diff --git a/CLAUDE.md b/CLAUDE.md
index f3ddc381..8d01ce66 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -116,8 +116,10 @@ hand-maintained per-file tree drifts out of sync with the code.
   speaks to `hive-c0re`. Same split rationale as the two above; the shared
   payload types it references stay in `hive-sh4re`.
 - **`hive-agent-sock/`** — wire types for the *in-agent* socket, served by
-  the harness to in-container producers (matrix / bash MCP daemons,
-  `forge_notify`). Carries the loose-ends-v2 **todo** ops plus
+  the harness to in-container producers — matrix / bash MCP daemons and
+  `forge_notify` are the built-in ones, but any user-configured MCP server
+  can push todos here too, nothing restricts the `subsystem` set. Carries
+  the loose-ends-v2 **todo** ops plus
   harness-local reminders + questions. ⚠️ Distinct from
   `hive-core-agent-sock` above: **this socket never leaves the container**
   and `hive-c0re` is not in the path at all — no broker round-trip, no
diff --git a/docs/turn-loop/README.md b/docs/turn-loop/README.md
index 08e145f0..6c8f3aa7 100644
--- a/docs/turn-loop/README.md
+++ b/docs/turn-loop/README.md
@@ -101,11 +101,13 @@ the login flow first (`NeedsLogin`). (The forge notification poller
 used to be spawned here too; it is its own process now —
 `hive-forge-notify`, see [`forge.md`](../forge.md).)
 
-`spawn_todo_socket` opens the todos store, the socket the in-container
-producers dial (matrix / bash / forge-notify daemons), and an
-in-process `disk_watch` todo producer for low state-disk space. See
+`spawn_todo_socket` opens the todos store and the socket the in-container
+producers dial. Matrix / bash / forge-notify daemons and the in-process
+`disk_watch` todo producer (low state-disk space) are the built-in
+producers, but the socket accepts any `subsystem` marker — a
+user-configured MCP server can push its own todos the same way. See
 [`docs/persistence.md`](../persistence.md#state-dirs-per-agent) for
-what each todo producer watches and how the store + `get_loose_ends`
+what each built-in todo producer watches and how the store + `get_loose_ends`
 merge work.
 
 Plugin install failures are not fatal: each entry comes back as a
diff --git a/docs/web-ui/agent.md b/docs/web-ui/agent.md
index 33c3aeb4..e69c76a1 100644
--- a/docs/web-ui/agent.md
+++ b/docs/web-ui/agent.md
@@ -162,8 +162,10 @@ are acked, the harness won't receive wake-prompts for them. A `{
 marked: N }` pill surfaces the count. After the drain the inbox list
 empties on reload (the filter is `acked_at IS NULL`, so drained
 messages disappear). Todos flyout ("loose-ends v2"): the harness-local
-todos other subsystems (matrix, forge, bash) push at this agent
-(`GET /api/todos`) — each row shows the producing subsystem, an
+todos other subsystems push at this agent (`GET /api/todos`) — matrix,
+forge, and bash are the built-in producers, but any user-configured MCP
+server can push its own via the same in-agent socket. Each row shows the
+producing subsystem, an
 optional source label, a summary, and age. A checkbox per row plus a
 select-all / select-none / `✓ mark done` bulk row above the list POSTs
 the checked ids to `POST /api/todos/mark-done`, which dismisses them
diff --git a/frontend/packages/agent/src/app.js b/frontend/packages/agent/src/app.js
index d5862ee5..6a66e6bf 100644
--- a/frontend/packages/agent/src/app.js
+++ b/frontend/packages/agent/src/app.js
@@ -768,8 +768,9 @@ window.marked = marked;
     }
     renderStateBadge();
   }
-  // Todos section: in-agent todos (loose-ends v2) pushed by subsystems
-  // (matrix, forge, bash). Best-effort fetch on cold load + after every
+  // Todos section: in-agent todos (loose-ends v2) pushed by subsystems —
+  // matrix, forge, bash are the built-in ones, but any user-configured MCP
+  // server can push its own. Best-effort fetch on cold load + after every
   // turn_end. Silent failure keeps the pill at zero.
   async function refreshTodos() {
     try {
diff --git a/hive-agent-mcp/src/mcp/render.rs b/hive-agent-mcp/src/mcp/render.rs
index 085c54a2..c093e569 100644
--- a/hive-agent-mcp/src/mcp/render.rs
+++ b/hive-agent-mcp/src/mcp/render.rs
@@ -139,7 +139,8 @@ fn msg_id_tag(id: i64) -> String {
 /// Hard cap on how many individual `Todo` lines `render_loose_ends` will
 /// emit. Approvals/questions/reminders stay naturally bounded (they're
 /// triaged interactively and don't self-multiply), but todos are pushed by
-/// unattended producers (matrix/bash/forge) — an agent that goes a long
+/// unattended producers — matrix/bash/forge are the built-in ones, but any
+/// user-configured MCP server can push its own too — an agent that goes a long
 /// stretch without calling `get_loose_ends`, or whose producers outpace its
 /// triage, can accumulate hundreds of them. Rendering all of them
 /// unconditionally risks producing a tool result too large for the MCP
diff --git a/hive-agent-sock/README.md b/hive-agent-sock/README.md
index 6a772dd3..d1ff9956 100644
--- a/hive-agent-sock/README.md
+++ b/hive-agent-sock/README.md
@@ -1,9 +1,12 @@
 # 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`). Unlike the host-served sockets, this one **never leaves the
-container**.
+*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 it carries
 
diff --git a/hive-agent-sock/src/lib.rs b/hive-agent-sock/src/lib.rs
index 294a4b43..76d8fb5b 100644
--- a/hive-agent-sock/src/lib.rs
+++ b/hive-agent-sock/src/lib.rs
@@ -1,9 +1,12 @@
 //! 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`. Carries the loose-ends-v2 *todo* op family plus the
-//! harness-local *reminder* and *question* op families; more in-agent
-//! request families may be added over time (the socket is deliberately
-//! named for the agent, not the todos).
+//! 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* and *question* op families; 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
@@ -23,12 +26,16 @@ pub const DEFAULT_AGENT_SOCKET: &str = "/run/hive/agent.sock";
 
