test(account): cover missing picker business date

docs/tests/integration/eligible-intern-picker.md

@@ -3,8 +3,8 @@
 - **Test type:** Integration
 - **Requirement IDs:** ACC-014, ACC-019–ACC-021, AUTH-001, PRJ-017, TST-001–TST-010
 - **Scenario IDs:** AC-ACC-009, AC-ACC-010, AC-PRJ-010 (selection-eligibility support)
-- **Test class/method:** com.lab.labtimesheet.feature.account.service.EligibleInternOptionIntegrationTest#listsOnlyActiveInternsWithActiveInclusiveInternshipsInPickerOrder
-- **Implementation commit:** Pending
+- **Test class/method:** com.lab.labtimesheet.feature.account.service.EligibleInternOptionIntegrationTest#listsOnlyActiveInternsWithActiveInclusiveInternshipsInPickerOrder; #rejectsMissingBusinessDate
+- **Implementation commit:** e70159a81b6445825f6d5f912ecf3c4aa3c1aa85
 
 ## Protected behavior
 
@@ -12,6 +12,8 @@ Pending, locked, deactivated, non-Intern, not-started, completed, and date-expir
 Account-owned Intern picker. An option is selectable only when both account and internship are ACTIVE and the
 explicit business date lies within the inclusive internship range. The returned numeric user ID is the internal
 submission identity, and options sort by display name then student code.
+The public query rejects a missing business date with the documented actionable message instead of issuing an
+ambiguous null-bound database query.
 
 ## Test method
 
@@ -19,12 +21,16 @@ The PostgreSQL 18.4 integration test persists valid account/profile combinations
 entities and repositories. It uses SQL only as a test fixture for future lock, deactivation, and completion states
 whose production transitions are outside this change. It calls the public Account service query and compares the
 complete immutable DTO sequence, including both inclusive date boundaries and unique user IDs.
+Its separate null-date regression calls the same public service method and asserts the exact
+<code>IllegalArgumentException</code> message documented by that method.
 
 ## Hand-derived expected result
 
 For business date 2026-08-14, profiles starting on that date and ending on that date remain eligible. The only
 expected options are Alpha / STU-100, Alpha / STU-200, and Zeta / STU-300, in that order. Every other seeded
 row fails at least one account role/state, internship state, or inclusive date condition.
+For a missing business date, the service must immediately throw
+<code>IllegalArgumentException("Business date is required")</code>.
 
 ## RED
 
@@ -65,6 +71,49 @@ Tests run: 1, Failures: 0, Errors: 0, Skipped: 0
 BUILD SUCCESS
 ~~~
 
+## Review follow-up: missing business date
+
+The public guard was temporarily removed solely to prove the new regression fails for the intended reason, then
+restored exactly before the GREEN checks. The follow-up commit contains only the regression test and evidence.
+
+### RED
+
+**Command**
+
+~~~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=EligibleInternOptionIntegrationTest#rejectsMissingBusinessDate' test
+~~~
+
+**Observed result**
+
+~~~text
+Tests run: 1, Failures: 1, Errors: 0, Skipped: 0
+java.lang.AssertionError: Expecting code to raise a throwable.
+BUILD FAILURE
+~~~
+
+### GREEN
+
+**Command**
+
+~~~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=EligibleInternOptionIntegrationTest#rejectsMissingBusinessDate' test
+~~~
+
+**Observed result**
+
+~~~text
+PostgreSQL 18.4 Testcontainers started and Flyway applied V1 baseline.
+Tests run: 1, Failures: 0, Errors: 0, Skipped: 0
+BUILD SUCCESS
+~~~
+
 ## Affected suite
 
 **Command and result**
@@ -90,6 +139,21 @@ Tests run: 105, Failures: 0, Errors: 0, Skipped: 0
 BUILD SUCCESS
 ~~~
 
+### Review follow-up affected account-service checks
+
+~~~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=EligibleInternOptionIntegrationTest,AccountActivationIntegrationTest,BootstrapIntegrationTest' test
+
+EligibleInternOptionIntegrationTest: 2 tests, 0 failures, 0 errors, 0 skipped
+BootstrapIntegrationTest: 4 tests, 0 failures, 0 errors, 0 skipped
+AccountActivationIntegrationTest: 2 tests, 0 failures, 0 errors, 0 skipped
+Selected account-service reports: 8 tests, 0 failures, 0 errors, 0 skipped.
+BUILD SUCCESS
+~~~
+
 ## External-test boundaries
 
 This query does not authorize Project membership itself; the consuming Project transaction must still recheck