feat(mcp): derive env vars from the framework's real struct tags (#3)

Minor to v1.1.0. Make the whole environment-variable surface derive from the
indexed component-config tags instead of a hand-maintained list that drifts.
Also folds in the scaffold-symbol fixes staged as v1.0.1 (never tagged); the
generated scaffold compiles clean against einherjar v1.0.0.

internal/envspec (new):
- Parse index struct tags into env vars {name, module, struct, field, required,
  default}. One source of truth: ParseTag, ForModule, FindStruct, All, KnownNames.

internal/tools:
- get_config_env: list the real env vars a component config reads (or all).
- check_env: flag unknown EINHERJAR_* names, required vars missing for the
  composed modules, and dead vars (set for an uncomposed module).
- get_scaffold: .env.example is now DERIVED from the index — required vars
  uncommented with a dev value, defaulted vars commented with their default.
  The scaffold now composes logz.Config (Log logz.Config) so EINHERJAR_LOG_*
  are live and documented, not hardcoded/ignored (log format is env-driven).
- validate_snippet: inject the real env-var name set into the rules package.

internal/index/builtins (wire conventions):
- Route the incremental "compose a component later" flow to get_config_env /
  check_env; distinguish framework EINHERJAR_* from app-owned APP_* (JWT).
- Compose logz.Config in the config + Run() examples, to match the scaffold.

internal/rules:
- config.unknown-env-var (twelfth rule): reject an env:"EINHERJAR_*" struct tag
  the framework doesn't declare. No-op until the server injects the name set, so
  it never fires on incomplete knowledge.

Fixed (was v1.0.1): scaffold health hook + wire builtin used logz.Logger (real:
contracts/logging.Logger) and postgres.Component (hooks take Provider); env tags
were EINHERJAR_SERVER_ADDR / EINHERJAR_PG_DATABASE (real: _HOST/_PORT / _PG_NAME).

Tests: envspec unit tests; env tools against the real data/index.json; the rule.
Verified by generating the scaffold, building it against local einherjar v1.0.0
(exit 0), and runtime-loading the composed logz.Config (EINHERJAR_LOG_LEVEL=DEBUG
-> slog.LevelDebug, EINHERJAR_LOG_JSON=true). Version bumped to v1.1.0 (badge +
serverVersion). No dependency changes.

Reviewed-on: #3
Co-authored-by: Rene Nochebuena Guerrero <rene@nochebuena.dev>
Co-committed-by: Rene Nochebuena Guerrero <rene@nochebuena.dev>

internal/index/builtins/README.md

@@ -84,6 +84,7 @@ import (
 
 	"github.com/caarlos0/env/v11"
 
+	"code.nochebuena.dev/einherjar/core/logz"
 	"code.nochebuena.dev/einherjar/db-postgres"
 	"code.nochebuena.dev/einherjar/web/server"
 )
@@ -108,6 +109,7 @@ type Config struct {
 
 	// Framework component configs — composed verbatim. Their own EINHERJAR_* tags
 	// load through this one env.Parse call.
+	Log    logz.Config     // EINHERJAR_LOG_*
 	Server server.Config   // EINHERJAR_SERVER_*
 	PG     postgres.Config // EINHERJAR_PG_*
 }
@@ -133,6 +135,21 @@ var, the same change adds its `env:"..."` tag to `config` **and** a documented l
 `.env.example`. This is not optional bookkeeping — it is what stops a long feature from shipping
 and then failing at boot because nobody knew which variables to set.
 
