Engine: macro.check and the footprint: where a macro writes, worked out before it runs

Split from the pull request below at the review's request; the code is the runner's footprint
as reviewed there, unchanged.

- `macro.run` first runs the macro in dry-run mode on the real workbook (unless the rule is
  `overwrite`) and puts everything back: the workbook, its selection and history through the
  dry run's undo group, and the session state a dry run may touch (`Saved`: the active
  workbook, open documents, the saved mark, selections, unlocked ranges, trust, clipboard,
  preferences, mode, journal and recording, queued requests, format painter, find, ruler,
  hidden windows, drawing tool and the comment panes).
- Cells it would write outside its inputs that hold data, and sheets and objects it would
  delete, are conflicts: `ask` asks before anything runs, `fail` fails, and `shiftDown` and
  `shiftRight` insert cells over the block of every written cell and check again. A shift is
  refused when it would move an input, when the macro deletes sheets or objects, or when the
  touch log is full.
- A dry run stops before a file step and before Solver; the footprint is then partial, and the
  run checks each step as it goes.
- The dry runs and the run share one clock, one time limit and one step budget.
- `macro.check` reports the inputs, the output anchor, approval needed and the footprint.
- Tests: the footprint tests that moved with this code.

crates/engine/src/cmd/macros.rs

@@ -6,15 +6,26 @@ use serde_json::Value as Json;
 use super::*;
 
 pub fn specs() -> Vec<CommandSpec> {
-    vec![cmd!(
-        "macro.run",
-        "Run Macro",
-        [],
-        None,
-        "{name, inputs?: {Input: \"B2:D9\"} | \"B2:D9\", onConflict?: ask|fail|overwrite|shiftDown|shiftRight, overwrite?: bool, approve?: bool, timeLimit?: seconds} runs as one undo step; any error rolls it all back → {macro, ran, inputs, stopped?, shifted?}",
-        has_doc,
-        run
-    )]
+    vec![
+        cmd!(
+            "macro.run",
+            "Run Macro",
+            [],
+            None,
+            "{name, inputs?: {Input: \"B2:D9\"} | \"B2:D9\", onConflict?: ask|fail|overwrite|shiftDown|shiftRight, overwrite?: bool, approve?: bool, timeLimit?: seconds} runs as one undo step; any error rolls it all back → {macro, ran, inputs, stopped?, shifted?}",
+            has_doc,
+            run
+        ),
+        cmd!(
+            query "macro.check",
+            "Check Macro",
+            [],
+            None,
+            "{name, inputs?, timeLimit?: seconds} validates the inputs and dry-runs the macro on the workbook (then puts everything back) → {ok, errors?, needsApproval?, inputs, output?, conflicts, footprint}",
+            has_doc,
+            check
+        ),
+    ]
 }
 
 fn name_param<'a>(cmd: &str, p: &'a Json) -> Result<&'a str> {
@@ -25,3 +36,8 @@ fn run(s: &mut Session, p: &Json) -> Result<Json> {
     let name = name_param("macro.run", p)?;
     crate::macros::run::run(s, name, p)
 }
+
+fn check(s: &mut Session, p: &Json) -> Result<Json> {
+    let name = name_param("macro.check", p)?;
+    crate::macros::run::check(s, name, p)
+}