Oneshot

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 (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 a single in-session implement-and-verify loop
• 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 (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 cancel and restart with 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:

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.

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:

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, then transition to implementing. Field mutation and phase mutation are separate actions: update writes the plan artifacts (phase is a reserved field update cannot touch), then transition advances the phase — guards read the most recent state, so the plan lands before the oneshot-plan-set guard evaluates:

exarchos:exarchos_workflow({
  action: "update",
  featureId: "fix-readme-typo",
  updates: {
    "artifacts.plan": "<plan text>",
    "oneshot.planSummary": "<one-line summary>"
  }
})

exarchos:exarchos_workflow({
  action: "transition",
  featureId: "fix-readme-typo",
  target: "implementing"
})

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 loop, with verification scaled to the change's risk (the ladder in @skills/_shared/references/verification.md). A oneshot defaults to the low tier — static analysis suffices for a trivial fix. When the change touches a higher-blast surface (schema/type/API/shared contract, or it crosses an I/O boundary), it is a higher-tier task: cover the new/changed behavior with tests (test-after is fine) and expect the check_test_adequacy kill-probe to reject tests that cannot actually fail.

For each higher-tier behavior in the plan:

1. Implement the behavior.
2. Add the tests its tier requires (scoped tests for the change; an integration test across the seam at high tier), named Method_Scenario_Outcome.
3. Refactor while the tests stay green.

Granular per-behavior red-green is available as an explicit opt-in, never a requirement.

Commit each logical change as a single atomic 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 tier-scaled verification (static analysis plus, above the low tier, the check_test_adequacy kill-probe) 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:

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:

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:

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. Report completion:

## Oneshot Complete (direct-commit)

Workflow: <featureId>
Plan: <one-line summary>
Tests added: N
Commits: <hash list>
Path: direct-commit

Step 5b — Synthesize path

If finalize resolved to synthesize, hand off to the standard synthesis flow — see @skills/synthesize/SKILL.md. The same prepare_synthesis / validate_pr_body / create_pr machinery used by the feature workflow applies, including prepare_synthesis's required repoRoot: pass the absolute path of the repo you have been committing into, since every readiness leg runs there rather than in the server's own working directory. 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 delegate or review for an opt-in oneshot synthesize. Those phases do not exist in the oneshot playbook. The PR review is the only review. Report completion:

## Oneshot Complete (synthesize)

Workflow: <featureId>
PR: <url>
Tests: X pass | Build: 0 errors
Path: synthesize → PR review → merge

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 update {
       featureId: "fix-readme-typo",
       phase: "implementing",                   // top-level
       updates: {
         "artifacts.plan": "...",
         "oneshot.planSummary": "..."
       }
     }
  4. edits README, fixes typo (low tier — a docs one-liner; static analysis
        suffices, no test-first ceremony)
  5. verifies: greps README for 'recieve' → 0 matches
  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. adds the null-input validation to parseConfig
  5. adds a test for the null-input case (test-after)
  6. refactors: extracts validateInput helper (tests stay green)
  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/synthesize/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 + implement + verify + 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:

exarchos:exarchos_workflow({
  action: "update",
  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/checkpoint/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:

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", "update"] }) 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.

Verification scales with risk

The verification ladder from @skills/_shared/references/verification.md applies to oneshot. A oneshot defaults to the cheap (low) tier — a one-line fix or config tweak leans on static analysis (typecheck + lint), no test-first ceremony — unless risk signals say otherwise. Specifically:

• A low-risk change (docs/config/rename-only, near-zero blast radius) needs only static analysis to pass; add a focused test only if behavior is non-obvious.
• If the change touches a higher-blast surface (schema/type/API/shared contract, or it crosses an I/O boundary), it is not a low-tier task: cover the new/changed behavior with tests (test-after is fine), and expect the check_test_adequacy kill-probe to flag tests that cannot actually fail.
• Commits stay atomic — one logical change per commit, regardless of tier.

The temptation in a oneshot is to assume everything is "just one line" and skip verification entirely. Resist that for anything past the low tier. The point of oneshot is auditability at the right cost — not zero verification, and not the full feature ceremony on a trivial edit.

Anti-patterns

Completion criteria

• exarchos_workflow init called with workflowType: "oneshot"
• One-page plan persisted to artifacts.plan
• Phase transitioned to implementing
• All planned behaviors implemented and verified to their risk tier, 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/synthesize/SKILL.md and merged