fix(test): address round-2 review findings for M4 E2E test

- Remove redundant Library imports (String, Collections already in common_e2e.resource)
- Add missing INTERNAL error check on plan status JSON steps (8 and 15)
- Fix is_terminal assertion to verify value is true, not just key presence

ISSUES CLOSED: #744

robot/e2e/m4_acceptance.robot

@@ -7,8 +7,6 @@ Documentation     E2E acceptance test for M4 (v3.3.0): Corrections, Subplans, an
 ...
 ...               Zero mocking — all CLI invocations use real providers.
 Resource          common_e2e.resource
-Library           String
-Library           Collections
 Suite Setup       E2E Suite Setup
 Suite Teardown    E2E Suite Teardown
 
@@ -126,6 +124,7 @@ M4 Corrections Subplans And Checkpoints
     ...    plan    status    ${plan_id}    --format    json
     ...    timeout=60s
     Should Not Contain    ${r_status_json.stdout}${r_status_json.stderr}    Traceback
+    Should Not Contain    ${r_status_json.stdout}${r_status_json.stderr}    INTERNAL
     Should Not Be Empty    ${r_status_json.stdout}
     Log    Plan status JSON: ${r_status_json.stdout}
     # Extract checkpoint ID if present
@@ -200,10 +199,11 @@ M4 Corrections Subplans And Checkpoints
     ...    plan    status    ${plan_id}    --format    json
     ...    timeout=60s
     Should Not Contain    ${r_final.stdout}${r_final.stderr}    Traceback
+    Should Not Contain    ${r_final.stdout}${r_final.stderr}    INTERNAL
     Should Not Be Empty    ${r_final.stdout}
     Log    Final plan status JSON: ${r_final.stdout}
-    # Verify plan reached terminal state (is_terminal: true)
-    Should Contain    ${r_final.stdout}    "is_terminal"
+    # Verify plan reached terminal state (is_terminal must be true)
+    Should Contain    ${r_final.stdout}    "is_terminal": true
     # Check for applied or terminal processing state
     Should Match Regexp    ${r_final.stdout}
     ...    "processing_state"\\s*:\\s*"(applied|cancelled|constrained)"