feat(platform): I3 contracts, lines, status machine, and audit API

Add Flyway V3 tables, contract CRUD and line endpoints, PATCH status transitions with validation, M10-F01 audit-events listing, 409 handler, and integration tests. Refresh OpenAPI contract snapshot. Made-with: Cursor
2026-06-09 10:00:30 +08:00 · 2026-04-06 21:29:21 +08:00
parent 5b50bf0fd8
commit 69f7ee11df
26 changed files with 2439 additions and 0 deletions
@@ -170,6 +170,139 @@
        }
      }
    },
+    "/api/v1/contracts/{id}" : {
+      "get" : {
+        "tags" : [ "contract-controller" ],
+        "operationId" : "get_2",
+        "parameters" : [ {
+          "name" : "id",
+          "in" : "path",
+          "required" : true,
+          "schema" : {
+            "type" : "integer",
+            "format" : "int64"
+          }
+        } ],
+        "responses" : {
+          "200" : {
+            "description" : "OK",
+            "content" : {
+              "*/*" : {
+                "schema" : {
+                  "$ref" : "#/components/schemas/ContractResponse"
+                }
+              }
+            }
+          }
+        }
+      },
+      "put" : {
+        "tags" : [ "contract-controller" ],
+        "operationId" : "update_2",
+        "parameters" : [ {
+          "name" : "id",
+          "in" : "path",
+          "required" : true,
+          "schema" : {
+            "type" : "integer",
+            "format" : "int64"
+          }
+        } ],
+        "requestBody" : {
+          "content" : {
+            "application/json" : {
+              "schema" : {
+                "$ref" : "#/components/schemas/ContractUpdateRequest"
+              }
+            }
+          },
+          "required" : true
+        },
+        "responses" : {
+          "200" : {
+            "description" : "OK",
+            "content" : {
+              "*/*" : {
+                "schema" : {
+                  "$ref" : "#/components/schemas/ContractResponse"
+                }
+              }
+            }
+          }
+        }
+      }
+    },
+    "/api/v1/contracts/{id}/lines/{lineId}" : {
+      "put" : {
+        "tags" : [ "contract-controller" ],
+        "operationId" : "updateLine",
+        "parameters" : [ {
+          "name" : "id",
+          "in" : "path",
+          "required" : true,
+          "schema" : {
+            "type" : "integer",
+            "format" : "int64"
+          }
+        }, {
+          "name" : "lineId",
+          "in" : "path",
+          "required" : true,
+          "schema" : {
+            "type" : "integer",
+            "format" : "int64"
+          }
+        } ],
+        "requestBody" : {
+          "content" : {
+            "application/json" : {
+              "schema" : {
+                "$ref" : "#/components/schemas/ContractLineRequest"
+              }
+            }
+          },
+          "required" : true
+        },
+        "responses" : {
+          "200" : {
+            "description" : "OK",
+            "content" : {
+              "*/*" : {
+                "schema" : {
+                  "$ref" : "#/components/schemas/ContractLineResponse"
+                }
+              }
+            }
+          }
+        }
+      },
+      "delete" : {
+        "tags" : [ "contract-controller" ],
+        "operationId" : "deleteLine",
+        "parameters" : [ {
+          "name" : "id",
+          "in" : "path",
+          "required" : true,
+          "schema" : {
+            "type" : "integer",
+            "format" : "int64"
+          }
+        }, {
+          "name" : "lineId",
+          "in" : "path",
+          "required" : true,
+          "schema" : {
+            "type" : "integer",
+            "format" : "int64"
+          }
+        } ],
+        "responses" : {
+          "204" : {
+            "description" : "No Content"
+          }
+        }
+      }
+    },
    "/api/v1/projects" : {
      "get" : {
        "tags" : [ "project-controller" ],
@@ -317,6 +450,160 @@
        }
      }
    },
+    "/api/v1/contracts" : {
+      "get" : {
+        "tags" : [ "contract-controller" ],
+        "operationId" : "list_2",
+        "parameters" : [ {
+          "name" : "page",
+          "in" : "query",
+          "required" : false,
+          "schema" : {
+            "type" : "integer",
+            "format" : "int32",
+            "default" : 0,
+            "minimum" : 0
+          }
+        }, {
+          "name" : "size",
+          "in" : "query",
+          "required" : false,
+          "schema" : {
+            "type" : "integer",
+            "format" : "int32",
+            "default" : 20,
+            "maximum" : 200,
+            "minimum" : 1
+          }
+        }, {
+          "name" : "customerId",
+          "in" : "query",
+          "required" : false,
+          "schema" : {
+            "type" : "integer",
+            "format" : "int64"
+          }
+        }, {
+          "name" : "projectId",
+          "in" : "query",
+          "required" : false,
+          "schema" : {
+            "type" : "integer",
+            "format" : "int64"
+          }
+        }, {
+          "name" : "keyword",
+          "in" : "query",
+          "required" : false,
+          "schema" : {
+            "type" : "string"
+          }
+        } ],
+        "responses" : {
+          "200" : {
+            "description" : "OK",
+            "content" : {
+              "*/*" : {
+                "schema" : {
+                  "$ref" : "#/components/schemas/PageResponseContractResponse"
+                }
+              }
+            }
+          }
+        }
+      },
+      "post" : {
+        "tags" : [ "contract-controller" ],
+        "operationId" : "create_2",
+        "requestBody" : {
+          "content" : {
+            "application/json" : {
+              "schema" : {
+                "$ref" : "#/components/schemas/ContractCreateRequest"
+              }
+            }
+          },
+          "required" : true
+        },
+        "responses" : {
+          "201" : {
+            "description" : "Created",
+            "content" : {
+              "*/*" : {
+                "schema" : {
+                  "$ref" : "#/components/schemas/ContractResponse"
+                }
+              }
+            }
+          }
+        }
+      }
+    },
+    "/api/v1/contracts/{id}/lines" : {
+      "get" : {
+        "tags" : [ "contract-controller" ],
+        "operationId" : "listLines",
+        "parameters" : [ {
+          "name" : "id",
+          "in" : "path",
+          "required" : true,
+          "schema" : {
+            "type" : "integer",
+            "format" : "int64"
+          }
+        } ],
+        "responses" : {
+          "200" : {
+            "description" : "OK",
+            "content" : {
+              "*/*" : {
+                "schema" : {
+                  "type" : "array",
+                  "items" : {
+                    "$ref" : "#/components/schemas/ContractLineResponse"
+                  }
+                }
+              }
+            }
+          }
+        }
+      },
+      "post" : {
+        "tags" : [ "contract-controller" ],
+        "operationId" : "addLine",
+        "parameters" : [ {
+          "name" : "id",
+          "in" : "path",
+          "required" : true,
+          "schema" : {
+            "type" : "integer",
+            "format" : "int64"
+          }
+        } ],
+        "requestBody" : {
+          "content" : {
+            "application/json" : {
+              "schema" : {
+                "$ref" : "#/components/schemas/ContractLineRequest"
+              }
+            }
+          },
+          "required" : true
+        },
+        "responses" : {
+          "201" : {
+            "description" : "Created",
+            "content" : {
+              "*/*" : {
+                "schema" : {
+                  "$ref" : "#/components/schemas/ContractLineResponse"
+                }
+              }
+            }
+          }
+        }
+      }
+    },
    "/api/v1/auth/login" : {
      "post" : {
        "tags" : [ "auth-controller" ],
@@ -349,6 +636,43 @@
        }
      }
    },
+    "/api/v1/contracts/{id}/status" : {
+      "patch" : {
+        "tags" : [ "contract-controller" ],
+        "operationId" : "patchStatus",
+        "parameters" : [ {
+          "name" : "id",
+          "in" : "path",
+          "required" : true,
+          "schema" : {
+            "type" : "integer",
+            "format" : "int64"
+          }
+        } ],
+        "requestBody" : {
+          "content" : {
+            "application/json" : {
+              "schema" : {
+                "$ref" : "#/components/schemas/ContractStatusPatchRequest"
+              }
+            }
+          },
+          "required" : true
+        },
+        "responses" : {
+          "200" : {
+            "description" : "OK",
+            "content" : {
+              "*/*" : {
+                "schema" : {
+                  "$ref" : "#/components/schemas/ContractResponse"
+                }
+              }
+            }
+          }
+        }
+      }
+    },
    "/api/v1/ping" : {
      "get" : {
        "tags" : [ "ping-controller" ],
@@ -398,6 +722,62 @@
          }
        }
      }
+    },
+    "/api/v1/audit-events" : {
+      "get" : {
+        "tags" : [ "audit-controller" ],
+        "operationId" : "list_3",
+        "parameters" : [ {
+          "name" : "entityType",
+          "in" : "query",
+          "required" : true,
+          "schema" : {
+            "type" : "string",
+            "minLength" : 1
+          }
+        }, {
