diff --git a/src/contracts/context-graph-integrity.ts b/src/contracts/context-graph-integrity.ts
new file mode 100644
index 0000000..07b8d87
--- /dev/null
+++ b/src/contracts/context-graph-integrity.ts
@@ -0,0 +1,93 @@
+/**
+ * Context Graph integrity validators. Implements TC-CG-01 (context
+ * parameters surfaced), TC-CG-02 (constraints surfaced), TC-CG-03
+ * (contextualises edges to decisions), per RFC-0004.
+ *
+ * The Context Graph is derived from the COTS alone; these validators check
+ * the data-level contract that makes the derivation complete: every
+ * parameter key is present, every constraint is declared, and every
+ * decision is linked to the context.
+ *
+ * See: https://github.com/Source-Engineering/source-engineering-specifications/blob/main/compatibility-test-suite.md
+ */
+
+import type { Cots } from "../types.js";
+import { type Result, combine, fail } from "../result.js";
+
+/** TC-CG-01: every context parameter is recorded and therefore surfaceable. */
+export const validateContextParametersSurfaced = (cots: Cots): Result => {
+  const errors: Result[] = [];
+  const p = cots.context.parameters;
+
+  const required: Array<[string, unknown]> = [
+    ["temperature", p.temperature],
+    ["top_p", p.top_p],
+    ["prompt_cache_id", p.prompt_cache_id],
+    ["tool_budget", p.tool_budget],
+    ["retrieval_depth", p.retrieval_depth],
+  ];
+
+  for (const [key, value] of required) {
+    if (value === undefined) {
+      errors.push(
+        fail("TC-CG-01", `context.parameters.${key} is missing; it cannot be surfaced in the Context Graph`)
+      );
+    }
+  }
+
+  for (const key of Object.keys(p.additional ?? {})) {
+    if (p.additional?.[key] === undefined) {
+      errors.push(
+        fail("TC-CG-01", `context.parameters.additional.${key} is present but undefined; it cannot be surfaced`)
+      );
+    }
+  }
+
+  return combine(...errors);
+};
+
+/** TC-CG-02: every constraint is declared with an id so it can carry a constrains edge. */
+export const validateConstraintsSurfaced = (cots: Cots): Result => {
+  const errors: Result[] = [];
+
+  for (let i = 0; i < cots.context.constraints.length; i++) {
+    const c = cots.context.constraints[i];
+    if (!c.id || !/^[a-z][a-z0-9+\-.]*:/i.test(c.id)) {
+      errors.push(
+        fail("TC-CG-02", `context.constraints[${i}].id is missing or not a valid URI ('${c.id}'); the constraint cannot be surfaced in the Context Graph`)
+      );
+    }
+  }
+
+  return combine(...errors);
+};
+
+/** TC-CG-03: every decision is made under the recorded context. */
+export const validateDecisionsContextualised = (cots: Cots): Result => {
+  const errors: Result[] = [];
+
+  if (cots.decisions.length === 0) {
+    return combine();
+  }
+
+  const paramKeys = Object.keys(cots.context.parameters).filter(
+    (k) => k !== "additional"
+  );
+  if (paramKeys.length === 0) {
+    errors.push(
+      fail("TC-CG-03", "context.parameters has no named parameters; no contextualises edge can be drawn to any decision")
+    );
+  }
+
+  for (let i = 0; i < cots.decisions.length; i++) {
+    const d = cots.decisions[i];
+    const chain = cots.evidence.evidence_chain.find((c) => c.decision_id === d.id);
+    if (!chain) {
+      errors.push(
+        fail("TC-CG-03", `decisions[${i}] (${d.id}) has no evidence chain; the decision cannot be contextualised in the Context Graph`)
+      );
+    }
+  }
+
+  return combine(...errors);
+};
diff --git a/src/fixtures/cg-bad-constraint.json b/src/fixtures/cg-bad-constraint.json
new file mode 100644
index 0000000..6438bfe
--- /dev/null
+++ b/src/fixtures/cg-bad-constraint.json
@@ -0,0 +1,157 @@
+{
+  "cots_version": "0.1.0",
