feat(orchestration): add orchestration system with task scheduling

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

backend/app/agents/orchestration/scheduler.py

@@ -0,0 +1,93 @@
+from __future__ import annotations
+
+from collections import defaultdict, deque
+from uuid import uuid4
+
+from app.agents.orchestration.budget import build_subtask_budget
+from app.agents.schemas.orchestration import SubTaskSpec, TaskGraph, TaskNode
+
+
+class ParallelExecutionScheduler:
+    def plan(self, task_graph: TaskGraph, *, query_text: str) -> list[SubTaskSpec]:
+        ordered_nodes = _topological_nodes(task_graph)
+        specs: list[SubTaskSpec] = []
+        for node in ordered_nodes:
+            budget = build_subtask_budget(
+                execution_mode=node.execution_mode,
+                max_parallel_tasks=max(1, task_graph.max_parallelism),
+                metadata={
+                    "task_graph_id": task_graph.graph_id,
+                    "depends_on": node.depends_on,
+                },
+            )
+            specs.append(
+                SubTaskSpec(
+                    subtask_id=node.node_id,
+                    parent_run_id=task_graph.graph_id,
+                    title=node.title,
+                    role=node.role or "master",
+                    goal=node.goal or query_text,
+                    context_slice=_build_context_slice(node, query_text),
+                    allowed_tools=[],
+                    budget_tokens=1200,
+                    budget_tool_calls=budget.max_tool_calls or 2,
+                    expected_output_schema={
+                        "summary": "string",
+                        "evidence": "list",
+                        "status": "completed|failed|blocked",
+                    },
+                    expected_evidence=node.expected_evidence,
+                    dependencies=node.depends_on,
+                )
+            )
+        return specs
+
+
+def build_subtask_specs(task_graph: TaskGraph, *, query_text: str) -> list[SubTaskSpec]:
+    return ParallelExecutionScheduler().plan(task_graph, query_text=query_text)
+
+
+def _build_context_slice(node: TaskNode, query_text: str) -> dict[str, object]:
+    return {
+        "query": query_text,
+        "role": node.role,
+        "title": node.title,
+        "goal": node.goal,
+        "depends_on": node.depends_on,
+    }
+
+
+def _topological_nodes(task_graph: TaskGraph) -> list[TaskNode]:
+    by_id = {node.node_id: node for node in task_graph.nodes}
+    indegree = {node.node_id: 0 for node in task_graph.nodes}
+    edges: dict[str, list[str]] = defaultdict(list)
+
+    for node in task_graph.nodes:
+        for dep in node.depends_on:
+            if dep not in by_id:
+                continue
+            edges[dep].append(node.node_id)
+            indegree[node.node_id] += 1
+
+    ready = deque(node_id for node_id, count in indegree.items() if count == 0)
+    ordered: list[TaskNode] = []
+
+    while ready:
+        node_id = ready.popleft()
+        ordered.append(by_id[node_id])
+        for target in edges.get(node_id, []):
+            indegree[target] -= 1
+            if indegree[target] == 0:
+                ready.append(target)
+
+    if len(ordered) != len(task_graph.nodes):
+        return list(task_graph.nodes)
+    return ordered
+
+
+def ensure_child_links(specs: list[SubTaskSpec]) -> dict[str, list[str]]:
+    graph: dict[str, list[str]] = defaultdict(list)
+    for spec in specs:
+        for dep in spec.dependencies:
+            graph[dep].append(spec.subtask_id)
+    return dict(graph)