remove random selection policy — consumers can shuffle client-side

Plano should only handle ranking that requires server-side data
(cost metrics, latency). Random shuffling is trivial for callers.

config/plano_config_schema.yaml

@@ -493,7 +493,6 @@ properties:
               enum:
                 - cheapest
                 - fastest
-                - random
                 - none
           additionalProperties: false
           required:

crates/brightstaff/src/router/model_metrics.rs

@@ -126,7 +126,6 @@ impl ModelMetricsService {
                 }
                 rank_by_ascending_metric(models, &data)
             }
-            SelectionPreference::Random => shuffle(models),
             SelectionPreference::None => models.to_vec(),
         }
     }
@@ -161,24 +160,6 @@ fn rank_by_ascending_metric(models: &[String], data: &HashMap<String, f64>) -> V
         .collect()
 }
 
-fn shuffle(models: &[String]) -> Vec<String> {
-    use std::time::{SystemTime, UNIX_EPOCH};
-    let seed = SystemTime::now()
-        .duration_since(UNIX_EPOCH)
-        .map(|d| d.subsec_nanos() as usize)
-        .unwrap_or(0);
-    let mut result = models.to_vec();
-    let mut state = seed;
-    for i in (1..result.len()).rev() {
-        state = state
-            .wrapping_mul(6364136223846793005)
-            .wrapping_add(1442695040888963407);
-        let j = state % (i + 1);
-        result.swap(i, j);
-    }
-    result
-}
-
 #[derive(serde::Deserialize)]
 struct CostEntry {
     input_per_million: f64,

crates/common/src/configuration.rs

@@ -109,7 +109,6 @@ pub enum StateStorageType {
 pub enum SelectionPreference {
     Cheapest,
     Fastest,
-    Random,
     /// Return models in the same order they were defined — no reordering.
     None,
 }

docs/routing-api.md

@@ -41,7 +41,7 @@ POST /v1/chat/completions
 | `name` | string | yes | Route identifier. Must match the LLM router's route classification. |
 | `description` | string | yes | Natural language description used by the router to match user intent. |
 | `models` | string[] | yes | Ordered candidate pool. At least one entry required. Must be declared in `model_providers`. |
-| `selection_policy.prefer` | enum | yes | How to rank models: `cheapest`, `fastest`, `random`, or `none`. |
+| `selection_policy.prefer` | enum | yes | How to rank models: `cheapest`, `fastest`, or `none`. |
 
 ### `selection_policy.prefer` values
 
@@ -49,7 +49,6 @@ POST /v1/chat/completions
 |---|---|
 | `cheapest` | Sort by ascending cost from the metrics endpoint. Models with no data appended last. |
 | `fastest` | Sort by ascending latency from the metrics endpoint. Models with no data appended last. |
-| `random` | Shuffle the model list randomly on each request. |
 | `none` | Return models in the order they were defined — no reordering. |
 
 ### Notes