+  "cots_id": "urn:source-engineering:cots:00000000-0000-0000-0000-000000000001",
+  "produced_at": "2026-10-11T12:00:00Z",
+  "produced_by": {
+    "system_name": "test-fixture",
+    "system_version": "0.1.0"
+  },
+  "inputs": {
+    "source_artifacts": [
+      {
+        "id": "urn:source-engineering:source:contract-2026-001",
+        "origin": {
+          "system_name": "Acme Contracts",
+          "system_version": "1.0.0",
+          "configuration_hash": "0000000000000000000000000000000000000000000000000000000000000001"
+        },
+        "version": {
+          "content_hash": "1111111111111111111111111111111111111111111111111111111111111111",
+          "issued_at": "2026-10-10T08:00:00Z"
+        },
+        "authority": {
+          "asserted_by": "acme-contracts",
+          "trust_score": 0.95
+        },
+        "temporal_validity": {
+          "valid_from": "2026-10-10T08:00:00Z",
+          "valid_until": null
+        },
+        "content_reference": {
+          "uri": "https://example.com/contracts/2026-001.pdf",
+          "media_type": "application/pdf"
+        }
+      }
+    ]
+  },
+  "context": {
+    "model": {
+      "model_name": "claude-sonnet-4-5",
+      "model_version": "2026-09-15"
+    },
+    "parameters": {
+      "temperature": 0.3,
+      "top_p": 0.95,
+      "prompt_cache_id": null,
+      "tool_budget": 8,
+      "retrieval_depth": 5
+    },
+    "constraints": [
+      {
+        "id": "not-a-uri",
+        "type": "jurisdiction",
+        "scope": "all_decisions",
+        "value": "US-NY"
+      }
+    ]
+  },
+  "decisions": [
+    {
+      "id": "urn:source-engineering:decision:00000000-0000-0000-0000-000000000001",
+      "decision_text": "The contract is a standard commercial services agreement with mutual indemnification, a 30-day termination notice, and a New York governing-law clause.",
+      "basis_id": "urn:source-engineering:basis:00000000-0000-0000-0000-000000000001",
+      "evidence_chain_ref": "urn:source-engineering:evidence-chain:00000000-0000-0000-0000-000000000001",
+      "validation_status": {
+        "status": "pending",
+        "last_changed_at": "2026-10-11T12:00:00Z",
+        "last_changed_by": "test-fixture"
+      },
+      "responsible_authority": {
+        "authority_id": "claude-sonnet-4-5",
+        "authority_type": "automated"
+      },
+      "audit_history": [
+        {
+          "id": "urn:source-engineering:audit:00000000-0000-0000-0000-000000000001",
+          "action": "created",
+          "performed_by": "test-fixture",
+          "performed_at": "2026-10-11T12:00:00Z",
+          "notes": "Initial creation."
+        }
+      ],
+      "created_at": "2026-10-11T12:00:00Z"
+    }
+  ],
+  "evidence": {
+    "evidence_chain": [
+      {
+        "decision_id": "urn:source-engineering:decision:00000000-0000-0000-0000-000000000001",
+        "supporting_evidence": [
+          {
+            "id": "urn:source-engineering:evidence:00000000-0000-0000-0000-000000000001",
+            "claim_id": "urn:source-engineering:claim:00000000-0000-0000-0000-000000000001",
+            "source_id": "urn:source-engineering:source:contract-2026-001",
+            "transformation": {
+              "operation": "extract_clause",
+              "inputs": [
+                "https://example.com/contracts/2026-001.pdf#section-7"
+              ],
+              "output": "Section 7.1: Each party shall indemnify and hold harmless...",
+              "recorded_at": "2026-10-11T12:00:00Z"
+            },
+            "uncertainty": {
+              "calibrated_score": 0.92,
+              "basis": "Direct extraction from the section 7.1 text."
