school_compare/docs/superpowers/plans/2026-09-21-similar-schools-nearby.md

# Similar Schools Nearby Implementation Plan

> **For agentic workers:** REQUIRED SUB-SKILL: Use superpowers:subagent-driven-development (recommended) or superpowers:executing-plans to implement this plan task-by-task. Steps use checkbox (`- [ ]`) syntax for tracking.

**Goal:** Add a "Similar schools nearby" section to the school detail page,
showing up to three crawlable links to nearby schools of the same phase and a
comparable intake, each addable to the comparison basket.

**Architecture:** A pure backend function ranks candidates out of the cached
latest-year DataFrame using hard filters (never relaxed) and tiered soft
preferences, and its result rides in the existing `/api/schools/{urn}` payload.
The frontend renders it as a server component inside `SchoolDetailShell`, with a
single client island for the add-to-compare button.

**Tech Stack:** FastAPI + pandas/numpy (backend), Next.js App Router + React
server components + CSS modules (frontend), pytest, Jest + Testing Library,
Playwright.

**Spec:** `docs/superpowers/specs/2026-09-21-similar-schools-nearby-design.md`

## Global Constraints

- **Branch:** `feat/similar-schools-nearby`, already created from `origin/main`.
  Never push to `main`; open a PR. Do not trigger the production promotion
  workflow.
- **Do not start a local server** to check the application. Use the unit tests
  in this plan.
- **Target 3 cards, minimum 2.** Fewer than 2 qualifying schools renders no
  section and no nav item.
- **Tier radii, in miles:** tier 1 = 3.0, tier 2 = 5.0, tier 3 = 10.0.
- **Hard filters never relax:** self, non-open status, missing coordinates,
  different phase group, special↔mainstream, selective↔non-selective,
  Boys↔Girls.
- **Every new `.module.css` must use tokens only.** No hex values, no `rgb()`,
  no named colours. `__tests__/components/darkThemeSafety.test.ts` scans every
  stylesheet under `components/` and fails on hardcoded colour.
- **Exact GIAS display strings** (from `backend/gias_codes.py`):
  `admissions_policy` is one of `"Not applicable"`, `"Selective"`,
  `"Non-selective"`, `""`; `religious_denomination` includes `"Does not apply"`,
  `"None"`, `"Church of England"`, `"Roman Catholic"` and others; `gender` is
  `"Mixed"`, `"Boys"` or `"Girls"`.
- **Copy rule:** the lede says "with a similar intake" only when no card is
  tier 3. A missing metric renders the exact string `Not published`.
- **The neighbour's metric never carries a valence colour.** No
  `--status-above` / `--status-below` anywhere in this feature.
- **Backend tests:**
  ```sh
  python3.11 -m venv /tmp/schoolcompare-backend-venv
  /tmp/schoolcompare-backend-venv/bin/python -m pip install -r requirements.txt pytest 'httpx<0.28' pyyaml
  /tmp/schoolcompare-backend-venv/bin/python -m pytest backend/tests -q
  ```
- **Frontend tests:** from `nextjs-app/`, `npm test -- --runInBand` and
  `npm run typecheck`. There is no `npm run lint`.

## File Structure

| File | Responsibility |
|---|---|
| `backend/similar_schools.py` *(new)* | Pure selection logic: hard filters, tiers, chips. No I/O, no FastAPI. |
| `backend/app.py` *(modify)* | Thin `_similar_schools_payload(urn)` wrapper + one key on the detail response. |
| `backend/tests/test_similar_schools.py` *(new)* | Unit tests for the pure module and one payload integration test. |
| `nextjs-app/lib/types.ts` *(modify)* | `SimilarSchool` type + optional key on the detail response type. |
| `nextjs-app/components/school/SimilarSchoolsSection.tsx` *(new)* | Server component: gates, lede, disclosure, cards, CTA. |
| `nextjs-app/components/school/SimilarSchools.module.css` *(new)* | Section styles, tokens only. |
| `nextjs-app/components/school/AddToCompareButton.tsx` *(new)* | Client island: the per-card basket toggle. |
| `nextjs-app/components/school/SimilarSchoolsCompareBar.tsx` *(new)* | Client island: the selection count and the CTA into `/compare`. |
| `nextjs-app/lib/schoolSections.ts` *(modify)* | `similar` nav item in both builders. |
| `nextjs-app/components/school/PrimarySchoolSections.tsx` *(modify)* | Render the section last. |
| `nextjs-app/components/school/SecondarySchoolSections.tsx` *(modify)* | Render the section last. |
| `nextjs-app/app/(frontend)/school/[slug]/page.tsx` *(modify)* | Pass `similar_schools` through. |
| `nextjs-app/__tests__/components/SimilarSchoolsSection.test.tsx` *(new)* | Render gates, lede wording, chips, "Not published". |
| `e2e/tests/journeys.spec.ts` *(modify)* | Journey covering the section and the compare hand-off. |

Two client islands rather than one, because they need different things: the
button needs a single school, the bar needs the whole selection. Keeping them
apart means a card never re-renders when the count changes.

The selection logic lives in its own module rather than in `app.py` because
`app.py` is already ~1700 lines, and because a pure function over a DataFrame is
testable without a TestClient, a database or a monkeypatch.

---

### Task 1: Selection logic

**Files:**
- Create: `backend/similar_schools.py`
- Test: `backend/tests/test_similar_schools.py`

**Interfaces:**
- Consumes: nothing from earlier tasks.
- Produces: `select_similar(frame: pd.DataFrame, urn: int, is_secondary: bool) -> list[dict]`.
  Each dict has keys `urn` (int), `school_name` (str), `distance_miles` (float),
  `school_type` (str | None), `age_range` (str | None), `shared` (list[str]),
  `tier` (int), `metric_value` (float | None), `metric_key` (str),
  `metric_year` (int | None). Returns `[]` when fewer than 2 qualify.

