feat(datastore): add Maven remote version size_bytes writer

What

Adds MavenRemoteVersionStore.AddMavenRemoteVersionSizeBytes, the Maven twin of npm's AddNpmRemoteVersionSizeBytes: a delta-based writer for maven_remote_versions.size_bytes (UPDATE ... SET size_bytes = GREATEST(size_bytes + delta, 0), soft_deleted_at IS NULL filter, zero-delta short-circuit, identifier-free error wrap).

Why

Step 3 of the Maven version size accounting plan (issue #550 (closed)). The column and index exist with zero writers; this ships the writer. The first caller is the S14 Track B cache-fill step, recorded as a dependency in the plan — until it lands, the mirrored test suite is the only exerciser, npm-parity style.

Notes for reviewers

• Mirrored subtest-for-subtest from the npm twin suite (guards, zero-delta, clamp, transient-error wrap, live delta round-trip, soft-delete/missing/cross-namespace no-ops).
• One deliberate, plan-documented divergence from the npm twin: the error wrap is identifier-free per docs/dev/database-query-patterns.md; the future caller logs namespace_id/version_id as its own structured fields.
• Also touches: query_names.go (query-name constant for the new statement), maven_remote_cache.go (comment-honesty edit — the old text claimed no store existed), npm_remote_write_test.go (measured //nolint:dupl justification for the zero-delta twins), and the plan file.
• Validated with /validate-step (ADVISORIES ONLY; advisories resolved in-branch).

Related to #550 (closed)

Database Review Evidence

Queries

Note

Plans are from EXPLAIN (ANALYZE, BUFFERS) against an ephemeral PostgreSQL 17 container (matching GL_PG_CURR_VERSION from .gitlab-ci-other-versions.yml), with synthesized seed data rolled back per query and the container torn down at the end of the run. Numbers reflect moderate cardinality and do not capture production-scale effects. See Database review evidence for seed sizing, methodology, and the anomalies the skill flags. Expand each row's details for the seed shape, rendered SQL, bound args, and raw plan.

Method	Plan node	Index	Rows (plan / actual)	Cost	Time	Buffers (hit / read)	Partitions
datastore.AddMavenRemoteVersionSizeBytes	Update	n/a	1 / 1	0.00..1.75	1.042ms	24 / 2	1/64

datastore.AddMavenRemoteVersionSizeBytes

Summary: Point UPDATE on maven_remote_versions keyed by namespace + version id, exactly matching the method's intent (a buffered-counter delta write). The namespace_id partition key is bound, so the planner prunes to a single partition (1 of 64, p37 at seed) and the FK-constraint trigger checks add trivial overhead. At the recipe's 50-row seed the planner correctly picks a Seq Scan over the whole tiny partition — the pk_maven_remote_versions (id, namespace_id) index loses on cost at this cardinality and is not flagged; at production partition sizes the index serves the id predicate. No anomalies.

Seed shape: namespaces=1, repositories=1, maven_remote_repositories=1, maven_remote_packages=1, maven_remote_versions=50 (49 siblings share the target's namespace partition)

Rendered SQL:

UPDATE public.maven_remote_versions
SET size_bytes = GREATEST(maven_remote_versions.size_bytes + $1, $2)
WHERE ((maven_remote_versions.namespace_id = $3::uuid) AND (maven_remote_versions.id = $4::uuid)) AND (maven_remote_versions.soft_deleted_at IS NULL)

Bound args: [5, 0, e4a050c1-e1e6-4fb4-b522-425a213a2446, a75141ae-9e05-4d43-bb88-83d0bd337da9]

Plan (EXPLAIN (ANALYZE, BUFFERS) output):

Update on maven_remote_versions  (cost=0.00..1.75 rows=0 width=0) (actual time=0.147..0.148 rows=0 loops=1)
   Update on maven_remote_versions_p37 maven_remote_versions_1
   Buffers: shared hit=24 read=2
   ->  Seq Scan on maven_remote_versions_p37 maven_remote_versions_1  (cost=0.00..1.75 rows=1 width=18) (actual time=0.005..0.007 rows=1 loops=1)
         Filter: ((soft_deleted_at IS NULL) AND (namespace_id = 'e4a050c1-e1e6-4fb4-b522-425a213a2446'::uuid) AND (id = 'a75141ae-9e05-4d43-bb88-83d0bd337da9'::uuid))
         Rows Removed by Filter: 49
         Buffers: shared hit=1
   Planning:
     Buffers: shared hit=433
   Planning Time: 0.783 ms
   Trigger for constraint fk_maven_remote_versions_maven_remote_package_id on maven_remote_versions_p37: time=0.590 calls=1
   Trigger for constraint fk_maven_remote_versions_namespace_id_namespaces on maven_remote_versions_p37: time=0.202 calls=1
   Execution Time: 1.042 ms

Timings: planning 0.783ms, execution 1.042ms, total 1.825ms.