docs(modules): rewrite cabana, wire, towel, festival, compass, backpack READMEs

modules/backpack/README.md

@@ -1,3 +1,88 @@
 # backpack
 
-`backpack` provides the application container that holds configuration, services, events, and activated plugin IDs. Framework boot code and Fonoteka plugin assembly import it; start with `backpack.App` and `backpack.New` in `app.go`.
+Per-instance application container that holds the configuration, a typed service registry, the event bus and the set of activated plugins.
+
+`import "git.golem15.com/golem15/summercms/modules/backpack"`
+
+## Overview
+
+`backpack` plays the role of the Laravel service container that WinterCMS plugins reach through `App::make` and singleton bindings, without any process-global state: every `backpack.App` is independent, so tests and multiple instances in one process do not interfere. The generated `main` of an application loads configuration with [compass](../compass/README.md), creates the container with `backpack.New`, and hands it to [party](../party/README.md), which passes it to every plugin's Register and Boot. `backpack` deliberately does not import `party`, which keeps the dependency graph acyclic.
+
+## Features
+
+- `backpack.New` wires a container around a loaded `*compass.Config`: `backpack.App.Config`, a fresh service registry in `backpack.App.Services` and a new [festival](../festival/README.md) bus in `backpack.App.Events`.
+- Typed services keyed by the type argument: `backpack.App.Publish` stores a value under its type T and `backpack.App.Lookup` returns it. Publishing the same T twice or publishing nil is an error, so two plugins cannot silently replace each other's service. Framework modules share their infrastructure this way (for example the database handles published by [lagoon](../lagoon/README.md), or the translator from [phrasebook](../phrasebook/README.md)).
+- Plugin presence checks: `backpack.App.SetPlugins` records the complete activated set before any plugin boots, and `backpack.App.HasPlugin` answers whether an optional integration partner is part of this build (the equivalent of WinterCMS's `PluginManager::exists`).
+- `backpack.Registry` can be used on its own through `backpack.NewRegistry`; it is safe for concurrent use.
+- Nil-safe methods: calls on a nil container or registry return an error or a zero value instead of panicking.
+
+## Usage
+
+```go
+package blog
+
+import (
+	"git.golem15.com/golem15/summercms/modules/backpack"
+	"git.golem15.com/golem15/summercms/modules/compass"
+)
+
+// Feed is a service the blog plugin offers to other plugins.
+type Feed interface {
+	Latest(n int) []string
+}
+
+type staticFeed struct{}
+
+func (staticFeed) Latest(n int) []string { return []string{"hello-world"} }
+
+func setup() error {
+	cfg, err := compass.Load("config")
+	if err != nil {
+		return err
+	}
+	app := backpack.New(cfg)
+	app.SetPlugins([]string{"acme.blog", "acme.search"})
+
+	// Provider side, usually in the plugin's Register step.
+	var feed Feed = staticFeed{}
+	if err := app.Publish(feed); err != nil { // published under Feed, not staticFeed
+		return err
+	}
+
+	// Consumer side, usually in another plugin's Boot step.
+	if app.HasPlugin("acme.blog") {
+		if found, ok := app.Lookup[Feed](); ok {
+			_ = found.Latest(5)
+		}
+	}
+	return nil
+}
+```
+
+Publish under an interface type when consumers should not depend on the concrete implementation; the lookup must use exactly the same type argument.
+
+## API reference
+
+| Identifier | Description |
+|------------|-------------|
+| `backpack.App` | The application container: configuration, service registry, event bus and the activated plugin set. |
+| `backpack.New` | Creates a `backpack.App` around a loaded configuration, with an empty registry and a new event bus. |
+| `backpack.App.Publish` / `backpack.App.Lookup` | Store and retrieve an app-scoped service by type. |
+| `backpack.App.SetPlugins` / `backpack.App.HasPlugin` | Record the activated plugin IDs and check whether one is present. |
+| `backpack.Registry` | Concurrency-safe typed service catalog behind `backpack.App.Services`. |
+| `backpack.NewRegistry` | Returns an empty registry. |
+| `backpack.Registry.Publish` / `backpack.Registry.Lookup` | Registry-level publish and lookup behind the `backpack.App` methods. |
+
+## Dependencies
+
+- SummerCMS modules: [compass](../compass/README.md), [festival](../festival/README.md).
+- Third-party: none.
+- Standard library: `fmt`, `reflect`, `sync`.
+
+## Testing
+
+```sh
+go test ./modules/backpack/...
+```
+
+The tests build containers in memory and need no external services.