fix(observe): skip Windows AppInstallerPythonRedirector.exe in resolve_python_cmd (#1511)

On Windows 10/11 without Python installed from the Microsoft Store, the
"App Execution Alias" stubs at %LOCALAPPDATA%\Microsoft\WindowsApps\python.exe
and python3.exe are symlinks to AppInstallerPythonRedirector.exe. These
stubs neither launch Python nor honor `-c`; calls print a bare "Python "
line and exit, silently breaking every JSON-parsing step in observe.sh.

Net effect: observations.jsonl is never written, CLV2 appears installed
correctly, and the only residual artifact is `.last-purge`.

This commit:
  1. Adds `_is_windows_app_installer_stub` helper that detects the stub
     via `command -v` output and optional `readlink -f` resolution.
  2. Teaches `resolve_python_cmd` to skip stub candidates and fall
     through to the next real interpreter (typically C:\...\Python3xx\python.exe).
  3. Exports the stub-aware CLV2_PYTHON_CMD before sourcing
     detect-project.sh, which already honors an already-set value,
     so the shared helper does not re-resolve and re-select the stub.

POSIX-compatible. No behavior change on macOS / Linux / WSL where no
such stub exists.

Refs: observations.jsonl empty on Windows Claude Desktop users.

skills/continuous-learning-v2/hooks/observe.sh

@@ -27,18 +27,45 @@ if [ -z "$INPUT_JSON" ]; then
   exit 0
 fi
 
+_is_windows_app_installer_stub() {
+  # Windows 10/11 ships an "App Execution Alias" stub at
+  #   %LOCALAPPDATA%\Microsoft\WindowsApps\python.exe
+  #   %LOCALAPPDATA%\Microsoft\WindowsApps\python3.exe
+  # Both are symlinks to AppInstallerPythonRedirector.exe which, when Python
+  # is not installed from the Store, neither launches Python nor honors "-c".
+  # Calls to it hang or print a bare "Python " line, silently breaking every
+  # JSON-parsing step in this hook. Detect and skip such stubs here.
+  local _candidate="$1"
+  [ -z "$_candidate" ] && return 1
+  local _resolved
+  _resolved="$(command -v "$_candidate" 2>/dev/null || true)"
+  [ -z "$_resolved" ] && return 1
+  case "$_resolved" in
+    *AppInstallerPythonRedirector.exe|*AppInstallerPythonRedirector.EXE) return 0 ;;
+  esac
+  # Also resolve one level of symlink on POSIX-like shells (Git Bash, WSL).
+  if command -v readlink >/dev/null 2>&1; then
+    local _target
+    _target="$(readlink -f "$_resolved" 2>/dev/null || readlink "$_resolved" 2>/dev/null || true)"
+    case "$_target" in
+      *AppInstallerPythonRedirector.exe|*AppInstallerPythonRedirector.EXE) return 0 ;;
+    esac
+  fi
+  return 1
+}
+
 resolve_python_cmd() {
   if [ -n "${CLV2_PYTHON_CMD:-}" ] && command -v "$CLV2_PYTHON_CMD" >/dev/null 2>&1; then
     printf '%s\n' "$CLV2_PYTHON_CMD"
     return 0
   fi
 
-  if command -v python3 >/dev/null 2>&1; then
+  if command -v python3 >/dev/null 2>&1 && ! _is_windows_app_installer_stub python3; then
     printf '%s\n' python3
     return 0
   fi
 
-  if command -v python >/dev/null 2>&1; then
+  if command -v python >/dev/null 2>&1 && ! _is_windows_app_installer_stub python; then
     printf '%s\n' python
     return 0
   fi
@@ -52,6 +79,11 @@ if [ -z "$PYTHON_CMD" ]; then
   exit 0
 fi
 
+# Propagate our stub-aware selection so detect-project.sh (which is sourced
+# below) does not re-resolve and silently fall back to the App Installer stub.
+# detect-project.sh honors an already-set CLV2_PYTHON_CMD.
+export CLV2_PYTHON_CMD="${CLV2_PYTHON_CMD:-$PYTHON_CMD}"
+
 # ─────────────────────────────────────────────
 # Extract cwd from stdin for project detection
 # ─────────────────────────────────────────────