eafd15f0ef
PR #182 review (post-fix pass) surfaced two latent correctness risks in the new MessageItem memo: the per-message signature tracks only [type, text length, state, error/output presence] + metadata, so a part kind whose VISIBLE content can change WITHOUT changing those fields would silently freeze a stale row. Neither is reachable with the current toolset (tool output is set once; streaming is append-only with a fixed id), so the correct fix is to harden the documented invariant rather than hash output content on every delta (getPage returns full page content — hashing it per-delta would tax the hot path this PR optimizes). Add a WARNING in messageSignature naming the two future triggers (a tool that streams `preliminary` output; a client-side regenerate/edit that mutates a finalized row in place) and the required action (extend the signature). No behavior change (comment only). vitest src/features/ai-chat 189/189 pass, tsc clean for the touched files. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
45 lines
2.0 KiB
TypeScript
45 lines
2.0 KiB
TypeScript
import type { UIMessage } from "@ai-sdk/react";
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/** Cheap content signature for one message: changes iff something VISIBLE in the
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* row changed. Streaming is APPEND-ONLY (text parts only grow, parts are only
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* appended, a tool/text part flips state once), so a per-part [type, text
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* length, state, error/output presence] tuple + the persisted metadata
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* (error/finishReason) is a sufficient change signal without comparing full
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* strings on every delta. WARNING — load-bearing for the MessageItem memo:
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* if a future part kind's VISIBLE content can change WITHOUT changing [type,
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* text length, state, error/output presence] (e.g. a tool that streams
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* `preliminary` output, or a client-side regenerate that edits a finalized
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* row in place), extend this signature or the memo will freeze a stale row. */
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export function messageSignature(message: UIMessage): string {
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const parts = message.parts
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.map((p) => {
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const any = p as {
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type: string;
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text?: string;
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state?: string;
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errorText?: string;
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output?: unknown;
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};
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return [
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any.type,
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any.text?.length ?? 0,
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any.state ?? "",
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any.errorText ? 1 : 0,
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any.output !== undefined ? 1 : 0,
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].join(":");
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})
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.join("|");
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const meta = message.metadata as
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| { error?: string; finishReason?: string; usage?: { reasoningTokens?: number } }
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| undefined;
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// `usage.reasoningTokens` is neither append-only nor part-bound: the authoritative
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// turn total arrives on the final `finish-step` AFTER the reasoning text length and
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// state are already frozen. Without it in the signature the row's signature would be
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// unchanged at that point and the re-render skipped, so the "Thinking · N tokens"
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// header (reasoningTokensForPart) would keep the live estimate instead of snapping
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// to the exact figure.
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return `${message.id}#${message.role}#${parts}#${meta?.error ?? ""}#${
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meta?.finishReason ?? ""
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}#${meta?.usage?.reasoningTokens ?? ""}`;
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}
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