adr: +0009 spend-gate rescope +0010 spearhead 4.5 benchmark/sim; amend 0004

Maintainer-ratified from the 2026-07-03 review (R1-R3):
- ADR-0009: retire "structurally impossible for a 3-vendor stack" post-0007;
  restate the gate's true guarantees (credential isolation, unskippable
  mediation, media-plane enforcement, audit co-location). Propagated to
  README pillar 3, ARCHITECTURE, PORT_PLAN s10; amendment note on ADR-0002.
- ADR-0010: insert step 4.5 (benchmark + simulation harness, rutster-sim
  seed, CI-regressed p50/p99 + kill-time) after barge-in; pull rung-2
  escalation ahead of steps 5-6. Spearhead lists updated.
- ADR-0004: delete the legally-broken AGPL escape hatch; GPL-3.0-or-later
  permanent, no CLA; tap protocol/SDKs intended permissive (future ADR).
- README: add brain-vendor-direct competitor row (review D2).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018vNe64BBDkgo5oQVkBa3XF

docs/ARCHITECTURE.md

@@ -84,8 +84,11 @@ trusted, battle-tested OSS kept outside the boundary** — not an over-claim tha
   REST/gRPC + a WebSocket/SSE event stream. "The dialplan" disappears — replaced by declarative
   routing + external services reacting to call events (the ARI/Stasis model).
 - **In-boundary spend / abuse gate** — spend caps, pacing caps, deny-by-default routing,
-  rate-limits, toll-fraud pattern detection. **Co-located with trunk termination** so a runaway
-  brain structurally cannot exceed spend or pacing — it doesn't hold the wire.
+  rate-limits, toll-fraud pattern detection. **Co-located with the tap + the provider
+  call-control client**: the brain never holds provider credentials, so every brain-initiated
+  action passes the gate; pacing/half-duplex/playout are enforced over media the core terminates
+  ([ADR-0009](adr/0009-spend-gate-honest-rescope.md) — pair with provider-side caps for defense
+  in depth).
 - **Audiohook primitive** — tap/inject/volume behind recording, ChanSpy/whisper/barge, and
   human-agent escalation (rung 2: an agent takes over a call via WebRTC + audiohook handoff).