feat(ag-ui): add ACTIVITY_SNAPSHOT and ACTIVITY_DELTA event support#1137
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omeraplak merged 3 commits intoVoltAgent:mainfrom Mar 24, 2026
Merged
feat(ag-ui): add ACTIVITY_SNAPSHOT and ACTIVITY_DELTA event support#1137omeraplak merged 3 commits intoVoltAgent:mainfrom
omeraplak merged 3 commits intoVoltAgent:mainfrom
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The AG-UI adapter now converts activity-related stream parts and tool
results into proper AG-UI activity events, enabling frontends to render
rich interactive UI (e.g. A2UI surfaces, CopilotKit panels) from
VoltAgent tool results.
Changes:
1. Tool result activity detection — when a tool returns an object with
`{ activityType, content }`, the adapter emits an ACTIVITY_SNAPSHOT
event alongside the regular TOOL_CALL_RESULT. This lets tools signal
that their output should be rendered as interactive UI rather than
shown as raw JSON.
2. Explicit activity stream parts — adds handlers for custom
"activity-snapshot" and "activity-delta" stream part types. These
allow VoltAgent hooks or custom implementations to emit activity
events directly into the AG-UI stream.
3. Improved activity message round-tripping — incoming activity messages
from the AG-UI client now preserve their activityType when folded
into the VoltAgent message format, giving the model better context
about prior activity state.
Co-Authored-By: Claude Opus 4.6 <[email protected]>
🦋 Changeset detectedLatest commit: ad46281 The changes in this PR will be included in the next version bump. This PR includes changesets to release 1 package
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No actionable comments were generated in the recent review. 🎉 ℹ️ Recent review info⚙️ Run configurationConfiguration used: defaults Review profile: CHILL Plan: Pro Run ID: 📒 Files selected for processing (1)
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📝 WalkthroughWalkthroughThis PR expands AG-UI integration to surface ACTIVITY_SNAPSHOT and ACTIVITY_DELTA events, detects activity structures inside Changes
Sequence Diagram(s)sequenceDiagram
participant Client
participant VoltAgent
participant Tool
participant AG_UI
Client->>VoltAgent: send stream parts (text / tool-result / activity-snapshot / activity-delta)
VoltAgent->>VoltAgent: inspect stream part type
alt activity-snapshot / activity-delta
VoltAgent->>AG_UI: emit ACTIVITY_SNAPSHOT / ACTIVITY_DELTA (messageId, activityType, content/patch, replace)
VoltAgent->>Client: optionally fold activity into assistant text (prefix with [Activity: <type>])
else tool-result
VoltAgent->>Tool: forward or process tool-result
Tool-->>VoltAgent: tool-result payload (object or array)
VoltAgent->>VoltAgent: tryExtractActivityFromToolResult(tool-result)
alt activity extracted
VoltAgent->>AG_UI: emit ACTIVITY_* event(s)
VoltAgent->>Client: emit original TOOL_CALL_RESULT as well
else no activity
VoltAgent->>Client: emit original TOOL_CALL_RESULT
end
end
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1 issue found across 1 file
Prompt for AI agents (unresolved issues)
Check if these issues are valid — if so, understand the root cause of each and fix them. If appropriate, use sub-agents to investigate and fix each issue separately.
<file name="packages/ag-ui/src/voltagent-agent.ts">
<violation number="1" location="packages/ag-ui/src/voltagent-agent.ts:599">
P2: Single-object tool results with `{ activityType, patch }` are not converted into `ACTIVITY_DELTA` events, creating an inconsistent API where deltas work for arrays but not single objects.</violation>
</file>
Reply with feedback, questions, or to request a fix. Tag @cubic-dev-ai to re-run a review.
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Actionable comments posted: 2
🤖 Prompt for all review comments with AI agents
Verify each finding against the current code and only fix it if needed.
Inline comments:
In `@packages/ag-ui/src/voltagent-agent.ts`:
- Around line 600-606: The event construction for AGUIActivitySnapshotEvent is
generating a fresh messageId via generateId() which detaches single-object
activity results from their assistant message; change the messageId assignment
in the AGUIActivitySnapshotEvent creation (where EventType.ACTIVITY_SNAPSHOT is
set) to prefer (obj.messageId as string) if present, otherwise use the existing
fallbackMessageId variable instead of calling generateId(), so single-object {
activityType, content } results remain attached and behave like the array and
direct "activity-snapshot" paths.
- Around line 408-410: The shared union type VoltAgentTextStreamPart is missing
the "activity-snapshot" and "activity-delta" discriminants, causing callers to
cast to any and forcing `as string` workarounds; update the
VoltAgentTextStreamPart definition to include variants for "activity-snapshot"
and "activity-delta" (matching the runtime shapes handled in the switch cases
around lines 524 and 544) so callers can create those parts without type
assertions and the switch can use the literal discriminants directly.
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packages/ag-ui/src/voltagent-agent.ts
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🧹 Nitpick comments (1)
.changeset/slimy-yaks-talk.md (1)
5-5: Consider expanding the changeset description for CHANGELOG clarity.Changeset descriptions become CHANGELOG entries read by package consumers. The current description is quite terse and doesn't explain what these new events provide or when they're emitted.
