Side B fixes an actual algorithmic bug (bipartite/oscillating Markov chain in the ranking power-iteration) with a correct, well-justified change grounded in the cited paper, plus regression tests in both Rust and Clojure across multiple topologies. Side A is purely a planning document and a thin wrapper struct (RouteContext) that just delegates to existing ThreadNav methods without migrating any call sites, providing no functional change or real refactor yet—its value is aspirational/documentation only.
constitution · epochs · watch · epoch 3
comparison
c_7ec67b9cef2c (tommy-mor) vs c_48aeaf9b52c3 (tommy-mor)
download prompt · raw event · cmp_14d12b78a8fffe
council reasoning
B fixes a real ranking correctness bug (star topology yielding uniform scores from bipartite oscillation) by switching to paper-correct degree-based d_max, with Rust and Clojure regression coverage. A mostly adds a forward-looking plan.md plus a thin RouteContext newtype that still delegates to ThreadNav/CanonicalItemUrl without finishing the identity refactor.
Side B fixes a real correctness bug in `server/src/ranking.rs` by switching the Rank Centrality transition matrix to use degree-based `d_max`, preventing oscillation and producing correct rankings for star topologies. It also adds focused Rust and Clojure regression tests with ranking fixtures, while Side A primarily adds a long design plan and a `RouteContext` wrapper around `ThreadNav` that introduces little functional change.
sides
A — c_7ec67b9cef2c (tommy-mor)
message
[1c914c6e] stage set
diff preview
diff --git a/plan.md b/plan.md
new file mode 100644
index 0000000000000000000000000000000000000000..00d6867a1e0ed144a16a020ea037f685ce646c73
--- /dev/null
+++ b/plan.md
@@ -0,0 +1,155 @@
+# Plan: `ItemId` + `RouteContext` (identity vs hrefs)
+
+This document is for **the next agent** to continue the refactor without re-deriving context from chat. It supersedes ad-hoc notes: treat it as the checklist of record until the work lands and this file is deleted or trimmed.
+
+## Goal
+
+- **Identity** (what lives in the reducer graph, votes, indexes) becomes a **structural `ItemId` enum** in `slug-types`, not a canonical `String` / `CanonicalItemUrl` newtype.
+- **Presentation** (tilde / dash display, breadcrumbs) derives from `ItemId` via explicit methods, not string stripping.
+- **Routing** (browser `href`s for public vs room) goes through **`RouteContext`** (started in `server/src/html/routing.rs`) so Maud/handlers do not stitch `/r/…` vs `/~` ad hoc.
+
+**Non-goals for v1 of the migration:** backward-compatible JSONL or dual-read of old canonical strings in the event log (project has accepted breaking changes). If you reintroduce compat, document it here.
+
+## Current state (as of this plan)
+
+- **`CanonicalItemUrl`** (`types/src/paths.rs`): newtype around `String`; `parse` / `parent` / `display_path` / `tilde_tail` / etc. Reducer `ContentState`, `VoteData`, ranking, RPC, search, garden, breadcrumbs all use it or `String` keys derived from it.
+- **`ThreadNav`** (`server/src/html/forum/nav.rs`): encodes scope prefixes for threads and garden URLs; **`RouteContext`** now wraps `ThreadNav` (`server/src/html/routing.rs`, re-exported from `server/src/html/mod.rs`) but **most HTML still takes `&ThreadNav` directly** — migration incomplete.
+- **URL normalization** lives in `types/src/url_normalize.rs` + `canonicalize_item` / `finalize_external_identity_url` in `paths.rs` (YouTube, sorted query params, room path `room_route_segment` in `paths.rs`).
+- **Room HTTP paths** are `/r/{short}{slug}` (fused segment); wire **`room_id`** remains `short/slug` for RPC/events.
