diff --git a/scanners/ide-extension-scanner.mjs b/scanners/ide-extension-scanner.mjs
index f33a1c2..8666cfe 100644
--- a/scanners/ide-extension-scanner.mjs
+++ b/scanners/ide-extension-scanner.mjs
@@ -628,6 +628,30 @@ function runJetBrainsChecks(ext, manifest, topList, blocklist, relLocation) {
 // Reused-scanner orchestration per extension
 // ---------------------------------------------------------------------------
 
+/**
+ * Result envelope for an extension that could not be scanned at all.
+ * Shape-compatible with a normal per-extension result so the top-level
+ * aggregation loop can consume it without special-casing.
+ * @param {object} ext
+ * @param {...string} reasons
+ */
+function unscannableExtension(ext, ...reasons) {
+  return {
+    id: ext.id,
+    version: ext.version,
+    type: ext.type,
+    location: ext.location,
+    publisher: ext.publisher,
+    source: ext.source,
+    is_builtin: ext.isBuiltin,
+    signed: ext.signed,
+    scanner_results: {},
+    warnings: reasons.filter(Boolean),
+    aggregate: { counts: { critical: 0, high: 0, medium: 0, low: 0, info: 0 }, risk_score: 0, risk_band: 'Low', verdict: 'ALLOW' },
+    duration_ms: 0,
+  };
+}
+
 async function scanOneExtension(ext, options) {
   const started = Date.now();
   const warnings = [];
@@ -636,19 +660,16 @@ async function scanOneExtension(ext, options) {
   const parsed = ext.type === 'jetbrains'
     ? await parseIntelliJPlugin(ext.location)
     : await parseVSCodeExtension(ext.location);
-  if (!parsed) {
+  // Two "unparseable" shapes reach here: parseVSCodeExtension returns a bare
+  // null, parseIntelliJPlugin returns a TRUTHY { manifest: null, warnings }.
+  // Both must short-circuit — otherwise the null manifest is dereferenced below.
+  if (!parsed || !parsed.manifest) {
     return {
-      id: ext.id,
-      version: ext.version,
-      type: ext.type,
-      location: ext.location,
-      publisher: ext.publisher,
-      source: ext.source,
-      is_builtin: ext.isBuiltin,
-      signed: ext.signed,
-      scanner_results: {},
-      warnings: [`failed to parse manifest for ${ext.id}`],
-      aggregate: { counts: { critical: 0, high: 0, medium: 0, low: 0, info: 0 }, risk_score: 0, risk_band: 'Low', verdict: 'ALLOW' },
+      ...unscannableExtension(
+        ext,
+        `failed to parse manifest for ${ext.id}`,
+        ...(parsed?.warnings || []),
+      ),
       duration_ms: Date.now() - started,
     };
   }
@@ -935,8 +956,17 @@ export async function scan(target, options = {}) {
   const targetBase = singleTargetPath || (rootsScanned[0] || process.cwd());
   const concurrency = Math.max(1, Math.min(options.concurrency || 4, 16));
 
-  const perExt = await mapConcurrent(extensions, concurrency, ext =>
-    scanOneExtension(ext, { targetBase, online: options.online === true }));
+  // Fault isolation (belt): one unscannable extension must never abort the run.
+  // scanOneExtension is hardened against the known null-manifest case, but any
+  // future throw would otherwise reject mapConcurrent's Promise.all and fail the
+  // entire ide-scan because of a single bad plugin on disk.
+  const perExt = await mapConcurrent(extensions, concurrency, async ext => {
+    try {
+      return await scanOneExtension(ext, { targetBase, online: options.online === true });
+    } catch (err) {
+      return unscannableExtension(ext, `scan failed: ${err?.message || err}`);
+    }
+  });
 
