[bob-particular-agent]

Targets report-platform-tool-startup-failure, the branch for #684.

ServiceControl’s stderr handler stays attached while the tool runs, so the captured output can grow for the lifetime of the sample. Keep the most recent 8,192 characters, including line endings, and trim oversized lines before appending them. Synchronize appends and snapshots so reading the startup diagnostic cannot race a background stderr callback.

The change is limited to AppLauncher and an internal BoundedOutput class.

Validation:

• Release solution build and package generation pass with no warnings or errors.
• All three existing active NUnit tests pass on macOS arm64 with clean data and an isolated .NET runtime. The explicit network test remains excluded.
• Local checks exercised multiple error lines, an oversized line, and a real missing-runtime diagnostic. Regression test files are not included in this PR.

[soujay]

• Closing this in favor of Stop capturing platform tool error output after startup #691