swarm: per-agent inference settings (model, effort, subagent_models) in KV

swarm-controller keeps each agent's inference settings in a new
`agent-inference` KV bucket, one key per agent, and is its only writer
(`GET`/`PUT`/`DELETE /api/agents/{name}/inference`; `swarmctl agent
inference get|set|clear`). Every field is optional. Each agent reads its
own key every 10 s through a direct-get grant on that key alone, and a
set `model` or `effort` replaces the Bus value, so the next turn runs on
it and the badge follows.

The swarm value is applied without persisting it: `Bus::set_model` and
`set_effort` are split into a persisting setter and a non-persisting
`apply_*`, and the poller uses the latter. Otherwise the swarm value
would overwrite `hyperhive-model`/`hyperhive-effort`, and clearing it, or
a restart, would no longer find the agent's own value. An unset field
changes nothing; a field cleared after being applied goes back to the
local value (`harness_state::local_model`/`local_effort`, the same
resolution `Bus::new` uses), read again at the clear.

`subagent_models` is validated, stored and shown by `get`; no agent
applies it yet.

Refs #5034

hive-agent/src/swarm_inference.rs

@@ -0,0 +1,316 @@
+//! Applies the model and effort the swarm sets for this agent.
+//!
+//! swarm-controller keeps the agent's settings under its key in the
+//! `agent-inference` KV bucket. This task reads that key every
+//! [`POLL_INTERVAL`] with the one subject the agent's own queue credential is
+//! granted there (`swarm_queue_client::agent_inference::read_own`).
+//!
+//! **A set field wins**: it replaces the Bus value, so the next turn runs on
+//! it and the web UI's badge follows. It is not persisted: `hyperhive-model`
+//! and `hyperhive-effort` keep the agent's local value.
+//!
+//! **An unset field changes nothing**, so an agent the swarm sets nothing for
+//! runs on its local value ([`crate::harness_state::local_model`] and
+//! [`crate::harness_state::local_effort`]). A field that was set and then
+//! cleared goes back to that local value, read again at that moment.
+//!
+//! A failed read changes nothing. Until the first successful read after a
+//! start, the agent runs on its local values.
+//!
+//! `subagent_models` is not read here.
+
+use std::time::Duration;
+
+use swarm_queue_client::agent_inference::{AgentInference, Effort, Read, read_own};
+
+use crate::events::Bus;
+use crate::harness_state::{configured_effort, configured_model, local_effort, local_model};
+
+/// How often the key is read. Also the longest a change can take to reach
+/// the agent's next turn.
+const POLL_INTERVAL: Duration = Duration::from_secs(10);
+
+/// Where the settings are applied, and where the local values come from.
+trait Target {
+    fn model(&self) -> String;
+    fn effort(&self) -> String;
+    fn apply_model(&self, value: String);
+    fn apply_effort(&self, value: String);
+    fn local_model(&self) -> String;
+    fn local_effort(&self) -> String;
+}
+
+/// The harness's Bus, with the nix values read once at start.
+struct Harness {
+    bus: Bus,
+    nix_model: Option<&'static str>,
+    nix_effort: Option<&'static str>,
+}
+
+impl Target for Harness {
+    fn model(&self) -> String {
+        self.bus.model()
+    }
+    fn effort(&self) -> String {
+        self.bus.effort()
+    }
+    fn apply_model(&self, value: String) {
+        self.bus.apply_model(value);
+    }
+    fn apply_effort(&self, value: String) {
+        self.bus.apply_effort(value);
+    }
+    fn local_model(&self) -> String {
+        local_model(self.nix_model)
+    }
+    fn local_effort(&self) -> String {
+        local_effort(self.nix_effort)
+    }
+}
+
+/// Which fields currently carry the swarm's value.
+#[derive(Debug, Default)]
+struct Overridden {
+    model: bool,
+    effort: bool,
+}
+
+/// What one field should become: the swarm's value while it sets one, the
+/// local value on the read after it stops, and otherwise `None` (left alone).
+/// Also `None` when the value is already what it should be.
+fn next(
+    swarm: Option<&str>,
+    overridden: &mut bool,
+    current: &str,
+    local: impl FnOnce() -> String,
