file transfer (dotnet): parse images/files, wire directive sink to Rust parity

[brentrager]

Problem

The .NET (C#) smooth-operator server handled send_message as text only — no multimodal images, no file attachments, and no host-directive channel. The file-transfer contract merged to main in #342 (send_message.files[] + the send_file directive convention on eventual_response.directive); Rust already implements it. This brings the .NET server to parity.

Solution

• Regenerate Types.cs from the updated spec via tools/Generator (adds SendMessageRequest.Files, and picks up Skill). Generated output, not hand-edited.
• images[] — parsed fail-soft in FrameDispatcher, attached as OpenAI image_url content parts. The engine (a fixed published NuGet) builds the live user turn from a string, so it can carry no content parts; instead the images ride an image-only ChatMessage seated on the thread immediately before the text turn — the model sees them adjacent to the question, with no empty or duplicated message. data: → DataContent, http(s) → UriContent; the optional vision detail hint rides on AdditionalProperties. Malformed/unsupported entries are dropped.
• files[] — parsed fail-soft and surfaced on a new per-turn TurnContext (files list + directive sink), published as an AsyncLocal around the run so a host tool the engine invokes can read them. Never sent to the model.
• send_file directive — a host tool writes an opaque directive onto TurnContext.Current.Directive; the runner drains it after the turn onto eventual_response.directive (last-write-wins, omitted when none for back-compat). ProtocolEvents.EventualResponse grew an optional directive param.

Backward compatible: absent images/files and no host directive is byte-for-byte the previous text-only behavior.

Verification

• dotnet build + dotnet test on the full solution in Release: all green (302 server tests incl. 8 new, plus integration/host/client/postgres projects).
• New FileTransferTests (8): images attach as content parts (UriContent+DataContent, detail on AdditionalProperties, live text turn preserved, no empty message), malformed images fail-soft, files surfaced on TurnContext and kept off the model, tool→directive→eventual_response.directive (spec-validated), and directive omission for back-compat.

Notes

• Publish gate: source-only. The .NET server consumes the engine as the published SmooAI.SmoothOperator.Core NuGet; this PR does not publish anything.
• Changeset added (minor on @smooai/smooth-operator-server).

🤖 Generated with Claude Code

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Latest commit: b5438a7

The changes in this PR will be included in the next version bump.

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