GatewayRunner._run_agent's run_sync() wrote the per-turn session key to
the process-global os.environ["HERMES_SESSION_KEY"]. Because os.environ
is shared across the whole process, concurrent gateway sessions (e.g.
two Discord threads) clobbered each other's value. A tool worker thread
whose approval contextvar was unset then fell back to os.environ via
get_current_session_key() and read whichever session ran run_sync()
last — routing "Command Approval Required" prompts to the wrong thread.
Session routing is already concurrency-safe via contextvars:
- gateway/session_context.py _SESSION_KEY (set in set_session_vars)
- tools/approval.py _approval_session_key (set via set_current_session_key
right before the agent runs, inherited by tool worker threads)
The only non-test readers of HERMES_SESSION_KEY (tools/approval.py,
tools/terminal_tool.py, tools/kanban_tools.py) all prefer the contextvar
with os.environ as a mere fallback. CLI/cron/TUI set their own os.environ
via separate export paths (e.g. the TUI parent exporting it into the
agent subprocess), so removing this in-process write does not affect them.
Adds regression tests asserting the resolver prefers the contextvar and
does not leak a concurrent session's cleared/clobbered os.environ value.
Closes#24100
Co-authored-by: Yosapol Jitrak <yosapol@jitrak.dev>
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