+
+## Target architecture
+
+### `ItemId` (types)
+
+Suggested shape (adjust after profiling `Ord` / `Hash` / serde size):
+
+```text
+ItemId::Root — tilde ontology root (today `SLUG_TILDE_ONTOLOGY_ROOT`)
+ItemId::Local { segments } — slug.social ~/… path as Vec<String> (lowercase segments, non-empty for non-root)
+ItemId::External { url: Url } — normalized `url::Url` (crate `url` already in `slug-types`)
+```
+
+**API surface (minimum):**
+
+- `ItemId::parse(&str) -> Option<ItemId>` — single entry from DSL / user input / legacy wire (internally may call `canonicalize_item` + structured split).
+- `ItemId::to_wire_url(&self) -> String` — only for **external** boundaries if needed (HTTP fetch, rare assertions); avoid using as the primary key once maps use `ItemId`.
+- `parent`, `display_path`, `tilde_tail` / `tilde_http_tail`, `tilde_segments`, `last_segment`, `normalized_storage` — port from `CanonicalItemUrl`.
+- **`Ord` + `Hash` + `Eq`** stable for `BTreeSet` / `HashMap` (see `write_actor` scope-rank snapshots).
+- **`Serialize` / `Deserialize`** — decide **tagged JSON** for any persisted or API-carried structs (e.g. `VoteData` in tests). If RPC must stay stringy for clients, use a **DTO layer** that converts `ItemId` ↔ wire at the boundary only.
+
+**Remove:** `CanonicalItemUrl` type and all `path_types::CanonicalItemUrl` / `slug_types::paths::CanonicalItemUrl` exports once call sites are migrated. **`Borrow<str>`** on the old newtype goes away; update `nav!` / any code that assumed map keys borrowed as `str`.
+
+### `RouteContext` (server HTML)
+
+- **File:** `server/src/html/routing.rs` — **`RouteContext(ThreadNav)`** with `item_href`, `item_href_raw`, `thread_url`, `garden_root_url`, `room_url`, `From`/`Into` `ThreadNav`.
+- **Direction:** new code and refactored Maud should take **`&RouteContext`** (or owned where appropriate) instead of `&ThreadNav` when building links. Long term, **`item_href(&ItemId)`** should not parse strings — it should pattern-match `ItemId` and append tilde tail or `/-/…` external tail using the same rules as today’s `ThreadNav::garden_item_url`.
+
+### Axum / garden routes
+
+- **No** single catch-all route (explicit decision): keep the existing router layout in `server/src/lib.rs`.
+- Room routes stay **`/r/:room_key/...`** with `room_key` fused; parsing via `slug_types::room_id_from_route_segment` / `room_route_segment` in `paths.rs`.
+
+## Phased execution (recommended order)
+
+### Phase 0 — Preconditions (quick)
+
+1. Read **`AGENTS.md`** (UI contract, durability matrix, `RpcCommand` vs `HtmlUiAction`).
+2. Run **`cargo test --workspace`** and **`./scripts/clj-test.sh`** on clean `main` before large diffs; repeat after each phase.
+
+### Phase 1 — `ItemId` in `slug-types` (no server yet)
+
+1. Add **`ItemId`** (new file e.g. `types/src/item_id.rs` **or** inline at bottom of `paths.rs` — see **Module cycle** below).
+2. Implement **`ItemId::parse`** using existing **`canonicalize_item`** + normalization; port **`CanonicalItemUrl`** methods to **`ItemId`** with tests ported from `paths.rs` `#[cfg(test)] mod tests`.
+3. **`GardenItemUrl::from_stored(&ItemId, room_wire)`** (and thread helpers) — build absolute hrefs from structure, not from re-parsing a canonical string.
+4. **`TildeHttpPathTail::to_item_id`** (rename from `to_canonical`) / **`tilde_http_path_to_item_id`**.
+5. **`TildeOntologyPath::from_stored(&ItemId)`**.
+6. Export **`ItemId`** from **`types/src/lib.rs`**; update **`server/src/path_types.rs`** re-exports.
+7. **Delete `CanonicalItemUrl`** and fix all **in-crate** references in `types` only until `cargo test` passes for `slug-types`.
