = resp
+        .json()
+        .await
+        .map_err(|e| format!("reddit token parse failed: {e}"))?;
+    Ok(body.access_token)
+}
+
+pub async fn reddit_fetch_user(
+    client: &Client,
+    cfg: &RedditConfig,
+    access_token: &str,
+) -> Result<RedditUser, String> {
+    let resp = client
+        .get(format!(
+            "{}/api/v1/me",
+            cfg.api_base.trim_end_matches('/')
+        ))
+        .header("User-Agent", &cfg.user_agent)
+        .bearer_auth(access_token)
+        .send()
+        .await
+        .map_err(|e| format!("reddit user request failed: {e}"))?;
+
+    if !resp.status().is_success() {
+        return Err(format!("reddit user HTTP {}", resp.status()));
+    }
+
+    resp.json()
+        .await
+        .map_err(|e| format!("reddit user parse failed: {e}"))
+}
+
+pub fn reddit_provider_id(user: &RedditUser) -> String {
+    user.id.clone()
+}
+
+// ── Shared helpers ──────────────────────────────────────────────────────────
+
 pub fn validate_pseudonym(raw: &str) -> Result<String, &'static str> {
     let trimmed = raw.trim();
     if trimmed.is_empty() {
@@ -144,3 +290,12 @@ pub fn validate_pseudonym(raw: &str) -> Result<String, &'static str> {
 pub fn sanitize_pseudonym(login: &str) -> String {
     validate_pseudonym(login).unwrap_or_else(|_| "user".to_string())
 }
+
+/// Display name for a provider key (`github` → `GitHub`). Never show provider ids.
+pub fn provider_label(provider: &str) -> &'static str {
+    match provider {
+        "github" => "GitHub",
+        "reddit" => "Reddit",
+        _ => "OAuth",
+    }
+}
diff --git a/server/src/lib.rs b/server/src/lib.rs
index 84f2565b105fb302241b949af64bd5e49916eab2..0d948af1457504fdbd34d0b14261f65ac58da0ec 100644
--- a/server/src/lib.rs
+++ b/server/src/lib.rs
@@ -47,6 +47,8 @@ pub fn create_app(state: AppState) -> Router {
         .route("/login/alias", get(crate::auth::alias_page))
         .route("/auth/github", get(crate::auth::github_start))
         .route("/auth/github/callback", get(crate::auth::github_callback))
+        .route("/auth/reddit", get(crate::auth::reddit_start))
+        .route("/auth/reddit/callback", get(crate::auth::reddit_callback))
         .route("/auth/logout", post(crate::auth::logout))
         .route("/auth/switch", post(crate::auth::switch_pseudonym))
         .route("/ui", post(crate::api::ui_html::post_ui_html))
diff --git a/server/src/projection_apply.rs b/server/src/projection_apply.rs
index 4fb4b48ee0a53b7f673fae0c9731eed5acc33332..f50458c2ff3c447a3cfd28adb298e6883a2da4e9 100644
--- a/server/src/projection_apply.rs
+++ b/server/src/projection_apply.rs
@@ -4,6 +4,8 @@
 //! child links, recent-vote appends) plus a cursor advance, all committed in
 //! one atomic `DisableWal` batch.
 
+use std::collections::HashMap;
+
 use crate::{
     event_log::EventLogError,
     events::{Event, EventRecord},
@@ -44,6 +46,8 @@ pub fn apply_records(
     let db = projection_store.db();
     let mut batch = db.batch();
     let mut last_seq = 0u64;
+    // Weight reads must see earlier writes in this same batch.
+    let mut pending_weights: HashMap<String, f64> = HashMap::new();
 
