Document requirements variable report fields

docs/cli.md

@@ -428,7 +428,13 @@ occurrence is a usage error even if a later assignment is valid.
 The successful report is YAML with selected identities, native completeness,
 and the input, variable, and issue inventories. False values and empty
 inventories are retained. Input metadata preserves null versus an empty string.
-The shape is:
+Variable entries contain `name`, `kind`, `supplied`, and `explanation`.
+`supplied` reports native exact-key presence, including an explicitly empty
+value, independently of `kind` and `complete`. Explanations and issue descriptions
+are upstream-owned human-readable summaries, not machine-readable details.
+
+For a prompt with the template `{{if .mode}}{{input "notes"}}{{end}}` and no
+input declarations, omitting `mode` can produce this partial report:
 
 ```yaml
 prompt_id: briefing
@@ -441,13 +447,17 @@ inputs:
     declared: false
     content_type: null
     description: null
+    explanation: This reference is not known to be reached on every execution path.
+variables:
+  - name: mode
+    kind: required
+    supplied: false
     explanation: ""
-variables: []
 issues:
   - code: missing_variable
     input_name: ""
     variable_name: mode
-    description: ""
+    description: A missing variable prevents selecting a dependency-bearing branch.
 ```
 
 PromptKit owns the inventory, classifications, explanations, completeness,