feat(#63,#31): broaden application/geo+json + byte parity with PostgREST 14.12

[milmazz]

Summary

Both issues shared one root cause: the advanced read path (embeds/aggregates/
spread/computed columns) pre-collapsed each row into a scalar
json_build_object(...) expression. PostgreSQL renders json_build_object
spaced ("k" : v), diverging from PostgREST's compact wire bytes (#31), and a
pre-collapsed JSON scalar is not a record ST_AsGeoJSON can consume — which is
why application/geo+json had been left flat-path-only (#63).

The restructure (spec §0-1). Bier.Embed.build_row_object/6 became a
select-list builder returning {select_items, lateral_joins, state} instead of
one scalar JSON expression: plain fields/aggregates/computed columns render as
expr AS "out_name"; non-spread embeds stay correlated scalar subqueries but
as named columns (:many → COALESCE(json_agg(...), '[]') over an ordered
subquery, :one → to_json of a LIMIT 1 subquery); spread embeds become
LEFT JOIN LATERAL with the child's columns pulled into the parent select
list (PostgREST's actual SQL shape), deleting the old (obj::jsonb || spread)::json merge and its null_template COALESCE hack. build_advanced
then mirrors build_simple's three-layer shape: an inner named-projection
subquery, a paging layer that projects the bare record (not
pre-rendered JSON) alongside a count(*) OVER() window, and an outer
json_agg that renders PostgREST's exact wire bytes — compact row objects
separated by , \n , jsonb-style embed internals (to_jsonb/json_agg( to_jsonb(...))) with key re-sorting. This also fixed the simple path,
which previously aggregated a pre-rendered JSON value and silently dropped the
, \n row separator on every multi-row response.

Producer broadening (spec §2). With every rendering path now able to
produce a real record, application/geo+json was safe to broaden beyond flat
reads:

• Mutations (POST/PATCH/PUT/DELETE) negotiate geo+json against the
  postgis-gated producer list unconditionally; whether the response carries a
  body (and thus a FeatureCollection) still depends on Prefer
  (return=representation renders one, return=minimal/headers-only
  don't). Bier.Mutation threads format: :geojson into the query executor
  so the representation body is a FeatureCollection.
  Preference-Applied handling is unchanged; Location and Content-Range were
  aligned with live PostgREST (see Resolved divergences below).
• RPC (Bier.Rpc) offers geo+json under the same PostGIS gate for both
  GET and POST dispatch. setof_rel results thread the format into the
  same read-builder path as table reads; scalar/composite/setof_record results
  gain a geojson variant wrapping the result in ST_AsGeoJSON. A relation or
  result without a geometry column raises SQLSTATE 22023 ("geometry column
  is missing") at execution — no new error shape, mirroring PostgREST.
• Edge: empty-payload mutation responses under geojson return an empty
  FeatureCollection ({"type":"FeatureCollection","features":[]}) rather than
  [] — live-verified.

Live PostgREST 14.12 diff — 17/17 requests byte-identical

Setup: PostgREST 14.12 on :3009 with db-schemas = "test, geotest",
db-anon-role = postgrest_test_anonymous, db-tx-end = rollback,
db-aggregates-enabled = true; Bier on :3010 with the mirrored config.
Identical requests issued to both; compared status, body bytes, and the
content-type, location, content-range, content-length,
content-profile, preference-applied headers.

#	Request	Result
1	GET /projects?select=id,name,clients(name)&order=id&limit=2	✓ ([{"id":1,"name":"Windows 7","clients":{"name": "Microsoft"}}, \n {...}])
2	GET /projects?select=name,tasks(name)&order=id&limit=1&tasks.order=id	✓
3a	GET /projects?select=id,...clients(client_name:name)&order=id&limit=1	✓
3b	…&id=eq.5 (missing to-one spread)	✓ ([{"id":5,"client_name":null}])
4	GET /projects?select=client_id,id.count()&order=client_id	✓ (, \n row separators)
5a	GET /projects?select=id,...tasks(task_names:name)&order=id&limit=1	✓ ([{"id":1,"task_names":["Design w7", "Code w7"]}])
5b	…&id=eq.5 (EMPTY to-many spread)	✓ ([{"id":5,"task_names":[]}] — PostgREST renders [], confirming Bier's per-key COALESCE(json_agg(...), '[]'))
6	geo+json read with embed (/shops?select=id,address,shop_geom,shop_bles(name)…)	✓ after fix (Content-Range)
7	POST /shops repr + geo+json	✓ after fix (Location)
8	POST /shops body [] repr + geo+json	✓ after fix (Content-Range); status 201, body exactly {"type" : "FeatureCollection", "features" : []} — Bier's hardcoded literal confirmed byte-for-byte
9a	PATCH /shops?id=eq.1 repr + geo+json	✓
9b	DELETE /shops?id=eq.3 repr + geo+json	✓
10a	GET /rpc/get_shops + geo+json	✓ after fix (Content-Range)
10b	POST /rpc/get_shops (body {}) + geo+json	✓ after fix (Content-Range)
11	GET /rpc/get_shop_geom?id=1 + geo+json	✓ after fix (Content-Range); body {"type" : "FeatureCollection", "features" : [{"type": "Feature", "geometry": {"type":"Point","coordinates":[-71.10044,42.373695]}, "properties": {}}]} — Bier's FeatureCollection-of-one shape confirmed
12a	GET /projects + geo+json (no geometry)	✓ 400 {"code":"22023","details":null,"hint":null,"message":"geometry column is missing"}
12b	POST /plain repr + geo+json	✓ same envelope

