diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 13f9611d65..b7669a9079 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -83,11 +83,16 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        python: ['3.7', '3.8', '3.9', '3.10']
+        python: ['3.7', '3.8', '3.9', '3.10', 'pypy-3.8-nightly', 'pypy-3.9-nightly']
         arch: ['x86', 'x64']
         lsp: ['']
         lsp_extract_file: ['']
         extra_name: ['']
+        exclude:
+          - python: 'pypy-3.8-nightly'
+            arch: 'x86'
+          - python: 'pypy-3.9-nightly'
+            arch: 'x86'
         include:
           - python: '3.8'
             arch: 'x64'
@@ -104,11 +109,15 @@ jobs:
           #  lsp: 'http://download.pctools.com/mirror/updates/9.0.0.2308-SDavfree-lite_en.exe'
           #  lsp_extract_file: ''
           #  extra_name: ', with non-IFS LSP'
-          - python: '3.8'  # <- not actually used
-            arch: 'x64'
-            pypy_nightly_branch: 'py3.8'
-            extra_name: ', pypy 3.8 nightly'
-
+    continue-on-error: >-
+      ${{
+        (
+          endsWith(matrix.python, '-dev')
+          || endsWith(matrix.python, '-nightly')
+        )
+        && true
+        || false
+      }}
     steps:
       - name: Retrieve the project source from an sdist inside the GHA artifact
         uses: re-actors/checkout-python-sdist@release/v1
@@ -116,7 +125,7 @@ jobs:
           source-tarball-name: ${{ needs.build.outputs.sdist-artifact-name }}
           workflow-artifact-name: ${{ env.dists-artifact-name }}
       - name: Setup python
-        uses: actions/setup-python@v2
+        uses: actions/setup-python@v4
         with:
           # This allows the matrix to specify just the major.minor version while still
           # expanding it to get the latest patch version including alpha releases.
@@ -149,26 +158,19 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        python: ['pypy-3.7', 'pypy-3.8', '3.7', '3.8', '3.9', '3.10', '3.11-dev']
+        python: ['pypy-3.7', 'pypy-3.8', 'pypy-3.9', '3.7', '3.8', '3.9', '3.10', '3.11', '3.12-dev', 'pypy-3.8-nightly', 'pypy-3.9-nightly']
         check_formatting: ['0']
-        pypy_nightly_branch: ['']
         extra_name: ['']
         include:
           - python: '3.8'
             check_formatting: '1'
             extra_name: ', check formatting'
-          - python: '3.7'  # <- not actually used
-            pypy_nightly_branch: 'py3.7'
-            extra_name: ', pypy 3.7 nightly'
-          - python: '3.8'  # <- not actually used
-            pypy_nightly_branch: 'py3.8'
-            extra_name: ', pypy 3.8 nightly'
     continue-on-error: >-
       ${{
         (
           matrix.check_formatting == '1'
-          || matrix.pypy_nightly_branch == 'py3.7'
           || endsWith(matrix.python, '-dev')
+          || endsWith(matrix.python, '-nightly')
         )
         && true
         || false
@@ -180,7 +182,7 @@ jobs:
           source-tarball-name: ${{ needs.build.outputs.sdist-artifact-name }}
           workflow-artifact-name: ${{ env.dists-artifact-name }}
       - name: Setup python
-        uses: actions/setup-python@v2
+        uses: actions/setup-python@v4
         if: "!endsWith(matrix.python, '-dev')"
         with:
           python-version: ${{ fromJSON(format('["{0}", "{1}"]', format('{0}.0-alpha - {0}.X', matrix.python), matrix.python))[startsWith(matrix.python, 'pypy')] }}
@@ -194,27 +196,63 @@ jobs:
       - name: Run tests
         run: ./ci.sh
         env:
-          PYPY_NIGHTLY_BRANCH: '${{ matrix.pypy_nightly_branch }}'
           CHECK_FORMATTING: '${{ matrix.check_formatting }}'
           # Should match 'name:' up above
           JOB_NAME: 'Ubuntu (${{ matrix.python }}${{ matrix.extra_name }})'
 
+  autofmt:
+    name: Autoformat dependabot PR
+    timeout-minutes: 10
+    if: github.actor == 'dependabot[bot]'
+    runs-on: 'ubuntu-latest'
+    # https://docs.github.com/en/code-security/dependabot/working-with-dependabot/automating-dependabot-with-github-actions#changing-github_token-permissions
+    permissions:
+      pull-requests: write
+      issues: write
+      repository-projects: write
+      contents: write
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v3
+        with:
+          ref: ${{ github.event.pull_request.head.ref }}
+      - name: Setup python
+        uses: actions/setup-python@v2
+        with:
+          python-version: "3.8"
+      - name: Check formatting
+        run: |
+          python -m pip install -r test-requirements.txt
+          ./check.sh
+      - name: Commit autoformatter changes
+        if: failure()
+        run: |
+          black setup.py trio
+          git config user.name 'github-actions[bot]'
+          git config user.email '41898282+github-actions[bot]@users.noreply.github.com'
+          git commit -am "Autoformatter changes"
+          git push
+
   macOS:
     name: 'macOS (${{ matrix.python }})'
     needs:
       - build
 
-    timeout-minutes: 10
+    timeout-minutes: 15
     runs-on: 'macos-latest'
     strategy:
       fail-fast: false
       matrix:
-        python: ['3.7', '3.8', '3.9', '3.10']
-        include:
-          - python: '3.8'  # <- not actually used
-            arch: 'x64'
-            pypy_nightly_branch: 'py3.8'
-            extra_name: ', pypy 3.8 nightly'
+        python: ['3.7', '3.8', '3.9', '3.10', 'pypy-3.8-nightly', 'pypy-3.9-nightly']
+    continue-on-error: >-
+      ${{
+        (
+          endsWith(matrix.python, '-dev')
+          || endsWith(matrix.python, '-nightly')
+        )
+        && true
+        || false
+      }}
     steps:
       - name: Retrieve the project source from an sdist inside the GHA artifact
         uses: re-actors/checkout-python-sdist@release/v1
@@ -222,7 +260,7 @@ jobs:
           source-tarball-name: ${{ needs.build.outputs.sdist-artifact-name }}
           workflow-artifact-name: ${{ env.dists-artifact-name }}
       - name: Setup python
-        uses: actions/setup-python@v2
+        uses: actions/setup-python@v4
         with:
           python-version: ${{ fromJSON(format('["{0}", "{1}"]', format('{0}.0-alpha - {0}.X', matrix.python), matrix.python))[startsWith(matrix.python, 'pypy')] }}
           cache: pip
diff --git a/.readthedocs.yml b/.readthedocs.yml
index 2a32d6c9b5..9fde00ef8f 100644
--- a/.readthedocs.yml
+++ b/.readthedocs.yml
@@ -5,8 +5,12 @@ formats:
   - htmlzip
   - epub
 
