diff --git a/src/claire/scheduler.py b/src/claire/scheduler.py
index 8bad17c..f745bb1 100644
--- a/src/claire/scheduler.py
+++ b/src/claire/scheduler.py
@@ -9,6 +9,7 @@ ranked ordering. This makes the logic trivially unit-testable.
 
 from __future__ import annotations
 
+import logging
 import sqlite3
 from collections.abc import Iterable
 from datetime import datetime, timedelta, timezone
@@ -19,6 +20,37 @@ from .domain import ProjectStatus, Session, Task, TaskStatus
 from .hlc import HLC
 
 
+_log = logging.getLogger(__name__)
+
+
+def unfinished_blockers(conn: sqlite3.Connection, task: Task) -> list[Task]:
+    """Return the tasks in `task.blocked_by` that are NOT yet `done`.
+
+    A task is "effectively blocked" iff this list is non-empty. A blocker
+    id that resolves to no existing task is treated as satisfied (it does
+    NOT block) so a stale/deleted id can't permanently wedge a task — such
+    ids are logged at WARNING level.
+    """
+    unfinished: list[Task] = []
+    for blocker_id in task.blocked_by:
+        blocker = read.get_task(conn, blocker_id)
+        if blocker is None:
+            _log.warning(
+                "task %s lists blocker %s which no longer exists — "
+                "treating as satisfied",
+                task.id, blocker_id,
+            )
+            continue
+        if blocker.status != TaskStatus.DONE:
+            unfinished.append(blocker)
+    return unfinished
+
+
+def is_blocked(conn: sqlite3.Connection, task: Task) -> bool:
+    """True iff `task` has at least one unfinished blocker."""
+    return bool(unfinished_blockers(conn, task))
+
+
 def rank_open_tasks(tasks: Iterable[Task]) -> list[Task]:
     """Order tasks by (priority asc, created_hlc asc).
 
@@ -285,9 +317,12 @@ def suggest_assignments(
     assigned_task_ids = {a.task_id for a in active}
     assigned_session_ids = {a.session_uuid for a in active}
 
-    unassigned_tasks = rank_open_tasks(
-        [t for t in open_tasks if t.id not in assigned_task_ids]
-    )
+    # Exclude effectively-blocked tasks: a task with an unfinished blocker
+    # is not workable, so Clare must not propose it for pairing.
+    unassigned_tasks = rank_open_tasks([
+        t for t in open_tasks
+        if t.id not in assigned_task_ids and not is_blocked(conn, t)
+    ])
     free_sessions = sorted(
         [s for s in read.list_sessions(conn) if s.uuid not in assigned_session_ids],
         key=lambda s: (-session_attention_score(s), s.host, str(s.uuid)),
diff --git a/src/claire/web/service.py b/src/claire/web/service.py
index ca0521f..6760682 100644
--- a/src/claire/web/service.py
+++ b/src/claire/web/service.py
@@ -1326,6 +1326,20 @@ def dispatch_task(
     if task.status in {TaskStatus.DONE}:
         return DispatchResult(False, str(task_id), "task already done")
 
+    from .. import scheduler as _sched
+
+    # Dependency gate — checked FIRST: being blocked is intrinsic to the
+    # task, unlike the transient budget/host gates below, so it's the
+    # truest reason to surface. Refuse a task whose `blocked_by` list
+    # still has an unfinished blocker — its prerequisites aren't met.
+    blockers = _sched.unfinished_blockers(conn, task)
+    if blockers:
+        titles = ", ".join(b.title for b in blockers)
+        return DispatchResult(
+            False, str(task_id),
+            f"blocked by {len(blockers)} unfinished task(s): {titles}",
+        )
+
     # Budget gate.
     bs = budget_status(conn)
     if bs["over_cap"]:
@@ -1341,7 +1355,6 @@ def dispatch_task(
 
