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Agent Architecture ​

Postmill's chat agent is a Mastra/CopilotKit agent that lives at /agents. It understands natural-language requests, delegates to domain specialists, calls tools, and asks for human confirmation before outward actions.

For the end-user view of what the agent can do, see Agent User Guide. For the MCP/A2A surfaces that expose the same tools to external clients, see MCP Server.

Verified against v1.0.0

High-level flow ​

┌─────────────────────────────────────────────────────────────────────┐
│                         User (browser)                              │
└──────────────────┬──────────────────────────────────────────────────┘
                   │  natural-language message
                   ▼
┌─────────────────────────────────────────────────────────────────────┐
│  CopilotKit provider  ──►  /copilot/agent  ──►  CopilotRuntime      │
│                         (cookies + CSRF header)                     │
└──────────────────┬──────────────────────────────────────────────────┘
                   │  GraphQL / streaming
                   ▼
┌─────────────────────────────────────────────────────────────────────┐
│  Mastra agent ("postmill")                                          │
│  ┌─────────────┐                                                    │
│  │ Supervisor  │  owns integrationList + groupList                  │
│  │   (when     │  routes intent to specialists                      │
│  │  AGENT_     │                                                    │
│  │ SUPERVISOR_ │                                                    │
│  │ ENABLED)    │                                                    │
│  └────┬──────┘                                                    │
│         │  delegates                                                │
│         ▼                                                           │
│  ┌─────────┬─────────┬──────────┬─────────┐                         │
│  │ content │  media  │ analytics │   ops   │  specialist agents     │
│  └────┬────┴────┬────┴─────┬────┴────┬────┘                         │
│       │         │          │         │                              │
│       ▼         ▼          ▼         ▼                              │
│  generatePost  media       analytics  posts/                          │
│  Content, run  studios,    tools,    campaigns,                      │
│  Generator,    search      watchlist comments                        │
│  runContentPipeline, brand memory                                    │
└─────────────────────────────────────────────────────────────────────┘
  • When AGENT_SUPERVISOR_ENABLED is not false, a supervisor agent routes to domain specialists (content, media, analytics, ops).
  • When the supervisor is disabled, a single flat agent owns all tools directly.
  • The same tool set is exposed through the MCP/A2A server; agent tools are not duplicated for MCP callers.

Specialist responsibilities ​

SpecialistDomainTool ids
contentDrafts, rewriting, brand voice, RAG/brand-memory searches, content pipelinegeneratePostContent, runGenerator, runContentPipeline, ragSearch, brandMemorySearch, brandProfile, brandMemoryReindex
mediaImage/video/audio generation, media studios, stock/library search, DesignergenerateImageTool, generateVideoTool, mediaStudioGenerate, mediaJobStatus, listMediaProviders, listMediaModels, filesSearch, stockSearch, uploadFromUrlTool, designerDesign
analyticsAnalytics overviews, best-time heatmap, recommendations, per-post metrics, watchlistanalyticsOverview, bestTime, recommendations, analyticsPost, watchlist
opsScheduling posts, campaign management, comments inbox/replies, post operationsintegrationSchema, triggerTool, schedulePostTool, listPosts, getPost, reschedulePost, deletePost, approveDraft, campaignCreate, campaignUpdate, campaignDashboard, campaignTag, commentsInbox, commentReply

The supervisor only owns integrationList and groupList directly; everything else is delegated.

Tool inventory ​

All tools live under libraries/nestjs-libraries/src/chat/tools/ and are registered in tool.list.ts. Every tool that mutates state is wrapped by the ToolFirewallService before being handed to the agent.

