Oneshot Workflow Skill

VCS Provider

This skill uses VCS operations through Exarchos MCP actions (create_pr, merge_pr, etc.) when the synthesize path is taken. These actions automatically detect and route to the correct VCS provider (GitHub, GitLab, Azure DevOps). No gh/glab/az commands needed — the MCP server handles provider dispatch.

A lean, four-phase workflow type for changes that are too small to justify the full feature flow (ideate → plan → plan-review → delegate → review → synthesize → completed) but still deserve event-sourced auditability and a planning step. The workflow is direct-commit by default with an opt-in PR path; the choice between the two is resolved at the end of implementing via a pure event-sourced guard, not a heuristic.

Read this first if you have never run a oneshot: the workflow has a choice state at the end of implementing. Whether you land on completed (direct commit) or transition through synthesize (PR) is decided by two inputs: the synthesisPolicy set at init, and whether the user emitted a synthesize.requested event during implementing. Both inputs are persisted; the decision is replay-safe.

When to use oneshot

Reach for oneshot when all of the following are true:

• The change is bounded — typically a single file, or a tightly-coupled cluster of 2-3 files
• No subagent dispatch is needed — the work fits comfortably in one TDD loop in a single session
• No design document is required — the goal is obvious from the task description, and a one-page plan is enough scaffolding
• No two-stage review is required — either the change is trivial enough that direct-commit is acceptable, or a single PR review will suffice

Concrete examples that fit oneshot:

• Fixing a typo in a README
• Bumping a dependency version
• Adding a missing null-check in one function
• Tweaking a CI workflow YAML
• Renaming a config key everywhere it's referenced
• Adding a one-off helper script
• Exploratory spikes that may or may not be kept

When NOT to use oneshot

Do not use oneshot for any of the following — use the full feature workflow instead (/exarchos:ideate):

• Cross-cutting refactors that touch many files or modules
• Multi-file features that benefit from subagent decomposition
• Anything that needs design exploration or competing approaches weighed
• Anything that needs spec-review + quality-review (two-stage)
• Anything that needs to coordinate with another agent team
• Changes that should land in stages (stacked PRs)
• Anything where you'd want a written design doc to look back at

If you start a oneshot and discover the change is bigger than expected, the right move is /exarchos:cancel and restart with /exarchos:ideate. Don't try to grow a oneshot into a feature workflow mid-stream; the playbooks have different shapes and you'll fight the state machine.

Synthesis policy — three options

The synthesisPolicy field on a oneshot workflow declares the user's intent up front about whether the change should be turned into a PR. It takes one of three values, persisted on state.oneshot.synthesisPolicy:

Policy	Behavior	When to use
always	Always transition implementing → synthesize at finalize, regardless of events. A PR is always created.	The user wants a paper trail / review for every change in this workflow, even small ones.
never	Always transition implementing → completed at finalize, regardless of events. No PR is created — commits go directly to the current branch.	The user is iterating on personal/scratch work and explicitly opts out of PRs.
on-request (default)	Direct-commit by default. The user can opt in to a PR mid-implementing by calling request_synthesize; if any synthesize.requested event is on the stream at finalize, the workflow transitions to synthesize instead of completed.	The common case: start with the assumption of direct-commit, but leave the door open for the user to change their mind once they see the diff.

The default is on-request because it's the least surprising: the user gets the lightweight path until they explicitly ask for the heavy one.

Policy wins over event. If synthesisPolicy: 'never' is set and a synthesize.requested event is somehow on the stream (e.g. the user called the action on a workflow they thought was on-request), the guard still routes to completed. Policy is the user's declared intent and overrides runtime signal.

Lifecycle

     plan ──────► implementing ──┬── [synthesisOptedOut] ──► completed
                                 │
                                 └── [synthesisOptedIn]  ──► synthesize ──► completed

Four phases. The fork after implementing is a UML choice state, implemented via two mutually-exclusive HSM transitions whose guards are pure functions of state.oneshot.synthesisPolicy and the synthesize.requested event count.

