model/context: configurable default model + model-derived context window

hive-ag3nt/src/events.rs

@@ -275,13 +275,51 @@ pub enum TurnState {
     Compacting,
 }
 
-/// Default claude model when nothing's been set at runtime. The
-/// operator can switch via `/model <name>` in the web terminal; the
-/// chosen model lives in `Bus::model` for the rest of the harness
-/// process's life (resets on restart, by design — operator overrides
-/// shouldn't survive accidentally).
+/// Default claude model when nothing's been set at runtime. Overridable
+/// via the `HIVE_DEFAULT_MODEL` env var (set from `hyperhive.model` in
+/// the container's `agent.nix`). The operator can also switch at runtime
+/// via `/model <name>` in the web terminal; the chosen model is persisted
+/// to the state dir so it survives restarts.
 pub const DEFAULT_MODEL: &str = "haiku";
 
+/// Return the initial default model name: `HIVE_DEFAULT_MODEL` env var if
+/// set to a non-empty string, otherwise `DEFAULT_MODEL`.
+#[must_use]
+pub fn default_model() -> &'static str {
+    // Leak once at startup — acceptable for a single config value.
+    std::env::var("HIVE_DEFAULT_MODEL")
+        .ok()
+        .filter(|s| !s.trim().is_empty())
+        .map_or(DEFAULT_MODEL, |s| Box::leak(s.into_boxed_str()))
+}
+
+/// Context-window size in tokens for a given model name.
+///
+/// Recognises the model families that Claude Code supports:
+/// - `haiku` family: 200 000 tokens
+/// - `sonnet` / `opus` families: 1 000 000 tokens
+/// - anything else: 200 000 tokens (conservative default)
+///
+/// Overridable at runtime via `HIVE_CONTEXT_WINDOW_TOKENS` (useful for
+/// future models or when the operator knows the exact limit). The env
+/// var takes precedence over the model-name heuristic.
+#[must_use]
+pub fn context_window_tokens(model: &str) -> u64 {
+    if let Ok(s) = std::env::var("HIVE_CONTEXT_WINDOW_TOKENS") {
+        if let Ok(v) = s.trim().parse::<u64>() {
+            if v > 0 {
+                return v;
+            }
+        }
+    }
+    let m = model.to_ascii_lowercase();
+    if m.contains("sonnet") || m.contains("opus") {
+        1_000_000
+    } else {
+        200_000
+    }
+}
+
 #[derive(Clone)]
 pub struct Bus {
     tx: Arc<broadcast::Sender<BusEvent>>,
@@ -351,7 +389,7 @@ impl Bus {
             }
         };
         let (tx, _) = broadcast::channel(CHANNEL_CAPACITY);
-        let initial_model = load_model().unwrap_or_else(|| DEFAULT_MODEL.to_owned());
+        let initial_model = load_model().unwrap_or_else(|| default_model().to_owned());
         // Restore rate_limited from the sentinel file — if the harness
         // crashed while parked, we should still show the right status on
         // cold load until the next turn clears it.