+          "name" : "entityId",
+          "in" : "query",
+          "required" : true,
+          "schema" : {
+            "type" : "integer",
+            "format" : "int64"
+          }
+        }, {
+          "name" : "page",
+          "in" : "query",
+          "required" : false,
+          "schema" : {
+            "type" : "integer",
+            "format" : "int32",
+            "default" : 0,
+            "minimum" : 0
+          }
+        }, {
+          "name" : "size",
+          "in" : "query",
+          "required" : false,
+          "schema" : {
+            "type" : "integer",
+            "format" : "int32",
+            "default" : 20,
+            "maximum" : 200,
+            "minimum" : 1
+          }
+        } ],
+        "responses" : {
+          "200" : {
+            "description" : "OK",
+            "content" : {
+              "*/*" : {
+                "schema" : {
+                  "$ref" : "#/components/schemas/PageResponseAuditEventResponse"
+                }
+              }
+            }
+          }
+        }
+      }
    }
  },
  "components" : {
@@ -496,6 +876,167 @@
          }
        }
      },
+      "ContractUpdateRequest" : {
+        "type" : "object",
+        "properties" : {
+          "title" : {
+            "type" : "string",
+            "maxLength" : 256,
+            "minLength" : 0
+          },
+          "remarks" : {
+            "type" : "string",
+            "maxLength" : 4000,
+            "minLength" : 0
+          }
+        }
+      },
+      "ContractLineResponse" : {
+        "type" : "object",
+        "properties" : {
+          "id" : {
+            "type" : "integer",
+            "format" : "int64"
+          },
+          "contractId" : {
+            "type" : "integer",
+            "format" : "int64"
+          },
+          "sortOrder" : {
+            "type" : "integer",
+            "format" : "int32"
+          },
+          "itemName" : {
+            "type" : "string"
+          },
+          "quantity" : {
+            "type" : "number"
+          },
+          "unit" : {
+            "type" : "string"
+          },
+          "amount" : {
+            "type" : "number"
+          },
+          "remark" : {
+            "type" : "string"
+          },
+          "createdAt" : {
+            "type" : "string",
+            "format" : "date-time"
+          },
+          "updatedAt" : {
+            "type" : "string",
+            "format" : "date-time"
+          }
+        }
+      },
+      "ContractResponse" : {
+        "type" : "object",
+        "properties" : {
+          "id" : {
+            "type" : "integer",
+            "format" : "int64"
+          },
+          "customerId" : {
+            "type" : "integer",
+            "format" : "int64"
+          },
+          "projectId" : {
+            "type" : "integer",
+            "format" : "int64"
+          },
+          "title" : {
+            "type" : "string"
+          },
+          "remarks" : {
+            "type" : "string"
+          },
+          "status" : {
+            "type" : "string"
+          },
+          "createdAt" : {
+            "type" : "string",
+            "format" : "date-time"
+          },
+          "updatedAt" : {
+            "type" : "string",
+            "format" : "date-time"
+          },
+          "lines" : {
+            "type" : "array",
+            "items" : {
+              "$ref" : "#/components/schemas/ContractLineResponse"
+            }
+          }
+        }
+      },
+      "ContractLineRequest" : {
+        "type" : "object",
+        "properties" : {
+          "sortOrder" : {
+            "type" : "integer",
+            "format" : "int32"
+          },
+          "itemName" : {
+            "type" : "string",
+            "maxLength" : 256,
+            "minLength" : 0
+          },
+          "quantity" : {
+            "type" : "number",
+            "minimum" : 1.0E-4
+          },
+          "unit" : {
+            "type" : "string",
+            "maxLength" : 32,
+            "minLength" : 0
+          },
+          "amount" : {
+            "type" : "number"
+          },
+          "remark" : {
+            "type" : "string",
+            "maxLength" : 512,
+            "minLength" : 0
+          }
+        },
+        "required" : [ "itemName", "quantity" ]
+      },
+      "ContractCreateRequest" : {
+        "type" : "object",
+        "properties" : {
+          "customerId" : {
+            "type" : "integer",
+            "format" : "int64"
+          },
+          "projectId" : {
+            "type" : "integer",
+            "format" : "int64"
+          },
+          "title" : {
+            "type" : "string",
+            "maxLength" : 256,
+            "minLength" : 0
+          },
+          "remarks" : {
+            "type" : "string",
+            "maxLength" : 4000,
+            "minLength" : 0
+          }
+        },
+        "required" : [ "customerId", "projectId" ]
+      },
+      "ContractStatusPatchRequest" : {
+        "type" : "object",
+        "properties" : {
+          "status" : {
+            "type" : "string",
+            "minLength" : 1
+          }
+        },
+        "required" : [ "status" ]
+      },
      "PageResponseProjectResponse" : {
        "type" : "object",
        "properties" : {
@@ -556,6 +1097,87 @@
            "format" : "int32"
          }
        }
+      },
+      "PageResponseContractResponse" : {
+        "type" : "object",
+        "properties" : {
+          "content" : {
+            "type" : "array",
+            "items" : {
+              "$ref" : "#/components/schemas/ContractResponse"
+            }
+          },
+          "totalElements" : {
+            "type" : "integer",
+            "format" : "int64"
+          },
+          "number" : {
+            "type" : "integer",
+            "format" : "int32"
+          },
+          "size" : {
+            "type" : "integer",
+            "format" : "int32"
+          }
+        }
+      },
+      "AuditEventResponse" : {
+        "type" : "object",
+        "properties" : {
+          "id" : {
+            "type" : "integer",
+            "format" : "int64"
+          },
+          "entityType" : {
+            "type" : "string"
+          },
+          "entityId" : {
+            "type" : "integer",
+            "format" : "int64"
+          },
+          "action" : {
+            "type" : "string"
+          },
+          "fieldName" : {
+            "type" : "string"
+          },
+          "oldValue" : {
+            "type" : "string"
+          },
+          "newValue" : {
+            "type" : "string"
+          },
+          "actorUserId" : {
+            "type" : "string"
+          },
+          "createdAt" : {
+            "type" : "string",
+            "format" : "date-time"
+          }
+        }
+      },
+      "PageResponseAuditEventResponse" : {
+        "type" : "object",
+        "properties" : {
+          "content" : {
+            "type" : "array",
+            "items" : {
+              "$ref" : "#/components/schemas/AuditEventResponse"
+            }
+          },
+          "totalElements" : {
+            "type" : "integer",
+            "format" : "int64"
+          },
+          "number" : {
+            "type" : "integer",
+            "format" : "int32"
+          },
+          "size" : {
+            "type" : "integer",
+            "format" : "int32"
+          }
+        }
      }
    },
    "securitySchemes" : {
@@ -0,0 +1,14 @@
+package cn.craftlabs.platform.api.audit;
+
+/** 审计动作常量（M10-F01）。 */
+public final class AuditActions {
+
+    public static final String CONTRACT_CREATED = "CONTRACT_CREATED";
+    public static final String CONTRACT_UPDATED = "CONTRACT_UPDATED";
+    public static final String CONTRACT_LINE_ADDED = "CONTRACT_LINE_ADDED";
+    public static final String CONTRACT_LINE_UPDATED = "CONTRACT_LINE_UPDATED";
+    public static final String CONTRACT_LINE_DELETED = "CONTRACT_LINE_DELETED";
+    public static final String CONTRACT_STATUS_CHANGED = "CONTRACT_STATUS_CHANGED";
+
+    private AuditActions() {}
+}
@@ -0,0 +1,35 @@
+package cn.craftlabs.platform.api.audit;
+
+import cn.craftlabs.platform.api.service.AuditService;
+import cn.craftlabs.platform.api.web.dto.AuditEventResponse;
+import cn.craftlabs.platform.api.web.dto.PageResponse;
+import jakarta.validation.constraints.Max;
+import jakarta.validation.constraints.Min;
+import jakarta.validation.constraints.NotBlank;
+import jakarta.validation.constraints.NotNull;
+import org.springframework.validation.annotation.Validated;
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.RequestMapping;
+import org.springframework.web.bind.annotation.RequestParam;
+import org.springframework.web.bind.annotation.RestController;
+
+@RestController
+@RequestMapping("/api/v1/audit-events")
+@Validated
+public class AuditController {
+
+    private final AuditService auditService;
+
+    public AuditController(AuditService auditService) {
+        this.auditService = auditService;
+    }
+
+    @GetMapping
+    public PageResponse<AuditEventResponse> list(
+            @RequestParam("entityType") @NotBlank String entityType,
+            @RequestParam("entityId") @NotNull Long entityId,
+            @RequestParam(value = "page", defaultValue = "0") @Min(0) int page,
+            @RequestParam(value = "size", defaultValue = "20") @Min(1) @Max(200) int size) {
+        return auditService.page(entityType, entityId, page, size);
+    }
+}
@@ -0,0 +1,8 @@
+package cn.craftlabs.platform.api.audit;
+
+public final class AuditEntityTypes {
+