Phase	What happens	Exit criteria
plan	Lightweight one-page plan: goal, approach, files to touch, tests to add. No design doc. No subagent dispatch.	artifacts.plan set → transition to implementing
implementing	In-session TDD loop. Write a failing test, make it pass, refactor. Commit as you go. The TDD iron law applies — no production code without a failing test first.	Tests pass + typecheck clean + finalize_oneshot called
synthesize	Reached only when synthesisOptedIn is true. Hands off to the existing synthesis flow — see @skills/synthesis/SKILL.md. PR created via exarchos_orchestrate({ action: "create_pr" }), auto-merge enabled, CI gates apply.	PR merged → completed
completed	Terminal. For direct-commit path, commits are already on the branch — there's nothing more to do. For synthesize path, the PR merge event terminates the workflow.	—

cancelled is also reachable from any phase via the universal cancel transition, same as every other workflow type.

Step-by-step

Step 1 — Init

Call exarchos_workflow with action: 'init', workflowType: 'oneshot', and an optional synthesisPolicy:

mcp__plugin_exarchos_exarchos__exarchos_workflow({
  action: "init",
  featureId: "fix-readme-typo",
  workflowType: "oneshot",
  synthesisPolicy: "on-request" // optional — defaults to 'on-request'
})

If the user has been clear up front ("I want a PR for this"), pass synthesisPolicy: "always". If they've been clear ("don't open a PR, just commit it"), pass synthesisPolicy: "never". Otherwise, omit the field and rely on the on-request default — you can always escalate later in the implementing phase.

The init returns the new workflow state; the workflow lands in plan.

Step 2 — Plan phase

Produce a one-page plan. This is intentionally lightweight — no design doc, no parallelization analysis, no decomposition into N tasks. The plan should answer four questions in 5-10 lines each:

1. Goal — what is the user trying to accomplish?
2. Approach — what's the one-line implementation strategy?
3. Files — which files will be touched? (1-5 typically)
4. Tests — which test cases will be added? (named, not described)

Persist the plan and transition to implementing in a single set call. phase is a top-level argument of set, not a field inside updates:

mcp__plugin_exarchos_exarchos__exarchos_workflow({
  action: "set",
  featureId: "fix-readme-typo",
  phase: "implementing",
  updates: {
    "artifacts.plan": "<plan text>",
    "oneshot.planSummary": "<one-line summary>"
  }
})

The plan goes on artifacts.plan for parity with the feature workflow; the human-readable one-liner goes on oneshot.planSummary for the pipeline view. Only artifacts.plan is enforced by the oneshot-plan-set guard — planSummary is an optional pipeline-view label and is not a substitute for a real plan artifact.

Step 3 — Implementing phase

Run an in-session TDD loop. Same iron law as every other workflow:

NO PRODUCTION CODE WITHOUT A FAILING TEST FIRST

For each behavior in the plan:

1. [RED] Write a failing test. Run the test. Confirm it fails for the right reason.
2. [GREEN] Write the minimum production code to make the test pass. Run the test. Confirm it passes.
3. [REFACTOR] Clean up while keeping the test green.

Commit each red-green-refactor cycle as a single commit. Do not batch multiple unrelated changes into one commit — keeping commits atomic matters even more in oneshot, where there's no separate review phase to catch bundled changes.

There is no subagent dispatch in oneshot. The main agent does the work directly. There is no separate review phase. Quality is maintained by the TDD loop and (if the user opts in) the synthesize PR review.

Mid-workflow: opting in to a PR

If at any point during plan or implementing the user decides they want a PR after all (policy is on-request, default), they can opt in by calling the request_synthesize orchestrate action:

mcp__plugin_exarchos_exarchos__exarchos_orchestrate({
  action: "request_synthesize",
  featureId: "fix-readme-typo",
  reason: "user requested review of the parser changes"
})

The trigger for this is conversational, not a magic keyword. Listen for phrases like:

• "actually, let's open a PR for this"
• "I want a review on this before it lands"
• "make this a PR"
• "let's get eyes on this"
• "synthesize this"

When you hear any of those, call request_synthesize immediately. The handler appends a synthesize.requested event to the workflow's event stream; the synthesisOptedIn guard reads the stream at finalize and routes accordingly.

request_synthesize is accepted from both plan and implementing phases — call it whenever you know you want the PR path, even before implementing starts. Terminal phases (synthesize, completed, cancelled) are rejected.

