fix(agent): harden live diagnosis skill observability

openspec/specs/evidence-trace-hardening/spec.md

@@ -84,3 +84,27 @@ The system SHALL provide offline tests for the hardened evidence contract and de
 - **WHEN** the test suite runs the focused `ChatService` fallback tests
 - **THEN** it SHALL verify the missing-output, invalid-JSON, `LOW_CONFID`, and `REJECT` degraded paths without requiring a real LLM or database
 
+### Requirement: Evidence summaries SHALL preserve strongest concrete support across merged invocations
+When multiple invocations are merged into one verifier-facing summary entry, the summary SHALL preserve concrete support from the strongest successful invocation.
+
+#### Scenario: Merged log calls include one direct hit
+- **WHEN** repeated `query_logs` calls for the same topic are merged
+- **AND** at least one call contains a concrete direct evidence hit
+- **THEN** the merged summary SHALL include a bounded direct-hit excerpt
+- **AND** it SHALL preserve all contributing `source_invocation_ids`
+
+#### Scenario: Truncated preview still contains direct evidence
+- **WHEN** a persisted output preview is marked truncated
+- **AND** the preview contains a concrete direct evidence hit
+- **THEN** the summary SHALL treat the row as successful evidence
+- **AND** it SHALL NOT downgrade the row to no-evidence only because the raw output was truncated
+
+### Requirement: Live trace counts SHALL distinguish model steps from evidence tool invocations
+The persisted trace SHALL make it possible to audit model step counts separately from evidence tool invocation counts.
+
+#### Scenario: Diagnosis session exposes aggregate counts
+- **WHEN** a diagnosis session completes
+- **THEN** `diagnosis_session.step_count` SHALL count persisted Agent model steps
+- **AND** `diagnosis_session.tool_call_count` SHALL count persisted evidence-tool invocation rows
+- **AND** helper workflow calls that are not evidence rows SHALL be auditable from agent steps or logs without inflating `tool_invocation`
+