     for record in records {
         match &record.event {
@@ -85,6 +89,7 @@ pub fn apply_records(
                 ensure_path_writes(&mut batch, &parsed);
             }
             Event::PrincipalCreated { uuid, .. } => {
+                pending_weights.insert(uuid.clone(), BASE_TRUST_WEIGHT);
                 batch.write(
                     Store::root()
                         .user_weights()
@@ -112,17 +117,25 @@ pub fn apply_records(
                     }
                 } else {
                     batch.write(Store::root().oauth_links().key(&link_key).set(uuid));
-                    let current = Store::root()
-                        .user_weights()
-                        .key(&uuid.clone())
-                        .get(db)
-                        .map_err(|e| EventLogError::Apply(e.to_string()))?
+                    let current = pending_weights
+                        .get(uuid)
+                        .copied()
+                        .or_else(|| {
+                            Store::root()
+                                .user_weights()
+                                .key(&uuid.clone())
+                                .get(db)
+                                .ok()
+                                .flatten()
+                        })
                         .unwrap_or(BASE_TRUST_WEIGHT);
+                    let next = trust_weight_after_link(current);
+                    pending_weights.insert(uuid.clone(), next);
                     batch.write(
                         Store::root()
                             .user_weights()
                             .key(&uuid.clone())
-                            .set(&trust_weight_after_link(current)),
+                            .set(&next),
                     );
                 }
             }
@@ -205,6 +218,15 @@ mod tests {
                 ),
                 record(
                     3,
+                    Event::OauthLinked {
+                        uuid: uuid.into(),
+                        provider: "reddit".into(),
+                        provider_id: "t2_abc".into(),
+                        ts,
+                    },
+                ),
+                record(
+                    4,
                     Event::PseudonymClaimed {
                         uuid: uuid.into(),
                         pseudonym: "octocat".into(),
@@ -219,8 +241,12 @@ mod tests {
             oauth_link_owner(store.db(), "github", "42").unwrap(),
             Some(uuid.to_string())
         );
+        assert_eq!(
+            crate::storage_schema::linked_providers_for_uuid(store.db(), uuid).unwrap(),
+            vec!["github".to_string(), "reddit".to_string()]
+        );
         assert_eq!(resolve_actor_uuid(store.db(), "octocat").unwrap(), uuid);
-        assert_eq!(user_trust_weight(store.db(), uuid).unwrap(), 1.5);
+        assert_eq!(user_trust_weight(store.db(), uuid).unwrap(), 2.0);
         let aliases = Store::root()
             .user_pseudonyms()
             .key(&uuid.to_string())
diff --git a/server/src/storage_schema.rs b/server/src/storage_schema.rs
index b942810afd96d3bf01b7765718303a39be4ef8d2..dac6f8e6080e3f5683c24dbb8861f5a981d456c4 100644
--- a/server/src/storage_schema.rs
+++ b/server/src/storage_schema.rs
@@ -103,6 +103,25 @@ pub fn oauth_link_owner(db: &Db, provider: &str, provider_id: &str) -> durable::
         .get(db)
 }
 
+/// Provider names linked to a UUID (`github`, `reddit`, …). Private — for the
+/// account owner's page only; never expose which providers are linked publicly.
+pub fn linked_providers_for_uuid(db: &Db, uuid: &str) -> durable::Result<Vec<String>> {
+    let mut providers = Vec::new();
+    for (key, owner) in Store::root().oauth_links().iter(db)? {
+        if owner != uuid {
+            continue;
+        }
+        let Some((provider, _)) = key.split_once(':') else {
+            continue;
+        };
+        if !providers.iter().any(|p| p == provider) {
+            providers.push(provider.to_string());
+        }
+    }
+    providers.sort();
+    Ok(providers)
+}
+
 pub const RECENT_VOTES_CAP: u64 = 200;
 
