SUBAGENTS.md

Sub-Agents

Sub-agents are the user-facing vocabulary for nested worker assignments: a parent launches a focused role (explore, review, implementer, verifier, ...) through agent and gets back an agent_id plus transcript handle while the worker runs.

Architecturally, sub-agents should not be a second execution substrate. The durable primitive is the fleet-backed worker run described in AGENT_RUNTIME.md: retries, terminal status, receipts, artifact refs, inspection, and restart behavior belong there. The model-facing launcher is the single agent tool and detached work should converge on the same lifecycle as Agent Fleet.

The current agent implementation delegates to the durable sub-agent runtime while that cutover completes. It can still be useful for short in-session delegation, but if a child fails once on a transient provider timeout while an equivalent fleet worker would retry from the ledger, that is a runtime unification gap. For work that must survive provider hiccups, process restarts, sleep, or remote execution, prefer Fleet or a WhaleFlow-backed fleet run.

Sub-agents inherit the parent's tool registry by default, but child agents are leaf workers: they do not receive agent or nested lifecycle tools. agent launches detached background work: cancelling the parent turn stops the parent wait path, but it does not kill already-opened child runs.

This doc covers the role taxonomy and current compatibility controls. The active orchestration surface is agent; see crates/tui/src/prompts/constitution.md "Sub-Agent Strategy" and the in-line tool description.

Role taxonomy

The type field on agent selects a system-prompt posture for the child (agent_type is accepted as a compatibility alias). Each role is a distinct stance toward the work — not just a different label.

Maintainer posture

Sub-agents help CodeWhale move faster, but the parent agent still owns the maintainer decision. Use children to gather evidence, review patches, and run verification while keeping the community posture in AGENT_ETHOS.md: issues are open intake, PR gates are review-load controls, and harvested work needs clear contributor credit.

When a child reviews community work, the parent should still inspect the PR diff, linked issues, tests, and CI before merging, harvesting, closing, or deferring it. A sub-agent's result is a working set, not a substitute for stewardship.

Role	Stance	Writes?	Shell posture	Typical use
general	flexible; do whatever the parent says	yes	yes	the default; multi-step tasks
explore	read-only; map the relevant code fast	no	read-only	"find every call site of Foo"
plan	analyse and produce a strategy	minimal	minimal	"design the migration; don't execute"
review	read-and-grade with severity scores	no	read-only	"audit this PR for bugs"
implementer	land a specific change with min edit	yes	yes	"rewrite bar.rs::Foo::bar to do X"
verifier	run tests / validation, report outcome	no	test-focused	"run cargo test --workspace, report"
custom	explicit narrow tool allowlist	depends	depends	locked-down dispatch with hand-picked tools

Each role's full system prompt lives in crates/tui/src/tools/subagent/mod.rs (search for *_AGENT_PROMPT). The prompt prefix loads automatically when the child agent boots; the parent's assignment prompt becomes the first turn's user message.

Context forking

agent starts fresh by default: the child gets its role prompt plus the task you pass. Use fork_context: true when the child should continue from the parent's current request prefix instead. In fork mode the runtime keeps the parent prefill/prompt prefix byte-identical where available, appends a structured state snapshot, then adds the sub-agent role instructions and task at the tail. That preserves DeepSeek prefix-cache reuse while giving the child the context needed for continuation, review, summarization, or compaction work.

Use fresh sessions for independent exploration. Use forked sessions when the task depends on decisions, files, todos, or plan state already in the parent transcript.

