docs: fix four dead links to the Multi Round-Trip Requests section (#1159)

### What was broken

Four links in `docs/client.md` point at a section that does not exist.

Three of them sit right where a reader needs them — at the end of the
**Roots**, **Sampling**
and **Elicitation** sections, on the sentence explaining that from
protocol version
`2026-07-28` these requests are delivered via the Multi Round-Trip
Requests pattern:

```
[Multi Round-Trip Requests](protocol.md#multi-round-trip-requests-mrtr)
```

`protocol.md` has no MRTR section. Following the link drops you at the
top of a page that
never mentions the pattern — while the explanation you were promised is
one screen further
down the *same* page you were already on (`client.md` → *Multi
Round-Trip Requests*).

The fourth one is in that MRTR section itself, sending you to the server
side:

```
[server-side documentation](server.md#multi-round-trip-requests-mrtr).
```

`server.md` does have the section, but its heading is `## Multi
Round-Trip Requests`, so the
slug is `#multi-round-trip-requests` — the trailing `-mrtr` is stale.

### How I checked

Against the published site, not just the source:

```
$ curl -sL https://go.sdk.modelcontextprotocol.io/protocol | grep -o 'id="[^"]*round[^"]*"'
            # (no output)
$ curl -sL https://go.sdk.modelcontextprotocol.io/client  | grep -o 'id="[^"]*round[^"]*"'
id="multi-round-trip-requests"
$ curl -sL https://go.sdk.modelcontextprotocol.io/server  | grep -o 'id="[^"]*round[^"]*"'
id="multi-round-trip-requests"
```

So `/protocol` carries no anchor containing `round` at all, and both
live targets use the
plain slug.

`git log -S` says the links arrived with b9e6fc5 ("mcp: add
documentation for new protocol
version", #1019, 2026-06-23) and that `protocol.src.md` has never
contained a
`Multi Round-Trip Requests` heading — the section landed in
`client.src.md` and
`server.src.md` instead, and these four references were never repointed.

I also ran a small link/anchor checker over `docs/`: 4 bad anchors
before, 0 after. (Two
"broken links" it also reports in `server.md` are its own false
positives — Go generics
inside a fence, `jsonschema.For[WeatherInput](opts)`, read as markdown
link syntax. Not
touched.)

### What it is now

The three per-feature links become same-page references, matching how
`client.md` already
links its own sections (`(see [Capabilities](#capabilities))`):

```
[Multi Round-Trip Requests](#multi-round-trip-requests)
```

and the cross-page one drops the stale suffix:

```
[server-side documentation](server.md#multi-round-trip-requests).
```

Change is in `internal/docs/client.src.md`; `docs/client.md` regenerated
with
`go generate ./...`, both committed together. Locally `go generate
./...` leaves the tree
clean afterwards, which is what `docs-check` asserts. Docs-only, four
link targets, no prose
and no code paths touched.

---
Assisted-by: Claude Opus 5 — this PR was drafted and verified by Anton's
AI cofounder running
on his account; every command and output above is from a real run on
this machine, not a
reconstruction.

Co-authored-by: tonydzi <dzyatkovskiy.a@gmail.com>

internal/docs/client.src.md

@@ -30,7 +30,7 @@ method. To receive notifications about root changes, set
 [`ServerOptions.RootsListChangedHandler`](https://pkg.go.dev/github.com/modelcontextprotocol/go-sdk/mcp#ServerOptions.RootsListChangedHandler).
 For protocol versions `2026-07-28` and later, `ListRoots` requests are
 delivered via the
-[Multi Round-Trip Requests](protocol.md#multi-round-trip-requests-mrtr)
+[Multi Round-Trip Requests](#multi-round-trip-requests)
 pattern.
 
 %include ../../mcp/client_example_test.go roots -
@@ -57,7 +57,7 @@ This function is invoked whenever the server requests sampling.
 
 For protocol versions `2026-07-28` and later, sampling requests are
 delivered via the
-[Multi Round-Trip Requests](protocol.md#multi-round-trip-requests-mrtr)
+[Multi Round-Trip Requests](#multi-round-trip-requests)
 pattern.
 
 %include ../../mcp/client_example_test.go sampling -
@@ -79,7 +79,7 @@ you must declare that capability explicitly (see [Capabilities](#capabilities))
 
 For protocol versions `2026-07-28` and later, elicitation requests are
 delivered via the
-[Multi Round-Trip Requests](protocol.md#multi-round-trip-requests-mrtr)
+[Multi Round-Trip Requests](#multi-round-trip-requests)
 pattern.
 
 %include ../../mcp/client_example_test.go elicitation -
@@ -117,7 +117,7 @@ For legacy (`<= 2025-11-25`) servers, the SDK transparently sends server
 requests on the legacy server-initiated channel; the MRTR machinery is a
 no-op in that direction. For legacy clients talking to MRTR-style servers,
 the server SDK applies the inverse compatibility shim — see the
-[server-side documentation](server.md#multi-round-trip-requests-mrtr).
+[server-side documentation](server.md#multi-round-trip-requests).
 
 ## Capabilities