swarm ui: a soft context limit field in an agent's inference settings

A whole percent from 5 to 100 of the model's context window, sent as
soft_context_percent next to max_subagents. The inference row shows it, the
edit dialog and the create form take it, and an archetype can carry it.

frontend/packages/swarm-ui/src/agent/detail/AgentInference.tsx

@@ -26,6 +26,11 @@ import { FormStack } from "../../ui/form-stack/FormStack.js";
 import "../../ui/badge-row/BadgeRow.css";
 import "./AgentInference.css";
 import { MAX_SUBAGENTS, maxSubagentsValue } from "./max-subagents.js";
+import {
+  MAX_SOFT_CONTEXT_PERCENT,
+  MIN_SOFT_CONTEXT_PERCENT,
+  softContextValue,
+} from "./soft-context.js";
 
 type Source = "swarm" | "agent_nix" | "local_file" | "default";
 
@@ -35,6 +40,7 @@ interface Settings {
   effort?: string;
   subagent_models?: string[];
   max_subagents?: number;
+  soft_context_percent?: number;
 }
 
 // Mirrors `EffectiveInference`.
@@ -81,13 +87,14 @@ function inferenceUrl(agent: string): string {
   return `/api/agents/${encodeURIComponent(agent)}/inference`;
 }
 
-// The four inference boxes as typed. Shared by the editor here and the
+// The inference boxes as typed. Shared by the editor here and the
 // create-agent form, which send what `draftBody` makes of them.
 export interface InferenceDraft {
   model: string;
   effort: string;
   subagents: string;
   maxSubagents: string;
+  softContext: string;
 }
 
 export const EMPTY_INFERENCE_DRAFT: InferenceDraft = {
@@ -95,6 +102,7 @@ export const EMPTY_INFERENCE_DRAFT: InferenceDraft = {
   effort: "",
   subagents: "",
   maxSubagents: "",
+  softContext: "",
 };
 
 // Why the draft would be refused, or null when it is fine to send.
@@ -106,6 +114,9 @@ export function draftProblem(d: InferenceDraft): string | null {
       .find((p) => p !== null) ??
     (maxSubagentsValue(d.maxSubagents) === null
       ? `max subagents is a whole number from 0 (no subagents) to ${MAX_SUBAGENTS}, or empty for no cap`
+      : null) ??
+    (softContextValue(d.softContext) === null
+      ? `soft context limit is a whole percent from ${MIN_SOFT_CONTEXT_PERCENT} to ${MAX_SOFT_CONTEXT_PERCENT}, or empty for the agent's own`
       : null)
   );
 }
@@ -115,7 +126,8 @@ export function draftIsEmpty(d: InferenceDraft): boolean {
     d.model.trim() === "" &&
     d.effort === "" &&
     parseModels(d.subagents).length === 0 &&
-    d.maxSubagents.trim() === ""
+    d.maxSubagents.trim() === "" &&
+    d.softContext.trim() === ""
   );
 }
 
@@ -128,6 +140,8 @@ export function draftBody(d: InferenceDraft): Settings {
   if (models.length > 0) body.subagent_models = models;
   const max = maxSubagentsValue(d.maxSubagents);
   if (typeof max === "number") body.max_subagents = max;
+  const soft = softContextValue(d.softContext);
+  if (typeof soft === "number") body.soft_context_percent = soft;
   return body;
 }
 
@@ -174,6 +188,14 @@ export function InferenceFields({
         pattern="[0-9]*"
         onInput={(maxSubagents) => onChange({ ...draft, maxSubagents })}
       />
+      <TextField
+        id={`${idPrefix}-soft-context`}
+        label="soft context limit (%)"
+        value={draft.softContext}
+        placeholder="empty for the agent's own"
+        pattern="[0-9]*"
+        onInput={(softContext) => onChange({ ...draft, softContext })}
+      />
       {problem ? <Hint tone="error">{problem}</Hint> : null}
     </>
   );
@@ -278,11 +300,22 @@ export function AgentInference({ agent }: { agent: string }) {
               }
             />
           </li>
+          <li>
+            <Badge
+              label="soft context limit"
+              value={
+                configured?.soft_context_percent === undefined
+                  ? "its own"
+                  : `${configured.soft_context_percent}%`
+              }
+              title="the agent compacts at the end of a turn once its context passes this share of the window; a turn can run past it"
+            />
+          </li>
         </ul>
         <Badge
           variant="quiet"
           value="edit"
-          title={`set the swarm's model, effort, subagent models and subagent cap for ${agent}`}
+          title={`set the swarm's model, effort, subagent models, subagent cap and soft context limit for ${agent}`}
           onClick={() => setEditing(true)}
         />
       </div>
@@ -325,6 +358,7 @@ function InferenceForm({
     effort: configured?.effort ?? "",
     subagents: (configured?.subagent_models ?? []).join(", "),
     maxSubagents: configured?.max_subagents?.toString() ?? "",
+    softContext: configured?.soft_context_percent?.toString() ?? "",
   });
   const [busy, setBusy] = useState(false);
   const [problem, setProblem] = useState<ProblemDetails | null>(null);

frontend/packages/swarm-ui/src/agent/detail/soft-context.ts

@@ -0,0 +1,22 @@
+// The create form's and the inference dialog's `soft_context_percent` field,
+// kept out of the component so `npm test` can run it.
+
+/** The lowest `soft_context_percent` the swarm accepts. */
+export const MIN_SOFT_CONTEXT_PERCENT = 5;
+/** The highest: the whole context window. */
+export const MAX_SOFT_CONTEXT_PERCENT = 100;
+
+/**
+ * `soft_context_percent` as typed: `undefined` for empty (the agent's own
+ * default), the number for a whole number from [`MIN_SOFT_CONTEXT_PERCENT`]
+ * to [`MAX_SOFT_CONTEXT_PERCENT`], else `null`.
+ */
+export function softContextValue(text: string): number | null | undefined {
+  const t = text.trim();
+  if (t === "") return undefined;
+  if (!/^\d+$/.test(t)) return null;
+  const n = Number(t);
+  return n >= MIN_SOFT_CONTEXT_PERCENT && n <= MAX_SOFT_CONTEXT_PERCENT
+    ? n
+    : null;
+}

frontend/packages/swarm-ui/src/pages/CreateAgentArchetype.ts

@@ -14,6 +14,7 @@ export interface Archetype {
     effort?: string;
     subagent_models?: string[];
     max_subagents?: number;
+    soft_context_percent?: number;
   };
   prompt?: string;
   /** The archetype's icon as SVG text. */
@@ -69,6 +70,10 @@ export function prefill(
         inference.max_subagents === undefined
           ? ""
           : String(inference.max_subagents),
+      softContext:
+        inference.soft_context_percent === undefined
+          ? ""
+          : String(inference.soft_context_percent),
     },
   };
 }

frontend/packages/swarm-ui/test/create-agent-archetype.test.mjs

@@ -15,7 +15,13 @@ const empty = {
   permissions: defaults,
   cpu: "",
   memory: "",
-  inference: { model: "", effort: "", subagents: "", maxSubagents: "" },
+  inference: {
+    model: "",
+    effort: "",
+    subagents: "",
+    maxSubagents: "",
+    softContext: "",
+  },
 };
 
 test("no archetype is the default permissions and empty settings", () => {
@@ -34,6 +40,7 @@ test("an archetype's settings fill the form", () => {
       effort: "high",
       subagent_models: ["haiku", "sonnet"],
       max_subagents: 0,
+      soft_context_percent: 20,
     },
   };
   assert.deepEqual(prefill(reviewer, defaults), {
@@ -45,6 +52,7 @@ test("an archetype's settings fill the form", () => {
       effort: "high",
       subagents: "haiku, sonnet",
       maxSubagents: "0",
+      softContext: "20",
     },
   });
 });

frontend/packages/swarm-ui/test/soft-context.test.mjs

@@ -0,0 +1,33 @@
+// The soft context limit field: what counts as empty, valid and refused. Run
+// by `npm test`, which imports the `.ts` module as it is.
+import assert from "node:assert/strict";
+import { test } from "node:test";
+import {
+  MAX_SOFT_CONTEXT_PERCENT,
+  MIN_SOFT_CONTEXT_PERCENT,
+  softContextValue,
+} from "../src/agent/detail/soft-context.ts";
+
+test("an empty box leaves the agent on its own limit", () => {
+  assert.equal(softContextValue(""), undefined);
+  assert.equal(softContextValue("   "), undefined);
+});
+
+test("a whole percent from 5 to 100 is taken", () => {
+  assert.equal(softContextValue("20"), 20);
+  assert.equal(softContextValue(" 75 "), 75);
+  assert.equal(
+    softContextValue(String(MIN_SOFT_CONTEXT_PERCENT)),
+    MIN_SOFT_CONTEXT_PERCENT,
+  );
+  assert.equal(
+    softContextValue(String(MAX_SOFT_CONTEXT_PERCENT)),
+    MAX_SOFT_CONTEXT_PERCENT,
+  );
+});
+
+test("anything else is refused", () => {
+  for (const text of ["0", "4", "101", "-20", "20.5", "abc", "1e1", "20%"]) {
+    assert.equal(softContextValue(text), null, text);
+  }
+});