add cross_service flag to trace tool for seamless boundary traversal (#256)

Agents expected trace to cross service boundaries but couldn't control it.
Add `cross_service: bool = False` parameter — when True, BFS continues
through HTTP_CALLS/ASYNC_CALLS boundaries into downstream services.
EXPOSES is auto-added as scaffolding (exempt from fan_out_cap) so
Route -> Handler is followed automatically. Default preserves existing
boundary-stop behavior.

Co-authored-by: Claude Opus 4.7 <noreply@anthropic.com>

Author: HumanBean17

mcp_hints.py

@@ -570,24 +570,33 @@ def _trace_structured_hints(payload: dict[str, Any]) -> tuple[list[_StructuredHi
     # (c) Cross-service boundary hint (no stats dependency).
     xs_edges = [e for e in edges if e.get("cross_service_boundary")]
     if xs_edges:
-        for xe in xs_edges[:3]:
-            to_id = str(xe.get("to_id") or "")
-            from_id = str(xe.get("from_id") or "")
-            confidence = xe.get("attrs", {}).get("confidence") if isinstance(xe.get("attrs"), dict) else None
-            conf_str = f"confidence={confidence}" if confidence is not None else "low confidence"
+        # When cross_service=True, BFS already continued through boundaries.
+        # Emit a lighter informational advisory instead of an action hint.
+        was_seamless = bool(payload.get("cross_service"))
+        if was_seamless:
             advisories.append((
                 PRIORITY_META,
-                f"Cross-service boundary: {from_id} -> {to_id} ({conf_str}). "
-                f"Use trace('{to_id}', 'out', ['EXPOSES','CALLS'], max_depth=4) to continue in the downstream service, "
-                f"or describe('{to_id}') for route details.",
-            ))
-            struct_pairs.append(_StructuredHint(
-                "trace",
-                {"ids": [to_id], "direction": "out", "edge_types": ["EXPOSES", "CALLS"], "max_depth": 4},
-                True, PRIORITY_LEAF_FOLLOWUP,
-                LABEL_CROSS_SERVICE_BOUNDARY,
-                f"cross-service boundary: {from_id} -> {to_id}",
+                f"trace crossed {len(xs_edges)} service boundary(ies).",
             ))
+        else:
+            for xe in xs_edges[:3]:
+                to_id = str(xe.get("to_id") or "")
+                from_id = str(xe.get("from_id") or "")
+                confidence = xe.get("attrs", {}).get("confidence") if isinstance(xe.get("attrs"), dict) else None
+                conf_str = f"confidence={confidence}" if confidence is not None else "low confidence"
+                advisories.append((
+                    PRIORITY_META,
+                    f"Cross-service boundary: {from_id} -> {to_id} ({conf_str}). "
+                    f"Use trace('{to_id}', 'out', ['EXPOSES','CALLS'], max_depth=4) to continue in the downstream service, "
+                    f"or describe('{to_id}') for route details.",
+                ))
+                struct_pairs.append(_StructuredHint(
+                    "trace",
+                    {"ids": [to_id], "direction": "out", "edge_types": ["EXPOSES", "CALLS"], "max_depth": 4},
+                    True, PRIORITY_LEAF_FOLLOWUP,
+                    LABEL_CROSS_SERVICE_BOUNDARY,
+                    f"cross-service boundary: {from_id} -> {to_id}",
+                ))
 
     return (finalize_structured_hints(struct_pairs), finalize_advisories(advisories))
 

mcp_trace.py

@@ -498,6 +498,7 @@ def trace_v2(
     fan_out_cap: int = 5,
     collapse_trivial: bool = True,
     include_unresolved: bool = False,
+    cross_service: bool = False,
     graph: KuzuGraph | None = None,
 ) -> TraceOutput:
     """Multi-hop BFS traversal with pruning."""
@@ -601,6 +602,12 @@ def trace_v2(
     # Determine if cross-service detection is active.
     cross_service_active = bool(set(edge_types) & _CROSS_SERVICE_EDGE_TYPES)
 
