docs: rework Phase 12 — hub minimization deferred by operator decision

Operator decisions (tmp-decisions.md D1/D2/D4):
  - the hub keeps serving the web UI (zero-install path stays)
  - a native desktop client is offered ALONGSIDE it, not as a replacement
  - hub minimization is off the critical path and may be dropped

Phase 12 was "Hub minimization: registrar and nothing more". Most of it is
dropped: route-inventory blindness test, opaque private-group metadata,
chat_notify metadata minimization, residual schema cleanup. The swarm item
already shipped in 11.5.18.

Two items are kept, because the decision makes them more relevant rather than
less — the hub stays in the trusted path by choice, so what it can substitute
and what code it serves both still matter:

  12.1 key transparency + safety numbers [H3]. This is the last open High
       finding and nothing else fixes it: the hub is the public key directory,
       so substituting a key during an invite hands it the group key silently,
       with no JWT forgery and no code injection. Dropping Phase 12 wholesale
       would have left it open indefinitely.
  12.2 served-SPA integrity: CSP, SRI, and a hub-published signed digest of the
       bundle so a native client can verify what the browser was given.
  12.3 honest labelling of /app/ as the hub-served path.
  12.4 written threat model — the thing that stops the overclaiming pattern.

Recorded consequence: T3 is now accepted permanently for browser users. A hub
that serves the code can exfiltrate keys from the page whatever the protocol
does. The claim that still holds, and that the docs should make, is "the hub
cannot read your content unless it actively attacks you" — not "unreadable by
other parties, even the hub".

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

1 files changed, 33 insertions, 15 deletions

diff --git a/tmp-decisions.md b/tmp-decisions.md
index 97a27ea..347d771 100644
--- a/tmp-decisions.md
+++ b/tmp-decisions.md
@@ -1,7 +1,8 @@
-# Open decisions — client architecture
+# Client architecture — decisions
 
-> Working note, not a spec. Created 2026-08-13 after the second security review.
-> Delete or fold into `docs/meshbay-draft-v5.md` once decided.
+> Created 2026-08-13 after the second security review. D1/D2/D3 decided the same day;
+> D4 (hub minimization) deferred. Fold into `docs/meshbay-draft-v5.md`.
+> The analysis below is kept as the rationale behind the decisions, not as open questions.
 
 ---
 
@@ -9,18 +10,35 @@
 
 | # | Decision | State |
 |---|---|---|
-| D1 | Does the hub keep serving the web UI? | **Open** — leaning yes |
-| D2 | Browser extension, native desktop client, or both? | **Open** — needs time |
+| D1 | Does the hub keep serving the web UI? | ✅ **DECIDED 2026-08-13 — yes** |
+| D2 | Browser extension, native desktop client, or both? | ✅ **DECIDED 2026-08-13 — native client, offered alongside the hub-served SPA** |
 | D3 | Transport: aiortc primary, QUIC at parity, TCP+HTTP removed | ✅ Decided 2026-08-13 |
+| D4 | Hub minimization (old Phase 12) | ⏸️ **Deferred, may be dropped** |
 
-**Neither D1 nor D2 blocks anything right now.** Phase 11.5 (security remediation),
-Phase 12 (hub minimization), Phase 14 (node CLI) and Phase 15 (Sender Keys) are entirely
-client-agnostic — every finding they close is node-side or hub-side. Phase 11.5 is in
-progress on that basis.
+**What was decided.** The hub keeps serving the web UI — that is the zero-install path
+and it stays. A native desktop client is offered *in addition*, not as a replacement.
+Hub minimization is off the critical path and may be dropped entirely.
 
----
+**What that means, stated once and then respected.** Keeping the hub in the trusted path
+is a legitimate product call, and this project is not obliged to defend against its own
+operator. But two consequences should be carried deliberately rather than by accident:
+
+1. **T3 is accepted permanently for browser users.** A hub that serves the code can
+   exfiltrate keys from the page regardless of what the protocol does. The native client
+   gives users who care an alternative; browser users are trusting meshbay.org, and the
+   docs should say so plainly rather than claiming end-to-end integrity.
+2. **H3 was the last open High finding and its only fix lived in the dropped phase.**
+   The hub is the public key directory: substituting a key during an invite hands it the
+   group key, silently, with no forgery and no code injection. So key transparency and
+   safety numbers were kept and are now Phase 12.1 — everything else from hub
+   minimization is dropped. If Phase 12 is later dropped too, H3 stays open by choice,
+   and "unreadable by other parties, even the hub" stops being a claim the project can
+   make about an adversarial hub.
+
+The honest framing that survives all of this: **the hub cannot read your content unless
+it actively attacks you.** That is still a strong property, and it is defensible.
 
-## Why these are open
+## Rationale — why the native client is not a T3 fix
 
 The second review recommended a native client and claimed *"T3 disappears — code integrity
 stops depending on the hub."* **That claim was wrong and has been corrected** in
@@ -52,12 +70,12 @@ It should not be justified as the fix for T3 unless 18.7 ships with it.
 
 ---
 
-## D1 — Should the hub keep serving the UI?
+## D1 rationale — hub keeps serving the UI ✅
 
 Keeping it is defensible. It is how anyone tries the platform without installing anything,
 and it stays the fallback when a device has no client installed.
 
-What must be true if it stays (all already scheduled in Phase 12.6):
+What must be true now that it stays (Phase 12.2/12.3):
 
 - strict CSP and Subresource Integrity on the bundle
 - the hub publishes a **signed digest** of the served bundle, so any third party — an
@@ -69,7 +87,7 @@ The honest framing: hub-served SPA is a **convenience tier**, not the secure tie
 
 ---
 
-## D2 — Extension vs native: what each actually covers
+## D2 rationale — native chosen; extension not taken up
 
 Three shapes, cheapest first:
 
@@ -85,7 +103,7 @@ hub operator does not control**. Manifest V3 forbids remote code, which works in
 the structure enforces exactly what we want. Keys live in extension storage, isolated from
 page JS. Moderate effort.
 
-**Option C — Native desktop client (pywebview + aiortc)**
+**Option C — Native desktop client (pywebview + aiortc)** ← **CHOSEN**
 Phase 13. Full control, durable keys in an OS keystore, QUIC, hub-less access, best UX.
 Highest effort, and the security argument depends on 18.7.