docs: record F11-1 closed — boundedness needs a resolved Client

Design v3.7 §6.1.1 gains the round-13 box (the rule, the ordering that is
load-bearing in both directions, and why bridging deliberately still uses the
full union); the phase-5 results file records the close with the measurement
the deferral was waiting for; the impl plan's phase-6 gate note drops F11-1.

pixelpass c78eb2d is the implementation.

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

docs/screenshare-audio-exclusion-impl-plan.md

@@ -472,9 +472,10 @@ observable in Phase 5 before they gate anything real.
 > **The eligible half of row 1 is the only thing that exposed it** — the verdict was
 > fail-closed and silent.
 >
-> ⚠️ **Phase 6 is NOT unblocked by this file alone.** F11-1 is a separate open gate (see §4's
-> owner-union note and `owner_is_bounded`'s doc), as are phases 0b/0c/0d and the "Stereo Mix"
-> design call.
+> ⚠️ **Phase 6 is NOT unblocked by this file alone.** F11-1 was the other gate and is now
+> **closed** (2026-07-26, pixelpass `c78eb2d`: key 4 bounds an owner only when the node's
+> Client resolves; measured cost on the live graph, zero — see the results file). Phases
+> 0b/0c/0d and the "Stereo Mix" design call still precede phase 6.
 >
 > Two things to keep when re-running: **every partition row must run with `AEC=off`** (a
 > configured-but-unvalidated AEC shuts the fan-out gate and empties the eligible half of every