Improperly formed request

### 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 26.4.0 (25E246)

### Expected behaviour

Kiro chat would respond back to me

### Actual behaviour

I got an error instead

Kiro is having trouble responding right now:
0: Failed to send the request: An unknown error occurred: ValidationException
1: An unknown error occurred: ValidationException
2: unhandled error (ValidationException)
3: service error
4: unhandled error (ValidationException)
5: Error { code: "ValidationException", message: "Improperly formed request.", aws_request_id: "b2e642b1-8fe3-4960-b0d5-61b56c467365" }

Location:
crates/chat-cli/src/cli/chat/mod.rs:1786

Backtrace omitted. Run with RUST_BACKTRACE=1 environment variable to display it.
Run with RUST_BACKTRACE=full to include source snippets.

### Steps to reproduce

This is happening every time I type something in "kiro-cli --classic" after I get in.

It also does the same thing when I use regular "kiro-cli". It just didn't give me as much detail about the error. It only has the aws_request_id and the ValidationException error.

### Environment

```yaml

[q-details]
version = "2.2.0"
hash = "c96876dd5075aa453fe731882a863ab8216a9a3a"
date = "2026-04-28T21:18:48.310682Z (16h ago)"
variant = "full"

[system-info]
os = "macOS 26.4.0 (25E246)"
chip = "Apple M2 Max"
total-cores = 12
memory = "32.00 GB"

[environment]
cwd = "/Users/USER"
cli-path = "/Users/USER"
os = "Mac"
shell-path = "/bin/zsh"
shell-version = "5.9"
terminal = "macOS"
install-method = "brew"

[env-vars]
PATH = "/Users/USER/.nvm/versions/node/v22.22.2/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:/opt/pkg/env/active/bin:/opt/pmk/env/global/bin:/Users/USER/.local/bin:/Users/USER/Library/Application Support/JetBrains/Toolbox/scripts"
QTERM_SESSION_ID = "60c4588b958b44e18c528321c1926a42"
Q_SET_PARENT_CHECK = "1"
Q_TERM = "2.2.0"
SHELL = "/bin/zsh"
TERM = "xterm-256color"
__CFBundleIdentifier = "com.apple.Terminal"
```

Inizia da crates/chat-cli/src/cli/chat/mod.rs:1786 e riproduci il malfunzionamento sia con `kiro-cli --classic` sia con `kiro-cli`. Confronta l’output dettagliato di ValidationException dopo aver eseguito `q doctor` e `q restart`, quindi traccia il percorso della richiesta per identificare il motivo per cui il servizio la rifiuta. Il lavoro è completato quando le richieste di chat ricevono una risposta senza la ValidationException.

Scritto dal modello di indicizzazione a partire dal testo della issue.