/compact with a custom prompt no longer seems to work

### 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 15.5.0 (24F74)

### Expected behaviour

When I type /compact with a custom prompt, it should compact the previous conversation and reduce the token usage.

### Actual behaviour

It writes the summary based on the custom prompt out, but the usage remains the same.

### Steps to reproduce

Start a conversation, go for a while, then use /compact

### Environment

```yaml

[q-details]
version = "1.12.2"
hash = "b9100eb751546269f095585705a0e7fc3ea55419"
date = "2025-06-30T22:40:01.105251Z (4d ago)"

[system-info]
os = "macOS 15.5.0 (24F74)"
chip = "Apple M1 Pro"
total-cores = 10
memory = "32.00 GB"

[environment]
cwd = "/Users/USER"
cli-path = "/Users/USER"
install-method = "unknown"

[env-vars]
DISPLAY = "c889f3bc7462"
PATH = "/Users/USER/.nvm/versions/node/v22.14.0/bin:/Users/USER/.nvm/versions/node/v22.14.0/bin:/Users/USER/.asdf/shims:/Users/USER/.virtualenvs/ds12/bin:/Users/USER/.nvm/versions/node/v22.14.0/bin:/Users/USER/.nvm/versions/node/v22.14.0/bin:/Users/USER/.asdf/shims:/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:/Users/USER/.nvm/versions/node/v22.14.0/bin:/Users/USER/.asdf/shims:/Users/USER/.local/bin:/Applications/Emacs.app/Contents/MacOS/bin-arm64-11:/Applications/Emacs.app/Contents/MacOS/libexec-arm64-11:/Library/TeX/texbin:/Users/USER/.toolbox/bin:/Users/USER/.cargo/bin:/Users/USER/.toolbox/bin:/Users/USER/.cargo/bin:/Users/USER/.toolbox/bin:/Users/USER/.cargo/bin"
Q_SET_PARENT_CHECK = "1"
SHELL = "/bin/zsh"
TERM = "eterm-color"
__CFBundleIdentifier = "org.gnu.Emacs"
```

Beginne am Einstiegspunkt des Befehls /compact und reproduziere das Problem, indem du eine Unterhaltung gefolgt von /compact mit einer benutzerdefinierten Eingabeaufforderung verwendest. Verfolge, ob die benutzerdefinierte Zusammenfassung auf den Unterhaltungskontext angewendet wird, und überprüfe, ob die resultierende Token-Nutzung wie erwartet abnimmt.

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