Building Workflows

Building, Testing, and Improving Toil Workflows

Practical guide for developing toil workflows — from writing YAML to analyzing production runs and iterating on agent prompts.

Workflow Development Cycle

1. Write/edit workflow YAML + shell scripts
2. Validate: go test ./internal/definitions/
3. Build: make build && go build -o bin/tgwm ./cmd/tgwm/
4. Restart server: kill server, make serve-daemon
5. Trigger a run
6. Analyze results: API + events.jsonl + serf transcripts
7. Identify issues → go to 1

Building Workflows

Workflow YAML Structure

id: my_workflow
name: My Workflow
version: 1
description: What this workflow does
interview: on_issue
max_loop_iterations: 5
inputs:
  spec: string
  project_dir: string
prompt_inputs_mode: declared
workspace_defaults:
  mode: project
  path: ${PROJECT_DIR}    # cwd for runners — not the run dir
nodes:
  - id: my_node
    kind: role          # role (single agent) or subworkflow
    runner: serf         # serf, shell, or human
    context: fresh       # fresh = new session each attempt
    prompt: |
      Your prompt here
    inputs:
      spec: "${workflow_input.spec}"   # run-start input → workflow_input (NOT input) in an inputs: block
    decisions:
      - id: done
      - id: needs_work
        tags: [override]         # optional — attaches cross-cutting meaning.
                                 # See "Decision Tags" below.

edges:
  - from: my_node
    to: next_node
    when: done
    prompt: |
      Context for the next node about why it's being triggered.

Key Patterns

Workspace is PROJECT_DIR, not the run dir. The engine creates PROJECT_DIR if it doesn't exist. Runners run from there. The run dir (TOIL_CURRENT_WORKFLOW_DIR) is toil's metadata — runners access its outputs subdirectory through the TOIL_WORKFLOW_OUTPUTS env var, not cwd-relative paths.

Failure routing: any node can have edges when: "status == 'failed'". When the node fails (runner crash, timeout, unhandled loop exhaustion), the engine routes through matching failure edges. Without a failure edge, failure is fatal. The engine builds structured failure context on node.X.data.failure.* — includes child_run, decision_history, failed_child for subworkflow nodes.

Loop escapes: loop_exhausted_to: <node-id> on a node declares where to route when max_loop_iterations is hit. Good for bouncing review loops.

Shell nodes output structured JSON with decision, message, data, artifacts:

cat <<ENDJSON
{
  "decision": "merged",
  "message": "Clean merge",
  "data": {},
  "artifacts": []
}
ENDJSON

Both branches of any conditional must include data: {}.

Converging paths: Two edges into a node without join: all — node runs on whichever edge fires first. Use for mutually exclusive paths (e.g., clean merge OR conflict resolution both lead to export).

Subworkflow env inheritance: Child workflows inherit parent's TOIL_CURRENT_WORKFLOW_DIR, PROJECT_DIR, TOIL_ROOT. TOIL_RUN_ID is always the current run's ID (not inherited).

Decision tags: decisions can carry tags: [...] to surface them generically in dashboard badges, toil inspect aspects, and tree.tagged.<name> expressions — without the harness hardcoding decision names. See Decision Tags below.

Expression resolution: input/prompt/edge values are ${...} template strings over six namespaces — workflow_input, input, node, env, run, tree. The input vs workflow_input distinction, the closed set of node fields, and the silent-nil-without-! behavior are each easy to get wrong. See Expression Reference below; tree.tagged.<tag> is covered under Decision Tags.

Expression Reference

Input, prompt, and edge-passes values are ${...} template strings — not an expr: map. A value that is exactly one ${...} keeps the resolved native type (list, map, number); a ${...} embedded in surrounding text interpolates as a string. Write a literal dollar-brace as $${.

input vs workflow_input. In inputs: and edge passes: blocks you MUST use ${workflow_input.X} for run-start inputs; ${input.X} is rejected there — it exists only in the Phase-5 dispatch map that prompts and emit-output see. This is the single most common authoring mistake.

node.<id>.<field> — closed field set: decision, message, artifacts, data, session_id, tags, status, attempts, last_routing_decision, loop_iterations. Reach into data with ${node.x.data.a.b}; bare ${node.x} returns the whole output map. Any other field — ${node.x.output}, ${node.x.result}, or a typo like ${node.x.mesage} — is a load-time error.

