feat(cli): auto-detect when to emit colors, honor NO_COLOR and FORCE_COLOR

ANSI escape codes no longer leak into piped output, files, log captures or
CI artefacts — colors are auto-disabled when stdout/stderr isn't a TTY.
The NO_COLOR and FORCE_COLOR environment variables are now respected.
stdout and stderr are decided independently, so warnings keep their colour
when stdout is piped but stderr is still on the terminal. Explicit \`--color\`
/ \`--no-color\` still override everything.

Refs: https://no-color.org/

Author: d-biehl

packages/plugin/src/robotcode/plugin/__init__.py

@@ -115,12 +115,35 @@ def show_diagnostics(self) -> bool:
     def show_diagnostics(self, value: bool) -> None:
         self._show_diagnostics = value
 
+    def color_for(self, file: Optional[IO[Any]] = None, err: bool = False) -> bool:
+        """Resolve the color decision for a specific output destination.
+
+        Honors the explicit ``--color`` / ``--no-color`` choice first, then the
+        ``FORCE_COLOR`` / ``NO_COLOR`` conventions (https://no-color.org/), and
+        finally the TTY status of the relevant stream — which may be stdout,
+        stderr, or an explicit ``file=``.  This matters because stdout and
+        stderr can be redirected independently: piping ``stdout`` into a file
+        should not disable colour on warnings written to ``stderr`` if that
+        is still attached to a terminal.
+        """
+        pref = self.config.colored_output
+        if pref == ColoredOutput.NO:
+            return False
+        if pref == ColoredOutput.YES:
+            return True
+        if os.environ.get("FORCE_COLOR"):
+            return True
+        if os.environ.get("NO_COLOR"):
+            return False
+        stream = file if file is not None else (sys.stderr if err else sys.stdout)
+        isatty = getattr(stream, "isatty", None)
+        return bool(isatty()) if callable(isatty) else False
+
     @property
     def colored(self) -> bool:
-        return self.config.colored_output in [
-            ColoredOutput.AUTO,
-            ColoredOutput.YES,
-        ]
+        """Shortcut for the color decision on stdout — used for branching
+        between rich and plain rendering paths that always target stdout."""
+        return self.color_for()
 
     @property
     def has_rich(self) -> bool:
@@ -139,12 +162,13 @@ def verbose(
         err: Optional[bool] = True,
     ) -> None:
         if self.config.verbose:
+            err_resolved = err if err is not None else True
             click.secho(
                 message() if callable(message) else message,
                 file=file,
                 nl=nl if nl is not None else True,
-                err=err if err is not None else True,
-                color=self.colored,
+                err=err_resolved,
+                color=self.color_for(file=file, err=err_resolved),
                 fg="bright_black",
             )
 
@@ -167,7 +191,7 @@ def progressbar(
             show_percent=show_percent,
             show_pos=show_pos,
             file=sys.stderr,
-            color=self.colored,
+            color=self.color_for(file=sys.stderr),
         )
 
     def warning(
@@ -177,12 +201,13 @@ def warning(
         nl: Optional[bool] = True,
         err: Optional[bool] = True,
     ) -> None:
+        err_resolved = err if err is not None else True
         click.secho(
             f"[ {click.style('WARN', fg='yellow')} ] {message() if callable(message) else message}",
             file=file,
             nl=nl if nl is not None else True,
-            err=err if err is not None else True,
-            color=self.colored,
+            err=err_resolved,
+            color=self.color_for(file=file, err=err_resolved),
             fg="bright_yellow",
         )
 
@@ -193,12 +218,13 @@ def error(
         nl: Optional[bool] = True,
         err: Optional[bool] = True,
     ) -> None:
+        err_resolved = err if err is not None else True
         click.secho(
             f"[ {click.style('ERROR', fg='red')} ] {message() if callable(message) else message}",
             file=file,
             nl=nl if nl is not None else True,
-            err=err if err is not None else True,
-            color=self.colored,
+            err=err_resolved,
+            color=self.color_for(file=file, err=err_resolved),
         )
 
     def print_data(
@@ -267,7 +293,7 @@ def echo(
             message() if callable(message) else message,
             file=file,
             nl=nl,
-            color=self.colored,
+            color=self.color_for(file=file, err=err),
             err=err,
         )
 

src/robotcode/cli/__init__.py

@@ -105,7 +105,10 @@ def __init__(self, *args: Any, defaults: Any = None, **kwargs: Any) -> None:
     "--color / --no-color",
     "color",
     default=None,
-    help="Whether or not to display colored output (default is auto-detection).",
+    help=(
+        "Force or disable colored output. Default (no flag): auto-detect — colors only when stdout is a TTY,"
+        " disabled if `NO_COLOR` is set, forced if `FORCE_COLOR` is set."
+    ),
     show_envvar=True,
 )
 @click.option(