MacOS Disk Images not unmounted

### 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

macOS 26.5.2 (25F84)

### Expected behaviour

When updating kiro-cli mounts a dmg file to install the update. On completion it should unmount this volume to ensure that dangling volumes don't consume disk space.

### Actual behaviour

Kiro-cli does not unmount the volume, instead leaving the dangling volume and creating a new one each time. Over time this consume GiB of disk space due to these dangling volumes that don't ever appear to be cleaned up. The user has to manually unmount them (e.g. `sudo diskutil unmount force`) in order to clean them up.

### Steps to reproduce

On a MacOS system that has had multiple kiro-cli updates run `df -hal`. On the affected systems there were multiple Kiro CLI volumes of the form:

```
/dev/disk7s1 1.3Gi 1.3Gi 2.7Mi 100% 101 4.3G 0% /Volumes/Kiro CLI 1
/dev/disk8s1 1.3Gi 1.3Gi 2.6Mi 100% 101 4.3G 0% /Volumes/Kiro CLI 2
/dev/disk9s1 1.3Gi 1.3Gi 2.7Mi 100% 101 4.3G 0% /Volumes/Kiro CLI 3
/dev/disk10s1 1.3Gi 1.3Gi 2.6Mi 100% 101 4.3G 0% /Volumes/Kiro CLI 4
/dev/disk11s1 1.3Gi 1.3Gi 2.6Mi 100% 101 4.3G 0% /Volumes/Kiro CLI 5
/dev/disk12s1 1.3Gi 1.3Gi 2.6Mi 100% 101 4.3G 0% /Volumes/Kiro CLI 6
```

### Environment

```yaml

[q-details]
version = "2.16.0"
hash = "ac4bc3b1417d7cec0c95266cd23b5e7feb8aa3f6"
date = "2026-07-30T22:38:17.601521Z (3d ago)"
variant = "full"

[system-info]
os = "macOS 26.5.2 (25F84)"
chip = "Apple M1 Pro"
total-cores = 10
memory = "32.00 GB"

[environment]
cwd = "/Users/USER/workspaces/EC2ReleaseVelocityAICapabilities/src/EC2ReleaseVelocityProgram"
cli-path = "/Users/USER/workspaces/EC2ReleaseVelocityAICapabilities/src/EC2ReleaseVelocityProgram"
os = "Mac"
shell-path = "/bin/zsh"
shell-version = "5.9"
terminal = "iTerm 2"
install-method = "unknown"

[env-vars]
PATH = "/Users/USER/.local/state/fnm_multishells/3700_1784712440745/bin:/Users/USER/.bun/bin:/Users/USER/.aim/mcp-servers:/Users/USER/.pyenv/shims:/usr/local/opt/mysql@5.7/bin:/Users/USER/.rbenv/shims:/usr/local/sbin:/Users/USER/.toolbox/bin:/Users/USER/bin:/usr/local/bin:/Users/USER/node_modules/.bin:/opt/homebrew/bin:/opt/homebrew/sbin:/usr/local/bin:/System/Cryptexes/App/usr/bin:/usr/bin:/bin:/usr/sbin:/sbin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/local/bin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/bin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/appleinternal/bin:/pkg/env/global/bin:/Library/Apple/usr/bin:/usr/local/go/bin:/Users/USER/.cargo/bin:/Applications/iTerm.app/Contents/Resources/utilities:/Users/USER/.local/bin:/Users/USER/.local/bin:/Users/USER/Library/Application Support/Coursier/bin:/Users/USER/.cargo/bin"
QTERM_SESSION_ID = "3b7b6f69962c40cca712476e539c545e"
Q_SET_PARENT_CHECK = "1"
Q_TERM = "2.13.0"
SHELL = "/bin/zsh"
TERM = "xterm-256color"
__CFBundleIdentifier = "com.googlecode.iterm2"
```

Start by reproducing the issue after multiple Kiro CLI updates and run `df -hal` to confirm the dangling volumes. Trace the macOS update path that mounts the DMG and compare it with the documented cleanup command, `diskutil unmount force`. Done means completed updates leave no new Kiro CLI volumes mounted and existing update behavior still works.

Written by the indexing model from the issue text.