+    public static final String CONTRACT = "CONTRACT";
+
+    private AuditEntityTypes() {}
+}
@@ -0,0 +1,21 @@
+package cn.craftlabs.platform.api.config;
+
+import org.springframework.http.ResponseEntity;
+import org.springframework.web.bind.annotation.ExceptionHandler;
+import org.springframework.web.bind.annotation.RestControllerAdvice;
+import org.springframework.web.server.ResponseStatusException;
+
+import java.util.LinkedHashMap;
+import java.util.Map;
+
+@RestControllerAdvice
+public class ApiExceptionHandler {
+
+    @ExceptionHandler(ResponseStatusException.class)
+    public ResponseEntity<Map<String, Object>> handleResponseStatus(ResponseStatusException ex) {
+        Map<String, Object> body = new LinkedHashMap<>();
+        body.put("status", ex.getStatusCode().value());
+        body.put("message", ex.getReason() != null ? ex.getReason() : "");
+        return ResponseEntity.status(ex.getStatusCode()).body(body);
+    }
+}
@@ -0,0 +1,100 @@
+package cn.craftlabs.platform.api.contracts;
+
+import cn.craftlabs.platform.api.service.ContractService;
+import cn.craftlabs.platform.api.web.dto.ContractCreateRequest;
+import cn.craftlabs.platform.api.web.dto.ContractLineRequest;
+import cn.craftlabs.platform.api.web.dto.ContractLineResponse;
+import cn.craftlabs.platform.api.web.dto.ContractResponse;
+import cn.craftlabs.platform.api.web.dto.ContractStatusPatchRequest;
+import cn.craftlabs.platform.api.web.dto.ContractUpdateRequest;
+import cn.craftlabs.platform.api.web.dto.PageResponse;
+import jakarta.validation.Valid;
+import jakarta.validation.constraints.Max;
+import jakarta.validation.constraints.Min;
+import org.springframework.http.HttpStatus;
+import org.springframework.validation.annotation.Validated;
+import org.springframework.web.bind.annotation.DeleteMapping;
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.PatchMapping;
+import org.springframework.web.bind.annotation.PathVariable;
+import org.springframework.web.bind.annotation.PostMapping;
+import org.springframework.web.bind.annotation.PutMapping;
+import org.springframework.web.bind.annotation.RequestBody;
+import org.springframework.web.bind.annotation.RequestMapping;
+import org.springframework.web.bind.annotation.RequestParam;
+import org.springframework.web.bind.annotation.ResponseStatus;
+import org.springframework.web.bind.annotation.RestController;
+
+import java.util.List;
+
+/** 合同 API：头信息与行挂在同一资源树下（嵌套路由）。 */
+@RestController
+@RequestMapping("/api/v1/contracts")
+@Validated
+public class ContractController {
+
+    private final ContractService contractService;
+
+    public ContractController(ContractService contractService) {
+        this.contractService = contractService;
+    }
+
+    @GetMapping
+    public PageResponse<ContractResponse> list(
+            @RequestParam(value = "page", defaultValue = "0") @Min(0) int page,
+            @RequestParam(value = "size", defaultValue = "20") @Min(1) @Max(200) int size,
+            @RequestParam(value = "customerId", required = false) Long customerId,
+            @RequestParam(value = "projectId", required = false) Long projectId,
+            @RequestParam(value = "keyword", required = false) String keyword) {
+        return contractService.page(page, size, customerId, projectId, keyword);
+    }
+
+    @PostMapping
+    @ResponseStatus(HttpStatus.CREATED)
+    public ContractResponse create(@Valid @RequestBody ContractCreateRequest request) {
+        return contractService.create(request);
+    }
+
+    @GetMapping("/{id}")
+    public ContractResponse get(@PathVariable("id") long id) {
+        return contractService.getById(id);
+    }
+
+    @PutMapping("/{id}")
+    public ContractResponse update(
+            @PathVariable("id") long id, @Valid @RequestBody ContractUpdateRequest request) {
+        return contractService.update(id, request);
+    }
+
+    @PatchMapping("/{id}/status")
+    public ContractResponse patchStatus(
+            @PathVariable("id") long id, @Valid @RequestBody ContractStatusPatchRequest request) {
+        return contractService.patchStatus(id, request);
+    }
+
+    @GetMapping("/{id}/lines")
+    public List<ContractLineResponse> listLines(@PathVariable("id") long contractId) {
+        return contractService.listLines(contractId);
+    }
+
+    @PostMapping("/{id}/lines")
+    @ResponseStatus(HttpStatus.CREATED)
+    public ContractLineResponse addLine(
+            @PathVariable("id") long contractId, @Valid @RequestBody ContractLineRequest request) {
+        return contractService.addLine(contractId, request);
+    }
+
+    @PutMapping("/{id}/lines/{lineId}")
+    public ContractLineResponse updateLine(
+            @PathVariable("id") long contractId,
+            @PathVariable("lineId") long lineId,
+            @Valid @RequestBody ContractLineRequest request) {
+        return contractService.updateLine(contractId, lineId, request);
+    }
+
+    @DeleteMapping("/{id}/lines/{lineId}")
+    @ResponseStatus(HttpStatus.NO_CONTENT)
+    public void deleteLine(@PathVariable("id") long contractId, @PathVariable("lineId") long lineId) {
+        contractService.deleteLine(contractId, lineId);
+    }
+}
@@ -0,0 +1,20 @@
+package cn.craftlabs.platform.api.domain;
+
+/**
+ * 合同生命周期状态。
+ *
+ * <p>允许的状态迁移（非法迁移返回 409）：
+ *
+ * <ul>
+ *   <li>{@link #DRAFT} → {@link #PENDING_EFFECTIVE} → {@link #EFFECTIVE}
+ *   <li>{@link #EFFECTIVE} → {@link #CHANGING} → {@link #EFFECTIVE}
+ *   <li>{@link #EFFECTIVE} → {@link #TERMINATED}（自生效态终止；终止后不可再迁移）
+ * </ul>
+ */
+public enum ContractStatus {
+    DRAFT,
+    PENDING_EFFECTIVE,
+    EFFECTIVE,
+    CHANGING,
+    TERMINATED;
+}
@@ -0,0 +1,110 @@
+package cn.craftlabs.platform.api.persistence.audit;
+
+import com.baomidou.mybatisplus.annotation.IdType;
+import com.baomidou.mybatisplus.annotation.TableField;
+import com.baomidou.mybatisplus.annotation.TableId;
+import com.baomidou.mybatisplus.annotation.TableName;
+
+import java.time.OffsetDateTime;
+
+@TableName("platform_audit_event")
+public class PlatformAuditEvent {
+
+    @TableId(type = IdType.AUTO)
+    private Long id;
+
+    @TableField("entity_type")
+    private String entityType;
+
+    @TableField("entity_id")
+    private Long entityId;
+
+    private String action;
+
+    @TableField("field_name")
+    private String fieldName;
+
+    @TableField("old_value")
+    private String oldValue;
+
+    @TableField("new_value")
+    private String newValue;
+
+    @TableField("actor_user_id")
+    private String actorUserId;
+
+    @TableField("created_at")
+    private OffsetDateTime createdAt;
+
+    public Long getId() {
+        return id;
+    }
+
+    public void setId(Long id) {
+        this.id = id;
+    }
+
+    public String getEntityType() {
+        return entityType;
+    }
+
+    public void setEntityType(String entityType) {
+        this.entityType = entityType;
+    }
+
+    public Long getEntityId() {
+        return entityId;
+    }
+
+    public void setEntityId(Long entityId) {
+        this.entityId = entityId;
+    }
+
+    public String getAction() {
+        return action;
+    }
+
+    public void setAction(String action) {
+        this.action = action;
+    }
+
+    public String getFieldName() {
+        return fieldName;
+    }
+
+    public void setFieldName(String fieldName) {
+        this.fieldName = fieldName;
+    }
+
+    public String getOldValue() {
+        return oldValue;
+    }
+
+    public void setOldValue(String oldValue) {
+        this.oldValue = oldValue;
+    }
+
+    public String getNewValue() {
+        return newValue;
+    }
+
+    public void setNewValue(String newValue) {
+        this.newValue = newValue;
+    }
+
+    public String getActorUserId() {
+        return actorUserId;
+    }
+
+    public void setActorUserId(String actorUserId) {
+        this.actorUserId = actorUserId;
+    }
+
+    public OffsetDateTime getCreatedAt() {
+        return createdAt;
+    }
+
+    public void setCreatedAt(OffsetDateTime createdAt) {
+        this.createdAt = createdAt;
+    }
+}
@@ -0,0 +1,7 @@
+package cn.craftlabs.platform.api.persistence.audit;
+
+import com.baomidou.mybatisplus.core.mapper.BaseMapper;
+import org.apache.ibatis.annotations.Mapper;
+
+@Mapper
+public interface PlatformAuditEventMapper extends BaseMapper<PlatformAuditEvent> {}
@@ -0,0 +1,97 @@
+package cn.craftlabs.platform.api.persistence.contract;
+
+import com.baomidou.mybatisplus.annotation.IdType;
+import com.baomidou.mybatisplus.annotation.TableField;
+import com.baomidou.mybatisplus.annotation.TableId;
+import com.baomidou.mybatisplus.annotation.TableName;
+
+import java.time.OffsetDateTime;
+
+@TableName("platform_contract")
+public class PlatformContract {
+
+    @TableId(type = IdType.AUTO)
+    private Long id;
+
+    @TableField("customer_id")
+    private Long customerId;
+
+    @TableField("project_id")
+    private Long projectId;
+
+    private String title;
+
+    private String remarks;
+
+    private String status;
+
+    @TableField("created_at")
+    private OffsetDateTime createdAt;
+
+    @TableField("updated_at")
+    private OffsetDateTime updatedAt;
+
+    public Long getId() {
+        return id;
+    }
+
+    public void setId(Long id) {
+        this.id = id;
+    }
+
+    public Long getCustomerId() {
+        return customerId;
+    }
+
+    public void setCustomerId(Long customerId) {
+        this.customerId = customerId;
+    }
+
+    public Long getProjectId() {
+        return projectId;
+    }
+
+    public void setProjectId(Long projectId) {
+        this.projectId = projectId;
+    }
+
+    public String getTitle() {
+        return title;
+    }
+