- [ ] **Step 1: Write the failing test**

Create `backend/tests/test_similar_schools.py`:

```python
"""Selection rules for the "similar schools nearby" section.

The hard filters encode claims the section is not allowed to make — that a
selective school is an alternative to a non-selective one, that a special
school is comparable to a mainstream one, or that a Girls school is an option
for a Boys school's reader. They never relax. The soft preferences describe
how close the intake is, and they do.
"""

import numpy as np
import pandas as pd

from backend.similar_schools import select_similar

# Roughly 0.7 miles apart in latitude at this longitude.
BASE_LAT, BASE_LON = 51.5000, -0.1000


def _row(urn, name, **overrides):
    base = {
        "urn": urn,
        "school_name": name,
        "local_authority": "Testshire",
        "school_type": "Community school",
        "phase": "Primary",
        "age_range": "4-11",
        "status": "Open",
        "gender": "Mixed",
        "religious_denomination": "None",
        "admissions_policy": "Not applicable",
        "latitude": BASE_LAT,
        "longitude": BASE_LON,
        "year": 202425,
        "rwm_expected_pct": 70.0,
        "attainment_8_score": np.nan,
    }
    base.update(overrides)
    return base


def _frame(*rows):
    return pd.DataFrame(list(rows))


def _at(miles):
    """A latitude `miles` north of BASE_LAT."""
    return BASE_LAT + miles / 69.0


def test_returns_nearest_same_phase_schools():
    frame = _frame(
        _row(100001, "Subject"),
        _row(100002, "Near", latitude=_at(0.5)),
        _row(100003, "Mid", latitude=_at(1.0)),
        _row(100004, "Far", latitude=_at(2.0)),
    )
    result = select_similar(frame, 100001, is_secondary=False)
    assert [s["urn"] for s in result] == [100002, 100003, 100004]
    assert result[0]["distance_miles"] == 0.5


def test_excludes_the_subject_school():
    frame = _frame(
        _row(100001, "Subject"),
        _row(100002, "A", latitude=_at(0.5)),
        _row(100003, "B", latitude=_at(0.6)),
    )
    assert 100001 not in {s["urn"] for s in select_similar(frame, 100001, is_secondary=False)}


def test_selective_never_meets_non_selective():
    frame = _frame(
        _row(100001, "Grammar", phase="Secondary", admissions_policy="Selective"),
        _row(100002, "Comp A", phase="Secondary", admissions_policy="Non-selective", latitude=_at(0.5)),
        _row(100003, "Comp B", phase="Secondary", admissions_policy="Non-selective", latitude=_at(0.6)),
    )
    assert select_similar(frame, 100001, is_secondary=True) == []

    reverse = select_similar(frame, 100002, is_secondary=True)
    assert 100001 not in {s["urn"] for s in reverse}


def test_special_schools_match_only_each_other():
    frame = _frame(
        _row(100001, "Special", school_type="Community special school"),
        _row(100002, "Mainstream A", latitude=_at(0.5)),
        _row(100003, "Mainstream B", latitude=_at(0.6)),
    )
    assert select_similar(frame, 100001, is_secondary=False) == []
    assert select_similar(frame, 100002, is_secondary=False) == []


def test_boys_never_meets_girls():
    frame = _frame(
        _row(100001, "Boys School", gender="Boys"),
        _row(100002, "Girls School", gender="Girls", latitude=_at(0.5)),
        _row(100003, "Mixed School", gender="Mixed", latitude=_at(0.6)),
        _row(100004, "Another Mixed", gender="Mixed", latitude=_at(0.7)),
    )
    urns = {s["urn"] for s in select_similar(frame, 100001, is_secondary=False)}
    assert 100002 not in urns
    assert urns == {100003, 100004}


def test_closed_schools_and_missing_coordinates_are_dropped():
    frame = _frame(
        _row(100001, "Subject"),
        _row(100002, "Closed", status="Closed", latitude=_at(0.5)),
        _row(100003, "No coords", latitude=np.nan, longitude=np.nan),
        _row(100004, "Good A", latitude=_at(0.6)),
        _row(100005, "Good B", latitude=_at(0.7)),
    )
    assert {s["urn"] for s in select_similar(frame, 100001, is_secondary=False)} == {100004, 100005}


def test_tiers_relax_faith_before_gender():
    frame = _frame(
        _row(100001, "Subject", gender="Boys", religious_denomination="Roman Catholic"),
        # Tier 1: same gender and same faith.
        _row(100002, "Tier one", gender="Boys", religious_denomination="Roman Catholic", latitude=_at(2.0)),
        # Tier 2: same gender, different faith — closer, but a weaker match.
        _row(100003, "Tier two", gender="Boys", religious_denomination="None", latitude=_at(0.5)),
        # Tier 3: mixed gender, different faith.
        _row(100004, "Tier three", gender="Mixed", religious_denomination="None", latitude=_at(0.6)),
    )
    result = select_similar(frame, 100001, is_secondary=False)
    tier_by_urn = {s["urn"]: s["tier"] for s in result}
    assert tier_by_urn == {100002: 1, 100003: 2, 100004: 3}
    # Selected by tier, displayed by distance.
    assert [s["urn"] for s in result] == [100003, 100004, 100002]


def test_a_school_is_never_taken_twice():
    frame = _frame(
        _row(100001, "Subject"),
        _row(100002, "A", latitude=_at(0.5)),
        _row(100003, "B", latitude=_at(0.6)),
    )
    result = select_similar(frame, 100001, is_secondary=False)
    assert len(result) == len({s["urn"] for s in result})


def test_fewer_than_two_matches_returns_empty():
    frame = _frame(
        _row(100001, "Subject"),
        _row(100002, "Only neighbour", latitude=_at(0.5)),
    )
    assert select_similar(frame, 100001, is_secondary=False) == []


def test_beyond_the_widest_radius_is_not_offered():
    frame = _frame(
        _row(100001, "Subject"),
        _row(100002, "A", latitude=_at(11.0)),
        _row(100003, "B", latitude=_at(12.0)),
    )
    assert select_similar(frame, 100001, is_secondary=False) == []


def test_all_through_is_offered_on_both_phase_sides():
    frame = _frame(
        _row(100001, "Primary subject", phase="Primary"),
        _row(100002, "All through", phase="All-through", latitude=_at(0.5)),
        _row(100003, "Primary peer", phase="Primary", latitude=_at(0.6)),
    )
    assert 100002 in {s["urn"] for s in select_similar(frame, 100001, is_secondary=False)}

    secondary = _frame(
        _row(100010, "Secondary subject", phase="Secondary"),
        _row(100002, "All through", phase="All-through", latitude=_at(0.5)),
        _row(100011, "Secondary peer", phase="Secondary", latitude=_at(0.6)),
    )
    assert 100002 in {s["urn"] for s in select_similar(secondary, 100010, is_secondary=True)}


def test_chips_state_only_what_the_tier_earned():
    frame = _frame(
        _row(100001, "Subject", phase="Secondary", gender="Mixed",
             religious_denomination="None", admissions_policy="Non-selective"),
        _row(100002, "Full match", phase="Secondary", gender="Mixed",
             religious_denomination="None", admissions_policy="Non-selective", latitude=_at(0.5)),
        _row(100003, "Faith differs", phase="Secondary", gender="Mixed",
             religious_denomination="Church of England", admissions_policy="Non-selective", latitude=_at(0.6)),
    )
    by_urn = {s["urn"]: s for s in select_similar(frame, 100001, is_secondary=True)}
    assert by_urn[100002]["shared"] == ["Mixed", "Non-selective", "No religious character"]
    assert by_urn[100003]["shared"] == ["Mixed", "Non-selective"]


def test_tier_three_chip_is_the_plain_phase():
    frame = _frame(
        _row(100001, "Subject", gender="Boys"),
        _row(100002, "A", gender="Mixed", latitude=_at(0.5)),
        _row(100003, "B", gender="Mixed", latitude=_at(0.6)),
    )
    result = select_similar(frame, 100001, is_secondary=False)
    assert all(s["shared"] == ["Primary school"] for s in result)


def test_metric_follows_the_template_not_the_neighbour():
    frame = _frame(
        _row(100001, "Subject", phase="Secondary", attainment_8_score=50.0),
        _row(100002, "A", phase="Secondary", attainment_8_score=52.8, latitude=_at(0.5)),
        _row(100003, "B", phase="Secondary", attainment_8_score=np.nan, latitude=_at(0.6)),
    )
    by_urn = {s["urn"]: s for s in select_similar(frame, 100001, is_secondary=True)}
    assert by_urn[100002]["metric_key"] == "attainment_8_score"
    assert by_urn[100002]["metric_value"] == 52.8
    assert by_urn[100002]["metric_year"] == 202425
    assert by_urn[100003]["metric_value"] is None


def test_values_are_json_safe_native_types():
    frame = _frame(
        _row(100001, "Subject"),
        _row(100002, "A", latitude=_at(0.5)),
        _row(100003, "B", latitude=_at(0.6)),
    )
    for school in select_similar(frame, 100001, is_secondary=False):
        assert isinstance(school["urn"], int)
        assert isinstance(school["distance_miles"], float)
        assert not isinstance(school["metric_value"], np.generic)
```