+    # Effective scaffolding set: when cross_service=True, EXPOSES is also scaffolding
+    # so Route -> Handler is followed automatically in downstream services.
+    effective_scaffolding = _SCAFFOLDING_EDGE_TYPES
+    if cross_service:
+        effective_scaffolding = _SCAFFOLDING_EDGE_TYPES | frozenset({"EXPOSES"})
+
     # BFS state.
     visited: set[str] = set(seed_ids)
     frontier: list[str] = list(seed_ids)
@@ -639,7 +646,7 @@ def trace_v2(
         query_edge_types = list(edge_types)
         # Cross-service: also query scaffolding edges when cross-service is active.
         if cross_service_active:
-            for scaffold_et in _SCAFFOLDING_EDGE_TYPES:
+            for scaffold_et in effective_scaffolding:
                 if scaffold_et not in query_edge_types:
                     query_edge_types.append(scaffold_et)
 
@@ -672,7 +679,7 @@ def trace_v2(
 
             for row in src_rows:
                 et = str(row.get("edge_type") or "")
-                if et in _SCAFFOLDING_EDGE_TYPES:
+                if et in effective_scaffolding:
                     scaffolding_rows.append(row)
                 else:
                     signal_rows.append(row)
@@ -703,7 +710,7 @@ def trace_v2(
                 edge_type = str(row.get("edge_type") or "")
 
                 # --- Cross-service boundary detection ---
-                if edge_type in _SCAFFOLDING_EDGE_TYPES and cross_service_active:
+                if edge_type in effective_scaffolding and cross_service_active:
                     # Follow scaffolding edge to Client/Producer node.
                     # Record the scaffolding edge and include the node.
                     try:
@@ -791,9 +798,16 @@ def trace_v2(
                         edges.append(cross_edge)
                         edge_id_map[cross_edge_id] = cross_edge
                         visited.add(cross_target_id)
-                        # Do NOT add downstream node to frontier — boundary-stop.
-
-                    # Do NOT add Client/Producer to frontier either.
+                        # Track incoming edge for downstream node.
+                        if cross_target_id not in node_to_incoming_edge_id:
+                            node_to_incoming_edge_id[cross_target_id] = cross_edge_id
+                        # When cross_service=True, add downstream node to frontier
+                        # so BFS continues into the downstream service.
+                        if cross_service:
+                            new_frontier.add(cross_target_id)
+
+                    # Do NOT add Client/Producer to frontier — its cross-service
+                    # edges were already queried inline above.
                     continue
 
                 # --- Standard edge processing ---

server.py

@@ -587,8 +587,8 @@ async def resolve(
             "are exempt. `collapse_trivial` merges wrapper chains (A→B→C where B is trivial). "
             "Result: `nodes` dict (id → NodeRef), `edges` list with BFS metadata (hop, parent_edge_id, "
             "collapsed, cross_service_boundary), ranked `paths` (root-to-leaf), and `stats` with pruning counts. "
-            "Cross-service boundary: BFS records the cross-service edge and includes the downstream Route/Producer "
-            "in `nodes` but stops the frontier — the agent decides whether to continue."
+            "Cross-service boundary: by default BFS stops at service boundaries. "
+            "Set `cross_service=True` to continue traversal through HTTP_CALLS/ASYNC_CALLS boundaries."
         ),
     )
     async def trace(
@@ -628,6 +628,10 @@ async def trace(
             default=False,
             description="Include UnresolvedCallSite edges (CALLS out only)",
         ),
+        cross_service: bool = Field(
+            default=False,
+            description="Continue BFS through service boundaries (HTTP_CALLS/ASYNC_CALLS). Default: stop at boundaries.",
+        ),
     ) -> mcp_trace.TraceOutput:
         return await asyncio.to_thread(
             mcp_trace.trace_v2,
@@ -643,6 +647,7 @@ async def trace(
             fan_out_cap if fan_out_cap is not None else 5,
             collapse_trivial,
             include_unresolved,
+            cross_service,
             None,
         )
 