Duplicate calls are routing-idempotent but not event-idempotent: each call appends a new synthesize.requested event, but the guard treats any count >= 1 as "opted in", so the routing decision is the same whether you call once or five times. The event stream will contain each duplicate for audit purposes.

Calling request_synthesize does not transition the phase. The workflow stays in its current phase. The decision is only acted on when you call finalize_oneshot in step 4.

Step 4 — Finalize (the choice point)

When the implementing loop is done — tests pass, typecheck clean, all commits made — call finalize_oneshot to resolve the choice state:

mcp__plugin_exarchos_exarchos__exarchos_orchestrate({
  action: "finalize_oneshot",
  featureId: "fix-readme-typo"
})

The handler:

1. Reads the current state and verifies workflowType === 'oneshot' and phase === 'implementing'.
2. Hydrates _events from the event store so the guard sees the same view the HSM will see during the actual transition.
3. Evaluates guards.synthesisOptedIn against the state. The guard inspects state.oneshot.synthesisPolicy and the _events array.
4. Calls handleSet with the resolved target phase (synthesize or completed). The HSM re-evaluates the guard at the transition boundary, so any race between the read and the transition is caught safely.

Possible outcomes:

synthesisPolicy	synthesize.requested event present?	Resolved target	Path
always	(any)	synthesize	PR path
never	(any)	completed	direct-commit path
on-request (default)	yes	synthesize	PR path
on-request (default)	no	completed	direct-commit path

Step 5a — Direct-commit path (terminal)

If finalize resolved to completed, you're done. The commits made during implementing are already on the current branch. Push them if they aren't already pushed:

git push

The workflow is now in completed and will not appear in the default pipeline view.

Step 5b — Synthesize path

If finalize resolved to synthesize, hand off to the standard synthesis flow — see @skills/synthesis/SKILL.md. The same prepare_synthesis / validate_pr_body / create_pr machinery used by the feature workflow applies. After the PR merges, the workflow transitions synthesize → completed via the existing mergeVerified guard, same as every other workflow type.

You do not need to run /exarchos:delegate or /exarchos:review for an opt-in oneshot synthesize. Those phases do not exist in the oneshot playbook. The PR review is the only review.

Example invocations

Example A — Direct-commit (default on-request policy, no opt-in)

User: "Quick fix — there's a typo in the README, 'recieve' should be 'receive'.
       Use oneshot."

Agent:
  1. exarchos_workflow init { featureId: "fix-readme-typo", workflowType: "oneshot" }
     → workflow created in 'plan' phase, synthesisPolicy defaults to 'on-request'
  2. Produces a 4-line plan: goal=fix typo, approach=sed, files=[README.md],
     tests=[readme has no occurrence of 'recieve']
  3. exarchos_workflow set {
       featureId: "fix-readme-typo",
       phase: "implementing",                   // top-level
       updates: {
         "artifacts.plan": "...",
         "oneshot.planSummary": "..."
       }
     }
  4. [RED] writes test that greps README for 'recieve' and expects 0 matches
        — fails (1 match exists)
  5. [GREEN] edits README, fixes typo
        — test passes
  6. git commit -m "docs: fix 'recieve' typo in README"
  7. exarchos_orchestrate finalize_oneshot { featureId: "fix-readme-typo" }
     → guard sees policy='on-request' + no synthesize.requested event
     → resolves to 'completed'
  8. git push
     "Done. Workflow completed via direct-commit path."

Example B — Mid-implementing opt-in (on-request → user changes mind)

User: "Add input validation to the parseConfig helper. Oneshot."

Agent:
  1. exarchos_workflow init { workflowType: "oneshot" }
     → 'plan' phase, default 'on-request'
  2. plans (goal: validate input, files: [parser.ts, parser.test.ts])
  3. transitions to 'implementing'
  4. [RED] writes test for null-input case
  5. [GREEN] adds null check
  6. [REFACTOR] extracts validateInput helper
  7. commits

User: "Actually, this is touching the parser — I want a review on it before
       it lands."

Agent:
  8. exarchos_orchestrate request_synthesize {
       featureId, reason: "user requested review of parser changes"
     }
     → appends synthesize.requested event
  9. exarchos_orchestrate finalize_oneshot { featureId }
     → guard sees policy='on-request' + 1 synthesize.requested event
     → resolves to 'synthesize'
 10. hands off to @skills/synthesis/SKILL.md → prepare_synthesis →
     validate_pr_body → create_pr → merge

Example C — synthesisPolicy: 'always' (PR mandatory)

User: "I want a PR for any change to the auth module, even small ones.
       Use oneshot but always make a PR."

Agent:
  1. exarchos_workflow init {
       workflowType: "oneshot",
       synthesisPolicy: "always"
     }
  2-7. plan + TDD + commits, identical to Example A
  8. exarchos_orchestrate finalize_oneshot { featureId }
     → guard sees policy='always' (short-circuits — no event check needed)
     → resolves to 'synthesize'
  9. synthesis flow → PR

State management

Track oneshot-specific state under the oneshot key on the workflow state:

mcp__plugin_exarchos_exarchos__exarchos_workflow({
  action: "set",
  featureId: "<id>",
  updates: {
    "oneshot": {
      "synthesisPolicy": "on-request",
      "planSummary": "Fix off-by-one in pagination helper"
    }
  }
})

The synthesisPolicy field is optional and defaults to 'on-request' per the schema in servers/exarchos-mcp/src/workflow/schemas.ts. Setting it explicitly is recommended when the user has stated a preference.

Phase Transitions and Guards

For the full transition table for oneshot, consult @skills/workflow-state/references/phase-transitions.md.

Note: The engine's exarchos_workflow describe playbook="oneshot" output and the HSM definitions in hsm-definitions.ts are the canonical sources for transition behavior. phase-transitions.md is a prose reference that can drift — when discrepancies arise, prefer engine describe output.

Quick reference for oneshot:

From	To	Guard
plan	implementing	oneshotPlanSet (requires non-empty artifacts.plan)
implementing	synthesize	synthesisOptedIn
implementing	completed	synthesisOptedOut
synthesize	completed	mergeVerified
(any)	cancelled	universal — always allowed

synthesisOptedIn and synthesisOptedOut are pure functions of state.oneshot.synthesisPolicy and state._events. They are mutually exclusive across all 4 meaningful combinations — always and never each map to one outcome (ignoring the event flag), and on-request branches on whether a synthesize.requested event is present or absent. Exactly one guard returns true at any given time.

Schema discovery

Use exarchos_workflow({ action: "describe", actions: ["init", "set"] }) for parameter schemas (including the synthesisPolicy enum) and exarchos_workflow({ action: "describe", playbook: "oneshot" }) for the phase transitions, guard names, and playbook prose. Use exarchos_orchestrate({ action: "describe", actions: ["request_synthesize", "finalize_oneshot"] }) for the orchestrate action schemas.

TDD is still mandatory

The iron law from @rules/tdd.md applies to oneshot. There is no exemption for "small" changes. Specifically:

• Every behavior change starts with a failing test
• Every test must fail before its implementation is written
• Tests must be run after each change to verify state
• Commits stay atomic — one logical change per commit

The temptation in a oneshot is to skip the test "because it's just one line". Resist that. The test is what makes the change auditable, and auditability is the entire reason oneshot exists alongside the lighter "bypass workflows entirely" path.

Anti-patterns

Don't	Do Instead
Skip the plan phase ("it's obvious")	Write the four-line plan anyway — it's the artifact future-you reads
Skip the TDD loop in implementing	Always RED → GREEN → REFACTOR, even for one-liners
Use oneshot for multi-file refactors	Use /exarchos:ideate and the full feature workflow
Try to grow a oneshot into a feature workflow mid-stream	Cancel and restart with /exarchos:ideate
Call request_synthesize without listening for the user's intent	Wait for the user to ask for a PR, then call it
Bundle unrelated changes into one commit "since it's a oneshot"	Keep commits atomic — there's no review phase to catch bundling
Forget to call finalize_oneshot at the end	The workflow stays in implementing forever otherwise — call it explicitly

Completion criteria

• exarchos_workflow init called with workflowType: "oneshot"
• One-page plan persisted to artifacts.plan
• Phase transitioned to implementing
• All planned behaviors implemented via TDD with atomic commits
• finalize_oneshot called and resolved to either completed or synthesize
• If direct-commit path: commits pushed
• If synthesize path: PR created via @skills/synthesis/SKILL.md and merged