feat: a run is capped by the memory it holds in MB instead of its live objects

Author: dylan-sutton-chavez

.github/actions/compiler/action.yml

@@ -129,6 +129,11 @@ runs:
       shell: bash
       run: cargo test --locked -p edge-python --features coverage coverage
 
+    # On its own too, it recounts every slot at each collection to prove the running count.
+    - name: Memory count
+      shell: bash
+      run: cargo test --locked --release -p edge-python --features memcheck --test tests vm::test::test_cases
+
     # compiler.wasm ships, the speed build goes under _build/ for the CLI jobs.
     - name: Stage on tmp
       uses: ./.github/actions/upload

CONTRIBUTING.md

@@ -55,7 +55,9 @@ deno lint js/
 
 ### Engine
 
-`cargo test --release` runs `tests/cases/vm.json` under `Limits::sandbox()`, so a budget, heap, or call-depth regression fails as a `MemoryError` or `RecursionError` instead of hanging. Every case must fit that budget, and two cases equal in every field fail the suite.
+`cargo test --release` runs `tests/cases/vm.json` under `Limits::sandbox()`, so a budget, memory, or call-depth regression fails as a `MemoryError` or `RecursionError` instead of hanging. Every case must fit that budget, and two cases equal in every field fail the suite.
+
+`--features memcheck` recounts every slot at each collection and fails a case whose running memory count drifted from it, and `tests/memory.rs` checks the memory model never counts less than the allocator hands out. A change that grows a container the heap holds keeps both green.
 
 ### Bench
 

Cargo.toml

@@ -18,11 +18,18 @@ doctest = false
 name = "tests"
 path = "tests/main.rs"
 
+# Its own binary, since it counts every allocation through a global allocator.
+[[test]]
+name = "memory"
+path = "tests/memory.rs"
+
 [features]
 default = ["std"]
 std = []
 # Records each instruction a run executes for `VM::ran`, method calls left unfused so every ip is the compiler's own.
 coverage = []
+# Recounts every slot at each collection and fails a vm.json case whose running memory count drifted.
+memcheck = []
 # The wrapper that makes compiler.wasm, its exports, host imports, allocator and panic handler.
 runtime = []