subagents: fold hive-extra-mcp into hive-agent-sock per mara's rescoping

hive-agent-sock/Cargo.toml

@@ -9,4 +9,6 @@ workspace = true
 
 [dependencies]
 serde.workspace = true
+serde_json.workspace = true
+tracing.workspace = true
 hive-sh4re.workspace = true

hive-agent-sock/README.md

@@ -1,14 +1,15 @@
 # hive-agent-sock
 
-Wire types for the **in-agent socket** — the one the `hive-agent` harness serves
-_inside_ the container to its local producers. The matrix / bash MCP daemons
-and `forge_notify` are the _built-in_ producers that ship today, but any
-user-configured MCP server declared in an agent's `agent.nix` can dial this
-socket and push its own todos with an arbitrary `subsystem` marker — the
-wire format doesn't restrict the set. Unlike the host-served sockets, this
-one **never leaves the container**.
+What's common across the in-container "agent plugins" — the matrix / bash /
+subagent MCP daemons and `forge_notify` today, plus any user-configured MCP
+server declared in an agent's `agent.nix`. Two things live here:
 
-## What it carries
+## Wire types for the in-agent socket
+
+The socket the `hive-agent` harness serves _inside_ the container to those
+local producers. Any producer can dial it and push its own todos with an
+arbitrary `subsystem` marker — the wire format doesn't restrict the set.
+Unlike the host-served sockets, this one **never leaves the container**.
 
 - the loose-ends-v2 **todo** op family
 - the harness-local **reminder** op family
@@ -16,14 +17,23 @@ one **never leaves the container**.
 More in-agent request families may be added over time — the socket is
 deliberately named for the agent, not for the todos.
 
-## Why in-container
+**Why in-container**: the harness owns the todo + reminder stores locally and
+signals its own turn loop directly, so `hive-c0re` is not in either path: no
+broker round-trip, no long-poll, no marker files. That locality is the
+point — it's also what lets these stores travel with the agent for hive
+portability.
 
-The harness owns the todo + reminder stores locally and signals its own turn
-loop directly, so `hive-c0re` is not in either path: no broker round-trip, no
-long-poll, no marker files. That locality is the point — it's also what lets
-these stores travel with the agent for hive portability.
+**Not to be confused with `hive-core-agent-sock`**: that crate is the
+_host_-served core↔agent protocol on `/run/hive/mcp.sock` (the harness
+talking out to `hive-c0re`). This socket is purely intra-container.
 
-## Not to be confused with `hive-core-agent-sock`
+## `extra_mcp`: the `hyperhive.extraMcpServers` spec
 
-That crate is the _host_-served core↔agent protocol on `/run/hive/mcp.sock`
-(the harness talking out to `hive-c0re`). This socket is purely intra-container.
+Not a socket protocol — a shared config type. Parses
+`/etc/hyperhive/extra-mcp.json` (the nix-rendered `hyperhive.extraMcpServers`
+option) and renders each entry into the shape claude expects in a
+`--mcp-config` blob. Shared by `hive-agent` (the main session's servers) and
+`hive-subagent-mcp` (the subagent-eligible subset, gated on
+`availableToSubagents`) — both already depend on this crate for the socket
+types above, so a new plugin-facing shared type belongs here rather than in
+a crate of its own.

