diff --git a/src/nsct/api/rest_research.py b/src/nsct/api/rest_research.py
index c0c81dc..0f35a6c 100644
--- a/src/nsct/api/rest_research.py
+++ b/src/nsct/api/rest_research.py
@@ -686,7 +686,11 @@ async def get_sources(research_id: str) -> SourcesResponse:
     run = _load_run(research_id)
     sources = [
         SourceListItem(
-            id=s.get("id", str(uuid.uuid4())),
+            # Pipeline models retain identifiers as UUID objects.  The public
+            # REST contract deliberately exposes JSON strings, so normalize
+            # here instead of letting strict Pydantic validation turn a
+            # successful research run into a 500 response.
+            id=str(s.get("id", uuid.uuid4())),
             url=s.get("url", ""),
             title=s.get("title"),
             domain=s.get("domain", ""),
@@ -712,9 +716,9 @@ async def get_claims(research_id: str) -> ClaimsResponse:
     run = _load_run(research_id)
     claims = [
         ClaimListItem(
-            id=c.get("id", str(uuid.uuid4())),
+            id=str(c.get("id", uuid.uuid4())),
             research_run_id=run.research_id,
-            source_id=c.get("source_id", ""),
+            source_id=str(c.get("source_id", "")),
             claim_text=c.get("claim_text", c.get("claim", "")),
             evidence_span=c.get("evidence_span", ""),
             claim_type=c.get("claim_type", "claim"),
@@ -737,7 +741,16 @@ async def get_claims(research_id: str) -> ClaimsResponse:
 async def get_evidence(research_id: str) -> EvidenceResponse:
     """Evidence-Scores für einen Research-Run abrufen."""
     run = _load_run(research_id)
-    scores = [EvidenceScoreItem(**s) for s in run.evidence_scores]
+    scores = [
+        EvidenceScoreItem(
+            **{
+                **score,
+                "claim_id": str(score.get("claim_id", "")),
+                "research_run_id": str(score.get("research_run_id", run.research_id)),
+            }
+        )
+        for score in run.evidence_scores
+    ]
     return EvidenceResponse(
         research_id=run.research_id,
         evidence=scores,
diff --git a/tests/test_rest_research.py b/tests/test_rest_research.py
index 46e2a06..bf7a8d0 100644
--- a/tests/test_rest_research.py
+++ b/tests/test_rest_research.py
@@ -4,6 +4,7 @@ from __future__ import annotations
 
 from typing import Generator
 from unittest.mock import MagicMock, patch
+from uuid import uuid4
 
 import pytest
 from fastapi.testclient import TestClient
@@ -307,6 +308,48 @@ def test_get_claims_empty(client: TestClient) -> None:
     assert body["claims"] == []
 
 
+def test_detail_endpoints_serialize_pipeline_uuid_identifiers(client: TestClient) -> None:
+    """Completed pipeline data must satisfy the string-based REST contract."""
+    from nsct.api.rest_research import _ResearchRunState, _research_store
+    from nsct.orchestration.budget import HardBudgetConfig
+
+    _research_store.clear()
+    research_id = str(uuid4())
+    source_id = uuid4()
+    claim_id = uuid4()
+    _research_store[research_id] = _ResearchRunState(
+        research_id=research_id,
+        query="UUID serialization",
+        language="de",
+        depth="quick",
+        budget=HardBudgetConfig(),
+        sources=[{"id": source_id, "url": "https://example.org/article"}],
+        claims=[
+            {
+                "id": claim_id,
+                "source_id": source_id,
+                "claim_text": "Eine überprüfbare Behauptung.",
+                "evidence_span": "Überprüfbare Passage.",
+                "claim_type": "claim",
+            }
+        ],
+        evidence_scores=[{"claim_id": claim_id, "research_run_id": uuid4()}],
+        report={"summary": "Zusammenfassung", "findings": [], "methodology": "Methodik"},
+    )
+
+    sources = client.get(f"/v1/research/{research_id}/sources")
+    claims = client.get(f"/v1/research/{research_id}/claims")
+    evidence = client.get(f"/v1/research/{research_id}/evidence")
+    report = client.get(f"/v1/research/{research_id}/report")
+
+    assert [response.status_code for response in (sources, claims, evidence, report)] == [200] * 4
+    assert sources.json()["sources"][0]["id"] == str(source_id)
+    assert claims.json()["claims"][0]["id"] == str(claim_id)
+    assert claims.json()["claims"][0]["source_id"] == str(source_id)
+    assert evidence.json()["evidence"][0]["claim_id"] == str(claim_id)
+    assert report.json()["methodology"] == "Methodik"
+
+
 # ---------------------------------------------------------------------------
 # GET /v1/research/{id}/evidence — evidence
 # ---------------------------------------------------------------------------