📝 clarify logger bind alias contract

docs/api/logger-bind.md

@@ -28,15 +28,18 @@ pub fn[S] Logger::bind(self : Logger[S], fields : Array[Field]) -> Logger[Contex
 
 #### output
 
-- `Logger[ContextSink[S]]` - New logger wrapper that prepends shared fields at write time.
+- `Logger[ContextSink[S]]` - New logger value whose visible sink type becomes `ContextSink[S]` and prepends shared fields at write time.
 
 ### Explanation
 
 Detailed rules explaining key parameters and behaviors
 
-- `bind(...)` delegates directly to `with_context_fields(...)`.
+- `bind(...)` delegates directly to `with_context_fields(...)`; it is an alias, not a different implementation.
-- The original logger value is not mutated; a wrapped logger is returned.
+- The original logger value is not mutated; a derived wrapped logger is returned.
+- The returned logger changes visible type from `Logger[S]` to `Logger[ContextSink[S]]` because the sink pipeline is extended with stored shared fields.
+- Stored target, minimum level, and timestamp behavior are preserved while the sink pipeline changes.
 - Shared fields are applied to every later log call emitted through the returned logger.
+- When a log call also passes per-record fields, the shared bound fields are prepended before those per-call fields because `bind(...)` inherits the same merge order as `with_context_fields(...)`.
 - This alias is useful when you prefer shorter chaining syntax in application code.
 
 ### How to Use
@@ -64,6 +67,8 @@ let worker = Logger::new(console_sink(), target="app")
 
 In this example, `bind(...)` communicates intent without changing underlying behavior.
 
+And the returned logger still keeps the same target and level-gating behavior as the source logger.
+
 ### Error Case
 
 e.g.:
@@ -77,3 +82,5 @@ e.g.:
 
 2. This alias exists for ergonomics, not for different semantics.
 
+3. Use `with_context_fields(...)` when the longer name makes the sink-type change to `ContextSink[S]` clearer at the call site.
+