+    public void setTitle(String title) {
+        this.title = title;
+    }
+
+    public String getRemarks() {
+        return remarks;
+    }
+
+    public void setRemarks(String remarks) {
+        this.remarks = remarks;
+    }
+
+    public String getStatus() {
+        return status;
+    }
+
+    public void setStatus(String status) {
+        this.status = status;
+    }
+
+    public OffsetDateTime getCreatedAt() {
+        return createdAt;
+    }
+
+    public void setCreatedAt(OffsetDateTime createdAt) {
+        this.createdAt = createdAt;
+    }
+
+    public OffsetDateTime getUpdatedAt() {
+        return updatedAt;
+    }
+
+    public void setUpdatedAt(OffsetDateTime updatedAt) {
+        this.updatedAt = updatedAt;
+    }
+}
@@ -0,0 +1,119 @@
+package cn.craftlabs.platform.api.persistence.contract;
+
+import com.baomidou.mybatisplus.annotation.IdType;
+import com.baomidou.mybatisplus.annotation.TableField;
+import com.baomidou.mybatisplus.annotation.TableId;
+import com.baomidou.mybatisplus.annotation.TableName;
+
+import java.math.BigDecimal;
+import java.time.OffsetDateTime;
+
+@TableName("platform_contract_line")
+public class PlatformContractLine {
+
+    @TableId(type = IdType.AUTO)
+    private Long id;
+
+    @TableField("contract_id")
+    private Long contractId;
+
+    @TableField("sort_order")
+    private Integer sortOrder;
+
+    @TableField("item_name")
+    private String itemName;
+
+    private BigDecimal quantity;
+
+    private String unit;
+
+    private BigDecimal amount;
+
+    private String remark;
+
+    @TableField("created_at")
+    private OffsetDateTime createdAt;
+
+    @TableField("updated_at")
+    private OffsetDateTime updatedAt;
+
+    public Long getId() {
+        return id;
+    }
+
+    public void setId(Long id) {
+        this.id = id;
+    }
+
+    public Long getContractId() {
+        return contractId;
+    }
+
+    public void setContractId(Long contractId) {
+        this.contractId = contractId;
+    }
+
+    public Integer getSortOrder() {
+        return sortOrder;
+    }
+
+    public void setSortOrder(Integer sortOrder) {
+        this.sortOrder = sortOrder;
+    }
+
+    public String getItemName() {
+        return itemName;
+    }
+
+    public void setItemName(String itemName) {
+        this.itemName = itemName;
+    }
+
+    public BigDecimal getQuantity() {
+        return quantity;
+    }
+
+    public void setQuantity(BigDecimal quantity) {
+        this.quantity = quantity;
+    }
+
+    public String getUnit() {
+        return unit;
+    }
+
+    public void setUnit(String unit) {
+        this.unit = unit;
+    }
+
+    public BigDecimal getAmount() {
+        return amount;
+    }
+
+    public void setAmount(BigDecimal amount) {
+        this.amount = amount;
+    }
+
+    public String getRemark() {
+        return remark;
+    }
+
+    public void setRemark(String remark) {
+        this.remark = remark;
+    }
+
+    public OffsetDateTime getCreatedAt() {
+        return createdAt;
+    }
+
+    public void setCreatedAt(OffsetDateTime createdAt) {
+        this.createdAt = createdAt;
+    }
+
+    public OffsetDateTime getUpdatedAt() {
+        return updatedAt;
+    }
+
+    public void setUpdatedAt(OffsetDateTime updatedAt) {
+        this.updatedAt = updatedAt;
+    }
+}
@@ -0,0 +1,7 @@
+package cn.craftlabs.platform.api.persistence.contract;
+
+import com.baomidou.mybatisplus.core.mapper.BaseMapper;
+import org.apache.ibatis.annotations.Mapper;
+
+@Mapper
+public interface PlatformContractLineMapper extends BaseMapper<PlatformContractLine> {}
@@ -0,0 +1,7 @@
+package cn.craftlabs.platform.api.persistence.contract;
+
+import com.baomidou.mybatisplus.core.mapper.BaseMapper;
+import org.apache.ibatis.annotations.Mapper;
+
+@Mapper
+public interface PlatformContractMapper extends BaseMapper<PlatformContract> {}
@@ -0,0 +1,90 @@
+package cn.craftlabs.platform.api.service;
+
+import cn.craftlabs.platform.api.persistence.audit.PlatformAuditEvent;
+import cn.craftlabs.platform.api.persistence.audit.PlatformAuditEventMapper;
+import cn.craftlabs.platform.api.web.dto.AuditEventResponse;
+import cn.craftlabs.platform.api.web.dto.PageResponse;
+import com.baomidou.mybatisplus.core.conditions.query.LambdaQueryWrapper;
+import com.baomidou.mybatisplus.core.toolkit.Wrappers;
+import com.baomidou.mybatisplus.extension.plugins.pagination.Page;
+import org.springframework.security.core.Authentication;
+import org.springframework.security.core.context.SecurityContextHolder;
+import org.springframework.stereotype.Service;
+import org.springframework.transaction.annotation.Transactional;
+import org.springframework.util.StringUtils;
+
+import java.time.OffsetDateTime;
+import java.time.ZoneOffset;
+import java.util.List;
+import java.util.stream.Collectors;
+
+@Service
+public class AuditService {
+
+    private final PlatformAuditEventMapper auditEventMapper;
+
+    public AuditService(PlatformAuditEventMapper auditEventMapper) {
+        this.auditEventMapper = auditEventMapper;
+    }
+
+    @Transactional
+    public void record(
+            String entityType,
+            long entityId,
+            String action,
+            String fieldName,
+            String oldValue,
+            String newValue) {
+        PlatformAuditEvent e = new PlatformAuditEvent();
+        e.setEntityType(entityType);
+        e.setEntityId(entityId);
+        e.setAction(action);
+        e.setFieldName(blankToNull(fieldName));
+        e.setOldValue(oldValue);
+        e.setNewValue(newValue);
+        e.setActorUserId(currentActorId());
+        e.setCreatedAt(OffsetDateTime.now(ZoneOffset.UTC));
+        auditEventMapper.insert(e);
+    }
+
+    @Transactional(readOnly = true)
+    public PageResponse<AuditEventResponse> page(
+            String entityType, Long entityId, int page, int size) {
+        LambdaQueryWrapper<PlatformAuditEvent> q =
+                Wrappers.lambdaQuery(PlatformAuditEvent.class)
+                        .eq(PlatformAuditEvent::getEntityType, entityType.trim())
+                        .eq(PlatformAuditEvent::getEntityId, entityId)
+                        .orderByDesc(PlatformAuditEvent::getId);
+        Page<PlatformAuditEvent> mpPage = new Page<>(page + 1L, size);
+        auditEventMapper.selectPage(mpPage, q);
+        List<AuditEventResponse> content =
+                mpPage.getRecords().stream().map(this::toResponse).collect(Collectors.toList());
+        return new PageResponse<>(content, mpPage.getTotal(), page, size);
+    }
+
+    private AuditEventResponse toResponse(PlatformAuditEvent e) {
+        AuditEventResponse r = new AuditEventResponse();
+        r.setId(e.getId());
+        r.setEntityType(e.getEntityType());
+        r.setEntityId(e.getEntityId());
+        r.setAction(e.getAction());
+        r.setFieldName(e.getFieldName());
+        r.setOldValue(e.getOldValue());
+        r.setNewValue(e.getNewValue());
+        r.setActorUserId(e.getActorUserId());
+        r.setCreatedAt(e.getCreatedAt());
+        return r;
+    }
+
+    private static String blankToNull(String s) {
+        return StringUtils.hasText(s) ? s : null;
+    }
+
+    private static String currentActorId() {
+        Authentication a = SecurityContextHolder.getContext().getAuthentication();
+        if (a == null || !a.isAuthenticated()) {
+            return null;
+        }
+        return a.getName();
+    }
+}
@@ -0,0 +1,376 @@
+package cn.craftlabs.platform.api.service;
+
+import cn.craftlabs.platform.api.audit.AuditActions;
+import cn.craftlabs.platform.api.audit.AuditEntityTypes;
+import cn.craftlabs.platform.api.domain.ContractStatus;
+import cn.craftlabs.platform.api.persistence.contract.PlatformContract;
+import cn.craftlabs.platform.api.persistence.contract.PlatformContractLine;
+import cn.craftlabs.platform.api.persistence.contract.PlatformContractLineMapper;
+import cn.craftlabs.platform.api.persistence.contract.PlatformContractMapper;
+import cn.craftlabs.platform.api.persistence.project.PlatformProject;
+import cn.craftlabs.platform.api.persistence.project.PlatformProjectMapper;
+import cn.craftlabs.platform.api.web.dto.ContractCreateRequest;
+import cn.craftlabs.platform.api.web.dto.ContractLineRequest;
+import cn.craftlabs.platform.api.web.dto.ContractLineResponse;
+import cn.craftlabs.platform.api.web.dto.ContractResponse;
+import cn.craftlabs.platform.api.web.dto.ContractStatusPatchRequest;
+import cn.craftlabs.platform.api.web.dto.ContractUpdateRequest;
+import cn.craftlabs.platform.api.web.dto.PageResponse;
+import com.baomidou.mybatisplus.core.conditions.query.LambdaQueryWrapper;
+import com.baomidou.mybatisplus.core.toolkit.Wrappers;
+import com.baomidou.mybatisplus.extension.plugins.pagination.Page;
+import com.fasterxml.jackson.core.JsonProcessingException;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import org.springframework.http.HttpStatus;
+import org.springframework.stereotype.Service;
+import org.springframework.transaction.annotation.Transactional;
+import org.springframework.util.StringUtils;
+import org.springframework.web.server.ResponseStatusException;
+
+import java.time.OffsetDateTime;
+import java.time.ZoneOffset;
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.stream.Collectors;
+
+@Service
+public class ContractService {
+
+    private final PlatformContractMapper contractMapper;
+    private final PlatformContractLineMapper lineMapper;
+    private final PlatformProjectMapper projectMapper;
+    private final ContractStatusTransitionService transitionService;
+    private final AuditService auditService;
+    private final ObjectMapper objectMapper;
