feat(CF-2502): proper E2E encryption with cross-signing and device lifecycle
Replace insecure auto-trust-all-devices with cross-signed-only trust policy. Extract cross-signing manager into reusable module with vault backup/recovery. Add device cleanup script and automatic old device pruning on startup. - device_trust.py: CrossSignedOnlyPolicy (only trust cross-signed devices) - cross_signing.py: Extracted from bot.py, adds vault seed backup + recovery - scripts/matrix_device_cleanup.py: Synapse Admin API bulk device cleanup CLI - bot.py: Use new modules, add _cleanup_own_devices() on startup Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
This commit is contained in:
Christian Gick
170
bot.py
170
bot.py
@@ -45,6 +45,8 @@ from livekit import api, rtc
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from voice import VoiceSession
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from article_summary import ArticleSummaryHandler
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from cron import CronScheduler
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from device_trust import CrossSignedOnlyPolicy
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from cross_signing import CrossSigningManager
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BOT_DEVICE_ID = "AIBOT"
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CALL_MEMBER_TYPE = "org.matrix.msc3401.call.member"
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@@ -1203,6 +1205,11 @@ class Bot:
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self._loaded_rooms: set[str] = set() # rooms where we've loaded state
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self._sync_token_received = False
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self._verifications: dict[str, dict] = {} # txn_id -> verification state
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self.trust_policy = CrossSignedOnlyPolicy()
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self.cross_signing = CrossSigningManager(
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HOMESERVER, STORE_PATH, BOT_PASS,
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vault_key=f"matrix.{BOT_USER.split(':')[0].lstrip('@')}.cross_signing_seeds",
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)
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self._room_document_context: dict[str, list[dict]] = {} # room_id -> [{type, filename, text, timestamp}, ...]
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# Article summary handler (Blinkist-style audio summaries)
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if self.llm and ELEVENLABS_API_KEY:
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@@ -1298,7 +1305,14 @@ class Bot:
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await self.client.keys_upload()
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# Bootstrap cross-signing if not already done
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await self._ensure_cross_signing()
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with open(CREDS_FILE) as f:
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creds = json.load(f)
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await self.cross_signing.ensure_cross_signing(
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creds["user_id"], creds["device_id"], creds["access_token"],
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)
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# Clean up own old devices (keep max 3, older than 30 days)
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await self._cleanup_own_devices(creds["device_id"], creds["access_token"])
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self.lkapi = api.LiveKitAPI(LK_URL, LK_KEY, LK_SECRET)
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self.client.add_event_callback(self.on_invite, InviteMemberEvent)
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@@ -1335,132 +1349,57 @@ class Bot:
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await self.client.sync_forever(timeout=30000, full_state=True)
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async def _ensure_cross_signing(self):
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"""Ensure bot device is cross-signed so Element clients don't show authenticity warnings."""
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xsign_file = os.path.join(STORE_PATH, "cross_signing_keys.json")
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with open(CREDS_FILE) as f:
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creds = json.load(f)
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user_id = creds["user_id"]
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device_id = creds["device_id"]
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token = creds["access_token"]
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headers = {"Authorization": f"Bearer {token}"}
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# Check if device already has a cross-signing signature on the server
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async def _cleanup_own_devices(self, current_device_id: str, access_token: str, keep: int = 3, max_age_days: int = 30):
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"""Remove own old devices via client API (no admin required)."""
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headers = {"Authorization": f"Bearer {access_token}"}
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try:
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async with httpx.AsyncClient(timeout=15.0) as hc:
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resp = await hc.post(
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f"{HOMESERVER}/_matrix/client/v3/keys/query",
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json={"device_keys": {user_id: [device_id]}},
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headers=headers,
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)
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if resp.status_code == 200:
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device_keys = resp.json().get("device_keys", {}).get(user_id, {}).get(device_id, {})
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sigs = device_keys.get("signatures", {}).get(user_id, {})
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device_key_id = f"ed25519:{device_id}"
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has_cross_sig = any(k != device_key_id for k in sigs)
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if has_cross_sig:
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logger.info("Device %s already cross-signed, skipping bootstrap", device_id)
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return
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except Exception as e:
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logger.warning("Cross-signing check failed: %s", e)
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resp = await hc.get(f"{HOMESERVER}/_matrix/client/v3/devices", headers=headers)
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if resp.status_code != 200:
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logger.warning("Device list failed: %d", resp.status_code)
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return
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# Load existing seeds or generate new ones
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if os.path.exists(xsign_file):
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with open(xsign_file) as f:
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seeds = json.load(f)
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master_seed = base64.b64decode(seeds["master_seed"])
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ss_seed = base64.b64decode(seeds["self_signing_seed"])
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us_seed = base64.b64decode(seeds["user_signing_seed"])
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logger.info("Loaded existing cross-signing seeds, re-signing device")
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else:
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master_seed = os.urandom(32)
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ss_seed = os.urandom(32)
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us_seed = os.urandom(32)
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logger.info("Generating new cross-signing keys")
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devices = resp.json().get("devices", [])
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if len(devices) <= keep:
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return
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master_key = olm.pk.PkSigning(master_seed)
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self_signing_key = olm.pk.PkSigning(ss_seed)
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user_signing_key = olm.pk.PkSigning(us_seed)
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# Sort by last_seen_ts descending
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devices.sort(key=lambda d: d.get("last_seen_ts") or 0, reverse=True)
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def make_key(usage, pubkey):
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return {
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"user_id": user_id,
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"usage": [usage],
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"keys": {"ed25519:" + pubkey: pubkey},
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}
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now_ms = time.time() * 1000
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to_delete = []
