diff --git a/features/decomposition_max_child_depth.feature b/features/decomposition_max_child_depth.feature
new file mode 100644
index 000000000..262232235
--- /dev/null
+++ b/features/decomposition_max_child_depth.feature
@@ -0,0 +1,38 @@
+Feature: Decomposition respects max_child_depth limit
+  As a plan orchestrator
+  I want the decomposition service to enforce plan.max-child-depth
+  So that child plans cannot nest deeper than the configured limit
+
+  Background:
+    Given a decomposition service
+
+  Scenario: Decomposition stops recursing when max_child_depth limit is reached
+    Given a project with 500 files across 8 directory levels
+    When I decompose with max_child_depth 2 and max_depth 10
+    Then the decomposition result should have max_depth_reached <= 2
+    And the decomposition warning log should contain "max-child-depth limit"
+
+  Scenario: Decomposition with default max_child_depth allows standard depth
+    Given a project with 2000 files across 5 directory levels
+    When I decompose with default max_child_depth
+    Then the decomposition result should have max_depth_reached >= 1
+    And the decomposition result should have max_depth_reached <= 5
+
+  Scenario: max_child_depth guard triggers before max_depth when more restrictive
+    Given a project with 500 files across 8 directory levels
+    When I decompose with max_child_depth 1 and max_depth 10
+    Then the decomposition result should have max_depth_reached <= 1
+    And the decomposition warning log should contain "max-child-depth limit"
+
+  Scenario: max_depth can be more restrictive than max_child_depth
+    Given a project with 500 files across 8 directory levels
+    When I decompose with max_child_depth 10 and max_depth 2
+    Then the decomposition result should have max_depth_reached <= 2
+
+  Scenario: Default config includes max_child_depth with expected value
+    Given default decomposition config
+    Then max_child_depth should be 5
+
+  Scenario: Invalid max_child_depth value is rejected
+    When I create a config with max_child_depth 0
+    Then a decomposition ValueError should be raised
diff --git a/features/large_project_decomposition.feature b/features/large_project_decomposition.feature
index e006ce210..ae16f2df7 100644
--- a/features/large_project_decomposition.feature
+++ b/features/large_project_decomposition.feature
@@ -114,6 +114,7 @@ Feature: Large-project hierarchical decomposition
   Scenario: Default config has expected values
     Given default decomposition config
     Then max_depth should be 4
+    And max_child_depth should be 5
     And max_files_per_subplan should be 500
     And max_tokens_per_subplan should be 100000
     And min_files_per_subplan should be 10
diff --git a/features/steps/decomposition_max_child_depth_steps.py b/features/steps/decomposition_max_child_depth_steps.py
new file mode 100644
index 000000000..c5bc10933
--- /dev/null
+++ b/features/steps/decomposition_max_child_depth_steps.py
@@ -0,0 +1,81 @@
+"""Step implementations for decomposition_max_child_depth.feature.
+
+Tests the enforcement of max_child_depth in DecompositionService._build_hierarchy.
+Reuses existing steps from large_project_decomposition_steps.py where applicable.
+Only new, unique step patterns are defined here.
+"""
+
+from __future__ import annotations
+
+from typing import Any
+from unittest.mock import patch
+
+from behave import then, when  # type: ignore[import-untyped]
+
+from cleveragents.application.services.decomposition_models import (
+    DecompositionConfig,
+)
+
+# ---------------------------------------------------------------------------
+# Constants
+# ---------------------------------------------------------------------------
+
+_DECOMP_SVC_LOGGER = "cleveragents.application.services.decomposition_service.logger"
+
+
+# ---------------------------------------------------------------------------
+# Whens
+# ---------------------------------------------------------------------------
+
+
+@when("I decompose with max_child_depth {mcd:d} and max_depth {md:d}")
+def step_when_decompose_max_child_depth_and_max_depth(
+    context: Any,
+    mcd: int,
+    md: int,
+) -> None:
+    cfg = DecompositionConfig(
+        max_child_depth=mcd,
+        max_depth=md,
+        max_files_per_subplan=30,
+    )
+    with patch(_DECOMP_SVC_LOGGER) as mock_logger:
+        context.result = context.svc.decompose(context.files, cfg)
+        context.mock_logger = mock_logger
+
+
+@when("I decompose with default max_child_depth")
+def step_when_decompose_default_mcd(context: Any) -> None:
+    cfg = DecompositionConfig(
+        max_child_depth=5,
+        max_files_per_subplan=30,
+    )
+    with patch(_DECOMP_SVC_LOGGER) as mock_logger:
+        context.result = context.svc.decompose(context.files, cfg)
+        context.mock_logger = mock_logger
+
+
+@when("I create a config with max_child_depth {n:d}")
+def step_when_create_bad_max_child_depth(context: Any, n: int) -> None:
+    try:
+        DecompositionConfig(max_child_depth=n)
+    except ValueError as exc:
+        context.error = exc
+
+
+# ---------------------------------------------------------------------------
+# Thens
+# ---------------------------------------------------------------------------
+
+
+@then('the decomposition warning log should contain "{text}"')
+def step_then_warning_log_contains(context: Any, text: str) -> None:
+    assert context.mock_logger is not None, "Mock logger was not set"
+    assert context.mock_logger.warning.called, "Expected logger.warning to be called"
+    args_str = str(context.mock_logger.warning.call_args_list)
+    assert text in args_str, f"Expected '{text}' in warning calls, got: {args_str}"
+
+
+@then("max_child_depth should be {n:d}")
+def step_then_cfg_max_child_depth(context: Any, n: int) -> None:
+    assert context.decomp_config.max_child_depth == n
diff --git a/src/cleveragents/application/services/decomposition_models.py b/src/cleveragents/application/services/decomposition_models.py
index 6701cf7f7..679f137ab 100644
--- a/src/cleveragents/application/services/decomposition_models.py
+++ b/src/cleveragents/application/services/decomposition_models.py
@@ -47,6 +47,7 @@ class DecompositionConfig:
 
