feat(skills): preserve all skills in prompt via compact fallback before dropping (#47553)

* feat(skills): add compact format fallback for skill catalog truncation

When the full-format skill catalog exceeds the character budget,
applySkillsPromptLimits now tries a compact format (name + location
only, no description) before binary-searching for the largest fitting
prefix. This preserves full model awareness of registered skills in
the common overflow case.

Three-tier strategy:
1. Full format fits → use as-is
2. Compact format fits → switch to compact, keep all skills
3. Compact still too large → binary search largest compact prefix

Other changes:
- escapeXml() utility for safe XML attribute values
- formatSkillsCompact() emits same XML structure minus <description>
- Compact char-budget check reserves 150 chars for the warning line
  the caller prepends, preventing prompt overflow at the boundary
- 13 tests covering all tiers, edge cases, and budget reservation
- docs/.generated/config-baseline.json: fix pre-existing oxfmt issue

* docs: document compact skill prompt fallback

---------

Co-authored-by: Frank Yang <frank.ekn@gmail.com>

CHANGELOG.md

@@ -29,6 +29,7 @@ Docs: https://docs.openclaw.ai
 - Docs/Zalo: clarify the Marketplace-bot support matrix and config guidance so the Zalo channel docs match current Bot Creator behavior more closely. (#47552) Thanks @No898.
 - secrets: harden read-only SecretRef command paths and diagnostics. (#47794) Thanks @joshavant.
 - Browser/existing-session: support `browser.profiles.<name>.userDataDir` so Chrome DevTools MCP can attach to Brave, Edge, and other Chromium-based browsers through their own user data directories. (#48170) thanks @velvet-shark.
+- Skills/prompt budget: preserve all registered skills via a compact catalog fallback before dropping entries when the full prompt format exceeds `maxSkillsPromptChars`. (#47553) Thanks @snese.
 
