fix: resolve deadlocks related to open inbound http connections

[mattjohnsonpint]

Previously, if an SSE connection was open and streaming subscriptions, we'd get a hung deadlock until the connection was closed, after reloading the wasm module (such as if user code changes were deployed, or in a modus dev loop).

The main deadlock was related to the map in our "dynamic mux". I replaced it with a lock-free xsync map to resolve that issue.

I also found that an open subscription was preventing clean shutdown, which was resolve by keeping track of open subscriptions and cancelling them during shutdown.

Also includes a few other misc bugs that were noticed along the way.

[linear]

HYP-3483 Open subscriptions are blocking some runtime operations

[Copilot]

Pull Request Overview

This PR addresses a deadlock issue related to open inbound HTTP connections by replacing the locking mechanism in the dynamic mux with a lock-free xsync map, and by canceling open GraphQL subscriptions during shutdown.

• Replace the sync-based route handling with xsync.Map in the HTTP dynamic mux.
• Introduce cancellation for GraphQL subscriptions on shutdown.
• Minor refactor in the actor event publishing for clarity.

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
runtime/httpserver/server.go	Registers a shutdown callback to cancel GraphQL subscriptions.
runtime/httpserver/dynamicMux.go	Replaces sync map with xsync.Map and updates route replacement.
runtime/graphql/graphql.go	Adds cancellation support for GraphQL subscription contexts.
runtime/actors/agents.go	Refactors error handling in getActorPid usage.
CHANGELOG.md	Updates the changelog to document the fix.

Comments suppressed due to low confidence (2)

runtime/httpserver/dynamicMux.go:71

• [nitpick] Consider renaming the variable 'temp' to 'newRoutes' to more clearly indicate its purpose in the ReplaceRoutes function.

temp := maps.Clone(routes)

runtime/httpserver/dynamicMux.go:53

• [nitpick] Consider renaming the variable 'found' to 'handled' to better convey that it flags whether a matching route was handled during the Range iteration.

var found bool