+            },
+            "polarity": "supports"
+          }
+        ],
+        "contradicting_evidence": [
+          {
+            "id": "urn:source-engineering:evidence:00000000-0000-0000-0000-000000000002",
+            "claim_id": "urn:source-engineering:claim:00000000-0000-0000-0000-000000000001",
+            "source_id": "urn:source-engineering:source:contract-2026-001",
+            "transformation": {
+              "operation": "search_clause",
+              "inputs": [
+                "https://example.com/contracts/2026-001.pdf#section-12"
+              ],
+              "output": "Section 12.4: This agreement shall be governed by the laws of the State of Delaware.",
+              "recorded_at": "2026-10-11T12:00:00Z"
+            },
+            "uncertainty": {
+              "calibrated_score": 0.78,
+              "basis": "Contradictory governing-law clause in section 12.4 (the model rejected it because section 14.1 is the prevailing clause)."
+            },
+            "polarity": "contradicts"
+          }
+        ],
+        "claims": [
+          {
+            "id": "urn:source-engineering:claim:00000000-0000-0000-0000-000000000001",
+            "decision_record_id": "urn:source-engineering:decision:00000000-0000-0000-0000-000000000001",
+            "claim_text": "The contract contains a mutual indemnification clause in section 7.1.",
+            "claim_type": "factual",
+            "supporting_evidence": [
+              "urn:source-engineering:evidence:00000000-0000-0000-0000-000000000001"
+            ],
+            "contradicting_evidence": [
+              "urn:source-engineering:evidence:00000000-0000-0000-0000-000000000002"
+            ]
+          }
+        ]
+      }
+    ]
+  },
+  "validation": {
+    "feedback_surfaces": [
+      {
+        "id": "urn:source-engineering:surface:00000000-0000-0000-0000-000000000001",
+        "type": "appeal",
+        "target": "urn:source-engineering:decision:00000000-0000-0000-0000-000000000001",
+        "endpoint": "https://example.com/appeal/00000000-0000-0000-0000-000000000001",
+        "description": "File an appeal against this decision."
+      }
+    ]
+  }
+}
\ No newline at end of file
diff --git a/src/fixtures/cg-missing-param.json b/src/fixtures/cg-missing-param.json
new file mode 100644
index 0000000..fbaf16f
--- /dev/null
+++ b/src/fixtures/cg-missing-param.json
@@ -0,0 +1,156 @@
+{
+  "cots_version": "0.1.0",
+  "cots_id": "urn:source-engineering:cots:00000000-0000-0000-0000-000000000001",
+  "produced_at": "2026-10-11T12:00:00Z",
+  "produced_by": {
+    "system_name": "test-fixture",
+    "system_version": "0.1.0"
+  },
+  "inputs": {
+    "source_artifacts": [
+      {
+        "id": "urn:source-engineering:source:contract-2026-001",
+        "origin": {
+          "system_name": "Acme Contracts",
+          "system_version": "1.0.0",
+          "configuration_hash": "0000000000000000000000000000000000000000000000000000000000000001"
+        },
+        "version": {
+          "content_hash": "1111111111111111111111111111111111111111111111111111111111111111",
+          "issued_at": "2026-10-10T08:00:00Z"
+        },
+        "authority": {
+          "asserted_by": "acme-contracts",
+          "trust_score": 0.95
+        },
+        "temporal_validity": {
+          "valid_from": "2026-10-10T08:00:00Z",
+          "valid_until": null
+        },
+        "content_reference": {
+          "uri": "https://example.com/contracts/2026-001.pdf",
+          "media_type": "application/pdf"
+        }
+      }
+    ]
+  },
+  "context": {
+    "model": {
+      "model_name": "claude-sonnet-4-5",
+      "model_version": "2026-09-15"
+    },
+    "parameters": {
+      "top_p": 0.95,
+      "prompt_cache_id": null,
+      "tool_budget": 8,
+      "retrieval_depth": 5
+    },
+    "constraints": [
+      {
+        "id": "urn:source-engineering:constraint:jurisdiction-001",
+        "type": "jurisdiction",
+        "scope": "all_decisions",
+        "value": "US-NY"
+      }
+    ]
+  },
+  "decisions": [
+    {
+      "id": "urn:source-engineering:decision:00000000-0000-0000-0000-000000000001",
+      "decision_text": "The contract is a standard commercial services agreement with mutual indemnification, a 30-day termination notice, and a New York governing-law clause.",
+      "basis_id": "urn:source-engineering:basis:00000000-0000-0000-0000-000000000001",
+      "evidence_chain_ref": "urn:source-engineering:evidence-chain:00000000-0000-0000-0000-000000000001",
+      "validation_status": {
+        "status": "pending",
+        "last_changed_at": "2026-10-11T12:00:00Z",
+        "last_changed_by": "test-fixture"
+      },
+      "responsible_authority": {
+        "authority_id": "claude-sonnet-4-5",
+        "authority_type": "automated"
+      },
+      "audit_history": [
+        {
+          "id": "urn:source-engineering:audit:00000000-0000-0000-0000-000000000001",
+          "action": "created",
+          "performed_by": "test-fixture",
+          "performed_at": "2026-10-11T12:00:00Z",
+          "notes": "Initial creation."
