diff --git a/hive-agent-mcp/src/mcp/args.rs b/hive-agent-mcp/src/mcp/args.rs
index 9f7e4e54..dfb78a77 100644
--- a/hive-agent-mcp/src/mcp/args.rs
+++ b/hive-agent-mcp/src/mcp/args.rs
@@ -41,6 +41,15 @@ pub struct AckUntilArgs {
     pub up_to: i64,
 }
 
+/// MCP tool args for `mark_todos_done`.
+#[derive(Debug, serde::Deserialize, schemars::JsonSchema)]
+pub struct MarkTodosDoneArgs {
+    /// Todo ids to clear (from `get_loose_ends`'s `todo #N` lines). Only
+    /// these ids are acked — not a range. Unknown/already-acked ids are
+    /// silently skipped.
+    pub ids: Vec<i64>,
+}
+
 /// MCP tool args for `remind`. Exactly one of `delay_seconds` or
 /// `at_unix_timestamp` must be set; both / neither is a tool-side error.
 /// Hides the tagged `ReminderTiming` enum behind a flatter schema so the
diff --git a/hive-agent-mcp/src/mcp/mod.rs b/hive-agent-mcp/src/mcp/mod.rs
index dd78d313..d8e4d64c 100644
--- a/hive-agent-mcp/src/mcp/mod.rs
+++ b/hive-agent-mcp/src/mcp/mod.rs
@@ -26,16 +26,16 @@ mod render;
 pub use args::{
     AckUntilArgs, AgentGetLooseEndsArgs, AnswerArgs, AskArgs, CancelLooseEndArgs,
     CancelScheduleArgs, CreateRepoArgs, EditScheduleArgs, FireScheduleNowArgs, GetAgentMetaArgs,
-    GetHostJournalArgs, GetLogsArgs, KillArgs, RecvArgs, RemindArgs, RequestInitConfigArgs,
-    RequestSchedulePromptArgs, RestartArgs, SendArgs, SetStatusArgs, StartArgs, UpdateArgs,
-    UpdateMetaInputsArgs,
+    GetHostJournalArgs, GetLogsArgs, KillArgs, MarkTodosDoneArgs, RecvArgs, RemindArgs,
+    RequestInitConfigArgs, RequestSchedulePromptArgs, RestartArgs, SendArgs, SetStatusArgs,
+    StartArgs, UpdateArgs, UpdateMetaInputsArgs,
 };
 pub use render::{annotate_retries, format_ack, format_agent_meta, format_recv};
 
 use render::{
     dial_agent_socket, format_matrix_summary, local_questions, local_reminders, local_todos,
-    loose_end_kind_label, mark_local_todo_done, matrix_unread_summary, parse_loose_end_kind,
-    render_loose_ends, reply_err,
+    loose_end_kind_label, mark_local_todo_done, mark_local_todos_done, matrix_unread_summary,
+    parse_loose_end_kind, render_loose_ends, reply_err,
 };
 
 /// Write (or remove) the status file in the agent's own `state/` directory.
@@ -347,7 +347,9 @@ impl AgentServer {
         at turn start to remember what you owe / what's owed to you without scrolling \
         inbox history. Output is a short bulleted list with ids, ages in seconds, and \
         the relevant context. Each `question` or `reminder` row can be cancelled by \
-        passing its id + kind to `cancel_loose_end`. Empty result is reported clearly.\n\
+        passing its id + kind to `cancel_loose_end`. Empty result is reported clearly. Todos \
+        cap at 40 rows; a trailer line says how many more are pending — clear the shown ones \
+        with `mark_todos_done`, then call again for the rest.\n\
         Pass `agent: \"<name>\"` to inspect a specific peer agent's threads. Direct \
         child agents are always accessible. For non-children, the `query_agent_state` \
         capability is required — without it the request is rejected with an error."
@@ -471,11 +473,9 @@ impl AgentServer {
         `kind` may also be `\"approval\"` to withdraw a pending approval you submitted \
         (before the operator acts on it) — root agent (`ruth`) only; the server rejects \
         `approval` kind for all other callers.\n\
-        `kind` may also be `\"todo\"` to clear one of your own loose-ends-v2 todos \
-        (bash-task completions, matrix unread, forge activity — the id in the \
-        `get_loose_ends` `todo #N` line) — this dials the in-container socket directly, \
-        no bash task involved, so it's safe to call repeatedly without spawning more \
-        todos."