Missing references resolve to nil silently — mark mandatory ones with !. A reference to a missing upstream node, an absent data key, or an undeclared input — e.g. ${node.ghost.message}, ${node.plan.data.typo}, ${workflow_input.undeclared} — resolves to empty/nil and the node runs anyway, so a typo'd path or an absent upstream field fails quietly and downstream receives blanks. Append ! to fail loudly instead: ${node.plan.data.summary!}, ${workflow_input.spec!}. The suffix covers the whole reference, including data.* subpaths. Use it for anything required.

Validate before running. go test ./internal/definitions/ (equivalently toil validate) checks namespaces, the Phase-5 input rule, node field names, and !-satisfiability at load time. It cannot check intent — that a decision routes where you meant, or that a prompt asks for what the upstream data actually contains. Read the YAML and do a dry run for those.

Decision Tags

Decisions can carry semantic tags that let the harness surface them in generic ways — dashboard badges, toil inspect --aspect <X>, tree.tagged.<name> expressions, topology styling — without the harness hardcoding knowledge of specific decision names.

decisions:
  - id: force_approve
    description: "Accept with unresolved reviewer concerns"
    tags: [override]
  - id: send_back
    description: "Reviewer was right; engineer must address"
  - id: skip_task
    description: "Partial, move on"
    tags: [override]

How it flows:

1. Workflow author declares tags: [...] on decisions that carry cross-cutting meaning.
2. At node completion, the engine looks up the matched decision in the node's decisions: list and copies its Tags onto NodeState.Tags. Tags are also included in node_completed event data for live SSE consumers.
3. Downstream surfaces read NodeState.Tags generically: the dashboard renders override-tagged nodes with an amber badge + "Review Overrides" section; toil inspect --aspect review_overrides returns them; graph renderers can style them distinctly. Adding a new tag-aware surface means reading NodeState.Tags, not patching the engine.

Authoring guidelines:

• Tags are workflow conventions — pick names that read like what they mean. The canonical one today is override for review-escalation waivers. If a new concern emerges (e.g., risk acceptance, flake suppression, audit flags), pick a short descriptive tag name and apply it consistently.
• Tags are declared per-decision, not per-node. A node with decisions force_approve (tagged override) and send_back (untagged) correctly distinguishes waivers from resolutions.
• Tags are materialized at completion time — changes to the YAML after a run completes don't retroactively re-tag historical runs. This matters for audit trails.
• The string "force_approve" no longer has any special engine meaning. If a workflow doesn't tag its decisions, none of the surfaces engage — including the amber badge. This is deliberate: the harness stays generic.

Cross-run queries:

When a deep child run (e.g., debug_merge running inside integrate running inside integrate_component) needs to see decisions made in sibling or ancestor runs, use tree.tagged.<name> rather than threading data through every intermediate workflow:

# debug_merge.yaml — merge_engineer reads upstream waivers
inputs:
  upstream_overrides:
    expr: tree.tagged.override
    optional: true

The resolver walks the execution group rooted at the current run's top-level ancestor and returns all matching nodes. Each entry carries run_id, workflow_id, node_id, decision, message, data, and tags. Empty list (not error) when no matching nodes exist. Missing TreeResolver on the context (unit tests) errors loudly rather than silently returning empty.

Output Protocols for Tagged Decisions

When a decision carries a tag, downstream consumers often expect specific structure inside data. These are prompt-level protocols, not schema-enforced — the engine doesn't validate the data shape. Document the contract in the node's prompt and trust the agent.

Example: override tag expects data.waived_concerns.

The resolve_review_dispute node (in implement_task.yaml) has its prompt instruct the agent: when deciding force_approve or skip_task, emit a structured list:

{
  "decision": "force_approve",
  "data": {
    "waived_concerns": [
      {
        "source": "write_code",
        "concern": "Entrypoint smoke test unresolved",
        "justification": "Verified src/index.ts runs; the engineer's concern is stylistic"
      }
    ]
  }
}

The dashboard and toil inspect surface waived_concerns when present. If missing, a prominent warning surfaces — the prompt required it, so absence signals an unjustified waiver that needs manual audit. This is the recommended pattern for any tag that accepts risk: require structured justification, surface it prominently, flag absence.

