Open Service: Add delegated mode for Open Service transports

[JReinhold]

Closes #

What I did

Adds a new delegateMode to the open service runtime. When this is enabled, no local commands are ever executed even if they are implemented in the locally registered service - the runtime acts as if they are not registered, and asks other runtimes (via the channel) to execute the command instead.

This is necessary for the attached tools CLI, as it will have local implementations for eg. docgen.extractDocgen (because its service registry is identical to that of the dev server's), but we don't want to run the command in the tools CLI, we want to run the command on the dev server instead, to re-use its warm cache.

Linear: SB-1872. Independent. Base: next.

Checklist for Contributors

Testing

The changes in this PR are covered in the following automated tests:

• stories
• unit tests
• integration tests
• end-to-end tests

Manual testing

No UI change. Maintainer QA:

yarn test server.test

Documentation

• Add or update documentation reflecting your changes
• If you are deprecating/removing a feature, make sure to update MIGRATION.MD

Checklist for Maintainers

• When this PR is ready for testing, make sure to add ci:normal, ci:merged or ci:daily GH label to it to run a specific set of sandboxes. The particular set of sandboxes can be found in code/lib/cli-storybook/src/sandbox-templates.ts

• Declare whether manual QA will be needed for this PR during the next release, through qa:needed or qa:skip

• Make sure this PR contains one of the labels below:

  Available labels

  • bug: Internal changes that fixes incorrect behavior.
  • maintenance: User-facing maintenance tasks.
  • dependencies: Upgrading (sometimes downgrading) dependencies.
  • build: Internal-facing build tooling & test updates. Will not show up in release changelog.
  • cleanup: Minor cleanup style change. Will not show up in release changelog.
  • documentation: Documentation only changes. Will not show up in release changelog.
  • feature request: Introducing a new feature.
  • BREAKING CHANGE: Changes that break compatibility in some way with current major version.
  • other: Changes that don't fit in the above categories.

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[JReinhold]

@coderabbitai full review

[coderabbitai]

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[coderabbitai]

Walkthrough

The open service now supports runtime-wide delegated mode. Delegated runtimes route all commands through the attached Storybook, suppress incoming invokes, preserve local handlers for inspection, and expose delegation-specific timeout errors. Tests and documentation cover the new behavior.

Changes

Delegated Open Service

Layer / File(s)	Summary
Delegated mode state code/core/src/shared/open-service/service-registry.ts, code/core/src/shared/open-service/README.md	The shared registry stores and exposes delegated mode. Service wiring receives the mode, and clearRegistry resets it to false.
Delegated command transport code/core/src/shared/open-service/service-transport.ts, code/core/src/server-errors.ts, code/core/src/shared/open-service/README.md	Delegated runtimes route every command remotely, do not answer invoke requests, and retain local handlers for inspection. Timeout errors include delegation context. Documentation describes delegated loads, routing, and self-dispatch behavior.
Delegated mode validation code/core/src/shared/open-service/service-delegated-mode.test.ts, code/core/src/shared/open-service/README.md	Tests cover shared state, remote dispatch, acknowledgments, invoke suppression, timeout errors, local fallback, and thin-load state synchronization. Testing guidance documents the delegated-dispatch suite.

Sequence Diagram(s)

sequenceDiagram
  participant DelegatedRuntime
  participant ServiceTransport
  participant Channel
  participant AttachedStorybook
  DelegatedRuntime->>ServiceTransport: request command
  ServiceTransport->>Channel: dispatch command remotely
  Channel->>AttachedStorybook: invoke command
  AttachedStorybook-->>Channel: return acknowledgment or state patch
  Channel-->>ServiceTransport: deliver response
  ServiceTransport-->>DelegatedRuntime: resolve command request

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Merge Risk: ⚪ Minimal · up to 6dff6

The PR adds delegated execution routing so local commands can be intentionally forwarded to another runtime. The remaining concern is limited to test setup maintainability, with no actionable merge-blocking risk beyond normal review.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

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_{Comment @coderabbitai help to get the list of available commands.}

[JReinhold]

Thermos review

• [P1] Make delegated mode realm-global — service-registry.ts:74. The service inventory immediately above is intentionally stored under Symbol.for/globalThis so separate bundles or import paths in one realm share a runtime, but delegatedMode is module-local. If attachment enables the flag through one copy and config loading registers through another, the registering copy still sees false: a locally implemented command runs in the attached process instead of emitting services:command-invoke. I reproduced that on this head (controllerMode: true, registrationMode: false, zero invokes, local state mutated). Store and reset the mode in the same realm-global state and add a cross-module regression test.

