port: end the boot when BOTH builds have arrived, not when the plate lands

Moving the plate onto the shared clock moved the boot's exit with it: the run
quit at the overlay's settle (t=238) while build 4's own fade-in from black runs
to t=261. pteff00 is still ~7 % opaque there, so the capture came out visibly
darker than the previous one -- with nothing failing, no warning, and no line in
the log to say why. Caught only because there was an earlier capture beside it.

The boot now ends at max(view.settle_time(), overlay.settle_time()) and prints
the unit it is waiting for.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WM5XL4HfrHuxz8RiMWdCMC

docs/port/DECISIONS.md

@@ -1901,3 +1901,26 @@ declared 120 units at 60 units/s = **2.000 s of port time**, which is the
 true-30 Hz value both readings agree the disc means. This is a corpus
 consistency problem, not a port one — which is why it is filed rather than
 worked around.
+
+### The corrected boot ended one build too early, and the capture showed it
+
+Moving the plate onto the shared clock also moved the boot's exit, and the first
+capture taken afterwards was **visibly darker** than the one before it. The cause
+is `pteff00`, the title's black fade quad: it ramps `0xff000000` → `0x00000000`
+over t=16…261, so at t=243 — where the run was quitting, `overlay.settle_time()`
+after the overlay was raised — the frame is still ~7 % black.
+
+The plate arrives at t=238; **build 4 is not finished until t=261**. The boot now
+ends at the later of the two, and says which in the log:
+
+```
+  -> title at 145.79 s
+  overlay press_start raised at 145.79 s, 1 element(s), settles at t=238
+  boot ends at 150.14 s, once both builds have arrived (t=261)
+```
+
+Worth recording because of how it presented: nothing failed, no warning was
+printed, and the only symptom was a frame slightly darker than the previous
+run's. A gate artifact that silently drifts is the failure mode this project
+keeps meeting — and it was caught only because there was a previous capture to
+compare against.