deer-flow/backend/packages/harness/deerflow/agents/AGENTS.md

Agent System

Web runs may supply context.locale (en-US / zh-CN) as a response-language preference; explicit user language requests win. DynamicContext projects it as request-only human data, leaving the static system prompt independent of locale. Clients without a supported locale retain message-language inference.

AppConfig.lead_prompt_overlay wraps the fully rendered lead system prompt with literal operator prepend/append text. Do not template-format these extensions or source them from run context. The graph and assembly descriptor must see the same resulting prompt. Empty overlays preserve bytes.

Lead Agent (packages/harness/deerflow/agents/lead_agent/agent.py):

• make_lead_agent(config: RunnableConfig) is the published langgraph.json entry point; preserve its signature and bare-graph return type.
• Gateway calls assemble_lead_agent(config, *, app_config=None) for a LeadAgentAssembly(graph, descriptor, effective_model); make_lead_agent returns .graph. effective_model is available even when no observer requests a descriptor, so graph-root tracing can tag the selected default or fallback model. assembly_descriptor.py::build_assembly_descriptor() records the model after runtime overrides, rendered prompt hash, authorized tools and middleware order. Consumers must unwrap via runtime/runs/worker.py::_agent_graph to also accept third-party factories returning bare graphs. The hashed skill catalog preserves allowed_tools=None (field omitted), () (declared empty), and non-empty allowlists as distinct compatibility-metadata states; allowlist ordering does not affect the fingerprint. The field is exported metadata only and never filters tools.
• Dynamic model selection via create_chat_model() with thinking/vision support
• Tools loaded via get_available_tools() - combines sandbox, built-in, MCP, community, and subagent tools
• System prompt generated by apply_prompt_template() with skills, memory, and subagent instructions
• Custom Agent memory_enabled: false disables memory reads, writes, tools, and compaction flushes while retaining date context; manual compaction trusts the state-producing checkpoint's agent binding, and global disable stays authoritative. Embedded clients cache the named policy by agent/user until reset_agent(); unreadable configs keep the legacy enabled default and log a warning.
• Prompt trust: framework authority uses the system channel; user/model-influenced text uses the sanitized HumanMessage data channel. Never interpolate untrusted values into system text—even escaped tags do not neutralize natural-language injection (PR #5090).
• Pass the same rendered prompt and middleware objects to the graph and assembly descriptor so observers describe the live graph, including Custom Agent allowed_subagents scope.

ThreadState (packages/harness/deerflow/agents/thread_state.py):

• Extends AgentState with: sandbox, thread_data, title, artifacts, todos, uploaded_files, viewed_images, goal, promoted, delegations, skill_context, summary_text
• Uses custom reducers: merge_artifacts (deduplicate), merge_viewed_images (merge/clear), merge_goal (preserve the active goal across ordinary state updates unless the goal writer replaces it), merge_promoted (union deferred tools within one catalog/user turn; replace on scope change; hash-only tool updates inherit scope), merge_delegations (append task delegation entries, same (run,id) wins, terminal status never downgraded, capped to the most recent entries), and merge_skill_context (dedupe active-skill references by path, keep the most recently read entries; entries store a name/path/description reference, not the SKILL.md body). summary_text is a LastValue channel updated by summarization and projected into model requests as durable context data instead of being stored as a messages item.
• Delta-mode merge_message_writes normalizes the current message state once, then folds normalized writes in order with message-ID position indexes and deferred tombstone compaction. It preserves public add_messages behavior, including duplicate IDs, replacement position, removal errors, REMOVE_ALL_MESSAGES, null-write errors, and missing-ID allocation order, without rescanning the accumulated state for every write. Keep this full-parity contract covered by differential tests: LangGraph's private _messages_delta_reducer is also linear, but intentionally omits some of those public add_messages semantics and cannot be substituted directly.

Runtime Configuration (via config.configurable):

• thinking_enabled - Enable model's extended thinking
• model_name - Select specific LLM model
• is_plan_mode - Enable TodoList middleware
• subagent_enabled - Enable task delegation tool
• max_concurrent_subagents - Per-response task call concurrency limit (clamped by SubagentLimitMiddleware)
• max_total_subagents - Per-run total delegation cap override (unset/null uses subagents.max_total_per_run, clamped to 1-50) Gateway and DeerFlowClient.stream() always provide the runtime run_id; custom graph integrations must do the same. If it is absent, enforcement deliberately counts the thread's full delegation ledger (fail-restrictive) and emits a warning.

Direct subagent runtime: create_deerflow_agent(..., subagent_runtime=runtime) is the explicit dependency-injection path for direct graph callers. Reuse one deerflow.subagents.SubagentRuntime across every graph that belongs to the same application capacity boundary. With the default subagent feature it binds middleware concurrency/total limits, the ordinary task tool, one real execution controller, and any active durable-batch submitter to the same snapshot. A caller-owned batch repository requires await runtime.start() (or async with runtime) before graph construction and stop() at shutdown; the factory fails closed while that worker is stopped, and already-built bound batch tools must fail unavailable after it stops rather than falling through to another process-global submitter. The factory never creates SQL infrastructure, renders the caller-owned system_prompt, or mounts Gateway API/UI routes. Full middleware takeover cannot be combined with this runtime; direct callers and custom subagent middleware remain responsible for model-visible call-policy wording.