+build:
+  os: "ubuntu-22.04"
+  tools:
+    python: "3.11"
+
 python:
-  version: 3.7
   install:
     - requirements: docs-requirements.txt
 
diff --git a/check.sh b/check.sh
index 57f1e2db40..8416a9c5d1 100755
--- a/check.sh
+++ b/check.sh
@@ -28,6 +28,15 @@ mypy -m trio -m trio.testing --platform linux || EXIT_STATUS=$?
 mypy -m trio -m trio.testing --platform darwin || EXIT_STATUS=$?  # tests FreeBSD too
 mypy -m trio -m trio.testing --platform win32 || EXIT_STATUS=$?
 
+# Check pip compile is consistent
+pip-compile test-requirements.in
+pip-compile docs-requirements.in
+
+if git status --porcelain | grep -q "requirements.txt"; then
+    git status --porcelain
+    EXIT_STATUS=1
+fi
+
 # Finally, leave a really clear warning of any issues and exit
 if [ $EXIT_STATUS -ne 0 ]; then
     cat <<EOF
diff --git a/ci.sh b/ci.sh
index d4f9df3a94..f8c4f24d7d 100755
--- a/ci.sh
+++ b/ci.sh
@@ -26,40 +26,6 @@ function curl-harder() {
     return 1
 }
 
-################################################################
-# Bootstrap python environment, if necessary
-################################################################
-
-### PyPy nightly ###
-
-if [ "$PYPY_NIGHTLY_BRANCH" != "" ]; then
-    JOB_NAME="pypy_nightly_${PYPY_NIGHTLY_BRANCH}"
-    curl-harder -o pypy.tar.bz2 http://buildbot.pypy.org/nightly/${PYPY_NIGHTLY_BRANCH}/pypy-c-jit-latest-linux64.tar.bz2
-    if [ ! -s pypy.tar.bz2 ]; then
-        # We know:
-        # - curl succeeded (200 response code)
-        # - nonetheless, pypy.tar.bz2 does not exist, or contains no data
-        # This isn't going to work, and the failure is not informative of
-        # anything involving Trio.
-        ls -l
-        echo "PyPy3 nightly build failed to download – something is wrong on their end."
-        echo "Skipping testing against the nightly build for right now."
-        exit 0
-    fi
-    tar xaf pypy.tar.bz2
-    # something like "pypy-c-jit-89963-748aa3022295-linux64"
-    PYPY_DIR=$(echo pypy-c-jit-*)
-    PYTHON_EXE=$PYPY_DIR/bin/pypy3
-
-    if ! ($PYTHON_EXE -m ensurepip \
-              && $PYTHON_EXE -m pip install virtualenv \
-              && $PYTHON_EXE -m virtualenv testenv); then
-        echo "pypy nightly is broken; skipping tests"
-        exit 0
-    fi
-    source testenv/bin/activate
-fi
-
 ################################################################
 # We have a Python environment!
 ################################################################
diff --git a/docs-requirements.in b/docs-requirements.in
index 7d6abc0033..fab339e1f9 100644
--- a/docs-requirements.in
+++ b/docs-requirements.in
@@ -1,6 +1,6 @@
 # RTD is currently installing 1.5.3, which has a bug in :lineno-match:
 # sphinx-3.4 causes warnings about some trio._abc classes: GH#2338
-sphinx >= 1.7.0, < 3.4
+sphinx >= 1.7.0, < 6.2
 # jinja2-3.1 causes importerror with sphinx<4.0
 jinja2 < 3.1
 sphinx_rtd_theme
diff --git a/docs-requirements.txt b/docs-requirements.txt
index cdb4d4e9af..4c197c69b3 100644
--- a/docs-requirements.txt
+++ b/docs-requirements.txt
@@ -1,6 +1,6 @@
 #
-# This file is autogenerated by pip-compile with python 3.7
-# To update, run:
+# This file is autogenerated by pip-compile with Python 3.8
+# by the following command:
 #
 #    pip-compile docs-requirements.in
 #
@@ -12,11 +12,11 @@ attrs==22.2.0
     # via
     #   -r docs-requirements.in
     #   outcome
-babel==2.11.0
+babel==2.12.1
     # via sphinx
 certifi==2022.12.7
     # via requests
-charset-normalizer==3.0.1
+charset-normalizer==3.1.0
     # via requests
 click==8.1.3
     # via
@@ -24,7 +24,7 @@ click==8.1.3
     #   towncrier
 click-default-group==1.2.2
     # via towncrier
-docutils==0.17.1
+docutils==0.18.1
     # via
     #   sphinx
     #   sphinx-rtd-theme
@@ -38,6 +38,8 @@ imagesize==1.4.1
     # via sphinx
 immutables==0.19
     # via -r docs-requirements.in
+importlib-metadata==6.0.0
+    # via sphinx
 incremental==22.10.0
     # via towncrier
 jinja2==3.0.3
@@ -63,19 +65,21 @@ snowballstemmer==2.2.0
     # via sphinx
 sortedcontainers==2.4.0
     # via -r docs-requirements.in
-sphinx==3.3.1
+sphinx==6.1.3
     # via
     #   -r docs-requirements.in
     #   sphinx-rtd-theme
     #   sphinxcontrib-trio
-sphinx-rtd-theme==1.1.1
+sphinx-rtd-theme==1.2.0
     # via -r docs-requirements.in
-sphinxcontrib-applehelp==1.0.2
+sphinxcontrib-applehelp==1.0.4
     # via sphinx
 sphinxcontrib-devhelp==1.0.2
     # via sphinx
-sphinxcontrib-htmlhelp==2.0.0
+sphinxcontrib-htmlhelp==2.0.1
     # via sphinx
+sphinxcontrib-jquery==2.0.0
+    # via sphinx-rtd-theme
 sphinxcontrib-jsmath==1.0.1
     # via sphinx
 sphinxcontrib-qthelp==1.0.3
@@ -86,10 +90,12 @@ sphinxcontrib-trio==1.1.2
     # via -r docs-requirements.in
 tomli==2.0.1
     # via towncrier
-towncrier==22.8.0
+towncrier==22.12.0
     # via -r docs-requirements.in
 urllib3==1.26.14
     # via requests
+zipp==3.15.0
+    # via importlib-metadata
 
