docs(project): record locked task context evidence

docs/tests/unit/project-task-mutation-context.md

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+# Test Evidence: Locked Project context for Task mutations
+
+- **Test type:** Unit
+- **Requirement IDs:** `AUTH-001`, `AUTH-011`, `PRJ-012`
+- **Scenario IDs:** `AC-AUTH-001`, `AC-AUTH-010`, `AC-PRJ-006`
+- **Test class/method:** `com.lab.labtimesheet.feature.project.service.ProjectTaskMutationContextTest#loadsTheProjectForUpdateBeforeBuildingTheTaskMutationContext`
+- **Implementation commit:** `19a3518`
+
+## Protected behavior
+
+Task mutations obtain their Project authorization and current lifecycle, Leader, owning-Mentor, and active-member facts from a DTO-only Project service boundary after the Project row has been locked for update. Missing and unauthorized Projects retain the same non-disclosing denial behavior.
+
+## Test method
+
+The isolated service test invokes `ProjectService.taskMutationContext(actorUserId, projectId)`, verifies that `ProjectRepository.findLockedById` is used and the ordinary `findById` path is not used, and verifies that only the locked entity is passed to the existing Project-owned authorization and DTO mapper. The PostgreSQL integration test additionally exercises the public API with authorized, unauthorized, current-member, and former-member data.
+
+## Hand-derived expected result
+
+Exactly one pessimistic Project lookup occurs before context evaluation. The returned `ProjectTaskContext` exposes scalar/DTO facts only; no Project repository or entity crosses the feature boundary. When called from Task's active transaction, Spring's default `REQUIRED` propagation keeps the row lock in that transaction through its commit or rollback.
+
+## RED
+
+**Command**
+
+```text
+export JAVA_HOME=/opt/homebrew/opt/openjdk@25
+export PATH="$JAVA_HOME/bin:$PATH"
+./mvnw -Dtest=ProjectTaskMutationContextTest test
+```
+
+**Observed result**
+
+```text
+[ERROR] constructor ProjectService ... cannot be applied to given types
+[ERROR] incompatible types: ProjectEntity cannot be converted to long
+[INFO] BUILD FAILURE
+```
+
+The test failed to compile because Project had no mutation-context API and its context mapper accepted only an unlocked Project ID lookup.
+
+## GREEN
+
+**Command**
+
+```text
+export JAVA_HOME=/opt/homebrew/opt/openjdk@25
+export PATH="$JAVA_HOME/bin:$PATH"
+./mvnw -Dtest=ProjectTaskMutationContextTest test
+```
+
+**Observed result**
+
+```text
+[INFO] Running com.lab.labtimesheet.feature.project.service.ProjectTaskMutationContextTest
+[INFO] Tests run: 1, Failures: 0, Errors: 0, Skipped: 0
+[INFO] BUILD SUCCESS
+```
+
+## Affected suite
+
+**Command and result**
+
+```text
+export JAVA_HOME=/opt/homebrew/opt/openjdk@25
+export PATH="$JAVA_HOME/bin:$PATH"
+export DOCKER_HOST=unix:///Users/sechmachine/.orbstack/run/docker.sock
+./mvnw -Dtest='Project*Test' test
+
+[INFO] Tests run: 20, Failures: 0, Errors: 0, Skipped: 0
+[INFO] BUILD SUCCESS
+```
+
+## External-test boundaries
+
+The unit test proves the locked repository path and DTO-only handoff, while the integration coverage proves current Project authorization/member mapping against PostgreSQL 18.4. It does not orchestrate two concurrent database transactions; the lock-retention guarantee relies on the public method's `@Transactional` default `REQUIRED` propagation and the Task caller retaining its outer transaction.