feat(ce-plan): strengthen test scenario guidance across plan and work skills (#410)

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

plugins/compound-engineering/skills/ce-work/SKILL.md

@@ -104,6 +104,7 @@ This command takes a work document (plan, specification, or todo file) and execu
    - The full plan file path (for overall context)
    - The specific unit's Goal, Files, Approach, Execution note, Patterns, Test scenarios, and Verification
    - Any resolved deferred questions relevant to that unit
+   - Instruction to check whether the unit's test scenarios cover all applicable categories (happy paths, edge cases, error paths, integration) and supplement gaps before writing tests
 
    After each subagent completes, update the plan checkboxes and task list before dispatching the next dependent unit.
 
@@ -136,6 +137,15 @@ This command takes a work document (plan, specification, or todo file) and execu
    - Do not over-implement beyond the current behavior slice when working test-first
    - Skip test-first discipline for trivial renames, pure configuration, and pure styling work
 
+   **Test Scenario Completeness** — Before writing tests for a feature-bearing unit, check whether the plan's `Test scenarios` cover all categories that apply to this unit. If a category is missing or scenarios are vague (e.g., "validates correctly" without naming inputs and expected outcomes), supplement from the unit's own context before writing tests:
+
+   | Category | When it applies | How to derive if missing |
+   |----------|----------------|------------------------|
+   | **Happy path** | Always for feature-bearing units | Read the unit's Goal and Approach for core input/output pairs |
+   | **Edge cases** | When the unit has meaningful boundaries (inputs, state, concurrency) | Identify boundary values, empty/nil inputs, and concurrent access patterns |
+   | **Error/failure paths** | When the unit has failure modes (validation, external calls, permissions) | Enumerate invalid inputs the unit should reject, permission/auth denials it should enforce, and downstream failures it should handle |
+   | **Integration** | When the unit crosses layers (callbacks, middleware, multi-service) | Identify the cross-layer chain and write a scenario that exercises it without mocks |
+
    **System-Wide Test Check** — Before marking a task done, pause and ask:
 
    | Question | What to do |