+        }
+      ],
+      "created_at": "2026-10-11T12:00:00Z"
+    }
+  ],
+  "evidence": {
+    "evidence_chain": [
+      {
+        "decision_id": "urn:source-engineering:decision:00000000-0000-0000-0000-000000000001",
+        "supporting_evidence": [
+          {
+            "id": "urn:source-engineering:evidence:00000000-0000-0000-0000-000000000001",
+            "claim_id": "urn:source-engineering:claim:00000000-0000-0000-0000-000000000001",
+            "source_id": "urn:source-engineering:source:contract-2026-001",
+            "transformation": {
+              "operation": "extract_clause",
+              "inputs": [
+                "https://example.com/contracts/2026-001.pdf#section-7"
+              ],
+              "output": "Section 7.1: Each party shall indemnify and hold harmless...",
+              "recorded_at": "2026-10-11T12:00:00Z"
+            },
+            "uncertainty": {
+              "calibrated_score": 0.92,
+              "basis": "Direct extraction from the section 7.1 text."
+            },
+            "polarity": "supports"
+          }
+        ],
+        "contradicting_evidence": [
+          {
+            "id": "urn:source-engineering:evidence:00000000-0000-0000-0000-000000000002",
+            "claim_id": "urn:source-engineering:claim:00000000-0000-0000-0000-000000000001",
+            "source_id": "urn:source-engineering:source:contract-2026-001",
+            "transformation": {
+              "operation": "search_clause",
+              "inputs": [
+                "https://example.com/contracts/2026-001.pdf#section-12"
+              ],
+              "output": "Section 12.4: This agreement shall be governed by the laws of the State of Delaware.",
+              "recorded_at": "2026-10-11T12:00:00Z"
+            },
+            "uncertainty": {
+              "calibrated_score": 0.78,
+              "basis": "Contradictory governing-law clause in section 12.4 (the model rejected it because section 14.1 is the prevailing clause)."
+            },
+            "polarity": "contradicts"
+          }
+        ],
+        "claims": [
+          {
+            "id": "urn:source-engineering:claim:00000000-0000-0000-0000-000000000001",
+            "decision_record_id": "urn:source-engineering:decision:00000000-0000-0000-0000-000000000001",
+            "claim_text": "The contract contains a mutual indemnification clause in section 7.1.",
+            "claim_type": "factual",
+            "supporting_evidence": [
+              "urn:source-engineering:evidence:00000000-0000-0000-0000-000000000001"
+            ],
+            "contradicting_evidence": [
+              "urn:source-engineering:evidence:00000000-0000-0000-0000-000000000002"
+            ]
+          }
+        ]
+      }
+    ]
+  },
+  "validation": {
+    "feedback_surfaces": [
+      {
+        "id": "urn:source-engineering:surface:00000000-0000-0000-0000-000000000001",
+        "type": "appeal",
+        "target": "urn:source-engineering:decision:00000000-0000-0000-0000-000000000001",
+        "endpoint": "https://example.com/appeal/00000000-0000-0000-0000-000000000001",
+        "description": "File an appeal against this decision."
