## Summary
- Adds deterministic `list_notebooks`/`get_notebook` fixtures (two
seeded notebooks, each with markdown/database/log cells) and stateful
in-memory `create_notebook`/`update_notebook` mocks to
`apps/studio/lib/ai/tools/mock-tools.ts`, so Braintrust evals can
exercise notebook tool calls without a real project.
- Both write-tool mocks force `needsApproval: false`, matching the
existing `execute_sql`/`deploy_edge_function` mock pattern — the eval
harness filters out tool-parts in `'approval-requested'` state and can
never answer an approval gate.
- All four notebook tools are wrapped from the real `getNotebookTools()`
definitions (only `execute`/`needsApproval` overridden), so evals
validate the model's arguments against the exact production schemas.
- Dedupes `describeOperationError` (previously duplicated between this
new mock and `notebook-tools.ts`) into a single exported
`describeNotebookOperationError` in `notebook-operations.ts`.
**Stacked on #48949** (`feature/notebooks-update-tool`) — this PR's base
branch is that PR, not `master`, because it reuses `update_notebook` and
the shared error helper that only exist there. Merge #48949 first, then
retarget/merge this one.
## Test plan
- [x] \`pnpm --filter studio typecheck\` passes
- [x] \`pnpm --filter studio test\` — all notebook-related suites pass
(\`mock-tools.test.ts\`, \`notebook-tools.test.ts\`,
\`data/content/notebooks/*\`)
- [x] \`eslint\` / \`prettier --check\` clean on all touched files
Charis
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