 ### Breaking
 

src/agents/skills/compact-format.test.ts

@@ -0,0 +1,230 @@
+import os from "node:os";
+import { formatSkillsForPrompt, type Skill } from "@mariozechner/pi-coding-agent";
+import { describe, expect, it } from "vitest";
+import type { SkillEntry } from "./types.js";
+import {
+  formatSkillsCompact,
+  buildWorkspaceSkillsPrompt,
+  buildWorkspaceSkillSnapshot,
+} from "./workspace.js";
+
+function makeSkill(name: string, desc = "A skill", filePath = `/skills/${name}/SKILL.md`): Skill {
+  return {
+    name,
+    description: desc,
+    filePath,
+    baseDir: `/skills/${name}`,
+    source: "workspace",
+    disableModelInvocation: false,
+  };
+}
+
+function makeEntry(skill: Skill): SkillEntry {
+  return { skill, frontmatter: {} };
+}
+
+function buildPrompt(
+  skills: Skill[],
+  limits: { maxChars?: number; maxCount?: number } = {},
+): string {
+  return buildWorkspaceSkillsPrompt("/fake", {
+    entries: skills.map(makeEntry),
+    config: {
+      skills: {
+        limits: {
+          ...(limits.maxChars !== undefined && { maxSkillsPromptChars: limits.maxChars }),
+          ...(limits.maxCount !== undefined && { maxSkillsInPrompt: limits.maxCount }),
+        },
+      },
+    } as any,
+  });
+}
+
+describe("formatSkillsCompact", () => {
+  it("returns empty string for no skills", () => {
+    expect(formatSkillsCompact([])).toBe("");
+  });
+
+  it("omits description, keeps name and location", () => {
+    const out = formatSkillsCompact([makeSkill("weather", "Get weather data")]);
+    expect(out).toContain("<name>weather</name>");
+    expect(out).toContain("<location>/skills/weather/SKILL.md</location>");
+    expect(out).not.toContain("Get weather data");
+    expect(out).not.toContain("<description>");
+  });
+
+  it("filters out disableModelInvocation skills", () => {
+    const hidden: Skill = { ...makeSkill("hidden"), disableModelInvocation: true };
+    const out = formatSkillsCompact([makeSkill("visible"), hidden]);
+    expect(out).toContain("visible");
+    expect(out).not.toContain("hidden");
+  });
+
+  it("escapes XML special characters", () => {
+    const out = formatSkillsCompact([makeSkill("a<b&c")]);
+    expect(out).toContain("a&lt;b&amp;c");
+  });
+
+  it("is significantly smaller than full format", () => {
+    const skills = Array.from({ length: 50 }, (_, i) =>
+      makeSkill(`skill-${i}`, "A moderately long description that takes up space in the prompt"),
+    );
+    const compact = formatSkillsCompact(skills);
+    expect(compact.length).toBeLessThan(6000);
+  });
+});
+
+describe("applySkillsPromptLimits (via buildWorkspaceSkillsPrompt)", () => {
+  it("tier 1: uses full format when under budget", () => {
+    const skills = [makeSkill("weather", "Get weather data")];
+    const prompt = buildPrompt(skills, { maxChars: 50_000 });
+    expect(prompt).toContain("<description>");
+    expect(prompt).toContain("Get weather data");
+    expect(prompt).not.toContain("⚠️");
+  });
+
+  it("tier 2: compact when full exceeds budget but compact fits", () => {
+    const skills = Array.from({ length: 20 }, (_, i) => makeSkill(`skill-${i}`, "A".repeat(200)));
+    const fullLen = formatSkillsForPrompt(skills).length;
+    const compactLen = formatSkillsCompact(skills).length;
+    const budget = Math.floor((fullLen + compactLen) / 2);
+    // Verify preconditions: full exceeds budget, compact fits within overhead-adjusted budget
+    expect(fullLen).toBeGreaterThan(budget);
+    expect(compactLen + 150).toBeLessThan(budget);
+    const prompt = buildPrompt(skills, { maxChars: budget });
+    expect(prompt).not.toContain("<description>");
+    // All skills preserved — distinct message, no "included X of Y"
+    expect(prompt).toContain("compact format (descriptions omitted)");
+    expect(prompt).not.toContain("included");
+    expect(prompt).toContain("skill-0");
+    expect(prompt).toContain("skill-19");
+  });
+
+  it("tier 3: compact + binary search when compact also exceeds budget", () => {
+    const skills = Array.from({ length: 100 }, (_, i) => makeSkill(`skill-${i}`, "description"));
+    const prompt = buildPrompt(skills, { maxChars: 2000 });
+    expect(prompt).toContain("compact format, descriptions omitted");
+    expect(prompt).not.toContain("<description>");
+    expect(prompt).toContain("skill-0");
+    const match = prompt.match(/included (\d+) of (\d+)/);
+    expect(match).toBeTruthy();
+    expect(Number(match![1])).toBeLessThan(Number(match![2]));
+    expect(Number(match![1])).toBeGreaterThan(0);
+  });
+
+  it("compact preserves all skills where full format would drop some", () => {
+    const skills = Array.from({ length: 50 }, (_, i) => makeSkill(`skill-${i}`, "A".repeat(200)));
+    const compactLen = formatSkillsCompact(skills).length;
+    const budget = compactLen + 250;
+    // Verify precondition: full format must not fit so tier 2 is actually exercised
+    expect(formatSkillsForPrompt(skills).length).toBeGreaterThan(budget);
+    const prompt = buildPrompt(skills, { maxChars: budget });
+    // All 50 fit in compact — no truncation, just compact notice
+    expect(prompt).toContain("compact format");
+    expect(prompt).not.toContain("included");
+    expect(prompt).toContain("skill-0");
+    expect(prompt).toContain("skill-49");
+  });
+
+  it("count truncation + compact: shows included X of Y with compact note", () => {
+    // 30 skills but maxCount=10, and full format of 10 exceeds budget
+    const skills = Array.from({ length: 30 }, (_, i) => makeSkill(`skill-${i}`, "A".repeat(200)));
+    const tenSkills = skills.slice(0, 10);
+    const fullLen = formatSkillsForPrompt(tenSkills).length;
+    const compactLen = formatSkillsCompact(tenSkills).length;
+    const budget = compactLen + 200;
+    // Verify precondition: full format of 10 skills exceeds budget
+    expect(fullLen).toBeGreaterThan(budget);
+    const prompt = buildPrompt(skills, { maxChars: budget, maxCount: 10 });
+    // Count-truncated (30→10) AND compact (full format of 10 exceeds budget)
+    expect(prompt).toContain("included 10 of 30");
+    expect(prompt).toContain("compact format, descriptions omitted");
+    expect(prompt).not.toContain("<description>");
+  });
+
+  it("extreme budget: even a single compact skill overflows", () => {
+    const skills = [makeSkill("only-one", "desc")];
+    // Budget so small that even one compact skill can't fit
+    const prompt = buildPrompt(skills, { maxChars: 10 });
+    expect(prompt).not.toContain("only-one");
+    const match = prompt.match(/included (\d+) of (\d+)/);
+    expect(match).toBeTruthy();
+    expect(Number(match![1])).toBe(0);
+  });
+
+  it("count truncation only: shows included X of Y without compact note", () => {
+    const skills = Array.from({ length: 20 }, (_, i) => makeSkill(`skill-${i}`, "short"));
+    const prompt = buildPrompt(skills, { maxChars: 50_000, maxCount: 5 });
+    expect(prompt).toContain("included 5 of 20");
+    expect(prompt).not.toContain("compact");
+    expect(prompt).toContain("<description>");
+  });
+
+  it("compact budget reserves space for the warning line", () => {
+    // Build skills whose compact output exactly equals the char budget.
+    // Without overhead reservation the compact block would fit, but the
+    // warning line prepended by the caller would push the total over budget.
+    const skills = Array.from({ length: 50 }, (_, i) => makeSkill(`s-${i}`, "A".repeat(200)));
+    const compactLen = formatSkillsCompact(skills).length;
+    // Set budget = compactLen + 50 — less than the 150-char overhead reserve.
+    // The function should NOT choose compact-only because the warning wouldn't fit.
+    const prompt = buildPrompt(skills, { maxChars: compactLen + 50 });
+    // Should fall through to compact + binary search (some skills dropped)
+    expect(prompt).toContain("included");
+    expect(prompt).not.toContain("<description>");
+  });
+
+  it("budget check uses compacted home-dir paths, not canonical paths", () => {
+    // Skills with home-dir prefix get compacted (e.g. /home/user/... → ~/...).
+    // Budget check must use the compacted length, not the longer canonical path.
+    // If it used canonical paths, it would overestimate and potentially drop
+    // skills that actually fit after compaction.
+    const home = os.homedir();
+    const skills = Array.from({ length: 30 }, (_, i) =>
+      makeSkill(
+        `skill-${i}`,
+        "A".repeat(200),
+        `${home}/.openclaw/workspace/skills/skill-${i}/SKILL.md`,
+      ),
+    );
+    // Compute compacted lengths (what the prompt will actually contain)
+    const compactedSkills = skills.map((s) => ({
+      ...s,
+      filePath: s.filePath.replace(home, "~"),
+    }));
+    const compactedCompactLen = formatSkillsCompact(compactedSkills).length;
+    const canonicalCompactLen = formatSkillsCompact(skills).length;
+    // Sanity: canonical paths are longer than compacted paths
+    expect(canonicalCompactLen).toBeGreaterThan(compactedCompactLen);
+    // Set budget between compacted and canonical lengths — only fits if
+    // budget check uses compacted paths (correct) not canonical (wrong).
+    const budget = Math.floor((compactedCompactLen + canonicalCompactLen) / 2) + 150;
+    const prompt = buildPrompt(skills, { maxChars: budget });
+    // All 30 skills should be preserved in compact form (tier 2, no dropping)
+    expect(prompt).toContain("skill-0");
+    expect(prompt).toContain("skill-29");
+    expect(prompt).not.toContain("included");
+    expect(prompt).toContain("compact format");
+    // Verify paths in output are compacted
+    expect(prompt).toContain("~/");
+    expect(prompt).not.toContain(home);
+  });
+
+  it("resolvedSkills in snapshot keeps canonical paths, not compacted", () => {
+    const home = os.homedir();
+    const skills = Array.from({ length: 5 }, (_, i) =>
+      makeSkill(`skill-${i}`, "A skill", `${home}/.openclaw/workspace/skills/skill-${i}/SKILL.md`),
+    );
+    const snapshot = buildWorkspaceSkillSnapshot("/fake", {
+      entries: skills.map(makeEntry),
+    });
+    // Prompt should use compacted paths
+    expect(snapshot.prompt).toContain("~/");
+    // resolvedSkills should preserve canonical (absolute) paths
+    expect(snapshot.resolvedSkills).toBeDefined();
+    for (const skill of snapshot.resolvedSkills!) {
+      expect(skill.filePath).toContain(home);
+      expect(skill.filePath).not.toMatch(/^~\//);
+    }
+  });
+});

