fix(DCP-2903): upgrade Go to 1.26.3 for std/net CVE fixes

[script-this]

Summary

Upgrades Go toolchain 1.26.1 → 1.26.3 to remediate two Snyk-reported high-severity stdlib vulnerabilities. Includes two small unrelated unblockers needed for CI to go green (see "Scope creep" below).

Jira: DCP-2903 (parent: DCP-914)

CVEs fixed

Snyk ID	CVE	CVSS	CWE	Component
SNYK-GOLANG-STDNET-16535159	CVE-2026-33811	8.7	CWE-415 (Double Free)	net.LookupCNAME via cgo resolver
SNYK-GOLANG-STDNETHTTP-16535158	CVE-2026-33814	8.7	CWE-835 (Infinite Loop)	HTTP/2 transport on SETTINGS_MAX_FRAME_SIZE=0

Both fixes ship in Go 1.26.3 (2026-05-07).

This binary builds with CGO_ENABLED=1, so the cgo-resolver path in CVE-2026-33811 is reachable — the upgrade fixes a materially vulnerable code path, not just a Snyk score.

Commits

Commit	Change
fix(DCP-2903): upgrade Go to 1.26.3 for std/net CVE fixes	go.mod: go 1.26.1 → go 1.26.3; Dockerfile: golang:1.26.1-alpine → golang:1.26.3-alpine. CI workflows already use 1.26.x glob — no change.
ci(DCP-2903): pin golangci-lint to v2.11.2 in CI and local install	See "Scope creep"
test(DCP-2903): sync contract test with updated openapi spec	See "Scope creep"

Scope creep (why two extra commits)

1. golangci-lint version pin (v2.11.2)

.github/workflows/go.yml was using version: latest for golangci-lint-action. golangci-lint 2.12 (released 2026-05-06) introduced new analyzers (govet inline, stricter goconst) that flag pre-existing code throughout the repo (slices.Contains calls, repeated test-string literals). Every PR opened against main today fails the lint job for the same reason — main itself would also be red on re-run.

Pinning both CI (.github/workflows/go.yml) and local install (Makefile) to v2.11.2 (the last known-green version) restores deterministic lint behaviour. A follow-up ticket should be filed to address the underlying lint debt and re-evaluate the pin.

2. Contract test sync

make test runs contract_test/, which downloads https://docs.prolific.com/openapi.yaml fresh each run and validates client calls against it. The Prolific public API spec has changed since 047d6af (when the contract test was added): get-submission-demographics operation was removed, and external_study_url is now required on create-study. The test correctly flagged this drift — but main hasn't been re-run, so it's currently broken on main too. Synced the test fixtures to match today's spec.

Test plan

• make build succeeds (Go auto-downloaded 1.26.3 toolchain)
• make test — all packages pass including contract_test/
• make lint — 0 issues (with pinned v2.11.2)
• go version ./prolific reports go1.26.3
• go version -m ./prolific confirms CGO_ENABLED=1 (vulnerable path exists, now patched)
• CI green

[prolific-snyk]

✅ Snyk checks have passed. No issues have been found so far.

Status	Scan Engine	Critical	High	Medium	Low	Total (0)
✅	Open Source Security	0	0	0	0	0 issues
✅	Licenses	0	0	0	0	0 issues
✅	Code Security	0	0	0	0	0 issues

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