## Stack Context

PR 2 of 6 in a stack that migrates every Coder MCP surface from the
archived `github.com/mark3labs/mcp-go` library to the official
`github.com/modelcontextprotocol/go-sdk` v1.7.0.

Stack: #28056 -> #28057 -> #28058 -> #28059 -> #28060 -> #28061

## Why

`coder exp mcp server` (stdio) now uses the official SDK server with
`mcp.IOTransport` over the invocation's stdin/stdout, and reuses the
shared `coderd/mcp.RegisterSDKTool` helper from PR #28056 so both
servers register tools identically.

- A `nopWriteCloser` prevents the SDK from closing the invocation's
stdout.
- Tests send spec-compliant initialize params and
`notifications/initialized` before `tools/list` because the official SDK
enforces the protocol lifecycle.

> Mux created this PR on Mike's behalf.

…al Go SDK (#28058)

## Stack Context

PR 3 of 6 in a stack that migrates every Coder MCP surface from the
archived `github.com/mark3labs/mcp-go` library to the official
`github.com/modelcontextprotocol/go-sdk` v1.7.0.

Stack: #28056 -> #28057 -> #28058 -> #28059 -> #28060 -> #28061

## Why

The chatd external MCP client (admin-configured MCP servers used by
Agent chat) now holds `*mcp.ClientSession` connections created via
`mcp.NewClient` and `Client.Connect`, with `StreamableClientTransport`
or `SSEClientTransport` per server config.

- Auth and identity headers are injected through a custom
`http.RoundTripper` because the official SDK has no per-header transport
options.
- Tool input schemas are extracted from the SDK's `map[string]any`
decoding.
- Content conversion handles the official pointer content types; the SDK
decodes blob resources into raw bytes, so binary content is handled
without an extra base64 round trip.
- Test fixtures are official stateless Streamable HTTP servers.

> Mux created this PR on Mike's behalf.

…l Go SDK (#28059)

## Stack Context

PR 4 of 6 in a stack that migrates every Coder MCP surface from the
archived `github.com/mark3labs/mcp-go` library to the official
`github.com/modelcontextprotocol/go-sdk` v1.7.0.

Stack: #28056 -> #28057 -> #28058 -> #28059 -> #28060 -> #28061

## Why

The workspace agent MCP manager now stores `*mcp.ClientSession` per
configured server.

- stdio servers use `mcp.CommandTransport` with an `exec.Cmd` built from
Coder's `agentexec.Execer`, preserving environment enrichment; the
command uses the manager's parent context so a stdio subprocess outlives
the connect handshake and stops when the session closes.
- HTTP and SSE servers use header-injecting HTTP clients.
- Binary tool content is re-encoded to base64 for the agent API because
the official SDK decodes it into raw bytes.
- The reload test now triggers config diffs via an environment variable
because the official SDK drops connections on non-protocol stdout output
(flags like `-test.v` made the fake server chatty).

> Mux created this PR on Mike's behalf.

## Stack Context

PR 6 of 6 in a stack that migrates every Coder MCP surface from the
archived `github.com/mark3labs/mcp-go` library to the official
`github.com/modelcontextprotocol/go-sdk` v1.7.0.

Stack: #28056 -> #28057 -> #28058 -> #28059 -> #28060 -> #28061

## Why

With every production surface migrated, this PR removes the mark3labs
dependency entirely and converts the remaining test fixtures.

- Migrates the remaining mark3labs test fixtures (coderd MCP e2e tests,
chatd fixtures, mcpclient fixtures, and the Force On MCP policy tests)
to official stateless SDK servers.
- Removes `github.com/mark3labs/mcp-go` from `go.mod` and drops the
corresponding dependabot ignore entry. Zero references remain repo-wide.
- Updates the MCP docs for the 2026-07-28 protocol: stateless Streamable
HTTP behavior, the supported 2024-11-05 through 2026-07-28 protocol
range, and explicit non-features (resources, prompts, structured output,
elicitation, MCP Tasks).
- The e2e ping assertion is removed because MCP 2026-07-28 removed the
ping method.

> Mux created this PR on Mike's behalf.

…er#28060)

## Stack Context

PR 5 of 6 in a stack that migrates every Coder MCP surface from the
archived `github.com/mark3labs/mcp-go` library to the official
`github.com/modelcontextprotocol/go-sdk` v1.7.0.

Stack: coder#28056 -> coder#28057 -> coder#28058 -> coder#28059 -> coder#28060 -> coder#28061

## Why

The aibridge injected-MCP proxy now owns an official `*mcp.Client`,
`*mcp.StreamableClientTransport`, and `*mcp.ClientSession`.

- The proxy constructor accepts an optional `*http.Client` instead of
mark3labs options; the header-injecting wrapper shallow-copies a
supplied client so its Timeout, Jar, and redirect policy survive.
- Manual protocol version negotiation and the mark3labs five-second
close workaround are removed; the SDK negotiates during `Connect` and
fails when no mutually supported version exists.
- Repeated `Init` closes the previous session, and a failed tool fetch
closes the just-created session so transports do not leak.
- Tool and intercept types use the official pointer content types;
embedded resource blobs are re-encoded to base64 for model-facing text
because the SDK decodes them into raw bytes.
- `aibridge/mcpmock` is regenerated, and its stale `go:generate` source
path is corrected.

> Mux created this PR on Mike's behalf.