feat(canvas): add linked agent inbox notifications

[brendon-jewell]

Summary

• add an opt-in notify --node <id> canvas-control verb for linked agent coordination
• deliver only a fixed Nodeterm-authored inbox prompt to context-linked agent targets
• rate-limit each source-target pair while retaining confirmations for arbitrary write and close commands

Validation

• npm test (4,220 passed, 8 skipped)
• npm run typecheck
• npm run build

[eneskirca]

Two notes from a batch review of the open PRs.

The rate limit is bypassable by concurrent requests. Canvas.tsx:6400 writes the throttle timestamp after await api.pty.sendText(...) at :6395. Nothing serializes control requests — the hook server awaits its handler per HTTP request on a concurrent node:http server — so N requests fired together all read lastSentAt at :6389 before any of them records one, and all N pass. Each delivered line is a submitted turn in the target. A failed send also records nothing, so an unreachable target can be retried without limit. Moving the set above the await fixes both.

The link check rests on an asserted identity. sourceNodeId reaches the handler from the request body, and the hook token is one value shared by every spawned session, so an agent can name a source it is not. Combined with list (which returns every node id on the project), an unlinked agent can iterate ids as claimed sources until one satisfies the link test. The payload here is a fixed string, so this is noise rather than takeover — but it is the same gate #112 and #113 now lean on much harder. I have written the shared analysis and the fix (bind the hook token per node, resolve the acting node from the token instead of the body) on #112 and #113; this PR benefits from the same change rather than needing its own.

Worth deciding alongside #113: that PR covers the same ground with arbitrary-text write plus per-pair grants that are pruned when a node is deleted — which also solves the never-pruned agentNotifyAtRef map here. The two overlap enough that taking them together, on top of the token fix, is probably cleaner than landing both as-is.

Verified by reading Canvas.tsx:6366-6410, hook-server.ts:171/180/453; not reproduced with a crafted POST.

[eneskirca]

Thank you for this, and sorry it sat open.

I am not going to merge it, but not because there is anything wrong with it. The agent-messaging design I am implementing right now covers the same ground, and it folds in both of the ideas that make this PR work:

• the notify verb as the shape for an agent telling a linked node something, rather than overloading write
• the 10 second throttle, which is the right instinct — an inbox that can be flooded by a loop is worse than no inbox

Both are going in with credit to you. I would rather do that than have you rebase a 111-line PR onto a design that is about to move underneath it.

If you want to stay involved in the messaging work, say so and I will loop you in on the design before it lands — you clearly thought about the failure modes here.

[brendon-jewell]

@eneskirca, thank you for the reply! Glad to see the feature implemented, and I was happy to contribute. I have thoroughly enjoyed using nodeterm thus far and am excited for things to come. Keep up the great work!