PHLEGM v8 compiler countdown ETA - checkpoint 26

When a previous successful duration is available and the immediately preceding build did not fail, the running Compiler UI shows a live ETA in minutes:seconds.milliseconds format (nn:ss.fff) instead of elapsed time.
Example: Last good 00:02:22 · ETA: 01:12.345
The ETA counts down using actual time since build start and clamps at 00:00.000 if the current build exceeds the last good duration; it never shows a negative estimate or falsely marks the build complete.
The progress percentage remains animated and does not reach 100.000% until confirmed success.
Unknown-duration builds continue to display elapsed time. Completion/failure/cancellation messages continue to display actual elapsed time.
No Python dependencies or scripts are included in the distribution.