+**Two kinds of var, two ways to keep them honest:**
+
+- **Framework component vars (`EINHERJAR_*`)** — when you compose a new component later (e.g.
+  `cachevalkey.Config`, `minio.Config`, `smtp.Config`), the MCP knows its real vars: call
+  `get_config_env("<module>")` for the exact set (name, required, default) and add each to
+  `.env.example`. The `config.unknown-env-var` rule rejects any `EINHERJAR_*` tag the framework
+  doesn't declare, so a typo like `EINHERJAR_PG_DATABASE` is caught at `validate_snippet` time.
+- **App-owned vars (`APP_*`)** — like `APP_JWT_SECRET` above: the framework can't know these, so
+  keeping them in `.env.example` is your discipline, not something it can name-check.
+
+After you compose a component, run **`check_env`** with the modules the app composes: it flags
+`EINHERJAR_*` names that don't exist, required vars you forgot to document, and vars set for a
+module you don't actually compose (dead vars). `get_scaffold` already emits a `.env.example`
+derived from these same tags, so the starting point is correct by construction.
+
 ```bash
 # .env.example — copy to .env for local dev. Every var the app reads lives here.
 
@@ -142,19 +159,25 @@ APP_CORS_ORIGINS=*
 APP_JWT_SECRET=change-me
 APP_JWT_ISSUER=myapp
 
+# ── Einherjar: logging (EINHERJAR_LOG_*) ──────────────────────────────────
+# EINHERJAR_LOG_LEVEL=INFO
+# EINHERJAR_LOG_JSON=false
+
 # ── Einherjar: HTTP server (EINHERJAR_SERVER_*) ───────────────────────────
-EINHERJAR_SERVER_ADDR=:8080
+EINHERJAR_SERVER_HOST=0.0.0.0
+EINHERJAR_SERVER_PORT=8080
 
 # ── Einherjar: PostgreSQL (EINHERJAR_PG_*) ────────────────────────────────
 EINHERJAR_PG_HOST=localhost
 EINHERJAR_PG_PORT=5432
 EINHERJAR_PG_USER=postgres
 EINHERJAR_PG_PASSWORD=postgres
-EINHERJAR_PG_DATABASE=myapp
+EINHERJAR_PG_NAME=myapp
 ```
 
-To discover the full set, walk every `env:"..."` tag reachable from `config.Config` (including the
-nested framework configs) — every one of them belongs in `.env.example`.
+To discover the full set for any component you compose, use `get_config_env("<module>")` rather
+than reading source by hand; every var it returns belongs in `.env.example`, and `check_env`
+confirms none are missing, misspelled, or dead.
 
 ## wire.go — Run()
 
@@ -166,8 +189,6 @@ appended, then feature hooks, then `lc.Run()`.
 package wire
 
 import (
-	"strings"
-
 	"github.com/google/uuid"
 
 	authjwt "code.nochebuena.dev/einherjar/auth-jwt"
@@ -189,10 +210,11 @@ func Run() error {
 		return err
 	}
 
-	logger := logz.New(logz.Config{
-		JSON:       !strings.EqualFold(cfg.AppEnv, "local"),
-		StaticArgs: []any{"service", "myapp", "env", cfg.AppEnv},
-	})
+	// logz.Config is composed in config, so EINHERJAR_LOG_LEVEL / _JSON load from
+	// the environment; StaticArgs are set here (they carry no env tag).
+	logCfg := cfg.Log
+	logCfg.StaticArgs = []any{"service", "myapp", "env", cfg.AppEnv}
+	logger := logz.New(logCfg)
 
 	signer := authjwt.NewHMACSigner([]byte(cfg.JWT.Secret))
 
@@ -239,9 +261,9 @@ registration — lives inside the closure.
 package wire
 
 import (
+	"code.nochebuena.dev/einherjar/contracts/logging"
 	"code.nochebuena.dev/einherjar/contracts/security"
 	"code.nochebuena.dev/einherjar/core/launcher"
-	"code.nochebuena.dev/einherjar/core/logz"
 	"code.nochebuena.dev/einherjar/core/valid"
 	"code.nochebuena.dev/einherjar/db-postgres"
 	"code.nochebuena.dev/einherjar/web/server"
@@ -255,8 +277,8 @@ import (
 func withUsers(
 	lc       launcher.Launcher,
 	srv      server.Server,
-	db       postgres.Component,
-	logger   logz.Logger,
+	db       postgres.Provider,
+	logger   logging.Logger,
 	provider security.PermissionProvider,
 	v        valid.Validator,
 ) {