src/agents/skills/workspace.ts

@@ -526,10 +526,47 @@ function loadSkillEntries(
   return skillEntries;
 }
 
+function escapeXml(str: string): string {
+  return str
+    .replace(/&/g, "&")
+    .replace(/</g, "&lt;")
+    .replace(/>/g, "&gt;")
+    .replace(/"/g, "&quot;")
+    .replace(/'/g, "&apos;");
+}
+
+/**
+ * Compact skill catalog: name + location only (no description).
+ * Used as a fallback when the full format exceeds the char budget,
+ * preserving awareness of all skills before resorting to dropping.
+ */
+export function formatSkillsCompact(skills: Skill[]): string {
+  const visible = skills.filter((s) => !s.disableModelInvocation);
+  if (visible.length === 0) return "";
+  const lines = [
+    "\n\nThe following skills provide specialized instructions for specific tasks.",
+    "Use the read tool to load a skill's file when the task matches its name.",
+    "When a skill file references a relative path, resolve it against the skill directory (parent of SKILL.md / dirname of the path) and use that absolute path in tool commands.",
+    "",
+    "<available_skills>",
+  ];
+  for (const skill of visible) {
+    lines.push("  <skill>");
+    lines.push(`    <name>${escapeXml(skill.name)}</name>`);
+    lines.push(`    <location>${escapeXml(skill.filePath)}</location>`);
+    lines.push("  </skill>");
+  }
+  lines.push("</available_skills>");
+  return lines.join("\n");
+}
+
+// Budget reserved for the compact-mode warning line prepended by the caller.
+const COMPACT_WARNING_OVERHEAD = 150;
+
 function applySkillsPromptLimits(params: { skills: Skill[]; config?: OpenClawConfig }): {
   skillsForPrompt: Skill[];
   truncated: boolean;
-  truncatedReason: "count" | "chars" | null;
+  compact: boolean;
 } {
   const limits = resolveSkillsLimits(params.config);
   const total = params.skills.length;
@@ -537,31 +574,41 @@ function applySkillsPromptLimits(params: { skills: Skill[]; config?: OpenClawCon
 
   let skillsForPrompt = byCount;
   let truncated = total > byCount.length;
-  let truncatedReason: "count" | "chars" | null = truncated ? "count" : null;
+  let compact = false;
 
