BUG: Python plugin JSON output with non-ASCII text fails UTF-8 deserialization

### Description

Flow Launcher raised an unhandled exception while querying the third-party Python plugin **Forward Slash Path 1.1.0**. The first result's SubTitle contained non-ASCII text written by Python using the Windows console code page, while Flow Launcher attempted to deserialize the stream as UTF-8.

### Environment

- Flow Launcher version: 2.1.1
- OS Version: 26100.7623
- IntPtr Length: 8
- x64: True
- Python Path: C:\Users\eason\AppData\Local\Programs\Python\Python314\python.exe
- Node Path:
- Date: 07/12/2026 02:24:08
- Plugin: Forward Slash Path
- Plugin website: https://github.com/Flow-Launcher/Flow.Launcher
- Plugin author: Codex
- Plugin version: 1.1.0

### Exception

```text
System.Text.DecoderFallbackException: Unable to translate bytes [A1] at index 8 from specified code page to Unicode.
Source: System.Private.CoreLib
TargetAssembly: System.Private.CoreLib, Version=9.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e
TargetModule: System.Private.CoreLib.dll
TargetSite: Void Throw(Byte[], Int32)
at System.Text.DecoderExceptionFallbackBuffer.Throw(Byte[] bytesUnknown, Int32 index)
at System.Text.DecoderExceptionFallbackBuffer.Fallback(Byte[] bytesUnknown, Int32 index)
at System.Text.Encoding.GetCharCountWithFallback(ReadOnlySpan`1 bytes, Int32 originalBytesLength, DecoderNLS decoder)
at System.Text.Encoding.GetCharCountWithFallback(Byte* pBytesOriginal, Int32 originalByteCount, Int32 bytesConsumedSoFar)
at System.Text.Json.JsonReaderHelper.TranscodeHelper(ReadOnlySpan`1 utf8Unescaped)

System.InvalidOperationException: Cannot transcode invalid UTF-8 JSON text to UTF-16 string.
Source: System.Text.Json.Rethrowable
TargetAssembly: System.Text.Json, Version=9.0.0.0, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51
TargetModule: System.Text.Json.dll
TargetSite: System.String TranscodeHelper(System.ReadOnlySpan`1[System.Byte])
at System.Text.Json.JsonReaderHelper.TranscodeHelper(ReadOnlySpan`1 utf8Unescaped)
at System.Text.Json.JsonReaderHelper.GetUnescapedString(ReadOnlySpan`1 utf8Source)
at System.Text.Json.Utf8JsonReader.GetString()
at System.Text.Json.Serialization.Metadata.JsonPropertyInfo`1.ReadJsonAndSetMember(Object obj, ReadStack& state, Utf8JsonReader& reader)
at System.Text.Json.Serialization.Converters.ObjectDefaultConverter`1.OnTryRead(Utf8JsonReader& reader, Type typeToConvert, JsonSerializerOptions options, ReadStack& state, T& value)
at System.Text.Json.Serialization.JsonConverter`1.TryRead(Utf8JsonReader& reader, Type typeToConvert, JsonSerializerOptions options, ReadStack& state, T& value, Boolean& isPopulatedValue)
at System.Text.Json.Serialization.JsonCollectionConverter`2.OnTryRead(Utf8JsonReader& reader, Type typeToConvert, JsonSerializerOptions options, ReadStack& state, TCollection& value)
at System.Text.Json.Serialization.JsonConverter`1.TryRead(Utf8JsonReader& reader, Type typeToConvert, JsonSerializerOptions options, ReadStack& state, T& value, Boolean& isPopulatedValue)
at System.Text.Json.Serialization.JsonConverter`1.TryReadAsObject(Utf8JsonReader& reader, Type typeToConvert, JsonSerializerOptions options, ReadStack& state, Object& value)
at System.Text.Json.Serialization.Converters.LargeObjectWithParameterizedConstructorConverter`1.ReadAndCacheConstructorArgument(ReadStack& state, Utf8JsonReader& reader, JsonParameterInfo jsonParameterInfo)
at System.Text.Json.Serialization.Converters.ObjectWithParameterizedConstructorConverter`1.ReadConstructorArgumentsWithContinuation(ReadStack& state, Utf8JsonReader& reader, JsonSerializerOptions options)
at System.Text.Json.Serialization.Converters.ObjectWithParameterizedConstructorConverter`1.OnTryRead(Utf8JsonReader& reader, Type typeToConvert, JsonSerializerOptions options, ReadStack& state, T& value)
at System.Text.Json.Serialization.JsonConverter`1.TryRead(Utf8JsonReader& reader, Type typeToConvert, JsonSerializerOptions options, ReadStack& state, T& value, Boolean& isPopulatedValue)
