kandev/apps/backend/internal/agentctl/AGENTS.md

agentctl — HTTP server, adapters, ACP protocol

Scoped guidance for apps/backend/internal/agentctl/. Higher-level backend architecture is in apps/backend/AGENTS.md.

API Groups

agentctl exposes these route groups (see server/api/):

• /health, /info, /status - Health and status
• /instances/* - Multi-instance management
• /processes/* - Agent subprocess management (start/stop)
• /agent/configure, /agent/stream - Agent configuration and event streaming
• /git/* - Git operations (status, commit, push, pull, rebase, stage, create PR, etc.)
• /shell/* - Shell session management
• /workspace/* - File operations, search, tree
• /vscode/* - VS Code integration proxy

Pull request creation (server/process/git_pr_providers.go)

GitOperator.CreatePR picks a host CLI from origin:

Remote host	CLI	Notes
github.com, *.github.com	gh pr create	Requires gh on PATH (included in the Kandev Docker image).
dev.azure.com, ssh.dev.azure.com, *.visualstudio.com	az repos pr create	Requires az on PATH, azure-devops extension (both in the Kandev Docker image). Auth: az login or AZURE_DEVOPS_EXT_PAT.
Other hosts (e.g. GitLab)	—	Returns an unsupported-remote error. Use host-specific CLIs outside agentctl (e.g. /pr skill glab for GitLab).

Azure PR URLs are returned to the client but do not trigger backend onPRCreated / TaskPR linkage (GitHub-only today). The web UI keeps a session-scoped pending PR URL so the changes panel hides Create PR after a successful Azure create.

Adapter Model

Protocol adapters in server/adapter/transport/ normalize different agent CLIs:

• AgentAdapter interface defines Start(), Stop(), Prompt(), Cancel()
• Transports: acp (Claude Code), codex (OpenAI Codex), opencode, shared, streamjson
• Top-level adapters: CopilotAdapter (GitHub Copilot SDK), AmpAdapter (Sourcegraph Amp)
• process.Manager owns subprocess, wires stdio to adapter
• Factory pattern in server/adapter/factory.go selects adapter by agent type

The acp transport is split by concern across adapter_*.go files: adapter.go (core/lifecycle), adapter_session.go (initialize/new/load/resume), adapter_prompt.go (prompt/cancel), adapter_updates.go (session/update notification fan-out), adapter_tools.go (convertToolCallUpdate / convertToolCallResultUpdate → normalized payloads), adapter_permissions.go, and adapter_helpers.go. Tool-call conversion lives in adapter_tools.go, not adapter.go.

ACP Protocol

JSON-RPC 2.0 over stdin/stdout between agentctl and agent process. Requests: initialize, session/new, session/load, session/prompt, session/cancel. Notifications: session/update with types message_chunk, tool_call, tool_update, complete, error, permission_request, context_window.

ACP frame debug logging (adapter/transport/shared/acplog.go)

When KANDEV_DEBUG_AGENT_MESSAGES=true (on by default in the dev profile), the ACP adapter dumps every raw + normalized frame to per-session JSONL files:

• Files: raw-{protocol}-{agentID}-{sessionID}.jsonl and normalized-{protocol}-{agentID}-{sessionID}.jsonl (the raw-/normalized- prefix + .jsonl suffix is a contract with the reader in internal/debug).
• Dir resolution: KANDEV_DEBUG_LOG_DIR (explicit override) → <KANDEV_HOME_DIR>/logs/acp (honors dev/e2e isolation — KANDEV_HOME_DIR is already the Kandev root, so no extra .kandev segment) → ~/.kandev/logs/acp/ → process CWD.
• One kept-open buffered writer + dedicated mutex per session (no global lock on the hot path); rotates on a per-file byte cap.
• A shared.Janitor (owned by cmd/agentctl/main.go run(), Start/Stop) flushes periodically and prunes oldest-by-mtime first, enforcing a total-file cap and an age cap so an always-on dev session can't fill the disk. It also closes idle writers so handles don't leak.
• Dev-only live tail of a stuck session from an in-memory ring buffer (zero disk growth): GET /api/v1/debug/acp/{session}?n=200.

Env knobs (all optional): KANDEV_DEBUG_ACP_MAX_FILES (default 200), KANDEV_DEBUG_ACP_RETENTION_HOURS (default 48), KANDEV_DEBUG_ACP_MAX_FILE_BYTES (default 8 MiB).

PRIVACY / PERF: frames carry the full prompt, file, and tool-call content. Keep this strictly behind the debug flag and local-dev-scoped — never enable in a shared/production deployment. When agentctl runs inside a Docker executor the files land inside the container, so this is meant for standalone/dev.