 fn id_key(id: &ItemId) -> String {
diff --git a/test/support/harness.clj b/test/support/harness.clj
index 4505ece5aa193e826ca61c52f1467d252080d66b..741024aab1d14269e225791189633287980ae2e4 100644
--- a/test/support/harness.clj
+++ b/test/support/harness.clj
@@ -48,12 +48,15 @@
          "GITHUB_CLIENT_SECRET" "test-secret"
          "GITHUB_OAUTH_BASE" (str "http://127.0.0.1:" oauth-port)
          "GITHUB_API_BASE" (str "http://127.0.0.1:" oauth-port)
+         ;; Reddit import fixtures + Reddit OAuth on reddit-port.
          "REDDIT_API_BASE" (str "http://127.0.0.1:" reddit-port)
+         "REDDIT_CLIENT_ID" "test-reddit"
+         "REDDIT_CLIENT_SECRET" "test-reddit-secret"
          "REDDIT_OAUTH_BASE" (str "http://127.0.0.1:" reddit-port)
-         "REDDIT_CLIENT_ID" ""
-         "REDDIT_CLIENT_SECRET" ""
-         "REDDIT_APP_ID" ""
-         "REDDIT_APP_SECRET" ""}))
+         "REDDIT_OAUTH_AUTHORIZE_BASE" (str "http://127.0.0.1:" reddit-port)
+         "REDDIT_OAUTH_TOKEN_BASE" (str "http://127.0.0.1:" reddit-port)
+         "REDDIT_OAUTH_API_BASE" (str "http://127.0.0.1:" reddit-port)
+         "REDDIT_USER_AGENT" "web:sorter2-test:v0 (by /u/test)"}))
 
 (defn with-auth-servers
   "Start mock Reddit + mock OAuth + release sorter2-server.
diff --git a/test/support/mock_oauth.clj b/test/support/mock_oauth.clj
index 909d7a7be8b159ea54a122d69c46af3db3318118..5ba7e9be3cf6d2226648e9609a09ed45f306930f 100644
--- a/test/support/mock_oauth.clj
+++ b/test/support/mock_oauth.clj
@@ -1,5 +1,5 @@
 (ns test.support.mock-oauth
-  "In-process HTTP stub for GitHub OAuth (authorize, token, /user)."
+  "In-process HTTP stub for GitHub + Reddit OAuth (authorize, token, user)."
   (:require [clojure.string :as str])
   (:import [com.sun.net.httpserver HttpServer HttpHandler HttpExchange]
            [java.net InetSocketAddress URLDecoder]))
@@ -12,11 +12,14 @@
                 (URLDecoder/decode (or v "") "UTF-8"))))
           (str/split query #"&"))))
 
-(defn- parse-mock-user [raw]
+(defn- parse-mock-user
+  "GitHub-style `id:login` (numeric id). Reddit-style `t2_xxx:name`."
+  [raw]
   (let [s (or raw "1002:newbie")
         [id login] (str/split s #":" 2)]
-    {:id (Long/parseLong id)
-     :login (or login "newbie")}))
+    {:id id
+     :login (or login "newbie")
+     :numeric? (re-matches #"\d+" id)}))
 
 (defn- send-json [^HttpExchange ex status body]
   (let [bytes (.getBytes body "UTF-8")]
@@ -31,9 +34,10 @@
   (.sendResponseHeaders ex 302 -1)
   (.close (.getResponseBody ex)))
 
-(defn- read-form-code [^HttpExchange ex]
+(defn- read-form [^HttpExchange ex]
   (let [body (slurp (.getInputStream ex))]
-    (query-param body "code")))
+    {:code (query-param body "code")
+     :grant (query-param body "grant_type")}))
 
 (defn- bearer-token [^HttpExchange ex]
   (some-> (.getRequestHeaders ex)
@@ -44,8 +48,18 @@
   (when (str/starts-with? token "mock:")
     (parse-mock-user (subs token 5))))
 
+(defn- authorize-redirect [exchange query]
+  (let [redirect-uri (query-param query "redirect_uri")
+        state (query-param query "state")
+        mock-user (query-param query "mock_user")
+        user (parse-mock-user mock-user)
+        code (str "mock:" (:id user) ":" (:login user))
+        loc (str redirect-uri "?code=" (java.net.URLEncoder/encode code "UTF-8")
+                 "&state=" (java.net.URLEncoder/encode state "UTF-8"))]
+    (send-redirect exchange loc)))
+
 (defn start-mock-oauth
-  "Start mock GitHub OAuth on `port`. Returns a zero-arg `stop` function."
+  "Start mock GitHub + Reddit OAuth on `port`. Returns a zero-arg `stop` function."
   [port]
   (let [server (HttpServer/create (InetSocketAddress. "127.0.0.1" port) 0)
         handler
@@ -53,28 +67,45 @@
           (handle [^HttpExchange exchange]
             (let [uri (.getRequestURI exchange)
                   path (.getPath uri)
-                  query (.getQuery uri)]
+                  query (.getQuery uri)
+                  method (.getRequestMethod exchange)]
               (cond
+                ;; GitHub authorize
                 (str/ends-with? path "/login/oauth/authorize")
-                (let [redirect-uri (query-param query "redirect_uri")
-                      state (query-param query "state")
-                      mock-user (query-param query "mock_user")
-                      user (parse-mock-user mock-user)
-                      code (str "mock:" (:id user) ":" (:login user))
-                      loc (str redirect-uri "?code=" (java.net.URLEncoder/encode code "UTF-8")
-                               "&state=" (java.net.URLEncoder/encode state "UTF-8"))]
-                  (send-redirect exchange loc))
+                (authorize-redirect exchange query)
+
+                ;; Reddit authorize
+                (str/ends-with? path "/api/v1/authorize")
+                (authorize-redirect exchange query)
 
