fix(coding): teach agents terminal env state persists

Tell coding agents to activate shell setup once per session instead of re-sourcing it before every command, and pin the existing LocalEnvironment env-snapshot behavior with regression tests.

tools/terminal_tool.py

@@ -834,7 +834,7 @@ import sys
 
 
 # Tool description for LLM
-TERMINAL_TOOL_DESCRIPTION = """Execute shell commands on a Linux environment. Filesystem usually persists between calls.
+TERMINAL_TOOL_DESCRIPTION = """Execute shell commands on a Linux environment. Filesystem, current working directory, and exported environment variables persist between calls.
 
 Do NOT use cat/head/tail to read files — use read_file instead.
 Do NOT use grep/rg/find to search — use search_files instead.
@@ -842,6 +842,7 @@ Do NOT use ls to list directories — use search_files(target='files') instead.
 Do NOT use sed/awk to edit files — use patch instead.
 Do NOT use echo/cat heredoc to create files — use write_file instead.
 Reserve terminal for: builds, installs, git, processes, scripts, network, package managers, and anything that needs a shell.
+Because exported environment state persists, activate a virtualenv or export setup variables once per session; do not re-source the same environment before every command unless a command proves the shell state was reset.
 
 Foreground (default): Commands return INSTANTLY when done, even if the timeout is high. Set timeout=300 for long builds/scripts — you'll still get the result in seconds if it's fast. Prefer foreground for short commands.
 Background: Set background=true to get a session_id. Almost always pair with notify_on_complete=true — bg without notify runs SILENTLY and you have no way to learn it finished short of calling process(action='poll') yourself. Two legitimate uses: