chore(pack): per-dir .npmignore for Python bytecode + tarball hygiene test

npm 11 ignores the root .npmignore inside files[]-allowlisted directories,
so 24 __pycache__/*.pyc entries were shipping in the tarball. Per-dir
.npmignore files in mcp-server/ and prd_taskmaster/ do the real filtering;
the root file documents the trap defensively. New test asserts the
npm pack --dry-run manifest stays free of bytecode and marketplace.json.

Imported-From: prd-taskmaster-plugin@v5-final (f140490)
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
(cherry picked from commit 82ac1b0)

Author: claude

.npmignore

@@ -0,0 +1,19 @@
+# Root .npmignore — Python bytecode + dev-loopback marketplace patterns.
+#
+# IMPORTANT (npm 11 behavior): when package.json `files` lists a directory
+# like "mcp-server/" as an allowlist, the root .npmignore is NOT honored
+# for files INSIDE that directory. Filters must live in per-subdirectory
+# .npmignore files to actually take effect.
+#
+# The root entries below are kept defensively for:
+#   - future npm versions that may honor root .npmignore with directory files
+#   - fallback if a subdir .npmignore is ever accidentally deleted
+#   - self-documentation of the filtering intent
+#
+# The ACTUAL working filters live at:
+#   - mcp-server/.npmignore     (excludes __pycache__, *.pyc)
+#   - prd_taskmaster/.npmignore (excludes __pycache__, *.pyc)
+#   - .claude-plugin/.npmignore (excludes marketplace.json dev config)
+**/__pycache__
+*.pyc
+.claude-plugin/marketplace.json

mcp-server/.npmignore

@@ -0,0 +1,2 @@
+__pycache__
+*.pyc

prd_taskmaster/.npmignore

@@ -0,0 +1,2 @@
+__pycache__
+*.pyc

tests/plugin/test_packaging_identity.py

@@ -1,4 +1,8 @@
 import json
+import shutil
+import subprocess
+
+import pytest
 from pathlib import Path
 
 
@@ -55,3 +59,24 @@ def test_product_spec_marks_backend_abstraction_shipped_v41():
     assert "auto|taskmaster|native" in content
     assert "detect/init/parse_prd/expand/rate" in content
     assert "agent_action_required" in content
+
+
+@pytest.mark.skipif(shutil.which("npm") is None, reason="npm not available")
+def test_npm_pack_excludes_python_bytecode():
+    # npm 11 does not honor the root .npmignore inside `files[]`-allowlisted
+    # directories; per-subdir .npmignore files carry the real filtering. This
+    # test guards the tarball against __pycache__/*.pyc regressions.
+    result = subprocess.run(
+        ["npm", "pack", "--dry-run", "--json"],
+        cwd=REPO_ROOT,
+        capture_output=True,
+        text=True,
+        timeout=120,
+    )
+    assert result.returncode == 0, result.stderr
+
+    manifest = json.loads(result.stdout)
+    paths = [entry["path"] for entry in manifest[0]["files"]]
+    offenders = [p for p in paths if ".pyc" in p or "__pycache__" in p]
+    assert offenders == []
+    assert not any("marketplace.json" in p for p in paths)