Bootstrap-From-Clean Verification

A recurring class of bug: a scaffold or merged tree passes tests on the author's machine because their PATH has tsc, eslint, or similar, but a fresh clone without dependencies installed can't even build. The tests "pass" deceptively and the issue surfaces later at integration.

definitions/workflows/build_component/bootstrap_check.sh is a reusable shell-level gate that proves the committed tree bootstraps from zero. It:

1. Copies HEAD into a scratch directory via git archive HEAD | tar -x — no pre-existing node_modules/, vendor/, target/, .venv/ leaks in.
2. Detects the stack from manifest presence (package.json → node, go.mod → go, Cargo.toml → rust, pyproject.toml/requirements.txt → python).
3. Runs the canonical install → build → lint → test sequence for each detected stack.
4. Outputs JSON {decision, message, data} with decisions pass, fail, or no_stack_detected.

When to wire it in:

• After scaffold tasks — gates commit_component in build_component.yaml. Catches scaffolds that pass because of local toolchain state.
• Pre-merge — gates verify_integration in integrate_component.yaml. The exported merged tree must bootstrap before integration starts.
• As a companion to env_bootstrap_failed — integrate.yaml's integration_tester and e2e_tester can distinguish toolchain failures (exit 127, command not found, missing manifest modules) from code-level failures. Route env_bootstrap_failed to bootstrap_repair_integration / bootstrap_repair_e2e (shell runner that installs deps in place) rather than debug_merge — repair is cheap; LLM debugging is expensive.

Both scripts are in definitions/workflows/build_component/ and definitions/workflows/integrate/; integrate_component/bootstrap_check.sh is a symlink so behavior stays single-sourced.

Authoring rule for scaffold tasks: the scaffold task's acceptance_criteria must include a bootstrap-from-clean clause:

Starting from a fresh checkout with no dependency cache, the canonical command sequence — install → build → lint → test — completes successfully.

plan_tasks in build_component.yaml enforces this for greenfield scaffolds. Workflows that create or modify scaffolds elsewhere should mirror the convention.

ForEach: Iterating Over Items

A ForEach is declared as two nodes: a template (what one item does) and an orchestrator (the loop). The template is a normal node with kind, runner, and prompt — it defines the per-item work. The orchestrator has a for_each: block that references the template via body:. The engine expands the template into one copy per item (implement::0, implement::1, ...), runs them, and when all items have settled the orchestrator emits an aggregate decision.

Canonical Example — build_component.yaml

nodes:
  # Template: defines what one task does. No incoming edges.
  - id: implement_one_task
    kind: subworkflow
    workflow: implement_task
    inputs:
      project_dir:
        expr: input.project_dir

  # Orchestrator: runs the loop. No kind/runner/workflow.
  - id: implement_tasks
    for_each:
      list: node.plan_tasks.data.plan.tasks   # expression resolving to a list
      item: task                              # each item is passed as "task"
      depends_on: depends_on                  # field name on each item (DAG mode)
      body: implement_one_task                # REQUIRED: the template node's ID
    decisions: [all_succeeded, some_failed, all_failed]

edges:
  # Per-item failure edge — routes a failed item back to the orchestrator.
  # This marks the item as "handled" so siblings continue running.
  - from: implement_one_task
    to: implement_tasks
    when: "status == 'failed'"

  # Aggregate edges — fire after ALL items have settled.
  - from: implement_tasks
    to: verifier
    when: all_succeeded
  - from: implement_tasks
    to: plan_tasks
    when: some_failed
    prompt: |
      Some build tasks failed. node.implement_tasks.data.items has per-item
      status and failure_context for each failed item. Re-plan only the
      failed tasks.
  - from: implement_tasks
    to: plan_tasks
    when: all_failed
    prompt: |
      All build tasks failed. node.implement_tasks.data.items has per-item
      failure_context with decision history. Produce a revised plan.

Required Fields in for_each:

• list: — expression that resolves to the list of items (e.g., node.plan_tasks.data.plan.tasks, input.items).
• item: — variable name; each item is injected into the template's input context under this name. Reference it in template inputs as expr: item or expr: item.some_field.
• body: — REQUIRED. The node ID of the per-item template.
• depends_on: — optional. Field name on each item that lists the IDs of items it must wait for. Enables DAG scheduling (see below). Omit for fully concurrent execution.