+
+**Module cycle trap:** `item_id.rs` must not `use crate::paths::{...}` if `paths.rs` also imports `ItemId` for `GardenItemUrl` in the same module. **Fix one of:**
+
+- **A)** Put `ItemId` **inside `paths.rs`** below `canonicalize_item` / helpers (simplest, large file), or
+- **B)** Split **`canonicalize_item`** (+ dash host helpers + `finalize_external_identity_url`) into **`types/src/item_wire.rs`**, then `paths.rs` + `item_id.rs` both depend on `item_wire` only (cleaner, more files).
+
+### Phase 2 — Reducer + ranking (server core)
+
+1. **`server/src/reducer.rs`**: `ContentState` / `GroupState` / **`VoteData`** — replace **`CanonicalItemUrl`** with **`ItemId`** on all maps, sets, deques, vectors.
+2. **`apply_vote`**: normalize `a`/`b` via **`ItemId::parse`** or **`ItemId`**-aware logic (remove string round-trip).
+3. **`apply_ingest_to_content`**: **`dsl`** still yields strings for item titles in statements; normalize to **`ItemId`** at ingest boundary via **`ItemId::parse`** once per item.
+4. **`server/src/ranking.rs`**, **`server/src/scope_rank.rs`**, **`server/src/api/write_actor.rs`** (including **`BTreeSet`** ordering), **`server/src/api/validate.rs`**, **`server/src/api/helpers.rs`** — propagate **`ItemId`**.
+5. **`server/tests/basic.rs`** and any reducer tests constructing **`VoteData`** — use **`ItemId::parse(...).unwrap()`** or helpers.
+
+### Phase 3 — RPC + search + external resolver
+
+1. **`server/src/api/rpc.rs`**: rank/pair/matchup/search payloads; today many paths use **`GardenItemUrl::from_storage_str(item.as_str(), …)`** — switch to **`ItemId`** + **`GardenItemUrl::from_stored(&item_id, …)`** (or equivalent).
+2. **`server/src/html/search.rs`**: scoring uses item path strings — derive from **`ItemId::display_path`** / **`to_wire_url`** only at the scoring boundary if needed.
+3. **`server/src/external_resolver.rs`**: take **`&ItemId`** or **`ItemId::external_url()`** instead of **`&CanonicalItemUrl`**.
+
+### Phase 4 — HTML / Maud
+
+1. **`ThreadNav::garden_item_url`**: overload or replace with **`garden_item_href(&self, item: &ItemId)`** (no `CanonicalItemUrl::parse` inside).
+2. **`RouteContext`**: extend **`item_href(&ItemId)`**; migrate call sites from **`ThreadNav`** to **`RouteContext`** where only link-building is needed (keep **`ThreadNav`** where scope / auth helpers need the full struct).
+3. **`server/src/html/garden.rs`**, **`breadcrumb_path.rs`**, **`forum/*`**, **`editor.rs`**: replace **`CanonicalItemUrl`** with **`ItemId`**; breadcrumbs should walk **`ItemId::parent`** without string `rsplit`.
+4. **`types` JSON types** (`RankRow`, etc.): decide whether **`GardenItemUrl`** stays string for JSON or becomes a structured field; keep **one** wire format for the public API.
+
+### Phase 5 — Cleanup + docs
+
+1. Remove dead **`canonical_path`** / **`breadcrumb_path`** string logic if fully superseded.
+2. Update **`AGENTS.md`** if durability, `POST /ui`, or command surfaces change.
+3. Delete or shrink **`plan.md`** when done.
