v0.17.0

[0.17.0] — 2026-07-29

Migrates to mcp 2.x, which closes the OBS-001 criterion that 0.16.0 had
to leave open. Protocol version moves from 2025-11-25 to 2026-07-28.

The pinned tests did their job

0.16.0 shipped two tests asserting that protocol errors carry code 0, with a
stated purpose: "when the SDK starts emitting a real code this test fails,
which is the point." It fails now.

Under 2.0 a protocol error carries a real JSON-RPC code — resources/read on a
missing resource answers -32602 (INVALID_PARAMS), prompts/get answers
-32603. The spec made the same correction independently: 2026-07-28 moved
resource-not-found from -32002 to -32602 to align with JSON-RPC and
partitioned the server-error range, reserving -32020…-32099 for MCP.

Both tests were rewritten from pins into assertions, plus a range check so a
regression to 0 cannot pass unnoticed. OBS-001 criterion 3 is met.

Unchanged, and still pinned: an unknown tool is delivered as a tool result with
is_error: true rather than as a protocol error. And mask_error_details does
not exist in 2.0 either, so OBS-002 stays test-enforced rather than configured.
One thing did improve there — prompts/get used to echo the raw ValueError
("Unknown prompt: nope") and now answers "Internal server error", keeping the
detail server-side.

API changes, and why they are small

The SDK surface this server touches turned out to be two imports:

• mcp.server.fastmcp.FastMCP → mcp.server.mcpserver.MCPServer. Same
  constructor kwargs; @mcp.tool(annotations=…), mcp.run(), sse_app() and
  streamable_http_app() are unchanged.
• mcp.settings.host / .port / .stateless_http are gone. Host and port now
  go straight from the environment to uvicorn, which is where they were always
  headed — the settings object was a detour. stateless_http became an argument
  of streamable_http_app(), which is better: the mode is a property of the app
  being built rather than global state a later reader has to hunt for.

Tests needed more, all in one file plus three renames: McpError → MCPError,
create_connected_server_and_client_session → mcp.Client(server), and
camelCase → snake_case throughout (isError → is_error, inputSchema →
input_schema). The MCP_STATELESS tests moved from reading a global to
recording what actually reaches the SDK — a better assertion than the one they
replaced. Mutation-tested: dropping the flag fails 2 tests, routing SSE through
the streamable builder fails 1, dropping the lifespan fails 1.

What the new spec means for the accepted risks

2026-07-28 removes protocol-level sessions: no initialize handshake, no
Mcp-Session-Id, no SSE stream resumability. It also reclassifies HTTP+SSE as
Deprecated with a twelve-month removal window.

Nothing breaks today — the SDK still ships the legacy transports, and _cors.py
was re-verified against the starlette 1.3.1 that mcp 2.0 pulls in (preflight
200, session header allowed and exposed, DELETE allowed). But it changes what
SEC-009 and SCALE-002 are about: they move from controls this server has
not implemented toward controls the protocol no longer defines. They stay fail
until the audit catalogue catches up, because reclassifying a finding on our own
authority is exactly the kind of quiet drift these documents exist to prevent.
ROADMAP.md now carries retiring SSE as dated work rather than a someday.

232 tests pass (one more than 0.16.0 — a negative control for the stateless
flag), ruff check and ruff format clean.