[fclairamb]

Fixes the red Backend Postgres Tests job on main (run 40973235887).

Cause

internal/db/postgres hit go test's default 10-minute per-package timeout. Its ~107 tests each boot an embedded PostgreSQL and run every migration, almost all of them serially (~624s total). Green runs had already crept up from 413s to 566s. The failing commit didn't touch this package; it just tipped it over the limit.

Fix

• New testsupport.FreePort(t): a port assigned by the kernel and deduplicated in-process. It comes from the ephemeral range, so it can't clash with the 14xxx/15xxx fixed ports other packages use.
• Every test in the package uses it in place of a hard-coded port constant (same-file tests used to share one), and calls t.Parallel().
• The old nolint:paralleltest reason ("pwfile extraction race") no longer holds: embeddedpg gives each instance its own runtime dir.
• Still serial: the 5 headroom tests that swap the global slog default, and the subtests of TestGetLastSignalForChecks_Postgres, which share one instance in order.

Verification

• Locally: SP_TEST_REQUIRE_POSTGRES=1 go test -parallel 4 ./internal/db/postgres/ passes in 78s, 0 skips.
• golangci-lint run on the touched packages: 0 issues.

🤖 Generated with Claude Code

[codecov]

Codecov Report

❌ Patch coverage is 70.58824% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.75%. Comparing base (208ff0a) to head (2eda961).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
server/internal/testsupport/port.go	70.58%	5 Missing ⚠️

❌ Your patch status has failed because the patch coverage (70.58%) is below the target coverage (87.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #713      +/-   ##
==========================================
- Coverage   89.76%   89.75%   -0.01%     
==========================================
  Files        1296     1297       +1     
  Lines      132198   132215      +17     
==========================================
+ Hits       118672   118676       +4     
- Misses      13517    13530      +13     
  Partials        9        9              

Files with missing lines	Coverage Δ
server/internal/testsupport/port.go	70.58% <70.58%> (ø)

... and 21 files with indirect coverage changes

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