docs(plan): Task 3b data-preserving upsert + abstract recovery step after the 2026-09-08 clobber (refs #615)

docs/superpowers/plans/2026-09-08-comment-pipeline-seal-and-skip.md

@@ -668,6 +668,82 @@ git commit -m "feat(bib): Store.upsert_status — identical re-upsert writes not
 
 ---
 
+### Task 3b: Data-preserving upsert — never blank a stored value
+
+**Files:**
+- Modify: `src/bib/store.py` (`upsert_status`)
+- Test: `tests/bib/test_store_upsert_noop.py` (extend)
+
+**Why (incident 2026-09-08):** the fetch list walk builds a `Source` whose `abstract` is empty (the list endpoint has no body) and re-upserts every comment it sees. With the old upsert that overwrote 17,607 enriched bodies in CMS-2026-2377 and 1,115 in CMS-2017-0092. Task 3's comparison alone would still call that "updated" and write the empty abstract. Upsert must merge, not replace: an empty incoming value carries no information.
+
+**Interfaces:**
+- Consumes: `Store.upsert_status` from Task 3.
+- Produces: same signature; for every column in `_COMPARE_COLS` (except `extra_json`) an empty incoming string keeps the stored value. `extra_json` is compared/written as today (it is always a full serialization).
+
+- [ ] **Step 1: Write the failing tests** (append to `tests/bib/test_store_upsert_noop.py`)
+
+```python
+def test_empty_incoming_abstract_keeps_stored_body():
+    """A list-walk row (no body) must not blank an enriched comment."""
+    s = _store()
+    key, _ = s.upsert_status(_item(abstract="enriched body"))
+    _, status = s.upsert_status(_item(abstract=""))
+    assert status == "unchanged"
+    assert s.get(key).abstract == "enriched body"
+
+
+def test_empty_incoming_title_keeps_stored_title():
+    s = _store()
+    it = _item(); it.title = "Org: CMS-2026-2377-1"
+    key, _ = s.upsert_status(it)
+    it2 = _item(); it2.title = ""
+    _, status = s.upsert_status(it2)
+    assert status == "unchanged"
+    assert s.get(key).title == "Org: CMS-2026-2377-1"
+
+
+def test_non_empty_incoming_still_updates():
+    s = _store()
+    key, _ = s.upsert_status(_item(abstract="v1"))
+    _, status = s.upsert_status(_item(abstract="v2"))
+    assert status == "updated" and s.get(key).abstract == "v2"
+```
+
+- [ ] **Step 2: Run to verify failure**
+
+Run: `uv run --no-sync pytest tests/bib/test_store_upsert_noop.py -q -p no:cacheprovider`
+Expected: the first two new tests FAIL (`status == "updated"`, abstract/title blanked).
+
+- [ ] **Step 3: Implement**
+
+In `upsert_status`, after `cur_row = current.to_row()` and before the `same_cols` check:
+
+```python
+        # Merge, don't replace: an empty incoming value carries no
+        # information (a list-walk row has no body), so the stored value
+        # wins. extra_json is always a full serialization and is exempt.
+        for c in self._COMPARE_COLS:
+            if c != "extra_json" and not new_row.get(c) and cur_row.get(c):
+                new_row[c] = cur_row[c]
+                setattr(item, c, cur_row[c])
+```
+
+`setattr(item, c, …)` keeps the later `item.to_row()` (used to build the written row) consistent with the merged values. `Item` is a pydantic model; plain attribute assignment is allowed on these fields.
+
+- [ ] **Step 4: Run to verify pass**
+
+Run: `uv run --no-sync pytest tests/bib -q -p no:cacheprovider`
+Expected: pass.
+
+- [ ] **Step 5: Commit**
+
+```bash
+git add src/bib/store.py tests/bib/test_store_upsert_noop.py
+git commit -m "fix(bib): upsert never blanks a stored value — empty incoming columns keep the stored ones (refs #615)"
+```
+
+---
+
 ### Task 4: Idempotent `attach_file`
 
 **Files:**
@@ -3409,6 +3485,19 @@ uv run stack comments dockets                               # reopens the store
 sqlite3 data/bib.sqlite "SELECT name FROM sqlite_master WHERE name='idx_attachments_item_filename'"
 ```
 
+- [ ] **Step 2b: Recover the abstracts blanked on 2026-09-08**
+
+The old upsert overwrote 17,607 enriched bodies in CMS-2026-2377 and 1,115 in CMS-2017-0092 with '' (incident in the SDD ledger). They still carry `enriched:ok`, so backfill skips them. Clear the tag on those rows and re-enrich from the mirror (idempotent attach + data-preserving upsert are in place by now):
+
+```bash
+for d in CMS-2026-2377 CMS-2017-0092; do
+  sqlite3 data/bib.sqlite "DELETE FROM item_tags WHERE tag_id=(SELECT id FROM tags WHERE name='enriched:ok') AND item_id IN (SELECT id FROM items WHERE url LIKE 'https://www.regulations.gov/comment/$d-%' AND coalesce(abstract,'')='')"
+  uv run stack bib backfill-comments --docket $d --mirror
+done
+sqlite3 data/bib.sqlite "SELECT substr(url,37,13), count(*), sum(coalesce(abstract,'')<>'') FROM items WHERE url LIKE 'https://www.regulations.gov/comment/CMS-2026-2377-%' OR url LIKE 'https://www.regulations.gov/comment/CMS-2017-0092-%' GROUP BY 1"
+```
+Expected: non-empty abstracts ≈ total for both dockets (a few genuinely empty bodies are fine). Then re-run `stack comments extract` and `stack llm index --collection comments` so any comment whose text was lost from combined.md/index is restored (the index still holds pre-wipe text; fingerprints change because `updated_at` moved, hash-skip absorbs unchanged text).
+
 - [ ] **Step 3: Seal the historical dockets**
 
 ```bash