fix: persist explicit usage models on replay

hub/src/store/usage.ts

@@ -128,6 +128,13 @@ export function recordUsageScan(
                     last_cache_creation_tokens = excluded.last_cache_creation_tokens
                 WHERE usage_events.kind = 'delta'
             `)
+            const updateCumulativeModel = db.prepare(`
+                UPDATE usage_events
+                SET model = ?
+                WHERE session_id = ?
+                    AND source_key = ?
+                    AND kind = 'cumulative'
+            `)
 
             for (const event of events) {
                 statement.run({
@@ -147,6 +154,9 @@ export function recordUsageScan(
                     last_cache_read_tokens: event.lastCacheReadTokens,
                     last_cache_creation_tokens: event.lastCacheCreationTokens
                 })
+                if (event.kind === 'cumulative' && event.model !== null) {
+                    updateCumulativeModel.run(event.model, event.sessionId, event.sourceKey)
+                }
             }
         }
 

hub/src/sync/usageService.test.ts

@@ -256,6 +256,43 @@ describe('usage service', () => {
         store.close()
     })
 
+    it('replaces a cumulative fallback model when a replay adds an explicit model', () => {
+        const store = new Store(':memory:')
+        const session = store.sessions.getOrCreateSession(
+            'codex-explicit-model-replay-test',
+            { path: '/tmp', host: 'test', flavor: 'codex' },
+            null,
+            'default',
+            'deepseek-v4-flash'
+        )
+        const tokenCount = (model?: string) => ({
+            type: 'codex',
+            data: {
+                type: 'token_count',
+                model,
+                thread_id: 'thread-1',
+                turn_id: 'turn-1',
+                info: {
+                    total_token_usage: { input_tokens: 100, output_tokens: 10 },
+                    last_token_usage: { input_tokens: 100, output_tokens: 10 }
+                }
+            }
+        })
+
+        addAgentMessage(store, session.id, tokenCount())
+        expect(getUsageSummary(store, 'default', 'all').byModel).toEqual([
+            expect.objectContaining({ key: 'deepseek-v4-flash', totalTokens: 110, requests: 1 })
+        ])
+
+        addAgentMessage(store, session.id, tokenCount('gpt-5.6-sol'))
+        const result = getUsageSummary(store, 'default', 'all')
+        expect(result.totals).toEqual(expect.objectContaining({ totalTokens: 110, requests: 1 }))
+        expect(result.byModel).toEqual([
+            expect.objectContaining({ key: 'gpt-5.6-sol', totalTokens: 110, requests: 1 })
+        ])
+        store.close()
+    })
+
     it('preserves event-level models across model switches and epoch rebuilds', () => {
         const store = new Store(':memory:')
         const session = store.sessions.getOrCreateSession(