feat: on low wasm memory hook

[mraszyk]

This proposal is based on this forum post and has already been approved by motion proposal 106146.

Canister developers have to actively monitor their canisters to know if they are low on wasm memory. If detected too late, a canister can be completely stuck and forever un-upgradable.

To address this, we introduce a hook called on_low_wasm_memory. When defined, it is triggered whenever the canister's memory usage exceeds some developer-defined threshold.

[mraszyk]

If the canister gets frozen immediately after the function is scheduled for execution, the function will run once the canister's unfrozen if the canister's wasm memory remains above the threshold t.

This property is not established by the implementation.

[mraszyk]

The implementation only considers stable memory and ignores, e.g., the chunk store and snapshot size, when deriving the wasm memory capacity.

[mraszyk]

The hook should not run after an upgrade/reinstall/uninstall/install if the condition is not satisfied after the upgrade (although the condition was satisfied before the upgrade and the hook did not execute yet).

[github-actions]

🤖 Here's your preview: https://xaml7-fiaaa-aaaam-abdka-cai.icp0.io

[dragoljub-duric]

Regarding the point:
"The hook should not run after an upgrade/reinstall/uninstall/install if the condition is not satisfied after the upgrade (although the condition was satisfied before the upgrade and the hook did not execute yet)."
Because the hook condition is checked whenever the canister tries to grow wasm memory, can it ever happen that the canister does not try to grow wasm memory when running upgrade/reinstall/uninstall/install?

[mraszyk]

Because the hook condition is checked whenever the canister tries to grow wasm memory, can it ever happen that the canister does not try to grow wasm memory when running upgrade/reinstall/uninstall/install?

Yes, e.g., if the canister does not have any pre- and post-upgrade hooks (in which case there's no wasm execution during canister installation).