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for i, dev in enumerate(devices):
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if dev["device_id"] == current_device_id:
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continue
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if i < keep:
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continue
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last_seen = dev.get("last_seen_ts") or 0
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if last_seen > 0 and (now_ms - last_seen) < max_age_days * 86400 * 1000:
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continue
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to_delete.append(dev["device_id"])
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master_obj = make_key("master", master_key.public_key)
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ss_obj = make_key("self_signing", self_signing_key.public_key)
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us_obj = make_key("user_signing", user_signing_key.public_key)
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if not to_delete:
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return
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# Sign sub-keys with master key
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ss_canonical = canonicaljson.encode_canonical_json(ss_obj)
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ss_obj["signatures"] = {user_id: {"ed25519:" + master_key.public_key: master_key.sign(ss_canonical)}}
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us_canonical = canonicaljson.encode_canonical_json(us_obj)
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us_obj["signatures"] = {user_id: {"ed25519:" + master_key.public_key: master_key.sign(us_canonical)}}
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try:
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async with httpx.AsyncClient(timeout=15.0) as hc:
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# Upload cross-signing keys with password auth
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resp = await hc.post(
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f"{HOMESERVER}/_matrix/client/v3/keys/device_signing/upload",
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# Bulk delete own devices (requires password re-auth)
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del_resp = await hc.post(
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f"{HOMESERVER}/_matrix/client/v3/delete_devices",
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json={
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"master_key": master_obj,
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"self_signing_key": ss_obj,
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"user_signing_key": us_obj,
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"devices": to_delete,
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"auth": {
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"type": "m.login.password",
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"identifier": {"type": "m.id.user", "user": user_id},
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"identifier": {"type": "m.id.user", "user": BOT_USER},
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"password": BOT_PASS,
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},
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},
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headers=headers,
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)
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if resp.status_code != 200:
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logger.error("Cross-signing upload failed: %d %s", resp.status_code, resp.text)
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return
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logger.info("Cross-signing keys uploaded")
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# Fetch device keys to sign
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qresp = await hc.post(
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f"{HOMESERVER}/_matrix/client/v3/keys/query",
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json={"device_keys": {user_id: [device_id]}},
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headers=headers,
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)
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device_obj = qresp.json()["device_keys"][user_id][device_id]
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device_obj.pop("signatures", None)
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device_obj.pop("unsigned", None)
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# Sign device with self-signing key
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dk_canonical = canonicaljson.encode_canonical_json(device_obj)
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dk_sig = self_signing_key.sign(dk_canonical)
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device_obj["signatures"] = {user_id: {"ed25519:" + self_signing_key.public_key: dk_sig}}
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resp2 = await hc.post(
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f"{HOMESERVER}/_matrix/client/v3/keys/signatures/upload",
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json={user_id: {device_id: device_obj}},
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headers=headers,
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)
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if resp2.status_code != 200:
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logger.error("Device signature upload failed: %d %s", resp2.status_code, resp2.text)
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return
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logger.info("Device %s cross-signed successfully", device_id)
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if del_resp.status_code == 200:
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logger.info("Cleaned up %d old devices (kept %d)", len(to_delete), keep)
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else:
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logger.warning("Device cleanup failed: %d %s", del_resp.status_code, del_resp.text)
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except Exception as e:
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logger.error("Cross-signing bootstrap failed: %s", e, exc_info=True)
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return
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# Save seeds if new
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if not os.path.exists(xsign_file):
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with open(xsign_file, "w") as f:
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json.dump({
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"master_seed": base64.b64encode(master_seed).decode(),
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"self_signing_seed": base64.b64encode(ss_seed).decode(),
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"user_signing_seed": base64.b64encode(us_seed).decode(),
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}, f)
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logger.info("Cross-signing seeds saved to %s", xsign_file)
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logger.warning("Device cleanup error (non-fatal): %s", e)
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async def _inject_rag_key(self):
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"""Load document encryption key from Matrix and inject into RAG service."""
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@@ -1502,7 +1441,7 @@ class Bot:
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await self.client.join(room.room_id)
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async def on_sync(self, response: SyncResponse):
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"""After each sync, trust all devices in our rooms."""
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"""After each sync, trust cross-signed devices only."""
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if not self._sync_token_received:
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self._sync_token_received = True
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logger.info("Initial sync complete, text handler active")
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@@ -1511,8 +1450,11 @@ class Bot:
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for user_id in list(self.client.device_store.users):
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for device in self.client.device_store.active_user_devices(user_id):
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if not device.verified:
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self.client.verify_device(device)
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logger.info("Auto-trusted device %s of %s", device.device_id, user_id)
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if self.trust_policy.should_trust(user_id, device):
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self.client.verify_device(device)
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logger.info("Cross-sign-verified device %s of %s", device.device_id, user_id)
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else:
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logger.debug("Skipped unverified device %s of %s (no cross-signing sig)", device.device_id, user_id)
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async def on_reaction(self, room, event: ReactionEvent):
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"""Handle reaction events for pipeline approval flow."""
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