agents: correct "both clocks" -- there is ONE, and F4 tests whether it is right

I wrote "whether the game snaps both clocks forward" into yesterday's F4 and the
human asked which clocks. There are none: authored/flow.json sets
`clock: "shared"`, so the title's two composited builds -- build 4 the artwork
(finishes t~=118) and build 2/3 the plate (full alpha t=236) -- run on ONE clock
started together. Left standing, that phrasing sends an agent hunting for a
second clock this corpus says does not exist.

Corrected in both briefs and in the playtest page, marked as a correction rather
than silently edited.

And the question is better than I first framed it. `clock: "shared"` is
AUTHORED, and the port's own plate-arrival-halves.md calls it "not falsified...
not confirmed to better than ~20 % either", with an unresolved anchor
disagreement inside one binary: the reconciliation picked t=118 while
settle_time() returns 160 and the boot prints "settles at t=160".

So F4 is a TEST OF THAT PREMISE, and the discriminator is observable -- press (A)
early, while the wordmark is still building in, and watch the ARTWORK rather
than the plate:

  advances the shared clock   -> the artwork SNAPS to finished
  only forces the plate       -> the artwork KEEPS ANIMATING its build-in

Both briefs now say to answer F4 before building on `shared`, and tell the port
not to choose what "jump" means.

docs/agents/port-loop.md

@@ -32,7 +32,7 @@ difficulty select comes first in the real game and that the port announces it.
 | **F1** | **The menu REPEATS on a held direction. Ours does not.** One step per deflection was authored as the safe choice; the human has now watched the real game and it repeats. | **Implement the mechanism. Take the RATE from the Decoder — do NOT ship a placeholder interval.** An invented rate here is indistinguishable from a measured one later, and this is the exact field where that already cost us. |
 | **F2** | **SFX too loud, and there is no mix at all.** Measured: `confirm` −17.7 dB mean / **−0.0 dB peak**, 3 dB hotter than the music; no gain value exists anywhere in `export/` or `authored/`. | Add gains **at playback, as data** — a bus per kind. ⚠️ **Do NOT normalise in the exporter**: re-levelling destroys the relationship between clips and a modder cannot undo it. The Decoder is checking whether the mix is on the disc. |
 | **F3** | **Something is missing on the title screen** — a track or a sting. The export has one music file and the port plays nothing on the title. | Wait for the Decoder; nothing to author yet. |
-| **F4** | **Ⓐ skips FORWARD through the boot, and we implement two of three presses.** Ⓐ#1 skips the video ✅, **Ⓐ#2 reveals the plate immediately ❌ missing**, Ⓐ#3 activates it ✅. | Make Ⓐ during the title build-in jump to the plate. ⚠️ Whether the game snaps **both** clocks forward or only reveals the plate is a question — ask rather than choose. |
+| **F4** | **Ⓐ skips FORWARD through the boot, and we implement two of three presses.** Ⓐ#1 skips the video ✅, **Ⓐ#2 reveals the plate immediately ❌ missing**, Ⓐ#3 activates it ✅. | Make Ⓐ during the title build-in jump to the plate — but **do not choose what "jump" means.** 🔴 It is a **test of `clock: "shared"`**, which is authored and, in your own words, *"not confirmed to better than ~20 %"*. If Ⓐ advances the shared clock the artwork **snaps**; if it only forces the plate visible the artwork **keeps animating**. Those look different on an early press, so the oracle can settle it. **Answer it before building on `shared`.** (Correction: an earlier draft of this brief said "both clocks" — there is only ONE, and hunting for a second would waste an iteration.) |
 
 **H3, the plate delay, is ACCEPTED** — *"feels the same… sufficient"*. Stop
 working on it. Leave the row unattributed rather than closing it green.