Evidence chain capture — link decisions to source evidence

[Demwunz]

Problem

Arx captures decisions ("Use PostgreSQL for storage") but not the evidence chain that led to each decision. If an LLM call step recommends a technology choice, arx records what was decided but not why — which files were consulted, what search results informed it, or what reasoning the LLM produced.

This matters for:

• Regulated environments: Decision rationale is legally required in finance/healthcare/government
• Team handoffs: "Why did we choose this?" is unanswerable without evidence
• Audit: Provenance tracks that something happened; arx should track why

Scope

• Add optional evidence field to arx journal entries
• Evidence types: file references, topo query results, LLM reasoning excerpts, external sources
• arx record --evidence "src/main.rs:42-50" for manual evidence attachment
• arx show <id> displays evidence chain alongside decision

Design Considerations

• Evidence should be references (file paths, line ranges, URLs), not full content — keep entries small
• LLM reasoning excerpts should be truncated summaries, not full outputs
• Evidence is append-only like the rest of arx — never modified after capture
• Profile-aware: solo = evidence optional, regulated = evidence required on all decisions

Prior Art

RLMAgents (libs/rlmagents/) tracks evidence (citations, sources, data points) across the entire tool call chain. When the agent produces a final answer, it includes provenance for every claim — which tool call produced which evidence, with get_evidence + finalize pattern.

Wobot Integration

Once this lands in arx, wobot's ArxObserver will auto-capture evidence from preceding pipeline steps when recording decisions. Tracked upstream: Demwunz/wobot#151

---

Migrated from Demwunz/wobot#151