JVNAUTOSCI-1205: turn execution coverage, synthesis backfill, and write-path guardrails

[witbrock]

Summary

This PR delivers deterministic turn-execution coverage instrumentation and recovery for historical and forward chat turns.

It includes:

• namespace-level coverage diagnostics for chat-history vs projection quality
• synthesis-capable historical backfill from legacy llm_debug_data
• workflow-routing inference during synthesis so projected records are workflow-attributed
• forward write-path guardrail in add_message_to_history(...) to synthesise and persist missing turn_execution_record payloads
• stdio/catalogue/manifest exposure and regression tests

Key changes

• Added turn_execution_namespace_coverage_report MCP read tool.
• Extended turn_execution_backfill_from_chat_history with synthesise_missing_records (default true).
• Added shared routing inference (infer_turn_execution_workflow_routing_from_debug) and applied it to backfill + forward write synthesis.
• Hardened chat_history_service.add_message_to_history(...) to self-heal missing assistant turn execution records and keep projection aligned.
• Updated docs in docs/engineering/turn_execution_completion_schema_proposal.md.

Validation

• pyright on changed Python files: 0 errors.
• Targeted pytest slices passed repeatedly (32, 29, 26, 21, 10 pass runs across impacted suites).
• Live test-db canary for forward writes:
  • assistant message stored with embedded turn_execution_record
  • projection row present
  • inferred selected_workflow_id=#V#tool_calling_workflow

Operational evidence

Primary namespace: #V#michael_witbrock@university_of_auckland_strong_ai_lab

Historical recovery:

• dry-run synthesis: candidate_records=728
• execute backfill: inserted_count=728, then idempotent rerun inserted_count=0, upserted_count=728

Post-recovery coverage:

• projected_records_total=728
• request_id_overlap_rate_pct=100.0
• projected_records_missing_selected_workflow_id=0

Benchmark readiness:

• scanned_count=200
• likely_failure_count=146
• workflow breakdown now available:
  • #V#tool_calling_workflow=172
  • #V#chat_assistant_workflow=28

Jira

• JVNAUTOSCI-1205
• Related: JVNAUTOSCI-1204, JVNAUTOSCI-1203