+        `kind` may also be `\"todo\"` to clear one of your own loose-ends-v2 todos (the id \
+        from a `get_loose_ends` `todo #N` line) — dials the in-agent socket directly, safe \
+        to call repeatedly."
     )]
     async fn cancel_loose_end(&self, Parameters(args): Parameters<CancelLooseEndArgs>) -> String {
         let log = format!("{args:?}");
@@ -547,6 +547,33 @@ impl AgentServer {
         .await
     }
 
+    #[tool(
+        description = "Bulk-clear specific todos by id in one call, instead of \
+        `cancel_loose_end`ing each one. List-based, not range-based — no `ack_until`-style \
+        'clear below id N' for todos, since a blind range-clear risks acking something you \
+        never saw. Pass the ids you've actually reviewed (typically what `get_loose_ends` \
+        just showed); unknown/already-acked ids are silently skipped. Returns how many were \
+        newly acked."
+    )]
+    async fn mark_todos_done(&self, Parameters(args): Parameters<MarkTodosDoneArgs>) -> String {
+        let log = format!("{args:?}");
+        run_tool_envelope("mark_todos_done", log, async move {
+            match mark_local_todos_done(args.ids).await {
+                Some(hive_agent_sock::Response::Acked { count }) => {
+                    format!("acked {count} todo(s)")
+                }
+                Some(hive_agent_sock::Response::Err { message }) => {
+                    format!("mark_todos_done failed: {message}")
+                }
+                Some(other) => format!("mark_todos_done unexpected response: {other:?}"),
+                None => "mark_todos_done: local todo socket unavailable \
+                         (HIVE_AGENT_SOCKET unset or harness unreachable)"
+                    .to_owned(),
+            }
+        })
+        .await
+    }
+
     #[tool(
         description = "Create a git repo through hive-c0re. You CANNOT create repos with your \
         own forge token (creation is disabled) — this is the only path. The repo is created in \
diff --git a/hive-agent-mcp/src/mcp/render.rs b/hive-agent-mcp/src/mcp/render.rs
index 8a06d98d..085c54a2 100644
--- a/hive-agent-mcp/src/mcp/render.rs
+++ b/hive-agent-mcp/src/mcp/render.rs
@@ -136,6 +136,124 @@ 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
+/// 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
+/// transport to return at all, which is worse than a bug: it's a deadlock
+/// (the agent can't even see what's pending to start clearing it). Capping
+/// here guarantees `get_loose_ends` always returns successfully; the
+/// truncation summary tells the agent to review the shown batch, bulk-clear
+/// the reviewed ids via `mark_todos_done`, then call again for the next
+/// batch — deliberately NOT a "clear everything below id N" range escape
+/// hatch (a reviewer's call: a range-based bulk-ack risks silently
+/// acking something the agent never actually looked at, since todos are
+/// heterogeneous unrelated items, not a sequentially-read stream the way
+/// inbox messages are).
+const MAX_RENDERED_TODOS: usize = 40;
+
+/// Render one non-`Todo` [`hive_sh4re::LooseEnd`] variant onto `out`. Split
+/// out of `render_loose_ends` to keep that function under clippy's
+/// `too_many_lines` limit — `Todo` stays inline there since it also needs
+/// the shared `shown_todos` counter.
