Add MCP sessions, SSE streaming, and interactive passthrough - #15
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Catch up with the real gateway's May-2026 protocol capabilities. - Serving mode: the default is now stateful sessions + SSE streaming (Mcp-Session-Id issued on initialize, responses as event streams) -- the modern faithful behavior. server.stateless: true restores the previous buffered stateless mode. BREAKING DEFAULT (0.x), called out in README/docs. - Progress + logging passthrough: an MCP target's mid-call progress and logging notifications re-emit to the calling client as they arrive (progressToken keyed by the SDK; log levels preserved). Outside a gateway request they drop silently. - Elicitation + sampling passthrough: a downstream server's elicitation (form mode) and sampling requests relay to OUR caller via the SDK ServerSession (raw requestedSchema forwarded 1:1; sampling carries system prompt, temperature, stop sequences, model preferences), the answer travelling back down. Requires sessions; stateless mode returns a clear error. URL-mode elicitation is a documented limitation. - Concurrent calls through one MCP target route upstream-initiated traffic to the most recent in-flight caller (documented; the real gateway scopes per user session, we have no inbound identity). Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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The extension arc since 0.2.1, one feature pack per PR:
- MCP-passthrough targets (streamable HTTP + local stdio) and ${VAR}
config expansion (#6)
- lcgw sync + lcgw tail: local admin surface, target re-sync without
restart, live invocation feed (#8)
- Hybrid debugging: aws-gateway targets (proxy a deployed AgentCore
Gateway, SigV4) and lambda backend: aws, behind the optional [aws]
extra (#9)
- Mock targets, contract checks (off/warn/error), and the public
localcore_gateway.testing module (#11)
- lcgw schema (config JSON Schema for editors) and lcgw preflight
(real-AgentCore deploy-constraint validation) (#12)
- Prompts and resources passthrough for MCP targets, with
resourcePriority routing (#14)
- MCP sessions + SSE streaming by default (server.stateless: true for
the old buffered mode -- BREAKING default) and progress/logging/
elicitation/sampling passthrough (#15)
- Smithy model targets, completing the real gateway's target-type
matrix (#16)
- Dependency security bumps clearing all Dependabot alerts (#13),
Japanese README (#7, #10)
Co-authored-by: Claude Fable 5 <noreply@anthropic.com>
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Summary
The big fidelity pack: catches the local gateway up with the real gateway's May-2026 protocol capabilities (sessions, progress, logging, elicitation, sampling). Nothing punted.
The gateway now serves stateful MCP sessions with SSE streaming by default (
Mcp-Session-Idon initialize,text/event-streamresponses) — matching the modern real gateway instead of its pre-May-2026 buffered behavior.server.stateless: truerestores the old mode. All integration behavior is tested in both modes (parametrized matrix), including the contract-checks SDK-bypass pin.Progress + logging passthrough
An MCP target's mid-call
progressandloggingnotifications now re-emit live to the calling client (previously they died at our upstream client). Progress is keyed to the caller's progressToken by the SDK; log levels/logger names are preserved. Outside a gateway request (lcgw invoke, direct target calls) they drop silently.Elicitation + sampling passthrough
A downstream server can now ask OUR caller mid-tool-execution:
requestedSchemais forwarded 1:1 via the SDK ServerSession (no Python re-typing), the answer travels back down. URL mode is a documented limitation (clear error).Documented caveats
Concurrent calls through one MCP target route upstream-initiated traffic to the most recent in-flight caller (the real gateway scopes per user session; we have no inbound identity). No per-user scoping or 1-hour timeout emulation. Prompt/resource reads don't carry the interactive relay (tools only, like invocation history).
Test plan
ruff check/ruff format --checkclean.🤖 Generated with Claude Code