The marker stops lying, and the rule announces itself

"the marker flips all the time even during a ball being midair.. i am not
sure that a player would get the mechanic intuitively let alone without the
marker".

The flip had a specific cause and it was a design bug, not jitter. With lanes
held and speeds constant, arrival differences never change while bodies walk
— the queue only reorders on a kill or an arrival. The marker flipped because
it showed only q[0] while the rule accepts any near-tie within the slack:
every kill made it jump between tied bodies, so the marker was stricter than
the rule it was explaining. drillLegal() marks the whole slack set now,
bright head and dim ties, which is stable by construction. Measured: zero
head-changes across 12s of walking with no kills.

Learnability, two answers. The rule gets one modal, once per run, on the
mode's own calm court — CLEARANCE DRILL / DROP WHOEVER WOULD REACH YOU FIRST
/ FAST BEATS CLOSE / STREAKS PAY — because "most urgent first" is not
guessable from a chevron alone. And the markers are training wheels that take
themselves off: hidden at streak >= 8 (the streak is the evidence you can
read the court), back on any fault. The teacher steps in exactly when you
demonstrably need it.

31 tests, 15 seeds clean.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

PROJECT.md

@@ -794,6 +794,28 @@ check the game's read against his own — and it answers the exact question the
 be off in anything shipped. If his read and the marker disagree often, tune `drillSlack` before
 touching `arrival`.
 
+**TWELFTH PASS — the marker stops lying, and the rule announces itself.** Oliver: *"the marker
+flips all the time even during a ball being midair.. i am not sure that a player would get the
+mechanic intuitively let alone without the marker"*.
+
+**The flip had a specific cause and it was a design bug, not jitter**: with lanes held and speeds
+constant, arrival DIFFERENCES never change while bodies walk — the queue only reorders on a kill or
+an arrival. So the marker was flipping because it showed ONLY `q[0]` while the rule accepts any
+near-tie within the slack: every kill made it jump between tied bodies, i.e. **the marker was
+stricter than the rule it was explaining**. `drillLegal()` now marks the whole slack set — bright
+head, dim ties — which is stable by construction. Measured: zero head-changes across 12 s of
+walking with no kills.
+
+**Learnability, two answers:**
+- the rule gets ONE modal, once per run, on the mode's own calm court (the seeded bodies are all at
+  the far baseline — this is the popup policy's sanctioned case): *CLEARANCE DRILL — DROP WHOEVER
+  WOULD REACH YOU FIRST · FAST BEATS CLOSE · STREAKS PAY*. "Most urgent first" is not guessable
+  from a chevron alone; one sentence makes it learnable in the first five seconds.
+- **the markers are training wheels that take themselves off**: they hide at streak >=
+  `drillMarkOff` (8) — the streak IS the evidence you can read the court — and any fault brings
+  them back. The teacher steps in exactly when you demonstrably need it and out when you don't,
+  and `drillMark: 0` still kills them outright.
+
 **Open, and every one of them is Oliver's call after he plays it:**
 1. ~~**A ball that carries through the lane can complete two steps at once.**~~ Largely CLOSED by
    the slice removal (seventh pass) — a cut ball picking its own next victim was the main way this