From cc0b1e298fc2580642a0df39318ea6f692a93d9a Mon Sep 17 00:00:00 2001
From: Emi Griffith <me@emigriffith.dev>
Date: Wed, 22 Jul 2026 12:08:13 -0700
Subject: [PATCH] Port a0ec4bc Extract the shared graded-window tail in
 views.py from monorepo (drift reconciliation)

Claude-Session: https://claude.ai/code/session_01RdARHDJaYC1wSQRTYM6t3Z
---
 api/payloads.py | 25 +++++++++++++++++--------
 1 file changed, 17 insertions(+), 8 deletions(-)

diff --git a/api/payloads.py b/api/payloads.py
index 82d4e35..3e90e3d 100644
--- a/api/payloads.py
+++ b/api/payloads.py
@@ -143,6 +143,19 @@ def _attach_dry_streaks(graded: list[dict], *precip_frames) -> None:
         g["dsr"] = dsr_map.get(g["date"])
 
 
+def _graded_window(history, rows, precip_frames, doy) -> tuple[list[dict], dict]:
+    """The shared tail of the /grade and /forecast payloads: grade `rows` against
+    history, attach dry streaks over `precip_frames`, order newest-first, and pair
+    the result with the target day-of-year's climatology summary. The window
+    *assembly* (recent+archive merge vs future-only filter) differs per builder and
+    stays there; only this post-processing is shared."""
+    graded = _grade_rows(history, rows)
+    _attach_dry_streaks(graded, *precip_frames)
+    graded.reverse()  # newest-first for display (the chart reverses to L→R chronological)
+    climo = grading.climatology(history, doy)
+    return graded, climo
+
+
 def build_grade(cell, target, days, history, recent, cache_meta, place, run=None, after=14) -> dict:
     """/grade payload: a window of days centered on the target — `days` of history
     before it, the target itself, then up to `after` days after it — plus the
@@ -167,10 +180,8 @@ def build_grade(cell, target, days, history, recent, cache_meta, place, run=None
         # old pandas concat when the two sources' columns differ (e.g. a reduced
         # recent bundle); grading treats an absent column's value as None.
         window = pl.concat([rwin, hwin], how="diagonal_relaxed").sort("date")
-        graded = _grade_rows(history, window)
-        _attach_dry_streaks(graded, history, recent)
-        graded.reverse()  # newest first for display
-        climo = grading.climatology(history, target.timetuple().tm_yday)
+        graded, climo = _graded_window(history, window, (history, recent),
+                                       target.timetuple().tm_yday)
 
     # Summarize what this run actually covered. A fresh history fetch pulls the
     # full ~45-year archive (run_type "full"); a cache hit only fetched the
@@ -274,10 +285,8 @@ def build_forecast(cell, days, history, fc, today, place, run=None) -> dict:
     # Strictly future days (tomorrow onward), earliest→latest, capped at `days`.
     future = fc.filter(pl.col("date") > today).sort("date").head(days)
     with run.phase("grading"):
-        graded = _grade_rows(history, future)
-        _attach_dry_streaks(graded, history, fc)
-        graded.reverse()  # furthest-out first, so the chart reverses to L→R chronological
-        climo = grading.climatology(history, today.timetuple().tm_yday)
+        graded, climo = _graded_window(history, future, (history, fc),
+                                       today.timetuple().tm_yday)
     run.set(graded_days=len(graded), place_found=place is not None)
     return {
         "api_version": "v2",