+
+## File / symbol checklist (non-exhaustive — grep-driven)
+
+Run periodically:
+
+```bash
+rg "CanonicalItemUrl" -g'*.rs'
+rg "path_types::CanonicalItemUrl" -g'*.rs'
+rg "tilde_http_path_to_canonical" -g'*.rs'
+```
+
+**High-touch files (from prior exploration):**
+
+| Area | Files |
+|------|--------|
+| Types | `types/src/paths.rs`, `types/src/lib.rs`, `types/src/url_normalize.rs`, (optional) `types/src/item_id.rs`, `types/src/item_wire.rs` |
+| Server re-exports | `server/src/path_types.rs`, `server/src/canonical_path.rs` |
+| Reducer / ingest | `server/src/reducer.rs`, `server/src/dsl.rs` (parse output types if changed) |
+| Ranking | `server/src/ranking.rs`, `server/src/scope_rank.rs` |
+| Writer / RPC | `server/src/api/write_actor.rs`, `server/src/api/rpc.rs`, `server/src/api/helpers.rs`, `server/src/api/validate.rs` |
+| HTML | `server/src/html/garden.rs`, `server/src/html/breadcrumb_path.rs`, `server/src/html/forum/nav.rs`, `server/src/html/routing.rs`, `server/src/html/search.rs`, `server/src/html/editor.rs`, `server/src/html/forum/ingest.rs`, … |
+| Tests | `server/tests/basic.rs`, `server/tests/integration.rs`, `types/src/paths.rs` tests, Clojure under `test/` if URLs/assertions mention canonical shapes |
+
+## Events / JSONL
+
+- **`Ingest`** events store **`raw` DSL** only — no change required for item identity inside the event.
+- If any future event type stores item ids as strings, migrate to **structured `ItemId` serde** or accept string only at the event boundary with immediate parse into **`ItemId`** on `apply_event`.
+
+## `nav!` macro (`server/src/paths.rs`)
+
+- Macros use **`keypath($key)`** with **`.clone()`** — **`ItemId`** must be **`Clone`** (already for enums). Remove any reliance on **`Borrow<str>`** for map keys.
+
+## Testing gate
+
+After each phase:
+
+```bash
+cargo test --workspace
+./scripts/clj-test.sh
+```
+
+## Risks / gotchas
+
+1. **`Ord` on `ItemId`**: must match prior **`CanonicalItemUrl`** / `String` ordering wherever **`BTreeSet`** is used (e.g. deterministic scope-rank snapshots in **`write_actor`**).
+2. **External `ItemId`**: **`Url`** equality / hashing — normalization is already centralized in **`url_normalize`**; ensure **`ItemId::parse`** always inserts normalized **`Url`** into **`External`**.
+3. **Fake parent URLs** in garden (e.g. **`https://.`** for external root ranking): find all **`parse("https://.")`** style hacks and express as **`ItemId`** or a dedicated sentinel.
+4. **Serde**: tests and any RPC clients that snapshot JSON may need expectation updates if **`VoteData`** shape changes.
+
+## Optional follow-ups (not blocking `ItemId`)
+
+- More **domain normalizers** in **`url_normalize.rs`** (e.g. `music.youtube.com`, Spotify, etc.).
+- **Room wire** vs **HTTP segment** helpers already in **`paths.rs`** (`ROOM_SHORT_ID_LEN`, `room_route_segment`, `room_id_from_route_segment`).
+
+---
+
+**End state criteria:** `rg CanonicalItemUrl` returns nothing; reducer maps use **`ItemId`**; HTML link generation for items goes through **`RouteContext` + `ItemId`**; tests and Kaocha green.