• [P3] Describe command delegation rather than no local execution — README.md:807. This says an attached runtime must not execute anything itself, but the same section correctly says loads execute locally, and the governing design also runs toolset/query logic caller-side. Please narrow this to no local command dispatch and qualify the earlier absolute claim that a runtime never requests a command it implements.

Validation: reviewed the exact five-file diff and Linear ADR context at f64cb2e8443402978f24ae1623a9d730a3d4291d; focused Vitest coverage passed (19/19), with changed-file lint and formatting clean.

Generated by Thermos with 5.6 Sol

[cursor]

Review follow-up for the Thermos comments on this PR.

[P1] Make delegated mode realm-global — done. The flag now lives on the same Symbol.for / globalThis inventory as the service map, and clearRegistry() still resets it. A regression test loads a second copy of the module after vi.resetModules() and checks that both copies read and write the same flag.

[P3] Describe command delegation rather than no local execution — done. The README now says an attached runtime must not dispatch commands locally, while loads, toolset methods, and query handlers still run here. The earlier “a runtime never requests a command it implements” sentence is qualified to the non-delegated case.

No inline review threads on this PR.

[storybook-app-bot]

Package Benchmarks

^{Commit: 6dff62c, ran on 21 August 2026 at 12:45:34 UTC}

The following packages have significant changes to their size or dependencies:

storybook

	Before	After	Difference
Dependency count	73	73	0
Self size	21.91 MB	21.89 MB	🎉 -18 KB 🎉
Dependency size	31.20 MB	31.20 MB	0 B
Bundle Size Analyzer	Link	Link

@storybook/cli

	Before	After	Difference
Dependency count	205	205	0
Self size	861 KB	860 KB	🎉 -1 KB 🎉
Dependency size	86.77 MB	86.75 MB	🎉 -18 KB 🎉
Bundle Size Analyzer	Link	Link

@storybook/codemod

	Before	After	Difference
Dependency count	198	198	0
Self size	44 KB	44 KB	🎉 -36 B 🎉
Dependency size	85.23 MB	85.22 MB	🎉 -18 KB 🎉
Bundle Size Analyzer	Link	Link

create-storybook

	Before	After	Difference
Dependency count	74	74	0
Self size	1.09 MB	1.09 MB	0 B
Dependency size	53.11 MB	53.09 MB	🎉 -18 KB 🎉
Bundle Size Analyzer	node	node

[coderabbitai]

Actionable comments posted: 1

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Inline comments:
In `@code/core/src/shared/open-service/service-delegated-mode.test.ts`:
- Around line 113-119: Replace all four direct vi.spyOn() calls for fixture
handlers with a top-level vi.mock('./fixtures.ts', { spy: true }) setup,
retrieve the nested handlers through vi.mocked(), and reset each mock’s call
state in beforeEach; remove the per-test onTestFinished mockRestore cleanup.

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📥 Commits

Reviewing files that changed from the base of the PR and between a14aa35 and 6dff62c.

📒 Files selected for processing (5)

• code/core/src/server-errors.ts
• code/core/src/shared/open-service/README.md
• code/core/src/shared/open-service/service-delegated-mode.test.ts
• code/core/src/shared/open-service/service-registry.ts
• code/core/src/shared/open-service/service-transport.ts

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[ndelangen]

Adds a new delegateMode to the open service runtime. When this is enabled, no local commands are ever executed even if they are implemented in the locally registered service - the runtime acts as if they are not registered, and asks other runtimes (via the channel) to execute the command instead.

I don't understand why we're adding this complexity, rather than ensuring the registration is "correct" (removed the command implementations)?