hive-agent-sock/src/extra_mcp.rs

@@ -0,0 +1,186 @@
+//! Shared spec for `hyperhive.extraMcpServers` entries: the on-disk JSON
+//! shape the nix module (`nix/agent-modules/mcp.nix`) renders to
+//! `/etc/hyperhive/extra-mcp.json`, plus the parsing and per-entry
+//! JSON-rendering logic every consumer needs. Lives in `hive-agent-sock`
+//! rather than a crate of its own: this crate is already what's common
+//! across the in-container "agent plugins" (matrix/bash/subagent MCP
+//! daemons, `forge_notify`) — the todo-socket wire types above, and now
+//! this — so a new plugin-facing shared type belongs here rather than in
+//! a fresh single-purpose crate.
+
+use std::collections::BTreeMap;
+use std::path::Path;
+
+/// Where the NixOS module writes the per-agent extra-MCP spec. Each entry
+/// becomes an additional `mcpServers.<key>` block in a rendered claude
+/// `--mcp-config`.
+pub const EXTRA_MCP_PATH: &str = "/etc/hyperhive/extra-mcp.json";
+
+/// An extra MCP server declared via `hyperhive.extraMcpServers`. Two
+/// transports: `Stdio` (the consumer spawns `command` fresh each turn, talks
+/// JSON-RPC over its stdin/stdout) and `Http` (point claude at a long-lived
+/// streamable-http `url` instead — no per-turn spawn, no re-registration
+/// race). Internally tagged on the nix-rendered `type` field; unrecognised
+/// fields for the inactive variant (e.g. `command` on an `Http` entry) are
+/// ignored by serde's default struct deserialization.
+#[derive(Debug, Clone, serde::Deserialize)]
+#[serde(tag = "type", rename_all = "snake_case")]
+pub enum ExtraMcpServer {
+    Stdio {
+        command: String,
+        #[serde(default)]
+        args: Vec<String>,
+        #[serde(default)]
+        env: BTreeMap<String, String>,
+        #[serde(default = "default_allowed_tools", rename = "allowedTools")]
+        allowed_tools: Vec<String>,
+        #[serde(default, rename = "availableToSubagents")]
+        available_to_subagents: bool,
+    },
+    Http {
+        url: String,
+        #[serde(default = "default_allowed_tools", rename = "allowedTools")]
+        allowed_tools: Vec<String>,
+        #[serde(default, rename = "availableToSubagents")]
+        available_to_subagents: bool,
+    },
+}
+
+impl ExtraMcpServer {
+    #[must_use]
+    pub fn allowed_tools(&self) -> &[String] {
+        match self {
+            Self::Stdio { allowed_tools, .. } | Self::Http { allowed_tools, .. } => allowed_tools,
+        }
+    }
+
+    /// Whether this entry is opted in to subagent sessions
+    /// (`hyperhive.extraMcpServers.<name>.availableToSubagents`, default
+    /// `false`). Subagents run `--strict-mcp-config` with no discovery, so
+    /// this flag is the only path an entry reaches a subagent's own
+    /// `--mcp-config` at all — see `hive-subagent-mcp`'s `mcp_config`
+    /// module.
+    #[must_use]
+    pub fn available_to_subagents(&self) -> bool {
+        match self {
+            Self::Stdio {
+                available_to_subagents,
+                ..
+            }
+            | Self::Http {
+                available_to_subagents,
+                ..
+            } => *available_to_subagents,
+        }
+    }
+
+    /// Render this entry into the shape claude expects under
+    /// `mcpServers.<name>` in a `--mcp-config` blob. `state_dir` is injected
+    /// as `HYPERHIVE_STATE_DIR` into a stdio entry's env when the entry
+    /// doesn't already set it, so an extra stdio MCP server can resolve the
+    /// agent's durable state dir without its author hard-coding it; an http
+    /// entry has no child-process env to inject into (the daemon behind the
+    /// URL resolves its own state dir independently).
+    #[must_use]
+    pub fn to_json_entry(&self, state_dir: &Path) -> serde_json::Value {
+        match self {
+            Self::Stdio {
+                command, args, env, ..
+            } => {
+                let mut env = env.clone();
+                env.entry("HYPERHIVE_STATE_DIR".to_owned())
+                    .or_insert_with(|| state_dir.display().to_string());
+                serde_json::json!({ "command": command, "args": args, "env": env })
+            }
+            Self::Http { url, .. } => serde_json::json!({ "type": "http", "url": url }),
+        }
+    }
+}
+
+fn default_allowed_tools() -> Vec<String> {
+    vec!["*".to_owned()]
+}
+
+/// Read + parse the extra-MCP spec from [`EXTRA_MCP_PATH`]. Returns an empty
+/// map when the file is missing or unparsable (the agent has none
+/// configured, or the file is malformed — both cases degrade to "no extra
+/// servers").
+#[must_use]
+pub fn load_extra_mcp() -> BTreeMap<String, ExtraMcpServer> {
+    let Ok(raw) = std::fs::read_to_string(EXTRA_MCP_PATH) else {
+        return BTreeMap::new();
+    };
+    serde_json::from_str(&raw).unwrap_or_else(|e| {
+        tracing::warn!(
+            path = EXTRA_MCP_PATH,
+            error = ?e,
+            "extra-mcp spec parse failed; ignoring",
+        );
+        BTreeMap::new()
+    })
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn available_to_subagents_defaults_false() {
+        let stdio: ExtraMcpServer =
+            serde_json::from_value(serde_json::json!({"type": "stdio", "command": "/bin/foo"}))
+                .unwrap();
+        assert!(!stdio.available_to_subagents());
+
+        let http: ExtraMcpServer = serde_json::from_value(
+            serde_json::json!({"type": "http", "url": "http://127.0.0.1:1/mcp"}),
+        )
+        .unwrap();
+        assert!(!http.available_to_subagents());
+    }
+
+    #[test]
+    fn available_to_subagents_true_is_read() {
+        let stdio: ExtraMcpServer = serde_json::from_value(serde_json::json!({
+            "type": "stdio",
+            "command": "/bin/foo",
+            "availableToSubagents": true,
+        }))
+        .unwrap();
+        assert!(stdio.available_to_subagents());
+    }
+
+    #[test]
+    fn to_json_entry_injects_state_dir_when_absent() {
+        let stdio: ExtraMcpServer = serde_json::from_value(serde_json::json!({
+            "type": "stdio",
+            "command": "/bin/foo",
+        }))
+        .unwrap();
+        let entry = stdio.to_json_entry(Path::new("/agents/x/state"));
+        assert_eq!(entry["env"]["HYPERHIVE_STATE_DIR"], "/agents/x/state");
+    }
+
+    #[test]
+    fn to_json_entry_respects_explicit_state_dir() {
+        let stdio: ExtraMcpServer = serde_json::from_value(serde_json::json!({
+            "type": "stdio",
+            "command": "/bin/foo",
+            "env": {"HYPERHIVE_STATE_DIR": "/custom"},
+        }))
+        .unwrap();
+        let entry = stdio.to_json_entry(Path::new("/agents/x/state"));
+        assert_eq!(entry["env"]["HYPERHIVE_STATE_DIR"], "/custom");
+    }
+
+    #[test]
+    fn http_entry_has_no_env() {
+        let http: ExtraMcpServer = serde_json::from_value(serde_json::json!({
+            "type": "http",
+            "url": "http://127.0.0.1:1/mcp",
+        }))
+        .unwrap();
+        let entry = http.to_json_entry(Path::new("/agents/x/state"));
+        assert_eq!(entry["url"], "http://127.0.0.1:1/mcp");
+        assert!(entry.get("env").is_none());
+    }
+}

