Disable pagers in non-interactive code execution shells

The code execution tool runs commands inside TTY-backed shells (local PTY and
remote SSH). Commands like `git diff`/`git log` detect the TTY and pipe output
through a pager (more/less). These shells never receive interactive input, so
the pager blocks forever and spins at 100% CPU per process — on a 16-core host
5 pager processes pegged 5 cores for 8+ hours (#1697).

Disable pagers in both session types:
- LocalInteractiveSession: inject PAGER=cat / GIT_PAGER=cat into the TTY env
- SSHInteractiveSession: export the same in the initial shell command

`cat` streams the output through instead of blocking, and also covers other
pager-using tools (man, systemctl, journalctl). Adds regression tests.

Fixes #1697

plugins/_code_execution/helpers/shell_local.py

@@ -1,3 +1,4 @@
+import os
 import platform
 import select
 import subprocess
@@ -8,6 +9,22 @@ from helpers import runtime
 from plugins._code_execution.helpers import tty_session
 from plugins._code_execution.helpers.shell_ssh import clean_string
 
+
+def disable_pagers_in_env(env: dict | None = None) -> dict:
+    """Return a copy of ``env`` with terminal pagers disabled.
+
+    Commands such as ``git diff``/``git log`` detect a TTY and pipe their output
+    through a pager (``more``/``less``). The non-interactive shells created by
+    the code execution tool never receive any user input, so the pager blocks
+    forever and spins at 100% CPU per process. Pointing the pager variables at
+    ``cat`` lets the output stream through instead. See issue #1697.
+    """
+    env = dict(env if env is not None else os.environ)
+    env["PAGER"] = "cat"
+    env["GIT_PAGER"] = "cat"
+    return env
+
+
 class LocalInteractiveSession:
     def __init__(self, cwd: str|None = None):
         self.session: tty_session.TTYSession|None = None
@@ -15,7 +32,11 @@ class LocalInteractiveSession:
         self.cwd = cwd
 
     async def connect(self):
-        self.session = tty_session.TTYSession(runtime.get_terminal_executable(), cwd=self.cwd)
+        self.session = tty_session.TTYSession(
+            runtime.get_terminal_executable(),
+            cwd=self.cwd,
+            env=disable_pagers_in_env(),
+        )
         await self.session.start()
         await self.session.read_full_until_idle(idle_timeout=1, total_timeout=1)
 

plugins/_code_execution/helpers/shell_ssh.py

@@ -8,6 +8,12 @@ from helpers.print_style import PrintStyle
 # from helpers.strings import calculate_valid_match_lengths
 
 
+# Injected into every new SSH shell to keep it safe for non-interactive use.
+# Pagers (more/less) would otherwise block forever waiting for input that
+# never arrives and spin at 100% CPU; see issue #1697.
+PAGER_DISABLE_COMMAND = "export GIT_PAGER=cat; export PAGER=cat"
+
+
 class SSHInteractiveSession:
 
     # end_comment = "# @@==>> SSHInteractiveSession End-of-Command  <<==@@"
@@ -63,7 +69,7 @@ class SSHInteractiveSession:
                 self.shell = self.client.invoke_shell(width=100, height=50)
 
                 # disable systemd/OSC prompt metadata and disable local echo
-                initial_command = "unset PROMPT_COMMAND PS0; stty -echo"
+                initial_command = f"unset PROMPT_COMMAND PS0; stty -echo; {PAGER_DISABLE_COMMAND}"
                 if self.cwd:
                     initial_command = f"cd {self.cwd}; {initial_command}"
                 self.shell.send(f"{initial_command}\n".encode())

tests/test_code_execution_pager.py

@@ -0,0 +1,32 @@
+"""Regression tests for issue #1697.
+
+Pagers (more/less) must be disabled in the non-interactive shells created by the
+code execution tool: without user input they block forever and spin at 100% CPU.
+"""
+
+from plugins._code_execution.helpers import shell_local, shell_ssh
+
+
+def test_local_env_disables_pagers_and_preserves_existing():
+    env = shell_local.disable_pagers_in_env({"PATH": "/usr/bin", "PAGER": "less"})
+    assert env["PAGER"] == "cat"
+    assert env["GIT_PAGER"] == "cat"
+    # pre-existing keys are preserved
+    assert env["PATH"] == "/usr/bin"
+
+
+def test_local_env_defaults_to_environ():
+    env = shell_local.disable_pagers_in_env()
+    assert env["PAGER"] == "cat"
+    assert env["GIT_PAGER"] == "cat"
+
+
+def test_local_env_does_not_mutate_input():
+    src = {"PATH": "/usr/bin"}
+    shell_local.disable_pagers_in_env(src)
+    assert src == {"PATH": "/usr/bin"}
+
+
+def test_ssh_command_disables_pagers():
+    assert "GIT_PAGER=cat" in shell_ssh.PAGER_DISABLE_COMMAND
+    assert "PAGER=cat" in shell_ssh.PAGER_DISABLE_COMMAND