Return "No results found." and accumulate repeated search results

CHANGELOG.md

@@ -1,6 +1,11 @@
 # Changelog
 ## [Unreleased]
 
+### Fixed
+
+- A capability search that matches nothing returns `No results found.` instead of an empty string.
+- Repeating a search query within a question accumulates the results of both calls instead of replacing the earlier ones.
+
 ## [0.76.0] - 2026-08-20
 
 ### Added

haiku_rag_slim/haiku/rag/capabilities/_base.py

@@ -27,7 +27,11 @@ from pydantic_ai.run import AgentRunResult
 from pydantic_ai.tools import ToolDefinition
 from pydantic_ai.toolsets import AgentToolset
 
-from haiku.rag.capabilities._tools import CodeExecutionEntry, search_corpus
+from haiku.rag.capabilities._tools import (
+    CodeExecutionEntry,
+    merge_results,
+    search_corpus,
+)
 from haiku.rag.capabilities.ledger import CapabilityEvidenceRecord, EvidenceRef
 from haiku.rag.client import HaikuRAG
 from haiku.rag.config.models import AppConfig
@@ -466,7 +470,9 @@ class RAGCapabilityBase[StateT: EvidenceState](AbstractCapability[Any]):
                 document_filter=self.state.document_filter,
             )
         state = self.state
-        state.searches[query] = results
+        # A model can search the same query twice with different limits, and the
+        # narrower return must not drop what the wider one already showed it.
+        merge_results(state.searches.setdefault(query, []), results)
         self._note_evidence()
         if self.vision and (parts := build_image_content_from_results(results)):
             return ToolReturn(return_value=formatted, content=parts)

haiku_rag_slim/haiku/rag/capabilities/_tools.py

@@ -1,3 +1,5 @@
+from collections.abc import Iterable
+
 from pydantic import BaseModel
 
 from haiku.rag.client import HaikuRAG
@@ -24,10 +26,26 @@ async def search_corpus(
         result.format_for_agent(rank=index + 1, total=len(results))
         for index, result in enumerate(results)
     )
-    return formatted, list(results)
+    return formatted or "No results found.", list(results)
+
+
+def merge_results(
+    existing: list[SearchResult], incoming: Iterable[SearchResult]
+) -> None:
+    """Add the results not already held.
+
+    Identity is the chunk id, which every stored chunk carries; results built by
+    hand without one cannot be told apart and collapse to the first.
+    """
+    seen = {result.chunk_id for result in existing}
+    for result in incoming:
+        if result.chunk_id not in seen:
+            existing.append(result)
+            seen.add(result.chunk_id)
 
 
 __all__ = [
     "CodeExecutionEntry",
+    "merge_results",
     "search_corpus",
 ]

haiku_rag_slim/haiku/rag/capabilities/analysis.py

@@ -17,6 +17,7 @@ from haiku.rag.capabilities._base import (
     RAGCapabilityBase,
     resolve_db_path,
 )
+from haiku.rag.capabilities._tools import merge_results
 from haiku.rag.config.models import AppConfig
 from haiku.rag.sandbox import AnalysisContext, Sandbox
 
@@ -112,13 +113,10 @@ class AnalysisCapability(RAGCapabilityBase[AnalysisState]):
         if result.success or result.stdout:
             self._note_evidence()
         if sandbox._search_results:
-            existing = self.state.searches.get("_sandbox", [])
+            merge_results(
-            seen = {item.chunk_id for item in existing}
+                self.state.searches.setdefault("_sandbox", []),
-            for item in sandbox._search_results:
+                sandbox._search_results,
-                if item.chunk_id not in seen:
+            )
-                    existing.append(item)
-                    seen.add(item.chunk_id)
-            self.state.searches["_sandbox"] = existing
         self.state.executions.append(
             CodeExecutionEntry(
                 code=code,

tests/capabilities/test_capabilities.py

@@ -314,6 +314,49 @@ async def test_a_spent_search_budget_fails_the_tool(temp_db_path):
         await capability._search("anything", None)
 
 
+def _stub_client(*batches: list[SearchResult]) -> AsyncMock:
+    """A client whose successive searches return the given result batches."""
+    client = AsyncMock()
+    client.search.side_effect = list(batches)
+    client.expand_context.side_effect = lambda results: results
+    return client
+
+
+@pytest.mark.asyncio
+async def test_a_fruitless_search_says_so(temp_db_path):
+    """A blank tool return reads as a broken tool, not as an empty corpus."""
+    capability = create_rag(db_path=temp_db_path, config=AppConfig())
+    capability.state = RAGState()
+    capability.borrowed_rag = _stub_client([])
+
+    assert await capability._search("nothing about this", None) == "No results found."
+
+
+@pytest.mark.asyncio
+async def test_a_narrower_repeat_keeps_what_the_wider_search_returned(temp_db_path):
+    """One query, two limits: the model can still cite the results it was shown."""
+    capability = create_rag(db_path=temp_db_path, config=AppConfig())
+    capability.state = RAGState()
+    capability.borrowed_rag = _stub_client(
+        [
+            SearchResult(content="first", score=1.0, chunk_id="chunk-1"),
+            SearchResult(content="second", score=0.9, chunk_id="chunk-2"),
+            SearchResult(content="third", score=0.8, chunk_id="chunk-3"),
+        ],
+        [SearchResult(content="first", score=1.0, chunk_id="chunk-1")],
+    )
+
+    await capability._search("Figure 3-1", 20)
+    await capability._search("Figure 3-1", None)
+
+    stored = capability.state.searches["Figure 3-1"]
+    assert [result.chunk_id for result in stored] == [
+        "chunk-1",
+        "chunk-2",
+        "chunk-3",
+    ]
+
+
 @pytest.mark.asyncio
 async def test_cite_resolves_direct_chunk_ids_and_reuses_document_lookup(temp_db_path):
     capability = create_rag(db_path=temp_db_path, config=AppConfig())