feat: add agent visibility APIs and harden runtime verification

Add Day 4 visibility endpoints and response models, strengthen collaboration/task verification behavior, and patch conversation schema startup migration for agent_state compatibility. Extend backend regression coverage for runtime schemas, verifier behavior, visibility APIs, router auth, and legacy conversation list loading.

backend/app/schemas/agent.py

@@ -1,4 +1,7 @@
-from pydantic import BaseModel
+from datetime import datetime
+from typing import Any
+
+from pydantic import BaseModel, Field
 
 
 class AgentCreate(BaseModel):
@@ -6,6 +9,7 @@ class AgentCreate(BaseModel):
     role: str
     description: str | None = None
     system_prompt: str
+    spawn_permission: bool = False
 
 
 class AgentOut(BaseModel):
@@ -55,3 +59,93 @@ class AgentConfigOut(BaseModel):
     selected_skill_ids: list[str]
 
     model_config = {"from_attributes": True}
+
+
+class AgentVisibilityEventOut(BaseModel):
+    event_id: str
+    event_type: str
+    timestamp: datetime
+    conversation_id: str | None = None
+    agent_id: str | None = None
+    sub_commander_id: str | None = None
+    task_id: str | None = None
+    parent_task_id: str | None = None
+    child_task_id: str | None = None
+    thread_id: str | None = None
+    message_id: str | None = None
+    interrupt_id: str | None = None
+    recovery_id: str | None = None
+    payload: dict[str, Any] = Field(default_factory=dict)
+    severity: str = "info"
+
+
+class AgentVisibilityEventsResponse(BaseModel):
+    conversation_id: str
+    total: int
+    limit: int
+    offset: int
+    items: list[AgentVisibilityEventOut]
+
+
+class AgentVisibilityTaskSummaryOut(BaseModel):
+    task_id: str
+    role: str | None = None
+    owner_agent_id: str | None = None
+    status: str | None = None
+    summary: str | None = None
+    evidence_count: int = 0
+
+
+class AgentVisibilityTopologyNodeOut(BaseModel):
+    agent_id: str
+    role: str | None = None
+    parent_agent_id: str | None = None
+    source: str
+    task_count: int = 0
+    completed_task_count: int = 0
+
+
+class AgentVisibilityTopologyOut(BaseModel):
+    conversation_id: str
+    root_agent_id: str | None = None
+    current_agent: str | None = None
+    nodes: list[AgentVisibilityTopologyNodeOut]
+    edges: list[dict[str, str]]
+    tasks: list[AgentVisibilityTaskSummaryOut]
+    task_hierarchy: dict[str, list[str]] = Field(default_factory=dict)
+
+
+class AgentVisibilityEvidenceOut(BaseModel):
+    conversation_id: str
+    task_id: str
+    task: dict[str, Any] | None = None
+    result: dict[str, Any] | None = None
+    tool_outcomes: list[dict[str, Any]] = Field(default_factory=list)
+    verifier: dict[str, Any]
+
+
+class AgentVisibilityThreadMessageOut(BaseModel):
+    message_id: str
+    thread_id: str
+    from_agent_id: str
+    to_agent_id: str
+    task_id: str | None = None
+    reply_to_message_id: str | None = None
+    message_type: str
+    content_summary: str
+    created_at: datetime
+    payload: dict[str, Any] = Field(default_factory=dict)
+
+
+class AgentVisibilityThreadOut(BaseModel):
+    conversation_id: str
+    thread_id: str
+    total: int
+    items: list[AgentVisibilityThreadMessageOut]
+
+
+class AgentVisibilityVerifierOut(BaseModel):
+    conversation_id: str
+    status: str | None = None
+    summary: str | None = None
+    evidence: list[dict[str, Any]] = Field(default_factory=list)