 /// A request on the in-agent socket. Serialised with a `cmd` tag so the
 /// in-container producers can emit a plain JSON line without linking a
-/// typed client (matrix/bash build the JSON by hand).
+/// typed client (matrix/bash build the JSON by hand; a user-configured
+/// MCP server can do the same with its own `subsystem` marker).
 #[derive(Debug, Clone, Serialize, Deserialize)]
 #[serde(tag = "cmd", rename_all = "snake_case")]
 pub enum Request {
-    /// Upsert a todo from an in-container subsystem (matrix / bash /
-    /// forge). `subsystem` is the producer marker; `key` the optional
+    /// Upsert a todo from an in-container subsystem — matrix / bash /
+    /// forge are the built-in producers, but any subsystem name is
+    /// accepted; nothing restricts `subsystem` to a fixed set, so a
+    /// user-configured MCP server can push its own todos here too.
+    /// `subsystem` is the producer marker; `key` the optional
     /// subsystem-specific dedup key (a matrix room id, a bash task id).
     /// A new-or-changed row signals the turn loop; an identical keyed
     /// re-push is a silent no-op. Keyless todos always insert as one-offs.
diff --git a/hive-agent/src/todo_server.rs b/hive-agent/src/todo_server.rs
index 39ff323c..3b628a76 100644
--- a/hive-agent/src/todo_server.rs
+++ b/hive-agent/src/todo_server.rs
@@ -1,7 +1,9 @@
 //! In-agent socket server (loose-ends v2 + harness-local reminders +
 //! questions mirror + self-service compact). Binds the harness-owned
 //! `HIVE_AGENT_SOCKET` and serves the `hive-agent-sock` protocol to the
-//! in-container producers (matrix / bash daemons, forge-notify) and to
+//! in-container producers — matrix / bash daemons and forge-notify are the
+//! built-in ones, but any user-configured MCP server can dial the same
+//! socket and push its own todos — and to
 //! `hive-agent-mcp`'s `ask`/`answer`/`remind`/`get_loose_ends`/
 //! `cancel_loose_end`/`compact` tool impls. Todo ops hit the harness-local
 //! [`Todos`] store; a new-or-changed upsert fires an in-process [`Notify`]
diff --git a/hive-c0re/src/coordinator.rs b/hive-c0re/src/coordinator.rs
index 3e210bcc..46b01658 100644
--- a/hive-c0re/src/coordinator.rs
+++ b/hive-c0re/src/coordinator.rs
@@ -1387,9 +1387,10 @@ impl Coordinator {
     /// Push a todo directly into `agent`'s in-container todo store — a
     /// best-effort *live* dial of its `hive-agent-sock` socket
     /// (`hive_host_sock::agent_todo_socket`), same `UpsertTodo` request
-    /// shape the in-container producers (matrix/bash/forge-notify)
-    /// already send. This is the migration target for `HelperEvent`
-    /// variants that are pure "FYI, check when convenient" notices: the
+    /// shape the built-in in-container producers (matrix/bash/forge-notify)
+    /// already send — `subsystem` isn't restricted to that set, any
+    /// producer can use the same shape. This is the migration target for
+    /// `HelperEvent` variants that are pure "FYI, check when convenient" notices: the
     /// event stops being a broker `Message` (which always drives an
     /// immediate turn) and becomes a todo instead, with the same
     /// dedup-by-key semantics as any other producer.
diff --git a/hive-sh4re/src/lib.rs b/hive-sh4re/src/lib.rs
index a9c9cef0..a61ad7a1 100644
--- a/hive-sh4re/src/lib.rs
+++ b/hive-sh4re/src/lib.rs
@@ -278,13 +278,18 @@ pub enum LooseEnd {
         #[serde(default)]
         summary: String,
     },
-    /// A dynamic, subsystem-pushed todo (loose-ends v2). Produced
-    /// by an in-container subsystem (matrix / forge / bash) via
-    /// `UpsertTodo`. Cleared by that subsystem (`ClearTodo`) or by the
-    /// agent itself (`MarkTodoDone`, by `id`).
+    /// A dynamic, subsystem-pushed todo (loose-ends v2). Produced by an
+    /// in-container subsystem via `UpsertTodo` — matrix/bash/forge are the
+    /// *built-in* producers that ship today, but `subsystem` is a plain
+    /// string, not a closed set: any user-configured MCP server declared
+    /// in an agent's `agent.nix` can dial the in-agent socket and push its
+    /// own todos the same way. Cleared by that subsystem (`ClearTodo`) or
+    /// by the agent itself (`MarkTodoDone`, by `id`).
     Todo {
         id: i64,
-        /// Producing subsystem marker (`"matrix"`, `"forge"`, `"bash"`, …).
+        /// Producing subsystem marker (`"matrix"`, `"forge"`, `"bash"`, …
+        /// — built-in producers; a user-configured MCP server can push
+        /// its own arbitrary marker here too, nothing enforces the set).
         subsystem: String,
         /// Optional subsystem-specific key (matrix room id, bash task id).
         #[serde(default, skip_serializing_if = "Option::is_none")]