feat(mcp): session-scoped notification delivery and wire-format negotiation

[vitaliyslion]

Summary

Daemon-socket MCP sessions (the transport used by gortex mcp proxying and bridge-style clients like Pi) were never registered with mcp-go's internal client-session tracking, so any server-initiated notification — tools/list_changed after a tools_search promotion, resources/updated, etc. — was silently dropped for them. This PR wires those sessions in so pushes actually reach the client, and adds a capability-based mechanism for clients to self-declare their compact wire-format support instead of relying solely on a server-side client-name allowlist.

Changes

• Added SessionStartedHook (internal/daemon/server.go): an optional hook MCPDispatcher implementations can satisfy to receive a write func([]byte) error callback per connection, invoked after the handshake ack and before the first frame is dispatched. Server-initiated frames now share the connection under one write lock so they never interleave with reply frames.
• Added ConnectSession / DisconnectSession / WithClientSession (internal/mcp/conn_session.go, new): registers a daemon-socket connection as a live mcp-go client session so SendNotificationToAllClients (which mcp-go gates on session-initialized state) can actually deliver to it.
• cmd/gortex/daemon_mcp.go: mcpDispatcher now implements SessionStarted/SessionEnded to connect/disconnect the session, and attaches the client session to the request context via WithClientSession before dispatch.
• Added a gortex/wire MCP capability: a client can declare its supported compact formats during initialize (capabilities["gortex/wire"]: ["gcx", "toon"], in preference order). maybeSnoopInitialize parses it and calls the new Server.NoteSessionWireFormats; resolveSessionFormat prefers this declaration over the hardcoded defaultFormatForClient name allowlist, so new clients get compact output without a server-side code change.
• internal/mcp/server.go: added sessionState.wireFormats + recordWireFormats/snapshotWireFormats, NoteSessionWireFormats, and formatFromWireCapability (maps the declared list to the first format this server can emit, skipping unknown/future format names).

Testing

• All tests pass (go test -race ./internal/mcp/... ./internal/daemon/... ./cmd/gortex/...)
• New tests added for new functionality (internal/mcp/conn_session_test.go, additions to internal/mcp/format_negotiation_test.go and internal/daemon/mcp_roundtrip_test.go)
• Benchmarks run if performance-relevant

Checklist

• Code follows existing patterns in the codebase
• No unnecessary abstractions added
• Language extractor includes Meta["methods"] for interfaces (if applicable)
• Methods have EdgeMemberOf edges to their containing type (if applicable)

[vitaliyslion]

On the gortex/wire capability: this PR adds it purely additively — defaultFormatForClient's hardcoded allowlist (claude-code, cursor, vscode, zed, aider, kilocode, opencode, openclaw, codex, omp-coding-agent) still stands as the fallback, and resolveSessionFormat only prefers a client's self-declared capabilities["gortex/wire"] over it when present.

Once this architecture is approved, the follow-up is to flip the model around: have each of the currently-allowlisted clients declare gortex/wire: ["gcx", ...] themselves during initialize (their bridge/plugin already knows what it can decode), and then delete knownAgentClients / defaultFormatForClient from the server entirely. That removes the need for a server-side release every time a new client wants compact output — the allowlist becomes a distributed fact each client owns, not a table Gortex maintains on their behalf.

Pi's own bridge (next PR) will be the first client built against this from day one — self-declaring instead of getting a server-side entry — so it'll double as the reference implementation for migrating the rest.

[zzet]

Hey @vitaliyslion,

Once this architecture is approved

The capability placement is hard to change later, and it's a one-door decision. According to the change, the client declares capabilities["gortex/wire"] as a top-level key under capabilities. That's non-standard MCP: custom capabilities belong under capabilities.experimental, and typed SDKs can't even emit a custom top-level key — mcp-go's own ClientCapabilities struct only has experimental/roots/sampling. So the exact clients this feature targets ("new clients without a server-side change") can't use it unless they hand-roll their initialize JSON.
I'd accept capabilities.experimental["gortex/wire"] as well (or instead) before this ships and third parties start depending on the current shape.

Also, such a change requires a documentation actualisation for a public protocol extension. docs/mcp.md:70 documents the client-name allowlist, but nothing anywhere mentions gortex/wire — and the entire point of the feature is that external client authors adopt it. At minimum, a paragraph in docs/mcp.md next to the allowlist description.