+      }
+    ]
+  }
+}
\ No newline at end of file
diff --git a/src/fixtures/cg-no-chain.json b/src/fixtures/cg-no-chain.json
new file mode 100644
index 0000000..b5bab55
--- /dev/null
+++ b/src/fixtures/cg-no-chain.json
@@ -0,0 +1,99 @@
+{
+  "cots_version": "0.1.0",
+  "cots_id": "urn:source-engineering:cots:00000000-0000-0000-0000-000000000001",
+  "produced_at": "2026-10-11T12:00:00Z",
+  "produced_by": {
+    "system_name": "test-fixture",
+    "system_version": "0.1.0"
+  },
+  "inputs": {
+    "source_artifacts": [
+      {
+        "id": "urn:source-engineering:source:contract-2026-001",
+        "origin": {
+          "system_name": "Acme Contracts",
+          "system_version": "1.0.0",
+          "configuration_hash": "0000000000000000000000000000000000000000000000000000000000000001"
+        },
+        "version": {
+          "content_hash": "1111111111111111111111111111111111111111111111111111111111111111",
+          "issued_at": "2026-10-10T08:00:00Z"
+        },
+        "authority": {
+          "asserted_by": "acme-contracts",
+          "trust_score": 0.95
+        },
+        "temporal_validity": {
+          "valid_from": "2026-10-10T08:00:00Z",
+          "valid_until": null
+        },
+        "content_reference": {
+          "uri": "https://example.com/contracts/2026-001.pdf",
+          "media_type": "application/pdf"
+        }
+      }
+    ]
+  },
+  "context": {
+    "model": {
+      "model_name": "claude-sonnet-4-5",
+      "model_version": "2026-09-15"
+    },
+    "parameters": {
+      "temperature": 0.3,
+      "top_p": 0.95,
+      "prompt_cache_id": null,
+      "tool_budget": 8,
+      "retrieval_depth": 5
+    },
+    "constraints": [
+      {
+        "id": "urn:source-engineering:constraint:jurisdiction-001",
+        "type": "jurisdiction",
+        "scope": "all_decisions",
+        "value": "US-NY"
+      }
+    ]
+  },
+  "decisions": [
+    {
+      "id": "urn:source-engineering:decision:00000000-0000-0000-0000-000000000001",
+      "decision_text": "The contract is a standard commercial services agreement with mutual indemnification, a 30-day termination notice, and a New York governing-law clause.",
+      "basis_id": "urn:source-engineering:basis:00000000-0000-0000-0000-000000000001",
+      "evidence_chain_ref": "urn:source-engineering:evidence-chain:00000000-0000-0000-0000-000000000001",
+      "validation_status": {
+        "status": "pending",
+        "last_changed_at": "2026-10-11T12:00:00Z",
+        "last_changed_by": "test-fixture"
+      },
+      "responsible_authority": {
+        "authority_id": "claude-sonnet-4-5",
+        "authority_type": "automated"
+      },
+      "audit_history": [
+        {
+          "id": "urn:source-engineering:audit:00000000-0000-0000-0000-000000000001",
+          "action": "created",
+          "performed_by": "test-fixture",
+          "performed_at": "2026-10-11T12:00:00Z",
+          "notes": "Initial creation."
+        }
+      ],
+      "created_at": "2026-10-11T12:00:00Z"
+    }
+  ],
+  "evidence": {
+    "evidence_chain": []
+  },
+  "validation": {
+    "feedback_surfaces": [
+      {
+        "id": "urn:source-engineering:surface:00000000-0000-0000-0000-000000000001",
+        "type": "appeal",
+        "target": "urn:source-engineering:decision:00000000-0000-0000-0000-000000000001",
+        "endpoint": "https://example.com/appeal/00000000-0000-0000-0000-000000000001",
+        "description": "File an appeal against this decision."
