feat(#2482): bootstrap cross-signing so agent matrix devices show verified

hive-matrix-mcp/src/client.rs

@@ -12,10 +12,15 @@
 //!
 //! E2EE is enabled via `with_encryption_settings(EncryptionSettings::default())`.
 //! Crypto keys are persisted in the sqlite store under `state_dir`
-//! (survives container restarts, lost on `--purge`). Cross-signing and
-//! automatic key backup are deliberately left at their defaults (disabled)
-//! for the first pass: bot accounts authenticated with a static bearer token
-//! can't bootstrap cross-signing without MSC3967 on the server side.
+//! (survives container restarts, lost on `--purge`).
+//!
+//! Cross-signing is bootstrapped best-effort after session restore
+//! (`ensure_cross_signing`) so the agent's device stops showing as
+//! "unverified" in other users' Matrix clients: the in-hive tuwunel accepts
+//! the initial device-signing-key upload on the bearer token alone (no UIAA
+//! re-auth). A homeserver that DID require UIAA just fails the call, which is
+//! swallowed — the session stays exactly as unverified as before. Automatic
+//! key backup is still left at its default (disabled).
 
 use std::path::Path;
 
@@ -204,6 +209,50 @@ async fn whoami(homeserver: &str, token: &str) -> Result<(OwnedUserId, OwnedDevi
     Ok((user_id, device_id))
 }
 
+/// Best-effort: bootstrap this account's cross-signing identity so its
+/// device stops showing as "unverified" in other users' Matrix clients.
+///
+/// `bootstrap_cross_signing_if_needed(None)` is idempotent — it queries the
+/// account's existing keys and only uploads the master / self-signing /
+/// user-signing key set when no cross-signing identity exists yet. That
+/// upload also self-signs the current device, which is what actually clears
+/// the unverified warning. On a restart with the identity already present
+/// it's a no-op.
+///
+/// The `None` is the UIAA auth: the in-hive tuwunel accepts the initial
+/// `device_signing/upload` on the bearer token alone (no interactive
+/// re-auth). If a homeserver required UIAA the call returns a `UiaaResponse`
+/// error we can't satisfy with a bare bearer token — so this is best-effort:
+/// the failure is logged and swallowed, leaving the session no worse off than
+/// before. Never breaks account bring-up.
+///
+/// Known gap (self-verify only): this signs the *current* device against a
+/// freshly-bootstrapped identity. A device re-provisioned under an already
+/// existing identity (new `device_id`, e.g. after a token reissue) would need
+/// the cross-signing secret keys via secret storage to re-sign itself —
+/// tracked as the longer-term mutual-verification follow-up.
+pub async fn ensure_cross_signing(client: &Client, account: &str) {
+    match client
+        .encryption()
+        .bootstrap_cross_signing_if_needed(None)
+        .await
+    {
+        Ok(()) => {
+            tracing::info!(
+                account,
+                "matrix cross-signing ensured (device self-verified)"
+            );
+        }
+        Err(e) => {
+            tracing::warn!(
+                account,
+                error = %format!("{e:#}"),
+                "matrix cross-signing bootstrap failed; session stays unverified (non-fatal)"
+            );
+        }
+    }
+}
+
 /// Best-effort: set this account's matrix avatar from the rasterized icon
 /// PNG. The path comes from `HIVE_ICON_PNG` (a nix-built derivation the
 /// harness forwards into the daemon env; absent when no icon resolves).

hive-matrix-mcp/src/main.rs

@@ -286,6 +286,10 @@ async fn bring_up_account(
     // the live (authenticated, correct-homeserver) Client. Replaces the old
     // curl oneshot; failures are swallowed inside sync_avatar.
     client::sync_avatar(&client, &cfg.state_dir, &cfg.name).await;
+    // Best-effort: bootstrap cross-signing so the account's device isn't
+    // flagged "unverified" in other users' clients. Idempotent + swallows
+    // failures (a UIAA-requiring homeserver) inside ensure_cross_signing.
+    client::ensure_cross_signing(&client, &cfg.name).await;
     timeline::install_message_handler(&client, hyperhive_socket.to_path_buf(), tag.clone());
 
     let sync_client = client.clone();