     Attributes:
         max_depth: Maximum recursion depth (root = 0).
+        max_child_depth: Maximum allowed child-plan nesting depth.
         max_files_per_subplan: Upper bound on files in a single leaf.
         max_tokens_per_subplan: Upper bound on estimated tokens per leaf.
         min_files_per_subplan: Below this, no further splitting.
@@ -55,6 +56,7 @@ class DecompositionConfig:
     """
 
     max_depth: int = 4
+    max_child_depth: int = 5
     max_files_per_subplan: int = 500
     max_tokens_per_subplan: int = 100_000
     min_files_per_subplan: int = 10
@@ -65,6 +67,8 @@ class DecompositionConfig:
     def __post_init__(self) -> None:
         if self.max_depth < 1:
             raise ValueError("max_depth must be >= 1")
+        if self.max_child_depth < 1:
+            raise ValueError("max_child_depth must be >= 1")
         if self.max_files_per_subplan < 1:
             raise ValueError("max_files_per_subplan must be >= 1")
         if self.max_tokens_per_subplan < 1:
diff --git a/src/cleveragents/application/services/decomposition_service.py b/src/cleveragents/application/services/decomposition_service.py
index c67a110fe..a96c88c46 100644
--- a/src/cleveragents/application/services/decomposition_service.py
+++ b/src/cleveragents/application/services/decomposition_service.py
@@ -209,15 +209,26 @@ class DecompositionService:
         # Leaf conditions
         # M6 requires deep hierarchical decomposition (4+ levels) for
         # large plans. To preserve this behavior, we only stop early when
-        # we hit max_depth or the workset is trivially small; otherwise we
-        # keep partitioning even when a cluster is already under the max
-        # file/token bounds.
+        # we hit max_depth, max_child_depth, or the workset is trivially
+        # small; otherwise we keep partitioning even when a cluster is
+        # already under the max file/token bounds.
+        reached_child_depth_limit = depth >= config.max_child_depth
         is_leaf = (
-            depth >= config.max_depth or len(files) <= config.min_files_per_subplan
+            depth >= config.max_depth
+            or reached_child_depth_limit
+            or len(files) <= config.min_files_per_subplan
         )
 
         node_id = _next_node_id()
         if is_leaf or len(files) <= config.min_files_per_subplan:
+            if reached_child_depth_limit:
+                logger.warning(
+                    "Decomposition reached max-child-depth limit (%d) "
+                    "at depth %d. Creating terminal node for %d files.",
+                    config.max_child_depth,
+                    depth,
+                    len(files),
+                )
             node = DecompositionNode(
                 node_id=node_id,
                 parent_id=parent_id,