step 3/4: sidecar routing keys become handles — NOT YET VERIFIED LIVE

Committed before restarting, deliberately: this changes the registration wire,
and the restart that proves it also bounces officer-claude-code, which is what
the session doing the work runs on. An uncommitted 25-file protocol change is
worse to inherit than one marked unverified.

`capabilities: ['music']` → `handles: ['music']` on the registration message,
across 20 sidecars, both plugins, the connector, the registry and the protocol
type. findSidecarByCapability → findSidecarHandling, waitForCapability →
waitForHandler.

The name: a sidecar already has `handleCommand`, so the list is literally what
it handles. `provider` was rejected — 390 existing uses and it already means
websocket door. `serves` was rejected — collides with HTTP serving, which
sidecars also do.

THIS IS A BREAKING WIRE CHANGE with no compatibility shim. A platform expecting
`handles` reads `undefined` from a sidecar sending `capabilities`, registers it
with an empty list, and every sendCommand finds nobody — chat, terminal and
music all fail with "No sidecar handling X is connected". So the whole estate
has to restart together; there is no rolling upgrade.

If it goes wrong: `git revert HEAD` and `pm2 restart all` again. The registry is
in-memory and nothing about this touches the database, so a revert is complete.

Found a fifth meaning of the word on the way, correctly named and untouched:
the pty sidecar's terminfo capability queries (XTGETTCAP escape sequences).
That is now five — permissions, the item store, routing keys, Lightning wallet
features, and terminfo.

tsgo clean, 797 tests, 787 pass, same 7. Not exercised against a live sidecar.

plugins/music/sidecar/index.ts

@@ -474,7 +474,7 @@ function handleCommand(cmd: SidecarCommand, reply: ReplyFn) {
 const connection = createSidecarConnector({
   apiUrl: `${API_URL}/api/sidecar/register`,
   name: 'music',
-  capabilities: ['music'],
+  handles: ['music'],
   onCommand(cmd, reply) {
     handleCommand(cmd as SidecarCommand, reply as ReplyFn);
   },

plugins/offscale/sidecar/index.ts

@@ -121,7 +121,7 @@ function handleCommand(cmd: SidecarCommand, reply: ReplyFn) {
 const connection = createSidecarConnector({
   apiUrl: `${API_URL}/api/sidecar/register`,
   name: 'headscale',
-  capabilities: ['headscale'],
+  handles: ['headscale'],
   onCommand(cmd, reply) {
     handleCommand(cmd as SidecarCommand, reply as ReplyFn);
   },