diff --git a/server/src/html/mod.rs b/server/src/html/mod.rs
index c3dccd03dc6da2a2f6f6fa828657e33a951884b
… preview truncated; 2,831 characters omittedB — c_48aeaf9b52c3 (tommy-mor)
message
[595b3850] Fix star-topology ranking by using degree-based d_max (#146). A pure forward star at the default `>` ratio (2:1) produced uniform 1/3 scores, and the alphabetical-fallback sort placed the unambiguous winner last. Root cause: `compute_scores_from_edges` divided by the max sum of pairwise-normalized weights, so every node ended up with P_ii = 0 — a bipartite Markov chain whose power iteration oscillated and, after the configured even iteration count, returned to the uniform initial state. Switch the divisor to the unweighted max neighbor degree, matching the canonical Rank Centrality definition in Negahban–Oh–Shah 2012 §3.1 (arXiv:1209.1688, eq. defP and the d_max definition in §6). This gives every non-saturated node a positive self-loop, makes the chain aperiodic, and converges the star to π_zebra = 1/2, π_alpha = π_beta = 1/4. Add Rust regression test and a Clojure test that drives the sorterc binary against four .sorter fixtures (star, inverse star, chain, cycle). Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
diff preview
diff --git a/server/src/ranking.rs b/server/src/ranking.rs
index 3710c9f64437f5bef3b2121905b6f3bcb7611047..38e6d09b4370e5f8cbae09c0e5760b4e7f1ef7db 100644
--- a/server/src/ranking.rs
+++ b/server/src/ranking.rs
@@ -1,4 +1,4 @@
-use std::collections::HashMap;
+use std::collections::{HashMap, HashSet};
use crate::path_types::ItemId;
use crate::reducer::GroupState;
@@ -143,23 +143,35 @@ fn compute_scores_from_edges(n: usize, edges: impl Iterator<Item = ((usize, usiz
}
}
+ // Rank Centrality (Negahban, Oh, Shah 2012, §3.1):
+ // P_ij = (1/d_max) * A_ij for i ≠ j compared
+ // P_ii = 1 - (1/d_max) * Σ_k A_ik
+ // where d_i is the *degree* (number of distinct neighbors compared) and
+ // d_max = max_i d_i. Using the unweighted degree — not the sum of
+ // pairwise-normalized weights — is what guarantees aperiodicity: it
+ // forces P_ii > 0 for every non-maximum-degree node, and for max-degree
+ // nodes whenever any neighbor weight is below 1 (i.e. not a unanimous
+ // loss). Without this, regular comparison graphs (e.g. a pure star at
+ // ratio 2:1) produce a bipartite chain that oscillates instead of
+ // converging — see issue #146.
let mut out_edges: Vec<Vec<(usize, f64)>> = vec![Vec::new(); n];
- let mut out_deg: Vec<f64> = vec![0.0; n];
+ let mut neighbors: Vec<HashSet<usize>> = vec![HashSet::new(); n];
for ((src, dst), w) in &normalized {
out_edges[*src].push((*dst, *w));
- out_deg[*src] += w;
+ neighbors[*src].insert(*dst);
+ neighbors[*dst].insert(*src);
}
- let mut max_out = 0.0f64;
- for &d in &out_deg {
- if d > max_out {
- max_out = d;
- }
- }
- if max_out <= 1e-12 {
+ let weight_sum: Vec<f64> = out_edges
+ .iter()
+ .map(|es| es.iter().map(|(_, w)| *w).sum())
+ .collect();
+ let d_max = neighbors.iter().map(|s| s.len()).max().unwrap_or(0);
+ if d_max == 0 {
return vec![1.0 / n as f64; n];
}
+ let d_max_f = d_max as f64;
let mut scores = vec![1.0 / n as f64; n];
let mut next = vec![0.0f64; n];
@@ -167,14 +179,14 @@ fn compute_scores_from_edges(n: usize, edges: impl Iterator<Item = ((usize, usiz
for _ in 0..max_iters {
next.fill(0.0);
for i in 0..n {
- let stay_prob = (max_out - out_deg[i]) / max_out;
+ let stay_prob = (d_max_f - weight_sum[i]) / d_max_f;
next[i] += scores[i] * stay_prob;
if out_edges[i].is_empty() {
continue;
}
for &(dst, w) in &out_edges[i] {
- next[dst] += scores[i] * (w / max_out);
+ next[dst] += scores[i] * (w / d_max_f);
}
}
@@ -270,6 +282,38 @@ mod tests {
}
}
+ /// Regression for issue #146: pure forward star at default `>` ratio (2:1).
+ /// Under the old (sum-of-weights) divisor every node had P_ii = 0 and the
+ /// chain was bipartite; power iteration oscillated and returned the
+ /// uniform initial distribution after an even number of steps. Using the
+ /// paper's degree-based d_max gives every node a positive self-loop and
+ /// the chain converges to the correct stationary distribution.
