model: runtime override via /model slash; fixes for port + bind

- runtime model override: Bus::{model,set_model} + POST /api/model
  (form-encoded {model: name}). turn.rs reads bus.model() per turn
  so a flip lands on the next claude invocation. /api/state grows
  a model field; agent page shows a 'model · <name>' chip in the
  state row. '/model <name>' slash command POSTs to the endpoint
  and refreshes state.

- port regression fix: agent_web_port no longer probes forward for
  *existing* agents (the previous fix shifted ports for any agent
  without a port file, including legacy ones whose container was
  already bound to the bare hashed port — dashboard rendered the
  new port, container was still on the old one, conn errors). new
  rule: port file exists → use it; absent + applied flake present
  → legacy, persist port_hash without probing; absent + no applied
  flake → fresh spawn, probe forward.

- SO_REUSEADDR on both the dashboard and per-agent web UI binds
  via tokio::net::TcpSocket. operator hit 12 retries failing on
  manager :8000 — REUSEADDR handles the TIME_WAIT case cleanly
  without a new dep; retry still covers the genuine
  process-still-alive overlap.

todo: drops the model-override entry (shipped); adds two new
items — model persistence (optional, future), and custom
per-agent MCP tools (groundwork for moving bitburner-agent into
hyperhive).

hive-ag3nt/src/events.rs

@@ -140,6 +140,13 @@ 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).
+pub const DEFAULT_MODEL: &str = "haiku";
+
 #[derive(Clone)]
 pub struct Bus {
     tx: Arc<broadcast::Sender<LiveEvent>>,
@@ -149,6 +156,9 @@ pub struct Bus {
     store: Option<Arc<EventStore>>,
     /// Current turn-loop state + since-when (unix seconds).
     state: Arc<Mutex<(TurnState, i64)>>,
+    /// Model name passed to `claude --model`. Default `haiku`; the
+    /// operator can override at runtime via `POST /api/model`.
+    model: Arc<Mutex<String>>,
 }
 
 impl Bus {
@@ -171,9 +181,23 @@ impl Bus {
             tx: Arc::new(tx),
             store,
             state: Arc::new(Mutex::new((TurnState::Idle, now_unix()))),
+            model: Arc::new(Mutex::new(DEFAULT_MODEL.to_owned())),
         }
     }
 
+    /// Currently-selected claude model name. Read on every turn so a
+    /// `/model <name>` flip takes effect on the next turn.
+    #[must_use]
+    pub fn model(&self) -> String {
+        self.model.lock().unwrap().clone()
+    }
+
+    /// Switch the model for future turns. The current turn (if any)
+    /// keeps the model it was already running.
+    pub fn set_model(&self, name: impl Into<String>) {
+        *self.model.lock().unwrap() = name.into();
+    }
+
     /// Update the harness's authoritative turn-loop state. Records
     /// the transition time so `state_snapshot` can return a since-age.
     pub fn set_state(&self, next: TurnState) {