Harden evidence trace semantics

devflow/projects/2026-07-04-evidence-trace-hardening/brief.md

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+# Brief: evidence-trace-hardening
+
+## Background
+
+The MVP already has persisted tool traces and a verifier, but the evidence contract is still only partially standardized. For interview-focused hardening, the project now needs a tighter contract for evidence persistence, no-evidence / failure semantics, and degraded-output behavior.
+
+## Goals
+
+1. Standardize the persisted evidence-tool contract across `lookup_knowledge`, `query_logs`, and `query_metrics`.
+2. Make verifier-facing summaries distinguish failed calls, no-hit calls, deduped retrievals, and actual supporting evidence.
+3. Add offline tests for verifier fallback and degraded-output paths.
+
+## Scope
+
+- `ToolInvocationRecorder`
+- `LookupKnowledgeTool`
+- `QueryLogsTools`
+- `QueryMetricsTools`
+- `ToolTraceSummaryService`
+- `ChatService`
+- Focused offline tests
+
+## Non-Goals
+
+- No new API or schema
+- No evaluation harness yet
+- No trace UI
+- No security/config cleanup
+
+## Related OpenSpec
+
+`openspec/changes/evidence-trace-hardening/`