Files
zero/internal
Vasanth T 027a67080b fix(mcp): name the non-text blocks a tool result drops (#874)
* fix(mcp): name the non-text blocks a tool result drops

TextContent keeps only blocks whose type is "text", so a server that
returns an image, audio, or an embedded resource produced "(empty MCP
tool result)". A screenshot or browser server would complete a call
successfully, hand back a perfectly good image, and the model would be
told nothing came back. It then usually retries, which spends another
call to reach the same empty answer, and the user never learns an image
existed at all.

Carrying the payload is the larger half of #823 and is not this change.
Dropping silently is the part that causes the retry loop, and it can be
fixed on its own.

Decode mimeType on Content, and add DroppedContentSummary, which
describes what TextContent discarded ("1 image/png block", "2 resource
blocks, 1 audio/wav block"), grouping by mime type and ordering by first
appearance so the same result always reads the same way. Servers that
omit mimeType fall back to the block type rather than printing an empty
label.

registryTool.Run appends that as a note, and only when something was
actually dropped, so a text-only result is byte-for-byte unchanged. The
note also says retrying will return the same thing, since telling the
model what happened without telling it not to retry only fixes half the
loop.

Refs #823.

* fix(mcp): do not promise a retry returns the same content

The dropped-block note said "Retrying will return the same thing".
registryTool.Run makes a fresh remote call on every retry, so the server
may well answer differently; that is a promise this code is in no
position to make.

What cannot change is that Zero still has nowhere to put a non-text
block, so the note now says retrying cannot RECOVER the payload. Same
guidance, a claim that is actually true.

The test pins both directions: the new wording must be present, and the
absolute claim must not come back.

Raised by CodeRabbit on #874.
2026-08-10 10:59:03 +08:00
..
2026-06-08 21:07:57 +05:30