review: update default model prices to current Anthropic list pricing

Per operator request on the PR: the built-in/default prices were the old
Claude 3 numbers (opus 15/75, etc.). Update opus + haiku to the current
Claude 4.x family list pricing (cache_write = the default 5-minute cache
TTL); sonnet was already correct:

- opus:   input 5, output 25, cache_read 0.5,  cache_write 6.25
- sonnet: input 3, output 15, cache_read 0.3,  cache_write 3.75  (unchanged)
- haiku:  input 1, output 5,  cache_read 0.1,  cache_write 1.25

Updated in both builtin_prices (hive_stats.rs) and the nix modelPrices
default (hive-c0re.nix), with cross-reference "keep in sync" notes on
both sides. Also addresses the earlier reviewer note: dropped the
over-strong "single source of truth" wording in the --model-prices arg
doc (the nix default does mirror the numbers in production).

hive-c0re/src/hive_stats.rs

@@ -98,23 +98,27 @@ pub struct Prices {
 /// every model uses [`builtin_prices`].
 pub type PriceTable = HashMap<String, Prices>;
 
-/// Built-in fallback pricing — the historical hard-coded table. Used
+/// Built-in fallback pricing, per **million** tokens. Used when the
-/// when the operator's [`PriceTable`] has no key matching the model.
+/// operator's [`PriceTable`] has no key matching the model. Figures are
+/// current Anthropic list prices for the Claude 4.x family (Opus 4.x,
+/// Sonnet 4.x, Haiku 4.5); `cache_write` uses the default 5-minute
+/// cache-TTL price. Keep in sync with the `services.hyperhive.modelPrices`
+/// nix default (`nix/modules/hive-c0re.nix`).
 fn builtin_prices(model: &str) -> Prices {
     let m = model.to_ascii_lowercase();
     if m.contains("opus") {
         Prices {
-            input: 15.0,
+            input: 5.0,
-            output: 75.0,
+            output: 25.0,
-            cache_read: 1.5,
+            cache_read: 0.5,
-            cache_write: 18.75,
+            cache_write: 6.25,
         }
     } else if m.contains("haiku") {
         Prices {
-            input: 0.8,
+            input: 1.0,
-            output: 4.0,
+            output: 5.0,
-            cache_read: 0.08,
+            cache_read: 0.1,
-            cache_write: 1.0,
+            cache_write: 1.25,
         }
     } else {
         // sonnet + unknown fallback

hive-c0re/src/main.rs

@@ -89,9 +89,10 @@ enum Cmd {
         /// model id; models not covered fall back to the built-in
         /// estimate. Set via the `services.hyperhive.modelPrices` NixOS
         /// option (whose default carries the full opus/sonnet/haiku
-        /// table). Defaults to `{}` here so a bare `hive-c0re serve`
+        /// table — kept in sync with the in-code `builtin_prices`).
-        /// leans entirely on the in-code `builtin_prices` fallback —
+        /// Defaults to `{}` here so a bare `hive-c0re serve` leans
-        /// keeping a single source of truth for the numbers.
+        /// entirely on `builtin_prices`; the NixOS default (every real
+        /// deployment) shadows it with the same operator-tunable table.
         #[arg(long, default_value = "{}")]
         model_prices: String,
     },

nix/modules/hive-c0re.nix

@@ -446,12 +446,16 @@ in
           };
         }
       );
+      # Current Anthropic list prices for the Claude 4.x family (Opus
+      # 4.x, Sonnet 4.x, Haiku 4.5); cache_write is the default 5-minute
+      # cache-TTL price. Keep in sync with `builtin_prices` in
+      # hive-c0re/src/hive_stats.rs.
       default = {
         opus = {
-          input = 15.0;
+          input = 5.0;
-          output = 75.0;
+          output = 25.0;
-          cache_read = 1.5;
+          cache_read = 0.5;
-          cache_write = 18.75;
+          cache_write = 6.25;
         };
         sonnet = {
           input = 3.0;
@@ -460,10 +464,10 @@ in
           cache_write = 3.75;
         };
         haiku = {
-          input = 0.8;
+          input = 1.0;
-          output = 4.0;
+          output = 5.0;
-          cache_read = 0.08;
+          cache_read = 0.1;
-          cache_write = 1.0;
+          cache_write = 1.25;
         };
       };
       example = {