hive-agent-sock/src/lib.rs

@@ -1,23 +1,31 @@
-//! Wire types for the *in-agent* socket, served by the hive-agent harness
-//! to the in-container producers. Matrix / bash MCP daemons and
-//! `forge_notify` are the built-in ones today, but `subsystem` on the todo
-//! ops below is a plain string, not a closed set: any user-configured MCP
-//! server declared in an agent's `agent.nix` can dial this socket and push
-//! its own todos the same way. Carries the loose-ends-v2 *todo* op family
-//! plus the harness-local *reminder* op family; more in-agent request
-//! families may be added over time (the socket is deliberately named for
-//! the agent, not the todos).
+//! Rescoped beyond its original name: what's common across the in-container
+//! "agent plugins" (matrix/bash/subagent MCP daemons, `forge_notify`, and any
+//! user-configured MCP server) — not just the in-agent socket wire types.
+//!
+//! **Wire types for the *in-agent* socket**, served by the hive-agent harness
+//! to those producers. `subsystem` on the todo ops below is a plain string,
+//! not a closed set: any user-configured MCP server declared in an agent's
+//! `agent.nix` can dial this socket and push its own todos the same way.
+//! Carries the loose-ends-v2 *todo* op family plus the harness-local
+//! *reminder* op family; more in-agent request families may be added over
+//! time (the socket is deliberately named for the agent, not the todos).
 //!
 //! Distinct from `hive-core-agent-sock`, the *host*-served core↔agent
 //! protocol on `/run/hive/mcp.sock`: this socket never leaves the
 //! container. The harness owns the todo + reminder stores locally and
 //! signals its own turn loop directly, so hive-c0re is not in either path —
 //! no broker round-trip, no long-poll, no marker files.
+//!
+//! **`extra_mcp`**: the `hyperhive.extraMcpServers` spec + parsing, shared by
+//! `hive-agent` (the main session's `--mcp-config`) and `hive-subagent-mcp`
+//! (the subagent-eligible subset) — not a socket protocol at all, but this
+//! crate is the natural home since both consumers already depend on it.
 
 use serde::{Deserialize, Serialize};
 
 use hive_sh4re::inbox::LooseEnd;
 
+pub mod extra_mcp;
 pub mod paths;
 
 /// In-container path of the harness-served in-agent socket. The harness