 # The following packages are considered to be unsafe in a requirements file:
 # setuptools
diff --git a/docs/source/_templates/layout.html b/docs/source/_templates/layout.html
index d3b0ca89fd..dbebf5c2ae 100644
--- a/docs/source/_templates/layout.html
+++ b/docs/source/_templates/layout.html
@@ -4,8 +4,13 @@
 {% extends "!layout.html" %}
 
 {% block sidebartitle %}
-<a class="logo" href="{{ pathto(master_doc) }}">
-  <img class="logo" src="{{ pathto('_static/' + logo, 1) }}" />
+
+{# the logo helper function was removed in Sphinx 6 and deprecated since Sphinx 4 #}
+{# the master_doc variable was renamed to root_doc in Sphinx 4 (master_doc still exists in later Sphinx versions) #}
+{# check sphinx_rtd_theme/layout.html:sidebartitle if this snippet has become outdated #}
+
+<a class="logo" href="{{ pathto(root_doc) }}">
+  <img class="logo" src="{{ logo_url }}" />
   {%- set nav_version = version %}
   {% if READTHEDOCS and current_version %}
     {%- set nav_version = current_version %}
diff --git a/docs/source/code-of-conduct.rst b/docs/source/code-of-conduct.rst
index fb0d003065..5d20cc3263 100644
--- a/docs/source/code-of-conduct.rst
+++ b/docs/source/code-of-conduct.rst
@@ -19,7 +19,7 @@ If you see a Code of Conduct violation, follow these steps:
    them to stop and/or edit their message(s) or commits.
 2. That person should immediately stop the behavior and correct the
    issue.
-3. If this doesn’t happen, or if you're uncomfortable speaking up,
+3. If this doesn't happen, or if you're uncomfortable speaking up,
    :ref:`contact the maintainers <coc-contacting-maintainers>`.
 4. As soon as possible, a maintainer will look into the issue, and take
    :ref:`further action (see below) <coc-further-enforcement>`, starting with
diff --git a/docs/source/conf.py b/docs/source/conf.py
index 7200d91375..cfac66576b 100755
--- a/docs/source/conf.py
+++ b/docs/source/conf.py
@@ -54,8 +54,14 @@
     ("py:class", "async function"),
     ("py:class", "sync function"),
     # https://github.com/sphinx-doc/sphinx/issues/7722
-    ("py:class", "SendType"),
-    ("py:class", "ReceiveType"),
+    # TODO: why do these need to be spelled out?
+    ("py:class", "trio._abc.ReceiveType"),
+    ("py:class", "trio._abc.SendType"),
+    ("py:class", "trio._abc.T"),
+    ("py:obj", "trio._abc.ReceiveType"),
+    ("py:obj", "trio._abc.SendType"),
+    ("py:obj", "trio._abc.T"),
+    ("py:obj", "trio._abc.T_resource"),
 ]
 autodoc_inherit_docstrings = False
 default_role = "obj"
@@ -91,6 +97,7 @@ def setup(app):
     "python": ("https://docs.python.org/3", None),
     "outcome": ("https://outcome.readthedocs.io/en/latest/", None),
     "pyopenssl": ("https://www.pyopenssl.org/en/stable/", None),
+    "sniffio": ("https://sniffio.readthedocs.io/en/latest/", None),
 }
 
 autodoc_member_order = "bysource"
@@ -132,7 +139,7 @@ def setup(app):
 #
 # This is also used if you do content translation via gettext catalogs.
 # Usually you set "language" from the command line for these cases.
-language = None
+language = "en"
 
 # List of patterns, relative to source directory, that match files and
 # directories to ignore when looking for source files.
diff --git a/docs/source/contributing.rst b/docs/source/contributing.rst
index 1a97dc9f44..7d66ae711d 100644
--- a/docs/source/contributing.rst
+++ b/docs/source/contributing.rst
@@ -556,7 +556,8 @@ then we'll figure something out.
 .. Possible references for future additions:
 
    """
-   Jumping into an unfamiliar codebase (or any for that matter) for the first time can be scary. Plus, if it’s your first time contributing to open source, it can even be scarier!
+   Jumping into an unfamiliar codebase (or any for that matter) for the first time can be scary.
+   Plus, if it's your first time contributing to open source, it can even be scarier!
 
