feat(mcp): migrate server to MCP 2026-07-28

Replace the MCP 1.4.1 stateful HTTP design with the official C# SDK 2.0.0 stateless transport. The SDK now owns protocol negotiation, server/discover, standard MCP headers, GET and DELETE handling, error serialization, caching hints, and legacy initialize compatibility; production code no longer maintains a custom wire-protocol workaround for MCP Inspector.

Separate transport state from application conversation state. HTTP does not issue Mcp-Session-Id, while the existing session_id remains an Agent conversation identifier. Preserve agent_run and agent_status for clients without Tasks support and add the official ModelContextProtocol.Extensions.Tasks 2.0.0 path for capable clients.

Add persistent MCP Task storage with atomic JSON replacement, user-only state location, configurable TTL and poll interval, restart recovery, cancellation correlation, and public Agent-to-MCP state mapping. Keep conformance-only tools and protocol exception fixtures in a test host so they cannot enter the Release Bundle.

Run administrator, BFE, WFP transaction, and filter add/delete preflight before binding. Fail fast with exit code 2 and actionable localized diagnostics when sandbox enforcement is unavailable. Emit ready only after the listener starts and keep stdio stdout protocol-pure.

Add shared rotating application and HTTP request logs. Record real socket endpoints, connection and trace identifiers, method, path, result, timing, media metadata, User-Agent, and MCP metadata. Do not trust X-Forwarded-For and do not log authorization, cookies, query data, request or response bodies, prompts, images, or Base64 payloads.

Add typed logging and Tasks configuration, Japanese and English messages, protocol and operations documentation, design/specification deltas, traceability, and exact conformance acquisition/offline runner scripts for @modelcontextprotocol/conformance 0.2.0-alpha.11. Node remains test-only and is not a runtime dependency.

Conformance evidence: server-stateless passed 28 of 28 checks with zero unexpected failures; DNS rebinding and multiple POST stream scenarios passed. The alpha Tasks lifecycle/cancel/error/required-task checks passed, while its wire-schema validator misclassifies CreateTaskResult and its MRTR composition remains incompatible with SDK 2.0.0. The aggregate conformance Gate is therefore recorded as PARTIAL, not PASS. Test-host fixture gaps for tools-list descriptions, JSON Schema diagnostics, caching fixtures, and a header-validation/required-Task capability conflict are also recorded without expected-failure masking.

Verification: Release build passed with 0 warnings and 0 errors; Planner tests 10/10 and Core tests 47/47 passed with skip 0. The last Windows suite run passed 19/25; five WFP cases require an elevated token and one symlink case requires unavailable host privilege, so the elevated security Gate remains open. A win-x64 self-contained 1.0.0 Bundle and ZIP were regenerated under build/Release/publish; runtime check was intentionally skipped in this non-elevated session. Evidence remains under ignored artifacts/evidence/mcp-2026-07-28.

Harden release regeneration when another shell holds the previous Bundle directory as its current directory: validate the target and remove only its children instead of deleting the directory itself. build/ and artifacts/ remain excluded from Git.

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