PM_K-1 docs: make the two-step flash explicit (main.py is not drag-and-drop)

A user dropped main.py onto the RPI-RP2 BOOTSEL drive (which only accepts a .uf2)
and it vanished on reboot. Clarify in pico/README.md and info-kit.html that
flashing is two distinct steps: (1) drag-and-drop the MicroPython .uf2, then
(2) copy main.py over USB serial with Thonny/mpremote — the Pico is not a USB
drive once MicroPython is running.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

info-kit.html

@@ -106,14 +106,19 @@
       <a class="dl" href="/pico-main.py" download="main.py">Download main.py ↓</a>
       <a class="dl alt" href="https://codeberg.org/VARASYS/metronome/src/branch/main/pico" target="_blank" rel="noopener">Source + README ↗</a>
     </p>
+    <p class="sub"><b>Two separate steps</b> — and <b><code>main.py</code> is not a drag‑and‑drop file.</b> The
+      <code>RPI‑RP2</code> drive only accepts a <code>.uf2</code> firmware file; a <code>.py</code> copied there is
+      discarded on reboot. You drag‑and‑drop the firmware once, then copy <code>main.py</code> over USB serial.</p>
     <ol class="steps">
-      <li>Install <b>MicroPython</b>: hold <b>BOOTSEL</b>, plug the Pico into USB, and drop the MicroPython
-        <code>.uf2</code> onto the <code>RPI‑RP2</code> drive
+      <li><b>Install MicroPython</b> (drag‑and‑drop, one time): hold <b>BOOTSEL</b>, plug the Pico into USB, and drop
+        the MicroPython <code>.uf2</code> onto the <code>RPI‑RP2</code> drive
         (<a href="https://micropython.org/download/RPI_PICO/" target="_blank" rel="noopener">Pico</a> /
-        <a href="https://micropython.org/download/RPI_PICO2/" target="_blank" rel="noopener">Pico 2</a>).</li>
-      <li>Copy <code>main.py</code> onto the Pico as <code>main.py</code> (in
-        <a href="https://thonny.org" target="_blank" rel="noopener">Thonny</a>: <i>File ▸ Save as ▸ Raspberry Pi Pico</i>,
-        or <code>mpremote cp main.py :main.py</code>).</li>
+        <a href="https://micropython.org/download/RPI_PICO2/" target="_blank" rel="noopener">Pico 2</a>). It reboots
+        on its own and the drive disappears — that's correct.</li>
+      <li><b>Copy <code>main.py</code></b> (the Pico is no longer a USB drive, so use a serial tool):
+        in <a href="https://thonny.org" target="_blank" rel="noopener">Thonny</a> pick the interpreter
+        <i>MicroPython (Raspberry Pi Pico)</i>, then <i>File ▸ Save as ▸ Raspberry Pi Pico</i> as <code>main.py</code>;
+        or <code>mpremote cp main.py :main.py</code>.</li>
       <li>Reset — it boots straight into the metronome.</li>
       <li>Add your own grooves by pasting program strings from the editor into the <code>PROGRAMS</code> list at the
         top of <code>main.py</code>. If colours, touch, or the joystick look off, flip a flag in the

pico/README.md

@@ -21,17 +21,35 @@ buzzer, joystick, the polymeter engine — no external libraries).
 
 The components are wired on the board — you don't breadboard anything; just seat the Pico.
 
-## Flash it
+## Flash it — TWO separate steps
 
-1. **MicroPython:** hold **BOOTSEL**, plug the Pico into USB, and copy the MicroPython UF2
-   onto the `RPI-RP2` drive that appears:
-   - Pico / Pico W → <https://micropython.org/download/RPI_PICO/>
+> ⚠️ **`main.py` is NOT a drag-and-drop file.** The `RPI-RP2` drive that appears in BOOTSEL mode
+> is the bootloader, and it *only* accepts a `.uf2` firmware file — anything else (like `main.py`)
+> is silently discarded on the next reboot. You first flash MicroPython with a `.uf2` (drag-and-drop),
+> and *then* copy `main.py` over the USB serial link with Thonny or mpremote. Two different steps.
+
+### Step 1 — install MicroPython (drag-and-drop a `.uf2`, one time)
+
+1. Download the MicroPython firmware **`.uf2`** for your board:
+   - Pico / Pico W → <https://micropython.org/download/RPI_PICO/> (or `RPI_PICO_W`)
    - Pico 2 / Pico 2 W → <https://micropython.org/download/RPI_PICO2/>
-2. **The firmware:** open `main.py` in [Thonny](https://thonny.org) (or `rshell`/`mpremote`)
-   and save it to the Pico **as `main.py`**.
-   - Thonny: open the file → **File ▸ Save as… ▸ Raspberry Pi Pico** → name it `main.py`.
-   - mpremote: `mpremote cp main.py :main.py`
-3. Reset (replug). It boots straight into the metronome.
+2. Hold **BOOTSEL**, plug into USB → the `RPI-RP2` drive appears.
+3. **Drag the `.uf2` file onto that drive.** It copies, the Pico reboots on its own, and the drive
+   **disappears** — that's correct and means MicroPython is installed. (Don't use BOOTSEL again unless
+   you're reinstalling the firmware.)
+
+### Step 2 — copy `main.py` (over USB serial, NOT to a drive)
+
+After step 1 the Pico runs MicroPython and **no longer shows up as a USB drive** — so you can't drag
+files to it. Use a tool that talks to it over USB serial:
+
+- **Thonny (easiest):** install [Thonny](https://thonny.org), plug the Pico in normally, then
+  bottom-right click the interpreter selector → **MicroPython (Raspberry Pi Pico)** (you should see
+  a `>>>` prompt in the Shell). Open `main.py`, then **File ▸ Save as… ▸ Raspberry Pi Pico** and save
+  it as exactly **`main.py`**.
+- **mpremote (command line):** `pip install mpremote` then `mpremote cp main.py :main.py`
+
+Reset (replug) and it boots straight into the metronome.
 
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