refactor(motoko): canister: import + --actor-env-alias for inter-canister calls (pub-sub, parallel_calls)

[marc0olo]

What

Migrates the two intra-project Motoko examples that make inter-canister calls — parallel_calls and pub-sub — to the typed canister:<name> import backed by moc's --actor-env-alias flag, replacing hand-written actor types + Runtime.envVar + actor(id).

This is the pattern we want to advertise going forward: the target canister's .did supplies the interface (no actor type in Motoko), while the principal stays runtime-resolved from PUBLIC_CANISTER_ID:<name>.

Changes

For each caller (caller → callee, subscriber → publisher):

• Import the target by name — import Callee "canister:callee" / import Publisher "canister:publisher". The hand-written CalleeActor / PublisherActor types and the Runtime.envVar + actor(id) helpers are gone.
• Commit the target's Candid interface — callee/callee.did, publisher/publisher.did, generated via mops generate candid <name>.
• Wire the import in mops.toml — --actor-env-alias <alias> PUBLIC_CANISTER_ID:<name> <did-path> on the caller. Per-canister args replace the global [moc].args, so the global flags (--default-persistent-actors, -W=...) are repeated. Added candid = ... on the target canister so its emitted interface is checked against the committed .did.
• READMEs — new "How the <target> is resolved" section describing the build/deploy/runtime split, plus an "Updating the Candid interface" note pointing to mops generate candid <name> (matches PR docs(motoko): align Candid regeneration to mops generate candid backend #1450's convention).

Build-time vs runtime (verified against the compiled Wasm)

• Build (moc): the .did gives the import its static type; the Wasm embeds only the env-var name + the IC env-var syscalls (ic0.env_var_*) — no principal. The build is told no principal and no target environment, so the same Wasm artifact runs in every environment.
• Deploy (icp-cli): sets the canister env var PUBLIC_CANISTER_ID:<name> to the target's principal — auto-injected for project canisters, overridable per-environment in icp.yaml.
• Runtime: the canister reads that env var and binds the reference at install/upgrade (verified: the env-var read is reachable only from canister_init/canister_post_upgrade/destabilization, not the update methods), then reuses the principal.

Testing

• mops build succeeds for both examples, including against the regenerated .did files.
• Deployed both to a local network: pub-sub's test.sh passes all 4 tests (registration + async callback delivery); parallel_calls sequential/parallel calls succeed.

🤖 Generated with Claude Code

[Copilot]

Pull request overview

This PR refactors the Motoko pub-sub and parallel_calls examples to use typed canister:<name> imports wired via moc --actor-env-alias, replacing manual Runtime.envVar + actor(id) plumbing and committing the target canisters’ Candid interfaces for compile-time typing.

Changes:

• Migrated inter-canister references to import <X> "canister:<x>" in the call-site canisters (subscriber, caller).
• Added committed .did files for the target canisters and configured mops.toml to type imports via --actor-env-alias and to check emitted Candid against the committed .did.
• Updated READMEs and the multi_subnet PocketIC harness to reflect the new “resolve-at-init from env var” binding model.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
motoko/pub-sub/subscriber/app.mo	Replaces runtime actor construction with typed canister:publisher import and direct calls.
motoko/pub-sub/README.md	Documents the new typed import + --actor-env-alias resolution model and Candid regeneration command.
motoko/pub-sub/publisher/publisher.did	Adds committed publisher Candid interface used to type the subscriber’s import.
motoko/pub-sub/mops.toml	Adds candid = ... for publisher and per-canister args for subscriber with --actor-env-alias.
motoko/parallel_calls/README.md	Documents the new typed import + --actor-env-alias resolution model and Candid regeneration command.
motoko/parallel_calls/multi_subnet/src/main.rs	Adjusts PocketIC install/settings order so env var is set before caller install/init binding.
motoko/parallel_calls/mops.toml	Adds per-canister args for caller with --actor-env-alias and candid = ... for callee.
motoko/parallel_calls/caller/app.mo	Replaces runtime actor construction with typed canister:callee import and direct calls.
motoko/parallel_calls/callee/callee.did	Adds committed callee Candid interface used to type the caller’s import.

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