[sijie-Z]

P0/P1 — trading safety. POST /api/trading/start built and started a new engine unconditionally; _live_engine was only ever overwritten:

engine = LiveTradingEngine(...)
engine.start()
_live_engine = engine      # replaces, never checks

What a second call used to do

• the first engine's TradingScheduler thread and broker kept running
• no handle remained, so POST /api/trading/stop could never reach it
• both engines wrote positions / P&L / orders into the same store — and positions is keyed on code alone, so their rows overwrote each other
• its kill switch became unreachable too, because _core_risk was rebound

LiveTradingEngine.start() does have if self._running: return, but that is per-instance and cannot see the newly constructed object.

Realistic trigger: a double-clicked button, two browser tabs, or a script — anything that sends the request twice before the first response returns.

Fix

Returns 409 with an explicit message. The guard keys on the engine's _running flag rather than on the global merely being set, so a stopped engine does not block a restart.

Tests

Test	Asserts
test_a_second_start_is_refused_while_one_is_running	409 + message
test_a_stopped_engine_does_not_block_a_restart	200, engine actually started
test_the_orphaned_engine_is_the_one_the_guard_protects	repeated attempts stay refused

Verified by removing the guard: tests 1 and 3 fail there, test 2 still passes — which is the point, it is the one asserting the guard does not over-block.

1326 passed, 1 skipped.

🤖 Generated with Claude Code

[coderabbitai]

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