add AGENTS.md

2026-07-04 17:19:09 -04:00
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+# AGENTS.md — go-app
+
+A small framework for bootstrapping logging, OTEL, and HTTP/gRPC servers from
+config + environment. Apps embed `*config.AppConfig` in a custom config struct
+and register services; the framework runs the servers and lifecycle.
+
+## The app init pattern (current, v0.17+)
+
+```go
+ctx, cncl := signal.NotifyContext(ctx, os.Interrupt, syscall.SIGTERM, syscall.SIGQUIT)
+defer cncl()
+
+// Custom config that embeds *config.AppConfig:
+ctx, cfg := app.MustLoadConfigInto(ctx, &config.ServiceConfig{})
+cfg.LoadEnv() // SEE GOTCHA 1 — custom-field env is the caller's job
+
+a := &app.App{AppContext: ctx}
+a.InitOTEL()
+
+for _, svc := range appServices { sdFunc, _ := svc.Init(ctx, cfg); ... }
+a.GRPC, a.HTTP = service.MergeServices(ctx, appServices...) // app-side helper
+a.MustRun()
+<-a.Done()
+// then run collected ShutdownFuncs within a grace period
+```
+
+- `MustLoadConfigInto` loads the `-config` YAML + env into a struct that embeds
+  `*config.AppConfig`; `MustSetupConfigAndLogging` is the simple (AppConfig-only)
+  variant. Config loading owns `flag.Parse`, so register app flags in `init()`.
+- `MustRun` starts gRPC then HTTP then a monitor goroutine; panics if neither is
+  enabled. `Done()` unblocks on ctx cancel or a server exit.
+
+## Registering servers
+
+Fill option structs and assign to `App.GRPC` / `App.HTTP` (or use a
+`service.AppService` + `MergeServices` convenience layer per app):
+
+- **gRPC** (`pkg/srv/grpc/opts.AppGRPC`): append `*GRPCService{Name, Type
+  (*grpc.ServiceDesc), Service (impl), GwRegistrationFuncs}`. At least one
+  service must add a transport-credentials **dial option** (e.g.
+  `insecure.NewCredentials()`) so the grpc-gateway can dial the server.
+  Instrumentation, protovalidate, reflection, and the gateway are auto-wired
+  from `GRPCConfig`.
+- **HTTP** (`pkg/srv/http/opts.AppHTTP`): `Funcs` (path + handler), `Handlers`
+  (`HTTPHandler{Prefix|Pattern, StripPrefix, Handler}` for muxes), and
+  `HealthChecks`. `/health` and the Prometheus endpoint are mounted for you.
+- **MCP** is not a framework feature: mount an MCP streamable-HTTP handler as an
+  `HTTPHandler{Prefix: "/api/mcp", Handler: ...}`.
+
+## OTEL / Prometheus
+
+`InitOTEL()` sets up tracer + meter providers (no-op if disabled). The meter
+provider **always** includes a Prometheus reader; the HTTP server mounts
+`promhttp` at `OTEL.PrometheusPath` (default `/metrics`). OTLP export
+auto-enables when `OTEL_EXPORTER_OTLP_ENDPOINT` is set. Helpers:
+`otel.GetTracer(ctx, name)`, `otel.GetMeter(ctx, name)`.
+
+## Config & schema
+
+`AppConfig` covers `APP_*` env (name/env/version, http, grpc, otel, logging).
+Custom fields are validated for schema via `app.CustomSchema(&cfg)`. Precedence
+for AppConfig: defaults → env → YAML file.
+
+## Known gotchas (fix candidates)
+
+1. **Custom-field env is NOT applied.** `MustLoadConfigInto` only parses env for
+   the embedded `AppConfig`; its own doc says custom env is "up to the caller."
+   So `env:"..."` tags on custom fields do nothing unless the app runs
+   `env.Parse` itself. `MustSetupConfigAndLoggingInto[T]` looks like the intended
+   helper but is currently an **empty stub** (returns its args unchanged).
+   → Good candidate: make `MustLoadConfigInto`/that stub run `env.Parse` over the
+   custom struct (skipping the embedded `AppConfig` to preserve precedence).
+2. **grpc-gateway path strip defaults to false.** `GRPCGatewayPath` defaults to
+   `/grpc-api` but `GRPCGatewayPathStrip` defaults `false`, so the gateway sees
+   the full prefixed path and 404s every route. Apps must set
+   `grpcGatewayPathStrip: true` (or accept requests must include the prefix in
+   the proto `google.api.http` path). Consider defaulting strip to true.
+3. **Prometheus unit suffixing.** The OTEL→Prometheus exporter appends the OTEL
+   unit as a name suffix, so `metric.WithUnit("°F")` on `econet_setpoint_fahrenheit`
+   yields `..._fahrenheit_F`. Either don't set WithUnit (bake units into names)
+   or enable `prometheus.WithoutUnits()` in the meter setup.
+4. README's example `main.go` is stale (references removed `app.AppHTTP` /
+   `srv.HTTPFunc`); trust the template app instead.
+
+## Layout
+
+`pkg/app` (bootstrap/lifecycle/schema) · `pkg/config` (AppConfig, env/yaml) ·
+`pkg/logging` (zerolog) · `pkg/otel` (providers + helpers) · `pkg/srv/grpc`
+(+gateway) · `pkg/srv/http` (+health, +prometheus).