fix(places): submit and link the phase variants

/schools/[place]/[phase] shipped as routes but reached nothing. The sitemap
emitted one URL per registry entry and the registry had no phase dimension, so
~950 pages were absent from every sitemap — and PlaceView did not link them
either, leaving them reachable by nothing at all.

That is the query shape the baseline actually showed: 'primary schools in
beccles', 'secondary schools in brentwood'. Publishing the routes without a
path in meant building for the demand and then hiding from it.

Place now carries phase_urns so the per-phase threshold can be applied without
re-querying, the sitemap emits a variant wherever a phase clears the threshold
on its own, and the API exposes the qualifying phases so the place page links
only variants that exist. Outcodes are excluded: nobody searches 'primary
schools in SW11' and those routes do not exist.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015mWQnpye9F299NVRCCSRvj

backend/places.py

@@ -14,7 +14,7 @@ from __future__ import annotations
 
 import logging
 import re
-from dataclasses import dataclass
+from dataclasses import dataclass, field
 
 logger = logging.getLogger(__name__)
 
@@ -30,6 +30,13 @@ class Place:
     name: str
     urns: tuple[int, ...]
     parent_authority: str | None    # authority NAME, for the 301 target
+    # URNs per phase, so the per-phase threshold can be applied without
+    # re-querying. A place with 30 primaries and 2 secondaries publishes a
+    # primary variant and no secondary one.
+    phase_urns: dict[str, tuple[int, ...]] = field(default_factory=dict)
+
+    def publishes_phase(self, phase: str) -> bool:
+        return len(self.phase_urns.get(phase, ())) >= MIN_SCHOOLS
 
     @property
     def key(self) -> str:
@@ -46,6 +53,24 @@ def _publishable_urns(df) -> set[int]:
     return set(df.loc[df[cols].notna().any(axis=1), "urn"].astype(int))
 
 
+def _phase_urns(group, publishable: set[int]) -> dict[str, tuple[int, ...]]:
+    """URNs per phase. All-through schools count toward both, matching the
+    PHASE_GROUPS mapping the search filters already use."""
+    from backend.app import PHASE_GROUPS
+
+    if "phase" not in group.columns:
+        return {}
+    lowered = group["phase"].fillna("").str.lower()
+    out: dict[str, tuple[int, ...]] = {}
+    for phase in ("primary", "secondary"):
+        wanted = PHASE_GROUPS.get(phase, set())
+        subset = group[lowered.isin(wanted)]
+        urns = tuple(sorted({int(u) for u in subset["urn"]} & publishable))
+        if urns:
+            out[phase] = urns
+    return out
+
+
 def _parent_authority(group) -> str | None:
     """The most common authority in a group — the useful 301 target.
 
@@ -79,6 +104,7 @@ def _group(df, column: str, kind: str, publishable: set[int]) -> dict[str, Place
         place = Place(
             kind=kind, slug=slug, name=name, urns=urns,
             parent_authority=_parent_authority(group) if kind == "town" else None,
+            phase_urns=_phase_urns(group, publishable),
         )
         out[place.key] = place
     return out
@@ -111,7 +137,8 @@ def _outcode_places(df, publishable: set[int]) -> dict[str, Place]:
         if len(urns) < MIN_SCHOOLS:
             continue
         place = Place(kind="outcode", slug=str(oc).lower(), name=str(oc),
-                      urns=urns, parent_authority=_parent_authority(group))
+                      urns=urns, parent_authority=_parent_authority(group),
+                      phase_urns=_phase_urns(group, publishable))
         out[place.key] = place
     return out
 
@@ -153,7 +180,8 @@ def _locality_places(df, publishable: set[int],
                 slug, ", ".join(outcodes), len(urns), MIN_SCHOOLS)
             continue
         place = Place(kind="locality", slug=slug, name=name, urns=urns,
-                      parent_authority=_parent_authority(group))
+                      parent_authority=_parent_authority(group),
+                      phase_urns=_phase_urns(group, publishable))
         out[place.key] = place
     return out