Aggregate Decisions

After all items settle, the orchestrator emits one of three decisions. Declare all three on the orchestrator and wire edges accordingly:

Edges out of the orchestrator use when: all_succeeded, when: some_failed, and when: all_failed.

Per-Item Failure Edge

Without a failure edge from the template, a single failed item aborts the entire ForEach (fail-fast). To let siblings continue:

- from: implement_one_task    # template ID, not expanded ID
  to: implement_tasks         # MUST route to the orchestrator
  when: "status == 'failed'"

When this edge exists, a failing item is recorded as failed-handled and its siblings keep running. The orchestrator waits for all items to settle before emitting some_failed or all_failed.

Edges from the template must route to the orchestrator. Routing template edges to any other node is a validation error — per-item complex recovery belongs inside the template (as a subworkflow or local recovery node), not as an edge to an arbitrary downstream node.

Items[] Structure

After the orchestrator completes, node.<orchestrator>.data.items[] holds a record for each item. Reference individual fields via expressions like node.implement_tasks.data.items.

{
  "items": [
    {
      "id": "task-0",           // item's "id" field, or index if absent
      "expanded_id": "implement_one_task::0",  // engine's state node ID
      "status": "succeeded",
      "decision": "approved",
      "message": "Implementation complete",
      "data": { }              // per-item output data
    },
    {
      "id": "task-1",
      "expanded_id": "implement_one_task::1",
      "status": "failed-handled",
      "decision": "",
      "message": "loop exhausted in review_code_quality",
      "failure_context": {
        "child_run": "abc-123",
        "last_decision": "test_changes_requested",
        "decision_history": [ ],
        "failed_child": { "node_id": "review_code_quality", "message": "loop exhausted" }
      }
    },
    {
      "id": "task-2",
      "expanded_id": "implement_one_task::2",
      "status": "skipped",
      "reason": "dependency task-1 failed"
    }
  ]
}

Status values:

• succeeded — item ran and completed cleanly.
• failed-handled — item failed and a failure edge exists; siblings continued. failure_context is populated.
• failed — item failed and no failure edge exists; the orchestrator itself failed (run is fatal without further error-handling edges on the orchestrator).
• skipped — DAG mode only; a dependency failed so this item never ran. reason is populated.

Downstream nodes can use node.implement_tasks.data.items in edge prompts and template inputs to reason about which items failed and why (see the some_failed edge prompt in the example above).

DAG Scheduling with depends_on:

When items carry dependency information, the depends_on: field on the orchestrator names the field on each item that lists the IDs of items it must wait for:

for_each:
  list: node.plan_tasks.data.plan.tasks
  item: task
  depends_on: depends_on    # each item has a "depends_on" field: ["task-0"]
  body: implement_one_task

Independent items run concurrently. An item only starts after all items it depends on have succeeded. If a dependency fails (with a failure edge), all transitive dependents are marked skipped rather than started. This lets an otherwise-independent subset of items continue running while a failed branch is skipped.

Omit depends_on: when items are fully independent — all items launch concurrently.

Note on exclude_inputs: Declare input filtering on the orchestrator, not the template. The orchestrator's exclude_inputs is applied once as the predecessor's output flows into the ForEach; the template's exclude_inputs has no effect today.

Per-item NodeState status: Absorbed failures set the expanded item's NodeState.Status to failed-handled (distinct from failed). This is what makes resume idempotent for handled-failure scenarios and what tools like toil inspect can use to distinguish absorbed from unhandled failures.

Access per-item fields via dotted indices: node.<orchestrator>.data.items.0.status, node.implement_tasks.data.items.0.failure_context.session_id, etc.

Validation Rules

• body: is required. for_each: without body: is a validation error.
• The template node must exist in the same workflow.
• The orchestrator may NOT have kind, runner, or workflow — those go on the template.
• Edges from: <template> must route to: <orchestrator>. Routing to any other node is a validation error.
• Nested ForEach is not supported (the template may not itself be a ForEach orchestrator).
• Self-reference (body: implement_tasks on implement_tasks) is not supported.

