fix(llm-security): normalization/discovery evasion + SIG embedded-base64 & custom rules (#21,#23,#30,#36,#42,#52,#55)

#21 the bash normalizer decoded only \xHH, leaving ANSI-C octal/\u/\U forms literal so canonical rm/curl never surfaced; now decodes all three. #23 file-discovery keyed on extname so .env.local/.env.example (extname .local/.example) were silently skipped; now matches multi-part suffixes. #42 a legitimate leading UTF-8 BOM was flagged HIGH (and the tool's own auto-cleaner refused to strip it); pos-0 BOM now excepted. #52 collapseLetterSpacing used a literal space, letting multi-space/tab spacing evade; now [ \t]+. #55 redact(_,60,0) did slice(-0) and leaked the whole unredacted URL; showEnd===0 now means no tail.

#30 embedded base64 (const x = "<base64>") never satisfied the whole-string decode, so the SIG identity engine never saw it; added decodeEmbeddedBase64 as an OPT-IN param on normalizeForScan (default off — appending a decoded copy would double-count per-match findings, e.g. content-extractor's injection scan) and enabled it only in signature-scanner, which dedups variants. #36 signature-scanner ignored the documented sig.custom_rules_path policy option; now loads+merges custom rules through the same family filter. Suite 2004/0.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Claude-Session: https://claude.ai/code/session_01TcQyMTQfyrsAapaCMPxTtQ

tests/lib/file-discovery.test.mjs

@@ -0,0 +1,76 @@
+// file-discovery.test.mjs — Tests for scanners/lib/file-discovery.mjs
+// Zero external dependencies: node:test + node:assert only.
+//
+// Regression focus (v7.8.3, #23): discovery keyed on extname(name), but
+// extname('.env.local') === '.local' and extname('.env.example') === '.example',
+// so the multi-part entries in TEXT_EXTENSIONS were dead and these common
+// secret files were silently skipped.
+
+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, writeFile, rm } from 'node:fs/promises';
+import { discoverFiles } from '../../scanners/lib/file-discovery.mjs';
+
+const created = [];
+
+async function makeRepo(files) {
+  const root = await mkdtemp(join(tmpdir(), 'llmsec-disc-'));
+  created.push(root);
+  for (const [name, content] of Object.entries(files)) {
+    await writeFile(join(root, name), content, 'utf8');
+  }
+  return root;
+}
+
+after(async () => {
+  for (const dir of created) await rm(dir, { recursive: true, force: true });
+});
+
+describe('file-discovery — multi-part extensions (v7.8.3, #23)', () => {
+  it('discovers .env.local and .env.example', async () => {
+    const root = await makeRepo({
+      '.env.local': 'API_KEY=sk-local-secret\n',
+      '.env.example': 'API_KEY=changeme\n',
+      '.env': 'API_KEY=sk-real-secret\n',
+    });
+    const { files } = await discoverFiles(root);
+    const relPaths = files.map(f => f.relPath);
+    assert.ok(relPaths.includes('.env'), '.env must be discovered (control)');
+    assert.ok(relPaths.includes('.env.local'), '.env.local must be discovered');
+    assert.ok(relPaths.includes('.env.example'), '.env.example must be discovered');
+  });
+
+  it('discovers a prefixed multi-part name like backend.env.local', async () => {
+    const root = await makeRepo({
+      'backend.env.local': 'DB_PASSWORD=hunter2\n',
+    });
+    const { files } = await discoverFiles(root);
+    assert.ok(
+      files.some(f => f.relPath === 'backend.env.local'),
+      'backend.env.local must be discovered'
+    );
+  });
+
+  it('still skips unknown binary-ish extensions', async () => {
+    const root = await makeRepo({
+      'photo.png': 'not really a png but the extension rules it out\n',
+      'archive.tar.gz': 'binary-ish\n',
+    });
+    const { files, skipped } = await discoverFiles(root);
+    assert.equal(files.length, 0, 'unknown extensions must be skipped');
+    assert.ok(skipped >= 2);
+  });
+
+  it('still discovers extensionless files and plain known extensions', async () => {
+    const root = await makeRepo({
+      'Makefile': 'all:\n\ttrue\n',
+      'index.mjs': 'export default 1;\n',
+    });
+    const { files } = await discoverFiles(root);
+    const relPaths = files.map(f => f.relPath);
+    assert.ok(relPaths.includes('Makefile'));
+    assert.ok(relPaths.includes('index.mjs'));
+  });
+});