-                (str/ends-with? path "/login/oauth/access_token")
-                (let [code (or (read-form-code exchange) "mock:1002:newbie")]
+                ;; GitHub token
+                (and (= method "POST") (str/ends-with? path "/login/oauth/access_token"))
+                (let [code (or (:code (read-form exchange)) "mock:1002:newbie")]
                   (send-json exchange 200 (str "{\"access_token\":\"" code "\",\"token_type\":\"bearer\"}")))
 
+                ;; Reddit token (client_credentials for import + authorization_code for login)
+                (and (= method "POST") (str/ends-with? path "/api/v1/access_token"))
+                (let [form (read-form exchange)
+                      grant (or (:grant form) "")
+                      code (or (:code form) "mock:t2_test:redditor")]
+                  (if (= grant "client_credentials")
+                    (send-json exchange 200 "{\"access_token\":\"app-token\",\"token_type\":\"bearer\",\"expires_in\":3600}")
+                    (send-json exchange 200 (str "{\"access_token\":\"" code "\",\"token_type\":\"bearer\",\"expires_in\":3600}"))))
+
+                ;; GitHub user
                 (= path "/user")
                 (let [token (bearer-token exchange)
-                      user (or (parse-token-user token) {:id 1002 :login "newbie"})]
+                      user (or (parse-token-user token) {:id "1002" :login "newbie" :numeric? true})]
                   (send-json exchange 200
                              (str "{\"id\":" (:id user) ",\"login\":\"" (:login user) "\"}")))
 
+                ;; Reddit /api/v1/me
+                (str/ends-with? path "/api/v1/me")
+                (let [token (bearer-token exchange)
+                      user (or (parse-token-user token) {:id "t2_test" :login "redditor"})]
+                  (send-json exchange 200
+                             (str "{\"id\":\"" (:id user) "\",\"name\":\"" (:login user) "\"}")))
+
                 :else
                 (send-json exchange 404 "{\"error\":\"not found\"}")))))]
     (.createContext server "/" handler)
diff --git a/test/support/mock_reddit.clj b/test/support/mock_reddit.clj
index 5efa92db3e1f79b8f423a2f1adcbda959123c1ad..a630cf0938722193e9af88382d60e777ff371be4 100644
--- a/test/support/mock_reddit.clj
+++ b/test/support/mock_reddit.clj
@@ -1,14 +1,56 @@
 (ns test.support.mock-reddit
-  "In-process HTTP stub for Reddit API fixtures (`test/fixtures/reddit/`)."
+  "In-process HTTP stub for Reddit API fixtures + OAuth login endpoints."
   (:require [clojure.java.io :as io]
             [clojure.string :as str])
   (:import [com.sun.net.httpserver HttpServer HttpHandler HttpExchange]
-           [java.net InetSocketAddress]))
+           [java.net InetSocketAddress URLDecoder]))
 
 (defn fixtures-dir
   ([] (fixtures-dir (System/getProperty "user.dir")))
   ([root] (str root "/test/fixtures/reddit")))
 
