docs: close gate 4 — cause=cellless was a probe-label artifact, not a coverage gap

The handoff carried gate 4 as unexercised with an UNESTABLISHED trigger after
route 7 invalidated the unwield-to-3D recipe. That was wrong, and the evidence
was already in the captured logs.

c5-gates.log shows the pickup-then-drop test reaching the teleport arm five
times for the exact guids in the [B.5] pickup lines, every one committed — all
labelled cause=teleport-ts. The classifier predicate is a short-circuit OR
(RuntimeAuthoritativePositionRouteClassifier.cs:391): TryApplyPickup zeroes the
item's cell so `cellless` is genuinely true at the drop, but ACE also advances
TELEPORT_TS, the first operand matches, and the probe reports teleport-ts. The
condition occurs, classifies, and commits correctly; only the label is
shadowed.

So the cell-less path has been exercised in both gate sessions all along. Gate
4 is closed rather than owed, and the successor is no longer sent hunting a
trigger that cannot produce the label.

The general rule is worth more than the finding: a probe that reports which
branch matched inside a short-circuit expression cannot distinguish "this
condition did not occur" from "it occurred but another matched first." A
load-bearing cause label must be computed from the conditions independently,
not from the winning branch. Same family as #319's unfalsifiable gate criterion
filed the same day — both are gates that cannot report the state they exist to
report.

Emitting both operands (cause=teleport-ts+cellless) retires the question, but
that is a probe change and belongs with the probe-family work in C5c.

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

docs/research/2026-08-05-c4-closeout-handoff.md

@@ -439,3 +439,48 @@ trigger was invalidated by route 7 and the replacement is UNESTABLISHED.
   exercised it either way.
 - Per both round-2 reviewers' condition, **this session is explicitly NOT
   scored as covering #318** (the end-to-end presentation composition test).
+
+---
+
+## Gate 4 (`cause=cellless`) — RESOLVED 2026-08-05: it was never a coverage gap
+
+The handoff previously carried gate 4 as "the cell-less half is unexercised,
+and route 7 invalidated its recorded trigger, so the replacement is
+UNESTABLISHED." **That framing was wrong, and the evidence to settle it was
+already in the captured logs.**
+
+`c5-gates.log` shows the user's pickup-then-drop test reaching the teleport arm
+five times, for the exact item guids in the `[B.5] pickup` lines
+(`0x800013B7`, `0x8000A6C6`), every one `hookRan=True placement=Committed` —
+but all labelled `cause=teleport-ts`.
+
+The classifier predicate is a SHORT-CIRCUIT OR
+(`RuntimeAuthoritativePositionRouteClassifier.cs:391`):
+
+```
+if (request.Authority.TeleportAdvanced || cellless)
+```
+
+`TryApplyPickup` zeroes the item's cell, so at the drop's classification
+`cellless` is genuinely TRUE — but ACE also advances TELEPORT_TS on the drop,
+so the FIRST operand matches and the probe reports `teleport-ts`. The
+cell-less condition occurs, classifies correctly, and commits correctly; only
+the probe's cause LABEL is shadowed by operand order.
+
+**Consequence: the cell-less path has been exercised in both gate sessions all
+along.** Gate 4 is closed, not owed. What was actually missing was never
+coverage — it was a probe whose label can be pre-empted by a co-occurring
+condition.
+
+**The general rule, worth more than the finding:** a probe that reports WHICH
+BRANCH MATCHED inside a short-circuit expression cannot distinguish "this
+condition did not occur" from "this condition occurred but another matched
+first." If a cause label is load-bearing for a gate, it must be computed from
+the conditions independently, not from the branch that won. Same family as
+#319's unfalsifiable criterion filed the same day: both are gates that cannot
+report the state they exist to report.
+
+To label it honestly, the probe would evaluate and emit both operands (e.g.
+`cause=teleport-ts+cellless`). Cheap, and it retires this whole question —
+but it is a probe change, so it belongs with the probe-family work in C5c, not
+as an urgent fix.