ci(s001): kill the Windows sidecar with taskkill; bash kill leaves it running

Run 34078281292 hung on Windows long past the 60 s bound I had just added, so the hang was not
in my loop. `kill` from Git-bash does not stop a native Windows process: the backgrounded
desktop_windows_x86_64.exe outlived the step and kept the job alive. Cancelled by hand, twice
now on this same step.

`taskkill /T /F` takes the wrapper and its BEAM together, which on Windows is also the only
thing that clears finding F1's orphan.

Linux and macOS are green in the same run, with the shell built, HTTP 200 and cold start
measured. **Windows has still never been observed serving** — it is the one CI question this
slice has not answered, and the next run answers it either way, because the loop above it is
now bounded and prints serve.log on failure.

mix gate exit=0.

Signed-off-by: Ayla Croft <aylacroft@proton.me>

Author: HackTuah

.github/workflows/package.yml

@@ -229,12 +229,22 @@ jobs:
           echo "COLD_START_MS=$elapsed" | tee -a "$GITHUB_ENV"
           echo "### ${{ matrix.name }} — cold start to first HTTP 200: **${elapsed} ms**" >> "$GITHUB_STEP_SUMMARY"
           test "$code" = "200"
-          CHILD=$(pgrep -P "$PID" 2>/dev/null || true)
-          kill "$PID" || true
-          # The wrapper does not forward termination to the BEAM it launched — finding F1,
-          # re-measured at G4 as an orphan still serving 200 past 7.6 s. Kill the child
-          # explicitly or the runner leaves it behind.
-          [ -n "$CHILD" ] && kill "$CHILD" 2>/dev/null || true
+          # Stopping it, and Windows needs its own verb. `kill` from Git-bash does not stop a
+          # native Windows process, so the backgrounded .exe outlived the step and the job hung
+          # long past the bounded loops above — run 34078281292, cancelled by hand. `taskkill
+          # /T` takes the wrapper and its BEAM together, which on Windows is also the only
+          # thing that clears finding F1's orphan.
+          if [ "${{ runner.os }}" = "Windows" ]; then
+            taskkill //PID "$PID" //T //F >/dev/null 2>&1 || true
+            taskkill //IM desktop_windows_x86_64.exe //T //F >/dev/null 2>&1 || true
+          else
+            CHILD=$(pgrep -P "$PID" 2>/dev/null || true)
+            kill "$PID" || true
+            # The wrapper does not forward termination to the BEAM it launched — finding F1,
+            # re-measured at G4 as an orphan still serving 200 past 7.6 s. Kill the child
+            # explicitly or the runner leaves it behind.
+            [ -n "$CHILD" ] && kill "$CHILD" 2>/dev/null || true
+          fi
 
       - uses: actions/upload-artifact@v4
         with: