fix(worker): seed planning brief via file to avoid newline truncation

tests/ClaudeDo.Worker.Tests/Planning/WindowsTerminalLauncherTests.cs

@@ -45,4 +45,28 @@ public sealed class WindowsTerminalLauncherTests
             sut.LaunchPlanningStartAsync(ctx, CancellationToken.None));
         Assert.Contains("Windows Terminal", ex.Message);
     }
+
+    [Fact]
+    public void BuildPlanningStartCommand_SeedsViaBriefFile_NotInlineText()
+    {
+        var ctx = MakeStartCtx();
+
+        var command = WindowsTerminalLauncher.BuildPlanningStartCommand("claude.exe", ctx);
+
+        // The brief is read from a file: the kickoff references the brief path, and its
+        // directory is exposed via --add-dir so the Read tool can open it.
+        Assert.Contains(ctx.Files.InitialPromptPath, command);
+        Assert.Contains($"--add-dir' '{ctx.Files.SessionDirectory}", command);
+
+        // The positional kickoff must follow the single-value --append-system-prompt-file
+        // flag, or a preceding variadic flag would swallow it.
+        var appendIdx = command.IndexOf("--append-system-prompt-file", StringComparison.Ordinal);
+        var addDirIdx = command.IndexOf("--add-dir", StringComparison.Ordinal);
+        Assert.True(appendIdx > addDirIdx, "--append-system-prompt-file must come after --add-dir");
+        Assert.True(command.IndexOf(ctx.Files.InitialPromptPath, StringComparison.Ordinal) > appendIdx,
+            "the kickoff prompt must be the last (positional) token");
+
+        // The legacy env-var indirection is gone.
+        Assert.DoesNotContain("CLAUDEDO_LAUNCH_PROMPT", command);
+    }
 }