[Makisuo]

What

After a cost source's first sync, the Cost page could keep showing a half-synced window for up to 15 minutes: the newest days were there, the month before was missing from the total, the filter rail and the table, while a slightly different window read correctly.

Cost reads are cached by their time range with the policy telemetry uses. That policy treats a window that ended more than 15 minutes ago as settled and holds its answer for 15 minutes, which is right for spans and wrong for cost: a sync writes past days. A source's history arrives in steps (the newest days first, older months after), so a read made between two steps was cached with part of the data and nothing changed its key.

The key now also carries when the org's cost sources were last written (the newest updated_at, which a sync stamps at every step). A sync step shows on the next read; between syncs the cache works as before.

How it was found

On the preview of #2541, with a real account: 13 minutes after the second sync step wrote October, the default window's total still covered November only. Other providers whose history arrives in steps are affected the same way on main.

Verification

• New test in cost-reads.test.ts over a cache that keeps answers by key: the same window twice computes once; after a source's updated_at moves, it computes again. It fails with the fix removed.
• cost-reads.test.ts (19) and registry/cost.test.ts (8) pass. Typecheck: query-engine, backend, api.
• The compiled SQL is unchanged (the new field is not a query parameter), so the SQL baseline does not move.

---

^{Open in [code]smith · Need help on this PR? Tag @codesmith-bot with what you need.}

[maple-review-bot]

Maple review

🟢 Confidence 10/10 · safe to merge. Cache-key-only field, verified to reach the real key, with a test that fails without it; no behavior outside cost reads changes.
_{no findings · tests covered · risk medium}

Cost reads now key their cached warehouse answers on the org's newest cost_sources.updated_at, so a sync step stops hiding behind the settled-window cache. Contained to cost reads and safe to merge.

• CostWindowPayload.written carries the newest source updated_at into the cache key only
• windowOf computes written as the max over the org's sources
• A new test proves the same window recomputes once a source moves

_{ffb4234 · What was checked, coverage and telemetry details are on the Maple / review check. Reply "won't fix" to dismiss a finding, or mention @maple-review-bot to ask about one.}

[coderabbitai]

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Commits

Reviewing files that changed from the base of the PR and between 55baa25 and ffb4234.

Files selected for processing: 5

• docs/cloud-cost-plan.md
• packages/backend/src/queries/cost-reads.test.ts
• packages/backend/src/queries/cost-reads.ts
• packages/query-engine/src/registry/cost.test.ts
• packages/query-engine/src/registry/cost.ts

• Autofix · Keep fixing CodeRabbit findings and required CI, and resolving merge conflicts

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