     # Host-load gate.
     cfg = load_or_init()
-    from .. import scheduler as _sched
     if not _sched.host_has_capacity(conn, host, per_host_max=cfg.limits.per_host_max):
         return DispatchResult(
             False, str(task_id),
diff --git a/tests/test_task_deps.py b/tests/test_task_deps.py
index 8e7d043..8dc2ac4 100644
--- a/tests/test_task_deps.py
+++ b/tests/test_task_deps.py
@@ -10,11 +10,15 @@ the projection + read layer.
 from __future__ import annotations
 
 import sqlite3
+import uuid as _uuid
+from dataclasses import dataclass
+from uuid import UUID
 
 import pytest
 
 from claire import events as ev
-from claire import read
+from claire import read, scheduler
+from claire.domain import TaskStatus
 from claire.hlc import HLCGenerator
 from claire.web import service
 
@@ -200,3 +204,186 @@ def test_list_tasks_returns_blocked_by(
     assert by_id[task.id].blocked_by == [blocker.id]
     # A task with no blockers projects to an empty list.
     assert by_id[blocker.id].blocked_by == []
+
+
+# --- blocked-check helper --------------------------------------------------
+
+
+def test_unfinished_blockers_excludes_done(
+    conn: sqlite3.Connection, gen: HLCGenerator
+) -> None:
+    service.create_project(conn, gen, name="alpha")
+    task = service.add_task(conn, gen, project="alpha", title="ship it")
+    b_open = service.add_task(conn, gen, project="alpha", title="open blocker")
+    b_done = service.add_task(conn, gen, project="alpha", title="done blocker")
+    service.transition_task_state(
+        conn, gen, task_id=b_done.id, to_state=TaskStatus.DONE
+    )
+    service.set_task_blockers(
+        conn, gen, task_ref=str(task.id),
+        blocker_refs=[str(b_open.id), str(b_done.id)],
+    )
+
+    fresh = read.get_task(conn, task.id)
+    assert fresh is not None
+    unfinished = scheduler.unfinished_blockers(conn, fresh)
+
+    # Only the still-open blocker counts.
+    assert [b.id for b in unfinished] == [b_open.id]
+    assert scheduler.is_blocked(conn, fresh) is True
+
+
+def test_unfinished_blockers_nonexistent_does_not_block(
+    conn: sqlite3.Connection, gen: HLCGenerator
+) -> None:
+    """A blocker id with no matching task is treated as satisfied."""
+    service.create_project(conn, gen, name="alpha")
+    task = service.add_task(conn, gen, project="alpha", title="ship it")
+    blocker = service.add_task(conn, gen, project="alpha", title="prereq")
+    service.set_task_blockers(
+        conn, gen, task_ref=str(task.id), blocker_refs=[str(blocker.id)]
+    )
+    # Hard-delete the blocker row directly so the id is now stale. The
+    # service layer never deletes tasks, so this simulates a stale id.
+    conn.execute("DELETE FROM tasks WHERE id = ?", (str(blocker.id),))
+
+    fresh = read.get_task(conn, task.id)
+    assert fresh is not None
+    assert scheduler.unfinished_blockers(conn, fresh) == []
+    assert scheduler.is_blocked(conn, fresh) is False
+
+
+# --- dispatch enforcement --------------------------------------------------
+
+
+@dataclass
+class _FakeSessionRow:
+    host: str
+    uuid: UUID
+    cwd: str
+    mtime_epoch: int
+    snippet: str = ""
+
+
+class _FakeRclaude:
+    """spawn() records the call and makes a new session discoverable."""
+
+    def __init__(self) -> None:
+        self._rows: list[_FakeSessionRow] = []
+        self.spawn_calls: list[dict] = []
+        self.send_calls: list[dict] = []
+
+    def list_sessions(self) -> list[_FakeSessionRow]:
+        return list(self._rows)
+
+    def list_tmux(self) -> list:
+        return []
+
+    def spawn(
+        self, *, host: str, cwd: str,
+        mcp_config: str | None = None, name: str | None = None,
+    ) -> str:
+        self.spawn_calls.append(
+            {"host": host, "cwd": cwd, "mcp_config": mcp_config, "name": name}
+        )
+        self._rows.append(_FakeSessionRow(
