feat: add Clear History button to delete all consumed instructions

- Backend: instruction_service.clear_consumed() bulk-deletes consumed rows
- Backend: DELETE /api/instructions/consumed route (preserves pending)
- Frontend: Clear button in consumed panel header (hidden when empty)
- Frontend: SSE handler for history.cleared event - instant UI update
- Frontend: api.clearConsumed() fetch wrapper

app/api/routes_instructions.py

@@ -57,6 +57,14 @@ def update_instruction(instruction_id: str, body: UpdateInstructionRequest):
     return InstructionCreateResponse(item=item)
 
 
+@router.delete("/consumed", status_code=200)
+def clear_consumed_instructions():
+    """Delete all consumed instructions. Pending instructions are never affected."""
+    count = instruction_service.clear_consumed()
+    event_service.broadcast("history.cleared", {"count": count})
+    return {"cleared": count}
+
+
 @router.delete("/{instruction_id}", status_code=204)
 def delete_instruction(instruction_id: str):
     try:

app/services/instruction_service.py

@@ -168,6 +168,19 @@ def delete_instruction(instruction_id: str) -> None:
     logger.info("Instruction deleted id=%s", instruction_id)
 
 
+def clear_consumed() -> int:
+    """Delete all consumed instructions. Returns the number of rows deleted."""
+    with get_write_conn() as conn:
+        row = conn.execute(
+            "SELECT COUNT(*) FROM instructions WHERE status = 'consumed'"
+        ).fetchone()
+        count = row[0] if row else 0
+        conn.execute("DELETE FROM instructions WHERE status = 'consumed'")
+
+    logger.info("Consumed instructions cleared count=%d", count)
+    return count
+
+
 def consume_next(agent_id: str = "unknown") -> Optional[InstructionItem]:
     """
     Atomically claim and return the next pending instruction.