feat: mysql integration ci

[cungminh2710]

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[greptile-apps]

Greptile Summary

This PR adds a mysql-integration CI job to the GitHub Actions workflow and accompanies it with an ADR documenting the design decision. The new job follows the same pattern already established by the postgres-integration job: a service container, a health-check, Go setup, and a targeted go test invocation with a dialect-specific DSN.

Key points:

• The job structure, Go version (1.26), timeout-minutes, and needs: [precommit] dependency are all consistent with the existing SQLite and Postgres jobs.
• The mysql:8.4 service container is correctly configured with MYSQL_DATABASE, MYSQL_USER, MYSQL_PASSWORD, and MYSQL_ROOT_PASSWORD.
• The RAIN_MYSQL_DSN DSN format (rain:rain@tcp(127.0.0.1:3306)/rain_test?parseTime=true) is correct for the go-sql-driver/mysql library.
• The ADR is thorough and accurately reflects what was implemented.
• One minor note: the health-check probe authenticates as the rain user; with MySQL 8.4's caching_sha2_password default this can occasionally timeout on the very first probe. Switching the probe to the root account is a common workaround.

Confidence Score: 5/5

Safe to merge — the new job is a clean incremental addition with no impact on existing jobs.

All findings are P2 style suggestions. The workflow change is additive, consistent with existing patterns, and has a supporting ADR. No correctness, data-integrity, or reliability issues were identified.

No files require special attention.

Important Files Changed

Filename	Overview
.github/workflows/ci.yml	Adds a mysql-integration job that mirrors the existing postgres-integration structure — service container, health check, Go setup, and test run via RAIN_MYSQL_DSN. One minor note: the health-check uses the non-root rain user, which can occasionally fail on cold-start with MySQL 8.4's caching_sha2_password default.
docs/adr/2026-03-29-mysql-integration-ci-design.md	New ADR documenting the decision to add a dedicated MySQL CI job; well-structured and accurately reflects the implementation choices in the workflow file.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    PR[Push / Pull Request] --> PC[precommit job\nmake precommit]
    PC --> SQ[integration job\nSQLite Integration Tests]
    PC --> PG[postgres-integration job\nPostgres Integration Tests]
    PC --> MY[mysql-integration job\nMySQL Integration Tests NEW]

    MY --> SVC[mysql:8.4 service container\nrain_test DB · rain user]
    SVC -->|health-check passes| GO[Setup Go 1.26]
    GO --> TEST["go test -race ./pkg/rain\n-run '^TestMySQLIntegration'"]

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This is a comment left during a code review.
Path: .github/workflows/ci.yml
Line: 96

Comment:
**Consider using root for the health-check user**

MySQL 8.4 defaults to the `caching_sha2_password` authentication plugin for newly created users. On the very first health-check probe (before any authentication cache is populated), `mysqladmin ping` with a `caching_sha2_password` account over a plain TCP connection can occasionally fail because the full RSA key-exchange handshake is required.

Using `root` for the health-check avoids this cold-start issue entirely, since the root account created by `MYSQL_ROOT_PASSWORD` commonly uses `mysql_native_password` in the official image:

```suggestion
          --health-cmd="mysqladmin ping -h 127.0.0.1 -uroot -proot"
```

The `rain` user is still the correct credential to put in `RAIN_MYSQL_DSN` for the actual test run; this change only affects the liveness probe.

How can I resolve this? If you propose a fix, please make it concise.

_{Reviews (1): Last reviewed commit: "." | Re-trigger Greptile}