feat(mcp): support modern task execution - #78
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- Bump ModelContextProtocol 1.4.1 -> 2.0.0-preview.3. - Remove the Tool.Execution mapping for .LongRunning() commands: SDK 2.0 dropped the experimental MCP Tasks tool augmentation (Tasks SEP deferred out of the 2.0 protocol release). The annotation stays in Repl's model; protocol-level task support returns with the SDK Tasks runtime. - Keep supporting Roots, Sampling, and Logging: deprecated by spec 2026-07-28 (SEP-2577, MCP9005) with no replacement, still relied on by current hosts. Scoped, documented pragmas at the feature touchpoints. - Document the SDK/protocol version posture in docs/mcp-reference.md. Full suite green against the new SDK (1312 passed, 1 known skip), including all MCP capability, tool-call, roots, sampling, and logging regressions. Note: re-pin to the stable 2.0.0 release before cutting stable 0.12. Refs #51
…e shape (review) - Correct the migration rationale: MCP Tasks was EXTRACTED to ModelContextProtocol.Extensions.Tasks (store, task results, client polling), not removed; the per-tool Tool.Execution augmentation is gone from the protocol surface. Comments and docs now say so, and Repl still deliberately does not advertise task support without the runtime. - Name the designated successor (SEP-2322 multi-round-trip requests) in the deprecation pragmas instead of claiming 'no replacement API'. - Narrow MCP9005 pragmas to their touchpoints in McpServerHandler and Given_McpIntegration (file-scoped kept only where usage is dense). - Lock the SDK-2.0 tools/list wire shape: a .LongRunning() tool serializes its annotations and emits no task/execution augmentation. - Align remaining .LongRunning() doc mentions (overview, coding-agents guide, package README) with the current no-advertisement posture.
…ed server field SDK 2.0's 2026-07-28 protocol path hands each request a destination-bound McpServer, and one handler can serve several sessions. The four capability services (roots, sampling, elicitation, feedback) stored the last-attached server in a shared mutable field, so a concurrent request from another session could cross-wire capabilities mid-call (IsSupported flipping while a handler was awaiting). - McpRequestServerAccessor: AsyncLocal request binding flowing with the invocation, session-level server as fallback for code outside a request (routing notifications, roots list-changed handler). - Services resolve the effective server through the accessor with a single read per operation (no torn check-then-use). - McpServerHandler splits session-level attach (RunAsync, once) from request-level binding (every handler); externally hosted servers adopt the first observed server for session concerns. - Deterministic regression: two sessions on one handler, sampling-capable client pauses mid-call while a sampling-less client is served — the paused call must keep observing ITS client's capabilities (RED observed: 'True|False' on the pre-fix code, exactly the reported repro).
… Tasks wording (review) - Regression pinning the last initialize-era protocol revision (2025-11-25): asserts the negotiated version and a tool list + call — the default client negotiates 2026-07-28 and never exercised the fallback path. - Roots/Sampling/Logging documented as legacy-compatibility only: deprecation notices in mcp-agent-capabilities.md and mcp-advanced.md steer new applications toward IReplInteractionChannel / soft roots; mcp-reference.md no longer reads as an endorsement. - Tasks wording corrected everywhere: the SDK has shipped the Tasks extension (ModelContextProtocol.Extensions.Tasks); what is pending is Repl's integration (issue #72) — including the CommandAnnotations.LongRunning XML doc that still promised task-based execution.
…le (review) - Hard roots are now SESSION state: entries keyed by destination server in a ConditionalWeakTable (weak keys die with the session), with a global version stamp for roots-list-changed invalidation. One session can no longer receive another session's cached workspace roots, and the root-dependent snapshot builds from the right workspace (RED observed: client B received client A's roots). - Session attachment is reference-counted: the handler tracks every active session, discovery notifications fan out to ALL of them, the accessor fallback moves to a surviving session on close, and the routing subscription is dropped only when the LAST session ends. A first-session close no longer silences the survivors (RED observed: surviving session timed out waiting for tools/list_changed). - Roots list-changed handler registered once per session (per-server registration replaces the single global flag).
One handler serves several sessions; everything that varied per client was still handler-global after the earlier point fixes. McpSessionContext now owns it all, per the architecture review: - hard AND soft roots: McpClientRootsService is one instance per session (plain fields again — the ConditionalWeakTable keying is gone); a session's 'workspace init' no longer sets another session's workspace. - generated snapshot + version + gate: the tool graph can be gated on session capabilities, so each session caches its own build against the handler-global routing version (RED observed: the roots-less session saw the roots-gated tool of the other session). - compatibility-shim intro: per-session flag, reset for every active session on routing invalidation (RED observed: only the first session received the discover_tools/call_tool intro). - per-session service overlay handed to McpServer.Create; request handlers recover their session through request.Server.Services instead of using a destination-bound per-request server as a surrogate session key. - externally hosted servers (BuildDynamicServerOptions) share one explicit lazy fallback context instead of racing a last-attached field. Request-bound OUTBOUND capabilities (sampling/elicitation/feedback) keep flowing through the per-request AsyncLocal accessor — finer than the session, unchanged. Related to #70 (per-session DI scopes generalize the lifetime contract; this context will construct from the session-scoped provider once both merge).
…in SDK 2.0 The deprecation pragmas and the reference doc claimed the SEP-2322 multi-round-trip successor was 'not yet consumable in the SDK'; preview.3 actually ships it experimentally (MrtrContext/MrtrContinuation/MrtrExchange). Reworded to 'shipped experimentally, not adopted by Repl yet' — adoption is a follow-up under the compliance track.
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Summary
Adds modern MCP Tasks support for Repl commands marked
.LongRunning().Behavior
ModelContextProtocol.Extensions.Tasks2.2.0 extension.io.modelcontextprotocol/tasksreceives a task handle for a long-running command and can poll or cancel it..LongRunning()remain synchronous.tools/callresponse.ReplMcpServerOptions.TaskStoreallows a durable shared store for HTTP or restart-resilient deployments.Documentation
Documents the modern-only protocol, the default store, and the current SDK limitation: task-backed MCP tools cannot compose with MRTR/interactive flows yet.
Validation
Closes #72.