+fn render_one_loose_end(out: &mut String, t: &hive_sh4re::LooseEnd) {
+    use std::fmt::Write as _;
+    match t {
+        hive_sh4re::LooseEnd::Approval {
+            id,
+            agent,
+            commit_ref,
+            description,
+            age_seconds,
+        } => {
+            let desc = description
+                .as_deref()
+                .map(|d| format!(" — {d}"))
+                .unwrap_or_default();
+            let _ = writeln!(
+                out,
+                "- approval #{id} ({agent} @ {commit_ref}, {age_seconds}s old){desc}"
+            );
+        }
+        hive_sh4re::LooseEnd::Question {
+            id,
+            asker,
+            target,
+            question,
+            age_seconds,
+        } => {
+            let to = target.as_deref().unwrap_or("operator");
+            let _ = writeln!(
+                out,
+                "- question #{id} ({asker} → {to}, {age_seconds}s old): {question}"
+            );
+        }
+        hive_sh4re::LooseEnd::Reminder {
+            id,
+            owner,
+            message,
+            due_at,
+            age_seconds,
+        } => {
+            let _ = writeln!(
+                out,
+                "- reminder #{id} ({owner}, scheduled {age_seconds}s ago, due_at={due_at}): {message}"
+            );
+        }
+        hive_sh4re::LooseEnd::PendingMessages { count } => {
+            let _ = writeln!(
+                out,
+                "- {count} pending inbox message(s) — drain with recv (recv(max: {count}) to batch)"
+            );
+        }
+        hive_sh4re::LooseEnd::UnreadMatrix { rooms, summary } => {
+            let _ = write!(out, "- unread matrix messages in {rooms} room(s)");
+            if summary.is_empty() {
+                let _ = writeln!(
+                    out,
+                    " — use list_rooms + read_room to view, mark_read to clear"
+                );
+            } else {
+                let _ = writeln!(out, ":");
+                for line in summary.lines() {
+                    let _ = writeln!(out, "  {line}");
+                }
+                let _ = writeln!(
+                    out,
+                    "  use list_rooms + read_room to view, mark_read to clear"
+                );
+            }
+        }
+        hive_sh4re::LooseEnd::Todo { .. } => {
+            // Handled inline by the caller (needs the shared shown-count).
+        }
+    }
+}
+
+/// Render one `Todo` [`hive_sh4re::LooseEnd`] onto `out`. Split out for the
+/// same `too_many_lines` reason as [`render_one_loose_end`].
+fn render_todo_loose_end(
+    out: &mut String,
+    id: i64,
+    subsystem: &str,
+    subsystem_key: Option<&str>,
+    summary: &str,
+    source: Option<&str>,
+    age_seconds: u64,
+) {
+    use std::fmt::Write as _;
+    let key = subsystem_key.map(|k| format!(" {k}")).unwrap_or_default();
+    let src = source.map(|s| format!(" — {s}")).unwrap_or_default();
+    let _ = writeln!(
+        out,
+        "- todo #{id} [{subsystem}{key}, {age_seconds}s old]: {summary}{src} \
+         (cancel_loose_end kind:\"todo\" id:{id} to clear)"
+    );
+}
+
 /// Inner renderer for a `Vec<LooseEnd>` already extracted from the socket
 /// reply. Called by the `get_loose_ends` handler, which injects the
 /// `UnreadMatrix` entry before formatting.
@@ -145,96 +263,42 @@ pub(super) fn render_loose_ends(loose_ends: &[hive_sh4re::LooseEnd]) -> String {
         return "(no loose ends)".to_owned();
     }
     let mut out = format!("{} loose end(s):\n", loose_ends.len());
+    let mut shown_todos = 0usize;
+    let mut hidden_todos = 0usize;
     for t in loose_ends {
-        match t {
-            hive_sh4re::LooseEnd::Approval {
-                id,
-                agent,
-                commit_ref,
-                description,
-                age_seconds,
-            } => {
-                let desc = description
-                    .as_deref()
-                    .map(|d| format!(" — {d}"))
-                    .unwrap_or_default();
-                let _ = writeln!(
-                    out,
-                    "- approval #{id} ({agent} @ {commit_ref}, {age_seconds}s old){desc}"
-                );
-            }
-            hive_sh4re::LooseEnd::Question {
-                id,
-                asker,
-                target,
-                question,
-                age_seconds,
-            } => {
-                let to = target.as_deref().unwrap_or("operator");
-                let _ = writeln!(
-                    out,
-                    "- question #{id} ({asker} → {to}, {age_seconds}s old): {question}"
-                );
