hydra-ahp

Serves hydra-acp sessions over the Agent Host Protocol (AHP), so VS Code's agent UI can list, watch and drive them. Runs as a hydra extension on localhost: VS Code connects to it like any remote agent host, and every session stays live and shared with hydra's other clients (the TUI, the browser, Slack). Start a turn in the TUI and watch it stream in VS Code, answer its permission prompt from either side, or start a new session in VS Code and pick it up later from the terminal.

VS Code authenticates with a token this extension mints for it and Hydra's own tokens never leave the daemon.

Install

hydra-ahp is a client of the hydra daemon, so install both:

npm install -g @hydra-acp/cli @hydra-acp/ahp

This drops the hydra-acp (and hydra) CLI plus a hydra-ahp binary on your PATH. If you have never run hydra before, its README covers the daemon; it starts itself the first time anything needs it, or hydra-acp daemon start brings it up ahead of time.

Register hydra-ahp as an extension:

hydra-acp extensions add hydra-ahp

extensions add is config-only. Either restart the daemon, or, if it is already running, start the extension:

hydra-acp extensions start hydra-ahp

Slash commands for an extension are /hydra <name> <verb>, and hydra drops a hydra- prefix, so this registration gives you /hydra ahp token ... in any hydra client and hydra-acp ahp ... on the command line (both need a recent hydra; on an older one register the extension as ahp with --command hydra-ahp instead). The listener is on 127.0.0.1:55590.

Logs: hydra-acp extensions log hydra-ahp -f.

Choosing an agent

hydra-ahp is not a coding agent. Every session it shows is a real agent that the hydra daemon runs, so which agents you can use, and how they log in, is hydra's business: see Choosing an agent. In short:

hydra-acp agent list          # what exists, and what you already have installed
hydra-acp agent set claude    # your default, then: hydra-acp daemon restart

VS Code lists every agent the daemon knows as a provider, and you pick one when you start a session there. Agents download on first use. An agent's model list fills in once a session of it has run on this host (hydra only learns models from a live session), and the same goes for its settings (see Settings).

Connect VS Code

You need a recent VS Code (Insiders 1.141 or later) with the agent host features on. chat.remoteAgentHostsEnabled is on by default.

Mint a token and get its URL:

hydra-ahp url vscode

ws://127.0.0.1:55590?tkn=...

The token is shown once (only its hash is stored), so each call mints a new one. Then, in either window:

• Agents window (code-insiders --agents, or Open Agents Window): run Add Remote Agent Host... from the command palette, paste the URL and give the host a name.

• Editor window (Insiders 1.145 or later): add an entry to chat.workspaceRemoteAgentHosts in settings.json (user settings, or a workspace's .vscode/settings.json) and reload. hydra-ahp token mint vscode prints the entry ready to paste:

  "chat.workspaceRemoteAgentHosts": [
    { "address": "127.0.0.1:55590", "name": "vscode", "connectionToken": "..." }
  ]

  Editor windows use this list instead of chat.remoteAgentHosts, which stays the Agents window's list, so serve both windows with an entry in each. The setting only applies in trusted workspaces. VS Code sends no folder to these hosts, so a chat started in an editor window begins in hydra's default directory, not the folder the window has open; the Agents window passes it.

Your hydra sessions then appear in VS Code's session list under the hydra host. Sessions show once they have had a real prompt; hydra hides never-prompted ones from every client.

The same verbs work from any hydra client as /hydra ahp token .... token list shows the tokens, and token revoke <id> revokes one and closes its connections at once. VS Code keeps reconnecting with the token it connected with, so after swapping the token in its settings, reload the window (or remove and add the host again). Tokens renew themselves on use, so you only re-paste after 90 idle days or a revoke. They do not appear in hydra-acp auth list.

Token levels

Every token can drive sessions, which means prompting agents and answering their permission requests, so any token can get a command run as you. The level only limits what a client can do directly, without going through an agent:

Level	Reads	Writes	Use it for
full (default)	Anywhere	Anywhere, plus terminals	VS Code, with terminals and file edits
read	Anywhere you can read	none	A client that should not write or get a shell
scoped	Inside the cwds of local sessions and files those sessions edited	none	The tightest file access

Pass --files read or --files scoped to url or token mint to mint a lower level. Direct access skips hydra's history and permission prompts, which is the difference full makes. At the scoped level the new-session folder picker lists directories only, under HYDRA_AHP_DIR_ROOTS. To change a token's level, mint a new one and revoke the old one.

Settings Sync

VS Code keeps connectionToken in plain text in settings.json. If Settings Sync includes that file, the token travels to your other machines and the sync service. Exclude chat.remoteAgentHosts and chat.workspaceRemoteAgentHosts from Settings Sync (Settings Sync: Configure, then ignore the settings). Keep the token out of a workspace's .vscode/settings.json, which is easy to commit.

Using it

Sessions and chats

An AHP session is a group of hydra sessions, each one a chat. A session nobody added chats to is a group of one. Creating a chat in VS Code adds a hydra session to the group; a fork copies the source chat's history up to a turn, and a side chat gets that history as context but shows only its own turns. Deleting a chat deletes its hydra session, and deleting the session deletes them all.

A session lives at <agent>:/<hydra session id>, because VS Code picks the content provider by the URI's scheme.

A message sent while the agent is working steers the running turn. AHP has no place for a message in the middle of a turn, so, as VS Code's own host does, the running turn ends there and the steering message opens a new one. Steers sent from the TUI or another client show up the same way.

Marking a chat read or done sticks: local sessions keep the mark in their own hydra extension_state (so it goes away with the session), federated sessions in this extension's flags.json. Hydra itself has no notion of done, so marking a chat done also lets its agent stop: if the hydra session is idle, it goes cold, keeping its record, and any client (the TUI, the browser) can resume it. A busy session keeps running. A new prompt after that, from any client, clears the done mark so the session shows up in VS Code again; just resuming or viewing it does not. Pins are VS Code's own and never reach hydra.

Settings

Every option the underlying agent advertises through hydra (effort, fast mode, session mode, and so on) appears as a picker under the chat input, along with hydra's own agent switch. The model has its own picker. Changing a setting goes through hydra to the agent, and the picker then shows what the agent reports (an agent may adjust other settings in response).

VS Code takes a chat's model from its turns and sends it with every prompt, so hydra-ahp stamps the session's current model on its turns; otherwise VS Code would fall back to the model it last used for that agent and switch the session to it. For a new session VS Code picks the first model listed, so each agent's default (hydra's sessionDefaults, through extends) is listed first.

Switching the agent moves the session to the new agent's URI, so VS Code shows it removed and listed again under the new agent. A session's settings come from attaching to it, so a cold session shows none until it has been opened live.

Permissions

Hydra sends every permission request to all attached clients and the first answer wins. A new request is held for half a second before VS Code sees it, so one an auto-approver (such as hydra-acp-approver) answers never flashes up.

Terminals

VS Code's Agents window opens a terminal for each session. For a full token, hydra-ahp starts your $SHELL in the session's directory on this machine; a terminal whose client stays away for 30 seconds is killed. read and scoped tokens are refused, which VS Code reports as an error each time it opens a session. Terminals need node-pty, an optional dependency; without it they are unavailable.

Changes

The Changes tab shows two changesets for each local session whose working directory is in a git repository:

• Session Changes: the files the agent edited in this session, as hydra aggregates them from its tool calls, each compared whole with the commit the branch was at when the session was created. Commits made since do not hide them. Your own edits to those files show too, and files changed only by shell commands do not.
• Uncommitted Changes: everything in the repository that differs from HEAD, staged, unstaged or untracked; a commit clears it.

Both refresh every couple of seconds while watched. They only read the repository: there are no review checkboxes and no commit or discard buttons. Federated and remote sessions get none, since their files are elsewhere. Session Changes needs a hydra that reports when each session was created; on an older one every edited file shows as new.

How it works

   hydra REST        +-------------+   AHP over WebSocket
   /v1/sessions <--- |             | <--------------------> VS Code
                     |  hydra-ahp  |   127.0.0.1:55590
   hydra WSS    <--> |             |
   /acp              +-------------+
                           |
                 ~/.hydra-acp/extensions/ahp/
                   tokens.json flags.json models.json configs.json

hydra-ahp is a hydra client downstream: it lists sessions over REST and attaches to each session VS Code opens over /acp, mapping ACP updates to AHP chat actions through the official AHP reducers. Upstream it is an AHP host: version negotiation, subscriptions with replay, and client actions validated before they reach hydra. The agents' model lists and option sets, and the read and done marks of federated sessions, are kept in its own files under ~/.hydra-acp/extensions/ahp/, all mode 0600; everything else it records lives in each session's hydra extension_state.

Configuration keys

Set these in the env block of the extension's entry in ~/.hydra-acp/config.json (hydra reads that block at startup):

"hydra-ahp": { "env": { "HYDRA_AHP_LOG_LEVEL": "debug" } }

The same keys can go in ~/.hydra-acp/extensions/ahp/ahp.conf (KEY=value lines); the process env wins over it, and a plain extension restart picks the file up. hydra ahp tailscale setup writes it for you: it mints a Tailscale cert into extensions/ahp/tls/, binds the tailnet IP, names the MagicDNS host, and offers to restart the extension. Re-run it within ~90 days to renew.

