refactor(api): rename IndexMap to KeyTable

The former name collided with the popular indexmap crate. KeyTable
lives in its own module. Public API unchanged beyond the rename.

Part of T2 of docs/superpowers/specs/2026-04-23-trueskill-engine-redesign-design.md.

benches/batch.rs

@@ -1,11 +1,11 @@
 use criterion::{Criterion, criterion_group, criterion_main};
 use trueskill_tt::{
-    BETA, GAMMA, IndexMap, MU, P_DRAW, SIGMA, agent::Agent, batch::Batch, drift::ConstantDrift,
+    BETA, GAMMA, KeyTable, MU, P_DRAW, SIGMA, agent::Agent, batch::Batch, drift::ConstantDrift,
     gaussian::Gaussian, player::Player, storage::AgentStore,
 };
 
 fn criterion_benchmark(criterion: &mut Criterion) {
-    let mut index = IndexMap::new();
+    let mut index = KeyTable::new();
 
     let a = index.get_or_create("a");
     let b = index.get_or_create("b");

examples/atp.rs

@@ -1,6 +1,6 @@
 use plotters::prelude::*;
 use time::{Date, Month};
-use trueskill_tt::{History, IndexMap};
+use trueskill_tt::{History, KeyTable};
 
 fn main() {
     let mut csv = csv::Reader::open("examples/atp.csv").unwrap();
@@ -12,7 +12,7 @@ fn main() {
     let from = Date::from_calendar_date(1900, Month::January, 1).unwrap();
     let time_format = time::format_description::parse("[year]-[month]-[day]").unwrap();
 
-    let mut index_map = IndexMap::new();
+    let mut index_map = KeyTable::new();
 
     for row in csv.records() {
         if &row["double"] == "t" {

src/batch.rs

@@ -400,12 +400,12 @@ mod tests {
 
     use super::*;
     use crate::{
-        IndexMap, agent::Agent, drift::ConstantDrift, player::Player, storage::AgentStore,
+        KeyTable, agent::Agent, drift::ConstantDrift, player::Player, storage::AgentStore,
     };
 
     #[test]
     fn test_one_event_each() {
-        let mut index_map = IndexMap::new();
+        let mut index_map = KeyTable::new();
 
         let a = index_map.get_or_create("a");
         let b = index_map.get_or_create("b");
@@ -481,7 +481,7 @@ mod tests {
 
     #[test]
     fn test_same_strength() {
-        let mut index_map = IndexMap::new();
+        let mut index_map = KeyTable::new();
 
         let a = index_map.get_or_create("a");
         let b = index_map.get_or_create("b");
@@ -560,7 +560,7 @@ mod tests {
 
     #[test]
     fn test_add_events() {
-        let mut index_map = IndexMap::new();
+        let mut index_map = KeyTable::new();
 
         let a = index_map.get_or_create("a");
         let b = index_map.get_or_create("b");

src/history.rs

@@ -437,13 +437,13 @@ mod tests {
 
     use super::*;
     use crate::{
-        ConstantDrift, EPSILON, Game, Gaussian, ITERATIONS, IndexMap, P_DRAW, Player,
+        ConstantDrift, EPSILON, Game, Gaussian, ITERATIONS, KeyTable, P_DRAW, Player,
         arena::ScratchArena,
     };
 
     #[test]
     fn test_init() {
-        let mut index_map = IndexMap::new();
+        let mut index_map = KeyTable::new();
 
         let a = index_map.get_or_create("a");
         let b = index_map.get_or_create("b");
@@ -513,7 +513,7 @@ mod tests {
 
     #[test]
     fn test_one_batch() {
-        let mut index_map = IndexMap::new();
+        let mut index_map = KeyTable::new();
 
         let a = index_map.get_or_create("a");
         let b = index_map.get_or_create("b");
@@ -620,7 +620,7 @@ mod tests {
 
     #[test]
     fn test_learning_curves() {
-        let mut index_map = IndexMap::new();
+        let mut index_map = KeyTable::new();
 
         let a = index_map.get_or_create("a");
         let b = index_map.get_or_create("b");
@@ -674,7 +674,7 @@ mod tests {
 
     #[test]
     fn test_env_ttt() {
-        let mut index_map = IndexMap::new();
+        let mut index_map = KeyTable::new();
 
         let a = index_map.get_or_create("a");
         let b = index_map.get_or_create("b");
@@ -721,7 +721,7 @@ mod tests {
 
     #[test]
     fn test_teams() {
-        let mut index_map = IndexMap::new();
+        let mut index_map = KeyTable::new();
 
         let a = index_map.get_or_create("a");
         let b = index_map.get_or_create("b");
@@ -811,7 +811,7 @@ mod tests {
 
     #[test]
     fn test_add_events() {
-        let mut index_map = IndexMap::new();
+        let mut index_map = KeyTable::new();
 
         let a = index_map.get_or_create("a");
         let b = index_map.get_or_create("b");
@@ -900,7 +900,7 @@ mod tests {
 
     #[test]
     fn test_only_add_events() {
-        let mut index_map = IndexMap::new();
+        let mut index_map = KeyTable::new();
 
         let a = index_map.get_or_create("a");
         let b = index_map.get_or_create("b");
@@ -989,7 +989,7 @@ mod tests {
 
