M2: finish the run journal wiring and the section 9 agent loop #42

Milestone M2 tracking issue. Continues draft PR #41 (feat/m2-run-aggregate); M2 stays In progress after this PR because chat mode, the loop-to-RunBloc application service and the section 2.8 metrics are still open.

Spec: docs/spec/domain.md sections 8-9, docs/spec/storage.md section 15, docs/spec/roadmap.md (M2).

Checklist

• 1. Fix the HiveJournal constructor declaration (unnecessary_type_name_in_constructor blocks CI)
• 2. Make run taints mutable via Run.addTaint
• 3. Add agent-loop seam types (RunResult, ToolSet, ToolRegistry, AgentConfig, ApprovalService, ContextBuilder, AgentDeps) and the truncateToolOutput helper
• 4. Implement the section 9 agent loop with a fake LlmPort and positive/negative tests
• 5. Wire the journal and agent dependencies into the composition root (DI)
• 6. Bring docs/plan/M2.md to the template and record open questions Q7-Q11

Out of scope (stays open in docs/plan/M2.md)

• chat mode end-to-end with a fake LlmPort
• the application service that binds the loop to RunBloc, journal state projection and StatePublisher
• section 2.8 target metrics
• section 14 profile/risk configuration and an interactive approval channel
• section 13 untrusted prompt wrapping