fix(sync): freeze workspace slug + frontmatter-only update to prevent deep-reading data loss

- Slug freeze: reuse existing workspace dir when title slug changes in Zotero
- Frontmatter-only: for existing notes, replace only YAML block, never touch body
- extract_preserved_deep_reading: match both ##精读 and ##🔍精读 + skip placeholder-only sections

paperforge/adapters/obsidian_frontmatter.py

@@ -226,19 +226,35 @@ def generate_review(candidates: list[dict]) -> str:
 def extract_preserved_deep_reading(text: str) -> str:
     if not text:
         return ""
-    match = re.search("^## 🔍 精读\\s*$", text, re.MULTILINE)
+    # Match "## 🔍 精读" or "## 精读" (emoji is optional)
+    match = re.search(r"^##\s*🔍?\s*精读\s*$", text, re.MULTILINE)
     if not match:
         return ""
     start = match.start()
     preserved = text[start:].strip()
+    # Skip if section body is empty or only contains placeholder text
+    body = re.sub(r"^##\s*🔍?\s*精读\s*$", "", preserved, flags=re.MULTILINE).strip()
+    if not body or _is_placeholder_only(body):
+        return ""
     return preserved
 
 
+_PLACEHOLDER_PATTERN = re.compile(r"（待补充）|\(待补充\)|\(TODO\)|\(TBD\)")
+
+
+def _is_placeholder_only(body: str) -> bool:
+    """Check if the deep reading body is only placeholder text (no real content)."""
+    cleaned = _PLACEHOLDER_PATTERN.sub("", body).strip()
+    cleaned = re.sub(r"^[-*]\s*$", "", cleaned, flags=re.MULTILINE).strip()
+    return not cleaned
+
+
 def has_deep_reading_content(text: str) -> bool:
     preserved = extract_preserved_deep_reading(text)
     if not preserved:
         return False
-    body = preserved.replace(DEEP_READING_HEADER, "").strip()
+    # Strip both "## 🔍 精读" and "## 精读" header variants
+    body = re.sub(r"^##\s*🔍?\s*精读\s*$", "", preserved, flags=re.MULTILINE).strip()
     if not body:
         return False
 

paperforge/worker/asset_index.py

@@ -262,13 +262,22 @@ def _build_entry(item: dict, vault: Path, paths: dict, domain: str, zotero_dir:
             write_json(meta_path, meta)
     title_slug = slugify_filename(item["title"])
     note_path = paths["literature"] / domain / f"{key} - {title_slug}.md"
+
+    # --- Freeze slug: reuse existing workspace if it exists under a different slug ---
+    workspace_dir = paths["literature"] / domain / f"{key} - {title_slug}"
+    if not workspace_dir.exists():
+        for candidate in (paths["literature"] / domain).glob(f"{key} - *"):
+            if candidate.is_dir():
+                workspace_dir = candidate
+                title_slug = workspace_dir.name.split(" - ", 1)[1] if " - " in workspace_dir.name else title_slug
+                break
+
     if note_path.parent.exists():
         for stale_note in note_path.parent.glob(f"{key} - *.md"):
             if stale_note != note_path:
                 stale_note.unlink()
 
     # Workspace paths (Phase 26: flat-to-workspace migration)
-    workspace_dir = paths["literature"] / domain / f"{key} - {title_slug}"
     main_note_path = workspace_dir / f"{key} - {title_slug}.md"
     deep_reading_file = workspace_dir / "deep-reading.md"
     target_fulltext = workspace_dir / "fulltext.md"
@@ -363,10 +372,24 @@ def _build_entry(item: dict, vault: Path, paths: dict, domain: str, zotero_dir:
     entry["maturity"] = compute_maturity(entry)
     entry["next_step"] = compute_next_step(entry)
 
-    # --- Workspace: always create and write to workspace path (Phase 38: no flat fallback) ---
-    existing_text = main_note_path.read_text(encoding="utf-8") if main_note_path.exists() else ""
-
-    main_note_path.write_text(frontmatter_note(entry, existing_text), encoding="utf-8")
+    # Slug already frozen above — for existing notes, update frontmatter only (preserve body)
+    if main_note_path.exists():
+        text = main_note_path.read_text(encoding="utf-8")
+        fm_close = text.find("---\n", 4)  # closing --- after opening ---
+        if fm_close != -1:
+            body = text[fm_close + 4:]  # everything after frontmatter
+            new_full = frontmatter_note(entry, "")
+            new_fm_close = new_full.find("---\n", 4)
+            if new_fm_close != -1:
+                new_fm = new_full[: new_fm_close + 4]  # new frontmatter block with closing ---\n
+                main_note_path.write_text(new_fm + body, encoding="utf-8")
+            else:
+                main_note_path.write_text(new_full, encoding="utf-8")
+        else:
+            main_note_path.write_text(frontmatter_note(entry, text), encoding="utf-8")
+    else:
+        existing_text = note_path.read_text(encoding="utf-8") if note_path.exists() else ""
+        main_note_path.write_text(frontmatter_note(entry, existing_text), encoding="utf-8")
 
     # Write per-workspace paper-meta.json (Phase 37: internal state outside frontmatter)
     write_paper_meta(workspace_dir, entry, paperforge_version=PAPERFORGE_VERSION)