+(defn- query-param [query key]
+  (when query
+    (some (fn [pair]
+            (let [[k v] (str/split pair "=" 2)]
+              (when (= k key)
+                (URLDecoder/decode (or v "") "UTF-8"))))
+          (str/split query #"&"))))
+
+(defn- parse-mock-user [raw]
+  (let [s (or raw "t2_test:redditor")
+        [id login] (str/split s #":" 2)]
+    {:id id :login (or login "redditor")}))
+
+(defn- send-bytes [^HttpExchange ex status ^bytes body content-type]
+  (.set (.getResponseHeaders ex) "Content-Type" content-type)
+  (.sendResponseHeaders ex status (alength body))
+  (doto (.getResponseBody ex)
+    (.write body)
+    (.close)))
+
+(defn- send-json [^HttpExchange ex status body]
+  (send-bytes ex status (.getBytes body "UTF-8") "application/json"))
+
+(defn- send-redirect [^HttpExchange ex location]
+  (.set (.getResponseHeaders ex) "Location" location)
+  (.sendResponseHeaders ex 302 -1)
+  (.close (.getResponseBody ex)))
+
+(defn- read-form [^HttpExchange ex]
+  (let [body (slurp (.getInputStream ex))]
+    {:code (query-param body "code")
+     :grant (query-param body "grant_type")}))
+
+(defn- bearer-token [^HttpExchange ex]
+  (some-> (.getRequestHeaders ex)
+          (.getFirst "Authorization")
+          (str/replace #"^[Bb]earer " "")))
+
+(defn- parse-token-user [token]
+  (when (str/starts-with? token "mock:")
+    (parse-mock-user (subs token 5))))
+
 (defn start-mock-reddit
   "Start a mock Reddit API on `port`. Returns a zero-arg `stop` function."
   ([port] (start-mock-reddit port (fixtures-dir)))
@@ -19,15 +61,38 @@
          handler
          (proxy [HttpHandler] []
            (handle [^HttpExchange exchange]
-             ;; `/r/<sub>/about.json` → subreddit entity; `/r/<sub>.json` → listing.
-             (let [path (.getPath (.getRequestURI exchange))
-                   body (if (str/includes? path "/about")
-                          about
-                          listing)]
-               (.sendResponseHeaders exchange 200 (alength body))
-               (let [out (.getResponseBody exchange)]
-                 (.write out body)
-                 (.close out)))))]
+             (let [uri (.getRequestURI exchange)
+                   path (.getPath uri)
+                   query (.getQuery uri)
+                   method (.getRequestMethod exchange)]
+               (cond
+                 (str/ends-with? path "/api/v1/authorize")
+                 (let [redirect-uri (query-param query "redirect_uri")
+                       state (query-param query "state")
+                       user (parse-mock-user (query-param query "mock_user"))
+                       code (str "mock:" (:id user) ":" (:login user))
+                       loc (str redirect-uri "?code=" (java.net.URLEncoder/encode code "UTF-8")
+                                "&state=" (java.net.URLEncoder/encode state "UTF-8"))]
+                   (send-redirect exchange loc))
+
+                 (and (= method "POST") (str/ends-with? path "/api/v1/access_token"))
+                 (let [form (read-form exchange)
+                       grant (or (:grant form) "")
+                       code (or (:code form) "mock:t2_test:redditor")]
+                   (if (= grant "client_credentials")
+                     (send-json exchange 200 "{\"access_token\":\"app-token\",\"token_type\":\"bearer\",\"expires_in\":3600}")
+                     (send-json exchange 200 (str "{\"access_token\":\"" code "\",\"token_type\":\"bearer\",\"expires_in\":3600}"))))
+
+                 (str/ends-with? path "/api/v1/me")
+                 (let [user (or (parse-token-user (bearer-token exchange))
+                                {:id "t2_test" :login "redditor"})]
+                   (send-json exchange 200
+                              (str "{\"id\":\"" (:id user) "\",\"name\":\"" (:login user) "\"}")))
+
+                 ;; `/r/<sub>/about.json` → subreddit entity; `/r/<sub>.json` → listing.
+                 :else
+                 (let [body (if (str/includes? path "/about") about listing)]
+                   (send-bytes exchange 200 body "application/json"))))))]
      (.createContext server "/" handler)
      (.setExecutor server nil)
      (.start server)