Refactor transit_api into a repo/routes module split

Split the 5,441-line index.js into an 86-line bootstrap, thin domain
route modules, shared lib/ helpers, and a repo/ layer that isolates the
DEV_MOCK branches (repo/*.mock.js). Repo methods return {statusCode, body};
routes are one-line wrappers. Pin search_path to "transit.bus" and
document the /bus/ prefix with legacy root aliases (Deprecation header).

Parity verified: 57/57 byte-identical on the stub differential harness
plus 24/24 live read-only responses vs the original against real
PostgreSQL. The only intentional behavior change: mock reorder/delete
bus-line endpoints no longer require a live DB (previously 500 in
DEV_MOCK=1 without PG). DEV_MOCK gate and node --check clean.

transit_api/repo/stops.js

@@ -0,0 +1,149 @@
+const db = require("../db");
+const { reportError } = require("../lib/report-error");
+
+// Stop repository methods (PostgreSQL mode). Each returns { statusCode, body }
+// mirroring the original handler's DB branch.
+
+async function listStops(req) {
+  try {
+    const result = await db.query(`
+      SELECT id, name, latitude, longitude, created_at, updated_at
+      FROM stops
+      ORDER BY id ASC
+    `);
+
+    return {
+      statusCode: 200,
+      body: {
+        stops: result.rows.map((row) => ({
+          id: row.id,
+          name: row.name,
+          latitude: parseFloat(row.latitude),
+          longitude: parseFloat(row.longitude),
+          createdAt: row.created_at,
+          updatedAt: row.updated_at,
+        })),
+      },
+    };
+  } catch (err) {
+    console.error(err);
+    reportError({ partofservice: `${req.method} ${req.originalUrl}`, error: err.stack || err.message });
+    return { statusCode: 500, body: { error: "internal_error", details: err.message } };
+  }
+}
+
+async function createStop(req) {
+  try {
+    const { name, latitude, longitude } = req.body;
+
+    if (!name || latitude === undefined || longitude === undefined) {
+      return { statusCode: 400, body: { error: "missing_required_fields" } };
+    }
+
+    const result = await db.query(
+      `
+      WITH next_id AS (
+        SELECT COALESCE(MAX(id), 0) + 1 AS id FROM stops
+      )
+      INSERT INTO stops (id, name, latitude, longitude)
+      SELECT next_id.id, $1, $2, $3
+      FROM next_id
+      RETURNING id, name, latitude, longitude, created_at, updated_at
+    `,
+      [name, latitude, longitude],
+    );
+
+    const stop = result.rows[0];
+    return {
+      statusCode: 201,
+      body: {
+        stop: {
+          id: stop.id,
+          name: stop.name,
+          latitude: parseFloat(stop.latitude),
+          longitude: parseFloat(stop.longitude),
+          createdAt: stop.created_at,
+          updatedAt: stop.updated_at,
+        },
+      },
+    };
+  } catch (err) {
+    console.error(err);
+    reportError({ partofservice: `${req.method} ${req.originalUrl}`, error: err.stack || err.message });
+    return { statusCode: 500, body: { error: "internal_error", details: err.message } };
+  }
+}
+
+async function deleteStop(req) {
+  try {
+    const { stopId } = req.params;
+
+    if (!stopId || !Number.isFinite(Number(stopId))) {
+      return { statusCode: 400, body: { error: "invalid_stop_id" } };
+    }
+
+    const result = await db.query(
+      `DELETE FROM stops WHERE id = $1 RETURNING id, name`,
+      [stopId],
+    );
+
+    if (result.rows.length === 0) {
+      return { statusCode: 404, body: { error: "stop_not_found" } };
+    }
+
+    return { statusCode: 200, body: { success: true, stop: result.rows[0] } };
+  } catch (err) {
+    console.error(err);
+    reportError({ partofservice: `${req.method} ${req.originalUrl}`, error: err.stack || err.message });
+    if (err.code === "23503") {
+      return { statusCode: 409, body: { error: "foreign_key_violation", message: "This stop is referenced by route_stops" } };
+    }
+    return { statusCode: 500, body: { error: "internal_error", details: err.message } };
+  }
+}
+
+async function updateStop(req) {
+  try {
+    const { stopId } = req.params;
+    const { name, latitude, longitude } = req.body;
+
+    if (!stopId || !Number.isFinite(Number(stopId))) {
+      return { statusCode: 400, body: { error: "invalid_stop_id" } };
+    }
+
+    const result = await db.query(
+      `UPDATE stops
+       SET name = COALESCE($1, name),
+           latitude = COALESCE($2, latitude),
+           longitude = COALESCE($3, longitude),
+           updated_at = NOW()
+       WHERE id = $4
+       RETURNING id, name, latitude, longitude, created_at, updated_at`,
+      [name ?? null, latitude ?? null, longitude ?? null, stopId],
+    );
+
+    if (!result.rows[0])
+      return { statusCode: 404, body: { error: "stop_not_found" } };
+
+    const stop = result.rows[0];
+    return {
+      statusCode: 200,
+      body: {
+        stop: {
+          id: stop.id,
+          name: stop.name,
+          latitude: parseFloat(stop.latitude),
+          longitude: parseFloat(stop.longitude),
+          createdAt: stop.created_at,
+          updatedAt: stop.updated_at,
+        },
+      },
+    };
+  } catch (err) {
+    console.error(err);
+    reportError({ partofservice: `${req.method} ${req.originalUrl}`, error: err.stack || err.message });
+    return { statusCode: 500, body: { error: "internal_error", details: err.message } };
+  }
+}
+
+module.exports = { listStops, createStop, updateStop, deleteStop };