# CLAUDE.md — Agent Instructions

This file is read automatically by Claude Code at the start of every session.
Keep it concise — the agent needs signal, not essays.

---

## Project overview

Go 1.25 template / PoC starter. Demonstrates: structured logging (slog),
config (flag), interfaces + manual fakes, linting (golangci-lint),
security scanning (gosec, govulncheck), git hooks, devcontainer, VSCode tasks.

Module: `gitea.djmil.dev/djmil/go-template` — update this when you fork.

---

## Project structure

```
cmd/app/main.go          composition root — wires deps, no logic here
internal/config/         flag-based config loader (config.Load)
internal/logger/         slog wrapper with WithField / WithFields
internal/greeter/        Example domain package (delete or repurpose)
tools.go                 Tool version pinning (build tag: tools)
.golangci.yml            Linter rules
.githooks/pre-push       Runs gofmt + go vet + golangci-lint + gosec before push
```

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## Project rules

- **Module imports** — always use the full module path `gitea.djmil.dev/djmil/go-template/...`
- **Packages** — keep `cmd/` thin (wiring only); business logic belongs in `internal/`
- **Interfaces** — define interfaces where they are *used*, not where they are *implemented*
- **Errors** — wrap with `fmt.Errorf("context: %w", err)`; never swallow errors silently
- **Logging** — use `log.WithField("key", val)` for structured context; never `fmt.Sprintf` in log messages; `log/slog` is the backend
- **Config** — all configuration through `internal/config` (flag-parsed); no hard-coded values in logic packages

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## Code style

- Follow `gofmt` + `goimports` formatting (enforced by linter and git hook)
- Imports: stdlib → blank line → external → blank line → internal (goimports handles this)
- Error variables: `err` for local, `ErrFoo` for package-level sentinels
- Constructors: `New(deps...) *Type` pattern
- Comment every exported symbol (golangci-lint will warn if missing)
- Max line length: 120 chars (configured in `.golangci.yml`)
- Prefer explicit over clever; PoC code should be readable first

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## Testing rules

- Tests use only the standard `testing` package — no third-party assertion libraries
- Test files: `package foo_test` (black-box) unless white-box access is needed
- Fake dependencies with **manual fakes** (implement the interface inline in `_test.go`)
- Use `logger.NewNop()` when the test doesn't care about log output
- Table-driven tests with `t.Run("description", ...)` for multiple cases
- The race detector is enabled in CI (`make test-race`); don't introduce data races
- Never use `time.Sleep` in tests; use channels or `t.Cleanup`

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## Development commands

```bash
make init          # first-time setup: fetch deps, install tools, git hooks
make build         # compile to ./bin/app
make run           # go run with default flags
make test          # run all tests
make test-race     # tests + race detector
make lint          # go vet + golangci-lint
make lint-fix      # go fix + golangci-lint auto-fix
make security      # gosec + govulncheck
make clean         # remove bin/
```

VSCode: `Ctrl+Shift+B` = build, `Ctrl+Shift+T` = test.
Debug: use launch config "Debug: app" (F5).

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## Adding new features (checklist)

1. Define the interface in `internal/<domain>/`
2. Write the implementation and its unit tests (using a manual fake for the interface)
3. Wire it in `cmd/app/main.go`
4. Run `make lint test` before committing

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## Known pitfalls

- `govulncheck` makes network calls; excluded from pre-push hook (run manually)
- `tools.go` has `//go:build tools` — it won't compile into the binary
- `go fix` rewrites source files; run `make lint-fix` before committing after a Go version bump

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## Recent work
<!-- Agent: append a dated bullet when completing a significant chunk of work.
     Keep this section to ~10 entries; remove stale items.
     Format: YYYY-MM-DD — what was done and why. -->

- 2026-03-29 — Stripped to stdlib-only: removed testify/mockery→manual fakes, zap→slog, viper→flag.
- 2026-03-29 — Pre-commit hook moved to pre-push; go vet + go fix added to lint pipeline.
- 2026-03-29 — Fixed stale docs and .golangci.yml local-prefixes; .vscode launch configs use CLI flags.