+
+    public ContractService(
+            PlatformContractMapper contractMapper,
+            PlatformContractLineMapper lineMapper,
+            PlatformProjectMapper projectMapper,
+            ContractStatusTransitionService transitionService,
+            AuditService auditService,
+            ObjectMapper objectMapper) {
+        this.contractMapper = contractMapper;
+        this.lineMapper = lineMapper;
+        this.projectMapper = projectMapper;
+        this.transitionService = transitionService;
+        this.auditService = auditService;
+        this.objectMapper = objectMapper;
+    }
+
+    @Transactional
+    public ContractResponse create(ContractCreateRequest request) {
+        validateProjectBelongsToCustomer(request.getProjectId(), request.getCustomerId());
+        OffsetDateTime now = OffsetDateTime.now(ZoneOffset.UTC);
+        PlatformContract c = new PlatformContract();
+        c.setCustomerId(request.getCustomerId());
+        c.setProjectId(request.getProjectId());
+        c.setTitle(blankToNull(request.getTitle()));
+        c.setRemarks(blankToNull(request.getRemarks()));
+        c.setStatus(ContractStatus.DRAFT.name());
+        c.setCreatedAt(now);
+        c.setUpdatedAt(now);
+        contractMapper.insert(c);
+        auditService.record(
+                AuditEntityTypes.CONTRACT,
+                c.getId(),
+                AuditActions.CONTRACT_CREATED,
+                null,
+                null,
+                toJson(headerSnapshot(c)));
+        return toResponse(c);
+    }
+
+    @Transactional(readOnly = true)
+    public PageResponse<ContractResponse> page(
+            int page, int size, Long customerId, Long projectId, String keyword) {
+        String kw = StringUtils.hasText(keyword) ? keyword.trim() : null;
+        LambdaQueryWrapper<PlatformContract> q =
+                Wrappers.lambdaQuery(PlatformContract.class)
+                        .eq(customerId != null, PlatformContract::getCustomerId, customerId)
+                        .eq(projectId != null, PlatformContract::getProjectId, projectId)
+                        .like(kw != null, PlatformContract::getTitle, kw)
+                        .orderByDesc(PlatformContract::getId);
+        Page<PlatformContract> mpPage = new Page<>(page + 1L, size);
+        contractMapper.selectPage(mpPage, q);
+        List<ContractResponse> content =
+                mpPage.getRecords().stream().map(this::toResponse).collect(Collectors.toList());
+        return new PageResponse<>(content, mpPage.getTotal(), page, size);
+    }
+
+    @Transactional(readOnly = true)
+    public ContractResponse getById(long id) {
+        PlatformContract c = requireContract(id);
+        ContractResponse r = toResponse(c);
+        r.setLines(listLines(id));
+        return r;
+    }
+
+    @Transactional
+    public ContractResponse update(long id, ContractUpdateRequest request) {
+        PlatformContract c = requireContract(id);
+        requireDraftForHeaderEdit(c);
+        if (request.getTitle() == null && request.getRemarks() == null) {
+            throw new ResponseStatusException(
+                    HttpStatus.BAD_REQUEST, "at least one of title or remarks must be provided");
+        }
+        String oldJson = toJson(headerSnapshot(c));
+        if (request.getTitle() != null) {
+            c.setTitle(blankToNull(request.getTitle()));
+        }
+        if (request.getRemarks() != null) {
+            c.setRemarks(blankToNull(request.getRemarks()));
+        }
+        c.setUpdatedAt(OffsetDateTime.now(ZoneOffset.UTC));
+        contractMapper.updateById(c);
+        auditService.record(
+                AuditEntityTypes.CONTRACT,
+                id,
+                AuditActions.CONTRACT_UPDATED,
+                null,
+                oldJson,
+                toJson(headerSnapshot(c)));
+        return toResponse(c);
+    }
+
+    @Transactional
+    public ContractResponse patchStatus(long id, ContractStatusPatchRequest request) {
+        PlatformContract c = requireContract(id);
+        ContractStatus from = parseStatus(c.getStatus());
+        ContractStatus to = parseStatusOrBadRequest(request.getStatus());
+        transitionService.requireTransition(from, to);
+        if (from == to) {
+            return toResponse(c);
+        }
+        String oldJson = toJson(Map.of("status", from.name()));
+        c.setStatus(to.name());
+        c.setUpdatedAt(OffsetDateTime.now(ZoneOffset.UTC));
+        contractMapper.updateById(c);
+        auditService.record(
+                AuditEntityTypes.CONTRACT,
+                id,
+                AuditActions.CONTRACT_STATUS_CHANGED,
+                "status",
+                oldJson,
+                toJson(Map.of("status", to.name())));
+        return toResponse(c);
+    }
+
+    @Transactional(readOnly = true)
+    public List<ContractLineResponse> listLines(long contractId) {
+        requireContract(contractId);
+        LambdaQueryWrapper<PlatformContractLine> q =
+                Wrappers.lambdaQuery(PlatformContractLine.class)
+                        .eq(PlatformContractLine::getContractId, contractId)
+                        .orderByAsc(PlatformContractLine::getSortOrder)
+                        .orderByAsc(PlatformContractLine::getId);
+        return lineMapper.selectList(q).stream().map(this::toLineResponse).collect(Collectors.toList());
+    }
+
+    @Transactional
+    public ContractLineResponse addLine(long contractId, ContractLineRequest request) {
+        PlatformContract c = requireContract(contractId);
+        requireDraftForLineMutation(c);
+        OffsetDateTime now = OffsetDateTime.now(ZoneOffset.UTC);
+        PlatformContractLine line = new PlatformContractLine();
+        line.setContractId(contractId);
+        line.setSortOrder(resolveSortOrder(contractId, request.getSortOrder()));
+        line.setItemName(request.getItemName().trim());
+        line.setQuantity(request.getQuantity());
+        line.setUnit(blankToNull(request.getUnit()));
+        line.setAmount(request.getAmount());
+        line.setRemark(blankToNull(request.getRemark()));
+        line.setCreatedAt(now);
+        line.setUpdatedAt(now);
+        lineMapper.insert(line);
+        auditService.record(
+                AuditEntityTypes.CONTRACT,
+                contractId,
+                AuditActions.CONTRACT_LINE_ADDED,
+                null,
+                null,
+                toJson(lineSnapshot(line)));
+        return toLineResponse(line);
+    }
+
+    @Transactional
+    public ContractLineResponse updateLine(long contractId, long lineId, ContractLineRequest request) {
+        PlatformContract c = requireContract(contractId);
+        requireDraftForLineMutation(c);
+        PlatformContractLine line = requireLine(contractId, lineId);
+        String oldJson = toJson(lineSnapshot(line));
+        line.setSortOrder(resolveSortOrder(contractId, request.getSortOrder(), line.getSortOrder()));
+        line.setItemName(request.getItemName().trim());
+        line.setQuantity(request.getQuantity());
+        line.setUnit(blankToNull(request.getUnit()));
+        line.setAmount(request.getAmount());
+        line.setRemark(blankToNull(request.getRemark()));
+        line.setUpdatedAt(OffsetDateTime.now(ZoneOffset.UTC));
+        lineMapper.updateById(line);
+        auditService.record(
+                AuditEntityTypes.CONTRACT,
+                contractId,
+                AuditActions.CONTRACT_LINE_UPDATED,
+                "line:" + lineId,
+                oldJson,
+                toJson(lineSnapshot(line)));
+        return toLineResponse(line);
+    }
+
+    @Transactional
+    public void deleteLine(long contractId, long lineId) {
+        PlatformContract c = requireContract(contractId);
+        requireDraftForLineMutation(c);
+        PlatformContractLine line = requireLine(contractId, lineId);
+        String oldJson = toJson(lineSnapshot(line));
+        lineMapper.deleteById(lineId);
+        auditService.record(
+                AuditEntityTypes.CONTRACT,
+                contractId,
+                AuditActions.CONTRACT_LINE_DELETED,
+                "line:" + lineId,
+                oldJson,
+                null);
+    }
+
+    private void validateProjectBelongsToCustomer(long projectId, long customerId) {
+        PlatformProject p = projectMapper.selectById(projectId);
+        if (p == null) {
+            throw new ResponseStatusException(HttpStatus.NOT_FOUND, "project not found");
+        }
+        if (!p.getCustomerId().equals(customerId)) {
+            throw new ResponseStatusException(
+                    HttpStatus.BAD_REQUEST, "project does not belong to the given customer");
+        }
+    }
+
+    private PlatformContract requireContract(long id) {
+        PlatformContract c = contractMapper.selectById(id);
+        if (c == null) {
+            throw new ResponseStatusException(HttpStatus.NOT_FOUND, "contract not found");
+        }
+        return c;
+    }
+
+    private PlatformContractLine requireLine(long contractId, long lineId) {
+        PlatformContractLine line = lineMapper.selectById(lineId);
+        if (line == null || !line.getContractId().equals(contractId)) {
+            throw new ResponseStatusException(HttpStatus.NOT_FOUND, "contract line not found");
+        }
+        return line;
+    }
+
+    private void requireDraftForHeaderEdit(PlatformContract c) {
+        if (parseStatus(c.getStatus()) != ContractStatus.DRAFT) {
+            throw new ResponseStatusException(
+                    HttpStatus.CONFLICT,
