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# Implementation Summary

**Session ID**: `phase24-session02-delta-aware-enrichment-spend-accounting` **Completed**: 2026-06-07 **Duration**: 3.5 hours

***

## Overview

Implemented Trend Finder delta-aware enrichment and spend accounting. The session added a private enrichment cache with atomic writes and pruning, cheap-first collector support for skipping unchanged enrichment, bounded spend summaries for Apify and Google Trends demand, and browser-safe cache and spend projections in Engine Replay and Sources.

***

## Deliverables

### Files Created

| File                                                                 | Purpose                                                                                              | Lines |
| -------------------------------------------------------------------- | ---------------------------------------------------------------------------------------------------- | ----- |
| `scripts/extensions/trend-finder/enrichment-cache.ts`                | Private enrichment cache keys, entry schema, atomic writes, merge helpers, and pruning summaries     | \~260 |
| `scripts/extensions/trend-finder/spend-accounting.ts`                | Bounded per-source and per-run spend summaries with exact, estimated, and cadence-unavailable states | \~180 |
| `scripts/extensions/trend-finder/__tests__/enrichment-cache.test.ts` | Cache key, validation, hit/miss, stale fingerprint, atomic write, and pruning coverage               | \~220 |
| `scripts/extensions/trend-finder/__tests__/spend-accounting.test.ts` | Spend helper coverage for actual usage, estimates, caps, and redaction                               | \~180 |

### Files Modified

| File                                                              | Changes                                                                                                      |
| ----------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------ |
| `scripts/extensions/trend-finder/sources/types.ts`                | Added enrichment cache and spend summary contracts for source adapters                                       |
| `scripts/lib/apify/types.ts`                                      | Carried safe usage and cap summaries through Apify run results                                               |
| `scripts/lib/apify/actors.ts`                                     | Mapped `usageTotalUsd` and max charge caps into safe run summaries                                           |
| `scripts/extensions/trend-finder/sources/apify-adapter.ts`        | Emitted per-source Apify spend summaries and cache-aware metadata                                            |
| `scripts/extensions/trend-finder/sources/google-trends-demand.ts` | Emitted Google Trends demand spend estimates and actual usage when available                                 |
| `scripts/extensions/trend-finder/collector.ts`                    | Added cheap-first cache merge, write, prune, and aggregate summary flow                                      |
| `scripts/extensions/trend-finder/engine-trace.ts`                 | Sanitized cache and spend trace events into bounded Engine Trace summaries                                   |
| `src/extensions/trend-finder/schema.ts`                           | Added Trend Finder cache and spend summary schemas with safe defaults                                        |
| `src/extensions/trend-finder/engine-trace.ts`                     | Added browser-safe cache and spend fields to Engine Trace                                                    |
| `src/extensions/trend-finder/engine-replay-model.ts`              | Projected cache and spend summaries into replay metrics and notes                                            |
| `src/extensions/trend-finder/views/sources-view.tsx`              | Displayed source spend and enrichment cache state in the Sources UI                                          |
| `src/extensions/trend-finder/fixtures.ts`                         | Added fixture rows for cache hits, skipped enrichment, pruned entries, and spend estimates                   |
| `src/data/live-data.example.json`                                 | Added fallback shape for additive cache and spend fields                                                     |
| `docs/extensions/trend-finder-pipeline.md`                        | Documented enrichment cache, retention, pruning, and spend accounting                                        |
| `docs/extensions/trend-finder-sources.md`                         | Documented per-source spend labels and cache summaries                                                       |
| `docs/extensions/trend-finder-runtime-and-provenance.md`          | Documented Engine Replay labels for skipped, saved, pruned, exact, estimated, and cadence-unavailable states |

***

## Technical Decisions

1. **Private cache only**: Enrichment cache state stays under the private trend-finder cache root and never enters browser payloads.
2. **Typed degradation**: Missing exact usage, cadence, or enrichment state falls back to explicit safe states instead of implicit assumptions.

***

## Test Results

| Metric   | Value                       |
| -------- | --------------------------- |
| Tests    | 4 focused commands          |
| Passed   | 4                           |
| Coverage | Not collected in validation |

***

## Lessons Learned

1. Additive schema defaults kept legacy Trend Finder payloads stable.
2. Keeping spend and cache traces to counts and labels avoided browser privacy regressions.

***

## Future Considerations

1. Session 03 can reuse the cache and provenance scaffolding for media assets and file hardening.
2. Session 05 can reuse the cadence-unavailable spend projection path once live scheduler state is surfaced.

***

## Session Statistics

* **Tasks**: 25 completed
* **Files Created**: 4
* **Files Modified**: 16
* **Tests Added**: 2
* **Blockers**: 0 resolved


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