feat(#73): publish trustworthy first usage history

- Schema migration 1-2: add segment_id to samples, unattributed bytes to day_aggregates

- Collector now derives hour observations and day aggregates from sample pairs

- Cross-hour deltas tracked as unattributed (no proportional allocation)

- Display states: 0 samples -> awaiting first, 1 sample -> awaiting another

- Monitoring period ensured open on each collection run

- Derivation failures preserve prior history

Closes #73

src/fenris/store.py

@@ -12,7 +12,7 @@ from typing import Optional
 
 
 # Schema version - increment on each migration
-SCHEMA_VERSION = 1
+SCHEMA_VERSION = 2
 
 
 # Packaged default placement (spec §8.3). The config may override it, but a
@@ -106,7 +106,8 @@ def _create_schema(conn: sqlite3.Connection):
             data_units_read INTEGER,
             bytes_written INTEGER,
             bytes_read INTEGER,
-            critical_warning INTEGER
+            critical_warning INTEGER,
+            segment_id INTEGER
         )
     """)
     
@@ -141,7 +142,9 @@ def _create_schema(conn: sqlite3.Connection):
             bytes_written_delta INTEGER DEFAULT 0,
             bytes_read_delta INTEGER DEFAULT 0,
             sample_count INTEGER DEFAULT 0,
-            coverage REAL DEFAULT 0.0
+            coverage REAL DEFAULT 0.0,
+            unattributed_bytes_written INTEGER DEFAULT 0,
+            unattributed_bytes_read INTEGER DEFAULT 0
         )
     """)
     
@@ -207,11 +210,25 @@ def _apply_migrations(conn: sqlite3.Connection, current_version: int):
     
     Spec: §3.6, §10.2
     """
-    # Migration 1→2: example placeholder
-    # if current_version < 2:
-    #     conn.execute("ALTER TABLE ...")
-    #     current_version = 2
-    pass
+    # Migration 1→2: add segment_id provenance to samples,
+    # unattributed byte tracking to day_aggregates (issue #73)
+    if current_version < 2:
+        # Defensive: only ALTER if table exists (handles minimal v1 stores)
+        tables = {row[0] for row in conn.execute(
+            "SELECT name FROM sqlite_master WHERE type='table'"
+        ).fetchall()}
+        if "samples" in tables:
+            # Check if column already exists (idempotent)
+            cols = {row[1] for row in conn.execute("PRAGMA table_info(samples)").fetchall()}
+            if "segment_id" not in cols:
+                conn.execute("ALTER TABLE samples ADD COLUMN segment_id INTEGER")
+        if "day_aggregates" in tables:
+            cols = {row[1] for row in conn.execute("PRAGMA table_info(day_aggregates)").fetchall()}
+            if "unattributed_bytes_written" not in cols:
+                conn.execute("ALTER TABLE day_aggregates ADD COLUMN unattributed_bytes_written INTEGER DEFAULT 0")
+            if "unattributed_bytes_read" not in cols:
+                conn.execute("ALTER TABLE day_aggregates ADD COLUMN unattributed_bytes_read INTEGER DEFAULT 0")
+        current_version = 2
 
 
 def migrate_to_latest(store_path: Path) -> int:
@@ -239,6 +256,14 @@ def migrate_to_latest(store_path: Path) -> int:
         conn.close()
         return 0  # Already up to date
     
+    # Version 0 means no schema — create fresh (issue #73)
+    if current_version == 0:
+        _create_schema(conn)
+        conn.execute(f"PRAGMA user_version={SCHEMA_VERSION}")
+        conn.commit()
+        conn.close()
+        return SCHEMA_VERSION
+    
     steps = SCHEMA_VERSION - current_version
     _apply_migrations(conn, current_version)
     conn.execute(f"PRAGMA user_version={SCHEMA_VERSION}")