    But, we at webpack believe:
 
diff --git a/newsfragments/2333.bugfix.rst b/newsfragments/2333.bugfix.rst
index efab3a6380..a0f4c9fd37 100644
--- a/newsfragments/2333.bugfix.rst
+++ b/newsfragments/2333.bugfix.rst
@@ -1 +1 @@
-Python raises a `TypeError` if you try to (re-)install a C signal handler.
+Fixed a crash that can occur when running Trio within an embedded Python interpreter, by handling the `TypeError` that is raised when trying to (re-)install a C signal handler.
diff --git a/newsfragments/2462.bugfix.rst b/newsfragments/2462.bugfix.rst
new file mode 100644
index 0000000000..9208289ed9
--- /dev/null
+++ b/newsfragments/2462.bugfix.rst
@@ -0,0 +1 @@
+Fix :func:`sniffio.current_async_library` when Trio tasks are spawned from a non-Trio context (such as when using trio-asyncio). Previously, a regular Trio task would inherit the non-Trio library name, and spawning a system task would cause the non-Trio caller to start thinking it was Trio.
diff --git a/newsfragments/970.doc.rst b/newsfragments/970.doc.rst
new file mode 100644
index 0000000000..6e114abf5b
--- /dev/null
+++ b/newsfragments/970.doc.rst
@@ -0,0 +1 @@
+Documented that :obj:`Nursery.start_soon` does not guarantee task ordering.
diff --git a/test-requirements.in b/test-requirements.in
index 85ca664925..eda15ef4b3 100644
--- a/test-requirements.in
+++ b/test-requirements.in
@@ -16,6 +16,7 @@ mypy; implementation_name == "cpython"
 types-pyOpenSSL; implementation_name == "cpython"
 flake8
 astor          # code generation
+pip-tools
 
 # https://github.com/python-trio/trio/pull/654#issuecomment-420518745
 # typed_ast is deprecated as of 3.8, and straight up doesn't compile on 3.10-dev as of 2021-12-13
diff --git a/test-requirements.txt b/test-requirements.txt
index a08f3b0b8e..cc80d23675 100644
--- a/test-requirements.txt
+++ b/test-requirements.txt
@@ -1,12 +1,12 @@
 #
-# This file is autogenerated by pip-compile with python 3.7
-# To update, run:
+# This file is autogenerated by pip-compile with Python 3.8
+# by the following command:
 #
 #    pip-compile test-requirements.in
 #
 astor==0.8.1
     # via -r test-requirements.in
-astroid==2.11.7
+astroid==2.15.0
     # via pylint
 async-generator==1.10
     # via -r test-requirements.in
@@ -17,15 +17,19 @@ attrs==22.2.0
     #   pytest
 backcall==0.2.0
     # via ipython
-black==22.12.0 ; implementation_name == "cpython"
+black==23.1.0 ; implementation_name == "cpython"
     # via -r test-requirements.in
+build==0.10.0
+    # via pip-tools
 cffi==1.15.1
     # via cryptography
 click==8.1.3
-    # via black
+    # via
+    #   black
+    #   pip-tools
 coverage[toml]==6.4.1
     # via pytest-cov
-cryptography==39.0.0
+cryptography==39.0.2
     # via
     #   -r test-requirements.in
     #   pyopenssl
@@ -35,6 +39,10 @@ decorator==5.1.1
     # via ipython
 dill==0.3.6
     # via pylint
+exceptiongroup==1.1.0 ; python_version < "3.11"
+    # via
+    #   -r test-requirements.in
+    #   pytest
 flake8==4.0.1
     # via -r test-requirements.in
 idna==3.4
@@ -59,9 +67,9 @@ mccabe==0.6.1
     # via
     #   flake8
     #   pylint
-mypy==0.991 ; implementation_name == "cpython"
+mypy==1.1.1 ; implementation_name == "cpython"
     # via -r test-requirements.in
-mypy-extensions==0.4.3 ; implementation_name == "cpython"
+mypy-extensions==1.0.0 ; implementation_name == "cpython"
     # via
     #   -r test-requirements.in
     #   black
@@ -69,22 +77,27 @@ mypy-extensions==0.4.3 ; implementation_name == "cpython"
 outcome==1.2.0
     # via -r test-requirements.in
 packaging==23.0
-    # via pytest
+    # via
+    #   black
+    #   build
+    #   pytest
 parso==0.8.3
     # via jedi
-pathspec==0.10.3
+pathspec==0.11.0
     # via black
 pexpect==4.8.0
     # via ipython
 pickleshare==0.7.5
     # via ipython
-platformdirs==2.6.0
+pip-tools==6.12.3
+    # via -r test-requirements.in
+platformdirs==3.1.0
     # via
     #   black
     #   pylint
 pluggy==1.0.0
     # via pytest
-prompt-toolkit==3.0.33
+prompt-toolkit==3.0.38
     # via ipython
 ptyprocess==0.7.0
     # via pexpect
@@ -96,11 +109,13 @@ pyflakes==2.4.0
     # via flake8
 pygments==2.14.0
     # via ipython
-pylint==2.14.5
+pylint==2.17.0
     # via -r test-requirements.in
 pyopenssl==23.0.0
     # via -r test-requirements.in
-pytest==7.2.1
+pyproject-hooks==1.0.0
+    # via build
+pytest==7.2.2
     # via
     #   -r test-requirements.in
     #   pytest-cov
@@ -110,24 +125,38 @@ sniffio==1.3.0
     # via -r test-requirements.in
 sortedcontainers==2.4.0
     # via -r test-requirements.in
+tomli==2.0.1
+    # via
+    #   black
+    #   build
+    #   coverage
+    #   mypy
+    #   pylint
+    #   pytest
 tomlkit==0.11.6
     # via pylint
-traitlets==5.8.1
+traitlets==5.9.0
     # via
     #   ipython
     #   matplotlib-inline
 trustme==0.9.0
     # via -r test-requirements.in
-types-pyopenssl==23.0.0.1 ; implementation_name == "cpython"
+types-pyopenssl==23.0.0.4 ; implementation_name == "cpython"
     # via -r test-requirements.in
-typing-extensions==4.4.0 ; implementation_name == "cpython"
+typing-extensions==4.5.0 ; implementation_name == "cpython"
     # via
     #   -r test-requirements.in
+    #   astroid
+    #   black
     #   mypy
-wcwidth==0.2.5
+    #   pylint
+wcwidth==0.2.6
     # via prompt-toolkit
-wrapt==1.14.1
+wheel==0.38.4
+    # via pip-tools
+wrapt==1.15.0
     # via astroid
 
 # The following packages are considered to be unsafe in a requirements file:
+# pip
 # setuptools
diff --git a/trio/_channel.py b/trio/_channel.py
index 1cecc55621..2059b1fb4b 100644
--- a/trio/_channel.py
+++ b/trio/_channel.py
@@ -1,18 +1,36 @@
+from __future__ import annotations
+
 from collections import deque, OrderedDict
+from collections.abc import Callable
 from math import inf
 
