fix(test): isolate pay tests from eager env.ts to remove parallel-load race

[AquiGorka]

Summary

Fixes the flaky test CI job (the pay unit tests intermittently failing 34 passed / 11 failed with Error: DATABASE_URL is not loaded). The failure is a parallel-module-load race, not a logic bug, and it is independent of any feature PR — re-running known-green code (feat/pg-notify-event-bus) in the current CI environment reproduces it identically.

Root cause

The pay tests are unit tests that mock their infra deps in src/http/v1/pay/tests/deno.json (config.ts→PGlite, logger, jwt, channel-service, channel-resolver). But the real src/config/env.ts still leaked into their module graph via the auth-middleware chain:

pay handler → @/http/middleware/auth → core/service/auth/service/service-auth-secret.ts
            → import { MODE, SERVICE_AUTH_SECRET } from "@/config/env.ts"

env.ts evaluates every requireEnv at module load:

export const DATABASE_URL = requireEnv("DATABASE_URL"); // line 6
export const PORT         = requireEnv("PORT");         // …+9 more eager reads

That eager read is a deliberate production fail-fast — the service must refuse to start half-configured — and is kept as-is. But in the pay tests there is no real env, so under deno test --parallel on a cold CI cache the eager evaluation became a load-order race (the first missing var, DATABASE_URL, throws; which tests it takes down is timing-dependent → intermittent 11 failed).

Fix

Complete the existing test isolation: mock service-auth-secret.ts in the pay test import map (same mechanism as the other mocks), so the pay tests never evaluate the real env.ts.

"@/core/service/auth/service/service-auth-secret.ts": "./mock_service_auth_secret.ts"

The mock mirrors the real module's exports + crypto-key shape with a fixed test secret. Production env.ts and service-auth-secret.ts are untouched (fail-fast preserved); not lazified.

Verification

• deno info confirms env.ts is no longer in any of the 11 previously-failing pay tests' module graphs (env.ts = 0 across all).
• Pay suite passes deterministically on a cold-cache-equivalent run (env -u DATABASE_URL DENO_DIR=$(mktemp -d) deno test --parallel --config src/http/v1/pay/tests/deno.json → 116 passed | 0 failed, repeated).
• Control experiment (before → after) reported on the PR.
• deno fmt --check + deno lint green.

[AquiGorka]

Closing — superseded by #120 (pin deno to 2.8.2).

The CI test failure was not a parallel-load race. Root cause: deno 2.8.3 (which setup-deno@v2's v2.x floated to) regressed import-map override resolution, so the pay tests' mocks (config.ts→PGlite, jwt, channel deps) stopped applying and the real src/config/env.ts eager-evaluated requireEnv("DATABASE_URL") at module load. Verified by bisection in Linux containers: green on 2.8.2 (deno info shows env.ts absent from the pay graph), red on 2.8.3 (real modules + env.ts in the graph; env-satisfied runs fail with assertion errors from real deps).

The existing mocks already isolate the pay tests correctly on 2.8.2, so the extra service-auth-secret mock here fixes a race that doesn't exist. #120 pins the toolchain instead.