+                    "contract header and lines can only be edited in DRAFT status");
+        }
+    }
+
+    private void requireDraftForLineMutation(PlatformContract c) {
+        requireDraftForHeaderEdit(c);
+    }
+
+    private static ContractStatus parseStatus(String raw) {
+        try {
+            return ContractStatus.valueOf(raw);
+        } catch (Exception e) {
+            throw new ResponseStatusException(
+                    HttpStatus.INTERNAL_SERVER_ERROR, "invalid contract status stored: " + raw);
+        }
+    }
+
+    private static ContractStatus parseStatusOrBadRequest(String raw) {
+        try {
+            return ContractStatus.valueOf(raw.trim());
+        } catch (Exception e) {
+            throw new ResponseStatusException(HttpStatus.BAD_REQUEST, "unknown contract status: " + raw);
+        }
+    }
+
+    private int resolveSortOrder(long contractId, Integer requested) {
+        return resolveSortOrder(contractId, requested, null);
+    }
+
+    private int resolveSortOrder(long contractId, Integer requested, Integer fallbackExisting) {
+        if (requested != null) {
+            return requested;
+        }
+        if (fallbackExisting != null) {
+            return fallbackExisting;
+        }
+        LambdaQueryWrapper<PlatformContractLine> q =
+                Wrappers.lambdaQuery(PlatformContractLine.class)
+                        .eq(PlatformContractLine::getContractId, contractId)
+                        .orderByDesc(PlatformContractLine::getSortOrder)
+                        .last("LIMIT 1");
+        PlatformContractLine last = lineMapper.selectOne(q);
+        return last == null || last.getSortOrder() == null ? 0 : last.getSortOrder() + 1;
+    }
+
+    private static String blankToNull(String s) {
+        return StringUtils.hasText(s) ? s.trim() : null;
+    }
+
+    private Map<String, Object> headerSnapshot(PlatformContract c) {
+        Map<String, Object> m = new LinkedHashMap<>();
+        m.put("id", c.getId());
+        m.put("customerId", c.getCustomerId());
+        m.put("projectId", c.getProjectId());
+        m.put("title", c.getTitle());
+        m.put("remarks", c.getRemarks());
+        m.put("status", c.getStatus());
+        return m;
+    }
+
+    private Map<String, Object> lineSnapshot(PlatformContractLine line) {
+        Map<String, Object> m = new LinkedHashMap<>();
+        m.put("id", line.getId());
+        m.put("contractId", line.getContractId());
+        m.put("sortOrder", line.getSortOrder());
+        m.put("itemName", line.getItemName());
+        m.put("quantity", line.getQuantity());
+        m.put("unit", line.getUnit());
+        m.put("amount", line.getAmount());
+        m.put("remark", line.getRemark());
+        return m;
+    }
+
+    private String toJson(Object value) {
+        try {
+            return objectMapper.writeValueAsString(value);
+        } catch (JsonProcessingException e) {
+            throw new IllegalStateException(e);
+        }
+    }
+
+    private ContractResponse toResponse(PlatformContract c) {
+        ContractResponse r = new ContractResponse();
+        r.setId(c.getId());
+        r.setCustomerId(c.getCustomerId());
+        r.setProjectId(c.getProjectId());
+        r.setTitle(c.getTitle());
+        r.setRemarks(c.getRemarks());
+        r.setStatus(c.getStatus());
+        r.setCreatedAt(c.getCreatedAt());
+        r.setUpdatedAt(c.getUpdatedAt());
+        return r;
+    }
+
+    private ContractLineResponse toLineResponse(PlatformContractLine line) {
+        ContractLineResponse r = new ContractLineResponse();
+        r.setId(line.getId());
+        r.setContractId(line.getContractId());
+        r.setSortOrder(line.getSortOrder());
+        r.setItemName(line.getItemName());
+        r.setQuantity(line.getQuantity());
+        r.setUnit(line.getUnit());
+        r.setAmount(line.getAmount());
+        r.setRemark(line.getRemark());
+        r.setCreatedAt(line.getCreatedAt());
+        r.setUpdatedAt(line.getUpdatedAt());
+        return r;
+    }
+}
@@ -0,0 +1,42 @@
+package cn.craftlabs.platform.api.service;
+
+import cn.craftlabs.platform.api.domain.ContractStatus;
+import org.springframework.http.HttpStatus;
+import org.springframework.stereotype.Service;
+import org.springframework.web.server.ResponseStatusException;
+
+/**
+ * 校验合同状态迁移是否合法；不合法时抛出 {@link HttpStatus#CONFLICT}。
+ *
+ * <p>自 {@link ContractStatus#EFFECTIVE} 可直接进入 {@link ContractStatus#TERMINATED}（业务上表示解约/终止生效合同）。
+ */
+@Service
+public class ContractStatusTransitionService {
+
+    public void requireTransition(ContractStatus from, ContractStatus to) {
+        if (from == to) {
+            return;
+        }
+        if (!isAllowed(from, to)) {
+            throw new ResponseStatusException(
+                    HttpStatus.CONFLICT,
+                    "illegal contract status transition: " + from + " -> " + to);
+        }
+    }
+
+    private boolean isAllowed(ContractStatus from, ContractStatus to) {
+        if (from == ContractStatus.DRAFT) {
+            return to == ContractStatus.PENDING_EFFECTIVE;
+        }
+        if (from == ContractStatus.PENDING_EFFECTIVE) {
+            return to == ContractStatus.EFFECTIVE;
+        }
+        if (from == ContractStatus.EFFECTIVE) {
+            return to == ContractStatus.CHANGING || to == ContractStatus.TERMINATED;
+        }
+        if (from == ContractStatus.CHANGING) {
+            return to == ContractStatus.EFFECTIVE;
+        }
+        return false;
+    }
+}
@@ -0,0 +1,88 @@
+package cn.craftlabs.platform.api.web.dto;
+
+import java.time.OffsetDateTime;
+
+public class AuditEventResponse {
+
+    private Long id;
+    private String entityType;
+    private Long entityId;
+    private String action;
+    private String fieldName;
+    private String oldValue;
+    private String newValue;
+    private String actorUserId;
+    private OffsetDateTime createdAt;
+
+    public Long getId() {
+        return id;
+    }
+
+    public void setId(Long id) {
+        this.id = id;
+    }
+
+    public String getEntityType() {
+        return entityType;
+    }
+
+    public void setEntityType(String entityType) {
+        this.entityType = entityType;
+    }
+
+    public Long getEntityId() {
+        return entityId;
+    }
+
+    public void setEntityId(Long entityId) {
+        this.entityId = entityId;
+    }
+
+    public String getAction() {
+        return action;
+    }
+
+    public void setAction(String action) {
+        this.action = action;
+    }
+
+    public String getFieldName() {
+        return fieldName;
+    }
+
+    public void setFieldName(String fieldName) {
+        this.fieldName = fieldName;
+    }
+
+    public String getOldValue() {
+        return oldValue;
+    }
+
+    public void setOldValue(String oldValue) {
+        this.oldValue = oldValue;
+    }
+
+    public String getNewValue() {
+        return newValue;
+    }
+
+    public void setNewValue(String newValue) {
+        this.newValue = newValue;
+    }
+
+    public String getActorUserId() {
+        return actorUserId;
+    }
+
+    public void setActorUserId(String actorUserId) {
+        this.actorUserId = actorUserId;
+    }
+
+    public OffsetDateTime getCreatedAt() {
+        return createdAt;
+    }
+
+    public void setCreatedAt(OffsetDateTime createdAt) {
+        this.createdAt = createdAt;
+    }
+}
@@ -0,0 +1,49 @@
+package cn.craftlabs.platform.api.web.dto;
+
+import jakarta.validation.constraints.NotNull;
+import jakarta.validation.constraints.Size;
+
+public class ContractCreateRequest {
+
+    @NotNull private Long customerId;
+
+    @NotNull private Long projectId;
+
+    @Size(max = 256)
+    private String title;
+
+    @Size(max = 4000)
+    private String remarks;
+
+    public Long getCustomerId() {
+        return customerId;
+    }
+
+    public void setCustomerId(Long customerId) {
+        this.customerId = customerId;
+    }
+
+    public Long getProjectId() {
+        return projectId;
+    }
+
+    public void setProjectId(Long projectId) {
+        this.projectId = projectId;
+    }
+
+    public String getTitle() {
+        return title;
+    }
+
+    public void setTitle(String title) {
+        this.title = title;
+    }
+
+    public String getRemarks() {
+        return remarks;
+    }
+
+    public void setRemarks(String remarks) {
+        this.remarks = remarks;
+    }
+}
@@ -0,0 +1,77 @@
+package cn.craftlabs.platform.api.web.dto;
+
+import jakarta.validation.constraints.DecimalMin;
+import jakarta.validation.constraints.NotBlank;
+import jakarta.validation.constraints.NotNull;
+import jakarta.validation.constraints.Size;
+
+import java.math.BigDecimal;
+
+public class ContractLineRequest {
+
+    private Integer sortOrder;
+
+    @NotBlank
+    @Size(max = 256)
+    private String itemName;
+
+    @NotNull
+    @DecimalMin(value = "0.0001", inclusive = true)
+    private BigDecimal quantity;
+
+    @Size(max = 32)
+    private String unit;
+
+    private BigDecimal amount;
+
+    @Size(max = 512)
+    private String remark;
+
+    public Integer getSortOrder() {
+        return sortOrder;
+    }
+
+    public void setSortOrder(Integer sortOrder) {
+        this.sortOrder = sortOrder;
+    }
+
+    public String getItemName() {
+        return itemName;
+    }
+
+    public void setItemName(String itemName) {
+        this.itemName = itemName;
+    }
+
+    public BigDecimal getQuantity() {
+        return quantity;
+    }
+
+    public void setQuantity(BigDecimal quantity) {
+        this.quantity = quantity;
+    }
+
+    public String getUnit() {
+        return unit;
+    }
+
+    public void setUnit(String unit) {