+from types import TracebackType
+from typing import (
+    Any,
+    Generic,
+    NoReturn,
+    TypeVar,
+    TYPE_CHECKING,
+    Tuple,  # only needed for typechecking on <3.9
+)
+
 import attr
 from outcome import Error, Value
 
-from .abc import SendChannel, ReceiveChannel, Channel
+from ._abc import SendChannel, ReceiveChannel, Channel, ReceiveType, SendType, T
 from ._util import generic_function, NoPublicConstructor
 
 import trio
-from ._core import enable_ki_protection
+from ._core import enable_ki_protection, Task, Abort, RaiseCancelT
+
+
+# Temporary TypeVar needed until mypy release supports Self as a type
+SelfT = TypeVar("SelfT")
 
 
-@generic_function
-def open_memory_channel(max_buffer_size):
+def _open_memory_channel(
+    max_buffer_size: int,
+) -> tuple[MemorySendChannel[T], MemoryReceiveChannel[T]]:
     """Open a channel for passing objects between tasks within a process.
 
     Memory channels are lightweight, cheap to allocate, and entirely
@@ -68,36 +86,57 @@ def open_memory_channel(max_buffer_size):
         raise TypeError("max_buffer_size must be an integer or math.inf")
     if max_buffer_size < 0:
         raise ValueError("max_buffer_size must be >= 0")
-    state = MemoryChannelState(max_buffer_size)
+    state: MemoryChannelState[T] = MemoryChannelState(max_buffer_size)
     return (
-        MemorySendChannel._create(state),
-        MemoryReceiveChannel._create(state),
+        MemorySendChannel[T]._create(state),
+        MemoryReceiveChannel[T]._create(state),
     )
 
 
+# This workaround requires python3.9+, once older python versions are not supported
+# or there's a better way of achieving type-checking on a generic factory function,
+# it could replace the normal function header
+if TYPE_CHECKING:
+    # written as a class so you can say open_memory_channel[int](5)
+    # Need to use Tuple instead of tuple due to CI check running on 3.8
+    class open_memory_channel(Tuple[MemorySendChannel[T], MemoryReceiveChannel[T]]):
+        def __new__(  # type: ignore[misc]  # "must return a subtype"
+            cls, max_buffer_size: int
+        ) -> tuple[MemorySendChannel[T], MemoryReceiveChannel[T]]:
+            return _open_memory_channel(max_buffer_size)
+
+        def __init__(self, max_buffer_size: int):
+            ...
+
+else:
+    # apply the generic_function decorator to make open_memory_channel indexable
+    # so it's valid to say e.g. ``open_memory_channel[bytes](5)`` at runtime
+    open_memory_channel = generic_function(_open_memory_channel)
+
+
 @attr.s(frozen=True, slots=True)
 class MemoryChannelStats:
-    current_buffer_used = attr.ib()
-    max_buffer_size = attr.ib()
-    open_send_channels = attr.ib()
-    open_receive_channels = attr.ib()
-    tasks_waiting_send = attr.ib()
-    tasks_waiting_receive = attr.ib()
+    current_buffer_used: int = attr.ib()
+    max_buffer_size: int = attr.ib()
+    open_send_channels: int = attr.ib()
+    open_receive_channels: int = attr.ib()
+    tasks_waiting_send: int = attr.ib()
+    tasks_waiting_receive: int = attr.ib()
 
 
 @attr.s(slots=True)
-class MemoryChannelState:
-    max_buffer_size = attr.ib()
-    data = attr.ib(factory=deque)
+class MemoryChannelState(Generic[T]):
+    max_buffer_size: int = attr.ib()
+    data: deque[T] = attr.ib(factory=deque)
     # Counts of open endpoints using this state
-    open_send_channels = attr.ib(default=0)
-    open_receive_channels = attr.ib(default=0)
+    open_send_channels: int = attr.ib(default=0)
+    open_receive_channels: int = attr.ib(default=0)
     # {task: value}
-    send_tasks = attr.ib(factory=OrderedDict)
+    send_tasks: OrderedDict[Task, T] = attr.ib(factory=OrderedDict)
     # {task: None}
-    receive_tasks = attr.ib(factory=OrderedDict)
+    receive_tasks: OrderedDict[Task, None] = attr.ib(factory=OrderedDict)
 
-    def statistics(self):
+    def statistics(self) -> MemoryChannelStats:
         return MemoryChannelStats(
             current_buffer_used=len(self.data),
             max_buffer_size=self.max_buffer_size,
@@ -109,28 +148,28 @@ def statistics(self):
 
 
 @attr.s(eq=False, repr=False)
-class MemorySendChannel(SendChannel, metaclass=NoPublicConstructor):
-    _state = attr.ib()
-    _closed = attr.ib(default=False)
+class MemorySendChannel(SendChannel[SendType], metaclass=NoPublicConstructor):
+    _state: MemoryChannelState[SendType] = attr.ib()
+    _closed: bool = attr.ib(default=False)
     # This is just the tasks waiting on *this* object. As compared to
     # self._state.send_tasks, which includes tasks from this object and
     # all clones.
-    _tasks = attr.ib(factory=set)
+    _tasks: set[Task] = attr.ib(factory=set)
 
-    def __attrs_post_init__(self):
+    def __attrs_post_init__(self) -> None:
         self._state.open_send_channels += 1
 
-    def __repr__(self):
+    def __repr__(self) -> str:
         return "<send channel at {:#x}, using buffer at {:#x}>".format(
             id(self), id(self._state)
         )
 
-    def statistics(self):
+    def statistics(self) -> MemoryChannelStats:
         # XX should we also report statistics specific to this object?
         return self._state.statistics()
 
     @enable_ki_protection
-    def send_nowait(self, value):
+    def send_nowait(self, value: SendType) -> None:
         """Like `~trio.abc.SendChannel.send`, but if the channel's buffer is
         full, raises `WouldBlock` instead of blocking.
 
@@ -150,7 +189,7 @@ def send_nowait(self, value):
             raise trio.WouldBlock
 
     @enable_ki_protection
-    async def send(self, value):
+    async def send(self, value: SendType) -> None:
         """See `SendChannel.send <trio.abc.SendChannel.send>`.
 