Validation

# Validate all definitions parse and pass structural checks
go test ./internal/definitions/ -v

# Build both binaries
make build && go build -o bin/tgwm ./cmd/tgwm/

# Full test suite
go test ./internal/... -count=1

Server Management

# Restart after workflow/runner/env changes
kill $(pgrep -f 'bin/toil serve')
make serve-daemon

# Definitions are loaded at startup — changes require restart

Analyzing Runs

toil inspect — Structured Run Analysis

toil inspect provides structured analysis of any run. All commands hit the API server; the CLI is a thin client.

# Overview — status, duration, nodes, models, tokens
toil inspect <run-id>

# Full run hierarchy — recursively follows child_run links
toil inspect <run-id> tree

# What each node decided and why
toil inspect <run-id> decisions

# Where time was spent, bottlenecks, concurrent nodes
toil inspect <run-id> timing

# Token usage, cache hit rate, estimated cost
toil inspect <run-id> tokens

# Decision flow with loop detection and steering annotations
toil inspect <run-id> flow

# Schema validation errors, steering events, silent exits
toil inspect <run-id> errors

# System prompts and edge prompts per node
toil inspect <run-id> prompts

# Run inputs
toil inspect <run-id> inputs

# Node outputs (message, data, artifacts)
toil inspect <run-id> outputs

# Side-by-side comparison of two runs
toil inspect <run-id> compare <other-run-id>

Node-scoped queries — drill into a specific node:

# Node overview
toil inspect <run-id> <node-id>

# Per-node transcript (tool calls grouped by attempt and round)
toil inspect <run-id> <node-id> transcript

# Node-specific tokens
toil inspect <run-id> <node-id> tokens

# Narrow to a specific attempt
toil inspect <run-id> <node-id> tokens --attempt 2

Live monitoring — SSE streaming for in-progress runs:

toil inspect <run-id> flow --follow

Quick Triage Workflow

1. Start with overview: toil inspect <run-id> — status, duration, node summary
2. Check the tree: toil inspect <run-id> tree — see full hierarchy, find the child run that matters
3. Check decisions: toil inspect <child-run-id> decisions — what did each node decide and why?
4. Check errors: toil inspect <child-run-id> errors — schema validation failures, steering events
5. Check flow: toil inspect <child-run-id> flow — look for loop annotations (same pair 3+ times)
6. Check timing: toil inspect <child-run-id> timing — find bottleneck nodes
7. Check tokens: toil inspect <child-run-id> tokens — cost and cache efficiency

Navigating the Run Hierarchy

implement_spec runs form trees. Use toil inspect <run-id> tree to see the full hierarchy:

implement_spec (signal-barley-ember) [completed] 493s
  build_one_component::0 → build_component (brisk-cedar-cirrus) 255s
    build_one_component::0 → build_component (banyan-spruce-ridge) 255s
      implement_one_task::0 → implement_task (ridge-wave-solstice) 141s
      implement_one_task::1 → implement_task (sparrow-ridge-flint) 57s
  integrate_one_component::0 → integrate_component (sparrow-grove-mist) 238s

ForEach items use :: notation with the TEMPLATE's ID as prefix: implement_one_task::0, implement_one_task::1 for the implement_tasks orchestrator whose body is implement_one_task.

Reading Raw events.jsonl

For analysis not covered by inspect aspects, the raw event log is available:

# Raw events for a run
curl -s http://localhost:8080/runs/<run-id>/events

# What structured event kinds exist in a run
grep 'node_output' runs/<run-id>/events.jsonl | python3 -c "
import sys, json
seen = set()
for line in sys.stdin:
    e = json.loads(line)
    text = e.get('text', '')
    if text.startswith('{'):
        try:
            inner = json.loads(text)
            kind = inner.get('kind', inner.get('type', ''))
            if kind and kind not in seen:
                seen.add(kind)
                print(kind)
        except: pass
"

Interviewing Serf Sessions

When a node behaves unexpectedly, resume its session and ask the agent directly:

# Find session ID from events
grep 'SESSION_START' runs/<run-id>/events.jsonl | python3 -c "
import sys, json
for line in sys.stdin:
    e = json.loads(line)
    inner = json.loads(e.get('text','{}'))
    if inner.get('kind') == 'SESSION_START':
        print(f'{e.get(\"node_id\")}: {inner.get(\"data\",{}).get(\"session_id\",\"\")}')"

# Resume with a different model and ask what happened
cd <any-dir> && \
set -a && source ../serf/.env && set +a && \
serf --model openai/gpt-5.4 \
  --reasoning-effort low \
  --state-dir ~/.local/state/serf/projects/<project-hash> \
  --resume <session_id> \
  "STOP. Do not use any tools. Just explain: what were you trying to do and why?"

