ACP produces no JSON-RPC response - IntelliJ integration broken (v2.13.0)

### Checks

- [x] I have searched [github.com/aws/amazon-q-developer-cli/issues](https://github.com/aws/amazon-q-developer-cli/issues?q=) and there are no duplicates of my issue
- [x] I have run `q doctor` in the affected terminal session
- [x] I have run `q restart` and replicated the issue again

### Operating system

Linux 6.8.0-136-generic - Ubuntu 24.04.4 LTS

### Expected behaviour

JSON-RPC response with agent capabilities on stdout

### Actual behaviour

No stdout output. Process exits 0.

Debug logs show: CLI reaches "launching q chat binary" then produces no further output. The internal ACP engine subprocess appears to not start or not receive stdin.

### Steps to reproduce

printf '{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"capabilities":{},"clientInfo":{"name":"test","version":"1.0"}}}\n' | kiro-cli acp

### Environment

```yaml

[q-details]
version = "2.13.0"
hash = "3afe42f288dc2f00504f51f904e134dafa58e7f2"
date = "2026-07-16T19:11:00.367233Z (5d ago)"
variant = "full"

[system-info]
chip = "12th Gen Intel(R) Core(TM) i7-1265U"
total-cores = 10
memory = "31.04 GB"

[system-info.os.linux]
kernel_version = "6.8.0-136-generic"
id = "ubuntu"
name = "Ubuntu"
pretty_name = "Ubuntu 24.04.4 LTS"
version_id = "24.04"
version = "24.04.4 LTS (Noble Numbat)"

[environment]
cwd = "/home/USER"
cli-path = "/home/USER"
os = "Linux"
shell-path = "/usr/bin/bash"
install-method = "unknown"

[env-vars]
DISPLAY = ":1"
PATH = "/home/USER/.rd/bin:/home/USER/.rd/bin:/home/USER/.local/bin:/opt/apache-maven/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin:/snap/bin:/home/USER/.local/bin:/home/USER/.local/share/JetBrains/Toolbox/scripts"
QTERM_SESSION_ID = "e6a5fb3e16434946b6407df84d4ba21b"
QT_IM_MODULE = "ibus"
Q_SET_PARENT_CHECK = "1"
Q_TERM = "2.13.0"
SHELL = "/bin/bash"
TERM = "xterm-256color"
XDG_CURRENT_DESKTOP = "ubuntu:GNOME"
XDG_SESSION_DESKTOP = "ubuntu"
XDG_SESSION_TYPE = "x11"
XMODIFIERS = "@im=ibus"
```

Start with the `kiro-cli acp` entry point and reproduce the issue using the provided `initialize` JSON-RPC input on Ubuntu. Follow the log boundary after "launching q chat binary" to determine why no response reaches stdout. Done means the command starts its internal ACP engine and returns an agent-capabilities JSON-RPC response.

Written by the indexing model from the issue text.