feat(daemon): implement CustomPaneBackend JSON-RPC protocol (Phase 1)#515
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feat(daemon): implement CustomPaneBackend JSON-RPC protocol (Phase 1)#515
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Implements KILD's side of the CustomPaneBackend protocol proposed in anthropics/claude-code#26572. This gives Claude Code a clean socket-based pane management API without tmux impersonation, running in parallel with the existing shim (Phase 1 — no regressions). Protocol: - Daemon socket (`~/.kild/daemon.sock`) now routes connections based on the first message: JSON with a `"method"` key → pane backend handler, otherwise → existing ClientMessage JSONL handler - Handshake: `initialize` with optional `session_hint`; daemon responds with `protocol_version`, `capabilities`, `self_context_id` - Methods: `spawn_agent`, `write`, `capture`, `kill`, `list` - Push events (no id): `context_output` (base64 PTY data), `context_exited` - Context IDs: `ctx_0` (leader, pre-registered from `session_hint`), `ctx_1`, `ctx_2`, … for spawned agents New env vars injected into daemon PTYs: - `CLAUDE_PANE_BACKEND_SOCKET` — socket path for Claude Code to connect to - `CLAUDE_PANE_BACKEND_SESSION_ID` — echoed back as `session_hint` on init Changes: - `protocol/pane_backend.rs` — request/response/event types + ContextMap - `server/pane_backend.rs` — async connection handler with full dispatch - `server/connection.rs` — `route_connection` detects protocol on first line; `handle_connection_with_first_line` handles the KILD protocol path - `session/state.rs` — `parent_session_id` field + `subscribe_output_passive` - `session/manager.rs` — `parent_session_id` param on `create_session`, `list_sessions_by_parent`, `subscribe_output_passive` - `daemon_helpers.rs` — inject pane backend env vars alongside shim vars The tmux shim and all existing shim vars are kept unchanged in Phase 1.
Moves protocol/pane_backend.rs and server/pane_backend.rs into a cohesive src/pane_backend/ module directory with three focused files: pane_backend/protocol.rs — all wire types (request/response/event/params) pane_backend/context.rs — ContextMap (ctx_id ↔ session_id mapping) pane_backend/handler.rs — connection handler + dispatch_request Pure structural move — zero logic changes. Makes the protocol easier to link in the upstream issue (anthropics/claude-code#26572) and to review when Anthropic requests changes.
…rotocol spec Two corrections from review against anthropics/claude-code#26572: 1. capture response: return {"text": "<utf-8 string>"} instead of {"data": "<base64>"}. Scrollback is human-readable terminal output, not raw binary — base64 encoding was only used for context_output streaming where arbitrary bytes flow. 2. InitializeParams: add capabilities: Vec<String> with #[serde(default)]. Claude Code sends {"capabilities": ["events"]} in the initialize params; the field was previously silently dropped. Deserialized but not yet acted upon — future handlers can gate behaviour on declared capabilities. Also adds test_deserialize_initialize_with_capabilities to protocol tests.
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Implements KILD's side of the CustomPaneBackend protocol proposed in
anthropics/claude-code#26572.
The daemon's Unix socket now speaks two protocols on the same path — the existing
KILD
ClientMessageJSONL protocol and a new JSON-RPC 2.0 pane backend protocol. Thefirst line from a new connection decides which handler is invoked:
This is Phase 1 (parallel support). The tmux shim and all shim env vars are kept
unchanged — no regressions.
Protocol
Changes
kild-daemonpane_backend/protocol.rs— wire types:PaneBackendRequest/Response/Event, params structs,JsonRpcErrorpane_backend/context.rs—ContextMapforctx_id ↔ daemon_session_idmappingpane_backend/handler.rs— async connection handler,dispatch_request, full method implementationserver/connection.rs—route_connectiondetects protocol on first linesession/state.rs—parent_session_idfield +subscribe_output_passivesession/manager.rs—parent_session_idparam oncreate_session,list_sessions_by_parent,subscribe_output_passivekild-coresessions/daemon_helpers.rs— injectsCLAUDE_PANE_BACKEND_SOCKETandCLAUDE_PANE_BACKEND_SESSION_IDinto daemon PTY env alongside existing shim varsNew env vars (injected into daemon PTYs)
CLAUDE_PANE_BACKEND_SOCKETCLAUDE_PANE_BACKEND_SESSION_IDsession_hintso daemon can correlate the connectionRelated
.claude/PRPs/plans/claude-code-teams-research/custom-pane-backend-protocol.md