Debugging Common Issues

Structured Output Rejected by Runner Schema

Symptom: A serf, claude, or codex node tries to emit nested data.* content and the runner's schema validator rejects it.

Cause: The node's outputs_schema: is too strict (typically additionalProperties: false on a field whose real value is an object the author didn't enumerate), or required keys don't match what the prompt actually produces.

Fix: Broaden or correct the schema so it describes the real output shape. For the data portion only — toil wraps {decision, message, data, artifacts} automatically. Run PROJECT_DIR=... go run ./cmd/toil validate to catch schema-compile errors before a run. See docs/specs/schemas.md ("outputs_schema") for the wrapping semantics.

Shell Node Fails Silently

Symptom: Shell node exits with code 1, no output captured.

Diagnosis: The script likely failed before producing JSON output. Check:

• Are env vars available? (set -euo pipefail + unset var = silent exit)
• Is the script executable? (chmod +x)
• Does $TOIL_WORKFLOW_SCRIPT_DIR resolve?

Reproduce: Run the script manually with the same env:

COMPONENT_ID=implementation \
TOIL_RUN_ID=test \
TOIL_ROOT=/path/to/toil \
PROJECT_DIR=/tmp/sample-app \
bash -x definitions/workflows/<workflow>/<script>.sh

Cross-Subworkflow Identity

Symptom: Merge phase can't find worktree created by build phase.

Cause: TOIL_RUN_ID differs between subworkflows. Worktree name using TOIL_RUN_ID in one subworkflow won't match in another.

Fix: Pass a stable identifier (e.g., the parent implement_spec run's ID) as parent_run_id input to both subworkflows. Use it for worktree names.

Bare Repo Identity

Symptom: shell node fails with --repo is required or operates on the wrong bare repo.

Cause: tgwm has exactly one way to identify a bare repo: --repo <path>. There is no env-var fallback, no slug guessing, no scanning of repos/.

Fix: At the top of the implement_spec workflow, capture the bare repo path from tgwm init's stdout: REPO=$(tgwm init --source "$PROJECT_DIR"). Thread it through every subworkflow as a repo input. Every shell node passes --repo "$REPO" to its tgwm calls.

Improving Agent Prompts

The Analysis Loop

1. Run the workflow against a test spec
2. Check timing: Which tasks took longest? Which nodes had multiple attempts?
3. Trace decisions: Extract the communicate calls to see what each node decided and why
4. Identify patterns: Are rejections legitimate? Are review loops productive or bouncing?
5. Check the prompts: Does the prompt clearly explain what the agent should do? Are the decision descriptions unambiguous?
6. Edit and re-run: Change the prompt, restart server, trigger new run, compare

What to Look For in Transcripts

Productive review loops: Reviewer found a real issue, engineer fixed it, reviewer approved. These are working correctly. Don't "fix" them.

Bouncing loops: Same issue goes back and forth between write_code and verify_code_meets_acceptance_criteria 3+ times. Usually means:

• The reviewer is looking at the wrong thing (code vs tests)
• The edge prompt doesn't give enough context about WHY this node was triggered
• The reviewer's rejection criteria are unclear

Wasted write_tests cycles: write_tests declares tests_already_passing without verifying existing tests cover the current task's acceptance criteria. Then verify_code_meets_acceptance_criteria rejects, sending work through unnecessary loops.

Slow rounds: A single round taking 60+ seconds usually means a large tool call (writing a big test file or patch). Check if the task is too large and should be decomposed further.

Steering events: Serf injecting steering prompts means the model is going off-track. Check if the node prompt is clear enough.

Task Schema Hierarchy

Every agent that receives a task should understand this hierarchy:

This hierarchy must be consistent across write_tests, write_code, verify_code_meets_acceptance_criteria, and review_code_quality prompts. If one agent treats guidance as binding and another treats it as advisory, review loops result.

Surgeon Decomposition Principles

File ownership determines independence. No two concurrent tasks may list the same file. Each task gets its own test file. Violation causes concurrent tasks to write conflicting changes to shared files.

