fix(remote): echo the client MCP protocol version in the oab initialize

[brettchien]

Root cause — confirmed on a live session (via #77's log)

reverse-MCP initialize — PROTOCOL MISMATCH: client requested 2025-06-18, server answered 2024-11-05
reverse-MCP — client sent initialized (handshake complete)

The reverse-MCP initialize shim answered a hardcoded 2024-11-05. The agent runtime requested 2025-06-18. The client completed the handshake (sent initialized) but then never issued tools/list — so the management agent saw no oab tools. The version downgrade is the cause.

(#77 was logging-only, on purpose — it confirmed this hypothesis. This PR is the actual fix.)

Fix

Echo the client's requested protocolVersion instead of pinning one:

let proto = params.get("protocolVersion").and_then(Value::as_str).unwrap_or("2024-11-05");
// … "protocolVersion": proto …

Studio's initialize is a thin shim over the already-initialized oab-mcp sidecar; tools/list / tools/call are forwarded verbatim and their shapes are stable across these versions, so echoing is safe. Fall back to 2024-11-05 only when the client omits a version.

How we'll know it worked

After deploy, the #77 log should read client requested X, server answered X (no PROTOCOL MISMATCH) and a tools/list — served N oab tool(s) line should follow — i.e. the management agent gets its oab tools.

Verification

src-tauri not built locally (dep tree OOMs this box, as on #74/#75/#77); CI build-test covers the compile.

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