+ #[test]
+ fn star_topology_winner_at_top_via_subset() {
+ let mut g = mk_group();
+ g.apply_vote(vote(1, "zebra", "alpha", 2, 1));
+ g.apply_vote(vote(2, "zebra", "beta", 2, 1));
+
+ let mut items: Vec<(usize, String)> = g
+ .idx_to_item
+ .iter()
+ .enumerate()
+ .map(|(i, it)| (i, it.as_str().to_string()))
+ .collect();
+ items.sort_by(|a, b| a.1.cmp(&b.1));
+ let idxs: Vec<usize> = items.iter().map(|(i, _)| *i).collect();
+
+ let ranked = ranked_items_subset(&g, &idxs, 10000, 1e-8);
+ for r in &ranked {
+ eprintln!("{}: {}", r.item.as_str(), r.score);
+ }
+ assert_eq!(
+ ranked[0].item.as_str(),
+ "https://slug.social/zebra",
+ "zebra won both votes and should rank #1"
+ );
+ }
+
#[test]
fn group_ranking_cache_dirty_flow() {
let mut g = mk_group();
diff --git a/test/fixtures/ranking/chain.sorter b/test/fixtures/ranking/chain.sorter
new file mode 100644
index 0000000000000000000000000000000000000000..912a96bdc08f631be27f3c9afc7e05004a2457c0
--- /dev/null
+++ b/test/fixtures/ranking/chain.sorter
@@ -0,0 +1,10 @@
+#t3
+
+~/t3/a { head of chain }
+~/t3/b { middle }
+~/t3/c { tail }
+
+{ a > b }
+~/t3/a > ~/t3/b
+{ b > c }
+~/t3/b > ~/t3/c
diff --git a/test/fixtures/ranking/cycle.sorter b/test/fixtures/ranking/cycle.sorter
new file mode 100644
index 0000000000000000000000000000000000000000..771731ae176e5d77e00ab89767ff2d7465bb7c6b
--- /dev/null
+++ b/test/fixtures/ranking/cycle.sorter
@@ -0,0 +1,12 @@
+#t4
+
+~/t4/a { node a }
+~/t4/b { node b }
+~/t4/c { node c }
+
+{ a > b }
+~/t4/a > ~/t4/b
+{ b > c }
+~/t4/b > ~/t4/c
+{ c > a }
+~/t4/c > ~/t4/a
diff --git a/test/fixtures/ranking/star.sorter b/test/fixtures/ranking/star.sorter
new file mode 100644
index 0000000000000000000000000000000000000000..135c9f9097d57b73c7ab18fac737ed3598d76fbe
--- /dev/null
+++ b/test/fixtures/ranking/star.sorter
@@ -0,0 +1,11 @@
+#repro
+
+~/repro/zebra { winner — beats both others }
+~/repro/alpha { loser — alphabetically first }
+~/repro/beta { loser — alphabetically middle }
+
+{ zebra beats alpha }
+~/repro/zebra > ~/repro/alpha
+
+{ zebra beats beta }
+~/repro/zebra > ~/repro/beta
diff --git a/test/fixtures/ranking/star_inverse.sorter b/test/fixtures/ranking/star_inverse.sorter
new file mode 100644
index 0000000000000000000000000000000000000000..dab842fa924e5124865ee216b9565f6c7471c812
--- /dev/null
+++ b/test/fixtures/ranking/star_inverse.sorter
@@ -0,0 +1,11 @@
+#t2
+
+~/t2/win { source of incoming edges (loses both) }
+~/t2/loss-a { winner }
+~/t2/loss-b { winner }
+
+{ loss-a beats win }
+~/t2/loss-a > ~/t2/win
+
+{ loss-b beats win }
+~/t2/loss-b > ~/t2/win
diff --git a/test/ranking.clj b/test/ranking.clj
new file mode 100644
index 0000000000000000000000000000000000000000..e1358783a84a264ee633bd79151ba29750b717cf
--- /dev/null
+++ b/test/ranking.clj
@@ -0,0 +1,74 @@
+(ns test.ranking
+ "Drives sorterc on .sorter fixtures and asserts ranking properties.
