can1357/oh-my-pi · error · AIError.ValidationError

Cursor blob not found

Error message

Cursor blob not found

What it means

Cursor's AgentService protocol references prompt blobs by id; readCursorBlob looks the id up in the per-conversation in-memory blob store and throws ValidationError when nothing is stored under that hex key. The blob needed to reconstruct the request is missing, so the conversation cannot continue.

Solutions

1. Start a new conversation/session so blobs are written to a fresh store before being referenced.
2. Keep the conversation and its blob store alive in the same process for the conversation's duration; persist blobs externally if sessions must survive restarts.
3. Verify the blob id key encoding matches (hex string of the Uint8Array) on both write and read.
4. Ensure conversationId rotation logic copies blob store entries to the rotated id.

Example fix

null

if (!conversationBlobStores.get(conversationId)?.has(Buffer.from(blobId).toString("hex"))) {
  // blob missing — start a fresh conversation instead of continuing
}

null

try {
  await streamCursor(model, ctx, { conversationId, ...options });
} catch (err) {
  if (err instanceof AIError.ValidationError && err.message === "Cursor blob not found") {
    // restart with a new conversationId (fresh blob store)
    return streamCursor(model, ctx, { conversationId: crypto.randomUUID(), ...options });
  }
  throw err;
}

When it happens

Trigger: Reading a blob id that was never written to the store for the current conversation — e.g. continuing a conversation whose blob store was discarded (process restart), referencing a blob from a different conversationId, or a stale/rotated conversation id mapping to a fresh empty Map.

Common situations: Server restart wiping the in-memory conversationBlobStores while conversation ids persist; resuming a session across processes; a blob id serialized/mismatched (hex vs raw bytes) so lookup misses.

Related errors

• Cursor cannot continue history from a different model ( /…
• Invalid RPC message cursor
• stale_cursor
• A postfix required element cannot follow an optional or…
• a user-supplied replacement endpoint is required

AI-assisted analysis of can1357/oh-my-pi@9690622007 (2026-08-31). Data as JSON: /api/errors/82f0c8af2c500aac. Report an issue: GitHub.

Appendix: source

Thrown at packages/ai/src/providers/cursor.ts:4564

	if (output.usage.contextTokens !== usedTokens) {
		output.usage.contextTokens = usedTokens;
	}
}

function createBlobId(data: Uint8Array): Uint8Array {
	return new Uint8Array(createHash("sha256").update(data).digest());
}

function storeCursorBlob(blobStore: Map<string, Uint8Array>, data: Uint8Array): Uint8Array {
	const blobId = createBlobId(data);
	blobStore.set(Buffer.from(blobId).toString("hex"), data);
	return blobId;
}

function readCursorBlob(blobStore: Map<string, Uint8Array>, blobId: Uint8Array): Uint8Array {
	const data = blobStore.get(Buffer.from(blobId).toString("hex"));
	if (!data) {
		throw new AIError.ValidationError("Cursor blob not found");
	}
	return data;
}

/**
 * Cursor AgentService reconstructs the model prompt from `requestContext.rules`,
 * not from the client-supplied `rootPromptMessagesJson` system blobs. Map each
 * OMP system-prompt entry to a global CursorRule so always-apply rules survive
 * that reconstruction.
 */
export function buildCursorRequestContextRules(systemPrompt: readonly string[] | undefined): CursorRule[] {
	return normalizeSystemPrompts(systemPrompt).map((content, index) =>
		create(CursorRuleSchema, {
			fullPath: `/omp/system-prompt/${index}.mdc`,
			content,
			source: CursorRuleSource.USER,
			type: create(CursorRuleTypeSchema, {
				type: {

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