+      }
+    ]
+  }
+}
\ No newline at end of file
diff --git a/src/runner.ts b/src/runner.ts
index 741ad36..6666216 100644
--- a/src/runner.ts
+++ b/src/runner.ts
@@ -12,6 +12,7 @@ import type { Cots } from "./types.js";
 import { type Result, combine } from "./result.js";
 import { validateSourceAddresses } from "./contracts/source-integrity.js";
 import { validateContextRecorded, validateSourceValidity } from "./contracts/contextual-integrity.js";
+import { validateContextParametersSurfaced, validateConstraintsSurfaced, validateDecisionsContextualised } from "./contracts/context-graph-integrity.js";
 import { validateEvidenceChain } from "./contracts/evidential-integrity.js";
 import { validateDecisionBasis, validateCounterevidence } from "./contracts/decision-integrity.js";
 import { validateAuditHistory, validateAuditHistoryOrdered } from "./contracts/lifecycle-integrity.js";
@@ -25,6 +26,9 @@ export const run = (cots: Cots): Result => {
     validateSourceAddresses(cots),
     validateContextRecorded(cots),
     validateSourceValidity(cots),
+    validateContextParametersSurfaced(cots),
+    validateConstraintsSurfaced(cots),
+    validateDecisionsContextualised(cots),
     validateEvidenceChain(cots),
     validateDecisionBasis(cots),
     validateCounterevidence(cots),
diff --git a/tests/context-graph.test.ts b/tests/context-graph.test.ts
new file mode 100644
index 0000000..b15fdf4
--- /dev/null
+++ b/tests/context-graph.test.ts
@@ -0,0 +1,62 @@
+/**
+ * TC-CG test cases (RFC-0004, context graph surfacing contract).
+ *
+ * See: https://github.com/Source-Engineering/source-engineering-specifications/blob/main/compatibility-test-suite.md
+ */
+
+import { describe, it, expect } from "vitest";
+import { readFileSync } from "node:fs";
+import { resolve } from "node:path";
+import { fileURLToPath } from "node:url";
+import { dirname, join } from "node:path";
+import { run } from "../src/runner.js";
+import type { Cots } from "../src/types.js";
+
+const __dirname = dirname(fileURLToPath(import.meta.url));
+const FIXTURES = join(__dirname, "..", "src", "fixtures");
+
+const load = (name: string): Cots => {
+  const p = resolve(FIXTURES, name);
+  return JSON.parse(readFileSync(p, "utf-8"));
+};
+
+describe("TC-CG: context graph surfacing (RFC-0004)", () => {
+  it("TC-CG-01: passes when every context parameter is recorded and surfaceable", () => {
+    const result = run(load("conformant.json"));
+    const errors = result.errors.filter((e) => e.test_id === "TC-CG-01");
+    expect(errors).toHaveLength(0);
+  });
+
+  it("TC-CG-01: fails when a parameter is missing and cannot be surfaced", () => {
+    const result = run(load("cg-missing-param.json"));
+    const errors = result.errors.filter((e) => e.test_id === "TC-CG-01");
+    expect(errors.length).toBeGreaterThan(0);
+    expect(errors[0].message).toContain("temperature");
+  });
+
+  it("TC-CG-02: passes when every constraint has a valid id", () => {
+    const result = run(load("conformant.json"));
+    const errors = result.errors.filter((e) => e.test_id === "TC-CG-02");
+    expect(errors).toHaveLength(0);
+  });
+
+  it("TC-CG-02: fails when a constraint id is not a valid URI", () => {
+    const result = run(load("cg-bad-constraint.json"));
+    const errors = result.errors.filter((e) => e.test_id === "TC-CG-02");
+    expect(errors.length).toBeGreaterThan(0);
+    expect(errors[0].message).toContain("not-a-uri");
+  });
+
+  it("TC-CG-03: passes when every decision has an evidence chain to contextualise", () => {
+    const result = run(load("conformant.json"));
+    const errors = result.errors.filter((e) => e.test_id === "TC-CG-03");
+    expect(errors).toHaveLength(0);
+  });
+
+  it("TC-CG-03: fails when a decision has no evidence chain", () => {
+    const result = run(load("cg-no-chain.json"));
+    const errors = result.errors.filter((e) => e.test_id === "TC-CG-03");
+    expect(errors.length).toBeGreaterThan(0);
+    expect(errors[0].message).toContain("contextualised");
+  });
+});