Recognizing claude-acp meta-tagged tools

claude-agent-acp tags certain tool calls with _meta.claudeCode.toolName (e.g. Monitor, ScheduleWakeup, Agent for subagents) and may carry results in _meta.claudeCode.toolResponse. These are normalized into typed streams.NormalizedPayload kinds in server/adapter/transport/acp/. The established pattern is one file per recognized tool (monitor.go, wakeup.go, subagent.go), each with a defensive untyped-map recognizer (recognize*/is*Meta/extract*), a typed payload, and a sibling *_test.go. convertToolCallUpdate stashes title/Meta into the normalizer args; result enrichment happens in convertToolCallResultUpdate. To add another claude-acp meta-tool, copy that shape — don't inline detection in adapter.go. Detection can also be cross-agent: subagent recognition keys off Claude's _meta, OpenCode's tool title, and Cursor's rawInput._toolName.

Subagent tool-call nesting: what each agent emits

Kandev renders subagents (the Task tool) as cards and wants to nest each subagent's internal tool calls under its card (via parent_tool_call_id, see tool-subagent-message.tsx). Reality differs per agent — verified from captured ~/.kandev/logs/acp/ frames of a "spawn 3 subagents that each run sleep 30" prompt:

Agent	Subagent-internal tool calls	Nestable?
Claude	emitted on the parent session, each tagged with _meta.claudeCode.parentToolUseId = the parent Task tool_call's id	Yes — parentToolUseID() reads it in adapter_tools.go and sets AgentEvent.ParentToolCallID, which becomes the message's parent_tool_call_id and nests under the card
Cursor	not emitted over ACP at all (Task tool_call_update carries only {durationMs, isBackground})	No — no child data exists
OpenCode	emitted into a separate child ACP session (the metadata.sessionId we store as SubagentTaskPayload.ChildSessionID)	Not yet — they never reach the parent stream; would require merging that child session via the stored child_session_id

Claude is the one that works today: claude-agent-acp (since PR #341) sets _meta.claudeCode.parentToolUseId on a subagent's internal calls, and its value already equals the parent Task tool_call id — so it maps straight onto our parent_tool_call_id. Cursor exposes nothing to nest. OpenCode needs a kandev-side child-session merge. (Top-level parentToolCallId is NOT in the ACP schema — _meta is the spec-compliant carrier.)

Process-group kill for HTTP-server agents (RequiresProcessKill)

Most ACP agents (Claude Code, Codex, Cursor, …) exit cleanly when stdin is closed. Some agents — notably opencode acp — keep their HTTP server and an MCP child tree alive after stdin EOF. For those agents, closing stdin on shutdown is not enough; the process group has to be SIGKILLed so the MCP children don't re-parent to init and leak (GH issue #1247).

The signal flows agent → adapter → process manager via a single bool:

1. agents.RuntimeConfig.RequiresProcessKill (set true on OpenCodeACP).
2. The lifecycle executors copy it into agentctl.CreateInstanceRequest.RequiresProcessKill.
3. instance.Manager stores it on config.InstanceConfig.RequiresProcessKill.
4. process.Manager.buildAdapterConfig forwards it into adapter.Config → shared.Config.
5. acp.Adapter.RequiresProcessKill() returns cfg.RequiresProcessKill.
6. On shutdown, process.Manager.killProcessGroupIfRequired consults the adapter and, when true, sends SIGKILL to the whole pgid via killProcessGroup (syscall.Kill(-pid, SIGKILL) on Unix). If Stop(ctx) further times out before the process exits, waitForProcessExit's ctx.Done branch re-runs the pgid SIGKILL (falling back to a leader-only kill if the group call errors) — belt-and-braces for any future ACP CLI that decides to ignore stdin close.

To add another agent that needs this: set RequiresProcessKill: true in its Runtime() config — that's all.

Idle-instance reaper (KANDEV_ACP_IDLE_TIMEOUT)

instance.Manager runs a background goroutine that reaps instances whose owning kandev backend appears to be gone. An instance is "idle" when it has zero in-flight HTTP requests and its most recent observed activity is older than the configured timeout. Activity is tracked by a middleware on the per-instance handler that bumps a counter on every request entry/exit, so a long-lived /agent/stream WebSocket keeps the instance "active" for as long as the stream is open.

Env knobs:

• KANDEV_ACP_IDLE_TIMEOUT (default 1h, 0 to disable)
• KANDEV_ACP_IDLE_REAPER_INTERVAL (default 1m)

Both accept any value time.ParseDuration accepts (30m, 2h, 500ms, …). Disabled mode is intended for tests and edge cases — production should keep the reaper on.

MCP stdio command validation

instance.Manager.buildMcpServerConfigs calls exec.LookPath on every stdio MCP Command before passing the list to the agent. Entries whose command can't be resolved are dropped with a warn log (URL-transport MCPs always pass through). This prevents the /snap/bin/brave repro in GH issue #1247 — an MCP whose binary was uninstalled after config save no longer causes a permanently broken child process to be spawned every session.

Further scoped notes

• server/api/AGENTS.md — reverse-proxy body rewriting (Accept-Encoding) and iframe-blocking header stripping.