docs: fix stale references to get_vars lazy-start

get_vars is now pure-read; the lazy-start lives in
require_background_worker. Updated the How It Works steps, the
named/catch-all bullets in Configuration, and the Caddyfile comment
that described the catch-all as "handles any unlisted name via
get_vars()".

Author: nicolas-grekas

docs/background-workers.md

@@ -7,8 +7,8 @@ They observe their environment and publish variables that HTTP threads (both [wo
 
 1. A background worker runs its own event loop (subscribe to Redis, watch files, poll an API...)
 2. It calls `frankenphp_set_vars()` to publish a snapshot of key-value pairs
-3. HTTP threads call `frankenphp_get_vars()` to read the latest snapshot
-4. The first `get_vars()` call blocks until the background worker has published - no startup race condition
+3. HTTP threads call `frankenphp_require_background_worker()` to declare a dependency and ensure the worker is running (lazy-started if needed, blocks until it has published at least once)
+4. HTTP threads then call `frankenphp_get_vars()` to read the latest snapshot (pure read, no blocking)
 
 ## Configuration
 
@@ -27,16 +27,16 @@ example.com {
             name feature-flags
         }
 
-        # Catch-all - handles any unlisted name via get_vars()
+        # Catch-all - handles any unlisted name via require_background_worker()
         worker /app/bin/console {
             background
         }
     }
 }
 ```
 
-- **Named** (with `name`): lazy-started on first `get_vars()` call, or auto-started at boot if `num 1` is set.
-- **Catch-all** (no `name`): also lazy-started. Use `max_threads` to cap how many can be created (defaults to 16). Not declaring a catch-all forbids unlisted names.
+- **Named** (with `name`): lazy-started on first `require_background_worker()` call, or auto-started at boot if `num 1` is set.
+- **Catch-all** (no `name`): lazy-started on demand too, for any name not matched by a `name` directive. Use `max_threads` to cap how many can be created (defaults to 16). Not declaring a catch-all forbids unlisted names.
 - Each `php_server` block has its own isolated scope - two blocks can use the same worker names without conflict.
 - `max_consecutive_failures`, `env`, and `watch` work the same as HTTP workers.
 
@@ -241,5 +241,5 @@ if (function_exists('frankenphp_get_vars')) {
 - `$_SERVER['FRANKENPHP_WORKER_NAME']` is set for all workers (HTTP and background)
 - `$_SERVER['FRANKENPHP_WORKER_BACKGROUND']` is `true` for background workers, `false` for HTTP workers
 - `$_SERVER['argv']` = `[entrypoint, name]` in background workers (for `bin/console` compatibility)
-- Crash recovery with automatic restart and exponential backoff. During the restart window, `get_vars` returns the last published data (stale but available). A warning is logged on crash (`background worker exited, restarting`).
+- Crash recovery with automatic restart and exponential backoff. During the restart window, `get_vars()` returns the last published data (stale but available) since the vars stay in persistent memory across crashes. A warning is logged on crash (`background worker exited, restarting`).
 - On shutdown/restart: the signaling stream is closed (EOF). Workers have 5 seconds to exit. Stuck workers are force-killed on Linux and Windows.