     #[test]
     fn test_log_evidence() {
-        let mut index_map = IndexMap::new();
+        let mut index_map = KeyTable::new();
 
         let a = index_map.get_or_create("a");
         let b = index_map.get_or_create("b");
@@ -1048,7 +1048,7 @@ mod tests {
 
     #[test]
     fn test_add_events_with_time() {
-        let mut index_map = IndexMap::new();
+        let mut index_map = KeyTable::new();
 
         let a = index_map.get_or_create("a");
         let b = index_map.get_or_create("b");
@@ -1237,7 +1237,7 @@ mod tests {
 
     #[test]
     fn test_1vs1_weighted() {
-        let mut index_map = IndexMap::new();
+        let mut index_map = KeyTable::new();
 
         let a = index_map.get_or_create("a");
         let b = index_map.get_or_create("b");

src/key_table.rs

@@ -0,0 +1,72 @@
+use std::{
+    borrow::{Borrow, ToOwned},
+    collections::HashMap,
+    hash::Hash,
+};
+
+use crate::Index;
+
+/// Maps user keys to internal `Index` handles.
+///
+/// Renamed from the former `IndexMap` to avoid colliding with the `indexmap`
+/// crate. Power users can promote `&K` to `Index` via `get_or_create` and
+/// skip the lookup on subsequent hot-path calls.
+#[derive(Debug)]
+pub struct KeyTable<K>(HashMap<K, Index>);
+
+impl<K> KeyTable<K>
+where
+    K: Eq + Hash,
+{
+    pub fn new() -> Self {
+        Self(HashMap::new())
+    }
+
+    pub fn get<Q: ?Sized + Hash + Eq + ToOwned<Owned = K>>(&self, k: &Q) -> Option<Index>
+    where
+        K: Borrow<Q>,
+    {
+        self.0.get(k).cloned()
+    }
+
+    pub fn get_or_create<Q: ?Sized + Hash + Eq + ToOwned<Owned = K>>(&mut self, k: &Q) -> Index
+    where
+        K: Borrow<Q>,
+    {
+        if let Some(idx) = self.0.get(k) {
+            *idx
+        } else {
+            let idx = Index::from(self.0.len());
+            self.0.insert(k.to_owned(), idx);
+            idx
+        }
+    }
+
+    pub fn key(&self, idx: Index) -> Option<&K> {
+        self.0
+            .iter()
+            .find(|&(_, value)| *value == idx)
+            .map(|(key, _)| key)
+    }
+
+    pub fn keys(&self) -> impl Iterator<Item = &K> {
+        self.0.keys()
+    }
+
+    pub fn len(&self) -> usize {
+        self.0.len()
+    }
+
+    pub fn is_empty(&self) -> bool {
+        self.0.is_empty()
+    }
+}
+
+impl<K> Default for KeyTable<K>
+where
+    K: Eq + Hash,
+{
+    fn default() -> Self {
+        KeyTable::new()
+    }
+}

src/lib.rs

@@ -1,9 +1,6 @@
 use std::{
-    borrow::{Borrow, ToOwned},
     cmp::Reverse,
-    collections::HashMap,
     f64::consts::{FRAC_1_SQRT_2, FRAC_2_SQRT_PI, SQRT_2},
-    hash::Hash,
 };
 
 pub mod agent;
@@ -17,6 +14,7 @@ pub(crate) mod factor;
 mod game;
 pub mod gaussian;
 mod history;
+pub mod key_table;
 mod matrix;
 pub mod player;
 pub(crate) mod schedule;
@@ -27,6 +25,7 @@ pub use error::InferenceError;
 pub use game::Game;
 pub use gaussian::Gaussian;
 pub use history::History;
+pub use key_table::KeyTable;
 use matrix::Matrix;
 pub use player::Player;
 pub use schedule::ScheduleReport;
@@ -54,59 +53,6 @@ impl From<usize> for Index {
     }
 }
 
-pub struct IndexMap<K>(HashMap<K, Index>);
-
-impl<K> IndexMap<K>
-where
-    K: Eq + Hash,
-{
-    pub fn new() -> Self {
-        Self(HashMap::new())
-    }
-
-    pub fn get<Q: ?Sized + Hash + Eq + ToOwned<Owned = K>>(&self, k: &Q) -> Option<Index>
-    where
-        K: Borrow<Q>,
-    {
-        self.0.get(k).cloned()
-    }
-
-    pub fn get_or_create<Q: ?Sized + Hash + Eq + ToOwned<Owned = K>>(&mut self, k: &Q) -> Index
-    where
-        K: Borrow<Q>,
-    {
-        if let Some(idx) = self.0.get(k) {
-            *idx
-        } else {
-            let idx = Index::from(self.0.len());
-
-            self.0.insert(k.to_owned(), idx);
-
-            idx
-        }
-    }
-
-    pub fn key(&self, idx: Index) -> Option<&K> {
-        self.0
-            .iter()
-            .find(|&(_, value)| *value == idx)
-            .map(|(key, _)| key)
-    }
-
-    pub fn keys(&self) -> impl Iterator<Item = &K> {
-        self.0.keys()
-    }
-}
-
-impl<K> Default for IndexMap<K>
-where
-    K: Eq + Hash,
-{
-    fn default() -> Self {
-        IndexMap::new()
-    }
-}
-
 fn erfc(x: f64) -> f64 {
     let z = x.abs();
     let t = 1.0 / (1.0 + z / 2.0);