-            }
-            hive_sh4re::LooseEnd::Reminder {
-                id,
-                owner,
-                message,
-                due_at,
-                age_seconds,
-            } => {
-                let _ = writeln!(
-                    out,
-                    "- reminder #{id} ({owner}, scheduled {age_seconds}s ago, due_at={due_at}): {message}"
-                );
-            }
-            hive_sh4re::LooseEnd::PendingMessages { count } => {
-                let _ = writeln!(
-                    out,
-                    "- {count} pending inbox message(s) — drain with recv (recv(max: {count}) to batch)"
-                );
-            }
-            hive_sh4re::LooseEnd::UnreadMatrix { rooms, summary } => {
-                let _ = write!(out, "- unread matrix messages in {rooms} room(s)");
-                if summary.is_empty() {
-                    let _ = writeln!(
-                        out,
-                        " — use list_rooms + read_room to view, mark_read to clear"
-                    );
-                } else {
-                    let _ = writeln!(out, ":");
-                    for line in summary.lines() {
-                        let _ = writeln!(out, "  {line}");
-                    }
-                    let _ = writeln!(
-                        out,
-                        "  use list_rooms + read_room to view, mark_read to clear"
-                    );
-                }
-            }
-            hive_sh4re::LooseEnd::Todo {
-                id,
-                subsystem,
-                subsystem_key,
-                summary,
-                source,
-                age_seconds,
-            } => {
-                let key = subsystem_key
-                    .as_deref()
-                    .map(|k| format!(" {k}"))
-                    .unwrap_or_default();
-                let src = source
-                    .as_deref()
-                    .map(|s| format!(" — {s}"))
-                    .unwrap_or_default();
-                let _ = writeln!(
-                    out,
-                    "- todo #{id} [{subsystem}{key}, {age_seconds}s old]: {summary}{src} \
-                     (cancel_loose_end kind:\"todo\" id:{id} to clear)"
-                );
-            }
+        let hive_sh4re::LooseEnd::Todo {
+            id,
+            subsystem,
+            subsystem_key,
+            summary,
+            source,
+            age_seconds,
+        } = t
+        else {
+            render_one_loose_end(&mut out, t);
+            continue;
+        };
+        if shown_todos >= MAX_RENDERED_TODOS {
+            hidden_todos += 1;
+            continue;
         }
+        render_todo_loose_end(
+            &mut out,
+            *id,
+            subsystem,
+            subsystem_key.as_deref(),
+            summary,
+            source.as_deref(),
+            *age_seconds,
+        );
+        shown_todos += 1;
+    }
+    if hidden_todos > 0 {
+        let _ = writeln!(
+            out,
+            "- {hidden_todos} more todo(s) not shown — clear reviewed ids with \
+             mark_todos_done(ids: [...]), then call get_loose_ends again for the rest"
+        );
     }
     out
 }
@@ -350,6 +414,13 @@ pub(super) async fn mark_local_todo_done(id: i64) -> Option<hive_agent_sock::Res
     dial_agent_socket(&hive_agent_sock::Request::MarkTodoDone { id }).await
 }
 
+/// Bulk-ack an explicit list of local todo ids, via the harness's in-agent
+/// socket — the multi-id analogue of `mark_local_todo_done`, for the
+/// `mark_todos_done` tool.
+pub(super) async fn mark_local_todos_done(ids: Vec<i64>) -> Option<hive_agent_sock::Response> {
+    dial_agent_socket(&hive_agent_sock::Request::MarkTodosDone { ids }).await
+}
+
 /// Format a `Vec<MatrixRoomUnread>` into a per-room summary string.
 /// Single room / single message collapses to one line; multi-room
 /// expands to a bulleted list. Returns an empty string for empty input.
diff --git a/hive-agent-sock/src/lib.rs b/hive-agent-sock/src/lib.rs
index e3cd83ed..294a4b43 100644
--- a/hive-agent-sock/src/lib.rs
+++ b/hive-agent-sock/src/lib.rs
@@ -59,6 +59,12 @@ pub enum Request {
     },
     /// The agent marks one of its own todos done, by id.
     MarkTodoDone { id: i64 },
+    /// The agent bulk-acks a specific, explicit list of its own todos in
+    /// one shot — for clearing a backlog that's piled up past the point of
+    /// per-id triage, without the range-based `ack_until`-style semantics
+    /// that risk silently acking something never actually looked at (see
+    /// `Todos::mark_done_many`'s doc for why it's ids, not a threshold).