         Memory channels allow multiple tasks to call `send` at the same time.
@@ -170,15 +209,16 @@ async def send(self, value):
         self._state.send_tasks[task] = value
         task.custom_sleep_data = self
 
-        def abort_fn(_):
+        def abort_fn(_: RaiseCancelT) -> Abort:
             self._tasks.remove(task)
             del self._state.send_tasks[task]
             return trio.lowlevel.Abort.SUCCEEDED
 
         await trio.lowlevel.wait_task_rescheduled(abort_fn)
 
+    # Return type must be stringified or use a TypeVar
     @enable_ki_protection
-    def clone(self):
+    def clone(self) -> "MemorySendChannel[SendType]":
         """Clone this send channel object.
 
         This returns a new `MemorySendChannel` object, which acts as a
@@ -206,14 +246,19 @@ def clone(self):
             raise trio.ClosedResourceError
         return MemorySendChannel._create(self._state)
 
-    def __enter__(self):
+    def __enter__(self: SelfT) -> SelfT:
         return self
 
-    def __exit__(self, exc_type, exc_val, exc_tb):
+    def __exit__(
+        self,
+        exc_type: type[BaseException] | None,
+        exc_val: BaseException | None,
+        exc_tb: TracebackType | None,
+    ) -> None:
         self.close()
 
     @enable_ki_protection
-    def close(self):
+    def close(self) -> None:
         """Close this send channel object synchronously.
 
         All channel objects have an asynchronous `~.AsyncResource.aclose` method.
@@ -241,30 +286,30 @@ def close(self):
             self._state.receive_tasks.clear()
 
     @enable_ki_protection
-    async def aclose(self):
+    async def aclose(self) -> None:
         self.close()
         await trio.lowlevel.checkpoint()
 
 
 @attr.s(eq=False, repr=False)
-class MemoryReceiveChannel(ReceiveChannel, metaclass=NoPublicConstructor):
-    _state = attr.ib()
-    _closed = attr.ib(default=False)
-    _tasks = attr.ib(factory=set)
+class MemoryReceiveChannel(ReceiveChannel[ReceiveType], metaclass=NoPublicConstructor):
+    _state: MemoryChannelState[ReceiveType] = attr.ib()
+    _closed: bool = attr.ib(default=False)
+    _tasks: set[trio._core._run.Task] = attr.ib(factory=set)
 
-    def __attrs_post_init__(self):
+    def __attrs_post_init__(self) -> None:
         self._state.open_receive_channels += 1
 
-    def statistics(self):
+    def statistics(self) -> MemoryChannelStats:
         return self._state.statistics()
 
-    def __repr__(self):
+    def __repr__(self) -> str:
         return "<receive channel at {:#x}, using buffer at {:#x}>".format(
             id(self), id(self._state)
         )
 
     @enable_ki_protection
-    def receive_nowait(self):
+    def receive_nowait(self) -> ReceiveType:
         """Like `~trio.abc.ReceiveChannel.receive`, but if there's nothing
         ready to receive, raises `WouldBlock` instead of blocking.
 
@@ -284,7 +329,7 @@ def receive_nowait(self):
         raise trio.WouldBlock
 
     @enable_ki_protection
-    async def receive(self):
+    async def receive(self) -> ReceiveType:
         """See `ReceiveChannel.receive <trio.abc.ReceiveChannel.receive>`.
 
         Memory channels allow multiple tasks to call `receive` at the same
@@ -306,15 +351,17 @@ async def receive(self):
         self._state.receive_tasks[task] = None
         task.custom_sleep_data = self
 
-        def abort_fn(_):
+        def abort_fn(_: RaiseCancelT) -> Abort:
             self._tasks.remove(task)
             del self._state.receive_tasks[task]
             return trio.lowlevel.Abort.SUCCEEDED
 
-        return await trio.lowlevel.wait_task_rescheduled(abort_fn)
+        # Not strictly guaranteed to return ReceiveType, but will do so unless
+        # you intentionally reschedule with a bad value.
+        return await trio.lowlevel.wait_task_rescheduled(abort_fn)  # type: ignore[no-any-return]
 
     @enable_ki_protection
-    def clone(self):
+    def clone(self) -> "MemoryReceiveChannel[ReceiveType]":
         """Clone this receive channel object.
 
         This returns a new `MemoryReceiveChannel` object, which acts as a
@@ -345,14 +392,19 @@ def clone(self):
             raise trio.ClosedResourceError
         return MemoryReceiveChannel._create(self._state)
 
-    def __enter__(self):
+    def __enter__(self: SelfT) -> SelfT:
         return self
 
-    def __exit__(self, exc_type, exc_val, exc_tb):
+    def __exit__(
+        self,
+        exc_type: type[BaseException] | None,
+        exc_val: BaseException | None,
+        exc_tb: TracebackType | None,
+    ) -> None:
         self.close()
 
     @enable_ki_protection
-    def close(self):
+    def close(self) -> None:
         """Close this receive channel object synchronously.
 
         All channel objects have an asynchronous `~.AsyncResource.aclose` method.
@@ -381,6 +433,6 @@ def close(self):
             self._state.data.clear()
 
     @enable_ki_protection
-    async def aclose(self):
+    async def aclose(self) -> None:
         self.close()
         await trio.lowlevel.checkpoint()
diff --git a/trio/_core/__init__.py b/trio/_core/__init__.py
index 8e3e526cfe..f9919b8323 100644
--- a/trio/_core/__init__.py
+++ b/trio/_core/__init__.py
@@ -55,6 +55,7 @@
 from ._traps import (
     cancel_shielded_checkpoint,
     Abort,
+    RaiseCancelT,
     wait_task_rescheduled,
     temporarily_detach_coroutine_object,
     permanently_detach_coroutine_object,
diff --git a/trio/_core/_instrumentation.py b/trio/_core/_instrumentation.py
index e14c1ef1e0..b133d47406 100644
--- a/trio/_core/_instrumentation.py
+++ b/trio/_core/_instrumentation.py
@@ -11,6 +11,7 @@
 
