Memory explainability & visibility: show why a memory was recalled, add memory status/dashboard

Summary

memory recall/search return results without explaining why a memory surfaced. There's no per-result breakdown (which signal matched, how strongly, which graph edge connected it) and no global visibility into the memory store (counts, age, superseded, confidence, gaps).

Current behavior

• Recall output shows only category, content, id, and a single relevance %.
• No per-signal scores (lexical/dense/graph), no retrieval path (BM25 vs vector vs cascade), no rerank rationale.
• No memory status/dashboard to inspect the store: how many entries, how many active vs superseded, age distribution, confidence decay, retrieval gaps.

Why it matters

• Trust & verification: users and agents can't tell why a memory was recalled or whether to trust it.
• Debugging: the near-literal miss and stale-memory problems (#960, #1103, #1104) are hard to diagnose without visibility into scores and paths.
• For workflows that gate on memory presence (e.g. "is there a protected memory touching this file?"), knowing why a result did or didn't surface is essential.

Proposed enhancement

1. Per-result breakdown in recall/search output:
   • Score per signal: lexical (BM25), dense (cosine), graph (cascade/edge weight).
   • Retrieval path: which retriever(s) found it, which graph edges connected it.
   • Rerank decision: whether the LLM reranker kept/dropped it and why (if rerank runs).
2. memory status/dashboard:
   • Counts by category, scope, active vs superseded, age distribution.
   • Confidence/decay state per entry.
   • Retrieval gaps (context had no relevant memories — gap detection already exists in the architecture doc).

References

• Parity: OpenMemory (explainable traces), agentmemory (per-signal hybrid with progressive disclosure), total-agent-memory (6-stage pipeline visibility).
• crates/jcode-app-core/src/tool/memory.rs (recall/search output formatting)
• crates/jcode-base/src/memory_rerank.rs (rerank rationale)
• docs/MEMORY_ARCHITECTURE.md (gap detection, post-retrieval maintenance)

Read crates/jcode-app-core/src/tool/memory.rs for recall/search output formatting, crates/jcode-base/src/memory_rerank.rs for rerank rationale, and docs/MEMORY_ARCHITECTURE.md for gap detection and post-retrieval maintenance. Define the scope of the per-result signals, retrieval paths, rerank explanation, and memory status/dashboard before implementation; done should provide the proposed visibility for recall/search and store status.