+        this.unit = unit;
+    }
+
+    public BigDecimal getAmount() {
+        return amount;
+    }
+
+    public void setAmount(BigDecimal amount) {
+        this.amount = amount;
+    }
+
+    public String getRemark() {
+        return remark;
+    }
+
+    public void setRemark(String remark) {
+        this.remark = remark;
+    }
+}
@@ -0,0 +1,98 @@
+package cn.craftlabs.platform.api.web.dto;
+
+import java.math.BigDecimal;
+import java.time.OffsetDateTime;
+
+public class ContractLineResponse {
+
+    private Long id;
+    private Long contractId;
+    private Integer sortOrder;
+    private String itemName;
+    private BigDecimal quantity;
+    private String unit;
+    private BigDecimal amount;
+    private String remark;
+    private OffsetDateTime createdAt;
+    private OffsetDateTime updatedAt;
+
+    public Long getId() {
+        return id;
+    }
+
+    public void setId(Long id) {
+        this.id = id;
+    }
+
+    public Long getContractId() {
+        return contractId;
+    }
+
+    public void setContractId(Long contractId) {
+        this.contractId = contractId;
+    }
+
+    public Integer getSortOrder() {
+        return sortOrder;
+    }
+
+    public void setSortOrder(Integer sortOrder) {
+        this.sortOrder = sortOrder;
+    }
+
+    public String getItemName() {
+        return itemName;
+    }
+
+    public void setItemName(String itemName) {
+        this.itemName = itemName;
+    }
+
+    public BigDecimal getQuantity() {
+        return quantity;
+    }
+
+    public void setQuantity(BigDecimal quantity) {
+        this.quantity = quantity;
+    }
+
+    public String getUnit() {
+        return unit;
+    }
+
+    public void setUnit(String unit) {
+        this.unit = unit;
+    }
+
+    public BigDecimal getAmount() {
+        return amount;
+    }
+
+    public void setAmount(BigDecimal amount) {
+        this.amount = amount;
+    }
+
+    public String getRemark() {
+        return remark;
+    }
+
+    public void setRemark(String remark) {
+        this.remark = remark;
+    }
+
+    public OffsetDateTime getCreatedAt() {
+        return createdAt;
+    }
+
+    public void setCreatedAt(OffsetDateTime createdAt) {
+        this.createdAt = createdAt;
+    }
+
+    public OffsetDateTime getUpdatedAt() {
+        return updatedAt;
+    }
+
+    public void setUpdatedAt(OffsetDateTime updatedAt) {
+        this.updatedAt = updatedAt;
+    }
+}
@@ -0,0 +1,93 @@
+package cn.craftlabs.platform.api.web.dto;
+
+import com.fasterxml.jackson.annotation.JsonInclude;
+
+import java.time.OffsetDateTime;
+import java.util.List;
+
+public class ContractResponse {
+
+    private Long id;
+    private Long customerId;
+    private Long projectId;
+    private String title;
+    private String remarks;
+    private String status;
+    private OffsetDateTime createdAt;
+    private OffsetDateTime updatedAt;
+    /** 仅详情接口填充；列表分页省略该字段。 */
+    @JsonInclude(JsonInclude.Include.NON_NULL)
+    private List<ContractLineResponse> lines;
+
+    public Long getId() {
+        return id;
+    }
+
+    public void setId(Long id) {
+        this.id = id;
+    }
+
+    public Long getCustomerId() {
+        return customerId;
+    }
+
+    public void setCustomerId(Long customerId) {
+        this.customerId = customerId;
+    }
+
+    public Long getProjectId() {
+        return projectId;
+    }
+
+    public void setProjectId(Long projectId) {
+        this.projectId = projectId;
+    }
+
+    public String getTitle() {
+        return title;
+    }
+
+    public void setTitle(String title) {
+        this.title = title;
+    }
+
+    public String getRemarks() {
+        return remarks;
+    }
+
+    public void setRemarks(String remarks) {
+        this.remarks = remarks;
+    }
+
+    public String getStatus() {
+        return status;
+    }
+
+    public void setStatus(String status) {
+        this.status = status;
+    }
+
+    public OffsetDateTime getCreatedAt() {
+        return createdAt;
+    }
+
+    public void setCreatedAt(OffsetDateTime createdAt) {
+        this.createdAt = createdAt;
+    }
+
+    public OffsetDateTime getUpdatedAt() {
+        return updatedAt;
+    }
+
+    public void setUpdatedAt(OffsetDateTime updatedAt) {
+        this.updatedAt = updatedAt;
+    }
+
+    public List<ContractLineResponse> getLines() {
+        return lines;
+    }
+
+    public void setLines(List<ContractLineResponse> lines) {
+        this.lines = lines;
+    }
+}
@@ -0,0 +1,17 @@
+package cn.craftlabs.platform.api.web.dto;
+
+import jakarta.validation.constraints.NotBlank;
+
+public class ContractStatusPatchRequest {
+
+    @NotBlank
+    private String status;
+
+    public String getStatus() {
+        return status;
+    }
+
+    public void setStatus(String status) {
+        this.status = status;
+    }
+}
@@ -0,0 +1,28 @@
+package cn.craftlabs.platform.api.web.dto;
+
+import jakarta.validation.constraints.Size;
+
+public class ContractUpdateRequest {
+
+    @Size(max = 256)
+    private String title;
+
+    @Size(max = 4000)
+    private String remarks;
+
+    public String getTitle() {
+        return title;
+    }
+
+    public void setTitle(String title) {
+        this.title = title;
+    }
+
+    public String getRemarks() {
+        return remarks;
+    }
+
+    public void setRemarks(String remarks) {
+        this.remarks = remarks;
+    }
+}
@@ -0,0 +1,45 @@
+-- M2 P0：合同与行；M10-F01：审计事件（PostgreSQL 15；H2 MODE=PostgreSQL 单测）
+CREATE TABLE platform_contract (
+    id BIGSERIAL PRIMARY KEY,
+    customer_id BIGINT NOT NULL REFERENCES platform_customer (id),
+    project_id BIGINT NOT NULL REFERENCES platform_project (id),
+    title VARCHAR(256),
+    remarks TEXT,
+    status VARCHAR(32) NOT NULL DEFAULT 'DRAFT',
+    created_at TIMESTAMP WITH TIME ZONE NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    updated_at TIMESTAMP WITH TIME ZONE NOT NULL DEFAULT CURRENT_TIMESTAMP
+);
+
+CREATE INDEX idx_platform_contract_customer_id ON platform_contract (customer_id);
+CREATE INDEX idx_platform_contract_project_id ON platform_contract (project_id);
+CREATE INDEX idx_platform_contract_status ON platform_contract (status);
+
+CREATE TABLE platform_contract_line (
+    id BIGSERIAL PRIMARY KEY,
+    contract_id BIGINT NOT NULL REFERENCES platform_contract (id) ON DELETE CASCADE,
+    sort_order INT NOT NULL DEFAULT 0,
+    item_name VARCHAR(256) NOT NULL,
+    quantity NUMERIC(18, 4) NOT NULL DEFAULT 1,
+    unit VARCHAR(32),
+    amount NUMERIC(18, 2),
+    remark VARCHAR(512),
+    created_at TIMESTAMP WITH TIME ZONE NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    updated_at TIMESTAMP WITH TIME ZONE NOT NULL DEFAULT CURRENT_TIMESTAMP
+);
+
+CREATE INDEX idx_platform_contract_line_contract_id ON platform_contract_line (contract_id);
+
+CREATE TABLE platform_audit_event (
+    id BIGSERIAL PRIMARY KEY,
+    entity_type VARCHAR(64) NOT NULL,
+    entity_id BIGINT NOT NULL,
+    action VARCHAR(64) NOT NULL,
+    field_name VARCHAR(256),
+    old_value TEXT,
+    new_value TEXT,
+    actor_user_id VARCHAR(256),
+    created_at TIMESTAMP WITH TIME ZONE NOT NULL DEFAULT CURRENT_TIMESTAMP
+);
+
+CREATE INDEX idx_platform_audit_event_entity ON platform_audit_event (entity_type, entity_id);
+CREATE INDEX idx_platform_audit_event_created_at ON platform_audit_event (created_at);
@@ -0,0 +1,159 @@
+package cn.craftlabs.platform.api.contracts;
+
+import cn.craftlabs.platform.api.support.JwtTestSupport;
+import com.fasterxml.jackson.databind.JsonNode;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import org.junit.jupiter.api.Test;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.autoconfigure.web.servlet.AutoConfigureMockMvc;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.http.MediaType;
+import org.springframework.test.web.servlet.MockMvc;
+import org.springframework.transaction.annotation.Transactional;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.hamcrest.Matchers.containsString;
+import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.get;
+import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.patch;
+import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.post;
+import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.jsonPath;
+import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;
+
+@SpringBootTest
+@AutoConfigureMockMvc
+@Transactional
+class ContractControllerTest {
+
+    @Autowired
+    private MockMvc mockMvc;
+
+    @Autowired
+    private ObjectMapper objectMapper;
+
+    @Test
+    void contractDraftLineTransitionAuditAndIllegalTransition() throws Exception {
+        String token = JwtTestSupport.obtainBearerToken(mockMvc, objectMapper);
+        String auth = "Bearer " + token;
+
+        String customerBody = "{\"name\":\"合同客户\",\"creditCode\":\"CC001\",\"status\":\"ACTIVE\"}";
+        String customerJson =
+                mockMvc.perform(
+                                post("/api/v1/customers")
+                                        .header("Authorization", auth)
+                                        .contentType(MediaType.APPLICATION_JSON)
+                                        .content(customerBody))
+                        .andExpect(status().isCreated())
+                        .andReturn()
+                        .getResponse()
+                        .getContentAsString();
+        long customerId = objectMapper.readTree(customerJson).get("id").asLong();
+
+        String projectBody =
+                String.format(
+                        "{\"customerId\":%d,\"name\":\"合同项目\",\"phase\":\"PLANNING\"}", customerId);
+        String projectJson =