 F = TypeVar("F", bound=Callable[..., Any])
 
+
 # Decorator to mark methods public. This does nothing by itself, but
 # trio/_tools/gen_exports.py looks for it.
 def _public(fn: F) -> F:
diff --git a/trio/_core/_run.py b/trio/_core/_run.py
index dc6ff21802..c07e29ab97 100644
--- a/trio/_core/_run.py
+++ b/trio/_core/_run.py
@@ -54,6 +54,7 @@
 
 FnT = TypeVar("FnT", bound="Callable[..., Any]")
 
+
 # Decorator to mark methods public. This does nothing by itself, but
 # trio/_tools/gen_exports.py looks for it.
 def _public(fn: FnT) -> FnT:
@@ -1021,18 +1022,17 @@ def aborted(raise_cancel):
     def start_soon(self, async_fn, *args, name=None):
         """Creates a child task, scheduling ``await async_fn(*args)``.
 
-        This and :meth:`start` are the two fundamental methods for
+        If you want to run a function and immediately wait for its result,
+        then you don't need a nursery; just use ``await async_fn(*args)``.
+        If you want to wait for the task to initialize itself before
+        continuing, see :meth:`start`, the other fundamental method for
         creating concurrent tasks in Trio.
 
         Note that this is *not* an async function and you don't use await
         when calling it. It sets up the new task, but then returns
-        immediately, *before* it has a chance to run. The new task won’t
-        actually get a chance to do anything until some later point when
-        you execute a checkpoint and the scheduler decides to run it.
-        If you want to run a function and immediately wait for its result,
-        then you don't need a nursery; just use ``await async_fn(*args)``.
-        If you want to wait for the task to initialize itself before
-        continuing, see :meth:`start`.
+        immediately, *before* the new task has a chance to do anything.
+        New tasks may start running in any order, and at any checkpoint the
+        scheduler chooses - at latest when the nursery is waiting to exit.
 
         It's possible to pass a nursery object into another task, which
         allows that task to start new child tasks in the first task's
@@ -1075,9 +1075,9 @@ async def start(self, async_fn, *args, name=None):
         The conventional way to define ``async_fn`` is like::
 
             async def async_fn(arg1, arg2, *, task_status=trio.TASK_STATUS_IGNORED):
-                ...
+                ...  # Caller is blocked waiting for this code to run
                 task_status.started()
-                ...
+                ...  # This async code can be interleaved with the caller
 
         :attr:`trio.TASK_STATUS_IGNORED` is a special global object with
         a do-nothing ``started`` method. This way your function supports
@@ -1553,11 +1553,24 @@ def spawn_impl(
         if nursery is None:
             assert self.init_task is None
 
+        ######
+        # Propagate contextvars, and make sure that async_fn can use sniffio.
+        ######
+        if context is None:
+            if system_task:
+                context = self.system_context.copy()
+            else:
+                context = copy_context()
+        # start_soon() or spawn_system_task() might have been invoked
+        # from a different async library; make sure the new task
+        # understands it's Trio-flavored.
+        context.run(current_async_library_cvar.set, "trio")
+
         ######
         # Call the function and get the coroutine object, while giving helpful
         # errors for common mistakes.
         ######
-        coro = coroutine_or_error(async_fn, *args)
+        coro = context.run(coroutine_or_error, async_fn, *args)
 
         if name is None:
             name = async_fn
@@ -1569,12 +1582,6 @@ def spawn_impl(
             except AttributeError:
                 name = repr(name)
 
-        if context is None:
-            if system_task:
-                context = self.system_context.copy()
-            else:
-                context = copy_context()
-
         if not hasattr(coro, "cr_frame"):
             # This async function is implemented in C or Cython
             async def python_wrapper(orig_coro):
@@ -1703,7 +1710,6 @@ def spawn_system_task(self, async_fn, *args, name=None, context=None):
           Task: the newly spawned task
 
         """
-        current_async_library_cvar.set("trio")
         return self.spawn_impl(
             async_fn,
             args,
@@ -1954,7 +1960,6 @@ def setup_runner(
     instruments = Instruments(instruments)
     io_manager = TheIOManager()
     system_context = copy_context()
-    system_context.run(current_async_library_cvar.set, "trio")
     ki_manager = KIManager()
 
     runner = Runner(
diff --git a/trio/_core/_traps.py b/trio/_core/_traps.py
index 95cf46de9b..aedf839a8d 100644
--- a/trio/_core/_traps.py
+++ b/trio/_core/_traps.py
@@ -8,6 +8,8 @@
 
 from . import _run
 
+from typing import Callable, NoReturn, Any
+
 
 # Helper for the bottommost 'yield'. You can't use 'yield' inside an async
 # function, but you can inside a generator, and if you decorate your generator
@@ -64,7 +66,12 @@ class WaitTaskRescheduled:
     abort_func = attr.ib()
 
 
-async def wait_task_rescheduled(abort_func):
+RaiseCancelT = Callable[[], NoReturn]  # TypeAlias
+
+
+# Should always return the type a Task "expects", unless you willfully reschedule it
+# with a bad value.
+async def wait_task_rescheduled(abort_func: Callable[[RaiseCancelT], Abort]) -> Any:
     """Put the current task to sleep, with cancellation support.
 