Tool idClassKindRequires write scopeHuman-in-the-loop in UI
integrationListIntegrationListToolreadnono
groupListGroupListToolreadnono
integrationSchemaIntegrationValidationToolreadnono
triggerToolIntegrationTriggerToolreadnono
schedulePostToolIntegrationSchedulePostToolwriteyesvia composer modal
generatePostContentGenerateContentToolread/AInono
runGeneratorRunGeneratorToolread/AInono
runContentPipelineRunContentPipelineToolread/AInono
generateImageToolGenerateImageToolwrite/AIyesno
generateVideoToolGenerateVideoToolwrite/AIyesno
uploadFromUrlToolUploadFromUrlToolwriteyesno
designerDesignDesignerDesignToolwriteyesno
analyticsOverviewAnalyticsOverviewToolreadnono
bestTimeAnalyticsBestTimeToolreadnono
recommendationsAnalyticsRecommendationsToolreadnono
analyticsPostAnalyticsPostToolreadnono
watchlistAnalyticsWatchlistToolreadnono
listMediaProvidersListMediaProvidersToolreadnono
listMediaModelsListMediaModelsToolreadnono
mediaStudioGenerateMediaStudioGenerateToolwrite/AIyesyes
mediaJobStatusMediaJobStatusToolreadnono
campaignCreateCampaignCreateToolwriteyesyes
campaignUpdateCampaignUpdateToolwriteyesyes
campaignDashboardCampaignDashboardToolreadnono
campaignTagCampaignTagToolwriteyesyes
commentsInboxCommentsInboxToolreadnono
commentReplyCommentReplyToolwriteyesyes
listPostsPostsListToolreadnono
getPostPostsGetToolreadnono
reschedulePostPostsRescheduleToolwriteyesyes
deletePostPostsDeleteToolwriteyesyes
approveDraftPostsApproveToolwriteyesyes
filesSearchFilesSearchToolreadnono
stockSearchStockSearchToolreadnono
ragSearchRagSearchToolreadnono
brandMemorySearchBrandMemorySearchToolreadnono
brandProfileBrandProfileToolreadnono
brandMemoryReindexBrandMemoryReindexToolwriteyesno

Content pipeline ​

runContentPipeline is not a single LLM call; it delegates to an in-process agent mesh (libraries/nestjs-libraries/src/chat/content-pipeline/). The pipeline registry (pipeline-registry.data.ts) defines four bundled agents — strategist, copywriter, brandCritic, finalizer — validated against AgentRegistrySchema at boot. The conductor runs them sequentially, applying brand voice, platform constraints, and a brand-critique pass before returning polished copy. The pipeline has a wall-clock deadline bounded by CONTENT_PIPELINE_TOTAL_TIMEOUT_MS (default 5 minutes); the deadline is checked between stages, not inside a stage.

Human-in-the-loop ​

When the request originates from the UI (/agents), the frontend intercepts outward actions with useCopilotAction/renderAndWaitForResponse and shows a confirmation card before the action is finalized:

  • schedulePostTool — opens the composer modal pre-filled with the draft.
  • commentReply — shows the draft message + post/comment id; calls the social comments API directly on approval.
  • mediaStudioGenerate — shows provider, operation, model, and prompt; calls POST /media/studio/:provider/generate on approval.
  • campaignCreate, campaignUpdate, campaignTag, reschedulePost, deletePost, approveDraft — show a confirmation card with the proposed change.

MCP/headless callers do not get a UI card; they rely on tool annotations (readOnlyHint, destructiveHint, etc.) and the mcp:posts:write scope.

Context injection ​

The frontend can push a compact "current view" payload via setAgentUiContext() (apps/frontend/src/components/agent/agent-context-bridge.tsx). The bridge forwards it to CopilotKit as a readable; the backend reads requestContext.get('ag-ui')?.context and appends a short "Current view" preamble to the agent instructions.

Last-view (not live-co-mount) semantics. The producers (/launches, /campaigns/[id], the post-detail modal) do not co-exist on the page with the agent chat route, so the store would be empty by the time the chat reads it if unmount deleted the contributed keys. Instead, a producer unmounting marks the snapshot stale (leftViewAt timestamp) rather than clearing it, and a producer mounting clears leftViewAt (a fresh view wins). The preamble then reads "currently viewing…" when fresh and "most recently viewed… (may be stale)" when leftViewAt is set. Stale ids are context, never implicit targets — the instructions tell the model to confirm the intended target before acting.

Payload is intentionally tiny: ids + labels only, never full post bodies.

Supported fields:

FieldMeaning
viewSurface name, e.g. "launches"
calendarWeekISO week or selected range
visiblePostIdsPost ids visible in the current calendar/list
selectedCampaignIdSelected campaign id
currentCustomerId / currentGroupIdSelected customer/group id
currentPostIdPost id when a post detail modal is open

Model resolution ​

The agent resolves its model per-call through AIModelProvider.languageModel(...). There is no env-key fallback; if the org has no active AI provider, the agent surface is off and the frontend routes the user to Settings → AI.

  • Flat agent: model: () => facade.languageModel('agent', orgId)
  • Supervisor: model: () => facade.languageModel('utility', orgId)
  • Specialists: content/analytics use 'agent'; media/ops use 'utility'

MCP / A2A preservation ​

The same LoadToolsService.loadTools() output is used by:

  1. The /agents chat surface (via CopilotKit + Mastra).
  2. The MCP server (/mcp, /mcp/:id, /mcp-oauth, /media-mcp).

start.mcp.ts builds the MCP tool union directly from LoadToolsService.loadTools() (the authoritative flat inventory), not by reflecting a private Mastra internal — so a Mastra rename can no longer silently collapse the exposed surface. A deterministic parity test (__evals__/routing.eval.ts) asserts that SUPERVISOR_TOOL_NAMES ∪ the four specialist *_TOOL_NAMES equals loadTools() exactly; pickTools throws on an unresolvable name. Adding a tool to tool.list.ts and assigning it to a specialist surfaces it everywhere automatically; forgetting to assign it fails the parity test.