When to pick which role

• general — when the task is "do this whole thing", not "go look", "design", or "verify". This is the right default; reach for a more specific role only when the posture matters.
• explore — when the parent needs evidence before deciding what to do next. Explorers are cheap and fast; open 2–3 in parallel for independent regions. They should orient first: confirm the project root, read relevant AGENTS.md/README.md guidance in unfamiliar trees, search only the likely scope, and return path:line-range evidence instead of a narrative tour. The role name to use is explore or explorer.
• plan — when the parent has an objective but no executable decomposition. Planners write artifacts (update_plan rows, checklist_write entries) but don't carry them out.
• review — when there's already a change and the parent wants it graded. Reviewers don't patch — they describe the fix in the finding so the parent can dispatch an Implementer if the verdict is "fix it".
• implementer — when the change is already specified and just needs to land. Implementers stay tightly scoped: minimum edit, no drive-by refactoring, run a quick verification before handing back.
• verifier — when the parent needs an authoritative pass/fail on the test suite or other validation. Verifiers don't fix failures; they capture the failing assertion + stack and put fix candidates under RISKS.
• custom — only when the parent needs to constrain the tool set explicitly. Pass the allowlist via the allowed_tools field on legacy/internal sub-agent records; the model-facing agent tool keeps the public schema intentionally small.

Aliases

The model can spell each role multiple ways:

Canonical	Aliases
general	worker, default, general-purpose
explore	explorer, exploration
plan	planning, planner, awaiter
review	reviewer, code-review, code_review
implementer	implement, implementation, builder
verifier	verify, verification, validator, tester
custom	(none; explicit allowed_tools array required)

All matching is case-insensitive. Unknown values produce a typed error listing the accepted set, so the model can self-correct on the next turn.

Concurrency cap

Up to 20 sub-agents run concurrently by default (configurable via [subagents].max_concurrent in ~/.codewhale/config.toml; the default equals the hard ceiling of 20). When the parent hits the cap, agent returns an error with the cap value; the parent should wait for background completion events before opening more agents, or ask the user.

By default every admitted child may start immediately — there is no artificial throttle. If you want gentler fan-out, lower [subagents].launch_concurrency (how many direct children start at once); children beyond that limit queue for a launch slot rather than bursting. launch_concurrency defaults to the resolved max_subagents cap. (The pre-v0.8.61 interactive_max_launch key is still accepted as a deprecated alias; the new key wins when both are set.)

The cap counts only running agents — completed / failed / cancelled records persist for inspection but don't occupy a slot. Agents that lost their task_handle (e.g. across a process restart) also don't count against the cap.

Per-role models (#3018)

Children can run on a different model than the parent. Two config surfaces feed the same override map ([subagents.models] keys win on conflict, keys are case-insensitive):

[subagents]
default_model  = "deepseek-v4-flash"   # fallback for every role
worker_model   = "deepseek-v4-pro"     # worker / general
explorer_model = "deepseek-v4-flash"   # explorer / explore
awaiter_model  = "deepseek-v4-flash"   # awaiter / plan
review_model   = "deepseek-v4-pro"     # review
custom_model   = "deepseek-v4-pro"     # custom

[subagents.models]
# Free-form role → model map; any role alias accepted by agent works.
implementation = "deepseek-v4-pro"

Model ids may be any model the active provider accepts — validation is provider-aware and happens at spawn time, not load time. On the official DeepSeek API only DeepSeek ids are accepted; every other provider passes the id through to the provider API, which is the authority. A non-DeepSeek example:

provider = "moonshot"
model = "kimi-k2.7-code"

[subagents]
worker_model = "kimi-k2.6"

Model ids are validated the same way when applied to a child route; an invalid id on the official DeepSeek API fails the spawn with the accepted-id list instead of an opaque provider 400.

With /model auto, sub-agent routing is provider-aware too: providers with a known big/cheap pair (DeepSeek, and the hosted DeepSeek routes on NVIDIA NIM, OpenRouter, Novita, SiliconFlow, SGLang, vLLM) route between that pair; providers without a known cheap tier (e.g. Ollama, Moonshot) skip the network router and keep children on the session model.

Per-step API timeout (#1806, #1808)

Each sub-agent step wraps its DeepSeek create_message call in a per-step timeout so a single stuck request can't pin the parent's completion wakeup channel indefinitely. The default is 120 seconds, which matches the legacy hardcoded value. Long-thinking children that legitimately exceed that, for example heavy plan or review work behind agent, can extend the timeout in ~/.codewhale/config.toml:

[subagents]
api_timeout_secs = 900  # 15 minutes; clamped to 1..=1800

Values are clamped to 1..=1800. 0 and unset keep the legacy 120 second default, so existing installs see no behavior change.

