refactor(llc/adapters): extract shared subprocess-lifecycle base (state/probe/cancel/timeout duplicated across claude_code + copilot_local) #9834

Consolidation: extract a shared subprocess-lifecycle base for LLC adapters

PR #9811 (#9789/#9769) introduced llc/adapters/subprocess_support.py to share the prompt + credential layer across the 4 subprocess adapters. But the subprocess lifecycle is still duplicated near-verbatim between the two base adapters (claude_code_adapter.py, 354 lines; copilot_local_adapter.py, 277 lines):

• _output_path, _state_path, _load_state (path-traversal-guarded JSON read)
• _probe_pid (os.kill(0) → RUNNING/COMPLETED/FAILED)
• _resolve_timeout (3-tier timeout hierarchy)
• status / _status (state load → timeout check → probe)
• _cancel (SIGTERM → grace loop → SIGKILL → unlink state) — byte-identical except log strings + claude's extra _clear_session
• constants: _SIGTERM_GRACE_SECONDS, _ADAPTER_TIMEOUT_SECONDS, _DEFAULT_OUTPUT_DIR

copilot_local_adapter's own docstring says it "mirrors ClaudeCodeAdapter" — the mirroring is the smell. ~150 lines of near-identical code that can drift (e.g. the #9763-class test bug, or timeout logic changing in one but not the other).

Proposed fix

Extract a SubprocessLifecycleAdapter base class (in subprocess_support.py or a new subprocess_base.py) owning state-file management, PID probe, timeout resolution, status, and cancel — parameterised by:

• a CLI resolver (_resolve_claude_cli / _resolve_gh_cli)
• output/state filename prefix (llc_agent_ vs llc_copilot_)
• an optional post-cancel hook (claude's _clear_session)

ClaudeCodeAdapter / CopilotLocalAdapter then only implement invoke (command assembly + their specific env). The subscription subclasses keep inheriting.

References

Discovered auditing the merged adapter-consolidation work (PR #9811). Builds on subprocess_support.py. Related: #9008, #9033.

Labels: enhancement · backend · agents · priority: low