Mirrored networking: port 5004 loopback TCP connections never complete (adjacent ports work)

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### Windows Version

Windows 11 25H2 (OS Build 26200.8875)

### WSL Version

```
WSL version: 2.7.10.0
Kernel version: 6.18.33.2-2
WSLg version: 1.0.73.2
MSRDC version: 1.2.6676
Direct3D version: 1.611.1-81528511
DXCore version: 10.0.26100.1-240331-1435.ge-release
Windows version: 10.0.26200.8875
```

### Are you using WSL 1 or WSL 2?

- [x] WSL 2
- [ ] WSL 1

### Kernel Version

6.18.33.2-microsoft-standard-WSL2

### Distro Version

Ubuntu 24.04.1 LTS (Noble Numbat)

### Other Software

- Vite 5.4.14 (dev server) — used initially; issue reproduces without Vite
- Node.js / Python 3 sockets — minimal reproducers below

### Repro Steps

1. Configure `%USERPROFILE%\.wslconfig`:

```ini
[wsl2]
networkingMode=mirrored
memory=6GB
processors=4
swap=8GB

[experimental]
autoMemoryReclaim=Disabled
```

2. Restart WSL: `wsl --shutdown`, then reopen the distro.

3. Run this Python loopback test inside WSL (no other process on port 5004):

```python
import socket, threading, time

port = 5004

def server():
s = socket.socket()
s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
s.bind(("127.0.0.1", port))
s.listen(5)
s.settimeout(3)
try:
conn, addr = s.accept()
print("accepted", addr)
conn.send(b"ok")
conn.close()
except Exception as e:
print("accept failed:", e)
s.close()

threading.Thread(target=server, daemon=True).start()
time.sleep(0.3)

c = socket.socket()
c.settimeout(3)
try:
c.connect(("127.0.0.1", port))
print("client ok:", c.recv(8))
except Exception as e:
print("client failed:", e)
```

4. Optionally compare adjacent ports by changing `port` to `5003`, `5005`, or `5008`.

### Expected Behavior

- Server prints `accepted ('127.0.0.1', )`
- Client prints `client ok: b'ok'`
- Same behavior as ports 5003 and 5005

### Actual Behavior

On **port 5004 only**:

- `bind()` and `listen()` succeed
- `accept()` times out (no connection received)
- Client `connect()` times out
- TCP handshake never completes on loopback

Adjacent ports work normally:

| Port | bind | listen | accept | client connect |
|------|------|--------|--------|----------------|
| 5003 | OK | OK | OK | OK |
| **5004** | OK | OK | **TIMEOUT** | **TIMEOUT** |
| 5005 | OK | OK | OK | OK |
| 5008 | OK | OK | OK | OK |

This is **not application-specific**. The same failure occurs with:

- Raw Python `socket` (above)
- Raw Node.js `http.createServer()` on `127.0.0.1:5004`
- Vite dev server (`vite serve --port 5004`) — prints `ready` but all HTTP requests hang indefinitely

A full PC restart does **not** fix the issue.

### Impact

Local development servers bound to port 5004 appear healthy (`ss` shows `LISTEN`, Vite prints `ready`) but are completely unreachable on `127.0.0.1:5004` from inside WSL. A reverse proxy (e.g. Vite hub on port 5000) fails with `ETIMEDOUT 127.0.0.1:5004`.

**Workaround:** Use a different port (e.g. 5008) or switch to `networkingMode=NAT`.

### Diagnostic Logs

**WSL side — port 5004 socket state while hung:**

```
$ ss -tlnp | grep 5004
LISTEN 0 128 127.0.0.1:5004 0.0.0.0:* users:(("python3",pid=...,fd=5))
```

**Windows side — no listener on 5004:**

```
> netstat -ano | findstr :5004
(no output)

> Get-NetTCPConnection -LocalPort 5004
(no connections)

> netsh int ipv4 show excludedportrange protocol=tcp
Start Port End Port
---------- --------
50000 50059 *
```

Port 5004 is **not** in the Windows excluded port range (50000–50059).

**Linux reserved/ephemeral ports:**

```
$ cat /proc/sys/net/ipv4/ip_local_reserved_ports
(empty)

$ sysctl net.ipv4.ip_local_port_range
net.ipv4.ip_local_port_range = 44620 48715
```

**Routing table (local):**

```
local 127.0.0.0/8 dev lo proto kernel scope host src 127.0.0.1
local 127.0.0.1 dev lo proto kernel scope host src 127.0.0.1
```

### Related issues

This may be related to #41102 (general mirrored-mode localhost TCP handshake failure) but differs in that **only port 5004 is affected** while immediately adjacent ports (5003, 5005) work correctly. That port-specific behavior suggests a distinct mirrored-networking port routing or exclusion bug.

### Additional Information

- Issue persists across PC restarts
- Only occurs with `networkingMode=mirrored` (not tested with NAT in this report, but NAT is the known workaround from related issues)
- WSL networking logs not yet attached; will add via `collect-wsl-logs.ps1 -LogProfile networking` if requested

Start by running the supplied Python loopback reproducer on port 5004 and comparing it with ports 5003 and 5005 under mirrored networking. If requested, collect networking logs with collect-wsl-logs.ps1 -LogProfile networking. Done means the port 5004 TCP handshake completes in mirrored mode without regressing adjacent ports.

Written by the indexing model from the issue text.