feat(campaign): govern attachment reuse

src/govoplan_campaign/backend/campaign/models.py

@@ -474,6 +474,24 @@ class ResidualFileMode(StrEnum):
     ATTACH = "attach"
 
 
+class AttachmentReuseAction(StrEnum):
+    ALLOW = "allow"
+    WARN = "warn"
+    REVIEW = "review"
+    BLOCK = "block"
+
+
+class AttachmentReuseAllowance(StrEnum):
+    NONE = "none"
+    SAME_RECIPIENT = "same_recipient"
+    SAME_MESSAGE = "same_message"
+
+
+class AttachmentReusePolicy(StrictModel):
+    action: AttachmentReuseAction = AttachmentReuseAction.ALLOW
+    allow_within: AttachmentReuseAllowance = AttachmentReuseAllowance.NONE
+
+
 class ResidualFileDispositionConfig(StrictModel):
     mode: ResidualFileMode = ResidualFileMode.NONE
     recipient: RecipientConfig | None = None
@@ -533,6 +551,9 @@ class AttachmentsConfig(StrictModel):
     global_: list[AttachmentConfig] = Field(default_factory=list, alias="global")
     missing_behavior: Behavior = Behavior.WARN
     ambiguous_behavior: Behavior = Behavior.ASK
+    reuse_policy: AttachmentReusePolicy = Field(
+        default_factory=AttachmentReusePolicy
+    )
     residual_files: ResidualFileDispositionConfig = Field(
         default_factory=ResidualFileDispositionConfig
     )