triggers and execution queue; subagents

backend/src/trigger/context.py

@@ -0,0 +1,61 @@
+"""
+Execution context tracking using Python's contextvars.
+
+Each execution gets a unique seq number that propagates through all async calls,
+allowing us to track which execution made which changes for conflict detection.
+"""
+
+import logging
+from contextvars import ContextVar
+from dataclasses import dataclass, field
+from typing import Optional
+
+logger = logging.getLogger(__name__)
+
+# Context variables - automatically propagate through async call chains
+_execution_context: ContextVar[Optional["ExecutionContext"]] = ContextVar(
+    "execution_context", default=None
+)
+
+
+@dataclass
+class ExecutionContext:
+    """
+    Execution context for a single trigger execution.
+
+    Automatically propagates through async calls via contextvars.
+    Tracks the seq number and which store snapshots were read.
+    """
+
+    seq: int
+    """Sequential execution number - determines commit order"""
+
+    trigger_name: str
+    """Name/type of trigger being executed"""
+
+    snapshot_seqs: dict[str, int] = field(default_factory=dict)
+    """Store name -> seq number of snapshot that was read"""
+
+    def record_snapshot(self, store_name: str, snapshot_seq: int) -> None:
+        """Record that we read a snapshot from a store at a specific seq"""
+        self.snapshot_seqs[store_name] = snapshot_seq
+        logger.debug(f"Seq {self.seq}: Read {store_name} at seq {snapshot_seq}")
+
+    def __str__(self) -> str:
+        return f"ExecutionContext(seq={self.seq}, trigger={self.trigger_name})"
+
+
+def get_execution_context() -> Optional[ExecutionContext]:
+    """Get the current execution context, or None if not in an execution"""
+    return _execution_context.get()
+
+
+def set_execution_context(ctx: ExecutionContext) -> None:
+    """Set the execution context for the current async task"""
+    _execution_context.set(ctx)
+    logger.debug(f"Set execution context: {ctx}")
+
+
+def clear_execution_context() -> None:
+    """Clear the execution context"""
+    _execution_context.set(None)