# KWP/FTDI edit checklist

You are about to edit timing-sensitive K-Line communication code in one of:
- `Infrastructure/Kwp/KwpCommon.cs`
- `Infrastructure/Kwp/KW1281Connection.cs`
- `Infrastructure/Kwp/FtdiInterface.cs`
- `Services/Impl/KwpService.cs`

Read the relevant file(s) first, then apply the following checks before and after your edit.

---

## Timing constraints

**`KW1281Connection.SendPacket`** calls `Thread.Sleep(5)` after each byte written.
This is the mandatory KWP inter-byte gap. Do not remove or reduce it.

**`KwpCommon.WakeUp`** implements the 5-baud slow-init sequence.
Any change to Sleep durations here will break ECU connection. Leave it alone unless
you are explicitly fixing a timing bug and have the KW1281 spec in front of you.

---

## FtdiInterface lifetime

`KwpService` constructs a `FtdiInterface` at the start of each operation and disposes it
at the end. This is intentional — the ECU expects a fresh session per dialog.
Do not try to hold `FtdiInterface` open across multiple `KwpService` calls.

`FtdiInterface._buf` is a reused `byte[1]` field for single-byte reads/writes.
Do not allocate a new array inside `ReadByte()` or `WriteByteRaw()`.

---

## Error handling invariant

Every `KwpService` method that opens an `FtdiInterface` must dispose it in all code paths:

```csharp
FtdiInterface? iface = null;
try
{
    iface = new FtdiInterface(port, KLineBaudRate);
    // ... work ...
}
catch (Exception ex) { /* log */ }
finally { iface?.Dispose(); }
```

If you add a new KwpService method, verify it follows this pattern.
K-Line errors throw `InvalidOperationException` or `TimeoutException`.
Do not catch and swallow these inside the method body — the ViewModel catch block depends on seeing them.

---

## Allocation patterns (known debt — do not worsen)

`KW1281Connection` uses `List<byte>` for packet buffers throughout.
If you want to reduce allocations, convert the entire packet path at once.
Converting one method in isolation creates a mixed pattern that is harder to reason about.

---

## After your edit, verify:

1. Search for `new FtdiInterface` — every occurrence has a matching `finally { iface?.Dispose(); }`
2. `Thread.Sleep(5)` in `SendPacket` is still present
3. `ProgressChanged` is still called with increasing percent values so the progress dialog updates
4. No new `Thread.Sleep`, `Console.Write`, or `Logger.WriteLine` was added inside a per-byte loop