fix(skills): don't conflate fs errors with binary/not-found in skill reads

packages/server/src/skill-projection.test.ts

@@ -1,5 +1,6 @@
 import { afterEach, beforeEach, describe, expect, test } from 'bun:test';
 import {
+  chmodSync,
   existsSync,
   lstatSync,
   mkdirSync,
@@ -172,6 +173,20 @@ describe('readSkillBundledFiles', () => {
   test('absent skill dir returns empty', () => {
     expect(readSkillBundledFiles(join(root, 'nope'))).toEqual([]);
   });
+
+  const isRoot = typeof process.getuid === 'function' && process.getuid() === 0;
+  test.skipIf(isRoot)('a genuine IO error THROWS rather than masquerading as binary', () => {
+    const dir = makeSkill('locked', '# Body');
+    mkdirSync(join(dir, 'reference'), { recursive: true });
+    const secret = join(dir, 'reference', 'secret.md');
+    writeFileSync(secret, '# Secret', 'utf-8');
+    chmodSync(secret, 0o000);
+    try {
+      expect(() => readSkillBundledFiles(dir)).toThrow();
+    } finally {
+      chmodSync(secret, 0o644); // restore so afterEach can clean up
+    }
+  });
 });
 
 describe('hostSkillsRootEscapes', () => {

packages/server/src/skill-projection.ts

@@ -233,7 +233,8 @@ export function readSkillBundledFiles(
       if (buf.length <= MAX_BUNDLED_FILE_BYTES && !buf.includes(0)) {
         text = buf.toString('utf-8');
       }
-    } catch {
+    } catch (err) {
+      if ((err as NodeJS.ErrnoException)?.code !== 'ENOENT') throw err;
       text = null;
     }
     out.push({ path: rel, text });

packages/server/src/skill-restore.test.ts

@@ -0,0 +1,31 @@
+import { describe, expect, test } from 'bun:test';
+import { isGitObjectNotFound } from './skill-restore.ts';
+
+describe('isGitObjectNotFound', () => {
+  test('classifies a genuinely-missing object/revision as not-found (→ 404)', () => {
+    for (const msg of [
+      "fatal: not a valid object name 'abc123'",
+      'fatal: bad revision',
+      'unknown revision or path not in the working tree',
+      'fatal: Not a valid object name HEAD~5',
+      'fatal: invalid object name deadbeef',
+      'fatal: not a tree object',
+    ]) {
+      expect(isGitObjectNotFound(msg)).toBe(true);
+    }
+  });
+
+  test('does NOT match genuine git I/O / server faults (→ 500)', () => {
+    for (const msg of [
+      'fatal: unable to read source tree',
+      'git binary not found',
+      'fatal: object file is empty',
+      'repository is corrupt',
+      'fatal: unable to read tree',
+      'EACCES: permission denied',
+      'spawn git ENOENT',
+    ]) {
+      expect(isGitObjectNotFound(msg)).toBe(false);
+    }
+  });
+});

packages/server/src/skill-restore.ts

@@ -16,6 +16,12 @@ export type RestoreSkillResult =
       error: string;
     };
 
+export function isGitObjectNotFound(message: string): boolean {
+  return /not a valid object name|not a tree object|bad revision|unknown revision|invalid object name/i.test(
+    message,
+  );
+}
+
 export async function restoreSkillVersion(opts: {
   shadow: ShadowHandle;
   contentDir: string;
@@ -33,12 +39,15 @@ export async function restoreSkillVersion(opts: {
   let fileList: string;
   try {
     fileList = await sg.raw('ls-tree', '-r', '--name-only', version, '--', shadowPath);
-  } catch {
-    return {
-      ok: false,
-      code: 'version-not-found',
-      error: `Version ${version.slice(0, 8)} not found.`,
-    };
+  } catch (e) {
+    const msg = e instanceof Error ? e.message : String(e);
+    return isGitObjectNotFound(msg)
+      ? { ok: false, code: 'version-not-found', error: `Version ${version.slice(0, 8)} not found.` }
+      : {
+          ok: false,
+          code: 'io-error',
+          error: `Failed to read version ${version.slice(0, 8)}: ${msg}`,
+        };
   }
   const files = fileList
     .split('\n')
@@ -68,10 +77,11 @@ export async function restoreSkillVersion(opts: {
     try {
       staged.push({ rel, destAbs, content: await sg.raw('show', `${version}:${shadowFile}`) });
     } catch (e) {
+      const msg = e instanceof Error ? e.message : String(e);
       return {
         ok: false,
         code: 'io-error',
-        error: `Failed reading ${rel} at ${version.slice(0, 8)}: ${(e as Error).message}`,
+        error: `Failed reading ${rel} at ${version.slice(0, 8)}: ${msg}`,
       };
     }
   }