fix(hub): stop no-op state churn — docks republish, message re-adds, a11y scan loop

[antfubot]

Intent

In examples/hub-vite, the devframe:docks shared state rebroadcast every ~1s with identical content, and hub:messages:add fired continuously — on any transport (the SSE work in #195 merely made it visible as an HTTP request stream). Stacked on #195 because its tests build on the SSE e2e harness; the bugs themselves predate it.

Root cause — a self-sustaining feedback loop

1. The a11y in-page agent's MutationObserver schedules a rescan on any body mutation (600ms debounce, no content gating).
2. Every scan mirrored itself into the messages feed unconditionally: the summary entry flipped loading → idle each pass, plus one identical add per violated rule.
3. The messages host had no content dedupe — an identical re-add still emitted message:updated.
4. Every message event republished the whole devframe:docks shared state with a fresh array and no change detection (and SharedState.mutate broadcasts unconditionally).
5. The hub-vite client re-rendered the dock rail with an unconditional innerHTML rewrite — which is a DOM mutation → back to (1). Period ≈ debounce + scan time ≈ 1s.

hub-next was immune only by accident: React reconciliation no-ops identical lists, so the observer stayed quiet — which confirmed the diagnosis.

Fixes (independent; any one breaks the cycle, together they also kill the wire waste)

• Hub context — hash-guard (devframe/utils/hash) the devframe:docks republish: dock/terminal/message events publish only when the dock list content actually changed.
• Messages host — content dedupe in update(): identical re-adds emit nothing and don't bump the delta clock; an identical re-add carrying autoDelete still resets the keep-alive timer.
• A11y agent — observer/interaction-driven rescans run in the background (no loading → idle summary churn); the messages reporter digest-gates each entry and re-sends only real changes (a removed rule that reappears is re-sent).
• hub-vite example — renderList skips identical innerHTML rewrites, so repainting an unchanged list is no longer a DOM mutation. (hub-next needs no change — React already reconciles.)
• Shared-state client host — applied server updates are no longer reflected back as server-state:set/patch events the server discards by syncId: one wasted wire message (a whole HTTP POST over SSE) per server-side state tick, on any transport.

Verification

• New tests: messages-host dedupe + autoDelete keep-alive; context-level "message events don't republish an unchanged dock list"; a11y reporter digest-gating (including rule-reappears re-send); SSE e2e asserts zero echo POSTs during server state ticks and exactly one POST per local mutation.
• Full suite 1103/1103, typecheck, lint, knip clean.
• Live check: an idle hub-vite over SSE now settles to exactly its intentional 2s drawer poll (20 parked-200 POSTs in a 20s window, zero 202s) — previously a continuous sub-second stream of identical ~2.7KB message-add frames.

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Created with the help of an agent.