     This is the lowest-level API for blocking in Trio. Every time a
diff --git a/trio/_core/tests/test_guest_mode.py b/trio/_core/tests/test_guest_mode.py
index a5d6d78e18..9fed232214 100644
--- a/trio/_core/tests/test_guest_mode.py
+++ b/trio/_core/tests/test_guest_mode.py
@@ -17,6 +17,7 @@
 from .tutil import gc_collect_harder, buggy_pypy_asyncgens, restore_unraisablehook
 from ..._util import signal_raise
 
+
 # The simplest possible "host" loop.
 # Nice features:
 # - we can run code "outside" of trio using the schedule function passed to
@@ -227,6 +228,7 @@ async def sit_in_wait_all_tasks_blocked(watb_cscope):
         async def get_woken_by_host_deadline(watb_cscope):
             with trio.CancelScope() as cscope:
                 print("scheduling stuff to happen")
+
                 # Altering the deadline from the host, to something in the
                 # future, will cause the run loop to wake up, but then
                 # discover that there is nothing to do and go back to sleep.
diff --git a/trio/_core/tests/test_run.py b/trio/_core/tests/test_run.py
index 17a9cfad58..4d2cf204fe 100644
--- a/trio/_core/tests/test_run.py
+++ b/trio/_core/tests/test_run.py
@@ -2006,11 +2006,25 @@ def test_sniffio_integration():
     async def check_inside_trio():
         assert sniffio.current_async_library() == "trio"
 
+    def check_function_returning_coroutine():
+        assert sniffio.current_async_library() == "trio"
+        return check_inside_trio()
+
     _core.run(check_inside_trio)
 
     with pytest.raises(sniffio.AsyncLibraryNotFoundError):
         sniffio.current_async_library()
 
+    async def check_new_task_resets_sniffio_library():
+        sniffio.current_async_library_cvar.set("nullio")
+        _core.spawn_system_task(check_inside_trio)
+        async with _core.open_nursery() as nursery:
+            nursery.start_soon(check_inside_trio)
+            nursery.start_soon(check_function_returning_coroutine)
+        assert sniffio.current_async_library() == "nullio"
+
+    _core.run(check_new_task_resets_sniffio_library)
+
 
 async def test_Task_custom_sleep_data():
     task = _core.current_task()
diff --git a/trio/_core/tests/test_windows.py b/trio/_core/tests/test_windows.py
index bd81ef0f33..eb94b82b87 100644
--- a/trio/_core/tests/test_windows.py
+++ b/trio/_core/tests/test_windows.py
@@ -91,7 +91,7 @@ async def read_region(start, end):
 
                 assert buffer == data
 
-                with pytest.raises(BufferError):
+                with pytest.raises((BufferError, TypeError)):
                     await _core.readinto_overlapped(handle, b"immutable")
         finally:
             kernel32.CloseHandle(handle)
diff --git a/trio/_core/tests/tutil.py b/trio/_core/tests/tutil.py
index 016e0fd3e1..74760df38f 100644
--- a/trio/_core/tests/tutil.py
+++ b/trio/_core/tests/tutil.py
@@ -62,7 +62,7 @@ def gc_collect_harder():
     # garbage collection, because executing their __del__ method to print the
     # warning can cause them to be resurrected. So we call collect a few times
     # to make sure.
-    for _ in range(4):
+    for _ in range(5):
         gc.collect()
 
 
diff --git a/trio/_socket.py b/trio/_socket.py
index 8bfa6d265a..b12126f7e1 100644
--- a/trio/_socket.py
+++ b/trio/_socket.py
@@ -353,6 +353,7 @@ async def wrapper(self, *args, **kwargs):
 # addresses everywhere. Split out into a standalone function so it can be reused by
 # FakeNet.
 
+
 # Take an address in Python's representation, and returns a new address in
 # the same representation, but with names resolved to numbers,
 # etc.
diff --git a/trio/_threads.py b/trio/_threads.py
index 15435d44aa..807212e0f9 100644
--- a/trio/_threads.py
+++ b/trio/_threads.py
@@ -313,7 +313,6 @@ async def await_in_trio_thread_task():
             )
 
     context = contextvars.copy_context()
-    context.run(current_async_library_cvar.set, "trio")
     return _run_fn_as_system_task(
         callback,
         afn,
diff --git a/trio/lowlevel.py b/trio/lowlevel.py
index f30fdcc4bd..004692475f 100644
--- a/trio/lowlevel.py
+++ b/trio/lowlevel.py
@@ -16,6 +16,7 @@
 from ._core import (
     cancel_shielded_checkpoint,
     Abort,
+    RaiseCancelT,
     wait_task_rescheduled,
     enable_ki_protection,
     disable_ki_protection,
diff --git a/trio/socket.py b/trio/socket.py
index 4bbc7d14f6..b9e9308dd9 100644
--- a/trio/socket.py
+++ b/trio/socket.py
@@ -118,7 +118,11 @@
         SCM_J1939_DEST_ADDR, SCM_J1939_DEST_NAME, SCM_J1939_ERRQUEUE,
         SCM_J1939_PRIO, SO_J1939_ERRQUEUE, SO_J1939_FILTER, SO_J1939_PROMISC,
         SO_J1939_SEND_PRIO, UDPLITE_RECV_CSCOV, UDPLITE_SEND_CSCOV, IP_RECVTOS,
-        TCP_KEEPALIVE, SO_INCOMING_CPU
+        TCP_KEEPALIVE, SO_INCOMING_CPU, FD_ACCEPT, FD_CLOSE, FD_CLOSE_BIT,
+        FD_CONNECT, FD_CONNECT_BIT, FD_READ, FD_WRITE, INFINITE,
+        WSA_FLAG_OVERLAPPED, WSA_INVALID_HANDLE, WSA_INVALID_PARAMETER,
+        WSA_IO_INCOMPLETE, WSA_IO_PENDING, WSA_NOT_ENOUGH_MEMORY,
+        WSA_OPERATION_ABORTED, WSA_WAIT_FAILED, WSA_WAIT_TIMEOUT,
     )
     # fmt: on
 except ImportError:
diff --git a/trio/tests/test_dtls.py b/trio/tests/test_dtls.py
index 680a8793eb..e771d8acbe 100644
--- a/trio/tests/test_dtls.py
+++ b/trio/tests/test_dtls.py
@@ -3,6 +3,7 @@
 import trio.testing
 from trio import DTLSEndpoint
 import random
+import sys
 import attr
 from contextlib import asynccontextmanager
 from itertools import count
@@ -101,7 +102,8 @@ async def test_smoke(ipv6):
 
 @slow
 async def test_handshake_over_terrible_network(autojump_clock):
-    HANDSHAKES = 1000
+    # PyPy is not fast enough
+    HANDSHAKES = 500 if sys.implementation.name == "pypy" else 1000
     r = random.Random(0)
     fn = FakeNet()
     fn.enable()