Step 5+6: event schema v1, core DDL, policy table, Slice 1 acceptance demo

- db/schema.sql: 9 core tables, append-only event log (trigger-enforced),
  deny-by-default policy_rule with seeded globals, runaway budgets on work items.
  Validated against Postgres 16 (DDL applies, trigger rejects UPDATE).
- engine/schemas/events.py: AgentMessage (flat, inference-enforced) +
  EventEnvelope pydantic models; models are the schema (ADR-003).
- adr/ADR-003: event schema and data model decisions.
- SLICE1_DEMO.md: verbatim acceptance script for Slice 1.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

SLICE1_DEMO.md

@@ -0,0 +1,28 @@
+# Slice 1 Acceptance Demo — verbatim script
+
+This is the acceptance test for Slice 1 (PRD_ADDENDUM §6). When every step below works end-to-end, Slice 1 ships. Nothing outside this script is in scope.
+
+## Cast
+
+- Company: **GasWatch Inc.** (first real subsidiary; brief: track local gas prices, tiny web app)
+- Employees: `Mara` (Manager), `Dev` (Engineer), `Quinn` (QA) — three Hermes profiles, qwen3.5:9b
+
+## Script
+
+1. `POST /companies` with the GasWatch brief → company row, event `company.created`, three employees hired (`employee.hired` ×3), Hermes profiles created via adapter.
+2. Engine asks Mara to decompose the brief → Mara returns plan; engine creates ~3 work items (`work_item.created`), one flagged as needing clarification.
+3. Clarification flows: Mara emits `clarification.requested` with 2–3 options + recommendation → surfaces in dashboard → user answers → `clarification.answered` → dependent task unblocks. Non-blocked tasks proceeded meanwhile.
+4. Dev picks up the feature task: engine dispatches to Hermes (`dispatch.sent`), worktree created on an isolated branch, code committed. Every agent report lands as validated `AgentMessage` events.
+5. Quinn runs pytest + one Playwright browser flow against the running app; screenshots + trace captured (`test.started` / `test.completed`, `artifact.created`).
+6. Seeded defect found by Quinn → defect work item → Dev fixes → Quinn re-verifies (defect loop closed).
+7. Evidence bundle assembled (commits, test output, screenshots, trace) → `artifact.created(kind=evidence_bundle)` → downloadable from dashboard.
+8. Dashboard (read-only) showed live truthful states the whole time: employee status, work item board, event feed, cost tally (`cost.recorded` per run).
+9. Runaway guard demonstrated: one task configured with `max_iterations: 2` trips `run.capped` and blocks cleanly instead of looping.
+10. Global pause: `POST /pause` mid-run → no new dispatches, in-flight inference drains, tool executions abort, state consistent, resume works.
+
+## Hard exit criteria
+
+- Zero free-form parsing: every agent→engine message validated against `AgentMessage`.
+- Event log replay tells the whole story; no state exists that lacks a causal event.
+- `task.blocked` from any agent was triaged by Mara before surfacing to user.
+- Kill Hermes mid-demo → engine marks run failed, work item re-dispatchable, no corruption.