Facing trouble in resuming conversation with kiro-cli chat --resume

### 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 26.2.0 (25C56)

### Expected behaviour

To resume the conversation as usual

### Actual behaviour

Getting this error-
```
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: "e33cce2f-2eba-468d-9304-2f12394b4e79" }

Location:
crates/chat-cli/src/cli/chat/mod.rs:1440

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

when run with RUST_BACKTRACE=full-
```
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: "2ede5244-6b11-4ce6-b2f3-0af27c9ab48f" }

Location:
crates/chat-cli/src/cli/chat/mod.rs:1440

BACKTRACE
5 frames hidden
6: chat_cli::cli::chat::ChatSession::next::{{closure}}::h489c988e2c15f2b7
at :
7: chat_cli::cli::chat::ChatSession::spawn::{{closure}}::h0d1b4f64b65c9fc2
at :
8: chat_cli::cli::chat::ChatArgs::execute::{{closure}}::h2d9cf3201d338d67
at :
9: chat_cli::cli::RootSubcommand::execute::{{closure}}::h8f6ba69b80c664ba
at :
10: chat_cli::cli::Cli::execute::{{closure}}::he15d19c32283c8a1
at :
11: tokio::runtime::park::CachedParkThread::block_on::hc140b0a5e9a2de9a
at :
12: tokio::runtime::context::runtime::enter_runtime::ha6355807cc8d5b5b
at :
13: tokio::runtime::runtime::Runtime::block_on::hc2491337fb6f189f
at :
14: chat_cli::main::h2a3fc99d94f5fd9b
at :
15: std::sys::backtrace::__rust_begin_short_backtrace::hfad22d3460983886
at :
16: std::rt::lang_start::{{closure}}::h5abf1e3f62a4dfa7
at :
17: std::rt::lang_start_internal::h1e9a2dfabf97dcbe
at :
18: _main
at :

Run with COLORBT_SHOW_HIDDEN=1 environment variable to disable frame filtering.
```

### Steps to reproduce

kiro-cli chat --resume in a conversation where I had done lot of work before.

### Environment

```yaml
[q-details]
version = "1.24.0"
hash = "0728b2464fed0b53e63abbb9ce12fa38a0542d69"
date = "2026-01-15T23:42:41.840104Z (12d ago)"
variant = "full"
```