feat(#2220): add low and max effort levels

claude --effort now accepts low, medium, high, xhigh, max.
Expand EFFORT_LEVELS from 3 to 5, update NixOS enum + description,
and fix the stale doc comment in web_ui.rs.

Closes #2220

hive-ag3nt/src/events.rs

@@ -583,7 +583,7 @@ pub const DEFAULT_EFFORT: &str = "medium";
 
 /// Valid claude `--effort` levels, ascending. The operator picker is
 /// constrained to these; [`is_valid_effort`] guards the persist path.
-pub const EFFORT_LEVELS: [&str; 3] = ["medium", "high", "xhigh"];
+pub const EFFORT_LEVELS: [&str; 5] = ["low", "medium", "high", "xhigh", "max"];
 
 /// True iff `level` is one of [`EFFORT_LEVELS`].
 #[must_use]

hive-ag3nt/src/web_ui.rs

@@ -461,7 +461,7 @@ struct StateSnapshot {
     /// runtime via `POST /api/effort`; applies on the next session.
     effort: String,
     /// Selectable effort levels for the picker, ascending. Fixed set
-    /// (`medium`, `high`, `xhigh`) — sourced from
+    /// (`low`, `medium`, `high`, `xhigh`, `max`) — sourced from
     /// [`crate::events::EFFORT_LEVELS`], not operator-configurable like
     /// `available_models`. The frontend renders one button per entry.
     available_efforts: Vec<String>,

nix/templates/harness-base.nix

@@ -219,9 +219,11 @@ in
 
   options.hyperhive.effortLevel = lib.mkOption {
     type = lib.types.enum [
+      "low"
       "medium"
       "high"
       "xhigh"
+      "max"
     ];
     default = "medium";
     example = "high";
@@ -231,12 +233,12 @@ in
       effort as operator-override-file → this env → built-in `"medium"`,
       and passes the result to `claude --effort` at turn launch.
 
-      `"medium"` (the default) keeps token spend low and works well with
-      the harness across families. `"high"` matches the current platform
-      default; `"xhigh"` is recommended for coding / high-autonomy work on
-      capable models (Opus 4.8+) at higher token cost. The operator can
-      override at runtime per-agent via the web UI (applied on the next
-      session); any rebuild that changes this option resets that override.
+      Ascending scale: `"low"` (minimal thinking budget), `"medium"`
+      (default — balanced), `"high"` (platform default), `"xhigh"`
+      (recommended for autonomous coding on capable models), `"max"`
+      (maximum thinking budget, highest cost). The operator can override
+      at runtime per-agent via the web UI (applied on the next session);
+      any rebuild that changes this option resets that override.
     '';
   };