A2A (/a2a) is deferred / not mounted. The prior bridge was written against an @reaatech/a2a-reference-mcp-bridge API that does not exist in the installed version (A2aAsMcpServer has no handleRequest), so every request 500-ed. It is tracked as a future feature rather than shipped broken — a correct build needs an in-process MCP transport pair + an A2A JSON-RPC HTTP layer over McpToolAdapter.executeTask, verified against a live consumer.

The ToolFirewallService wraps every execution, so budget, guardrail, and permission checks apply regardless of caller. DEV_DISABLE_AGENT only skips the agent-graph startup in start.mcp.ts; the MCP endpoints themselves remain available unless explicitly disabled separately.

Access model & governance ​

Every entrypoint stamps an access mode into the tool request context, and each tool enforces it in execute (defense-in-depth beyond the HTTP scope check):

ModeSet byRead allowedWrite allowed
userCopilotKit (/copilot/*)yesyes
mcp/mcp*, /ssewith mcp:readwith mcp:posts:write
headlessweekly digestyesnever (hard invariant)
  • requireRead(context) / requireWrite(context) (in tool.helpers.ts) gate every registered tool. A test (tools/__tests__/guard-coverage.spec.ts) asserts the guard is present and precedes the first await this._ (so a commented-out or post-spend guard fails), for every tool in tool.list.ts.
  • Text generation stays on requireRead; only artifact-spend is requireWrite. The artifact tools that create durable media (generateImageTool, generateVideoTool, designerDesign, mediaStudioGenerate) require write scope because an mcp:read token must not spend money on a stored artifact. The text-spend tools (generatePostContent, runGenerator, and runContentPipeline's text path) deliberately stay on requireRead: ephemeral text is the core utility of a read-scoped chat session, it is already bounded by the org agent budget cap, and "write" scope means outward / durable side effects, which transient text is not.
  • Org context is fail-closed: parseOrg throws when the resolved org has no .id, and checkAuth unwraps the MCP auth wrapper ({ org, userId, role }) to the bare org — otherwise where: { organizationId: undefined } would run cross-tenant queries.
  • Budget scope is unified onto agent: MCP/A2A entrypoints, CopilotKit, and the LangGraph /posts/generator run all gate on checkBudget('agent', orgId) and record spend under scope: 'agent'. The generator run is budget-gated up-front (before the first res.write, so a capped org gets a clean 4xx, not a truncated stream) and records spend against its real resolved provider/model.
  • OAuth pos_ tokens: expired-but-unrevoked tokens are rejected (findByAccessToken checks tokenExpiresAt), and the persisted scope string is mapped to MCP scopes (granted write scopes now honoured; mcp:read floor).

Feature flags ​

Env varDefaultEffect
AGENT_SUPERVISOR_ENABLEDtrueEnables the supervisor + specialists model. Set to false for a flat single agent. Read once at agent-build time — a change requires a process restart.
AGENT_DIGEST_ENABLEDunset (off)Weekly headless AI digest per org (requires USE_INNGEST=true + a member opting into the agent notification category). Skips cleanly for orgs with no active AI provider.
CONTENT_PIPELINE_TOTAL_TIMEOUT_MS300000Overall wall-clock deadline for a runContentPipeline run (checked between stages).
BACKEND_URLfalls back to NEXT_PUBLIC_BACKEND_URLServer-side backend URL for the MCP surface; start.mcp.ts fails fast at boot if neither is set.
MEDIA_MCP_AUDIT_LOG_PATH/tmp/media-mcp-audit.logFile path for the media-MCP audit logger.
DEV_DISABLE_AGENTunsetWhen set, /copilot/agent and /copilot/chat return 422/empty and MCP skips the agent surface.

Content-pipeline timeout is a caller-wait bound, not a hard cancel. The CONTENT_PIPELINE_TOTAL_TIMEOUT_MS Promise.race bounds only how long the caller waits; it does not abort in-flight agent-mesh work or its spend (no AbortSignal reaches dispatchToAgent). The deadline is re-checked between stages, so a stage already dispatched runs to completion even past the deadline — the run just rejects before starting the next one. Plumbing a real AbortSignal through agent-mesh is a tracked follow-up.

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