Update CLAUDE.md to reflect current multi-file architecture

Document the new file structure, both connection methods (serial/network),
both workflows (serial config and firmware update), key design notes
(auth credentials, firmware bug workaround, API paths), and the planned
network-based config workflow.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

CLAUDE.md

@@ -0,0 +1,76 @@
+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Running the Tool
+
+```bash
+python3 es24n_conf.py
+```
+
+The script requires root or appropriate serial device permissions. If the serial device is inaccessible, re-run with `sudo`.
+
+## What This Is
+
+An interactive CLI tool for configuring and updating TrueNAS ES24N expansion shelf IOM (I/O Module) controllers via the Redfish API. It supports two connection methods:
+
+- **Serial (loopback):** Connects via USB serial cable to the IOM1 console port, then reaches the Redfish API at `https://127.0.0.1` using `root` credentials. Used for initial network configuration when the IOM has no IP address yet.
+- **Network:** Connects directly to the IOM's management IP address using `Admin` credentials. Used for firmware updates and (planned) network reconfiguration once the IOM is reachable on the network.
+
+No external dependencies — Python 3 standard library only. Compatible with TrueNAS (FreeBSD) and Linux.
+
+## File Structure
+
+```
+es24n_conf.py          ← Entry point and main menu (run this)
+es24n/
+    ui.py              ← ANSI colours, display helpers, input prompts
+    serial_port.py     ← SerialPort class (termios/fcntl/select, no pyserial)
+    models.py          ← IOMConfig and ShelfConfig dataclasses
+    redfish.py         ← Redfish API client (shared by all workflows)
+    workflow_serial.py ← Serial-based IOM network configuration workflow
+    workflow_firmware.py ← IOM and Fabric Card firmware update workflow
+```
+
+`es24n_conf.py` adds `es24n/` to `sys.path` at startup so all inter-module imports work without a package structure.
+
+## Workflows
+
+### 1 — Serial Network Configuration (`workflow_serial.py`)
+5-step workflow using the USB serial cable:
+1. Detect USB serial device (`/dev/ttyUSB*`, `/dev/ttyACM*`, `/dev/ttyU*`)
+2. Open 115200-baud 8N1 connection and wake the IOM console
+3. Query current network settings via Redfish (`GET` over `127.0.0.1`)
+4. Collect new settings from user (Static IP or DHCP)
+5. Apply via Redfish `PATCH` over `127.0.0.1`
+
+### 2 — Firmware Update (`workflow_firmware.py`)
+Updates IOM firmware and/or Fabric Card firmware over the network:
+- Prompts for which IOM(s) to update (IOM1, IOM2, or both)
+- Uploads firmware via `POST` to `/redfish/v1/UpdateService` (multipart form)
+- Triggers update via Redfish `SimpleUpdate` action
+- Polls `/redfish/v1/TaskService/Tasks/` until completion
+- Restarts the IOM (and fabric card if applicable) after each update
+- The firmware file must be re-uploaded between the IOM and Fabric Card steps — it does not persist after the first update (firmware quirk, documented in `_update_fabric_fw()`)
+- Scans the current working directory for firmware files (`.bin`, `.img`, `.fw`, `.hex`, `.zip`, `.tar`, `.tgz`, `.gz`) and presents them as a numbered list before falling back to manual path entry
+
+## Key Design Notes
+
+**Static IP firmware bug workaround:** Setting a static IP requires two sequential PATCH requests:
+- Pass 1: set `IPv4StaticAddresses` (while DHCP is still enabled)
+- Pass 2: disable `DHCPv4` (after the address is committed)
+
+A single PATCH combining both fields fails due to a known ES24N firmware bug. Documented in `_apply_iom()` in `workflow_serial.py`.
+
+**Authentication:**
+- Serial loopback (`127.0.0.1`): username `root`
+- Network IP: username `Admin`
+
+**Redfish API paths:**
+- Network config: `/redfish/v1/Managers/{IOM1|IOM2}/EthernetInterfaces/1`
+- Firmware update: `/redfish/v1/UpdateService`
+- Fabric card: `/redfish/v1/Chassis/{IOM1|IOM2}/NetworkAdapters/1`
+
+## Planned Features
+
+- Network-based IOM network configuration (`workflow_network.py`) — same config workflow as serial but connecting via the IOM's existing IP address using `Admin` credentials, for cases where the IOM is already reachable on the network