+) -> Option<String> {
+    let wanted = match swarm {
+        Some(value) => {
+            *overridden = true;
+            value.to_owned()
+        }
+        None if std::mem::take(overridden) => local(),
+        None => return None,
+    };
+    (wanted != current).then_some(wanted)
+}
+
+impl Overridden {
+    /// Apply one read of the key to `target`.
+    fn apply(&mut self, read: &AgentInference, target: &impl Target) {
+        if let Some(model) = next(
+            read.model.as_deref(),
+            &mut self.model,
+            &target.model(),
+            || target.local_model(),
+        ) {
+            tracing::info!(%model, swarm = self.model, "inference: switching model");
+            target.apply_model(model);
+        }
+        if let Some(effort) = next(
+            read.effort.map(Effort::as_str),
+            &mut self.effort,
+            &target.effort(),
+            || target.local_effort(),
+        ) {
+            tracing::info!(%effort, swarm = self.effort, "inference: switching effort");
+            target.apply_effort(effort);
+        }
+    }
+}
+
+/// Run the poller for the harness's lifetime, if this agent has a label to
+/// name its key with.
+pub async fn run(bus: Bus) {
+    let agent = crate::identity::label();
+    if agent.is_empty() {
+        tracing::warn!("this agent has no label; not reading its swarm inference settings");
+        return;
+    }
+    let target = Harness {
+        bus,
+        nix_model: configured_model(),
+        nix_effort: configured_effort(),
+    };
+    let client = crate::swarm_queue::client().await;
+    tracing::info!(%agent, "reading swarm inference settings from the swarm queue");
+    let mut overridden = Overridden::default();
+    loop {
+        if let Some(read) = read(&client, &agent).await {
+            overridden.apply(&read, &target);
+        }
+        tokio::time::sleep(POLL_INTERVAL).await;
+    }
+}
+
+/// The key's current value, or `None` when it could not be read.
+async fn read(client: &async_nats::Client, agent: &str) -> Option<AgentInference> {
+    // An unconnected client does not fail a JetStream request, it hangs on it.
+    swarm_queue_client::ensure_connected(client).ok()?;
+    match read_own(client, agent).await {
+        Ok(Read::Current(current)) => Some(current),
+        Ok(Read::NoBucket) => {
+            tracing::debug!("inference: the agent-inference bucket does not answer yet");
+            None
+        }
+        Err(e) => {
+            tracing::warn!(error = %e, "inference: reading this agent's settings failed");
+            None
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::cell::RefCell;
+
+    use super::*;
+
+    /// A Bus stand-in recording every apply.
+    struct Fake {
+        model: RefCell<String>,
+        effort: RefCell<String>,
+        local_model: RefCell<String>,
+        local_effort: String,
+        applies: RefCell<usize>,
+    }
+
+    impl Fake {
+        fn new() -> Self {
+            Self {
+                model: RefCell::new("sonnet".to_owned()),
+                effort: RefCell::new("medium".to_owned()),
+                local_model: RefCell::new("sonnet".to_owned()),
+                local_effort: "medium".to_owned(),
+                applies: RefCell::new(0),
+            }
+        }
+        fn now(&self) -> (String, String) {
+            (self.model.borrow().clone(), self.effort.borrow().clone())
+        }
+    }
+
+    impl Target for Fake {
+        fn model(&self) -> String {
+            self.model.borrow().clone()
+        }
+        fn effort(&self) -> String {
+            self.effort.borrow().clone()
+        }
+        fn apply_model(&self, value: String) {
+            *self.applies.borrow_mut() += 1;
+            *self.model.borrow_mut() = value;
+        }
+        fn apply_effort(&self, value: String) {
+            *self.applies.borrow_mut() += 1;
+            *self.effort.borrow_mut() = value;
+        }
+        fn local_model(&self) -> String {
+            self.local_model.borrow().clone()
+        }
+        fn local_effort(&self) -> String {
+            self.local_effort.clone()
+        }
+    }
+
+    fn set(model: Option<&str>, effort: Option<Effort>) -> AgentInference {
+        AgentInference {
+            model: model.map(str::to_owned),
+            effort,
+            subagent_models: None,
+        }
+    }
+
+    fn pair(model: &str, effort: &str) -> (String, String) {
+        (model.to_owned(), effort.to_owned())
+    }
+
+    #[test]
+    fn a_set_field_replaces_the_bus_value() {
+        let fake = Fake::new();
+        let mut o = Overridden::default();
+        o.apply(&set(Some("opus"), Some(Effort::High)), &fake);
+        assert_eq!(fake.now(), pair("opus", "high"));
+        // Re-reading the same value applies nothing again.
+        o.apply(&set(Some("opus"), Some(Effort::High)), &fake);
+        assert_eq!(*fake.applies.borrow(), 2);
+    }
+
+    /// An absent key, and a key with every field unset, leave the agent on
+    /// whatever it runs now — even when that differs from its local value.
+    #[test]
+    fn an_absent_key_leaves_the_bus_alone() {
+        let fake = Fake::new();
+        *fake.model.borrow_mut() = "haiku".to_owned();
+        let mut o = Overridden::default();
+        for _ in 0..3 {
+            o.apply(&AgentInference::default(), &fake);
+        }
+        assert_eq!(fake.now(), pair("haiku", "medium"));
+        assert_eq!(*fake.applies.borrow(), 0);
+    }
+
+    /// Only the field the swarm sets moves; the other keeps its value.
+    #[test]
+    fn an_unset_field_beside_a_set_one_is_left_alone() {
+        let fake = Fake::new();
+        *fake.effort.borrow_mut() = "max".to_owned();
+        let mut o = Overridden::default();
+        o.apply(&set(Some("opus"), None), &fake);
+        assert_eq!(fake.now(), pair("opus", "max"));
+    }
+
+    #[test]
+    fn a_cleared_field_goes_back_to_the_local_value() {
+        let fake = Fake::new();
+        let mut o = Overridden::default();
+        o.apply(&set(Some("opus"), Some(Effort::Xhigh)), &fake);
+        assert_eq!(fake.now(), pair("opus", "xhigh"));
+        // The effort is cleared, the model still set.
+        o.apply(&set(Some("opus"), None), &fake);
+        assert_eq!(fake.now(), pair("opus", "medium"));
+        // The local value is read at the clear, not at start.
+        "haiku".clone_into(&mut fake.local_model.borrow_mut());
+        o.apply(&AgentInference::default(), &fake);
+        assert_eq!(fake.now(), pair("haiku", "medium"));
+        // Once reverted, a later unset read changes nothing.
+        *fake.model.borrow_mut() = "sonnet".to_owned();
+        o.apply(&AgentInference::default(), &fake);
+        assert_eq!(fake.now(), pair("sonnet", "medium"));
+    }
+
+    /// On the real Bus: the swarm's value reaches the Bus but not the
+    /// persisted files, so clearing it, or a restart, finds the local value.
+    #[test]
+    fn the_swarm_value_is_not_persisted_over_the_local_one() {
+        let dir = tempfile::tempdir().unwrap();
+        let prev = std::env::var_os("HYPERHIVE_HARNESS_DIR");
+        // SAFETY: no other test in this crate reads or sets this variable.
+        unsafe { std::env::set_var("HYPERHIVE_HARNESS_DIR", dir.path()) };
+        let bus = Bus::new();
+        bus.set_model("sonnet");
+        bus.set_effort("low");
+        let target = Harness {
+            bus: bus.clone(),
+            nix_model: None,
+            nix_effort: None,
+        };
+        let mut o = Overridden::default();
+        o.apply(&set(Some("opus"), Some(Effort::Max)), &target);
+        let swarm = (bus.model(), bus.effort());
+        let files = (
+            crate::harness_state::load_model(),
+            crate::harness_state::load_effort(),
+        );
+        o.apply(&AgentInference::default(), &target);
+        let cleared = (bus.model(), bus.effort());
+        match prev {
+            // SAFETY: as above.
+            Some(v) => unsafe { std::env::set_var("HYPERHIVE_HARNESS_DIR", v) },
+            None => unsafe { std::env::remove_var("HYPERHIVE_HARNESS_DIR") },
+        }
+        assert_eq!(swarm, pair("opus", "max"));
+        assert_eq!(files, (Some("sonnet".to_owned()), Some("low".to_owned())));
+        assert_eq!(cleared, pair("sonnet", "low"));
+    }
+}