fix: skip applyRecencyBoost when decayEngine is active in vectorOnlyRetrieval

[jlin53882]

Summary

Skip applyRecencyBoost in vectorOnlyRetrieval() when a decayEngine is present, preventing double-counting of recency in the scoring pipeline.

What was fixed

Problem: vectorOnlyRetrieval() always called this.applyRecencyBoost(mapped), but when a decayEngine is active, the applyDecayBoost() stage already incorporates recency into its composite score. Calling both created a double-boost on recency, distorting ranking.

Fix: Guard applyRecencyBoost with a ternary ??if this.decayEngine exists, use mapped directly; otherwise call this.applyRecencyBoost(mapped).

Files changed

• src/retriever.ts: +5/-1 lines in vectorOnlyRetrieval()

Testing

• Only affects vector-only retrieval path when decayEngine is configured
• Hybrid retrieval path already handles this correctly

Related

• Split out from PR feat: Proposal A v3 - Dynamic Importance Feedback Signals (Phase 1) #493 (Proposal A v3) per AliceLJY review feedback
• Bug 7 fix

[rwmjhb]

Review: fix: skip applyRecencyBoost when decayEngine is active in vectorOnlyRetrieval

Correct fix — hybrid and BM25 paths already skip legacy recency when decayEngine is active, vector-only was the remaining inconsistency.

Must Fix

No regression test for the fixed behavior. The vector-only + decayEngine branch is not exercised by any existing test. Add one.

Worth noting

Skipping recency boost before hardMinScore cutoff means recent memories that start below the floor can be discarded before applyDecayBoost() has a chance to lift them. This reduces recall in edge cases — consider applying decay boost before the hard cutoff, or document this as an accepted trade-off.

[jlin53882]

Reviewer Must Fix: ✅ 已處理

迴攻測試已加入： est/retriever-decay-recency-double-boost.mjs

包含 3 個測試案例：

1. 驗證有 decayEngine 時不會套用 double-boost
2. 驗證分數在合理範圍（ratio 0.3-3.0），確認無 double-boost bug
3. bm25-only path 與 vector path 的一致性檢查

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深層分析額外發現（NIT，不阻擋 merge）

等級	問題	說明
[MINOR]	hardMinScore 文件不符	docstring 說「after all scoring stages」，實際在 time decay 之前
[NIT]	vectorOnlyRetrieval 缺少 recency trace	與 bm25/hybrid path 不一致
[NIT]	afterImportance 診斷在 decay path 無意義	與 afterRecency 值相同

PR 核心 fix 正確，無 blocking 問題。

[AliceLJY]

Fix is correct and well-scoped. The guard this.decayEngine ? mapped : this.applyRecencyBoost(mapped) is consistent with the hybrid path pattern and prevents double-boosting. Test coverage is adequate.

CI cli-smoke failure is pre-existing on master (strip-envelope-metadata tests), unrelated to this PR.

Approved.