Plan the delta, not from scratch. When the workspace has existing code, plan_tasks should explore it and plan only what's missing or broken. Don't redesign interfaces that already satisfy the spec.

Dependencies are about data flow AND file conflicts. A task depends on another when:

• It can't start work without the other's output (imports, types)
• Both tasks need to modify the same file (file ownership conflict)

Smaller tasks are faster. Each task goes through a full TDD + review cycle. A task with one responsibility and 2-3 acceptance criteria moves through faster than a task with five responsibilities. More tasks with parallelism beats fewer sequential tasks.

Testing Prompt Changes

After editing a workflow prompt:

1. go test ./internal/definitions/ — structural validation
2. make build — rebuild
3. Kill server, make serve-daemon — restart with new definitions
4. Trigger an implement_spec run against a simple spec (e.g., "build a simple calculator app")
5. Compare results against the previous run:
   • Same number of tasks? Better decomposition?
   • Fewer review attempts? Less bouncing?
   • Faster total time?
   • Legitimate quality catches still working?

Serf Environment for Manual Testing

Run serf standalone to test prompt variants:

cd /tmp && \
set -a && source /path/to/serf/.env && set +a && \
serf --model openai/gpt-5.4 \
  --reasoning-effort low \
  --max-rounds 10 \
  "Your test prompt here"

Note: standalone serf doesn't have the toil communicate tool or output format instructions. For testing plan_tasks prompts, you need the full toil context (trigger a real run). For testing isolated logic, standalone works.

Workflow Design Principles

Shell for Mechanics, LLM for Judgment

The happy path should be fully mechanical (shell nodes) wherever possible. LLMs are reserved for tasks requiring judgment — planning, code generation, conflict resolution, code review. This minimizes hallucination risk and cost.

Example: integrate_component uses a shell node for the merge attempt. Only on conflict does an LLM resolver get involved.

Converging Paths Over Duplicate Nodes

When two paths lead to the same outcome, converge at a shared node rather than duplicating downstream nodes. Two edges into one node (without join: all) fires the node on whichever edge arrives.

Edge Prompts Carry Context

The prompt field on edges tells the next node WHY it was triggered. This is critical for nodes that receive input from multiple edges (e.g., verify_code_meets_acceptance_criteria can be reached from write_code via code_written, spec_issue, or from write_tests via tests_already_passing). The edge prompt should give the node enough context to act correctly.

Review Loop Circuit Breakers

When write_code escalates spec_issue and verify_code_meets_acceptance_criteria keeps deciding code_changes_requested, the loop is stuck. The edge prompt from spec_issue should tell verify_code_meets_acceptance_criteria to check TESTS first, since that's usually the root cause.

max_loop_iterations on the workflow provides a hard cap, but prompt-level guidance should prevent most bouncing before the cap is hit.

Serf Event Format Reference

Runner output is double-encoded: structured JSON from serf appears inside the text field of node_output events with stream: "stderr". Each event has a kind field. Here's where data actually lives:

Token Usage → ASSISTANT_TEXT_END

Token counts are in ASSISTANT_TEXT_END, NOT in ROUND_TIMINGS.

{"kind": "ASSISTANT_TEXT_END", "data": {
  "model": "gpt-5.4-2026-03-05",
  "usage": {
    "input_tokens": 12120,
    "output_tokens": 240,
    "cache_read_tokens": 11136,
    "reasoning_tokens": 45
  }
}}

Timing Breakdowns → ROUND_TIMINGS

Per-round nanosecond timing only. No token data.

{"kind": "ROUND_TIMINGS", "data": {
  "round": 0,
  "llm_call_ns": 5104100167,
  "tool_exec_ns": 1772417,
  "total_round_ns": 5112762375
}}

Session Info → SESSION_START

Model, provider, and session ID. Note: session_id is at the top level, not inside data.

{"kind": "SESSION_START", "session_id": "01KPJ5ZP...", "data": {
  "profile": "openai",
  "model": "gpt-5.4",
  "context_window_size": 128000
}}

Decisions → TOOL_CALL_START (communicate)

Agent decisions go through the communicate tool. The output is double-encoded as JSON inside arguments_json.

{"kind": "TOOL_CALL_START", "data": {
  "tool_name": "communicate",
  "arguments_json": "{\"output\":{\"decision\":\"approved\",\"message\":\"...\"}}"
}}

Other Event Kinds