docs: pin the landing page install command; wait on an event in the progress test

Two review nits on the previous commit:

- docs/index.md's install tabs were the last unpinned `mcp[cli]` commands
  in the book. They now pin 2.0.0a2 like installation.md and the README,
  and the warning box below them explains the pin instead of asking the
  reader to add one.
- The new test in tests/docs_src/test_progress.py waited for the gated
  callbacks with a sleep poll, which AGENTS.md tells contributors not to
  do, and used a 10s fail_after where 5 is the standard. The callback now
  sets an anyio.Event when the second value lands and the test waits on
  that, under fail_after(5).

Author: maxisbey

docs/index.md

@@ -20,22 +20,22 @@ Python 3.10+.
 === "uv"
 
     ```bash
-    uv add "mcp[cli]"
+    uv add "mcp[cli]==2.0.0a2"
     ```
 
 === "pip"
 
     ```bash
-    pip install "mcp[cli]"
+    pip install "mcp[cli]==2.0.0a2"
     ```
 
 The `[cli]` extra gives you the `mcp` command; you'll want it for development.
 
 !!! warning "Pin the version while v2 is in alpha"
-    Until v2 is stable, installers resolve `mcp` to the latest **v1.x** release, which this
-    documentation does not describe. Pin an alpha explicitly (`uv add "mcp[cli]==2.0.0a2"`;
-    check [PyPI](https://pypi.org/project/mcp/#history) for the newest pre-release).
-    See [Installation](installation.md) for the details.
+    Installers never select a pre-release unless you name one, so an unpinned `uv add "mcp[cli]"`
+    gives you the latest **v1.x** release, which this documentation does not describe. Check
+    [PyPI](https://pypi.org/project/mcp/#history) for the newest alpha before you copy the line
+    above. See [Installation](installation.md) for the details.
 
 ## Example
 

tests/docs_src/test_progress.py

@@ -51,20 +51,22 @@ async def test_over_a_wire_dispatcher_callbacks_race_the_result() -> None:
     you not to rule out.
     """
     release = anyio.Event()
+    done = anyio.Event()
     finished: list[float] = []
 
-    async def slow(progress: float, total: float | None, message: str | None) -> None:
+    async def gated(progress: float, total: float | None, message: str | None) -> None:
         await release.wait()
         finished.append(progress)
+        if len(finished) == 2:
+            done.set()
 
     async with Client(tutorial001.mcp, mode="legacy") as client:
-        with anyio.fail_after(10):
-            result = await client.call_tool("import_catalog", {"urls": URLS}, progress_callback=slow)
+        with anyio.fail_after(5):
+            result = await client.call_tool("import_catalog", {"urls": URLS}, progress_callback=gated)
         assert finished == []
         release.set()
-        with anyio.fail_after(10):
-            while len(finished) < 2:
-                await anyio.sleep(0.01)
+        with anyio.fail_after(5):
+            await done.wait()
     assert sorted(finished) == [1, 2]
     assert result.structured_content == {"result": "Imported 2 records."}