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.

services/research/service.py

@@ -1,11 +1,16 @@
 # services/research/service.py
 """Research service — deep research with LLM-in-the-loop."""
 
+import re
 from dataclasses import dataclass, field
 from typing import List, Optional, Callable
 
 from .research_handler import ResearchHandler
 
+# Markdown source links emitted by ResearchHandler._format_research_report,
+# e.g. "- [Some Title](https://example.com/page)".
+_SOURCE_LINK_RE = re.compile(r"^\s*-\s*\[(?P<title>[^\]]*)\]\((?P<url>[^)]+)\)\s*$")
+
 
 @dataclass
 class ResearchSource:
@@ -75,26 +80,70 @@ class ResearchService:
 
         duration = time.time() - start
 
-        # Parse result into structured format
-        sources = [
-            ResearchSource(
-                url=s.get("url", ""),
-                title=s.get("title", ""),
-                snippet=s.get("snippet", ""),
-                relevance=s.get("relevance", 0.0),
+        # call_research_service returns a formatted markdown report string
+        # (see ResearchHandler.call_research_service -> _format_research_report),
+        # not a dict. Treat it as such; tolerate an unexpected dict/None defensively.
+        if isinstance(result, dict):
+            sources = [
+                ResearchSource(
+                    url=s.get("url", ""),
+                    title=s.get("title", ""),
+                    snippet=s.get("snippet", ""),
+                    relevance=s.get("relevance", 0.0),
+                )
+                for s in result.get("sources", [])
+            ]
+            return ResearchResult(
+                query=topic,
+                summary=result.get("summary", result.get("answer", "")),
+                sources=sources,
+                sections=result.get("sections", []),
+                tokens_used=result.get("tokens_used", 0),
+                duration_seconds=duration,
             )
-            for s in result.get("sources", [])
-        ]
 
+        report = result if isinstance(result, str) else ""
         return ResearchResult(
             query=topic,
-            summary=result.get("summary", result.get("answer", "")),
-            sources=sources,
-            sections=result.get("sections", []),
-            tokens_used=result.get("tokens_used", 0),
+            summary=report,
+            sources=self._parse_sources(report),
             duration_seconds=duration,
         )
 
+    @staticmethod
+    def _parse_sources(report: str) -> List[ResearchSource]:
+        """Extract sources from the markdown ### Sources section of a report.
+
+        ResearchHandler emits one ``- [title](url)`` link per deduplicated
+        finding under a ``### Sources`` heading. Parse only that section so
+        inline links elsewhere in the body are not mistaken for sources.
+        """
+        if not report:
+            return []
+        sources: List[ResearchSource] = []
+        seen = set()
+        in_sources = False
+        for line in report.splitlines():
+            stripped = line.strip()
+            if stripped.startswith("###") or stripped.startswith("##"):
+                in_sources = stripped.lower().lstrip("#").strip() == "sources"
+                continue
+            if not in_sources:
+                continue
+            match = _SOURCE_LINK_RE.match(line)
+            if not match:
+                continue
+            url = match.group("url").strip()
+            if not url or url in seen:
+                continue
+            seen.add(url)
+            sources.append(
+                # snippet is required on ResearchSource; markdown source links
+                # carry no snippet, so default to empty (matches the dict path).
+                ResearchSource(url=url, title=match.group("title").strip(), snippet="")
+            )
+        return sources
+
     def start_background(
         self,
         session_id: str,