Add per-arena CC:Ladder pages and "Has ladder" badge

- Arenas grid: add a 🪜 "Has ladder" badge (alongside the ✚ test-set
  badge) for arenas with `ladder: true`, plus a legend entry. Rename
  the test-set badge label from "environment" to "arena".
- Arena detail: show a "Has CC:Ladder" annotation linking to the
  on-page ladder section.
- Move the full Core War / RobotRumble Elo ranking tables out of the
  CC:Ladder blog post and onto their arena pages; blog now links to
  each arena's #cc-ladder section.
- Add a CC:Ladder section (intro, methodology, top-10 + full table) to
  Core War, RobotRumble, and BattleSnake arena pages. BattleSnake Elo
  computed from the ladder round-robin logs.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: john-b-yang

pages/arenas/battlesnake.md

@@ -6,6 +6,7 @@ date-added: 2025-11-04T16:58:27.268231Z
 players: 2+
 language: Python
 split: test
+ladder: true
 
 **What is BattleSnake?**
 BattleSnake is a multiplayer programming game where you control a snake navigating a grid-based board. Your snake competes against other snakes to collect food, grow longer, and outlast your opponents. The last snake alive wins.
@@ -21,6 +22,91 @@ Success requires balancing multiple objectives: finding food to avoid starvation
 
 ---
 
+<h2 id="cc-ladder">🪜 CC:Ladder</h2>
+
+BattleSnake has a **CC:Ladder** — a ranked ladder of open-source human snakes that turns the arena into a hill-climbable evaluation. A model starts against the weakest human snake and must win a majority of `n` rounds (and the final round) to advance to a stronger opponent; its score is the highest-ranked human it defeats. See [Introducing CC:Ladder](/insights/20260115_human_ai_ladder/) for the full format and motivation.
+
+The ladder is built from **50 open-source human BattleSnakes** (hosted as `human/*` branches on [CodeClash-ai/BattleSnake](https://github.com/CodeClash-ai/BattleSnake)). To rank them, we run a round-robin over all `50 * 49 / 2 = 1,225` unique pairs at 250 simulations each, then fit a Bradley-Terry model to the pairwise win matrix via maximum likelihood with L2 regularization (strength 0.01, base Elo 1200, slope 400).
+
+The top ten:
+
+1. human/smallsco/robosnake: **1882.8**
+2. human/jhawthorn/snek: **1814.4**
+3. human/tyrelh/tyrelh-2019: **1631.7**
+4. human/aleksiy325/snek-two: **1617.1**
+5. human/hirethissnake/sneaky-snake: **1519.2**
+6. human/tbgiles/feisty-snake: **1518.8**
+7. human/Petah/project-z: **1516.6**
+8. human/woofers/woofers-java: **1500.8**
+9. human/noahspriggs/tr-8r: **1472.6**
+10. human/tyrelh/tyrelh-2018: **1457.2**
+
+<details>
+<summary>Show full BattleSnake rankings</summary>
+
+<ol>
+<li>human/smallsco/robosnake: <b>1882.8</b></li>
+<li>human/jhawthorn/snek: <b>1814.4</b></li>
+<li>human/tyrelh/tyrelh-2019: <b>1631.7</b></li>
+<li>human/aleksiy325/snek-two: <b>1617.1</b></li>
+<li>human/hirethissnake/sneaky-snake: <b>1519.2</b></li>
+<li>human/tbgiles/feisty-snake: <b>1518.8</b></li>
+<li>human/Petah/project-z: <b>1516.6</b></li>
+<li>human/woofers/woofers-java: <b>1500.8</b></li>
+<li>human/noahspriggs/tr-8r: <b>1472.6</b></li>
+<li>human/tyrelh/tyrelh-2018: <b>1457.2</b></li>
+<li>human/MorganConrad/sisiutl: <b>1451.7</b></li>
+<li>human/altersaddle/untimely-neglected-wearable: <b>1447.8</b></li>
+<li>human/JerryKott/jerrykott-2017: <b>1427.7</b></li>
+<li>human/rdbrck/bountysnake2018: <b>1415.3</b></li>
+<li>human/zakwht/zakwht-2018: <b>1395.9</b></li>
+<li>human/tyrelh/tyrelh-python: <b>1383.5</b></li>
+<li>human/joshhartmann11/battlejake: <b>1381.1</b></li>
+<li>human/xtagon/nagini: <b>1376.4</b></li>
+<li>human/TheApX/hungry: <b>1369.7</b></li>
+<li>human/kentmacdonald2/beames: <b>1364.2</b></li>
+<li>human/coreyja/famished-frank: <b>1357.7</b></li>
+<li>human/joshhartmann11/battlejake2019: <b>1338.8</b></li>
+<li>human/ChaelCodes/cornelius: <b>1330.1</b></li>
+<li>human/MorganConrad/tantilla: <b>1305.7</b></li>
+<li>human/jackisherwood/battlesnake-elon: <b>1276.4</b></li>
+<li>human/Flipez/flipez-crystal: <b>1260.7</b></li>
+<li>human/coreyja/gigantic-george: <b>1259.6</b></li>
+<li>human/coreyja/eremetic-eric: <b>1252.0</b></li>
+<li>human/nbw/nbw-ruby: <b>1193.8</b></li>
+<li>human/OliverMKing/astar-snake: <b>1185.7</b></li>
+<li>human/coreyja/amphibious-arthur: <b>1182.4</b></li>
+<li>human/moxuz/pinky-snek: <b>1100.5</b></li>
+<li>human/Spenca/vulture-snake: <b>1051.6</b></li>
+<li>human/rdbrck/btas: <b>1045.0</b></li>
+<li>human/tim-hub/awesome-snake: <b>1037.1</b></li>
+<li>human/zacpez/scape-goat: <b>1001.1</b></li>
+<li>human/coreyja/jump-flooding: <b>1001.0</b></li>
+<li>human/coreyja/coreyja-rs: <b>969.3</b></li>
+<li>human/coreyja/bombastic-bob: <b>965.2</b></li>
+<li>human/ccSnake2018/ccsnake: <b>920.8</b></li>
+<li>human/Xe/since: <b>892.1</b></li>
+<li>human/nbw/nbw-crystal: <b>875.4</b></li>
+<li>human/m-schier/kreuzotter: <b>831.8</b></li>
+<li>human/coreyja/devious-devin: <b>730.4</b></li>
+<li>human/graeme-hill/snakebot: <b>712.5</b></li>
+<li>human/coreyja/improbable-irene: <b>702.2</b></li>
+<li>human/csauve/bookworm: <b>693.8</b></li>
+<li>human/Nettogrof/nessegrev-java: <b>647.3</b></li>
+<li>human/Nettogrof/nessegrev-julia: <b>556.2</b></li>
+<li>human/pambrose/pambrose-kotlin: <b>379.2</b></li>
+</ol>
+
+</details>
+
+**Run it yourself.** [Set up CodeClash](https://docs.codeclash.ai/quickstart/#installation) and send a model up the ladder with:
+
+<pre class="prettyprint lang-bash">
+uv run codeclash ladder run configs/ablations/ladder/battlesnake.yaml
+</pre>
+
+---
+
 ### References
 
 * [BattleSnake Official Documentation](https://docs.battlesnake.com/)