+    MarkTodosDone { ids: Vec<i64> },
     /// Schedule a reminder that fires into this agent's own turn loop at
     /// `timing` (harness-local — no broker round-trip). Same semantics as
     /// the old broker `Remind` request. `file_path`, when set, is where the
diff --git a/hive-agent/prompts/system.md b/hive-agent/prompts/system.md
index b00a7389..e545ec0b 100644
--- a/hive-agent/prompts/system.md
+++ b/hive-agent/prompts/system.md
@@ -2,7 +2,7 @@ You are hyperhive agent `{label}` (qualified: `{qualified_label}`){hive_identity
 
 Tools (hyperhive surface). Full signature + behavior for each comes from the tool's own MCP description (you already received it via the MCP tool schema) — this is just the map of what exists and which ones are gated, so you know where to look:
 
-- **Inbox / messaging** (always available): `mcp__hyperhive__recv`, `mcp__hyperhive__ack_until`, `mcp__hyperhive__send`, `mcp__hyperhive__ask`, `mcp__hyperhive__answer`, `mcp__hyperhive__get_loose_ends`, `mcp__hyperhive__cancel_loose_end`, `mcp__hyperhive__remind`, `mcp__hyperhive__set_status`, `mcp__hyperhive__get_agent_meta`. Two habits worth internalizing beyond the tool descriptions themselves: prefer ending the turn over repeatedly polling `recv` when idle (only turn-boundaries observe in-container todo wakes — bash-task completions, matrix unread, forge activity — and ending the turn is also your checkpoint); and `ask`/`answer` are async — `ask` returns immediately with a question id, the reply lands later as a `question_answered` system event, never block a turn waiting on it inline.
+- **Inbox / messaging** (always available): `mcp__hyperhive__recv`, `mcp__hyperhive__ack_until`, `mcp__hyperhive__send`, `mcp__hyperhive__ask`, `mcp__hyperhive__answer`, `mcp__hyperhive__get_loose_ends`, `mcp__hyperhive__cancel_loose_end`, `mcp__hyperhive__mark_todos_done`, `mcp__hyperhive__remind`, `mcp__hyperhive__set_status`, `mcp__hyperhive__get_agent_meta`. Two habits worth internalizing beyond the tool descriptions themselves: prefer ending the turn over repeatedly polling `recv` when idle (only turn-boundaries observe in-container todo wakes — bash-task completions, matrix unread, forge activity — and ending the turn is also your checkpoint); and `ask`/`answer` are async — `ask` returns immediately with a question id, the reply lands later as a `question_answered` system event, never block a turn waiting on it inline. For a large todo backlog (`get_loose_ends` caps at 40 rows), clear reviewed ids in bulk with `mark_todos_done` rather than cancelling one at a time — there's no blind range-clear, only ids you've actually looked at.
 - **Extra MCP tools** (some agents only): `mcp__<server>__<tool>` — agent-specific (matrix client, scraper, db connector, etc.) declared in your `agent.nix` under `hyperhive.extraMcpServers`. First-class tools, already operator-approved at deploy time.
 - **Lifecycle** (_requires `lifecycle` tool group_, direct children only, no approval needed): `restart`, `kill`, `start`, `update`, `list_containers`.
 - **Approvals** (_requires `approvals` tool group_, queues an operator approval): `request_init_config`, `request_apply_commit`, `request_update_meta_inputs`.
diff --git a/hive-agent/src/todo_server.rs b/hive-agent/src/todo_server.rs
index c307e027..e5b845dc 100644
--- a/hive-agent/src/todo_server.rs
+++ b/hive-agent/src/todo_server.rs
@@ -202,6 +202,7 @@ fn dispatch(
         } => clear_todo(store, &subsystem, key.as_deref(), all),
         Request::ListTodos { subsystem } => list_todos(store, subsystem.as_deref()),
         Request::MarkTodoDone { id } => mark_todo_done(store, id),
+        Request::MarkTodosDone { ids } => mark_todos_done(store, &ids),
         Request::StoreReminder {
             message,
             timing,
@@ -417,6 +418,21 @@ fn mark_todo_done(store: &Todos, id: i64) -> Response {
     }
 }
 
+/// `MarkTodosDone` handler: bulk-acks an explicit list of todo ids — the
+/// escape hatch for a backlog too large to triage one-by-one (see
+/// `Todos::mark_done_many`'s doc for why it's ids, not a threshold).
