ux(recommendations): persist column filters across page reload (closes #163)

[cristim]

Summary

• Adds loadColumnFilters / saveColumnFilters helpers to recommendations.ts following the same pattern as the existing loadColumnVisibility / saveColumnVisibility functions (issue feat(frontend/recs): per-column show/hide for the recommendations table #318).
• localStorage key: cudly.recs.columnFilters.v1 (schema-versioned JSON blob).
• Column filters are persisted to localStorage on every mutation (categorical commit, numeric commit, per-column clear, and the "Clear filters (N)" badge), and restored on the first render of renderRecommendationsList via a columnFiltersSeeded flag.

Validation strategy

• Schema version field (schemaVersion: 1) enables forward-incompatible migrations to skip stale blobs cleanly.
• On load, each key is checked against the closed VALID_COLUMN_IDS set; unknown column ids (e.g. from a stale session after a column rename) are silently dropped.
• Filter values are structurally validated: kind:'set' requires a string array, kind:'expr' requires a non-empty string. Anything else is dropped without an error toast.
• JSON parse errors or localStorage unavailability (private browsing, quota-exceeded) fall back to empty filters silently.

Test plan

• loadColumnFilters returns {} when key is absent
• loadColumnFilters returns {} on JSON parse error
• loadColumnFilters returns {} when schemaVersion is wrong
• loadColumnFilters returns {} when filters is not an object
• Restores categorical (kind:'set') filter correctly
• Restores numeric (kind:'expr') filter correctly
• Silently drops unknown column keys (stale after deletion/rename)
• Silently drops filters with malformed shape
• Silently drops expr filter with empty-string expr
• saveColumnFilters writes correct schemaVersion:1 JSON shape
• saveColumnFilters writes empty filters:{} when no filters active
• Round-trips numeric expr filter through save + load
• Save then load restores full filter state
• Stored key with unknown column is silently dropped, no error thrown
• Corrupted JSON falls back to {}, no error thrown

334 tests passing, TypeScript clean.

Closes #163

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[cristim]

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: c3ff153b-4a20-473a-b577-155e3d3a4708

📥 Commits

Reviewing files that changed from the base of the PR and between eb85a50 and a76035a.

📒 Files selected for processing (2)

• frontend/src/__tests__/recommendations.test.ts
• frontend/src/recommendations.ts

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/163-wave7

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[cristim]

Rebased on feat/multicloud-web-frontend. Resolved additive conflicts in frontend/src/__tests__/recommendations.test.ts (kept both the base's renderUsageSparkline (#239) describe block and this PR's Column filters localStorage persistence (#163) describe block; merged the import line to keep both renderUsageSparkline and the new loadColumnFilters/saveColumnFilters/resetColumnFiltersState exports). frontend/src/recommendations.ts auto-merged cleanly.

Verification post-rebase: recommendations.test.ts passes (347 tests), npm run build succeeds. Note: pre-existing failures in recommendations-lookback.test.ts (#909) reproduce against the unmodified base recommendations.ts and are unrelated to this PR.

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@cristim Noted — the rebase context is clear. I'll kick off a fresh review of the updated branch, treating the renderUsageSparkline / loadColumnFilters import merge and the additive test-block consolidation as expected. Pre-existing failures in recommendations-lookback.test.ts tracked under #909 will be excluded from the review scope.

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🧠 Learnings used

Learnt from: cristim
Repo: LeanerCloud/CUDly PR: 0
File: :0-0
Timestamp: 2026-05-05T15:44:54.463Z
Learning: In the LeanerCloud/CUDly repository, when a CodeRabbit review flags something as "outside-diff" that was already implemented in an earlier commit of the same PR, it is likely a stale-snapshot artifact where the review diff was generated against a pre-fix view. The inline comment convention `(CR pass on PR #<number> Finding N)` is used by the maintainer (cristim) to mark lines that were changed in direct response to a prior CodeRabbit review pass.

---

Learnt from: cristim
Repo: LeanerCloud/CUDly PR: 277
File: frontend/src/__tests__/recommendations.test.ts:2472-2476
Timestamp: 2026-05-05T07:46:01.902Z
Learning: In the CUDly frontend (`frontend/src/recommendations.ts`), `effectiveSavingsPct` intentionally has NO plausibility guard (no null return or warning for reconstructed percentages above per-term ceilings). The maintainer explicitly rejected that approach in PR `#277`. The fix for inflated percentages (issue `#274`) is purely a data-path fix: plumbing the provider's canonical `on_demand_cost` through to the frontend so the denominator is not reconstructed from potentially misleading `monthly_cost + savings + amortized`. Tests that pin the reconstructed >80% behavior are intentional documentation of the pre-fix path, not bugs.

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