app: don't report ICMPv6 silence that was never measured

The per-network attribution fix worked — the finding named rmnet_data1
instead of the IPv4-only wifi — and immediately exposed a worse problem
underneath. Cellular's result was `ok: false` because binding a socket to
it failed with EPERM, so no echo request was ever sent; the finding then
reported "IPv6 is configured, but ICMPv6 gets no reply" about a network
the app had never pinged. That is an assertion about the user's carrier
with nothing behind it.

`attempted` now travels beside `ok`, set only once sendto has returned,
and the finding requires both. Failing to bind is a fact about this app's
permissions on this device; it says nothing about the network, and the
two must not share a boolean.

Verified on hardware with a VPN active: every network fails to bind with
EPERM, nothing is sent, and no ICMPv6 finding is emitted — where the
previous build would have blamed the carrier. Recorded in build-status:
Android blocks per-network binding entirely while a VPN holds the default
route, so per-network measurement is unavailable to anyone with one
connected. That needs a deliberate answer rather than a silently green run.

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

docs/build-status.md

@@ -1108,3 +1108,22 @@ when IPv6 works.
 The proper fix is corroboration: attempt a real IPv6 connection and only call it broken when that
 fails too. That needs a target, which runs into the hardcoded-reference-deployment issue already
 open above. **Both remain open.**
+
+## Per-network probing is blocked while a VPN is up (2026-08-01)
+
+`Network.bindSocket()` fails with `EPERM` for every underlying network when a VPN holds the
+default route — verified on the OnePlus 15 with Netbird active: `Binding socket to network 101
+failed: EPERM` for both cellular and wifi. This is Android preventing VPN leaks, not a bug to work
+around, and it means the whole per-network measurement approach is unavailable to any user with a
+VPN connected. Worth deciding deliberately rather than discovering per report:
+
+- The run currently succeeds and simply measures nothing per network. Honest, but silent — the
+  document records `attempted: false` and the UI says green.
+- A user with a corporate VPN permanently on would get a green run that measured almost nothing.
+
+Options are to detect the VPN and say so plainly ("this network cannot be measured while a VPN is
+active"), to measure the tunnel itself as the network under test, or both. Not yet decided.
+
+Related: `icmp.ping6` now records `attempted` alongside `ok` per network, because collapsing them
+made the app report "IPv6 is configured, but ICMPv6 gets no reply" about an interface it had never
+succeeded in sending on — a claim about the user's carrier with no evidence behind it.