fix(responses): reject stale scheduling answers

src/govoplan_scheduling/backend/schemas.py

@@ -2,8 +2,9 @@ from __future__ import annotations
 
 from datetime import datetime
 from typing import Any, Literal
+from zoneinfo import ZoneInfo, ZoneInfoNotFoundError
 
-from pydantic import BaseModel, ConfigDict, Field, model_validator
+from pydantic import AwareDatetime, BaseModel, ConfigDict, Field, field_validator, model_validator
 
 
 SchedulingStatus = Literal["draft", "collecting", "closed", "decided", "handed_off", "cancelled", "archived"]
@@ -13,6 +14,16 @@ SchedulingResultVisibility = Literal["organizer", "after_response", "after_close
 SchedulingAvailabilityValue = Literal["available", "maybe", "unavailable"]
 
 
+def _known_timezone(value: str | None) -> str | None:
+    if value is None:
+        return None
+    try:
+        ZoneInfo(value)
+    except ZoneInfoNotFoundError as exc:
+        raise ValueError("timezone must be a valid IANA timezone") from exc
+    return value
+
+
 class SchedulingCalendarPreferences(BaseModel):
     model_config = ConfigDict(extra="forbid")
 
@@ -28,12 +39,14 @@ class SchedulingCandidateSlotInput(BaseModel):
 
     label: str | None = Field(default=None, max_length=500)
     description: str | None = None
-    start_at: datetime
-    end_at: datetime
+    start_at: AwareDatetime
+    end_at: AwareDatetime
     timezone: str | None = Field(default=None, max_length=100)
     location: str | None = Field(default=None, max_length=500)
     metadata: dict[str, Any] = Field(default_factory=dict)
 
+    _validate_timezone = field_validator("timezone")(_known_timezone)
+
     @model_validator(mode="after")
     def validate_range(self) -> "SchedulingCandidateSlotInput":
         if self.end_at <= self.start_at:
@@ -52,12 +65,14 @@ class SchedulingCandidateSlotUpdateRequest(BaseModel):
 
     label: str | None = Field(default=None, min_length=1, max_length=500)
     description: str | None = None
-    start_at: datetime | None = None
-    end_at: datetime | None = None
+    start_at: AwareDatetime | None = None
+    end_at: AwareDatetime | None = None
     timezone: str | None = Field(default=None, min_length=1, max_length=100)
     location: str | None = Field(default=None, max_length=500)
     metadata: dict[str, Any] | None = None
 
+    _validate_timezone = field_validator("timezone")(_known_timezone)
+
     @model_validator(mode="after")
     def validate_range(self) -> "SchedulingCandidateSlotUpdateRequest":
         if self.start_at is not None and self.end_at is not None and self.end_at <= self.start_at:
@@ -94,6 +109,8 @@ class SchedulingRequestCreateRequest(BaseModel):
     create_participant_invitations: bool = True
     metadata: dict[str, Any] = Field(default_factory=dict)
 
+    _validate_timezone = field_validator("timezone")(_known_timezone)
+
 
 class SchedulingRequestUpdateRequest(BaseModel):
     model_config = ConfigDict(extra="forbid")
@@ -119,6 +136,7 @@ class SchedulingCandidateSlotResponse(BaseModel):
     timezone: str
     location: str | None = None
     position: int
+    revision: str
     freebusy_checked_at: datetime | None = None
     freebusy_status: str | None = None
     freebusy_conflicts: list[dict[str, Any]] = Field(default_factory=list)
@@ -192,6 +210,7 @@ class SchedulingAvailabilityAnswerInput(BaseModel):
 
     slot_id: str
     value: SchedulingAvailabilityValue
+    option_revision: str = Field(min_length=64, max_length=64, pattern=r"^[0-9a-f]{64}$")
 
 
 class SchedulingAvailabilityResponseRequest(BaseModel):