## The bug
Per-task token usage (and the cost figures derived from it) is
**silently dropped the moment a task is archived**. A task that burned
millions of tokens shows `0` — or nothing — everywhere once it leaves
the live board.
Root cause is a field whitelist plus a missing type field:
- `TaskStore.taskToArchiveEntry()` (`packages/core/src/store.ts`)
constructs the archived record from an **explicit property whitelist**.
It copies `modelId` / `modelProvider` / `planningModelId` / … but never
`task.tokenUsage`.
- `ArchivedTaskEntry` (`packages/core/src/types.ts`) has no `tokenUsage`
field, so even a stray copy would be dropped by the type.
At archival time the task is DB-hydrated and still carries `tokenUsage`,
and the live `tasks` row (with its `tokenUsage*` columns) is then
deleted — so the whitelist is the only place the data survives or dies.
Result: `archive.db` (`archived_tasks.taskJson`) never contains token
stats. Any tool that reports token/cost usage can only ever see the
small live working set, never the hundreds of finished tasks.
## The fix
Thread `tokenUsage` through the archive round-trip (5 lines, all
pass-through of the already-typed `TaskTokenUsage`):
- `ArchivedTaskEntry` gains an optional `tokenUsage?: TaskTokenUsage`
field.
- `taskToArchiveEntry()` copies `tokenUsage: task.tokenUsage` (write
path).
- `archiveEntryToTask()` and `unarchiveTask()` copy `tokenUsage:
entry.tokenUsage` (both restore paths), so restored tasks keep their
history too.
Because the archived entry is serialized into `taskJson`, no DB
migration/column is needed — the counts land in the existing JSON blob
and read back via `json_extract(taskJson, '$.tokenUsage.totalTokens')`
(and the `inputTokens` / `outputTokens` / `cachedTokens` /
`cacheWriteTokens` breakdown).
## Verification
Applied the equivalent change to the bundled `dist/bin.js` on a live
install and archived a 9.9M-token task into an isolated copy of the
store. The full breakdown survived into `archive.db`:
```
inputTokens=119 outputTokens=26100 cachedTokens=9637483 cacheWriteTokens=233674
totalTokens=9897376 modelId=claude-sonnet-4-6 (+ per-model split intact)
```
Without the change the same archival leaves `tokenUsage` absent from the
entry.
<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit
* **Bug Fixes**
* Archived tasks now keep token usage details when saved and restored,
so task history remains accurate across archive flows.
* Restored archived tasks now display the same usage accounting they had
before being archived.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
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