skills/explore-codebase/SKILL.md

@@ -178,7 +178,7 @@ Prefer **`resolve` -> `describe(id=...)`** over **`describe(fqn=...)`** when an
 | "What happens when route R is called?" | `find(kind="route")` then `trace(route_id, "out", ["EXPOSES","CALLS"], max_depth=4)` | `describe` on key nodes |
 | "Impact of changing method M" | `resolve` / `find` then `trace(id, "in", ["CALLS","OVERRIDES"], max_depth=3)` | `describe` on callers |
 | "Trace from X to database" | `trace(id, "out", ["CALLS"], max_depth=4, prune_roles=["DTO","EXCEPTION"])` | `neighbors` for pruned detail |
-| "What calls this across services?" | `trace(id, "out", ["CALLS","HTTP_CALLS","ASYNC_CALLS"], max_depth=5)` | `trace` on downstream route_id if needed |
+| "What calls this across services?" | `trace(id, "out", ["CALLS","HTTP_CALLS","ASYNC_CALLS"], max_depth=5, cross_service=True)` | `describe` on downstream routes |
 
 **Rules of thumb:**
 
@@ -216,7 +216,7 @@ Returns **edges** with `attrs` (`confidence`, `strategy`, `match`, ... on cross-
 
 ### `trace`
 
-Multi-hop BFS with pruning. Args: `ids` (string or list), **`direction`**, **`edge_types`** (stored labels only — no composed dot-keys), `max_depth` (default 3, clamped 1–5), `max_paths` (default 20), `max_nodes_discovered` (default 500, clamped 100–2000), optional `filter` (NodeFilter), optional `edge_filter` (CALLS only), optional `prune_roles` (soft gate — edges recorded, frontier stops), `fan_out_cap` (default 5, scaffolding edges exempt), `collapse_trivial` (default true), `include_unresolved` (default false).
+Multi-hop BFS with pruning. Args: `ids` (string or list), **`direction`**, **`edge_types`** (stored labels only — no composed dot-keys), `max_depth` (default 3, clamped 1–5), `max_paths` (default 20), `max_nodes_discovered` (default 500, clamped 100–2000), optional `filter` (NodeFilter), optional `edge_filter` (CALLS only), optional `prune_roles` (soft gate — edges recorded, frontier stops), `fan_out_cap` (default 5, scaffolding edges exempt), `collapse_trivial` (default true), `include_unresolved` (default false), `cross_service` (default false — set true to continue BFS through HTTP_CALLS/ASYNC_CALLS boundaries into downstream services).
 
 Returns `TraceOutput`: `success`, `seed_ids`, `direction`, `edge_types`, `actual_depth`, `nodes` (dict of id→NodeRef), `edges` (list of `TraceEdge`), `paths` (list of `TracePath`), `stats` (`TraceStats`), `advisories`.
 

tests/test_mcp_trace.py

@@ -923,9 +923,123 @@ def test_trace_cross_service_boundary_stops(kuzu_graph: KuzuGraph) -> None:
         assert len(downstream_edges) == 0
 
