chore(sync-service): upgrade Elixir to 1.20.0-rc.3

[alco]

Summary

• Upgrade Elixir from 1.19.5 to 1.20.0-rc.3 (Erlang/OTP 28.4 unchanged)
• Fix all Elixir 1.20 compatibility warnings in Electric source code:
  • Remove 7 unused require statements
  • Add pin operator (^) in 5 bitstring size patterns
  • Rename Changes.record() to Changes.row() (new built-in type conflict)
  • Remove unreachable :shutdown clause in pool.ex (improved type inference)
  • Use apply/3 in telemetry.ex to avoid compile-time conditional type warning
• Bump postgrex 0.21.1 -> 0.22.0 (+ transitive deps db_connection, telemetry)

Known issue

Postgrex.Types.define generates code that Elixir 1.20's compiler flags as having unused functions. This is a postgrex compatibility issue — the 2 warnings come from generated code and cannot be suppressed from our side. Electric's own source is warning-free.

Test plan

• mix compile passes (only 2 dep-generated warnings remain)
• mix format --check-formatted passes
• mix test passes (382 doctests, 8 properties, 1443 tests, 0 failures)
• CI passes

🤖 Generated with Claude Code

[claude]

Claude Code Review

Summary

This PR upgrades Elixir from 1.19.5 to 1.20.0-rc.3, fixes all resulting compatibility warnings in Electric's source, and bumps postgrex to a git commit with the Elixir 1.20 compatibility fix. The changes are mechanical and correct.

What's Working Well

• All previous review suggestions addressed: elixir-otp-upgrade-progress.md has been removed from the repo root (suggestion from iteration 1).
• Postgrex approach is sound: Pinning to a specific git commit hash (e4f79427e99bb0dc86376a769fc966b98edb7dfc) is safer than pinning to a branch — the commit can't change unilaterally and the mix.lock captures it exactly. The TODO comment with a link to the upstream issue (elixir-ecto/postgrex#760) makes the temporary nature explicit and actionable.
• apply/3 workaround is pragmatic: The change from Electric.telemetry_enabled?() to apply(Electric, :telemetry_enabled?, []) is also changed to use and instead of &&, which is the idiomatic Elixir boolean operator when short-circuit evaluation with non-boolean values isn't needed. Correct improvement.

Issues Found

Critical (Must Fix)

None.

Important (Should Fix)

Still upgrading to an RC, not a stable release

File: .tool-versions, packages/sync-service/Dockerfile

From iteration 1: the version being pinned is 1.20.0-rc.3. This is unchanged and is a deliberate choice. If 1.20.0 final is imminent, a follow-up issue to bump from RC to stable would ensure this doesn't get forgotten. The postgrex git dependency will also need to be resolved before/alongside that bump.

Suggestions (Nice to Have)

None remaining.

Issue Conformance

No linked issue (unchanged from iteration 1). The PR description clearly covers motivation and scope, so this is a minor point for a maintenance upgrade.

Previous Review Status

Issue	Status
elixir-otp-upgrade-progress.md committed to repo root	✅ Fixed — file removed
RC version warning	Still open (intentional)
No linked issue	Still open (minor)

The two fixup commits addressed the postgrex warnings by switching from a not-yet-released ~> 0.22 hex version to the specific upstream git commit that contains the fix — a clean and well-documented approach.

---

Review iteration: 2 | 2026-03-11

[codecov]

❌ 1 Tests Failed:

Tests completed	Failed	Passed	Skipped
2742	1	2741	1

View the full list of 1 ❄️ flaky test(s)

Elixir.ElectricTelemetry.CallHomeReporterTest::test reports all expected info when started under StackTelemetry

Flake rate in main: 46.39% (Passed 52 times, Failed 45 times)

Stack Traces | 0.0811s run time

3) test reports all expected info when started under StackTelemetry (ElectricTelemetry.CallHomeReporterTest)
     .../electric/telemetry/call_home_reporter_test.exs:77
     ** (exit) shutdown

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[blacksmith-sh]

Found 1 test failure on Blacksmith runners:

Failure

Test	View Logs
Elixir.ElectricTelemetry.CallHomeReporterTest/ test reports all expected info when started under StackTelemetry	View Logs