feat(chat): surface sidecar interactions via onInteraction on the chat-stream primitive

[drewstone]

What

Lifts the proven client-side chat-interaction handling into the web-react chat-stream primitive so any product on @tangle-network/agent-app gets live agent asks (kind question/plan/…) without hand-rolling the wire codec.

Closes the verified gap: the backend already threads backend.interactions into the stream (#166), so the sidecar interaction line IS in the stream — but the client parser (dispatchChatStreamLine / consumeChatStream / streamChatTurn) exposed callbacks for text/reasoning/tool/usage/metadata/error and no onInteraction, so it silently dropped the ask.

Refs #175.

Changes

• src/web-react/chat-interactions.ts (new) — the framework-agnostic interaction contract, lifted verbatim in semantics from the reference consumer (gtm-agent): the ChatInteraction type, wire↔persisted codecs (interactionFromWireRequest, interactionToPersistedPart, persistedPartToInteraction, parseInteractionRequest/parseInteractionCancel), and the pure helpers (dedupeQuestionInteractionsByContent, canTransitionInteractionStatus, cancelStatusFor, composerAnswerDeliveries/composerAnswerData/fieldAcceptsFreeText, isRenderableInteractionKind, part-key helpers). No React, no server imports — schema validation via the @tangle-network/agent-interface peer. One source of truth so gtm/tax/legal/physim stop forking it.
• ChatStreamCallbacks.onInteraction? — optional callback: (interaction: ChatInteraction) => void.
• dispatchChatStreamLine — recognizes the {type:'interaction', data:{request}} line (and the {kind:'event'} envelope form), validates with the shared codec, and fires onInteraction with the parsed ChatInteraction; a malformed ask is logged and skipped (never half-surfaced). Counts as received turn activity (the run is blocked on the user).
• src/web-react/index.tsx — barrel re-exports the contract next to the chat-stream primitives.
• src/web-react/chat-stream.test.ts (new) — feeds an interaction line through dispatchChatStreamLine and asserts onInteraction fires with the right ChatInteraction; covers the {kind:'event'} envelope, the consumeChatStream drain path, a malformed-line drop, and — proving non-breaking — a consumer with no onInteraction that parses the same stream unchanged.

Non-breaking

Purely additive: the callback is optional and no existing signature changed. Existing consumers compile and behave identically (covered by a dedicated "no onInteraction" test). Consumers opt in by wiring onInteraction and importing the shared contract instead of hand-rolling it.

Verification

• pnpm typecheck — clean.
• pnpm test — 137 files / 2227 tests green (includes 6 new interaction tests).
• pnpm build (tsup ESM + d.ts) — clean; onInteraction + the contract exports present in dist/web-react/index.d.ts.

Not published to npm — that's the separate gated release step.

[tangletools]

✅ Auto-approved drewstone PR — 5abf89de

This PR was opened by the trusted drewstone account.
The full PR reviewer audit still runs separately and will publish findings if it detects issues.

_{tangletools · auto-approval · reason: drewstone_author · 2026-07-08T19:25:09Z}