+fn mark_todos_done(store: &Todos, ids: &[i64]) -> Response {
+    match store.mark_done_many(ids) {
+        Ok(count) => {
+            tracing::debug!(n_ids = ids.len(), count, "todo bulk mark-done");
+            Response::Acked {
+                count: u64::try_from(count).unwrap_or(0),
+            }
+        }
+        Err(e) => err(&e),
+    }
+}
+
 /// `Request::Compact` handler: gate on context usage, then queue the same
 /// deferred `compact_pending` flag the operator's `/compact` button sets.
 /// Mirrors `hive-agent::web_ui::actions::post_compact` but reachable from
diff --git a/hive-agent/src/todos.rs b/hive-agent/src/todos.rs
index 4fc08465..53e5702e 100644
--- a/hive-agent/src/todos.rs
+++ b/hive-agent/src/todos.rs
@@ -245,6 +245,47 @@ impl Todos {
         Ok(n)
     }
 
+    /// Bulk-ack a specific, explicit list of todo ids in one shot. Exists
+    /// for the case a per-id `mark_done` loop isn't worth the round-trips:
+    /// an agent that hasn't called `get_loose_ends` in a long stretch (or
+    /// one whose producers pile up faster than it triages) can end up with
+    /// a backlog large enough that clearing it one call at a time is
+    /// impractical. Deliberately **explicit ids, not a `<= threshold`
+    /// range** — a reviewer's call on the design: a range-based
+    /// bulk-ack risks silently acking something the agent never actually
+    /// looked at, since todos are heterogeneous unrelated items (bash /
+    /// matrix / forge) rather than a sequentially-read stream the way inbox
+    /// messages are. The caller is expected to have looked at each id
+    /// (typically the ids `get_loose_ends` just rendered) before passing
+    /// them here. Same `acked`-not-deleted semantics as [`Self::mark_done`]
+    /// (a reconciled producer's next `upsert` still sees the row to compare
+    /// against). Unknown/already-acked ids are silently skipped — same "not
+    /// a new action" idempotence as the single-id path. Returns the number
+    /// of rows newly acked.
+    ///
+    /// # Errors
+    ///
+    /// Propagates the sqlite update failure.
+    ///
+    /// # Panics
+    ///
+    /// Panics if the connection mutex is poisoned.
+    pub fn mark_done_many(&self, ids: &[i64]) -> Result<usize> {
+        if ids.is_empty() {
+            return Ok(0);
+        }
+        let conn = self.conn.lock().unwrap();
+        let now = Utc::now().timestamp();
+        let mut total = 0usize;
+        for id in ids {
+            total += conn.execute(
+                "UPDATE todos SET acked = 1, acked_at = ?1 WHERE acked = 0 AND id = ?2",
+                params![now, id],
+            )?;
+        }
+        Ok(total)
+    }
+
     /// List todos, newest-updated first. `subsystem = Some(..)` filters to
     /// one producer's set; `None` returns all. Excludes acked rows — once
     /// the agent has dismissed a todo it stays out of its own list, even
@@ -476,6 +517,28 @@ mod tests {
         assert!(!s.has_any().unwrap(), "acked-only table reads as empty");
     }
 
+    /// `mark_done_many` acks exactly the ids passed, leaves the rest
+    /// untouched — no threshold/range semantics.
+    #[test]
+    fn mark_done_many_acks_only_the_listed_ids() {
+        let (_dir, s) = store();
+        let (id1, _) = s.upsert("bash", None, "task 1", None).unwrap();
+        let (id2, _) = s.upsert("bash", None, "task 2", None).unwrap();
+        let (id3, _) = s.upsert("bash", None, "task 3", None).unwrap();
+        assert_eq!(
+            s.mark_done_many(&[id1, id3]).unwrap(),
+            2,
+            "acks id1 and id3, not id2 — not a range"
+        );
+        let left = s.list(None).unwrap();
+        assert_eq!(left.len(), 1);
+        assert_eq!(left[0].id, id2);
+        // Idempotent: re-running over the same ids acks nothing new.
+        assert_eq!(s.mark_done_many(&[id1, id3]).unwrap(), 0);
+        // Empty input is a no-op, not an error.
+        assert_eq!(s.mark_done_many(&[]).unwrap(), 0);
+    }
+
     /// `reap_acked` only removes acked rows past the cutoff — a recent ack
     /// and any un-acked row both survive.
     #[test]