feat(agents): p50-lateness tolerance + per-project realness for overdue-task (#115)

Replaces snooze-rate heuristic with p50 of actual task lateness (completedAt − dueAt).
Adds project_realness inference: projects with chronic lateness get realness < 1 and
the agent softens its snippet language from "overdue" to "past target date".

- TaskCompletion added to UserHistory with lateness_days computed property
- _infer_lateness_tolerance: p50 of task_completions, clipped at 0, float
- _infer_project_realness: per-project median lateness normalised by global median
- Both InferredParams use 7d TTL; cold_start = 0.0 / {}
- AgentInferRequest accepts task_completions; endpoint wires them through
- 12 new tests covering punctual/chronic/mixed users and language softening
- Agent bumped to v1.2.0

Closes #115

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

ml/agents/inference/__init__.py

@@ -4,6 +4,6 @@ Each agent's manifest declares InferredParams; this package owns the
 scheduling contract, history data model, and write path to user_preferences.
 """
 from .framework import run_inference
-from .history import FeedbackEvent, UserHistory
+from .history import FeedbackEvent, TaskCompletion, UserHistory
 
-__all__ = ["run_inference", "FeedbackEvent", "UserHistory"]
+__all__ = ["run_inference", "FeedbackEvent", "TaskCompletion", "UserHistory"]

ml/agents/inference/history.py

@@ -23,7 +23,27 @@ class FeedbackEvent:
         return dt.hour
 
 
+@dataclass
+class TaskCompletion:
+    """A completed task that had a due date — used for lateness inference."""
+    project_id: str | None
+    completed_at: str   # ISO 8601
+    due_at: str         # ISO 8601
+
+    @property
+    def lateness_days(self) -> float:
+        """Days between due_at and completed_at. Negative = completed early."""
+        try:
+            def _parse(s: str) -> datetime:
+                dt = datetime.fromisoformat(s.replace("Z", "+00:00"))
+                return dt if dt.tzinfo else dt.replace(tzinfo=timezone.utc)
+            return (_parse(self.completed_at) - _parse(self.due_at)).total_seconds() / 86_400
+        except ValueError:
+            return 0.0
+
+
 @dataclass
 class UserHistory:
     user_id: str
     events: list[FeedbackEvent] = field(default_factory=list)
+    task_completions: list[TaskCompletion] = field(default_factory=list)