- [ ] **Step 2: Run the tests to verify they fail**

Run:
```sh
/tmp/schoolcompare-backend-venv/bin/python -m pytest backend/tests/test_similar_schools.py -q
```
Expected: collection error, `ModuleNotFoundError: No module named 'backend.similar_schools'`.

- [ ] **Step 3: Move PHASE_GROUPS out of app.py first**

`PHASE_GROUPS` lives in `backend/app.py:51-55`, and importing `app` from
`similar_schools` while `app` imports `similar_schools` is a cycle. Move the
constant to `backend/schemas.py`, which `app.py` already imports and which holds
the other shared column and display constants.

In `backend/schemas.py`, add near `SCHOOL_COLUMNS`:

```python
# Phase groups for search, place pages and similar-school matching. All-through
# schools belong to both sides, which is why this is a set per phase rather
# than a single phase string comparison.
PHASE_GROUPS: dict[str, set[str]] = {
    "primary": {"primary", "middle deemed primary", "all-through"},
    "secondary": {"secondary", "middle deemed secondary", "all-through", "16 plus"},
    "all-through": {"all-through"},
}
```

In `backend/app.py`, delete the `PHASE_GROUPS` definition at lines 51-55 and add
`PHASE_GROUPS` to the existing `from .schemas import (...)` list. Leave the call
sites at `app.py:762` and `app.py:1402` untouched — the name resolves the same.

- [ ] **Step 4: Write the implementation**

Create `backend/similar_schools.py`:

```python
"""Which nearby schools a detail page may offer as alternatives.

Two kinds of rule, and they are not interchangeable.

HARD FILTERS encode claims the section is not allowed to make. A selective
school is not an alternative to a non-selective one, a special school is not
comparable to a mainstream one, and a Girls school is not an option for a Boys
school's reader. These never relax, at any distance, even where that means the
section does not render at all.

SOFT PREFERENCES describe how closely an intake resembles this school's. They
relax in tiers, and every card reports the tier that actually took it so the
page can say what is shared rather than implying more.

Pure functions over a DataFrame: no I/O, no FastAPI, no database.
"""

from __future__ import annotations

import re

import numpy as np
import pandas as pd

from .schemas import PHASE_GROUPS

TARGET = 3
MINIMUM = 2

# (tier, radius in miles). Faith relaxes before gender: a faith mismatch
# changes the character of a school, while a gender mismatch can mean the
# school is not available to this reader's child at all.
TIERS: tuple[tuple[int, float], ...] = ((1, 3.0), (2, 5.0), (3, 10.0))

EARTH_RADIUS_MILES = 3958.8

_SPECIAL = re.compile(r"\bspecial\b|pupil referral|alternative provision", re.I)

# Values that mean "this school has no religious character".
_NO_FAITH = {"", "none", "does not apply", "not applicable"}


def is_special_provision(school_type: str | None) -> bool:
    """Mirror of isSpecialSchool() in nextjs-app/lib/utils.ts.

    Special schools carry a mainstream phase, so phase alone cannot identify
    them. The two implementations must agree: a school the frontend treats as
    special for benchmarking but this treats as mainstream would be dropped
    from its own England comparison and then offered as a peer to a mainstream
    school on the next page along.
    """
    return bool(_SPECIAL.search(school_type or ""))


def is_selective(admissions_policy: str | None) -> bool:
    """Strictly selective. Unknown counts as non-selective, which is the safe
    direction: it can only ever exclude a pairing, never invent one."""
    return (admissions_policy or "").strip().lower() == "selective"


def faith_key(denomination: str | None) -> str:
    value = (denomination or "").strip().lower()
    return "" if value in _NO_FAITH else value


def faith_label(denomination: str | None) -> str:
    return denomination.strip() if faith_key(denomination) else "No religious character"


def genders_compatible(a: str | None, b: str | None) -> bool:
    single = {"boys", "girls"}
    left, right = (a or "").strip().lower(), (b or "").strip().lower()
    return not (left in single and right in single and left != right)


def phase_label(phase: str | None) -> str:
    text = (phase or "").strip()
    if not text:
        return "School"
    if text.lower() == "all-through":
        return "All-through school"
    return f"{text.capitalize()} school"


def _phase_group(is_secondary: bool) -> set[str]:
    return PHASE_GROUPS["secondary" if is_secondary else "primary"]


def _haversine_miles(lat1: float, lon1: float, lat2, lon2):
    """Vectorised, matching the postcode search in app.py."""
    lat1_r, lon1_r = np.radians(lat1), np.radians(lon1)
    lat2_r, lon2_r = np.radians(lat2.astype(float)), np.radians(lon2.astype(float))
    dlat, dlon = lat2_r - lat1_r, lon2_r - lon1_r
    a = np.sin(dlat / 2) ** 2 + np.cos(lat1_r) * np.cos(lat2_r) * np.sin(dlon / 2) ** 2
    return 2 * EARTH_RADIUS_MILES * np.arcsin(np.sqrt(a))


def _native(value):
    """NaN and numpy scalars both reach JSONResponse badly; normalise here so
    the caller never has to remember to."""
    if value is None or (isinstance(value, float) and np.isnan(value)):
        return None
    if isinstance(value, np.generic):
        value = value.item()
    if isinstance(value, float) and np.isnan(value):
        return None
    return value


def _chips(subject: pd.Series, candidate: pd.Series, tier: int, is_secondary: bool) -> list[str]:
    if tier >= 3:
        return [phase_label(candidate.get("phase"))]

    chips = [str(subject.get("gender") or "").strip()]
    if is_secondary:
        policy = (candidate.get("admissions_policy") or "").strip()
        if policy and policy.lower() not in {"not applicable", "unknown"}:
            chips.append(policy)
    if tier == 1:
        chips.append(faith_label(candidate.get("religious_denomination")))
    return [chip for chip in chips if chip]


def select_similar(frame: pd.DataFrame, urn: int, is_secondary: bool) -> list[dict]:
    """Up to TARGET nearby schools this page may offer, or [] below MINIMUM.

    Selected by tier, displayed by distance: the tier decides which schools
    earn a slot, and the render order is then closest-first, because "nearby"
    is the promise in the heading.
    """
    subject_rows = frame[frame["urn"] == urn]
    if subject_rows.empty:
        return []
    subject = subject_rows.iloc[0]

    lat, lon = _native(subject.get("latitude")), _native(subject.get("longitude"))
    if lat is None or lon is None:
        return []

    metric_key = "attainment_8_score" if is_secondary else "rwm_expected_pct"

    candidates = frame[frame["urn"] != urn].copy()
    for column in ("latitude", "longitude"):
        candidates = candidates[candidates[column].notna()]
    if candidates.empty:
        return []

    # ── Hard filters ────────────────────────────────────────────────────
    allowed_phases = _phase_group(is_secondary)
    candidates = candidates[
        candidates["phase"].fillna("").str.lower().isin(allowed_phases)
    ]
    candidates = candidates[candidates["status"].fillna("").str.lower().str.startswith("open")]

    subject_special = is_special_provision(subject.get("school_type"))
    special = candidates["school_type"].apply(is_special_provision)
    candidates = candidates[special if subject_special else ~special]

    subject_selective = is_selective(subject.get("admissions_policy"))
    selective = candidates["admissions_policy"].apply(is_selective)
    candidates = candidates[selective if subject_selective else ~selective]

    subject_gender = subject.get("gender")
    candidates = candidates[
        candidates["gender"].apply(lambda g: genders_compatible(subject_gender, g))
    ]
    if candidates.empty:
        return []

    candidates["distance_miles"] = _haversine_miles(
        lat, lon, candidates["latitude"].values, candidates["longitude"].values
    ).round(1)

    # ── Soft preferences, in tiers ──────────────────────────────────────
    subject_faith = faith_key(subject.get("religious_denomination"))
    subject_gender_key = (subject_gender or "").strip().lower()
    same_gender = candidates["gender"].fillna("").str.strip().str.lower() == subject_gender_key
    same_faith = candidates["religious_denomination"].apply(faith_key) == subject_faith

    tier_masks = {
        1: same_gender & same_faith,
        2: same_gender,
        3: pd.Series(True, index=candidates.index),
    }

    picked: dict[int, tuple[int, pd.Series]] = {}
    for tier, radius in TIERS:
        if len(picked) >= TARGET:
            break
        within = candidates[tier_masks[tier] & (candidates["distance_miles"] <= radius)]
        for _, row in within.sort_values("distance_miles").iterrows():
            candidate_urn = int(row["urn"])
            if candidate_urn in picked:
                continue
            picked[candidate_urn] = (tier, row)
            if len(picked) >= TARGET:
                break

    if len(picked) < MINIMUM:
        return []

    selected = sorted(picked.values(), key=lambda pair: float(pair[1]["distance_miles"]))
    return [
        {
            "urn": int(row["urn"]),
            "school_name": str(row.get("school_name") or ""),
            "distance_miles": float(row["distance_miles"]),
            "school_type": _native(row.get("school_type")),
            "age_range": _native(row.get("age_range")),
            "shared": _chips(subject, row, tier, is_secondary),
            "tier": tier,
            "metric_value": _native(row.get(metric_key)),
            "metric_key": metric_key,
            "metric_year": _native(row.get("year")),
        }
        for tier, row in selected
    ]
```

