feat(ph-ai): subagent tool

[kappa90]

Problem

This PR adds a new "subagent" tool that allows the chat agent to delegate independent tasks to autonomous subagents that run in parallel.

Changes

• Added a new SubagentTool that can be used to delegate tasks to autonomous subagents
• Created a new Temporal workflow SubagentWorkflow for processing subagent activities
• Implemented Redis stream handling for subagent communication
• Added feature flag control via has_subagent_tool_feature_flag
• Updated the frontend to support and display subagent tool calls

How did you test this code?

Locally + tests coming soon

Changelog: (features only) Is this feature complete?

Could be in the changelog

[kappa90]

• #42052 : 2 dependent PRs (#42060 , #42704 ) 👈 (View in Graphite)
• #42888
• master

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[wiz-7ad640923b[bot]]

Wiz Scan Summary

Scanner	Findings
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IaC Misconfigurations	-
SAST Findings	-
Total	1

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[github-actions[bot]]

Size Change: +27 B (0%)

Total Size: 3.7 MB

ℹ️ View Unchanged

Filename	Size	Change
frontend/dist/toolbar.js	3.7 MB	+27 B (0%)

_{compressed-size-action}

[kappa90]

I made these updates:

• We now pass a SubagentType to the subagent workflow, right now it's fixed to GENERAL_PURPOSE but for example I'll have a read-only subagent for research
• Added a SubagentUpdateEvent which streams a subagent tool call
• If it's a subagent, the checkpointer is set to False, and we don't track chat with ai
• No new conversation for subagents, it's the same from the parent, this simplifies the read_data:artifacts PR I did on top of this one
• Subagents have a new prompt 😉 😉

[kappa90]

Main fixes:

• New subagent tool prompt
• new workflow for all chat agents
• workflow can determine an agent type, which registers certain modes and mode registries
• you can pass use_checkpointer to the workflow to turn on/off the checkpointer

[posthog-bot]

Query snapshots: Backend query snapshots updated

Changes: 1 snapshots (1 modified, 0 added, 0 deleted)

What this means:

• Query snapshots have been automatically updated to match current output
• These changes reflect modifications to database queries or schema

Next steps:

• Review the query changes to ensure they're intentional
• If unexpected, investigate what caused the query to change

Review snapshot changes →

[posthog-bot]

Visual regression: Storybook UI snapshots updated

Changes: 6 snapshots (6 modified, 0 added, 0 deleted)

What this means:

• Snapshots have been automatically updated to match current rendering
• Next CI run will switch to CHECK mode to verify stability
• If snapshots change again, CHECK mode will fail (indicates flapping)

Next steps:

• Review the changes to ensure they're intentional
• Approve if changes match your expectations
• If unexpected, investigate component rendering

Review snapshot changes →

[kappa90]

Edits:

• Subagent tool is now called task, the prompt has been improved accordingly
• Task tool accepts agent modes as parameters
• Fixed a problem with running parallel subagent, they would go in a deadlock due to the memory nodes being sync, fixed in this PR: https://github.com/PostHog/posthog/pull/42888
• You can now set a parent_span_id on a chat agent workflow, that will then track traces as a span rather than as a new trace, through a modified CallbackHandler, needed for the subagent flow
• Cancelling a workflow now cancels all subagent workflows
• Artifacts from subagents are not added to the stream, but rather summarized in the tool call result

[github-actions[bot]]

🔍 Migration Risk Analysis

We've analyzed your migrations for potential risks.

Summary: 1 Safe | 0 Needs Review | 0 Blocked

✅ Safe

Brief or no lock, backwards compatible

ee.0036_add_is_internal_to_conversation
  └─ #1 ✅ AddField
     Adding nullable field requires brief lock
     model: conversation, field: is_internal

📚 How to Deploy These Changes Safely

AddField:

This operation acquires a brief lock but doesn't rewrite the table.

Deployment uses lock timeouts with automatic retries, so lock contention will cause retries rather than connection pile-up.

Last updated: 2025-12-12 17:04 UTC (eed44ee)

[kappa90]

Merge activity

• Dec 12, 5:33 PM UTC: @kappa90 merged this pull request with Graphite.