Fyllo Signal

Fyllo Signal is a passive display protocol emitted by an ACP Agent inside Chat assistant text. It renders a schema-valid tag as lightweight visual information without asking for confirmation or triggering a business action.

Fyllo Signal shares the top-level standalone Markdown-block boundary used by fyllo-action, but the two protocols have different responsibilities:

Protocol	Purpose	User action	Persistence and attention
fyllo-action	Ask FylloCode to perform an action that requires confirmation	Confirm or cancel	May create Action state; some types enter the session event rail
fyllo-signal	Display lightweight information the Agent has already resolved	None	Creates no state, never enters the event rail, and does not change pending counts

Enabled Types

The initial release enables only show.time:

Field	Constraint
label	Required string, 1–200 characters, with no CR or LF

It is used for current date or time queries and renders label as a non-interactive pill with a clock icon. A response may emit at most one show.time.

Tag Format

A real Signal may use only the type attribute, and its body must be a strict JSON object matching that type's schema:

<fyllo-signal type="show.time">
{
  "label": "2026-07-30 14:30"
}
</fyllo-signal>

The fenced block above is a protocol example, so it remains literal code. To emit a real Signal, the Agent starts the opening tag at the beginning of a line and gives it a standalone top-level Markdown block. If prose appears before or after it, a blank line must separate the prose from the tag. Literal < and > characters inside payload strings must be encoded as \u003c and \u003e.

Parsing and Display Boundaries

Fyllo Signal is enabled only for assistant text parts in Chat. Specs, Guidelines, Knowledge, Proposal, user messages, reasoning, and tool content do not register the Signal tag, so identical text stays ordinary Markdown there.

FylloCode waits for the closing tag and a complete standalone-block boundary before rendering. An unclosed tag remains ordinary Markdown. A closed tag with an invalid type, JSON body, or payload shows the generic invalid-Signal fallback and does not invoke a type-specific component.

Historical Signals are rendered only by parsing saved assistant text again. Mounting or remounting a Signal never calls Action IPC, writes session actionStates, creates a separate storage record, or affects session attention.