- [ ] **Step 5: Run the tests to verify they pass**

Run:
```sh
/tmp/schoolcompare-backend-venv/bin/python -m pytest backend/tests/test_similar_schools.py -q
```
Expected: PASS, 14 tests.

- [ ] **Step 6: Run the whole backend suite for the `PHASE_GROUPS` move**

Run:
```sh
/tmp/schoolcompare-backend-venv/bin/python -m pytest backend/tests -q
```
Expected: PASS. Any failure here is the constant move, not the new module.

- [ ] **Step 7: Commit**

```bash
git add backend/similar_schools.py backend/tests/test_similar_schools.py backend/schemas.py backend/app.py
git commit -m "feat(api): decide which nearby schools a page may offer

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>"
```

---

### Task 2: Serve it on the detail endpoint

**Files:**
- Modify: `backend/app.py` (detail route at line 910, response dict at ~975)
- Test: `backend/tests/test_similar_schools.py` (append)

**Interfaces:**
- Consumes: `select_similar(frame, urn, is_secondary)` from Task 1.
- Produces: a `similar_schools` key on the `/api/schools/{urn}` JSON response —
  a list of the Task 1 dicts, `[]` when nothing qualifies. Never absent on a
  build that has this code.

- [ ] **Step 1: Write the failing test**

Append to `backend/tests/test_similar_schools.py`:

```python
import pytest
from fastapi.testclient import TestClient


def _endpoint_frame():
    return _frame(
        _row(100001, "Subject Primary"),
        _row(100002, "Neighbour A", latitude=_at(0.5)),
        _row(100003, "Neighbour B", latitude=_at(0.6)),
    )


@pytest.fixture()
def client(monkeypatch):
    from backend import app as app_module

    monkeypatch.setattr(app_module, "load_latest_school_data", _endpoint_frame)
    monkeypatch.setattr(app_module, "load_school_data", _endpoint_frame)
    monkeypatch.setattr(app_module, "get_supplementary_data", lambda db, urn: {})
    return TestClient(app_module.app, raise_server_exceptions=False)


def test_detail_payload_carries_similar_schools(client):
    resp = client.get("/api/schools/100001")
    assert resp.status_code == 200, resp.text
    similar = resp.json()["similar_schools"]
    assert [s["school_name"] for s in similar] == ["Neighbour A", "Neighbour B"]
    assert similar[0]["metric_key"] == "rwm_expected_pct"


def test_a_failure_in_selection_does_not_break_the_page(client, monkeypatch):
    from backend import app as app_module

    def _explode(*args, **kwargs):
        raise ValueError("selection blew up")

    monkeypatch.setattr(app_module, "select_similar", _explode)
    resp = client.get("/api/schools/100001")
    assert resp.status_code == 200, resp.text
    assert resp.json()["similar_schools"] == []
```

- [ ] **Step 2: Run the tests to verify they fail**

Run:
```sh
/tmp/schoolcompare-backend-venv/bin/python -m pytest backend/tests/test_similar_schools.py -q -k "detail_payload or failure_in_selection"
```
Expected: FAIL with `KeyError: 'similar_schools'`.

- [ ] **Step 3: Write the implementation**

In `backend/app.py`, add to the imports:

```python
from .similar_schools import select_similar
```

Add this helper beside `_places_payload`:

```python
def _similar_schools_payload(urn: int, phase: str | None) -> list[dict]:
    """Nearby schools this page may offer as alternatives.

    Wrapped: a failure in selection must never 500 a page that is otherwise
    complete, which is the posture get_supplementary_data already takes. The
    section simply does not render.
    """
    try:
        phase_text = (phase or "").lower()
        # All-through schools render with the primary template, which is what
        # decides the metric, so they are not secondary here.
        is_secondary = phase_text != "all-through" and "secondary" in phase_text
        return select_similar(load_latest_school_data(), int(urn), is_secondary)
    except Exception:
        logger.exception("similar schools selection failed for urn=%s", urn)
        return []
```

In the `/api/schools/{urn}` response dict, immediately after the `"places"` key:

```python
        # Nearby schools of the same phase and a comparable intake. Always
        # present on a build with this code; the frontend treats absent and
        # empty identically, which is what lets the two images deploy
        # independently.
        "similar_schools": _similar_schools_payload(urn, latest.get("phase")),
```

- [ ] **Step 4: Run the tests to verify they pass**

Run:
```sh
/tmp/schoolcompare-backend-venv/bin/python -m pytest backend/tests -q
```
Expected: PASS, whole suite.

