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/json/hypothesis.json

@@ -0,0 +1,164 @@
+{
+  "fluid_hypothesis": {
+    "audit": {
+      "decision_refs": [
+        "D-2811"
+      ],
+      "immutable_event_refs": [
+        "EV-990218"
+      ]
+    },
+    "backend_requirements": {
+      "required": false,
+      "requirement_refs": []
+    },
+    "candidate_revision_refs": [
+      "R-000221"
+    ],
+    "complexity": {
+      "expected_delta": {
+        "cognitive_load": -0.2,
+        "concept_count": 0,
+        "operation_count": 1,
+        "semantic_overlap": 0.1,
+        "surface_area": 1
+      },
+      "score": 0.18
+    },
+    "created_at": "2026-09-04T12:00:00Z",
+    "created_by": {
+      "id": "fluid-daimon/customer-finance-api",
+      "type": "daimon"
+    },
+    "economics": {
+      "currency": "EUR",
+      "estimated_experiment_cost": 18.0,
+      "estimated_implementation_cost": 40.0,
+      "expected_value_class": "MEDIUM"
+    },
+    "expected_outcomes": [
+      {
+        "baseline": 2.7,
+        "cohort": "all",
+        "direction": "lower",
+        "metric": "requests_per_completed_task",
+        "target": 1.2
+      },
+      {
+        "baseline": 1.0,
+        "cohort": "all",
+        "direction": "lower",
+        "metric": "client_side_sort_workarounds",
+        "target": 0.2
+      }
+    ],
+    "experiment_refs": [
+      "E-000093"
+    ],
+    "explanation": {
+      "claim": "Consumers treat \"latest invoice\" as a domain-level concept and the existing generic collection interface does not present that concept directly.\n",
+      "reach": {
+        "explains": [
+          "P-1831",
+          "P-1834"
+        ],
+        "notes": "Medium reach: explains several related request patterns but not broader financial-context pressure.\n",
+        "score": 0.42
+      }
+    },
+    "failure_criteria": {
+      "expression": "any hard guardrail violation OR adoption below 5% after 30 days when equally discoverable\n"
+    },
+    "fitness_dimensions": {
+      "expected": {
+        "client_utility": 0.7,
+        "compatibility": 0.0,
+        "correctness": 0.0,
+        "discoverability": 0.65,
+        "maintainability": -0.05,
+        "operational_cost": 0.0,
+        "performance": 0.1,
+        "reliability": 0.0,
+        "security": 0.0,
+        "simplicity": -0.15
+      }
+    },
+    "guardrails": [
+      {
+        "metric": "p95_latency_ms",
+        "operator": "<=",
+        "threshold": 315
+      },
+      {
+        "metric": "authorization_scope_change",
+        "operator": "==",
+        "threshold": false
+      },
+      {
+        "metric": "backend_query_count_delta",
+        "operator": "<=",
+        "threshold": 0
+      }
+    ],
+    "id": "H-000184",
+    "interface_id": "customer-finance-api",
+    "learning_value": {
+      "notes": "Useful signal for whether first-class convenience resources improve agent and partner integration behavior.\n",
+      "score": 0.56
+    },
+    "observation": {
+      "affected_cohorts": [
+        "partner-integrations",
+        "coding-agents"
+      ],
+      "evidence_refs": [
+        "telemetry:invoice-pattern-2026w36",
+        "feedback:F-9821"
+      ],
+      "observation_window": {
+        "end": "2026-09-01T00:00:00Z",
+        "start": "2026-08-15T00:00:00Z"
+      },
+      "summary": "A significant consumer cohort retrieves invoice collections, sorts them by issue date, and discards all but the first item.\n"
+    },
+    "outcome": {
+      "evidence_refs": [],
+      "status": null,
+      "summary": null
+    },
+    "pressure": {
+      "classes": [
+        "successful_but_inefficient_usage",
+        "repeated_expectation_mismatch"
+      ],
+      "confidence": 0.88,
+      "severity": 0.61
+    },
+    "priority": {
+      "decided_by": "optimization-policy-v3",
+      "score": 0.71
+    },
+    "proposed_adaptation": {
+      "candidate_contract": {
+        "method": "GET",
+        "path": "/customers/{id}/invoices/latest"
+      },
+      "class": "contract",
+      "implementation_scope": "interface_only",
+      "summary": "Add an explicit latest-invoice retrieval capability.\n"
+    },
+    "risk": {
+      "level": "LOW",
+      "reasons": [
+        "read-only operation",
+        "no authorization expansion"
+      ]
+    },
+    "schema_version": "0.1",
+    "state": "PRIORITIZED",
+    "success_criteria": {
+      "expression": "requests_per_completed_task <= 1.2 AND no hard guardrail violation\n"
+    },
+    "title": "Provide direct latest-invoice capability"
+  }
+}