Generate contract types, pin fixtures to spec, add build and ADRs

Completes FLUID-WP-0002. The record types in internal/contract are
generated from schemas/ by a dependency-free generator; fixtures
transcribed from the spec's worked examples validate against those
schemas and round-trip through the generated types with
DisallowUnknownFields, so a spec change that misses the schemas fails
CI rather than drifting silently.

Adds identifier prefix helpers, Makefile, GitHub Actions, and five ADRs
recording the Go choice, out-of-process attachment, the wire contract as
boundary, the evidence store, and revision identity.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014KmVxhJ35tCo7rE7UnLwWu

Assistant: claude-code
Assistant-Model: opus
Assistant-Process: 1116572@bnt-lap001
Assistant-Session: 8ba9bb93-a72a-4883-b189-2499cce5c400

conformance/fixtures/hypothesis.yaml

@@ -0,0 +1,156 @@
+fluid_hypothesis:
+  schema_version: "0.1"
+
+  id: "H-000184"
+  interface_id: "customer-finance-api"
+
+  state: "PRIORITIZED"
+
+  created_at: "2026-09-04T12:00:00Z"
+  created_by:
+    type: "daimon"
+    id: "fluid-daimon/customer-finance-api"
+
+  title: "Provide direct latest-invoice capability"
+
+  observation:
+    summary: >
+      A significant consumer cohort retrieves invoice collections,
+      sorts them by issue date, and discards all but the first item.
+    evidence_refs:
+      - "telemetry:invoice-pattern-2026w36"
+      - "feedback:F-9821"
+    affected_cohorts:
+      - "partner-integrations"
+      - "coding-agents"
+    observation_window:
+      start: "2026-08-15T00:00:00Z"
+      end: "2026-09-01T00:00:00Z"
+
+  pressure:
+    classes:
+      - "successful_but_inefficient_usage"
+      - "repeated_expectation_mismatch"
+    severity: 0.61
+    confidence: 0.88
+
+  explanation:
+    claim: >
+      Consumers treat "latest invoice" as a domain-level concept
+      and the existing generic collection interface does not present
+      that concept directly.
+    reach:
+      score: 0.42
+      explains:
+        - "P-1831"
+        - "P-1834"
+      notes: >
+        Medium reach: explains several related request patterns
+        but not broader financial-context pressure.
+
+  proposed_adaptation:
+    class: "contract"
+    summary: >
+      Add an explicit latest-invoice retrieval capability.
+    candidate_contract:
+      method: "GET"
+      path: "/customers/{id}/invoices/latest"
+    implementation_scope: "interface_only"
+
+  backend_requirements:
+    required: false
+    requirement_refs: []
+
+  expected_outcomes:
+    - metric: "requests_per_completed_task"
+      cohort: "all"
+      baseline: 2.7
+      target: 1.2
+      direction: "lower"
+    - metric: "client_side_sort_workarounds"
+      cohort: "all"
+      baseline: 1.0
+      target: 0.2
+      direction: "lower"
+
+  guardrails:
+    - metric: "p95_latency_ms"
+      operator: "<="
+      threshold: 315
+    - metric: "authorization_scope_change"
+      operator: "=="
+      threshold: false
+    - metric: "backend_query_count_delta"
+      operator: "<="
+      threshold: 0
+
+  fitness_dimensions:
+    expected:
+      client_utility: 0.70
+      correctness: 0.00
+      reliability: 0.00
+      performance: 0.10
+      discoverability: 0.65
+      simplicity: -0.15
+      compatibility: 0.00
+      security: 0.00
+      maintainability: -0.05
+      operational_cost: 0.00
+
+  complexity:
+    expected_delta:
+      surface_area: 1
+      concept_count: 0
+      operation_count: 1
+      semantic_overlap: 0.1
+      cognitive_load: -0.2
+    score: 0.18
+
+  risk:
+    level: "LOW"
+    reasons:
+      - "read-only operation"
+      - "no authorization expansion"
+
+  economics:
+    estimated_experiment_cost: 18.00
+    estimated_implementation_cost: 40.00
+    currency: "EUR"
+    expected_value_class: "MEDIUM"
+
+  learning_value:
+    score: 0.56
+    notes: >
+      Useful signal for whether first-class convenience resources
+      improve agent and partner integration behavior.
+
+  priority:
+    score: 0.71
+    decided_by: "optimization-policy-v3"
+
+  success_criteria:
+    expression: >
+      requests_per_completed_task <= 1.2
+      AND no hard guardrail violation
+
+  failure_criteria:
+    expression: >
+      any hard guardrail violation
+      OR adoption below 5% after 30 days when equally discoverable
+
+  candidate_revision_refs:
+    - "R-000221"
+
+  experiment_refs:
+    - "E-000093"
+
+  outcome:
+    status: null
+    summary: null
+    evidence_refs: []
+
+  audit:
+    decision_refs:
+      - "D-2811"
+    immutable_event_refs:
+      - "EV-990218"