-  const fits = (skills: Skill[]): boolean => {
-    const block = formatSkillsForPrompt(skills);
-    return block.length <= limits.maxSkillsPromptChars;
-  };
+  const fitsFull = (skills: Skill[]): boolean =>
+    formatSkillsForPrompt(skills).length <= limits.maxSkillsPromptChars;
 
-  if (!fits(skillsForPrompt)) {
-    // Binary search the largest prefix that fits in the char budget.
-    let lo = 0;
-    let hi = skillsForPrompt.length;
-    while (lo < hi) {
-      const mid = Math.ceil((lo + hi) / 2);
-      if (fits(skillsForPrompt.slice(0, mid))) {
-        lo = mid;
-      } else {
-        hi = mid - 1;
+  // Reserve space for the warning line the caller prepends in compact mode.
+  const compactBudget = limits.maxSkillsPromptChars - COMPACT_WARNING_OVERHEAD;
+  const fitsCompact = (skills: Skill[]): boolean =>
+    formatSkillsCompact(skills).length <= compactBudget;
+
+  if (!fitsFull(skillsForPrompt)) {
+    // Full format exceeds budget. Try compact (name + location, no description)
+    // to preserve awareness of all skills before dropping any.
+    if (fitsCompact(skillsForPrompt)) {
+      compact = true;
+      // No skills dropped — only format downgraded. Preserve existing truncated state.
+    } else {
+      // Compact still too large — binary search the largest prefix that fits.
+      compact = true;
+      let lo = 0;
+      let hi = skillsForPrompt.length;
+      while (lo < hi) {
+        const mid = Math.ceil((lo + hi) / 2);
+        if (fitsCompact(skillsForPrompt.slice(0, mid))) {
+          lo = mid;
+        } else {
+          hi = mid - 1;
+        }
       }
+      skillsForPrompt = skillsForPrompt.slice(0, lo);
+      truncated = true;
     }
-    skillsForPrompt = skillsForPrompt.slice(0, lo);
-    truncated = true;
-    truncatedReason = "chars";
   }
 
-  return { skillsForPrompt, truncated, truncatedReason };
+  return { skillsForPrompt, truncated, compact };
 }
 
 export function buildWorkspaceSkillSnapshot(
@@ -620,17 +667,24 @@ function resolveWorkspaceSkillPromptState(
   );
   const remoteNote = opts?.eligibility?.remote?.note?.trim();
   const resolvedSkills = promptEntries.map((entry) => entry.skill);
-  const { skillsForPrompt, truncated } = applySkillsPromptLimits({
-    skills: resolvedSkills,
+  // Derive prompt-facing skills with compacted paths (e.g. ~/...) once.
+  // Budget checks and final render both use this same representation so the
+  // tier decision is based on the exact strings that end up in the prompt.
+  // resolvedSkills keeps canonical paths for snapshot / runtime consumers.
+  const promptSkills = compactSkillPaths(resolvedSkills);
+  const { skillsForPrompt, truncated, compact } = applySkillsPromptLimits({
+    skills: promptSkills,
     config: opts?.config,
   });
   const truncationNote = truncated
-    ? `⚠️ Skills truncated: included ${skillsForPrompt.length} of ${resolvedSkills.length}. Run \`openclaw skills check\` to audit.`
-    : "";
+    ? `⚠️ Skills truncated: included ${skillsForPrompt.length} of ${resolvedSkills.length}${compact ? " (compact format, descriptions omitted)" : ""}. Run \`openclaw skills check\` to audit.`
+    : compact
+      ? `⚠️ Skills catalog using compact format (descriptions omitted). Run \`openclaw skills check\` to audit.`
+      : "";
   const prompt = [
     remoteNote,
     truncationNote,
-    formatSkillsForPrompt(compactSkillPaths(skillsForPrompt)),
+    compact ? formatSkillsCompact(skillsForPrompt) : formatSkillsForPrompt(skillsForPrompt),
   ]
     .filter(Boolean)
     .join("\n");