feat(transport): add sidepanel runtime context support

[dmagunov]

Summary

Adds sidepanel as a first-class runtime context for @webext-pegasus/transport, implementing the planned sidepanel support noted in the README.

Chrome's Side Panel API is now widely adopted, and extensions using Pegasus currently have to work around the missing context by importing from @webext-pegasus/transport/popup — which works but is semantically incorrect and could cause issues if context-specific routing is ever added.

Changes

• src/types.ts — Add 'sidepanel' to the RuntimeContext union type
• src/utils/endpoint-utils.ts — Add sidepanel to ENDPOINT_RE regex and serializeEndpoint's non-tabId context list (sidepanel, like popup, is a singleton context without tab association)
• sidepanel.ts — New entrypoint following the same pattern as popup.ts, using 'sidepanel' as the context identifier
• package.json — Add sidepanel.ts to tsup-build, add ./sidepanel export map entry, add typesVersions entry
• README.md (root + transport) — Update supported contexts, available entrypoints list, and security notes

Usage

// sidepanel.ts
import { initPegasusTransport } from '@webext-pegasus/transport/sidepanel';

initPegasusTransport();

[StyleT]

Thanks a lot!

[Copilot]

Pull request overview

Adds sidepanel as a supported runtime context in @webext-pegasus/transport, including a dedicated entrypoint and updated package exports/docs, so extensions can initialize transport in a semantically correct Side Panel context.

Changes:

• Extend runtime-context typing and endpoint parsing/serialization to recognize sidepanel.
• Add a new @webext-pegasus/transport/sidepanel entrypoint and wire it into build + exports.
• Update READMEs to list sidepanel as supported and document the new entrypoint.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
packages/transport/src/utils/endpoint-utils.ts	Adds sidepanel to endpoint regex and singleton-context serialization list.
packages/transport/src/types.ts	Extends RuntimeContext union with 'sidepanel'.
packages/transport/src/isInternalEndpoint.ts	Treats sidepanel as an internal endpoint context.
packages/transport/sidepanel.ts	New transport initializer entrypoint for sidepanel context.
packages/transport/package.json	Adds sidepanel to tsup build inputs, export map, and typesVersions.
packages/transport/README.md	Updates supported contexts, entrypoints list, and security note to include sidepanel.
packages/rpc/src/types.ts	Extends RPC RuntimeContext union with 'sidepanel'.
README.md	Updates root supported contexts list to include sidepanel (no longer “planned”).

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[Copilot]

ENDPOINT_RE allows endpoints without an @tabId suffix (e.g. sidepanel, popup, background). In deserializeEndpoint, those cases currently produce tabId: NaN (because +tabId where tabId is undefined), which violates Endpoint.tabId: number | null and can leak into routing logic (e.g. deserializeEndpoint(connArgs.endpointName) in background.ts). Consider setting tabId to null when the capture group is missing (and optionally rejecting missing tabId for contexts that require it).

[Copilot]

RuntimeContext now includes 'sidepanel', but packages/rpc/README.md still lists sidepanel as "planned". Either update the RPC README to reflect current support, or (if RPC isn’t intended to support sidepanel yet) avoid advertising it via the public RuntimeContext type until the rest of the RPC surface is ready.

Suggested change

| 'sidepanel'