fix: build_formatter routes the unknown-output warning through the setup buffer

build_formatter warned immediately via getLogger(__name__).warning, but
setup_logging calls it after _clear_owned strips the lib's handlers and before
any new handler attaches - so the warning hit a handler-less root and landed
on stderr via lastResort, never reaching the configured log. The v0.6.0
warnings buffer already threads this class of setup-time warning through for
an unknown rotate value; build_formatter now takes the same warnings list and
appends to it instead of emitting inline, so setup_logging can flush it once
handlers are attached like the others.

Signed-off-by: disqualifier <dev@disqualifier.me>

src/log_setup/formats.py

@@ -54,7 +54,7 @@ class JsonLinesFormatter(logging.Formatter):
         return json.dumps(payload, default=str)
 
 
-def build_formatter(output: str = "text", fmt=None, datefmt=None) -> logging.Formatter:
+def build_formatter(output: str = "text", fmt=None, datefmt=None, warnings: list = None) -> logging.Formatter:
     """build the formatter for the chosen output format
 
     `output="text"` (default) returns the human-readable text formatter, honoring
@@ -62,11 +62,19 @@ def build_formatter(output: str = "text", fmt=None, datefmt=None) -> logging.For
     structured `JsonLinesFormatter` (which ignores `fmt`/`datefmt` - it builds
     fields, not a format string). an unrecognized `output` falls back to text and
     warns, never raising - a bad format arg must not take the app down.
+
+    `warnings` is the setup-time buffer (see `setup_logging`): passing it appends
+    the unknown-output warning there instead of emitting immediately, so it lands
+    in the configured log like the other setup-time warnings rather than only
+    stderr. `None` (default) preserves the old immediate-emit behavior for direct
+    callers outside `setup_logging`.
     """
     if output == "json":
         return JsonLinesFormatter()
     if output != "text":
-        logging.getLogger(__name__).warning(
-            "log_setup: unknown output %r; falling back to 'text'", output
-        )
+        message = "log_setup: unknown output %r; falling back to 'text'"
+        if warnings is None:
+            logging.getLogger(__name__).warning(message, output)
+        else:
+            warnings.append((message, output))
     return logging.Formatter(fmt or DEFAULT_FORMAT, datefmt or DEFAULT_DATEFMT)

src/log_setup/setup.py

@@ -266,7 +266,7 @@ def setup_logging(
     _apply_module_levels(module_levels, warnings)
     _clear_owned(root, warnings)
 
-    formatter = build_formatter(output, fmt, datefmt)
+    formatter = build_formatter(output, fmt, datefmt, warnings)
     stem = _normalize_name(name)
     live_path = f"{stem}.log"
     # history_name if given, else the cwd basename; falls back to the live stem for a