feat(commands): E14 part 3 — /security mcp-baseline-reset slash command

Wave C step C3: closes E14 with the user-facing reset command.

After a legitimate MCP server upgrade the sticky baseline (added in C1)
becomes a stale "what the tool used to say" anchor and every subsequent
post-mcp-verify advisory will re-flag the change. /security mcp-baseline-reset
lets the user acknowledge the upgrade so the next call seeds a fresh
baseline.

New files:
- scanners/mcp-baseline-reset.mjs — small CLI wrapper around clearBaseline /
  listBaselines. Modes: --list (read-only), --target <name>, no-args (all).
  Outputs JSON summary on stdout. Exit 0 always (idempotent).
- commands/mcp-baseline-reset.md — dispatcher following mcp-inspect.md
  shape. Frontmatter: name=security:mcp-baseline-reset, sonnet model,
  Read/Bash/AskUserQuestion tools. 4-step body (list -> confirm scope
  -> execute -> confirm result).
- tests/scanners/mcp-baseline-reset.test.mjs — 10 CLI tests across
  --list, --target, clear-all, idempotency, history preservation, and
  bare-positional sugar.

Updated:
- commands/security.md — new row in commands table after mcp-inspect.
- CLAUDE.md — new commands-table row + new v7.3.0 narrative section
  describing the baseline schema, cumulative-drift detection, reset
  semantics, and the LLM_SECURITY_MCP_CACHE_FILE override.
- Plugin README.md — new MCP-baseline-reset row in commands table,
  scanner count 12 standalone -> 13 standalone, new "MCP Description
  Drift (E14, v7.3.0)" subsection explaining the sticky baseline,
  cumulative threshold, reset semantics, and env-var override.
- Root marketplace README.md — scanner count 22 -> 23 (10 orchestrated +
  13 standalone), command count 19 -> 20, test count 1511 -> 1768.

Wave C complete: 1738 -> 1768 tests (+30 across C1/C2/C3). Per plan,
Wave C does NOT bump the plugin version — that lands at the wave-bundle
release. The advisory text in post-mcp-verify already references the
new command path so the user has a ready remediation step.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

plugins/llm-security/scanners/mcp-baseline-reset.mjs

@@ -0,0 +1,101 @@
+#!/usr/bin/env node
+// mcp-baseline-reset.mjs — Reset MCP description-cache baselines.
+//
+// Purpose:
+//   The description cache (scanners/lib/mcp-description-cache.mjs) anchors a
+//   sticky baseline per MCP tool so that cumulative drift can be detected
+//   across many small updates. After a legitimate MCP server upgrade the
+//   baseline becomes a stale "what the tool used to say" reference and must
+//   be reset so the next call seeds a fresh baseline.
+//
+// Modes:
+//   --list                    Read-only — list current baselines as JSON.
+//   --target <toolName>       Clear baseline for one tool.
+//   (no args)                 Clear baselines for all tools.
+//
+// Output: JSON summary on stdout. Exit 0 always (idempotent).
+//
+// Used by /security mcp-baseline-reset slash command. Not part of
+// scan-orchestrator.
+
+import {
+  clearBaseline,
+  listBaselines,
+  loadCache,
+} from './lib/mcp-description-cache.mjs';
+
+function parseArgs(argv) {
+  const args = { list: false, target: null };
+  for (let i = 2; i < argv.length; i++) {
+    const a = argv[i];
+    if (a === '--list') {
+      args.list = true;
+    } else if (a === '--target' || a === '-t') {
+      args.target = argv[++i] || null;
+    } else if (a === '--help' || a === '-h') {
+      args.help = true;
+    } else if (!a.startsWith('--')) {
+      // bare positional treated as target for convenience
+      args.target = a;
+    }
+  }
+  return args;
+}
+
+function help() {
+  process.stdout.write(
+    'mcp-baseline-reset.mjs — Reset MCP description-cache baselines.\n\n' +
+    'Usage:\n' +
+    '  node scanners/mcp-baseline-reset.mjs --list\n' +
+    '  node scanners/mcp-baseline-reset.mjs --target <tool>\n' +
+    '  node scanners/mcp-baseline-reset.mjs            # clear all\n\n' +
+    'Output: JSON. Exit code 0 always.\n',
+  );
+}
+
+function emit(obj) {
+  process.stdout.write(JSON.stringify(obj, null, 2) + '\n');
+}
+
+function main() {
+  const args = parseArgs(process.argv);
+  if (args.help) {
+    help();
+    return 0;
+  }
+
+  if (args.list) {
+    const baselines = listBaselines();
+    emit({
+      mode: 'list',
+      count: baselines.length,
+      baselines: baselines.map((b) => ({
+        tool: b.tool,
+        baseline_excerpt: (b.baseline || '').slice(0, 120),
+        seen_at: b.seenAt,
+        last_seen: b.lastSeen,
+        history_events: b.history,
+      })),
+    });
+    return 0;
+  }
+
+  // Reset path
+  const result = clearBaseline(args.target || undefined);
+  // After clearing, count remaining baselines
+  const cache = loadCache();
+  let remaining = 0;
+  for (const entry of Object.values(cache)) {
+    if (entry && entry.baseline) remaining++;
+  }
+  emit({
+    mode: 'reset',
+    target: args.target || null,
+    cleared: result.cleared,
+    tools: result.tools,
+    remaining,
+  });
+  return 0;
+}
+
+process.exit(main());