- [ ] **Step 5: Commit**

```bash
git add backend/app.py backend/tests/test_similar_schools.py
git commit -m "feat(api): serve similar schools on the detail endpoint

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>"
```

---

### Task 3: Types and the section component

**Files:**
- Modify: `nextjs-app/lib/types.ts`
- Create: `nextjs-app/components/school/SimilarSchoolsSection.tsx`
- Create: `nextjs-app/components/school/SimilarSchools.module.css`
- Create: `nextjs-app/components/school/AddToCompareButton.tsx`
- Test: `nextjs-app/__tests__/components/SimilarSchoolsSection.test.tsx`

**Interfaces:**
- Consumes: the `similar_schools` payload from Task 2.
- Produces: `SimilarSchool` (exported from `lib/types.ts`) and
  `<SimilarSchoolsSection schoolName={string} phaseNoun={string} thisMetricValue={number | null} similar={SimilarSchool[]} />`,
  which returns `null` when it must not render. Also
  `shouldRenderSimilar(similar?: SimilarSchool[] | null): boolean`, exported
  from the same file and consumed by Task 4's nav gating, and
  `<SimilarSchoolsCompareBar thisUrn={number} candidates={SimilarSchool[]} />`.

- [ ] **Step 1: Write the failing test**

Create `nextjs-app/__tests__/components/SimilarSchoolsSection.test.tsx`:

```tsx
/**
 * The section's job is to be honest about what it matched. These tests pin the
 * three ways it could lie: rendering below the minimum, claiming a similar
 * intake at tier 3, and showing a missing figure as a number.
 */

import { render, screen } from '@testing-library/react';

import {
  SimilarSchoolsSection,
  shouldRenderSimilar,
} from '@/components/school/SimilarSchoolsSection';
import type { SimilarSchool } from '@/lib/types';

jest.mock('@/components/school/AddToCompareButton', () => ({
  AddToCompareButton: ({ school }: { school: SimilarSchool }) => (
    <button type="button">Add {school.school_name} to compare</button>
  ),
}));

jest.mock('@/components/school/SimilarSchoolsCompareBar', () => ({
  SimilarSchoolsCompareBar: ({ thisUrn }: { thisUrn: number }) => (
    <div data-testid="compare-bar">bar for {thisUrn}</div>
  ),
}));

function school(overrides: Partial<SimilarSchool> = {}): SimilarSchool {
  return {
    urn: 100002,
    school_name: 'Willow Lane Primary School',
    distance_miles: 0.6,
    school_type: 'Community school',
    age_range: '4-11',
    shared: ['Mixed', 'No religious character'],
    tier: 1,
    metric_value: 74,
    metric_key: 'rwm_expected_pct',
    metric_year: 202425,
    ...overrides,
  };
}

function renderSection(similar: SimilarSchool[]) {
  return render(
    <SimilarSchoolsSection
      urn={100001}
      schoolName="Meadowbrook Primary School"
      phaseNoun="primary"
      thisMetricValue={72}
      similar={similar}
    />,
  );
}

describe('render gates', () => {
  it.each([
    ['undefined', undefined],
    ['null', null],
    ['empty', []],
    ['a single school', [school()]],
  ])('renders nothing for %s', (_label, value) => {
    expect(shouldRenderSimilar(value as SimilarSchool[] | null | undefined)).toBe(false);
  });

  it('renders for two or more schools', () => {
    expect(shouldRenderSimilar([school(), school({ urn: 100003 })])).toBe(true);
  });

  it('returns null rather than an empty shell below the minimum', () => {
    const { container } = renderSection([school()]);
    expect(container).toBeEmptyDOMElement();
  });
});

describe('the claim the lede makes', () => {
  it('claims a similar intake when every card is tier 1 or 2', () => {
    renderSection([school({ tier: 1 }), school({ urn: 100003, tier: 2 })]);
    expect(screen.getByText(/with a similar intake/i)).toBeInTheDocument();
  });

  it('drops the claim when any card is tier 3', () => {
    renderSection([school({ tier: 1 }), school({ urn: 100003, tier: 3, shared: ['Primary school'] })]);
    expect(screen.queryByText(/with a similar intake/i)).not.toBeInTheDocument();
  });
});

describe('cards', () => {
  it('links each school to its canonical slug', () => {
    renderSection([school(), school({ urn: 100003, school_name: 'Oakfield Primary School' })]);
    const link = screen.getByRole('link', { name: /Willow Lane Primary School/ });
    expect(link).toHaveAttribute('href', '/school/100002-willow-lane-primary-school');
  });

  it('shows the distance and the shared characteristics', () => {
    renderSection([school(), school({ urn: 100003 })]);
    expect(screen.getAllByText('0.6 miles away').length).toBeGreaterThan(0);
    expect(screen.getAllByText('Mixed').length).toBeGreaterThan(0);
  });

  it('renders a missing figure as "Not published", never as a number', () => {
    renderSection([school({ metric_value: null }), school({ urn: 100003 })]);
    expect(screen.getByText('Not published')).toBeInTheDocument();
  });

  it('anchors each figure against this school', () => {
    renderSection([school(), school({ urn: 100003 })]);
    expect(screen.getAllByText('72% at this school').length).toBe(2);
  });

  it('offers the compare bar once, for this school', () => {
    renderSection([school(), school({ urn: 100003 })]);
    expect(screen.getByTestId('compare-bar')).toHaveTextContent('bar for 100001');
  });
});
```

- [ ] **Step 2: Run the test to verify it fails**

Run (from `nextjs-app/`):
```sh
npm test -- --runInBand SimilarSchoolsSection
```
Expected: FAIL, cannot resolve `@/components/school/SimilarSchoolsSection`.