   // Top-level aggregate
   const aggCounts = { critical: 0, high: 0, medium: 0, low: 0, info: 0 };
diff --git a/tests/scanners/ide-extension-null-manifest.test.mjs b/tests/scanners/ide-extension-null-manifest.test.mjs
new file mode 100644
index 0000000..74906eb
--- /dev/null
+++ b/tests/scanners/ide-extension-null-manifest.test.mjs
@@ -0,0 +1,92 @@
+// ide-extension-null-manifest.test.mjs — Regression tests for unparseable
+// JetBrains plugins.
+//
+// parseIntelliJPlugin signals "could not parse" as { manifest: null, warnings }
+// — a TRUTHY object — while parseVSCodeExtension signals it as a bare null.
+// scanOneExtension only guarded the bare-null form, so a JetBrains plugin with
+// no lib/ directory, an unreadable lib/, no jars, or no extractable jar reached
+// `manifest.hasSignature` and threw a TypeError. mapConcurrent had no per-item
+// isolation, so that one plugin aborted the entire ide-scan.
+
+import { describe, it, after } from 'node:test';
+import assert from 'node:assert/strict';
+import { join } from 'node:path';
+import { tmpdir } from 'node:os';
+import { mkdtemp, mkdir, writeFile, rm } from 'node:fs/promises';
+import { __testing } from '../../scanners/ide-extension-scanner.mjs';
+
+const { scanOneExtension } = __testing;
+const created = [];
+
+after(async () => {
+  for (const dir of created) await rm(dir, { recursive: true, force: true });
+});
+
+async function makePluginRoot(name) {
+  const root = await mkdtemp(join(tmpdir(), 'llmsec-jb-plugin-'));
+  created.push(root);
+  const dir = join(root, name);
+  await mkdir(dir, { recursive: true });
+  return dir;
+}
+
+function jbExt(location, id) {
+  return {
+    id,
+    version: '1.0.0',
+    type: 'jetbrains',
+    location,
+    publisher: 'unknown',
+    source: 'test',
+    isBuiltin: false,
+    signed: false,
+  };
+}
+
+describe('ide-extension-scanner — unparseable JetBrains plugin', () => {
+  it('does not throw when lib/ is missing entirely', async () => {
+    const dir = await makePluginRoot('NoLibPlugin');
+    const result = await scanOneExtension(jbExt(dir, 'NoLibPlugin'), { targetBase: dir });
+    assert.ok(result, 'expected a result object, not a throw');
+    assert.equal(result.id, 'NoLibPlugin');
+    assert.ok(
+      result.warnings.some(w => /lib/i.test(w)),
+      `expected a parse warning, got: ${JSON.stringify(result.warnings)}`
+    );
+    assert.equal(result.aggregate.verdict, 'ALLOW');
+  });
+
+  it('does not throw when lib/ exists but holds no jars', async () => {
+    const dir = await makePluginRoot('EmptyLibPlugin');
+    await mkdir(join(dir, 'lib'), { recursive: true });
+    await writeFile(join(dir, 'lib', 'notes.txt'), 'not a jar', 'utf8');
+    const result = await scanOneExtension(jbExt(dir, 'EmptyLibPlugin'), { targetBase: dir });
+    assert.ok(result, 'expected a result object, not a throw');
+    assert.ok(result.warnings.length >= 1);
+    assert.equal(result.aggregate.verdict, 'ALLOW');
+  });
+
+  it('does not throw when lib/ is a file rather than a directory', async () => {
+    const dir = await makePluginRoot('LibIsFilePlugin');
+    await writeFile(join(dir, 'lib'), 'this is not a directory', 'utf8');
+    const result = await scanOneExtension(jbExt(dir, 'LibIsFilePlugin'), { targetBase: dir });
+    assert.ok(result, 'expected a result object, not a throw');
+    assert.ok(result.warnings.length >= 1);
+  });
+
+  it('does not throw when the only jar is corrupt (unextractable)', async () => {
+    const dir = await makePluginRoot('CorruptJarPlugin');
+    await mkdir(join(dir, 'lib'), { recursive: true });
+    await writeFile(join(dir, 'lib', 'broken.jar'), 'PK truncated garbage', 'utf8');
+    const result = await scanOneExtension(jbExt(dir, 'CorruptJarPlugin'), { targetBase: dir });
+    assert.ok(result, 'expected a result object, not a throw');
+    assert.ok(result.warnings.length >= 1);
+  });
+
+  it('reports a parse failure without inventing findings', async () => {
+    const dir = await makePluginRoot('QuietPlugin');
+    const result = await scanOneExtension(jbExt(dir, 'QuietPlugin'), { targetBase: dir });
+    const counts = result.aggregate.counts;
+    assert.equal(counts.critical + counts.high + counts.medium, 0);
+  });
+});