 
-# ---------------------------------------------------------------------------
-# PR-TRACE-2 tests: MCP tool registration
-# ---------------------------------------------------------------------------
+def test_trace_cross_service_seamless_http(kuzu_graph: KuzuGraph) -> None:
+    """cross_service=True: BFS continues through HTTP_CALLS boundary into downstream service."""
+    seed_id = _find_method_with_declares_client(kuzu_graph)
+    if seed_id is None:
+        pytest.skip("No method with DECLARES_CLIENT in fixture")
+
+    out = trace_v2(
+        ids=seed_id,
+        direction="out",
+        edge_types=["CALLS", "HTTP_CALLS"],
+        max_depth=5,
+        fan_out_cap=0,
+        cross_service=True,
+        graph=kuzu_graph,
+    )
+    assert out.success is True
+
+    # Should have cross-service boundary edges.
+    xs_edges = [e for e in out.edges if e.cross_service_boundary]
+    if not xs_edges:
+        pytest.skip("No cross-service edges in result")
+
+    for xe in xs_edges:
+        assert xe.edge_type in ("HTTP_CALLS", "ASYNC_CALLS")
+        # Downstream node should be in nodes.
+        assert xe.to_id in out.nodes
+
+    # Key difference from boundary-stop: downstream Route should have edges FROM it
+    # (EXPOSES to handler, then CALLS from handler) because BFS continued through.
+    for xe in xs_edges:
+        downstream_edges = [e for e in out.edges if e.from_id == xe.to_id]
+        # At least one edge (EXPOSES to handler) should exist from the downstream Route.
+        if downstream_edges:
+            exposes_edges = [e for e in downstream_edges if e.edge_type == "EXPOSES"]
+            assert len(exposes_edges) >= 1, (
+                f"Expected EXPOSES edges from {xe.to_id}, got: {[e.edge_type for e in downstream_edges]}"
+            )
+
+
+def test_trace_cross_service_seamless_async(kuzu_graph: KuzuGraph) -> None:
+    """cross_service=True: BFS continues through ASYNC_CALLS boundary into downstream service."""
+    seed_id = _find_method_with_declares_producer(kuzu_graph)
+    if seed_id is None:
+        pytest.skip("No method with DECLARES_PRODUCER in fixture")
+
+    out = trace_v2(
+        ids=seed_id,
+        direction="out",
+        edge_types=["CALLS", "ASYNC_CALLS"],
+        max_depth=5,
+        fan_out_cap=0,
+        cross_service=True,
+        graph=kuzu_graph,
+    )
+    assert out.success is True
+
+    xs_edges = [e for e in out.edges if e.cross_service_boundary]
+    if not xs_edges:
+        pytest.skip("No cross-service edges in result")
+
+    for xe in xs_edges:
+        assert xe.edge_type in ("HTTP_CALLS", "ASYNC_CALLS")
+        assert xe.to_id in out.nodes
+
+
+def test_trace_cross_service_seamless_respects_budget(kuzu_graph: KuzuGraph) -> None:
+    """cross_service=True still respects max_nodes_discovered budget."""
+    seed_id = _find_method_with_declares_client(kuzu_graph)
+    if seed_id is None:
+        pytest.skip("No method with DECLARES_CLIENT in fixture")
+
+    out = trace_v2(
+        ids=seed_id,
+        direction="out",
+        edge_types=["CALLS", "HTTP_CALLS"],
+        max_depth=5,
+        max_nodes_discovered=100,
+        fan_out_cap=0,
+        cross_service=True,
+        graph=kuzu_graph,
+    )
+    assert out.success is True
+    # Budget may or may not have been hit depending on graph size,
+    # but if it was, the stats should reflect it.
+    if out.stats.budget_hit:
+        assert out.stats.total_nodes_discovered >= 100
+
+
+def test_trace_cross_service_seamless_exposes_as_scaffolding(kuzu_graph: KuzuGraph) -> None:
+    """EXPOSES edges from downstream Routes are exempt from fan_out_cap when cross_service=True."""
+    seed_id = _find_method_with_declares_client(kuzu_graph)
+    if seed_id is None:
+        pytest.skip("No method with DECLARES_CLIENT in fixture")
+
+    # Use fan_out_cap=1 — very tight, but EXPOSES should still come through.
+    out = trace_v2(
+        ids=seed_id,
+        direction="out",
+        edge_types=["CALLS", "HTTP_CALLS"],
+        max_depth=5,
+        fan_out_cap=1,
+        cross_service=True,
+        graph=kuzu_graph,
+    )
+    assert out.success is True
+
+    xs_edges = [e for e in out.edges if e.cross_service_boundary]
+    if xs_edges:
+        # Even with fan_out_cap=1, EXPOSES edges from downstream Routes should appear
+        # (they're scaffolding, exempt from cap).
+        for xe in xs_edges:
+            downstream_edges = [e for e in out.edges if e.from_id == xe.to_id]
+            if downstream_edges:
+                exposes_edges = [e for e in downstream_edges if e.edge_type == "EXPOSES"]
+                assert len(exposes_edges) >= 1, (
+                    f"EXPOSES should be exempt from fan_out_cap, but got: {[e.edge_type for e in downstream_edges]}"
+                )
 
 
 async def test_trace_registered_as_mcp_tool(mcp_server) -> None: