perf(skills): skip warm prompt search when minimum cannot fit (#157343)

Punchcard-Session: ember-river-harbor-t4

src/skills/loading/skill-contract.test.ts

@@ -3,6 +3,7 @@ import { formatSkillsForPrompt as upstreamFormatSkillsForPrompt } from "openclaw
 import { describe, expect, it } from "vitest";
 import { createCanonicalFixtureSkill } from "../test-support/test-helpers.js";
 import {
+  compactSkillsPromptForContext,
   formatSkillsForPromptCore,
   type Skill,
   formatSkillsCompactForPrompt as formatSkillsCompact,
@@ -18,6 +19,32 @@ function makeSkill(name: string, desc = "A skill", filePath = `/skills/${name}/S
   });
 }
 
+describe("compactSkillsPromptForContext", () => {
+  it("preserves nested entities and whole surrogate pairs while normalizing whitespace", () => {
+    const prompt = `<available_skills><description> \t&amp;lt; \n&lt;tag&gt; ${"a".repeat(49)}😀${" tail".repeat(20)}</description></available_skills>`;
+
+    expect(compactSkillsPromptForContext(prompt, 1)).toBe(
+      `<available_skills><description>&amp;lt; &lt;tag&gt; ${"a".repeat(49)}...</description></available_skills>`,
+    );
+  });
+
+  it.each(["&".repeat(50), "&     a"])(
+    "keeps the original when escaped projection is not strictly shorter: %s",
+    (description) => {
+      const prompt = `<available_skills><description>${description}</description></available_skills>`;
+      expect(compactSkillsPromptForContext(prompt, 1)).toBe(prompt);
+    },
+  );
+
+  it.each([undefined, 0, -1, Number.NaN, Number.POSITIVE_INFINITY])(
+    "keeps prompt bytes when the context budget is %s",
+    (budget) => {
+      const prompt = `<available_skills><description>  ${"long description ".repeat(30)}</description></available_skills>`;
+      expect(compactSkillsPromptForContext(prompt, budget)).toBe(prompt);
+    },
+  );
+});
+
 describe("formatSkillsCompact", () => {
   it("keeps the full-format XML output aligned with the upstream formatter for visible skills", () => {
     const skills = [

src/skills/loading/skill-contract.ts

@@ -86,14 +86,16 @@ export function compactSkillsPromptForContext(prompt: string, contextTokenBudget
   let lo = 64;
   let hi = COMPACT_DESCRIPTION_MAX_CHARS;
   let result = render(lo);
-  while (lo <= hi) {
-    const mid = Math.floor((lo + hi) / 2);
-    const candidate = render(mid);
-    if (candidate.length <= targetChars) {
-      result = candidate;
-      lo = mid + 1;
-    } else {
-      hi = mid - 1;
+  if (result.length <= targetChars) {
+    while (lo <= hi) {
+      const mid = Math.floor((lo + hi) / 2);
+      const candidate = render(mid);
+      if (candidate.length <= targetChars) {
+        result = candidate;
+        lo = mid + 1;
+      } else {
+        hi = mid - 1;
+      }
     }
   }
   return result.length < prompt.length ? result : prompt;

src/skills/loading/workspace-skill-prompt-resolution.test.ts

@@ -46,9 +46,9 @@ function createEntry(name: string): SkillEntry {
 }
 
 describe("resolveSkillsPrompt", () => {
-  it.each([8_192, 32_768])(
-    "compacts descriptions at %i tokens without changing admitted skill resources",
-    async (contextTokenBudget) => {
+  it.each([8_192, 32_768, "minimum", "above minimum"] as const)(
+    "compacts descriptions at %s without changing admitted skill resources",
+    async (budget) => {
       const entries = Array.from({ length: 24 }, (_, index) => {
         const entry = createEntry(`skill-${index}`);
         entry.skill.description = `Inspect records & preserve <identifiers>. ${"Detailed matching guidance. ".repeat(10)}`;
@@ -58,12 +58,31 @@ describe("resolveSkillsPrompt", () => {
       });
       const snapshot = await buildSkillSnapshot("/tmp/openclaw", { entries });
       const original = snapshot.prompt.trim();
+      const minimum = original.replace(
+        /<description>[\s\S]*?<\/description>/gu,
+        "<description>Inspect records &amp; preserve &lt;identifiers&gt;. Detailed matching g...</description>",
+      );
+      const contextTokenBudget =
+        typeof budget === "number"
+          ? budget
+          : (minimum.length + (budget === "above minimum" ? 24 * 10 : 0)) * 5;
       const projected = await resolveSkillsPrompt({
         workspaceDir: "/tmp/openclaw",
         skillsSnapshot: snapshot,
         contextTokenBudget,
       });
       expect(projected.length).toBeLessThan(original.length);
+      if (budget === "above minimum") {
+        expect(projected).toBe(
+          original.replace(
+            /<description>[\s\S]*?<\/description>/gu,
+            "<description>Inspect records &amp; preserve &lt;identifiers&gt;. Detailed matching guidance. D...</description>",
+          ),
+        );
+        expect(projected.length).toBe(Math.floor(contextTokenBudget / 5));
+      } else {
+        expect(projected).toBe(minimum);
+      }
       const omitDescriptions = (prompt: string) =>
         prompt.replace(/<description>[\s\S]*?<\/description>/gu, "");
       expect(omitDescriptions(projected)).toBe(omitDescriptions(original));