fix: account_age_days=None for scraper tier, stop false new_account flags

Scraper can't fetch seller profile age without following each listing's
seller link. Using 0 as sentinel caused every scraped seller to trigger
new_account and account_under_30_days red flags erroneously.

- Seller.account_age_days: int → Optional[int] (None = not yet fetched)
- Migration 003: recreate sellers table without NOT NULL constraint
- MetadataScorer: return None for unknown age → score_is_partial=True
- Aggregator: gate age flags on is not None
- Scraper: account_age_days=None instead of 0

app/db/migrations/003_nullable_account_age.sql

@@ -0,0 +1,23 @@
+-- Make account_age_days nullable — scraper tier cannot fetch it without
+-- following each seller's profile link, so NULL means "not yet fetched"
+-- rather than "genuinely zero days old". This prevents false new_account
+-- flags for all scraped listings.
+--
+-- SQLite doesn't support ALTER COLUMN, so we recreate the sellers table.
+
+CREATE TABLE sellers_new (
+    id                    INTEGER PRIMARY KEY AUTOINCREMENT,
+    platform              TEXT NOT NULL,
+    platform_seller_id    TEXT NOT NULL,
+    username              TEXT NOT NULL,
+    account_age_days      INTEGER,              -- NULL = not yet fetched
+    feedback_count        INTEGER NOT NULL,
+    feedback_ratio        REAL NOT NULL,
+    category_history_json TEXT NOT NULL DEFAULT '{}',
+    fetched_at            TEXT DEFAULT CURRENT_TIMESTAMP,
+    UNIQUE(platform, platform_seller_id)
+);
+
+INSERT INTO sellers_new SELECT * FROM sellers;
+DROP TABLE sellers;
+ALTER TABLE sellers_new RENAME TO sellers;

app/db/models.py

@@ -9,7 +9,7 @@ class Seller:
     platform: str
     platform_seller_id: str
     username: str
-    account_age_days: int
+    account_age_days: Optional[int]   # None = not yet fetched (scraper tier)
     feedback_count: int
     feedback_ratio: float           # 0.0–1.0
     category_history_json: str      # JSON blob of past category sales

app/platforms/ebay/scraper.py

@@ -202,7 +202,7 @@ def scrape_sellers(html: str) -> dict[str, Seller]:
                 platform="ebay",
                 platform_seller_id=username,
                 username=username,
-                account_age_days=0,       # not available from search HTML
+                account_age_days=None,    # not fetched at scraper tier
                 feedback_count=count,
                 feedback_ratio=ratio,
                 category_history_json="{}", # not available from search HTML

app/trust/aggregator.py

@@ -24,7 +24,7 @@ class Aggregator:
         red_flags: list[str] = []
 
         # Hard filters
-        if seller and seller.account_age_days < HARD_FILTER_AGE_DAYS:
+        if seller and seller.account_age_days is not None and seller.account_age_days < HARD_FILTER_AGE_DAYS:
             red_flags.append("new_account")
         if seller and (
             seller.feedback_ratio < HARD_FILTER_BAD_RATIO_THRESHOLD
@@ -33,7 +33,7 @@ class Aggregator:
             red_flags.append("established_bad_actor")
 
         # Soft flags
-        if seller and seller.account_age_days < 30:
+        if seller and seller.account_age_days is not None and seller.account_age_days < 30:
             red_flags.append("account_under_30_days")
         if seller and seller.feedback_count < 10:
             red_flags.append("low_feedback_count")

app/trust/metadata.py

@@ -15,7 +15,7 @@ class MetadataScorer:
         listing_price: float,
     ) -> dict[str, Optional[int]]:
         return {
-            "account_age":      self._account_age(seller.account_age_days),
+            "account_age":      self._account_age(seller.account_age_days) if seller.account_age_days is not None else None,
             "feedback_count":   self._feedback_count(seller.feedback_count),
             "feedback_ratio":   self._feedback_ratio(seller.feedback_ratio, seller.feedback_count),
             "price_vs_market":  self._price_vs_market(listing_price, market_median),

tests/platforms/test_ebay_scraper.py

@@ -267,10 +267,10 @@ class TestScrapeSellers:
         assert len(sellers) == 1
         assert "repeatguy" in sellers
 
-    def test_account_age_always_zero(self):
+    def test_account_age_is_none(self):
-        """account_age_days is 0 from scraper — causes score_is_partial=True."""
+        """account_age_days is None from scraper tier — causes score_is_partial=True."""
         sellers = scrape_sellers(_EBAY_HTML)
-        assert all(s.account_age_days == 0 for s in sellers.values())
+        assert all(s.account_age_days is None for s in sellers.values())
 
     def test_category_history_always_empty(self):
         """category_history_json is '{}' from scraper — causes score_is_partial=True."""