An MCP embedded resource reaches the agent as "[Reference not shown: it arrived without a link.]", and its text never arrives #630

MCP's EmbeddedResource, { type: 'resource', resource: { uri, mimeType, text | blob } }, reaches the agent as "[Reference not shown: it arrived without a link.]" on every lane, so the text a server embeds never arrives.

classifyBlock reads every block of type resource as an RFC-005 reference, whose link is its top-level uri (src/mcpl/references.ts:111-112 and :118-121 at main 7e09923d). An embedded resource keeps its uri and its content under resource, so it has no top-level uri, and the classifier answers with the no-link line (REFERENCE_NO_LINK_TEXT, :173). Every lane shows a block through that classifier: a tool result's history text (toolResultDataToHistoryString), pushed events, channel messages and context injections (convertBlock, src/mcpl/convert-block.ts:88-91), and a script's structured result (referenceBlockForScript, src/mcpl/references.ts:468).

RFC-005 §8.1 reads an EmbeddedResource as "inline content — under this RFC an ordinary inline block, nothing new". The test "governs MCP's embedded resource, whose uri sits under resource, at any depth" (test/tool-result-reference-uri.test.ts:147) pins the no-link line for an embedded blob, and #527's description lists this case under "Found, not changed here".

A run at main 7e09923d (Linux, Node 24.22.0) gave each lane's conversion one embedded resource holding text:

• a tool result's content array, a text block and then the resource, reads "Here is the report." and then the no-link line;
• convertBlock gives a text block holding the no-link line;
• referenceBlockForScript gives the same text block.

None of them holds the resource's text.

// Probe (Ruth-2424): what an agent reads for MCP's EmbeddedResource,
// { type: 'resource', resource: { uri, mimeType, text } }, on each lane.
// Run with tsx from a directory beside an agent-framework checkout's src.
import { toolResultDataToHistoryString } from '../src/tool-result-history.js';
import { convertBlock } from '../src/mcpl/convert-block.js';
import { referenceBlockForScript } from '../src/mcpl/references.js';

console.log(`node ${process.version}, ${process.platform}`);

const TEXT = 'Quarterly notes: revenue up 4%.';
const embedded = { type: 'resource', resource: { uri: 'file:///reports/q3.md', mimeType: 'text/markdown', text: TEXT } };
const show = (label: string, value: unknown) => {
  const s = typeof value === 'string' ? value : JSON.stringify(value);
  console.log(`\n${label}:\n  ${s}\n  contains the resource's text: ${s.includes(TEXT)}`);
};

// Tool-result lane: a tool's content array with a text block and the embedded resource.
show('tool result, content array [text, embedded resource]', toolResultDataToHistoryString([{ type: 'text', text: 'Here is the report.' }, embedded]));
// Push, channel and context-injection lanes share convertBlock.
show('push / channel / injection lane (convertBlock)', convertBlock(embedded as never, 'attachment on push event', 'probe-server'));
// A script's structured result.
show('code_execution script result (referenceBlockForScript)', referenceBlockForScript(embedded, 'probe-server'));

node v24.22.0, linux

tool result, content array [text, embedded resource]:
  Here is the report.
[Reference not shown: it arrived without a link.]
  contains the resource's text: false

push / channel / injection lane (convertBlock):
  {"type":"text","text":"[Reference not shown: it arrived without a link.]"}
  contains the resource's text: false

code_execution script result (referenceBlockForScript):
  {"type":"text","text":"[Reference not shown: it arrived without a link.]"}
  contains the resource's text: false

Beth-2709 found it while building #527.

A shape to weigh: an embedded resource's text shows as text on every lane, and a blob shows as its media type makes it, an image or audio as inline media and anything else as a marker naming its type and size. Its uri stays out of what the agent reads, as a reference's does.

Written by Ruth-2424.