All response bodies matched byte-for-byte on the first run (the #31
restructure and #63 broadening were already byte-correct). The divergences
found were all header-level; four were fixed in lib/:

Resolved divergences (Bier bugs, fixed)

1. Content-Range under geo+json reads and setof RPC (cases 6, 10a, 10b).
   PostgREST: Content-Range: 0-2/*; Bier: */*. PostgREST computes the range
   from the row window regardless of the negotiated media type; Bier's
   Response.row_count/1 decoded the FeatureCollection object to 0 rows.
   Fixed by counting features of a {"type":"FeatureCollection"} body as
   rows (lib/bier/response.ex).
2. Location on mutation representation/minimal responses (case 7).
   PostgREST emits Location ONLY for Prefer: return=headers-only
   (live-verified: POST repr with PK selected → no Location; no-Prefer POST →
   no Location; headers-only → Location: /shops?id=eq.6; matches the frozen
   suite's InsertSpec notes). Bier computed a Location on representation and
   minimal responses whenever the PK was in the selected output. Removed
   maybe_location (and pk_in_select?) from those branches
   (lib/bier/mutation.ex); the headers-only force_location and the
   response.headers GUC override (frozen case 1569) are unchanged.
3. Content-Range on the empty-payload mutation short-circuit (case 8).
   PostgREST: Content-Range: */* (both JSON and geo+json, repr and minimal);
   Bier omitted the header on the zero-row short-circuit. Added
   */{total_part(pref, 0)} to respond_empty_set (lib/bier/mutation.ex),
   so count=exact yields */0 like the SQL-backed path.
4. Content-Range on scalar/composite RPC without a count preference
   (case 11). PostgREST always emits a read-style range for the single-row
   result — 0-0/* by default (JSON and geo+json alike), 0-0/1 under
   count=exact (frozen case 1403). Bier emitted the header only when a count
   preference was present. maybe_scalar_content_range now emits 0-0/* for
   count=none (lib/bier/rpc.ex).
5. Content-Profile echo under multi-schema exposure (all non-error
   cases). With db-schemas = "test, geotest", PostgREST echoes
   Content-Profile: <resolved schema> on every success response (test for
   default-profile requests, geotest for explicit profiles) and omits it on
   error responses and single-schema configs. Bier only echoed through the
   db_profile_schemas/db_profile_default model built for the frozen
   MultipleSchemaSpec surface. Fixed additively
   (lib/bier/plugs/action_controller.ex): when that model is NOT configured,
   the resolved schema is echoed whenever more than one schema is exposed. The
   shared conformance instance (which configures the model) and single-schema
   instances are behaviorally unchanged; the frozen suite stays green.

Accepted divergence (out of scope)

See Follow-up below (PUT … Prefer: return=headers-only).

Follow-up

• PUT … Prefer: return=headers-only: live PostgREST returns 204 with
  no Location and no Content-Range, while Bier emits both. Not
  part of this branch's matrix and no frozen case covers PUT headers-only —
  candidate for a new issue.
• Bier.Embed.spread_entry is missing a child_cols == [] guard: a to-many
  spread of an empty projection currently emits a lateral with an empty
  select list, which is valid SQL that silently multiplies parent rows (one
  duplicate per child row) rather than erroring.
• No test covers the :composite ret_kind + geo+json result_sql branch.

Also in this branch

• mix hex.audit bumped plug (1.20.2 → 1.20.3) and postgrex (0.22.2 →
  0.22.3) past three upstream security advisories (cookie attribute
  injection, multipart DoS, Notifications reconnect SQL injection) — unrelated
  to [conformance-gap] Broaden application/geo+json: mutations, RPC, and the embed/advanced read path #63/[conformance][lib] Embed/advanced path renders spaced JSON via json_build_object #31 but required to keep CI's hex.audit gate green.
• Docs (README.md, docs/CONFORMANCE_IMPL.md, CHANGELOG.md) updated to
  describe the broadened application/geo+json availability (reads,
  representation-returning mutations, RPC, whenever PostGIS is installed) and
  the search_path note: ST_AsGeoJSON is emitted unqualified and resolves
  via the session search_path (matching PostgREST) — a PostGIS installed
  outside the search path fails at execution.

Closes #63
Closes #31

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