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]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 82.98%. Comparing base (69ba13c) to head (40ebf7e).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
...lient/lib/electric/client/ecto_adapter/postgres.ex	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3992      +/-   ##
==========================================
- Coverage   85.73%   82.98%   -2.75%     
==========================================
  Files          51       65      +14     
  Lines        3343     3814     +471     
  Branches      612      609       -3     
==========================================
+ Hits         2866     3165     +299     
- Misses        475      647     +172     
  Partials        2        2              

Flag	Coverage Δ
electric-telemetry	64.07% <ø> (?)
elixir	72.93% <0.00%> (-4.85%)	⬇️
elixir-client	77.18% <0.00%> (-0.60%)	⬇️
packages/experimental	87.73% <ø> (ø)
packages/react-hooks	86.48% <ø> (ø)
packages/start	82.83% <ø> (ø)
packages/typescript-client	93.93% <ø> (ø)
packages/y-electric	56.05% <ø> (ø)
typescript	88.74% <ø> (ø)
unit-tests	82.98% <0.00%> (-2.75%)	⬇️

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