- [ ] **Step 3: Add the type**

In `nextjs-app/lib/types.ts`, beside the other detail-payload types:

```ts
/** A nearby school of the same phase and a comparable intake.
 *  `tier` is carried explicitly rather than inferred from `shared`, because it
 *  drives two separate decisions — whether the lede may claim a similar intake,
 *  and whether a chip renders as a fill or a muted outline. */
export interface SimilarSchool {
  urn: number;
  school_name: string;
  distance_miles: number;
  school_type: string | null;
  age_range: string | null;
  shared: string[];
  tier: number;
  metric_value: number | null;
  metric_key: string;
  metric_year: number | null;
}
```

Add to the school detail response interface (the one `fetchSchoolDetails`
returns), keeping it optional so an older backend image still typechecks:

```ts
  similar_schools?: SimilarSchool[];
```

- [ ] **Step 4: Write the client island**

Create `nextjs-app/components/school/AddToCompareButton.tsx`:

```tsx
'use client';

/**
 * The only client JavaScript in the similar-schools section.
 *
 * The links are server-rendered, so the section works with JS off; this adds
 * the basket interaction on top rather than being what makes the section
 * function.
 */

import { useComparisonContext } from '@/context/ComparisonContext';
import type { School, SimilarSchool } from '@/lib/types';
import styles from './SimilarSchools.module.css';

export function AddToCompareButton({ school }: { school: SimilarSchool }) {
  const { addSchool, removeSchool, selectedSchools } = useComparisonContext();
  const selected = selectedSchools.some((s) => s.urn === school.urn);

  const toggle = () => {
    if (selected) {
      removeSchool(school.urn);
      return;
    }
    // The basket only needs identity and display fields; the compare page
    // fetches everything it renders by URN.
    addSchool({
      urn: school.urn,
      school_name: school.school_name,
      school_type: school.school_type,
      age_range: school.age_range,
    } as School);
  };

  return (
    <button
      type="button"
      className={styles.add}
      onClick={toggle}
      aria-pressed={selected}
    >
      {selected ? '✓ Added to compare' : '+ Add to compare'}
      <span className={styles.srOnly}> — {school.school_name}</span>
    </button>
  );
}
```

- [ ] **Step 5: Write the compare bar**

Create `nextjs-app/components/school/SimilarSchoolsCompareBar.tsx`:

```tsx
'use client';

/**
 * The selection count and the one decisive action in the section.
 *
 * The CTA is a real link, not a handler: /compare already parses `urns` from
 * the query string, so the hand-off needs no new compare plumbing. It counts
 * this school plus whatever the reader ticked, because comparing a shortlist
 * without the school they are looking at is not what they asked for.
 */

import Link from 'next/link';
import { useComparisonContext } from '@/context/ComparisonContext';
import type { SimilarSchool } from '@/lib/types';
import styles from './SimilarSchools.module.css';

export function SimilarSchoolsCompareBar({
  thisUrn,
  candidates,
}: {
  thisUrn: number;
  candidates: SimilarSchool[];
}) {
  const { selectedSchools } = useComparisonContext();

  // Only the schools this section offers, in the order the cards show them —
  // the basket may hold schools picked up elsewhere on the site, and this bar
  // speaks for this section.
  const offered = candidates
    .map((c) => c.urn)
    .filter((urn) => selectedSchools.some((s) => s.urn === urn));

  const count = offered.length;
  const href = `/compare?urns=${[thisUrn, ...offered].join(',')}`;

  return (
    <div className={styles.footer}>
      <p aria-live="polite">
        <strong>
          {count
            ? `${count} school${count === 1 ? '' : 's'} selected`
            : 'Compare side by side'}
        </strong>
        {count
          ? 'This school is included automatically.'
          : 'Add a school to compare it with this one.'}
      </p>
      {count ? (
        <Link className={styles.compare} href={href}>
          Compare {count + 1} schools →
        </Link>
      ) : (
        <span className={styles.compare} aria-disabled="true">
          Compare →
        </span>
      )}
    </div>
  );
}
```

- [ ] **Step 6: Write the section**

Create `nextjs-app/components/school/SimilarSchoolsSection.tsx`:

```tsx
/**
 * SimilarSchoolsSection — nearby schools of the same phase and a comparable
 * intake. Server component; only AddToCompareButton is client-side.
 *
 * The section is allowed to say exactly what the backend matched and no more.
 * The lede only claims a similar intake when no card came from tier 3, and a
 * card's chips list what that school actually shares rather than a match it
 * did not earn.
 */

import Link from 'next/link';
import type { SimilarSchool } from '@/lib/types';
import { schoolUrl } from '@/lib/utils';
import { AddToCompareButton } from './AddToCompareButton';
import { SimilarSchoolsCompareBar } from './SimilarSchoolsCompareBar';
import { Section } from './sectionShared';
import styles from './SimilarSchools.module.css';

const MINIMUM = 2;

export function shouldRenderSimilar(similar?: SimilarSchool[] | null): boolean {
  return (similar?.length ?? 0) >= MINIMUM;
}

function metricLabel(key: string): string {
  return key === 'attainment_8_score' ? 'Attainment 8' : 'Reading, writing & maths';
}

function formatMetric(value: number | null, key: string): string {
  if (value == null) return 'Not published';
  return key === 'attainment_8_score' ? value.toFixed(1) : `${Math.round(value)}%`;
}

export function SimilarSchoolsSection({
  urn,
  schoolName,
  phaseNoun,
  thisMetricValue,
  similar,
}: {
  urn: number;
  schoolName: string;
  phaseNoun: string;
  thisMetricValue: number | null;
  similar?: SimilarSchool[] | null;
}) {
  if (!shouldRenderSimilar(similar)) return null;
  const schools = similar as SimilarSchool[];

  // One card matched on phase alone, so the section may not claim the set
  // shares an intake with this school.
  const loosest = Math.max(...schools.map((s) => s.tier));
  const metricKey = schools[0].metric_key;

  return (
    <Section id="similar">
      <h2 className={styles.heading}>Similar schools nearby</h2>
      <p className={styles.lede}>
        {loosest >= 3
          ? `Other ${phaseNoun} schools near ${schoolName}.`
          : `Other ${phaseNoun} schools near ${schoolName}, with a similar intake.`}
      </p>

      <details className={styles.method}>
        <summary>How these schools are chosen</summary>
        <div>
          <p>
            Schools of the same phase, nearest first, preferring those whose intake
            resembles this one — gender, religious character, and whether the school
            selects by ability. Special schools are only ever compared with other
            special schools.
          </p>
          <p>
            The labels on each card list what that school actually shares with this
            one. Where nothing close enough was found nearby, the match is loosened
            and the labels say less.
          </p>
          <p>
            Distances are straight-line from this school, not road distance and not
            from your home. Being listed here is not a recommendation.
          </p>
        </div>
      </details>

      <ul className={styles.grid}>
        {schools.map((school) => (
          <li key={school.urn} className={styles.school}>
            <p className={styles.distance}>{school.distance_miles} miles away</p>
            <h3 className={styles.name}>
              <Link href={schoolUrl(school.urn, school.school_name)}>
                {school.school_name}
              </Link>
            </h3>
            <p className={styles.meta}>
              {[school.school_type, school.age_range && `Ages ${school.age_range}`]
                .filter(Boolean)
                .join(' · ')}
            </p>
            <ul className={styles.shared}>
              {school.shared.map((label) => (
                <li key={label} className={school.tier >= 3 ? styles.chipLoose : styles.chip}>
                  {label}
                </li>
              ))}
            </ul>
            <div className={styles.metric}>
              <p
                className={
                  school.metric_value == null ? styles.valueAbsent : styles.value
                }
              >
                {formatMetric(school.metric_value, school.metric_key)}
              </p>
              <p className={styles.metricLabel}>{metricLabel(school.metric_key)}</p>
              {thisMetricValue != null && (
                <p className={styles.metricRef}>
                  {formatMetric(thisMetricValue, metricKey)} at this school
                </p>
              )}
            </div>
            <AddToCompareButton school={school} />
          </li>
        ))}
      </ul>

      <SimilarSchoolsCompareBar thisUrn={urn} candidates={schools} />
    </Section>
  );
}
```

- [ ] **Step 7: Write the stylesheet**

Create `nextjs-app/components/school/SimilarSchools.module.css`. Tokens only —
`darkThemeSafety.test.ts` fails the build on any hardcoded colour:

```css
.heading { font-family: var(--font-display); font-size: 1.4rem; letter-spacing: -0.4px; margin: 0; }
.lede { margin: 0.5rem 0 0; color: var(--text-secondary); max-width: 64ch; }

.method { margin: 0.9rem 0 1.4rem; }
.method summary { cursor: pointer; color: var(--brand); font-size: 0.85rem; font-weight: 500; width: fit-content; }
.method div { margin-top: 0.6rem; padding: 0.9rem 1rem; background: var(--bg-secondary); border-radius: 8px; }
.method p { margin: 0 0 0.55rem; font-size: 0.82rem; color: var(--text-secondary); max-width: 70ch; }
.method p:last-child { margin-bottom: 0; }

.grid { display: grid; grid-template-columns: repeat(3, minmax(0, 1fr)); gap: 0.9rem; list-style: none; margin: 0; padding: 0; }
@media (max-width: 820px) { .grid { grid-template-columns: repeat(2, minmax(0, 1fr)); } }
@media (max-width: 560px) { .grid { grid-template-columns: 1fr; } }

.school { position: relative; display: flex; flex-direction: column; border: 1px solid var(--border); border-radius: 8px; padding: 1rem; background: var(--bg-card); }
.school:hover { border-color: var(--border-strong); }

.distance { margin: 0 0 0.6rem; font-size: 0.75rem; color: var(--text-muted); }
.name { font-family: var(--font-display); font-size: 1rem; line-height: 1.35; margin: 0 0 0.35rem; }
.name a { color: var(--text-primary); text-decoration: none; }
/* The whole card is the link target; the button sits above it on z-index. */
.name a::after { content: ""; position: absolute; inset: 0; border-radius: 8px; }
.name a:hover { color: var(--brand); text-decoration: underline; }
.meta { margin: 0 0 0.75rem; font-size: 0.78rem; color: var(--text-muted); }

.shared { display: flex; flex-wrap: wrap; gap: 0.35rem; list-style: none; margin: 0 0 0.85rem; padding: 0; }
.chip { font-size: 0.72rem; line-height: 1.4; padding: 0.25rem 0.5rem; border-radius: 999px; background: var(--brand-bg); color: var(--brand); border: 1px solid transparent; }
.chipLoose { font-size: 0.72rem; line-height: 1.4; padding: 0.25rem 0.5rem; border-radius: 999px; background: transparent; color: var(--text-muted); border: 1px solid var(--border); }

.metric { margin-top: auto; padding-top: 0.8rem; border-top: 1px solid var(--border); }
/* No valence colour here, deliberately: green and terracotta mean "against the
   England average" everywhere else on the site, and colouring a neighbour
   against this school would read as ranking the neighbours. */
.value { font-family: var(--font-display); font-size: 1.6rem; font-weight: 700; letter-spacing: -0.6px; margin: 0; color: var(--text-primary); }
.valueAbsent { font-size: 0.95rem; font-weight: 600; margin: 0; color: var(--text-muted); }
.metricLabel { margin: 0.25rem 0 0; font-size: 0.75rem; color: var(--text-secondary); }
.metricRef { margin: 0.1rem 0 0; font-size: 0.75rem; color: var(--text-muted); }

.add { position: relative; z-index: 1; margin-top: 0.85rem; width: 100%; min-height: 40px; font: inherit; font-size: 0.82rem; font-weight: 500; cursor: pointer; border-radius: 8px; border: 1px solid var(--border-strong); background: var(--bg-card); color: var(--brand); }
.add:hover { border-color: var(--brand); background: var(--brand-bg); }
.add[aria-pressed="true"] { border-color: var(--brand); background: var(--brand-bg); font-weight: 600; }

.footer { display: flex; flex-wrap: wrap; align-items: center; justify-content: space-between; gap: 0.85rem; margin-top: 1.25rem; padding-top: 1.1rem; border-top: 1px solid var(--border); }
.footer p { margin: 0; font-size: 0.78rem; color: var(--text-muted); }
.footer strong { display: block; font-size: 0.88rem; font-weight: 600; color: var(--text-primary); }
/* Coral is the one decisive action per screen, and in this section this is it. */
.compare { min-height: 44px; padding: 0 1.25rem; border-radius: 8px; font-size: 0.88rem; font-weight: 600; background: var(--action); color: var(--action-on); border: 1px solid var(--action); text-decoration: none; display: inline-flex; align-items: center; }
.compare:hover { background: var(--action-strong); border-color: var(--action-strong); }
.compare[aria-disabled="true"] { opacity: 0.45; pointer-events: none; }

.srOnly { position: absolute; width: 1px; height: 1px; padding: 0; margin: -1px; overflow: hidden; clip: rect(0 0 0 0); white-space: nowrap; border: 0; }
```

- [ ] **Step 8: Run the tests to verify they pass**

Run (from `nextjs-app/`):
```sh
npm test -- --runInBand SimilarSchoolsSection darkThemeSafety
npm run typecheck
```
Expected: PASS on both suites, and typecheck clean.

- [ ] **Step 9: Commit**

```bash
git add nextjs-app/lib/types.ts nextjs-app/components/school/SimilarSchoolsSection.tsx nextjs-app/components/school/SimilarSchools.module.css nextjs-app/components/school/AddToCompareButton.tsx nextjs-app/components/school/SimilarSchoolsCompareBar.tsx nextjs-app/__tests__/components/SimilarSchoolsSection.test.tsx
git commit -m "feat(web): similar schools section, honest about what it matched

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>"
```

---

### Task 4: Wire it into both templates

**Files:**
- Modify: `nextjs-app/lib/schoolSections.ts` (`buildNavItems` at line 143, `buildSecondaryNavItems`)
- Modify: `nextjs-app/components/school/PrimarySchoolSections.tsx`
- Modify: `nextjs-app/components/school/SecondarySchoolSections.tsx`
- Modify: `nextjs-app/app/(frontend)/school/[slug]/page.tsx`
- Test: `nextjs-app/__tests__/lib/schoolSections.test.ts` (append, or create if absent)

**Interfaces:**
- Consumes: `shouldRenderSimilar` and `SimilarSchoolsSection` from Task 3.
- Produces: nothing later tasks build on.

- [ ] **Step 1: Write the failing test**

Append to the existing `nextjs-app/__tests__/lib/schoolSections.test.ts`,
matching the imports already at the top of that file:

```ts
import { buildNavItems, buildSecondaryNavItems, computeSchoolFlags } from '@/lib/schoolSections';

const navInput = {
  ofsted: null,
  admissions: null,
  admissionDistance: null,
  hasLocation: true,
  yearlyDataLength: 1,
  hasSimilarSchools: true,
};

describe('the similar-schools nav item', () => {
  it('appears on both templates when the section renders', () => {
    const flags = computeSchoolFlags({
      schoolInfo: { phase: 'Primary' } as never,
      yearlyData: [], absenceData: [], census: null,
      deprivation: null, finance: null, destinations: null,
    });
    expect(buildNavItems(flags, navInput).map((i) => i.id)).toContain('similar');
    expect(buildSecondaryNavItems(flags as never, navInput).map((i) => i.id)).toContain('similar');
  });

  it('is absent when the section does not render', () => {
    const flags = computeSchoolFlags({
      schoolInfo: { phase: 'Primary' } as never,
      yearlyData: [], absenceData: [], census: null,
      deprivation: null, finance: null, destinations: null,
    });
    const without = { ...navInput, hasSimilarSchools: false };
    expect(buildNavItems(flags, without).map((i) => i.id)).not.toContain('similar');
    expect(buildSecondaryNavItems(flags as never, without).map((i) => i.id)).not.toContain('similar');
  });
});
```

- [ ] **Step 2: Run the test to verify it fails**

Run (from `nextjs-app/`):
```sh
npm test -- --runInBand schoolSections
```
Expected: FAIL — `'similar'` is not in the nav item ids.

- [ ] **Step 3: Add the nav item**

In `nextjs-app/lib/schoolSections.ts`, add `hasSimilarSchools: boolean;` to the
`NavItemsInput` interface, then destructure it in both builders and append, as
the **last** item in each (the section renders last, and the scroll-spy order
must match the DOM order):

```ts
  if (hasSimilarSchools) navItems.push({ id: 'similar', label: 'Similar schools' });
```

- [ ] **Step 4: Render the section in both templates**

In `PrimarySchoolSections.tsx` and `SecondarySchoolSections.tsx`: add
`similarSchools?: SimilarSchool[]` to the props interface, import
`SimilarSchoolsSection`, and render it as the last child, after every existing
section:

```tsx
      <SimilarSchoolsSection
        urn={schoolInfo.urn}
        schoolName={schoolInfo.school_name}
        phaseNoun={phaseNoun}
        thisMetricValue={thisMetricValue}
        similar={similarSchools}
      />
```

In `PrimarySchoolSections.tsx`, derive the two values from what the component
already has:

```tsx
  const phaseNoun = (schoolInfo.phase ?? '').toLowerCase() === 'all-through'
    ? 'all-through'
    : 'primary';
  const thisMetricValue = flags.latestResults?.rwm_expected_pct ?? null;
```

In `SecondarySchoolSections.tsx`:

```tsx
  const phaseNoun = 'secondary';
  const thisMetricValue = flags.latestResults?.attainment_8_score ?? null;
```

- [ ] **Step 5: Pass the payload through the page**

In `nextjs-app/app/(frontend)/school/[slug]/page.tsx`:

Add `similar_schools` to the destructure of `data` (around line 155):

```tsx
  // Absent on an older API build, exactly like `places` above.
  const similarSchools = data.similar_schools ?? [];
```

Add to `navInput` (around line 185):

```tsx
    hasSimilarSchools: shouldRenderSimilar(similarSchools),
```

importing `shouldRenderSimilar` from
`@/components/school/SimilarSchoolsSection`, and pass
`similarSchools={similarSchools}` to both `<PrimarySchoolSections>` and
`<SecondarySchoolSections>`.

- [ ] **Step 6: Run the full frontend suite**

Run (from `nextjs-app/`):
```sh
npm run typecheck && npm test -- --runInBand
```
Expected: PASS on both. Every existing caller of `buildNavItems` /
`buildSecondaryNavItems` now needs `hasSimilarSchools`; a typecheck failure here
is a caller you have not updated yet.

- [ ] **Step 7: Commit**

```bash
git add nextjs-app/lib/schoolSections.ts nextjs-app/components/school/PrimarySchoolSections.tsx nextjs-app/components/school/SecondarySchoolSections.tsx "nextjs-app/app/(frontend)/school/[slug]/page.tsx" nextjs-app/__tests__/lib/schoolSections.test.ts
git commit -m "feat(web): render similar schools on both detail templates

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>"
```

---

### Task 5: Journey and documentation

**Files:**
- Modify: `e2e/tests/journeys.spec.ts`
- Modify: `docs/ARCHITECTURE.md`

**Interfaces:**
- Consumes: the rendered section from Task 4.
- Produces: nothing.

- [ ] **Step 1: Write the journey**

Append to `e2e/tests/journeys.spec.ts`, following the file's existing
convention of asserting stable invariants rather than exact numbers:

```ts
/**
 * Similar schools nearby.
 *
 * The section is absent by design where fewer than two schools qualify, so
 * this walks from a search hit to a school page and asserts the section's
 * contract only where it renders — and asserts the compare hand-off, which is
 * the one part that can break silently.
 */
test('similar schools link on to other schools and into compare', async ({ page }) => {
  await searchByName(page, 'Primary');
  await schoolLinks(page).first().click();
  await page.waitForURL(/\/school\//);

  const section = page.locator('#similar');
  if ((await section.count()) === 0) {
    test.skip(true, 'No qualifying similar schools for this school');
  }

  // Every card is a real link to another school page.
  const links = section.locator('a[href^="/school/"]');
  expect(await links.count()).toBeGreaterThanOrEqual(2);
  const href = await links.first().getAttribute('href');
  expect(href).toMatch(/^\/school\/\d{6}-/);

  // A missing figure says so rather than showing a number.
  await expect(section.getByText(/miles away/).first()).toBeVisible();

  // The compare hand-off.
  await section.getByRole('button', { name: /Add to compare/ }).first().click();
  await expect(
    section.getByRole('button', { name: /Added to compare/ }).first(),
  ).toBeVisible();
});
```

- [ ] **Step 2: Note the staging gate**

Do **not** try to run this journey locally against a dev server. On this
project the E2E gate runs against staging *after* merge, so this journey is not
provable in the PR checks. Verify the PR on the unit suites, and check the
post-merge staging run.

- [ ] **Step 3: Document the section**

In `docs/ARCHITECTURE.md`, under "Frontend boundaries", after the sentence about
`components/school/`, add:

```markdown
The similar-schools section is selected in `backend/similar_schools.py` — hard
filters that never relax (phase, provision, selectivity, gender) and soft
preferences that do (religious character, then gender exactness) — and served on
`/api/schools/{urn}`. Its selection rules are presentation logic, deliberately
kept out of `marts.*` so they can be tuned by deploy rather than by pipeline run.
```

- [ ] **Step 4: Run every check before the PR**

Run:
```sh
/tmp/schoolcompare-backend-venv/bin/python -m pytest backend/tests pipeline/tests scripts/ci/tests -q
cd nextjs-app && npm run typecheck && npm test -- --runInBand
```
Expected: PASS on all three.

- [ ] **Step 5: Commit and open the PR**

```bash
git add e2e/tests/journeys.spec.ts docs/ARCHITECTURE.md
git commit -m "test(e2e): cover the similar-schools section and compare hand-off

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>"
git push -u origin feat/similar-schools-nearby
```

Open a PR against `main` with passing checks. Do not push to `main` directly and
do not trigger the promotion workflow.