fix: data integrity — deep-research result parsing + memory-extraction durability (#808)

Two independent data-integrity bugs:

- services/research/service.py: ResearchService.research() (the public deep-research
  API, re-exported from services/__init__) treated the handler return value as a
  dict (result.get("sources"/"summary"/...)), but call_research_service() returns a
  formatted markdown STRING -> AttributeError: str has no attribute get on EVERY
  successful call, making the API unusable for any non-error result. Now uses the
  string report as the summary and parses sources from the "### Sources" markdown
  section (section-bounded, URL-deduped), with a defensive dict branch for back-compat.

- services/memory/memory_extractor.py: extract_and_store guarded the vector-store
  find_similar/add calls only with the .healthy flag set ONCE at init. If the
  embedding/ChromaDB backend degraded LATER (OOM, evicted model, remote endpoint
  down), those calls raised, the exception escaped the dedup loop, skipped
  memory_manager.save(), and was swallowed by the outer try/except -> EVERY
  validated fact from the session was silently lost (the function docstring
  promises "never raised"). Now falls back to the existing text/fuzzy dedup so
  facts are still saved when the vector index is unavailable at runtime.

Tests: test_research_service.py, test_memory_extractor_vector_degraded.py.

tests/test_research_service.py

@@ -0,0 +1,153 @@
+"""Tests for ResearchService — correct handling of the handler's string report.
+
+ResearchHandler.call_research_service returns a *formatted markdown string*,
+not a dict. ResearchService.research() must consume that contract without
+raising (the previous code called ``.get()`` on the string and blew up on
+every successful research call).
+"""
+
+import asyncio
+
+import pytest
+
+from services.research.service import (
+    ResearchService,
+    ResearchResult,
+    ResearchSource,
+)
+
+
+# A faithful slice of what ResearchHandler._format_research_report emits.
+SAMPLE_REPORT = """---
+
+## Research Summary
+
+**Duration:** 12.3s | **Rounds:** 3 | **Queries:** 5 | **URLs Analyzed:** 7
+
+---
+
+# Findings
+
+Quantum error correction saw major advances in 2024. See [an inline note](https://inline.example/not-a-source) here.
+
+### Sources
+
+- [Surface Codes Paper](https://example.com/surface-codes)
+- [Lab Announcement](https://example.com/lab)
+- [Surface Codes Paper](https://example.com/surface-codes)
+
+---
+
+**The AI has analyzed all research findings above.**
+"""
+
+
+def _run(coro):
+    return asyncio.new_event_loop().run_until_complete(coro)
+
+
+class _StubHandler:
+    """Stands in for ResearchHandler; returns a string like the real one."""
+
+    def __init__(self, report):
+        self._report = report
+        self.called_with = None
+
+    async def call_research_service(self, topic, llm_endpoint, llm_model,
+                                    max_time=300, progress_callback=None):
+        self.called_with = (topic, llm_endpoint, llm_model, max_time)
+        return self._report
+
+
+class TestResearchOnStringReport:
+    def _service(self, report):
+        svc = ResearchService()
+        svc.handler = _StubHandler(report)
+        return svc
+
+    def test_does_not_raise_on_string_report(self):
+        svc = self._service(SAMPLE_REPORT)
+        result = _run(svc.research("quantum", "http://llm", "model"))
+        assert isinstance(result, ResearchResult)
+
+    def test_summary_is_the_report(self):
+        svc = self._service(SAMPLE_REPORT)
+        result = _run(svc.research("quantum", "http://llm", "model"))
+        assert "Quantum error correction" in result.summary
+        assert result.query == "quantum"
+
+    def test_sources_parsed_and_deduped(self):
+        svc = self._service(SAMPLE_REPORT)
+        result = _run(svc.research("quantum", "http://llm", "model"))
+        urls = [s.url for s in result.sources]
+        assert urls == [
+            "https://example.com/surface-codes",
+            "https://example.com/lab",
+        ]
+        assert all(isinstance(s, ResearchSource) for s in result.sources)
+
+    def test_inline_links_outside_sources_section_ignored(self):
+        svc = self._service(SAMPLE_REPORT)
+        result = _run(svc.research("quantum", "http://llm", "model"))
+        urls = [s.url for s in result.sources]
+        assert "https://inline.example/not-a-source" not in urls
+
+    def test_duration_recorded(self):
+        svc = self._service(SAMPLE_REPORT)
+        result = _run(svc.research("quantum", "http://llm", "model"))
+        assert result.duration_seconds >= 0.0
+
+    def test_empty_report_yields_no_sources(self):
+        svc = self._service("")
+        result = _run(svc.research("quantum", "http://llm", "model"))
+        assert result.sources == []
+        assert result.summary == ""
+
+
+class TestParseSources:
+    def test_returns_empty_for_empty_input(self):
+        assert ResearchService._parse_sources("") == []
+
+    def test_handles_titleless_link(self):
+        report = "### Sources\n\n- [](https://example.com/x)\n"
+        sources = ResearchService._parse_sources(report)
+        assert len(sources) == 1
+        assert sources[0].url == "https://example.com/x"
+        assert sources[0].title == ""
+
+    def test_section_ends_at_next_heading(self):
+        report = (
+            "### Sources\n\n"
+            "- [A](https://a.example)\n\n"
+            "### Notes\n\n"
+            "- [B](https://b.example)\n"
+        )
+        urls = [s.url for s in ResearchService._parse_sources(report)]
+        assert urls == ["https://a.example"]
+
+
+class TestDictBackCompat:
+    """A handler that returns a dict (legacy shape) must still work."""
+
+    def test_dict_result_still_parsed(self):
+        svc = ResearchService()
+
+        class _DictHandler:
+            async def call_research_service(self, *a, **k):
+                return {
+                    "summary": "done",
+                    "sources": [
+                        {"url": "https://x.example", "title": "X",
+                         "snippet": "s", "relevance": 0.9},
+                    ],
+                    "sections": ["intro"],
+                    "tokens_used": 42,
+                }
+
+        svc.handler = _DictHandler()
+        result = _run(svc.research("q", "http://llm", "model"))
+        assert result.summary == "done"
+        assert result.tokens_used == 42
+        assert result.sections == ["intro"]
+        assert result.sources[0].url == "https://x.example"
+        assert result.sources[0].relevance == 0.9