Consider expanding the description to help users understand the new functionality:
📝 Suggested enhanced description
-feat(ag-ui): add ACTIVITY_SNAPSHOT and ACTIVITY_DELTA event support +feat(ag-ui): add ACTIVITY_SNAPSHOT and ACTIVITY_DELTA event support + +The AG-UI adapter now emits ACTIVITY_SNAPSHOT and ACTIVITY_DELTA events alongside existing events when: +- Tool results contain activity objects with `activityType` and `content` fields +- Stream parts explicitly specify "activity-snapshot" or "activity-delta" types + +This enables frontends to receive structured activity UI payloads while maintaining backward compatibility—existing TOOL_CALL_RESULT events are still emitted.🤖 Prompt for AI Agents
Verify each finding against the current code and only fix it if needed. In @.changeset/slimy-yaks-talk.md at line 5, Update the changeset description for the feat entry that mentions ACTIVITY_SNAPSHOT and ACTIVITY_DELTA: replace the terse line with a short paragraph explaining what each event does (e.g., ACTIVITY_SNAPSHOT emits a full activity state snapshot, ACTIVITY_DELTA emits incremental updates), when they are emitted (initial load vs. subsequent changes), what key payload fields consumers can expect, and any migration or compatibility notes for existing listeners so the CHANGELOG entry is actionable for package users.
🤖 Prompt for all review comments with AI agents
Verify each finding against the current code and only fix it if needed.
Nitpick comments:
In @.changeset/slimy-yaks-talk.md:
- Line 5: Update the changeset description for the feat entry that mentions
ACTIVITY_SNAPSHOT and ACTIVITY_DELTA: replace the terse line with a short
paragraph explaining what each event does (e.g., ACTIVITY_SNAPSHOT emits a full
activity state snapshot, ACTIVITY_DELTA emits incremental updates), when they
are emitted (initial load vs. subsequent changes), what key payload fields
consumers can expect, and any migration or compatibility notes for existing
listeners so the CHANGELOG entry is actionable for package users.
ℹ️ Review info
⚙️ Run configuration
Configuration used: defaults
Review profile: CHILL
Plan: Pro
Run ID: 0743e464-41c5-446f-a9e1-129cc943709c
📒 Files selected for processing (1)
.changeset/slimy-yaks-talk.md
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Hey @corners99, |
5 tasks
@ag-ui/core v0.0.37 does not export ActivitySnapshotEvent, ActivityDeltaEvent, or ACTIVITY_SNAPSHOT/ACTIVITY_DELTA enum values. Define these types locally until upstream adds them. Move activity-snapshot/activity-delta handling from invalid `case` syntax to the default block with string comparison. Cast activity events to BaseEvent for subscriber.next() compatibility. https://claude.ai/code/session_01EdPoo8p31C68M2kJmayj9J
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Summary
Adds support for AG-UI
ACTIVITY_SNAPSHOTandACTIVITY_DELTAevents to the@voltagent/ag-uiadapter. These event types are defined in@ag-ui/corebut were not previously emitted by the VoltAgent adapter, making it impossible for frontends to receive structured activity messages from VoltAgent tools.Use Case
We're building a real estate development platform that uses VoltAgent with an Angular frontend and A2UI (Google's Agent-to-UI protocol). Our agents need to emit interactive UI surfaces (forms, confirmation cards, pricing grids) to the frontend. Without activity event support, tool results containing UI payloads are only available as raw JSON strings in
TOOL_CALL_RESULTevents — there's no way to signal that the result should be rendered as interactive UI.With this change, a VoltAgent tool can return:
And the adapter will emit an
ACTIVITY_SNAPSHOTevent that frontends can handle natively.Changes
1. Tool result activity detection
When a
tool-resultstream part contains an object with{ activityType: string, content: Record<string, any> }, the adapter emits anACTIVITY_SNAPSHOTevent in addition to the regularTOOL_CALL_RESULT(so the model's tool call is still properly resolved). Works with both single objects and arrays.2. Explicit activity stream part handlers
Adds
"activity-snapshot"and"activity-delta"cases toconvertVoltStreamPartToEvents(). These handle custom stream part types that VoltAgent hooks or future core changes may emit.3. Improved activity message round-tripping
Incoming
activityrole messages from the AG-UI client now preserve theiractivityTypeas a prefix when folded into VoltAgent messages, giving the model better context about prior activity state.No Breaking Changes
activityTypeare handled identically to beforeTOOL_CALL_RESULTevent is always emitted for tool results (even when activity events are also emitted)Test Plan
{ activityType: "test", content: { foo: "bar" } }emits bothACTIVITY_SNAPSHOTandTOOL_CALL_RESULTactivityType) emits onlyTOOL_CALL_RESULT(no regression)ACTIVITY_SNAPSHOTeventsactivityTypein converted messages"activity-snapshot"stream parts emitACTIVITY_SNAPSHOTevents"activity-delta"stream parts emitACTIVITY_DELTAevents🤖 Generated with Claude Code
Summary by cubic
Adds
ACTIVITY_SNAPSHOTandACTIVITY_DELTAsupport to the@voltagent/ag-uiadapter so tools can emit structured activity UI that frontends can render. No breaking changes;TOOL_CALL_RESULTis still emitted.New Features
ACTIVITY_SNAPSHOTwhen tool results include{ activityType, content }(single or array; arrays can mix snapshots and deltas viapatch).activity-snapshotandactivity-deltastream parts into activity events (snapshots usereplace, deltas usepatch).activityTypewhen folding incoming AG‑UI activity messages into VoltAgent messages by prefixing it in assistant text.Bug Fixes
@ag-ui/corev0.0.37 compatibility.activity-snapshot/activity-deltain the switch default via string checks and cast activity events toBaseEventto resolve type errors.Written for commit ad46281. Summary will update on new commits.
Summary by CodeRabbit
New Features
Chores