feat(scouts): add SourceConnector protocol and item types

app/scouts/connectors/base.py

@@ -0,0 +1,56 @@
+"""Source connector Protocol and shared item types.
+
+A SourceConnector adapts a third-party data source (Gmail, Slack, ...) to the
+shared ScoutEngine interface. Each connector owns:
+
+  * how to enumerate new items since the last poll (``list_new``)
+  * how to fetch a single item's metadata cheaply (``fetch_metadata``)
+  * how to fetch a single item's full content for in-memory triage
+    (``fetch_content``) — this content MUST NOT be persisted by the engine
+  * how to archive/trash an item (``archive``) for spam handling
+  * optional push-notification setup (``setup_watch`` / ``renew_watch``)
+"""
+
+from __future__ import annotations
+
+from datetime import datetime
+from typing import Literal, Protocol
+
+from pydantic import BaseModel, Field
+
+
+class ItemRef(BaseModel):
+    source_msg_ref: str
+    received_at: datetime | None = None
+
+
+class ItemMetadata(BaseModel):
+    subject: str | None = None
+    sender: str | None = None
+    snippet: str | None = None
+    received_at: datetime | None = None
+
+
+class ItemContent(BaseModel):
+    metadata: ItemMetadata
+    body_text: str
+    raw_headers: dict[str, str] = Field(default_factory=dict)
+
+
+class TriageVerdict(BaseModel):
+    verdict: Literal["relevant", "spam"]
+    reason: str
+    confidence: float = Field(ge=0.0, le=1.0)
+
+
+class SourceConnector(Protocol):
+    """Adapter for a third-party data source (Gmail, Slack, ...)."""
+
+    source_type: str  # e.g. "gmail"
+
+    async def list_new(self, scout) -> list[ItemRef]: ...
+    async def fetch_metadata(self, scout, ref: ItemRef) -> ItemMetadata: ...
+    async def fetch_content(self, scout, ref: ItemRef) -> ItemContent: ...
+    async def archive(self, scout, ref: ItemRef) -> None: ...
+    async def setup_watch(self, scout) -> None: ...
+    async def renew_watch(self, scout) -> None: ...