v1.16.19

### Added

- **Remote attaches over mosh (opt-in).** Interactive attaches to a remote (Enter in the TUI, the embedded terminal, Shift+Enter and `agent-deck remote attach`) can run over [mosh](https://mosh.org) instead of `ssh -tt`, so typing echoes locally on a high-latency link and the attach survives sleep and network changes. To enable it, set `transport = "mosh"` on the remote in `config.toml` (`[remotes.<name>]`), plus `mosh_server = "/path/to/mosh-server"` when `mosh-server` is not on the remote's non-login SSH PATH. Install `mosh` locally and `mosh-server` on the remote, and allow UDP 60000-61000 to reach it (Tailscale already does). When the remote cannot start `mosh-server`, the attach falls back to `ssh -tt`; listing, previews, sends and every other command stay on SSH. Details: docs/REMOTE-COMMANDS.md (#2375, thanks @c2keesey).
- Claude Opus 5.5 (`claude-opus-5-5`, and `anthropic/claude-opus-5-5` for opencode) and GPT-6 (`gpt-6-astra`, `gpt-6-sol`, `gpt-6-luna` for Codex) are in the model pickers (TUI and web) and `launch -capabilities`. `[claude] default_model = "claude-opus-5-5"` is now honored instead of silently dropped, and Codex sessions accept `--effort max` and `--effort ultra` instead of rejecting them at launch (#2387, thanks @na-bal).

### Fixed

- The web sidebar nests subgroups under their parent group in the same order as the TUI, nests sub-sessions under their parent session, and shares group collapse state with the TUI (#2347, thanks @dbeaudoin).
- Moving a running session to another account slot from the Edit Session dialog no longer silently does nothing on the first try: a background status poll landing while the confirmation was open used to cancel the switch (#2344, thanks @scottyallen).
- A Codex session whose pane still shows earlier text quoting "esc to interrupt" is no longer held busy over a live prompt; only a current Codex status or interrupt line counts as work in progress (#2351, thanks @p4p3r).
- A remote with a large session fleet is no longer reported unreachable when its SSH ControlMaster runs out of channels: a read-only command refused a channel is retried once over a dedicated connection (#2355, thanks @barjatiyasaurabh).

### Internal

- `go.opentelemetry.io/otel/sdk` 1.44.0 -> 1.45.0 (#2376). Dependabot holds `golang.org/x` minor bumps until the Go 1.26 toolchain move (#2390).