Stale-agent heartbeat (#2614)

Running agents also track manager-visible progress. If a child stops emitting progress for the heartbeat window, the manager auto-cancels it, releases its sub-agent slot, and keeps the cancelled record inspectable through the returned transcript handle and persisted worker record. The default is 5 minutes:

[subagents]
heartbeat_timeout_secs = 300  # clamped to 30..=3600

The effective heartbeat is kept at least 30 seconds above api_timeout_secs, so a configured long model request is not cancelled before its own request timeout can fire.

Lifecycle

Each opened session produces a record that progresses through:

Pending → Running → (Completed | Failed(reason) | Cancelled | Interrupted(reason))

Interrupted fires when the manager detects a Running agent whose task handle is gone — typically after a process restart that loaded the workspace's persisted state from .codewhale/state/subagents.v1.json. The parent can open a replacement session with the same assignment or treat it as a terminal state.

Session boundaries (#405)

Each SubAgentManager instance assigns itself a fresh session_boot_id on construction. Every new session stamps the agent with that id; the workspace state file records it for restart recovery.

Sidebar/status projections focus on current-session agents by default. Prior-session agents that are not still running are treated as archived records so the model does not mistake stale work for live work.

Records that loaded from a pre-#405 persisted state file (no session_boot_id field) classify as prior-session because the manager can't match them to the current boot.

Run receipts, follow-up, and takeover

Each compatibility sub-agent has a persisted worker record in .codewhale/state/subagents.v1.json. The record is the current run-ledger slice for sub-agent lanes until those lanes are backed directly by the fleet ledger: it stores run_id, objective, role/model, workspace/branch, lifecycle events, artifact refs, follow-up target, takeover target, usage provenance, and verification provenance.

agent returns a session projection with these fields at the top level and inside worker_record. The normal parent contract is not polling: keep working and consume the completion event when the child finishes. If audit detail is needed, inspect the returned transcript_handle with handle_read.

Legacy follow-up delivery is retained only for old transcripts and internal recovery. If a message was delivered, the worker record stores a bounded preview and timestamp. New model-facing flows should open a replacement agent when a child's assignment no longer fits.

Artifacts are symbolic refs. Use handle_read on the returned transcript_handle for transcript details, and treat result_summary as a child self-report unless verification.status points to a separate gate or receipt. usage.status is unknown until sub-agent token accounting is wired into the worker ledger.

Output contract

Every sub-agent produces a final result string with five sections, in order:

SUMMARY:    one paragraph; what you did and what happened
CHANGES:    files modified, with one-line descriptions; "None." if read-only
EVIDENCE:   path:line-range citations and key findings; one bullet each
RISKS:      what could go wrong / what the parent should double-check
BLOCKERS:   what stopped you; "None." if you finished cleanly

The exact format lives in crates/tui/src/prompts/subagent_output_format.md. The parent reads EVIDENCE as a working set for the next turn, so explorers and reviewers should be precise here.

Memory and the remember tool (#489)

Sub-agents inherit the parent's memory file when memory is enabled ([memory] enabled = true or DEEPSEEK_MEMORY=on). They can append durable notes via the remember tool — handy for an explorer that discovers a project convention worth carrying across sessions, or a verifier that learns "this test is flaky".

Memory writes are scoped to the user's own memory.md file; they don't go through the standard write-approval flow.

Implementation notes

• Source: crates/tui/src/tools/subagent/mod.rs.
• Persisted state: <workspace>/.codewhale/state/subagents.v1.json. Schema version 1 (forward-compatible — new optional fields use #[serde(default)]).
• SubAgentRuntime::background_runtime() starts from child_runtime() but replaces the turn-scoped child token with a fresh cancellation token, so parent turn cancellation does not stop detached background sessions.
• The is_running check ignores agents whose task_handle is None; this avoids counting persisted-but-detached records toward the concurrency cap (#509).
• SharedSubAgentManager is Arc<RwLock<...>> — read paths use read locks so /agents and the sidebar projection don't block the main loop during multi-agent fan-out (#510).