Key	Default	Notes
HYDRA_AHP_PORT	55590	Port the listener binds.
HYDRA_AHP_HOST	127.0.0.1	Bind address. Anything but loopback needs a TLS cert and key. When unset, the daemon's host is adopted along with its cert (see below).
HYDRA_AHP_TLS_CERT, HYDRA_AHP_TLS_KEY	daemon's	PEM paths; set both or neither. Explicit values win over the daemon's.
HYDRA_AHP_PREFERRED_HOST	daemon's publicHost	Name shown in token mint and token url, and accepted in the Host header.
HYDRA_AHP_ALLOWED_HOSTS	none	Extra Host header names accepted on a non-loopback bind (comma separated).
HYDRA_AHP_TOKEN_IDLE_DAYS	90	Days unused before a token expires.
HYDRA_AHP_DIR_ROOTS	home directory	Roots the new-session folder picker may browse (path-delimiter separated).
HYDRA_AHP_PERMISSION_DELAY_MS	500	How long a new permission request is held before clients see it; 0 shows them at once.
HYDRA_AHP_POLL_MS, HYDRA_AHP_WARM_POLL_MS	built in	Session list poll intervals.
HYDRA_AHP_LOG_LEVEL	info	debug logs one line per frame (method, channel, action type, never payloads).

Security

• Loopback by default; remote needs TLS. The listener binds 127.0.0.1 and refuses any other host without a cert and key. With no explicit settings it follows hydra-acp daemon listen (tailnet or all): the daemon's cert, host and public name are adopted at startup, the same way the browser extension does. Remote clients use wss://. A non-loopback bind also checks the Host header against the bound host, the public name and HYDRA_AHP_ALLOWED_HOSTS.
• A token is a remote shell. Any token can prompt an agent and approve its permission requests, whatever its file level. On 0.0.0.0 anyone who can reach the port can attempt a connection; prefer daemon listen tailnet.
• Own tokens. Clients authenticate with ?tkn=<token> (VS Code's browser transport cannot send headers) or Authorization: Bearer <token>. Tokens come from this extension's own registry, stored as hashes; hydra's admin token is never used or exposed.
• No web pages. WebSocket upgrades from web page origins are refused.
• Token levels gate files and terminals. See Token levels. File watches (createResourceWatch) follow the read scope: a scoped token can watch only what it can read, and never .git.
• Permission races. hydra-ahp never answers a permission request on a client's behalf; with no AHP client asked, it abstains and leaves the request to hydra's other clients.

Behavior worth knowing

• Daemon restarts. The listener lives and dies with the extension, so VS Code disconnects while the daemon restarts and reconnects to fresh state once the extension is back.
• Idle and unused sessions. Hydra closes idle sessions after daemon.sessionIdleTimeoutSeconds (they reload on demand) and garbage collects sessions that never had a prompt after 2 days cold.
• Protocol versions. VS Code currently negotiates AHP 0.9.0. hydra-ahp also serves 1.0.0 and uses no newer-version behavior on an older negotiated version.

Building from source

git clone https://github.com/smagnuso/hydra-ahp.git ~/dev/hydra-ahp
cd ~/dev/hydra-ahp
npm install
npm run build

Point the extension at the build instead of the npm binary:

hydra-acp extensions add hydra-ahp \
  --command node \
  --args ~/dev/hydra-ahp/dist/index.js

After a rebuild, restart (not start) is the right call:

hydra-acp extensions restart hydra-ahp

Hydra starts the extension with HYDRA_ACP_DAEMON_URL, HYDRA_ACP_TOKEN and HYDRA_ACP_WS_URL set; it does not run on its own.

Tests

npm test
npm run lint

Integration tests run against a scratch hydra daemon in a temp directory, with a fake agent, and never touch ~/.hydra-acp.

Status

Experimental. Covers session listing, live transcripts, prompting, steering, queued messages, cancel, permissions, settings and model pickers, read and archive marks, several chats per session (forks and side chats), file reads and @ completions, terminals, session and uncommitted changesets, and form elicitation (an agent's structured questions, such as Claude's AskUserQuestion, arrive as chat/inputRequested and are answered with chat/inputCompleted; a form AHP cannot express is left to the other clients). Out of scope: per-turn and branch changesets, changeset review and operations, automations, customizations, file watches, URL-mode elicitation, moving chats between sessions, and creating sessions on federated remotes (existing federated sessions are listed and driven).

License

MIT.