+                mockMvc.perform(
+                                post("/api/v1/projects")
+                                        .header("Authorization", auth)
+                                        .contentType(MediaType.APPLICATION_JSON)
+                                        .content(projectBody))
+                        .andExpect(status().isCreated())
+                        .andReturn()
+                        .getResponse()
+                        .getContentAsString();
+        long projectId = objectMapper.readTree(projectJson).get("id").asLong();
+
+        String contractBody =
+                String.format(
+                        "{\"customerId\":%d,\"projectId\":%d,\"title\":\"框架协议\",\"remarks\":\"备注\"}",
+                        customerId, projectId);
+        String contractJson =
+                mockMvc.perform(
+                                post("/api/v1/contracts")
+                                        .header("Authorization", auth)
+                                        .contentType(MediaType.APPLICATION_JSON)
+                                        .content(contractBody))
+                        .andExpect(status().isCreated())
+                        .andExpect(jsonPath("$.status").value("DRAFT"))
+                        .andReturn()
+                        .getResponse()
+                        .getContentAsString();
+        long contractId = objectMapper.readTree(contractJson).get("id").asLong();
+
+        mockMvc.perform(
+                        get("/api/v1/contracts")
+                                .header("Authorization", auth)
+                                .param("page", "0")
+                                .param("size", "10")
+                                .param("keyword", "框架"))
+                .andExpect(status().isOk())
+                .andExpect(jsonPath("$.content[0].id").value(contractId))
+                .andExpect(jsonPath("$.content[0].lines").doesNotExist());
+
+        String lineBody =
+                "{\"itemName\":\"交付项A\",\"quantity\":2,\"unit\":\"套\",\"amount\":10000,\"remark\":\"首行\"}";
+        mockMvc.perform(
+                        post("/api/v1/contracts/" + contractId + "/lines")
+                                .header("Authorization", auth)
+                                .contentType(MediaType.APPLICATION_JSON)
+                                .content(lineBody))
+                .andExpect(status().isCreated())
+                .andExpect(jsonPath("$.itemName").value("交付项A"));
+
+        mockMvc.perform(
+                        patch("/api/v1/contracts/" + contractId + "/status")
+                                .header("Authorization", auth)
+                                .contentType(MediaType.APPLICATION_JSON)
+                                .content("{\"status\":\"PENDING_EFFECTIVE\"}"))
+                .andExpect(status().isOk())
+                .andExpect(jsonPath("$.status").value("PENDING_EFFECTIVE"));
+
+        mockMvc.perform(
+                        patch("/api/v1/contracts/" + contractId + "/status")
+                                .header("Authorization", auth)
+                                .contentType(MediaType.APPLICATION_JSON)
+                                .content("{\"status\":\"EFFECTIVE\"}"))
+                .andExpect(status().isOk())
+                .andExpect(jsonPath("$.status").value("EFFECTIVE"));
+
+        mockMvc.perform(
+                        patch("/api/v1/contracts/" + contractId + "/status")
+                                .header("Authorization", auth)
+                                .contentType(MediaType.APPLICATION_JSON)
+                                .content("{\"status\":\"DRAFT\"}"))
+                .andExpect(status().isConflict())
+                .andExpect(
+                        jsonPath("$.message")
+                                .value(containsString("illegal contract status transition")));
+
+        String auditBody =
+                mockMvc.perform(
+                                get("/api/v1/audit-events")
+                                        .header("Authorization", auth)
+                                        .param("entityType", "CONTRACT")
+                                        .param("entityId", String.valueOf(contractId))
+                                        .param("page", "0")
+                                        .param("size", "50"))
+                        .andExpect(status().isOk())
+                        .andExpect(jsonPath("$.totalElements").value(4))
+                        .andReturn()
+                        .getResponse()
+                        .getContentAsString();
+
+        JsonNode root = objectMapper.readTree(auditBody);
+        boolean hasCreated = false;
+        boolean hasLine = false;
+        for (JsonNode row : root.get("content")) {
+            String action = row.get("action").asText();
+            if ("CONTRACT_CREATED".equals(action)) {
+                hasCreated = true;
+            }
+            if ("CONTRACT_LINE_ADDED".equals(action)) {
+                hasLine = true;
+            }
+        }
+        assertThat(hasCreated).isTrue();
+        assertThat(hasLine).isTrue();
+        assertThat(root.get("number").asInt()).isZero();
+    }
+}
@@ -0,0 +1,110 @@
+package cn.craftlabs.platform.api.service;
+
+import cn.craftlabs.platform.api.domain.ContractStatus;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.EnumSource;
+import org.springframework.http.HttpStatus;
+import org.springframework.web.server.ResponseStatusException;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatCode;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+
+class ContractStatusTransitionServiceTest {
+
+    private final ContractStatusTransitionService service = new ContractStatusTransitionService();
+
+    @Test
+    void sameStatusIsNoOp() {
+        assertThatCode(() -> service.requireTransition(ContractStatus.DRAFT, ContractStatus.DRAFT))
+                .doesNotThrowAnyException();
+        assertThatCode(() -> service.requireTransition(ContractStatus.EFFECTIVE, ContractStatus.EFFECTIVE))
+                .doesNotThrowAnyException();
+    }
+
+    @Test
+    void happyPathMainFlow() {
+        assertThatCode(
+                        () ->
+                                service.requireTransition(
+                                        ContractStatus.DRAFT, ContractStatus.PENDING_EFFECTIVE))
+                .doesNotThrowAnyException();
+        assertThatCode(
+                        () ->
+                                service.requireTransition(
+                                        ContractStatus.PENDING_EFFECTIVE, ContractStatus.EFFECTIVE))
+                .doesNotThrowAnyException();
+        assertThatCode(
+                        () ->
+                                service.requireTransition(
+                                        ContractStatus.EFFECTIVE, ContractStatus.CHANGING))
+                .doesNotThrowAnyException();
+        assertThatCode(
+                        () ->
+                                service.requireTransition(
+                                        ContractStatus.CHANGING, ContractStatus.EFFECTIVE))
+                .doesNotThrowAnyException();
+    }
+
+    /** 自 {@link ContractStatus#EFFECTIVE} 可进入 {@link ContractStatus#TERMINATED}（解约/终止）。 */
+    @Test
+    void effectiveToTerminatedAllowed() {
+        assertThatCode(
+                        () ->
+                                service.requireTransition(
+                                        ContractStatus.EFFECTIVE, ContractStatus.TERMINATED))
+                .doesNotThrowAnyException();
+    }
+
+    @ParameterizedTest
+    @EnumSource(
+            value = ContractStatus.class,
+            names = {"EFFECTIVE", "CHANGING", "TERMINATED"})
+    void draftRejectsSkipPendingEffective(ContractStatus to) {
+        assertConflict(ContractStatus.DRAFT, to);
+    }
+
+    @Test
+    void effectiveToDraftRejected() {
+        assertConflict(ContractStatus.EFFECTIVE, ContractStatus.DRAFT);
+    }
+
+    @Test
+    void changingToTerminatedRejected() {
+        assertConflict(ContractStatus.CHANGING, ContractStatus.TERMINATED);
+    }
+
+    @Test
+    void terminatedIsTerminal() {
+        assertThatCode(
+                        () ->
+                                service.requireTransition(
+                                        ContractStatus.TERMINATED, ContractStatus.TERMINATED))
+                .doesNotThrowAnyException();
+        for (ContractStatus to : ContractStatus.values()) {
+            if (to == ContractStatus.TERMINATED) {
+                continue;
+            }
+            assertConflict(ContractStatus.TERMINATED, to);
+        }
+    }
+
+    @Test
+    void illegalMessageMentionsTransition() {
+        assertThatThrownBy(() -> service.requireTransition(ContractStatus.DRAFT, ContractStatus.EFFECTIVE))
+                .isInstanceOfSatisfying(
+                        ResponseStatusException.class,
+                        ex -> {
+                            assertThat(ex.getStatusCode().value()).isEqualTo(409);
+                            assertThat(ex.getReason()).contains("illegal contract status transition");
+                        });
+    }
+
+    private void assertConflict(ContractStatus from, ContractStatus to) {
+        assertThatThrownBy(() -> service.requireTransition(from, to))
+                .isInstanceOfSatisfying(
+                        ResponseStatusException.class,
+                        ex -> assertThat(ex.getStatusCode()).isEqualTo(HttpStatus.CONFLICT));
+    }
+}