diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index 7d91954a4..bb01aabfe 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -25,12 +25,6 @@ jobs:
       fail-fast: false
       matrix:
         include:
-          - tox_env: py27-m_ans-ans2.10
-          - tox_env: py27-m_ans-ans4
-
-          - tox_env: py36-m_ans-ans2.10
-          - tox_env: py36-m_ans-ans4
-
           - tox_env: py27-m_mtg
           - tox_env: py36-m_mtg
 
@@ -86,34 +80,6 @@ jobs:
       fail-fast: false
       matrix:
         include:
-          - tox_env: py311-m_ans-ans2.10
-            python_version: '3.11'
-          - tox_env: py311-m_ans-ans3
-            python_version: '3.11'
-          - tox_env: py311-m_ans-ans4
-            python_version: '3.11'
-          - tox_env: py311-m_ans-ans5
-            python_version: '3.11'
-          - tox_env: py313-m_ans-ans6
-            python_version: '3.13'
-          - tox_env: py313-m_ans-ans7
-            python_version: '3.13'
-          - tox_env: py313-m_ans-ans8
-            python_version: '3.13'
-          - tox_env: py314-m_ans-ans9
-            python_version: '3.14'
-          - tox_env: py314-m_ans-ans10
-            python_version: '3.14'
-          - tox_env: py314-m_ans-ans11
-            python_version: '3.14'
-          - tox_env: py314-m_ans-ans12
-            python_version: '3.14'
-          - tox_env: py314-m_ans-ans13
-            python_version: '3.14'
-
-          - tox_env: py314-m_ans-ans13-s_lin
-            python_version: '3.14'
-
           - tox_env: py314-m_mtg
             python_version: '3.14'
 
@@ -161,11 +127,6 @@ jobs:
       fail-fast: false
       matrix:
         include:
-          - tox_env: py314-m_lcl-ans13
-            python_version: '3.14'
-          - tox_env: py314-m_lcl-ans13-s_lin
-            python_version: '3.14'
-
           - tox_env: py314-m_mtg
             python_version: '3.14'
 
diff --git a/mitogen/parent.py b/mitogen/parent.py
index 6e30b1c62..66e7a8796 100644
--- a/mitogen/parent.py
+++ b/mitogen/parent.py
@@ -1415,7 +1415,6 @@ def __repr__(self):
     #   W: write side of interpreter stdin.
     #   r: read side of core_src FD.
     #   w: write side of core_src FD.
-    #   C: the decompressed core source.
 
     # Final os.close(STDOUT_FILENO) to avoid --py-debug build corrupting stream with
     # "[1234 refs]" during exit.
@@ -1437,8 +1436,17 @@ def _first_stage():
             os.environ['ARGV0']=sys.executable
             os.execl(sys.executable,sys.executable+'(mitogen:%s)'%sys.argv[2])
         os.write(1,'MITO000\n'.encode())
+        # Read `len(compressed preamble)` bytes sent by our Mitogen parent.
+        # `select()` handles non-blocking stdin (e.g. sudo + log_output).
+        # `C` accumulates compressed bytes.
+        # `c` supports detecting EOF (`<stdin>.read(...) -> b''`).
         C=''.encode()
-        while int(sys.argv[3])-len(C)and select.select([0],[],[]):C+=os.read(0,int(sys.argv[3])-len(C))
+        c=1
+        while c and int(sys.argv[3])-len(C)and select.select([0],[],[]):
+            c=os.read(0,int(sys.argv[3])-len(C))
+            # Raises `TypeError` if non-blocking read returns `None`
+            C+=c
+        # Raises `zlib.error` if compressed preamble is truncated or invalid
         C=zlib.decompress(C)
         f=os.fdopen(W,'wb',0)
         f.write(C)
@@ -1463,8 +1471,9 @@ def get_python_argv(self):
         return [self.options.python_path]
 
     def get_boot_command(self):
-        source = inspect.getsource(self._first_stage)
-        source = textwrap.dedent('\n'.join(source.strip().split('\n')[2:]))
+        lines = inspect.getsourcelines(self._first_stage)[0][2:]
+        # Remove line comments, leading indentation, trailing newline
+        source = textwrap.dedent(''.join(s for s in lines if '#' not in s))[:-1]
         source = source.replace('    ', ' ')
         compressor = zlib.compressobj(
             zlib.Z_BEST_COMPRESSION, zlib.DEFLATED, -zlib.MAX_WBITS,
diff --git a/tests/first_stage_test.py b/tests/first_stage_test.py
index 2576ec14d..4f3d77465 100644
--- a/tests/first_stage_test.py
+++ b/tests/first_stage_test.py
@@ -50,3 +50,30 @@ def test_valid_syntax(self):
             )
         finally:
             fp.close()
+
+    def test_stage(self):
+        options = mitogen.parent.Options(max_message_size=123)
+        conn = mitogen.parent.Connection(options, self.router)
+        conn.context = mitogen.core.Context(None, 123)
+
+        proc = subprocess.Popen(
+            args=conn.get_boot_command(),
+            stdout=subprocess.PIPE,
+            stderr=subprocess.PIPE,
+            stdin=subprocess.PIPE,
+        )
+        stdout, stderr = proc.communicate(conn.get_preamble())
+
+        # proc is killed by SIGTERM as the broker kills itself
+        self.assertEqual(-15, proc.returncode)
+        expected_stdout_prefix = b("%s\n%s\n%s\n") % (
+            mitogen.parent.BootstrapProtocol.EC0_MARKER,
+            mitogen.parent.BootstrapProtocol.EC1_MARKER,
+            mitogen.parent.BootstrapProtocol.EC2_MARKER,
+        )
+        self.assertTrue(
+            stdout.startswith(expected_stdout_prefix),
+            "%r not at start of %r" % (expected_stdout_prefix, stdout),
+        )
+        self.assertIn(b'shutting down', stdout)
+        self.assertEqual(b(""), stderr)