feat(P5): IHF Phase 5 complete — agent-assisted distillation

Adds bounded AI support to the IHF governance loop. All AI outputs are
attributed (model_ref), reviewable (AgentReviewRecord), and reversible.
No autonomous decisions; no silent requirement promotion.

- T01: Schema — agent_proposals, agent_review_records,
  confidence_annotations (migration 1743379200)
- T02: AgentProposalsController (index/show/accept/reject, idempotent
  review guard), global nav "Agent" link
- T03: SummarizeClusterAction — Claude API cluster summary on widget show
- T04: DraftRequirementAction — AI requirement draft; acceptance creates
  RequirementCandidate (human-gated)
- T05: DetectDuplicatesAction — duplicate_flag proposal on candidate show
- T06: DetectPolicySensitivityAction — policy_flag with
  ConfidenceAnnotations per concern scope
- T07: ProposeImplementationAction — impl_proposal from decision show
- T08: AgentAuditDashboardAction — autoRefresh; KPI row, unreviewed queue,
  recent proposals, attribution log matrix
- T09: integration tests, SCOPE.md updated, phase5-summary.md, flake.nix
  adds http-conduit/aeson/string-conversions

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docs/phase5-summary.md

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+# Phase 5 Summary — Agent-Assisted Distillation and Suggestion
+
+**Workplan:** IHUB-WP-0005
+**Completed:** 2026-03-29
+**Phase:** 5 of 8 in the IHF specification
+
+---
+
+## What Was Built
+
+Phase 5 introduces bounded AI support into the IHF governance loop. All AI outputs are attributed (model_ref recorded), reviewable (AgentReviewRecord), and reversible (proposals can be rejected). No autonomous final decisions. No silent requirement promotion.
+
+### T01 — Schema
+
+Three new tables:
+- **`agent_proposals`** — stores every AI-generated output (summary, requirement_draft, duplicate_flag, policy_flag, impl_proposal). Status: `pending → accepted | rejected | superseded`. `model_ref` and optional `confidence` on every row.
+- **`agent_review_records`** — one per proposal (UNIQUE on `proposal_id`). Human decision: `accepted | rejected | modified`. Idempotent: second accept/reject returns "Already reviewed".
+- **`confidence_annotations`** — per-dimension breakdown of AI confidence (accuracy, relevance, completeness, policy_alignment). Linked to proposal via FK.
+
+### T02 — AgentProposalsController
+
+`AgentProposalsAction` (index filterable by type and status), `ShowAgentProposalAction`, `AcceptProposalAction`, `RejectProposalAction`. Proposals are immutable audit artifacts — no update/delete. Global nav "Agent" link added.
+
+### T03 — Cluster Summarization
+
+`SummarizeClusterAction` (POST from widget show page). Fetches last 20 annotations + threads, calls `claude-sonnet-4-6` with a factual distillation prompt (max_tokens=300), creates a `summary` AgentProposal. "Summarize Feedback" button on widget show page. API errors produce a user-visible flash message.
+
+### T04 — AI-Drafted Requirement Candidate
+
+`DraftRequirementAction` (POST from widget show page, gated on ≥ 3 annotations). Prompts Claude for JSON `{title, description}`. Creates a `requirement_draft` AgentProposal. On `AcceptProposalAction` for a requirement_draft: parses JSON and creates a `RequirementCandidate` with `category="friction"`, `status="open"`. No candidate is created without human acceptance.
+
+### T05 — Duplicate Candidate Detection
+
+`DetectDuplicatesAction` (POST from candidate show page). Sends target candidate + all others to Claude, requests JSON `{duplicates: [{id, reason}]}`. Creates a `duplicate_flag` AgentProposal. Informational only — no automated merging.
+
+### T06 — Policy-Sensitive Issue Detection
+
+`DetectPolicySensitivityAction` (POST from candidate show page). Sends candidate + widget `policy_scope` context to Claude, requests JSON `{concerns: [{scope, note}], severity}`. Creates a `policy_flag` AgentProposal with numeric `confidence` (low=0.3, medium=0.6, high=0.9). Creates one `ConfidenceAnnotation` per concern scope. Amber badge if concerns, green if clean.
+
+### T07 — Implementation Path Proposal
+
+`ProposeImplementationAction` (POST from decision show page). Fetches decision + requirement + existing impl refs, prompts Claude for JSON `{proposals: [{work_item_ref, system, rationale}]}`. Creates an `impl_proposal` AgentProposal. "Propose Implementation" button on decision show page.
+
+### T08 — Agent Audit Dashboard
+
+`AgentAuditDashboardAction` wrapped with `autoRefresh do`. Five panels:
+1. **KPI row**: total proposals / pending count / acceptance rate / rejection rate
+2. **Proposals by type**: count per type with color badges
+3. **Unreviewed queue**: pending proposals oldest-first with "Review" links
+4. **Recent proposals** (last 20): type, source widget, status, confidence, age
+5. **Attribution log**: model_ref × proposal_type count matrix
+
+Linked from hub show page (purple "Agent Audit" button).
+
+---
+
+## Governance Constraints Upheld
+
+- **Attributability**: every `AgentProposal` records `model_ref`. Reviewers see exactly which model produced the output.
+- **Human control**: no proposal auto-promotes. `requirement_draft` → `RequirementCandidate` only after explicit acceptance via `AcceptProposalAction`.
+- **Idempotency**: `UNIQUE (proposal_id)` on `agent_review_records`. Second accept/reject returns "Already reviewed" — no double-review.
+- **Error isolation**: all Claude API calls are wrapped; failures produce a flash message and redirect, never a 500.
+- **Confidence is optional**: `AgentProposal.confidence` is nullable. Summaries have no numeric score; policy flags derive confidence from severity.
+
+---
+
+## Known Limitations
+
+- **No streaming**: Claude API calls are synchronous within the controller action. For large annotation sets this may cause slow response times. Future work: background job with status polling.
+- **Confidence annotations for T06 use same score for all dimensions**: each concern dimension gets the overall severity score, not a per-dimension score from Claude. A refined prompt could request per-dimension scores.
+- **Duplicate detection scales linearly**: the full candidate list is sent to Claude. For large datasets (>100 candidates) the prompt will be large. Future work: embedding-based pre-filtering.
+- **No embeddings storage**: all intelligence is delegated to the Anthropic API. Phase 5 adds no local model serving or vector store.
+
+---
+
+## Phase 6 Readiness
+
+Phase 6 (Cross-Hub Integration) can build on:
+- `AgentProposal` as a structured output artifact that can be routed across hubs
+- `ConfidenceAnnotation` as a per-dimension quality signal for cross-hub filtering
+- The attribution log as an audit trail for multi-hub AI operations
+- All Phase 1–5 traceability chain intact: Widget → Annotation → Candidate → Decision → Deployment → OutcomeSignal → AgentProposal