+
+ Regression coverage for issue #146 — pure forward star at default ratio
+ (2:1 for `>`) used to produce tied uniform scores because the random walk
+ on the normalized edge weights was bipartite. Fixed by switching to the
+ degree-based d_max from Negahban–Oh–Shah rank centrality (§3.1)."
+ (:require [clojure.test :refer [deftest is testing]]
+ [babashka.process :as p]
+ [cheshire.core :as json]
+ [clojure.java.io :as io]))
+
+(def sorterc-bin
+ "Path to the locally-built sorterc binary. Builds on demand if missing."
+ (let [dbg "target/debug/sorterc"
+ release "target/release/sorterc"]
+ (cond
+ (.exists (io/file release)) release
+ (.exists (io/file dbg)) dbg
+ :else
+ (do (println "building sorterc…")
+ (let [r (p/shell {:out :string :err :string :continue true}
+ "cargo build -p sorterc")]
+ (when-not (zero? (:exit r))
+ (throw (ex-info "cargo build -p sorterc failed"
+ {:stderr (:err r)}))))
+ dbg))))
+
+(defn compile-sorter [fixture-path]
+ (let [{:keys [out exit]} (p/shell {:out :string :err :string :continue true}
+ sorterc-bin "compile" fixture-path)]
+ (when-not (zero? exit)
+ (throw (ex-info "sorterc exit nonzero" {:fixture fixture-path :out out})))
+ (json/parse-string out true)))
+
+(defn first-component-ranking [result]
+ (-> result :rankings first :components first :ranking))
+
+(defn item-leaf [item]
+ (last (clojure.string/split item #"/")))
+
+(deftest chain-ranks-head-first
+ (let [ranking (first-component-ranking (compile-sorter "test/fixtures/ranking/chain.sorter"))
+ names (mapv (comp item-leaf :item) ranking)]
+ (is (= ["a" "b" "c"] names)
+ "chain a>b>c should rank a, b, c in order")
+ (is (apply > (map :score ranking))
+ "scores should attenuate strictly down the chain")))
+
+(deftest inverse-star-puts-winners-on-top
+ (let [ranking (first-component-ranking (compile-sorter "test/fixtures/ranking/star_inverse.sorter"))
+ names (mapv (comp item-leaf :item) ranking)]
+ (is (= "win" (last names))
+ "the item that lost to both others should be ranked last")))
+
+(deftest cycle-produces-uniform-scores
+ (let [ranking (first-component-ranking (compile-sorter "test/fixtures/ranking/cycle.sorter"))
+ scores (map :score ranking)]
+ (is (every? #(< (Math/abs (- % 1/3)) 1e-3) scores)
+ "a perfectly symmetric 3-cycle should give every node ~1/3")))
+
+(deftest star-topology-winner-at-top
+ ;; Issue #146 regression: source-only star at default `>` ratio (2:1).
+ ;; Pre-fix produced uniform 1/3 scores; alphabetical fallback put the
+ ;; unambiguous winner at the bottom. Post-fix the chain is aperiodic and
+ ;; converges to π_zebra = 1/2, π_alpha = π_beta = 1/4.
+ (let [ranking (first-component-ranking (compile-sorter "test/fixtures/ranking/star.sorter"))
+ names (mapv (comp item-leaf :item) ranking)
+ by-name (into {} (map (juxt (comp item-leaf :item) :score) ranking))]
+ (is (= "zebra" (first names))
+ "zebra won both votes and should rank #1")
+ (is (< (Math/abs (- (by-name "zebra") 0.5)) 1e-3))
+ (is (< (Math/abs (- (by-name "alpha") 0.25)) 1e-3))
+ (is (< (Math/abs (- (by-name "beta") 0.25)) 1e-3))))
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