at System.Text.Json.Serialization.JsonConverter`1.ReadCore(Utf8JsonReader& reader, T& value, JsonSerializerOptions options, ReadStack& state)

System.Text.Json.JsonException: The JSON value could not be converted to System.String. Path: $.result[0].SubTitle | LineNumber: 0 | BytePositionInLine: 99.
Source: System.Text.Json
TargetAssembly: System.Text.Json, Version=9.0.0.0, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51
TargetModule: System.Text.Json.dll
TargetSite: Void ReThrowWithPath(System.Text.Json.ReadStack ByRef, System.Text.Json.Utf8JsonReader ByRef, System.Exception)
at System.Text.Json.ThrowHelper.ReThrowWithPath(ReadStack& state, Utf8JsonReader& reader, Exception ex)
at System.Text.Json.Serialization.JsonConverter`1.ReadCore(Utf8JsonReader& reader, T& value, JsonSerializerOptions options, ReadStack& state)
at System.Text.Json.Serialization.Metadata.JsonTypeInfo`1.ContinueDeserialize(ReadBufferState& bufferState, JsonReaderState& jsonReaderState, ReadStack& readStack, T& value)
at System.Text.Json.Serialization.Metadata.JsonTypeInfo`1.DeserializeAsync(Stream utf8Json, CancellationToken cancellationToken)
at Flow.Launcher.Core.Plugin.JsonRPCPlugin.DeserializedResultAsync(Stream output) in C:\projects\flow-launcher\Flow.Launcher.Core\Plugin\JsonRPCPlugin.cs:line 63
at Flow.Launcher.Core.Plugin.JsonRPCPlugin.DeserializedResultAsync(Stream output) in C:\projects\flow-launcher\Flow.Launcher.Core\Plugin\JsonRPCPlugin.cs:line 66
at Flow.Launcher.Core.Plugin.JsonRPCPlugin.QueryAsync(Query query, CancellationToken token) in C:\projects\flow-launcher\Flow.Launcher.Core\Plugin\JsonRPCPlugin.cs:line 240
at Flow.Launcher.Core.Plugin.PluginManager.<>c__DisplayClass32_0.<b__1>d.MoveNext() in C:\projects\flow-launcher\Flow.Launcher.Core\Plugin\PluginManager.cs:line 423
--- End of stack trace from previous location ---
at Flow.Launcher.Infrastructure.Stopwatch.DebugAsync(String className, String message, Func`1 action, String methodName) in C:\projects\flow-launcher\Flow.Launcher.Infrastructure\Stopwatch.cs:line 31
at Flow.Launcher.Core.Plugin.PluginManager.QueryForPluginAsync(PluginPair pair, Query query, CancellationToken token) in C:\projects\flow-launcher\Flow.Launcher.Core\Plugin\PluginManager.cs:line 422

Flow.Launcher.Core.ExternalPlugins.FlowPluginException: The JSON value could not be converted to System.String. Path: $.result[0].SubTitle | LineNumber: 0 | BytePositionInLine: 99.
Source: Flow.Launcher.Core
TargetAssembly: Flow.Launcher.Core, Version=2.1.1.0, Culture=neutral, PublicKeyToken=null
TargetModule: Flow.Launcher.Core.dll
TargetSite: Boolean b__2(Flow.Launcher.Plugin.ActionContext)
at Flow.Launcher.Core.Plugin.PluginManager.<>c__DisplayClass32_1.b__2(ActionContext _) in C:\projects\flow-launcher\Flow.Launcher.Core\Plugin\PluginManager.cs:line 452
at Flow.Launcher.Plugin.Result.ExecuteAsync(ActionContext context) in /_/Flow.Launcher.Plugin/Result.cs:line 281
at Flow.Launcher.ViewModel.MainViewModel.OpenResultAsync(String index) in C:\projects\flow-launcher\Flow.Launcher\ViewModel\MainViewModel.cs:line 520
at CommunityToolkit.Mvvm.Input.AsyncRelayCommand.AwaitAndThrowIfFailed(Task executionTask)
at System.Threading.Tasks.Task.<>c.b__128_0(Object state)
at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs)
at System.Windows.Threading.ExceptionWrapper.TryCatchWhen(Object source, Delegate callback, Object args, Int32 numArgs, Delegate catchHandler)
```

### Log file

[Flow.Launcher.2026-07-12.log](https://gist.githubusercontent.com/Easonoi/b965fa25838963959e6dd733ac09c827/raw/a97a409f749ac503713c86a53217782d83738856/Flow.Launcher.2026-07-12.log) (full log uploaded to GitHub as a secret gist)

Start in Flow.Launcher.Core/Plugin/JsonRPCPlugin.cs, especially DeserializedResultAsync(Stream output) at the stack-trace locations around lines 63 and 66. Reproduce the query with the Forward Slash Path plugin or equivalent non-ASCII Python output, then verify that the result JSON deserializes without an unhandled exception and preserves the SubTitle text.

Written by the indexing model from the issue text.