feat(client): hybrid sign-in — passphrase once, then this device's key

D4. The passphrase stays the account's credential and its only recovery path;
what changes is that it is not asked for on every launch.

**The renderer never holds the device key.** It is generated, stored and used
entirely in the main process, which signs `meshbay:user_auth:<username>:<ts>` on
request. Same rule as the save dialog, for the same reason: the renderer is the
part of this application that parses decrypted content from nodes, which is
attacker-controlled input. And this key is *not* a per-node identity key — those
are generated per node and never leave that relationship, so nothing here
correlates a person across operators.

First run asks which hub, with no default. A client that picks its own hub is a
client that can be pointed at one, and the address is the whole of what this
application trusts a hub for — the interface comes from the package.

Verified against a hub running this code, not against the deployed one:
register 201 → passphrase login 200 → device register 201 → **device sign-in 200
with a real session** → `/v1/users/me` 200 → a stranger's key 401. The
signature was also checked directly against the hub's own Python verifier before
any of that.

Inside the running application, over the debugging protocol: the bridge reaches
the main process, the renderer calls the hub **through it** (200 — the CORS fix
working end to end), and a call to a host that is not the configured hub is
refused.

**Not verified:** safeStorage persisting the key. This session has no secret
service, and standing one up in xvfb did not succeed. The application behaves
correctly there — it *refuses* rather than storing unprotected, and now says so
in Settings, which is a real case rather than a hypothetical one since it is
exactly what a headless or minimal desktop looks like.

Worth remembering for next time: meshbay.org runs whatever was last deployed. It
answered 405 on the Stage-C endpoints and reported MNP 0.2 while the tree had
0.3, so a local `uvicorn meshbay_hub.app:create_app --factory` on SQLite is what
tests hub changes. Nothing was deployed to production for this.

799 tests pass; e2e.py passes end to end.

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

1 files changed, 13 insertions, 0 deletions

diff --git a/CLAUDE.md b/CLAUDE.md
index 880756e..61d8e96 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -369,6 +369,19 @@ anything that assumes one key per person.
   directives, not text — the same mistake as reading a CSP out of the comment
   above the meta tag
 
+- **The device's hub key lives in the main process, never in the renderer.**
+  Generated, stored and used there; the interface asks for a signature over
+  `meshbay:user_auth:<username>:<ts>` and is never handed a key. Same rule as
+  the save dialog, for the same reason: the renderer parses decrypted content
+  from nodes, which is attacker-controlled input. It is **not** a per-node
+  identity key — nothing here correlates a person across operators
+
+- **A local hub is the way to test hub changes.** `uvicorn meshbay_hub.app:create_app
+  --factory` with a SQLite URL and a throwaway key runs the current code on
+  loopback in seconds. meshbay.org runs whatever was last deployed — it reported
+  MNP 0.2 and 405 on the Stage-C endpoints while the tree had 0.3 — so testing
+  against it proves what is deployed, not what is written
+
 ## Two lessons that cost four rounds of live testing
 
 - **`QE/deploy/e2e.py` cannot test `app.js`.** It is a second implementation of the