+            host=host, uuid=_uuid.uuid4(), cwd=cwd, mtime_epoch=999,
+        ))
+        return f"claude-tester-{len(self.spawn_calls)}"
+
+    def send(self, *, text: str, match: str, yes: bool = False, dry_run: bool = False):  # noqa: ARG002
+        self.send_calls.append({"text": text, "match": match, "yes": yes})
+        return None
+
+
+def _no_mcp_stager(host: str) -> str | None:  # noqa: ARG001
+    return None
+
+
+def test_dispatch_refuses_blocked_task(
+    conn: sqlite3.Connection, gen: HLCGenerator
+) -> None:
+    service.create_project(conn, gen, name="alpha")
+    task = service.add_task(conn, gen, project="alpha", title="ship it")
+    blocker = service.add_task(conn, gen, project="alpha", title="prereq work")
+    service.set_task_blockers(
+        conn, gen, task_ref=str(task.id), blocker_refs=[str(blocker.id)]
+    )
+    rcl = _FakeRclaude()
+
+    result = service.dispatch_task(
+        conn, gen, task_id=task.id, host="plum", cwd="/work",
+        rclaude=rcl, discover_timeout_s=2, mcp_stager=_no_mcp_stager,
+    )
+
+    assert result.dispatched is False
+    assert "blocked by 1 unfinished task" in result.reason
+    assert "prereq work" in result.reason
+    assert rcl.spawn_calls == []  # never spawned
+
+
+def test_dispatch_allows_task_once_blockers_done(
+    conn: sqlite3.Connection, gen: HLCGenerator
+) -> None:
+    service.create_project(conn, gen, name="alpha")
+    task = service.add_task(conn, gen, project="alpha", title="ship it")
+    blocker = service.add_task(conn, gen, project="alpha", title="prereq work")
+    service.set_task_blockers(
+        conn, gen, task_ref=str(task.id), blocker_refs=[str(blocker.id)]
+    )
+    # Complete the blocker.
+    service.transition_task_state(
+        conn, gen, task_id=blocker.id, to_state=TaskStatus.DONE
+    )
+    rcl = _FakeRclaude()
+
+    result = service.dispatch_task(
+        conn, gen, task_id=task.id, host="plum", cwd="/work",
+        rclaude=rcl, discover_timeout_s=2, mcp_stager=_no_mcp_stager,
+    )
+
+    assert result.dispatched is True
+    assert result.reason == "ok"
+    assert len(rcl.spawn_calls) == 1
+
+
+# --- scheduler enforcement -------------------------------------------------
+
+
+def _alive_session(conn: sqlite3.Connection, gen: HLCGenerator, host: str) -> UUID:
+    sid = _uuid.uuid4()
+    ev.append(conn, gen, ev.SessionObserved(session_uuid=sid, host=host, cwd="/w"))
+    conn.execute("UPDATE sessions SET liveness = 'alive' WHERE uuid = ?", (str(sid),))
+    return sid
+
+
+def test_suggest_assignments_excludes_blocked_task(
+    conn: sqlite3.Connection, gen: HLCGenerator
+) -> None:
+    service.create_project(conn, gen, name="alpha")
+    task = service.add_task(conn, gen, project="alpha", title="ship it")
+    blocker = service.add_task(conn, gen, project="alpha", title="prereq work")
+    service.set_task_blockers(
+        conn, gen, task_ref=str(task.id), blocker_refs=[str(blocker.id)]
+    )
+    _alive_session(conn, gen, "plum")
+
+    # While the blocker is open, the blocked task must not be paired or
+    # surfaced as a remaining (workable) task. The blocker itself is open
+    # and unassigned, so it CAN be surfaced.
+    out = scheduler.suggest_assignments(conn)
+    surfaced = {p["task_id"] for p in out["pairings"]} | {
+        t["id"] for t in out["remaining_tasks"]
+    }
+    assert str(task.id) not in surfaced
+    assert str(blocker.id) in surfaced
+
+    # Once the blocker is done, the previously-blocked task becomes eligible.
+    service.transition_task_state(
+        conn, gen, task_id=blocker.id, to_state=TaskStatus.DONE
+    )
+    out2 = scheduler.suggest_assignments(conn)
+    surfaced2 = {p["task_id"] for p in out2["pairings"]} | {
+        t["id"] for t in out2["remaining_tasks"]
+    }
+    assert str(task.id) in surfaced2